BIOLOGY
LIBRARY
G
HUMAN PHYSIOLOGY:
DESIGNED FOR
COLLEGES AND THE HIGHER CLASSES IN SCHOOLS,
FOR GENERAL READING.
BY WORTHINGTON HOOKER, M. D.,
PROFESSOR OF THE THEORY AND PRACTICE OF MEDICINE IN YALJC COI
AUTHOR OF "PHYSICIAN AND PATIENT."
Illustrated by nearly 200 Engravings.
NEW Y O E K :
PRATT, OAKLEY & COMPANY,
21 MURRAY STREET.
R1OLOGY
ENTERED, according to Act of Congress, in the year of our Lord.
One thousand eight hundred and fifty-four,
BY WORTIIIXGTOX HOOKER. M D.,
In the C'erk's Office of the District Court of Connecticut.
CONTENTS.
PART I.
CHAPTER I. PA3K .
ORGANIZED AND UNORGANIZED SUBSTANCES. . . .13
CHAPTER II.
THE DISTINCTION BETWEEN ANIMALS AND PLANTS. . 21
CHAPTER III.
MAN IN HIS RELATIONS TO THE THREE KINGDOMS OF NA-
TURE, 27
PART II.
CHAPTER IV.
GENERAL VIEWS or PHYSIOLOGY. WITH A BRIEF ACCOUNT
OK SOME OF THE STRUCTURES OF THE BODY, . 35
CHAPTER V.
DIGESTION, ......... 42
CHAPTER VI.
CIRCULATION OF THE BLOOD, . . . . 64
CHAPTER VII.
RESPIRATION, 86
CHAPTER VIII.
FORMATION AND REPAIR, 109
CHAPTER IX.
CELL LIFE, 123
IV CONTENTS.
PART III.
THE
CHAPTER X.
PAGE.
139
THE
CHAPTER XL
BONES,
170
THE
CHAPTER XII.
MUSCLES,
196
THE
CHAPTER XIII.
LANGUAGE OF THE MUSCLES, ....
222
THE
CHAPTER XIV.
VOICE,
243
THE
CHAPTER XV.
EAR,
271
THE
CHAPTER XVI.
EYE,
287
CHAPTER XVII.
CONNECTION OF THE MIND WITH THE BODY, . . ' 318
CHAPTER XVIII.
DIFFERENCES BETWEEN MAN AND THE INFERIOR ANIMALS, 347
CHAPTER XIX.
VARIETIES OF THE HUMAN RACE, 367
CHAPTER XX.
LIFE AND DEATH, 381
CHAPTER XXL
HYGIENE, , 390
APPENDIX, ... 411
PREFACE.
I HAVE aimed so to write this book, that it shall be fitted both for gen-
eral reading, and for instruction. It is designed for the family as well as
for the school. It seemed desirable that these two objects should be ao
complished at the same time, and I have not found them to be at all in-
compatible. The instruction needed by the family on this subject, differs
not from that which is required in the school-room, either in regard to
the facts to be communicated, or the manner in which it should be done.
No one will question the truth of this, so far as the facts are concerned.
But it is true even as to the mode of communicating them. In both cases
there need to be clearness in statement, and fullness of illustration. Actual
instruction is to be given in both cases, and to minds that are very nearly
in the same attitude. I could not, therefore, see the necessity of writing a
book on this subject for the people which should differ from one written
for the school. Besides, it has seemed to me desirable that there should
be a greater community of interest between the school and the family than
as yet exists ; and this object books equally interesting to both will tend
to promote.
It may be proper for me to say a word in relation to the style of the
work. I have adopted the style of the lecture-room, because, that while
it is not inconsistent with conciseness, it is the more natural mode of in-
struction, especially when so much reference is made to illustrative figures.
It has enabled me also to keep in view more effectually the attitude of the
minds I address. I have had my readers before me continually as an
imaginaiy audience. I have avoided technical terms as far as possible.
Whenever they are used they are sufficiently explained at the time, so
that no glossary is needed. Some points commonly considered hard to
be understood are treated of, but I have endeavored to simplify them, by
VI PKEFACE.
full illustration, and by a presentation of the truth uncomplicated with
speculations and hypotheses. And these points are so introduced, that
the mind is prepared by the previous investigation to understand them.
I have aimed so to arrange the topics, as to have a preparation constantly
going on in the mind of the student, fitting him for the proper under-
standing of what is to come after. By this natural gradation in the de-
velopment of the whole subject some of the deep things in Physiology
can be made clear, which it would otherwise be impossible for the student
to understand. It is proper to state here, that I intend to prepare a worK
for younger scholars, in which some of the simple points in Physiology
will be illustrated. This, by familiarizing their minds with the subject,
will fit them for a more thorough understanding of the present work.
Although Physiology is 1 becoming a prominent study in the schools and
colleges in some parts of our country, its importance is no where as yet
appreciated as it should be. It should be made a regular branch in our
Educational System. This has been already done in France. " A com-
petent knowledge," says Carpenter, " of Animal Physiology and Zoology
is there required from every candidate for University honors ; and men
of the highest scientific reputation do not think it beneath them to write
elementary books, for the instruction of the beginner."
The importance of Physiology as a study, will appear from various con*
siderations.
Many of the subjects comprised in Physiology have, in the case of
most students, been already studied in a different phase, or mode, in other
branches. Thus, if the student has attended to the Mechanical Powers
in his Natural Philosophy, he finds in the human body the principles of
the pulley and the lever illustrated in great variety and perfection. The
principles in relation to strength in the form and arrangement of struc-
ture he sees exemplified in the frame-work of the body in the most ad-
mirable manner. If he has studied Hydraulics, he sees in the body the
most perfect, and at the same time the most complicated hydraulic ma-
chinery, working incessantly throughout life in the circulation of the
blood. The principles of Pneumatics he finds applied in the respiration
those of Optics in the eye those of Acoustics in the ear and those of
Musical Sounds in the apparatus of the voice. And then, his chemical
PKEFACE. VII
knowledge meets with new applications in his observation of the changes
and the processes going on in the body.
The relations, then, of Physiology to some of the common branches
taught in the higher classes in schools, are of the most intimate charac-
ter. Physiology, in part, merely extends these branches into a new and
interesting field ; and the student who has once entered this field recurs
to these same branches with a renewed interest. Hydraulics, Pneuma-
tics, Optics, &c., have now a new attraction for him, from this, to him
novel, application of their principles. The interest thus awakened in
his mind is worth much in itself, aside from the mere addition made to
his knowledge. And the interest is enhanced by the consideration, that
in the human body he sees the applications of these principles to mechan-
ism that exhibits the skill of perfect wisdom and almighty power.
But there are relations of Physiology to still other studies which should
be noticed.
The analogies that exist between the human body and all other living
things, in relation to structure and growth, are numerous and striking.
Though life is so diverse in its processes and in the forms which we see
it evolve in the whole range of animated nature, it in some important re-
spects displays a great similarity, which it is interesting to trace through-
out its diversified manifestations. Growth, or nutrition, as you will see
in the following pages, is essentially the same in the Plant as it is in the
Animal. Botany, therefore, taught as it should be, has quite an intimate
relation to Animal Physiology. The Science of Life is, in many respects,
one Science ; and if, in studying any of its subdivisions, we fail to take
this broad view of it, and to trace out the analogies referred to, we lose a
large part of the interest of the study. Human Physiology, the subject
of study in this book, is but a part of a science which offers to the student
wide fields of observation exceedingly diversified and full of interest.
This being so, I could not avoid in the following pages making occasional
reference to the analogies existing between the phenomena of life as ex-
hibited in the human system, and those which we see in the living world
around us. So that as the student proceeds with the study, he will find
himself interested in the phenomena of life in whatever form they are
VU1 PREFACE.
This leads me to say that this study of nature, in its broad common re-
lations and its beautiful and extensive analogies, should be made very
prominent in our systems of education. It is the application of the prin-
ciples of abstract science to the forms, and especially the living forms of
nature all about us, that gives interest to these principles, and makes us
to understand and appreciate them. It is here that we find a very seri-
ous defect in the prevalent mode of education, even at the present time,
notwithstanding all our improvements. Let us look at it a moment. We
live in the midst of a material world, animate and inanimate, and have
daily converse, so to speak, with material forms of every variety, present-
ing phenomena of the highest interest and of endless diversity. And
yet, through almost all the period of childhood, and perhaps we may say
youth also, this book of nature is in the school-room very nearly a sealed
book. The very process of education shuts in the pupil from this broad
contemplation of the world in which he lives. He is drilled through
spelling, reading, grammar, &c., but he is left in total ignorance of the
beautiful flowers, and the majestic trees outside of the school-room. How
very few even of thoroughly educated adults, know the processes by
which a plant or a tree grows! And the same can be said of other
phenomena of nature.
The defect which I have pointed out runs through the whole of educa-
tion. We can see it even in the prevalent mode of teaching the natural
sciences themselves. One would suppose that here the facts, the phe-
nomena, would command the chief attention of the teacher and the stu-
dent. But it is very commonly not so. The mere technicalities and the
classification are made much too prominent. Botany, really one of the
most interesting of all branches of natural science, is thus ordinarily
made one of the driest of studies. To teach this aright, the phenomena
of vegetation, so varied and so beautiful, should constitute the chief ma-
terial of instruction, and the mere classification should be considered, al-
though necessary, as wholly a secondary thing.
The great facts of the world, both of mind and matter, should furnish
really the material for education, and those branches that are ordinarily
pursued with such assiduity should be considered as merely subsidiary to
the teaching of these facts. The whole order of education must be re-
PREFACE. IX
versed. Instead of beginning the child's education with learning to spell
and read, the object should be to make him an observer of nature, and
the spelling and reading should be done in connection with this, and as
subsidiary to it. Things and not words, or mere signs, should from the
first, constitute the substantial part of instruction. The child should be
made, at home, in the school, and everywhere, a naturalist in the largest
sense of that word. We should aim to impart to him a spirit in con-
sonance with the following precept of Hugh Miller, the famous self-
taught geologist. " Learn to make a right use of your eyes ; the com-
monest things are worth looking at even stones and weeds, and the
most familiar animals."
As it is now, no one becomes a naturalist early in life, except in spite
of the tendencies of his education. The study of nature is not only not
encouraged, but is absolutely discouraged in our educational system. If
any one, like Hugh Miller, by the force of a taste that can not be repress-
ed by the training of the school-room, undertakes to make a " right use
of his eyes," and curiously examines " stones and weeds," he is regard-
ed by the world of spellers and readers and grammarians and cipherers,
as a strange genius. But he is pursuing from an irresistible internal
force, the very course that I would have every student, even from his
childhood, encouraged to pursue, in a measure at least, by the external
circumstances of his education. The tendencies of his training should be
decidedly in this direction.
If the general mode of education were changed in the manner indicated,
education would have much less of the character of mere drudgery than
it now has. Not that there would be any the less labor ; but the labor
would be made lighter by the interest imparted to it the interest, which
always results from the study of facts and phenomena, and never from the
learning of mere words and technicalities and classifications. I would
gladly dwell on this subject, and show by varied illustrations how the
mode of instruction referred to, should be pursued, and especially with
younger scholars $ but the limits of a preface will not allow me to enter
BO large a field.
The change which I have pointed out can not be effected at once. It
will require tune. Confirmed traditional customs are to be done away,
PREFACE.
the habits of teachers are to be altered, and the proper books are to *
great extent to be yet written, especially such as are fitted for the first
years of education.
If the study of nature should be thus made prominent in education,
human physiology would be considered altogether its most interesting and
important branch, and for several reasons. First : there is no where to
be found so curious a collection of mechanisms, or so interesting and
wonderful a series of processes, as in the human body. In nothing else
in the wide world are the principles of so many departments of science
so extensively and perfectly exemplified. Life works here its most com-
plicated set of machinery. Secondly : the singular and mysterious con-
nection of the immaterial and immortal soul with the material and perish-
able body, gives intense interest to this study. In Physiology we do
not study matter alone, or spirit alone, but both matter and spirit united,
and often acting together. This circumstance distinguishes this from all
other studies. Thirdly : it is our own frames, moved by the spirit within
us, that we study. The subject has a personal interest for us, that is not
presented by most studies, and by none in so large a degree as in this.
And Fourthly : the study is of great importance, because a judicious and
efficient Hygiene must be based upon a knowledge of the laws of physi-
ology. We cannot know how to keep our functions in the condition of
health, without understanding the laws that regulate them. I have said
but little in this book in regard to hygiene, and that only incidentally, be-
cause that subject would require of itself a whole volume to elucidate it
properly.
I have not thought it proper to indulge to any great extent in those re-
flections, which the contemplation of so perfect and diversified a congeries
of mechanisms as are presented in man would naturally suggest, in regard
to the skill of the great builder of the universe. Such reflections would
extend the book to too great length. Besides, they are so readily sug-
gested to the mind of both teacher and scholar, that it is entirely un-
necessary for the author to dwell on them.
I have treated of some subjects, on which, from the difficulty of un-
derstanding them, there has been a disposition in many minds to go be-
*-ond what we know, and indulge in unwarranted speculation. On these
PKEFACE. XI
points I have taken pains to draw the line very distinctly between what is
known, and what is supposed. I deem it to bo important to prevent the
minds of the young from being led away from the simple truths of
science by ingenious speculations and plausible reasonings. Let me not
be understood to decry all hypothesis. I only object to the mingling of
facts and suppositions together in one indiscriminate mass, as is often
done. The disposition to do this, which is more common than is generally
supposed, exerts so injurious an influence upon the habile of the mind,
and so confuses its views of truth, that we ought to look upon it as one of
the most serious evils to be guarded against in education. It is really
one of the most prominent obstacles to the progress of truth on all sub-
jects, both in individual minds, and in the minds of the community at
large. This disposition, so apt to be fostered in the enthusiastic mind of
youth, by ingenious but dreamy speculations, should be corrected at tho
outset, and the mind should in its forming stage, ba habituated to the dis-
crimination between the proved, the true, and that which rests on pre-
sumptive, perhaps merely plausible evidence. This discrimination should
therefore be exemplified in books designed for instruction, and this I have
attempted in the present volume.
I have divided the book into Three Parts. The First, which I have
made as short as possible, is merely preliminary to the consideration of
the particular subject of the book. In the Second Part, I present the
human structure, simply as a structure, and show how it is constructed
and kept in repair. In the Third Part, I treat of all those subjects which
relate to the uses for which the structure is designed. This natural
division of the whole subject, not only presents it to the mind of the
student in an interesting point of view, but secures that natural grada-
tion in its development, which I have spoken of as being necessary to a
clear understanding of its deeper and more intricate portions.
NOTE.
SINCE the book was first published, the Author
has, in obedience to the requests of many Teachers,
added a chapter on HYGIENE, and also an APPENDIX
containing questions. A full INDEX is also subjoined.
PHYSIOLOGY
PART FIRST,
CONTAINING,
CHAPTER I ORGANIZED AND UNORGANIZED SUBSTANCES. CHAPTER II Tmt DisnNcnorr
BETWEEN ANIMALS AND PLANTS. CHAPTER III. MAJT IN HIS RELATIONS TO TIM Tmir*
KINGDOMS or NATURE.
CHAPTER I.
ORGANIZED AND UNORGANEED SUBSTANCES.
1. THE crystal and the plant are both wonderful growths.
As you look at them, you think -of the crystal as having been
formed, and of the plant as having grown. But in one sense
they have both grown to be what they are. The crystal was
once a minute nucleus, and the plant was once a little germ.
2. In one respect they are alike in their growth both have
increased from particles taken from things around them. But
the processes by which this is done are different in the two
cases. The crystal has increased or grown by layer after layer
of particles. There are no spaces or passages by which parti-
cles of matter can be introduced inside of it. Any part of it,
when once formed, is not altered. It can receive additions
upon the outside alone. But it is not so with the plant. This
enlarges by particles which are introduced into passages and
interstices. It grows, as it is expressed, by absorption or by in-
tussusception.
3. How, now, is this absorption effected? It is done by cer-
tain vessels or organs, constructed in the root of the plant for
this purpose. These take up or absorb fluid matter from the
earth. There are other organs which circulate this fluid through
all the plant ; and others still which use it for the purpose of
growth or formation. There are no such organs in the crystal,
for it has no inner growth. The plant is therefore said to be
an organized substance or being, and the crystal is an unor-
ganized substance. And so we speak of the organic structure,
or the organization of plants.
14 HUMAN PHYSIOLOGY.
Organized beings. Mechanical, chemical, and vital principles.
4. These organs, which thus absorb, and circulate, and con-
struct, do not act simply on mechanical principles. The plant
is not merely soaked with fluid, which the heat of the sun may
expel, as it does water from a porous mineral substance. These
organs are active agents, and they perform their duty with a
force, and after a manner, for which no mechanical principles
can account. No mechanical powers could alone supply the
leaves of the mighty tree of the forest with sap from its deep
roots ; much less could they form these leaves.
5. Neither do these organs act simply on chemical princi-
ples. While man, through the agency of chemistry, can form
some of the crystals which are found in nature, he can not by
any arrangement of constituents make a plant, a flower, or a
leaf. And the plant, left alone to the action of chemical prin-
ciples, wilts ; and at length ceases to be a plant, and becomes
common unorganized matter.
6. Mechanical and chemical principles, it is true, are both
employed to some extent in the growth of plants ; but they are
under the control of other principles, which we term vital. And
so we speak of the plant not only as an organized substance,
but as a living being.
7. What I have said of plants, in distinction from minerals,
may also be said of animals. They are also organized living
beings, and they have generally a more complex organization
than plants, as you will see as I proceed.
8. The whole material world, then, that we see around us,
we divide into two parts the unorganized and lifeless, and the
organized and living. The distinctions thus pointed out be-
tween organized and unorganized matter are essential and
fundamental. But let us look at some other distinctions, which
either arise from these or accompany them.
9. One distinction is this. All the parts of the mineral are
independent of each other, while it is otherwise with the plant
or the animal. Accordingly, we examine the properties of min-
erals in a different way from those of plants and animals. The
chemist can ascertain all the properties of a crystal or a rock,
if you give him but a small piece of it. But the botanist can
not ascertain all the properties of a plant by looking at some
one part of it. If he examine the flower, this gives him no
knowledge of the root. In order to know all about the plant,
he must examine every part by itself, and then look at it in its
relations to the other parts. The same can be said of tha
physiologist, in his investigation of the properties of animals.
ORGANIZED AND UNORGANIZED SUBSTANCES. 15
Assimilation in organized substances.
10. As the crystal is forming by layer after layer of particles,
no change is effected in these particles as they are becoming
arranged in the layers. But in the case of the living organ-
ized being, a change is produced in the particles which are
taken up by the absorbents. And the change, ordinarily, is
both a gradual and a complex one. In the plant, a change is
produced in the particles in the very act of absorption; but
this change is only the beginning of a process which is after-
wards perfected. The sap is not thoroughly fitted for nutrition
when it first begins to circulate. It is carried up through the
vessels of the trunk or stalk to the leaves. There the last step
of the process is taken, and the sap is now ready to be used in
the growth of the plant or tree. So, also, in the animal, the
nutritious part of the food, taken up by the absorbents in the
digestive organs, is first acted upon by certain little glands,
through which it passes, is then poured into the circulation, to
be mingled with the blood, and is carried with the blood to the
lungs, to be exposed to the air ; and thus it is fitted for the nu-
trition or growth of the body. This process, which is thus car-
ried on in the plant and in the animal, is very properly called
assimilation. For the particles that are taken up by the ab-
sorbents in the root of the plant are, by this process, made like
to the plant ; and the particles taken up by the absorbents in
the stomach * are made like to the animal. So obvious is this,
in the case of the animal, that some French physiologist speaks
of the blood as chair coulante, or running flesh.
11. Another prominent distinction between organized and
unorganized substances is in relation to permanency. Constant
change appears in all organized bodies ; while permanency is
written upon all substances which are unorganized. In organ-
ized beings, continual change is going on at every point. It is
a condition of their being. This is true, not only of the de-
cline of a plant or animal, but even of its growth. For, in its
growth, as the parts enlarge internally as well as externally,
they change not only the arrangement of the particles, but, to
a great extent, they change the particles themselves. It is
* The word stomach requires some little explanation, as it is used in physiology in two
senses in a limited sense, and also in an extended one. It is used in its limited sense, as
referring to the cavity at the beginning of the alimentary cann/, as it is termed; this lat-
ter term being applied to the series of cavities, the stomach and the small and large, intes-
tines, which are fuuod in the digestive apparatus in the higher orders of animals. In
comparisons, however, between these animals and those which have a more simple digest-
ive apparatus, the word stomach is used in a more extended sense, as being synonymou*
with the term alimentary canal. It is used in this sense, also, when, as in the present
oase, it is referred to in a comparison between animals and vegetables.
16 HUMAN PHYSIOLOGY.
Organized substances changing. Unorganized permanent.
true, as well of the towering tree as of the tiny plant, that
these changes have been going on during all its growth ; so
that, at its maturity, it is, both in relation to the arrangement
of its particles, and in relation to the particles themselves, a
very different thing from what it was when it pushed its germ
up through the ground, or even when it was but a small tree.
Not only has it received into its interstices and passages new
particles, but it has thrown off from the pores of its leaves,
those outlets for the refuse of plants, vast quantities of parti-
cles which are no longer of use in its structure. So, in all
animals, the same internal changes are going on, and to a
much greater extent ; because, from the activity of their na-
ture, there is more of wear and tear, and, therefore, more of
refuse matter to be disposed of. As you will see in another
part of this book, the human body, that most complicated of
organized beings, undergoes these changes very largely.
12. It is not thus with unorganized substances. The crys-
tal, so fast as it is formed, becomes permanent. No changes
occur within it. In itself, it is unchangeable. It can not
change its own particles, as the plant or the animal does. It
can be changed only by external addition, or by external dimi-
nution, through the influence of agents acting upon its surface.
13. With the constant changes going on in organic nature,
there is constant succession. Plants and animals produce other
plants and animals, and themselves die, making room for their
successors. But the crystal does not form other crystals, and
then crumble into dust. In itself, it is both unchangeable and
unproductive.
14. This distinction between organized and unorganized sub-
stances, in relation to change and succession, meets the eye
everywhere. The mountains, the rocks, and even the stones
under our feet, remain the same year after year, while all vege-
table and animal life is ever changing its forms and manifesta-
tions. There are the changes of growth, and the changes of
decay and death, all around and within us; and they are
strangely mingled together. There is death even in the
changes of life, as the waste particles are taken away, and are
replaced by the new ; and life springs out of the very bosom
of death, as from decayed nature new forms of vigor and
beauty arise. The mountains stand as they have stood, as the
passing generations have looked upon them, while the continual
changes of vegetation have been going on upon and around
them. The seasons crown their battlements with the emblemi
ORGANIZED AND UNORGANIZED SUBSTANCES. 17
Different forms of organized and unorganized substances.
of their ever-returning mutations of life, decay, and death;
and even the mighty trees, that have shed their leaves from
year to year, in obedience to the great law of change, but have
themselves stood, at length bow their heads to the same law,
and give place to other lords of the forest. From the " ever-
lasting hills," which thus remain the same, though change is
ever about and upon them, man gets the unchangeable and
imperishable rock to construct his habitation, while he himself
is changeable and perishable the creature of a day, whose
life is as a vapor. He wears the precious stones, and traffics
in the golden ores, which have existed from the creation of the
world, through all the changing and dying generations, and
passes away, leaving them to others as changeable and perish-
able as himself.
15. Another distinction between organized and unorganized
substances relates to the forms which they assume. There is
regularity in both, but it is different in each. Unorganized
matter is disposed to arrange its particles in straight lines, and
with angles mathematically exact. You see this in the beautiful
crystal ; and you also see it, less definitely, but magnificently,
displayed in the regular battlements and columns of rocks and
mountains. The tendency is to regularity ; and irregularity is
the result of interfering circumstances. A similar disposition
to regularity is manifest in organized substances, but in a
different manner. It is disposed to curved, rather than straight
lines, and seldom makes lines or angles with mathematical ex-
actness. We see this .law of regularity exemplified both in
animal and vegetable life. The leaf, for example, has the same
general shape, that is, the same general arrangement of par-
ticles, when it attains its full size, that it had when it was
small ; and the same can be said of the arm of the man, com-
pared with his arm when a child. Illustrations might be cited
to any extent, but these are sufficient.
16. While the law of regularity is not commonly as exact
in organized substances as it is in the unorganized, it is quite
as authoritative. While it does not ordinarily observe the per-
fectly straight lines and the unvarying angles which we always
find in the crystal, the general plan and contour are very strictly
preserved amid all the changes of animal and vegetable life.
And, in some cases, the same mathematical exactness that we
find in the mineral world is found in organized beings. I
know not that this is ever true of straight lines and angles ;
but it is often true of curved lines. There are many very
2*
18 HUMAN PHYSIOLOGY.
Regularity in form in some cases wonderful.
beautiful examples in the vegetable world. I will give but a
single one. If you look at the common 'white daisy, before tho
hundreds of little buds in its bosom have opened into tiny
flowers, you will see them arranged with great exactness in
crossing curved lines, such as you often see on the back of
a watch case. A similar arrangement you will find in many
flowers.
17. This regularity is more wonderful in organized sub-
stances than in the unorganized, because it rules in them in the
midst of constant change. In the case of the crystal, as there
are no internal changes in it, and as each layer of it, when
formed, is permanent, regularity is comparatively, so to speak,
easily secured. But in the case of the leaf, as it is growing to
its full size, and of the arm, as it grows from infancy to be
the stalwart arm of manhood, continual change is going on at
every point ; and regularity here is obviously a more difficult
achievement.
18. This regularity appears still more wonderful, when we
look at the infinite variety of forms in organized matter, in
both the vegetable and the animal world. In all these forms,
each part of every animal and of every plant maintains its
own peculiar plan and contour. Take, for example, the leaf in
its endless varieties. How definitely does each variety preserve
its individual character, and how easily is it distinguished from
every other variety ! The same can be said of every part of
every organized being.
19. Another circumstance still must be mentioned, as adding
to the wonderfulness of this regularity. It has been scrupu-
lously maintained, through all the changes of the world from
its creation, when God pronounced the works of his hands to
be "very good." The leaf of every tree, for example, is like
the leaf of its ancestral trees back to that time ; and so it will
be in all its successors to the end of the world. " The trees of
the garden," which delighted the eyes of our first parents, and
refreshed them with their shade in their innocence, and amid
which they hid themselves after their sin from the presence of
their Maker, undoubtedly had the same characteristic shapes,
and the same leaves and flowers which their successors present
to our eyes.
20. Again, it is interesting to notice that, in the midst of
this regularity, so strictly maintained in each specific form from
age to age, there is a measure of irregularity allowed. While
each kind of tree, for example, has specific characteristics in
ORGANIZED AND UNORGANIZED SUBSTANCES. 19
Variety of form ; yet regularity preserved. Size.
the arrangements of branches and other parts, and in the
shapes of "its leaves, no two trees of the same kind are exactly
alike, and there is always much variety in the leaves of the
same kind. The wonder is, that so much latitude is allowed
in this respect, and yet the specific characteristics of each kind
are so thoroughly preserved. We can readily see that if a
pattern, definite in all its details, were to be copied exactly in
each kind of vegetable and animal form, the distinctions between
them could be more easily preserved. But Omnipotence is
able to combine a wide latitude and variety of form in each
kind, with a strict and uniform preservation of its characteristic
contour and arrangement. We have a striking exemplification
of the above remarks in the variety of the human countenance.
While the face of man is so entirely different from the face of
every other animal, at the same time, among the hundreds of
millions of the human family, how uncommon it is to find two
faces that are very nearly alike.
21. In the animal world, we see remarkable examples of the
preservation of regularity of form in the exact correspondence
which exists so commonly between the two halves of the body.
For example, the brain has two halves, which are precisely alike,
and the same is true of the nerves which are distributed from
it. And so of other parts. But, mingled with this symmetri-
cal arrangement of parts, there are other parts which are irreg-
ular in their shape. This is the case with the stomach, the
heart, the liver, <fec. There are some animals which are alto-
gether destitute of this arrangement of two similar halves of
the body. The oyster is a familiar example. The shell of this
animal is strikingly in contrast, in this respect, with the shells
of some other of the bivalve tribe, as, for instance, the common
clam.
22. There is a distinction between organized and unorganized
substances, in regard to size, which must not pass unnoticed in
this connection. The size of unorganized bodies has no fixed
limit. A crystal or a rock may grow to any imaginable size,
if the particles forming 'it are sufficiently abundant. But or-
ganized bodies have limits fixed to their growth. There is, it
is true, more or less latitude to these limits ; but they are so
well defined in the case of most vegetables and animals, that
when growth reaches much beyond or below the limit, it is
recognized as a remarkable fact. Gigantic and dwarfish vari-
ties are rare exceptions to the general rule.
23. The last distinction, between organized and unorganized
20 HUMAN PHYSIOLOGY.
Difference between organized and unorganized in structure and elements.
substances, which I shall mention relates to their structure.
While unorganized substances are made of one form of matter,
either solid or liquid, or gaseous, organized bodies are made of
a mixture of fluids and solids. They are therefore more or less
soft and flexible; while the solid, unorganized substances are
hard and brittle. There is a still further difference in struc-
ture. Organized substances are much more compound than
the unorganized. Most of the unorganized substances are
composed of only two or three elements. Thus, air is com-
posed of oxygen and nitrogen, water of oxygen and hydro-
gen ; and most of the mineral salts are composed of three
elements as, for example, carbonate of lime, or chalk, which
is composed of oxygen, carbon, and calcium, the mineral base
of lime. But organized substances are composed of at least
three or four elements, and sometimes more. The four princi-
pal elements in the composition of organized bodies are, oxygen,
nitrogen, hydrogen, and carbon. But there are other elements
introduced for special purposes. Thus, carbonate of lime (a
combination of calcium with two of the common elements,
carbon and oxygen,) is diffused very generally throughout the
textures of plants, giving them firmness and strength. In the
grass tribe, silex is deposited under the surface, producing the
necessary combination of strength and lightness, a very small
quantity of the silex answering the purpose. In animals of
the higher orders, phosphate and carbonate of lime compose in
part the framework of the body. We find iron, too, in the
blood. Of the fifty-four elementary substances discovered in
mineral bodies, only eighteen or nineteen have been found in
plants and animals, and some of these in very small amounts.
The essential components of living substances are the four non-
metallic elements mentioned above oxygen, hydrogen, nitro-
gen, and carbon; while the bulk of the inorganic world is
composed of the metals and their compounds, viz., the alkalies
and the earths. And it is interesting to observe that, of the
four elements which compose the bulk of the animal and vege-
table world, both the fluids and the Solids, three are gaseous,
while but one, carbon, is a solid substance.
DISTINCTIONS BETWEEN ANIMALS AND PLANTS. 21
Locomotion. Stomach and other central organs.
CHAPTER II.
THE DISTINCTIONS BETWEEN ANBTALS AND PLANTS.
24. HAVING pointed out in the first chapter the distinctions
between organized and unorganized substances, I now proceed
to consider the distinctions between the two classes of organ-
ized beings animals and vegetables. I shall first notice those
differences which are obvious when we look at the great major-
ity of animals and vegetables ; and shall then point out those
which are essential, in order that we may have a clearer view of
those exceptional cases, in regard to which it is somewhat
difficult to decide to which of the two kingdoms they belong.
25. One of the most obvious distinctions is in relation to
locomotion. The plant remains in one place ; while the animal
moves about, in the air, or in the water, or upon the surface of
the earth. And the structures of the animal and the plant of
course differ, so as to accommodate these two very different
modes of existence. I will particularize. As the animal moves
from place to place, it must, for this reason, if for no other,
have an apparatus of nourishment and growth different from
that of the plant. The plant, by means of its absorbents in
the roots, takes up from the earth, in the form of sap, its nutri-
tion, or food, as it may very properly be called. The moving
about of the animal would in itself forbid its deriving its food
directly from the earth, even if the earth contained the proper
materials for its nourishment. Another contrivance must
therefore be resorted to, in order to effect nutrition in its case.
So a cavity is provided in its body, called a stomach, into
which nutritious substances can be introduced. And this cav-
ity is lined with absorbents, which there do for the animal
just what the absorbents in the roots of the plant do for the
plant.
26. Besides the stomach, there are other great central or-
gans which are peculiar to most animals, in distinction from
vegetables as the heart, the liver, the lungs, <kc. In the
plant, there are no such central organs upon which the whole
plant depends. Branches and roots may be cut off extensively,
and even a large portion of the stem or trunk may be des-
troyed ; and yet what remains of the plant may still live. And
22 HUMAN PHYSIOLOGY.
Feeling. Motion. Sensitive plant and catch-fly.
even more than this. A small portion of it may be made to
take root and live by itself. It is not so with most animals.
Mutilation can not be carried far without injuring some large
organ which is essential to the life of the whole ; and no part
taken from its extremities can be made in any way to live by
itself.
27. Another obvious distinction is this. Animals are sen-
tient and spontaneously-moving beings, while vegetables are not.
The animal feels the action of agents upon it, and this it can
not do without consciousness and thought. The evidences of the
existence of consciousness and thought, and the consequent spon-
taneous motion, are very slight in some animals. Still, there is no
doubt of their existence in these cases. We see these evidences
plainly in the great majority of animals ; and we infer, very
properly, the existence of sensation and thought in those excep-
tional cases, where the evidences are doubtful or absent, as we
find in them other marks of animal in distinction from vege-
table life.
28. The distinctions which I have mentioned are those which
we see generally existing. Let us see how far they are essential
and universal.
29. The distinction in regard to locomotion, if we look at
the animal as a whole, has its exceptions. There are some
animals that are entirely confined to one spot during all their
existence, as the coral animal and the sponge. But, while
some animals are thus confined, they have the power of spon-
taneous motion in some of their parts, which is exercised for
the purpose of obtaining food, and, in some cases, for the
avoidance of danger. This power is not possessed by any plant.
Some few plants, as the sensitive plant and the Venus catch-fly,
(dionaea muscipula,) exhibit a property which resembles it, but
it is essentially a different thing. In these cases, the influence
of the stimulus that excites the motion is communicated from
particle to particle, from the point where the stimulus is ap-
plied; and the motion is only in one direction, and not in
various directions, as is the case with spontaneous animal mo-
tions. This can be very readily seen, if we compare the motion
of the sensitive plant or the catch-fly with those of the little fresh-
water polype, called the Hydra. This animal, of which I give
you here an enlarged representation, and also a representation
of its natural size, is found in ponds. It attaches itself to any
floating object a stick or straw, as seen in the Figure by a
kind of sucker. Thus supporting itself, it stretches out its long
DISTINCTIONS BETWEEN ANIMALS AND PLANTS. 23
Digestive cavity. Nervous system. None in plants.
FIG. 1.
HYDRA.
arms, to take for its food any
minute worm or insect which
may float within their reach.
When it catches one, it directs
it to the mouth, a, which opens
into the stomach or general cav-
ity. Now, in doing all this,
there is a variety, a compound
character in the motion, which
is in plain contrast with the
simple motion of the leaves of
the catch-fly and the sensitive
plant.
30. The distinction, in rela-
tion to a digestive cavity, can
not be made out in the case of
some of the lower animals. And,
if it could be, it is not an essen-
tial distinction. For it only
relates to a mere difference of
arrangement in the absorbents
that take up the nutritious substance in the two cases. The
absorbents in the stomach of the animal, as before remarked,
perform the same office that the absorbents do in the root of
the plant. They only do it in a different place, and after a
different manner. The same remarks, substantially, can be
made in regard to the other large central organs which are
found in most animals.
31. The last of the distinctions, which I mentioned as being
commonly observed, is really the essential distinction between
plants and animals. I mean the capacity for sensation and
spontaneous motion, which exists only in the animal. There
is nothing truly analogous to this in the plant. And we, ac-
cordingly, find a peculiar structure in animals, devoted to these
functions, and others connected with them. This structure is
the nervous system. No trace of such a structure has ever
been discovered in any plant. If there were any true analogy
between animal motion and the motions of the sensitive plant
and the catch-fly, we should be able to find in them traces of ner-
vous structure ; for the structure of these plants is so plainly
developed, that its constituent parts are easily distinguished.
32. The nervous system is evidently not essential to nutri-
tion, for this is as well effected in the plant as in the animal.
24. HUMAN PHYSIOLOGY.
Thought and will. Instinctive and automatic motions.
This is accomplished in both in substantially the same way.
The means by which it is done, and its arrangements are modi-
fied, as you have seen, in the two cases, to suit the differing
circumstances. The nervous system, observe, then, is, for par-
ticular purposes, superadded in the animal to what ?.s common
both to the animal and the plant, and so constitutes the essen-
tial difference between them. And so, all the functions relating
to nutrition, which are of course common to plants and animals,
are called functions of organic life. But the functions which
are performed by the system superadded in the animal, the
chief of which are sensation and spontaneous motion, are
termed functions of animal life. These are sometimes also
called functions of relation, from the especial connection which
they form between the animal and all that is around him.
33. These animal functions, sensation and spontaneous mo-
tion, imply thought and will. The order of action is this:
sensation thought in regard to it action of the will in con-
sequence of thought then, from this action, an impression
carried through nerves to organs termed muscles motion in
them from their contraction. This order, however, is not
always observed. The first link, sensation, may be absent.
Thought, without any preceding sensation, may prompt the
will, and spontaneous motion results. The action of the will,
too, may be left out, or may be in opposition. Thus, emotions
may produce action of the muscles, the will not concurring,
and perhaps opposing ; as when we laugh at what is ridiculous,
or weep at what is sad, in spite of restraining efforts dictated
by the will.
34. There are also instinctive motions, and motions which
are termed automatic, with which the will has no direct con-
nection. And the connection of sensation with them is, in
some cases at least, doubtful. The action of the muscles, in
swallowing, breathing, &c., and the action of that compound
muscle, the heart, are examples of motions more or less dis-
connected from the will, and also from sensation. The action
of the heart is wholly removed from the direct influence of the
will, and it is at least not obvious that it is influenced directly
by sensation. It is influenced indirectly by both, through the
agency of emotions awakened by them. The muscles of breath-
ing, on the other hand, though ordinarily involuntary, may be
directly influenced both by the will and by sensation. You
can at will breathe faster and more deeply, and sensations of
uneasiness in the chest modify the breathing.
DISTINCTIONS BETWEEN ANIMALS AND PLANTS. 25
Central organs of nervous system. Most developed in man.
35. For all these different actions, thus produced in different
ways, there are central parts of the nervous system upon which
the causes of these actions produce the impressions or impulses
from which the actions result. Thus, when a sensation is fol-
lowed by a spontaneous action of muscles, an impression is
conveyed by nerves to the central organ ; the will there acts,
and the impulse there given by this action of the will is car-
ried by other nerves to the muscles, which execute the intended
movement.
36. These central parts or organs, which are the media, the
instruments of impressions, are in different parts of the body
of the animal; but the most important of them is what we
call the brain. This part is developed most in those animals
that give the greatest evidences of intelligence ; and, therefore,
it is more prominent in man than in any other animal.
37. It may be remarked, as a general truth, that the nervous
system, and its associate or subordinate system, the muscular,
are developed in different degrees or forms, to suit the different
characters and wants of animals. In man, they are more com-
plex and perfect than in any other animal. The brain, in him, is
a large organ, occupying the skull. The spinal marrow, and
other central parts, and the nerves, are largely developed. And
the muscles which are moved by this nervous system form a
large portion of the bulk of the body. The organs of nutrition,
analogous to those which make up nearly the whole of the
plant, occupy the two cavities of the trunk of the body, the
thoracic and the abdominal. But, as we descend in the animal
kingdom, the nervous system becomes continually less promi-
nent, and the system of mere nutrition more so. We at length
come to animals, in which the nervous system is a mere small
appendage to the system of nutrition, and only serves to direct
the muscles in securing the food of the animal. In some of
these, we not only do not find a brain, but we fail to discover
any traces of a nervous system. This is true of the Hydra,
noticed in 29.
38. The nervous system, which so clearly distinguishes most
animals from all plants, is fairly presumed to exist, though in
an exceedingly slight degree, in those beings in which it can
not be found, but in which we find other characteristics of the
animal kingdom. And it is presumed, also, that the exercise
of thought and the action of the will, which most animals so
plainly exhibit, while they become less and less obvious as we
descend in the scale, are not wholly obliterated in the very
26 HUMAN PHYSIOLOGY.
No nervous system in some animals; yet feeling and thought.
lowest animals. It may, perhaps, be said, that as muscular
action, as mentioned in 34, is sometimes produced even in
man without the intervention of thought or the will, it may be
produced in animals of the lowest order altogether in this way.
But we may more rationally infer that, as the chief object of
motion in them is the securing of food, it is guided by the
action of a will in obedience to their sensations. In other
words, it is truly a spontaneous, and not a mere automatic mo-
tion. And it is probable that there is in the very lowest of
animals some degree, though it may indeed be slight, of enjoy-
ment in the sensations received from the moving water about
it, and from the satisfying of its wants in the process of nutri-
tion. We will take the Hydra, a representation of which is
given in Fig. 1, page 23, as an illustration of the above remarks.
It is a minute gelatinous animal, in which no nervous or mus-
cular fibres can be found. And yet it has an extraordinary
power of extending and contracting itself. When it is alarmed,
it draws in its arms, and shrinks into the form of a little glob-
ule ; and if you should see it in this condition, you would not
suspect that it had any arms or tentacula. But when it is
searching for food, it often extends its body and its arms to a
great length ; and when it grasps its prey, it puts it into its
stomach, which constitutes, so far as we can see, its whole
body. We can not conceive of all these motions, thus exe-
cuted to effect certain definite objects, without the agency of a
will, and without sensations to prompt the will and guide the
motions. The animal must have a power of choice, or it would
put a bit of stick or straw into its stomach as readily as a
worm or an insect. But the tentacula never grasp, among the
various bits of things which float against them, any thing be-
side the appropriate food of the animal. And it undoubtedly
enjoys its food as really, though perhaps not as vividly, as any
human epicure ; and has in some measure the same pleasur-
able sensations which locomotion produces in us, as it floats
along so quietly, with its arms hanging down from its body.
Though there be no nervous fibres to be seen in the loose gela-
tinous structure of this little creature, yet, as the phenomena
which it exhibits are known to be produced by the nervous
system in those animals whose structure is more plainly and
thoroughly developed, we justly infer that there must be
nervous matter, in some form, in this and other similar ani-
mals.
39. One more important distinction between animals and
MAN IN HIS KELATIONS TO NATUKE. 27
Peculiar endowments of man. Abstract reasoning. Conscience.
plants remains to be noticed. It relates to their chemical com-
position. I stated, in 23, that organized substances are com-
posed mostly of four elements oxygen, hydrogen, nitrogen, and
carbon. Plants differ from animals, in having but little nitro-
gen in their composition. It was formerly supposed that they
contained none of this element. It is found only in particular
parts of plants, as the seeds. We may regard carbon as the
most characteristic constituent of vegetables, and nitrogen of
animals. And in this connection it is interesting to observe
that, while carbon is largely thrown off from the lungs of ani-
mals, in the shape of carbonic-acid gas, it is as largely absorbed
by the leaves of plants. Of this feet I shall take more par-
ticular notice when I come to the subject of respiration.
CHAPTER III.
MAN IN HIS RELATIONS TO THE THREE KINGDOMS OF NATURE.
40. MAN is commonly spoken of as being at the head of the
animal kingdom, and in the book of the naturalist is made an
order of the class termed Mammalia. As the basis of the
whole classification is mere material organization, and has no
reference at all to mental or spiritual endowments, the classifica-
tion, in regard to man, is in its principle correct. At the same
time, it must be admitted, that it fails to recognize altogether
the essential distinctions between man and other animals.
These distinctions, making, as they do, a wide gap " an im-
passable chasm," as Professor Guyot expresses it between man
and the inferior animals, are to be found in certain peculiar
spiritual endowments which man possesses. These I will no-
tice now in the briefest manner, leaving ij^ for another part of
this book to treat more fully of this and other kindred subjects.
One of these endowments is the power of abstract reasoning.
Other animals in a certain sense reason, that is, they make in-
ferences; but they never arrive at any general or abstract
truths. Another endowment is a moral one, linking man in his
spiritual nature to the Deity. It is conscience, or the knowledge
and sense of what is right, in distinction from what is wrong.
Other animals, in obedience to the passions of fear and love,
28 HUMAN PHYSIOLOGY.
Immortality. Real relation to the animal kingdom.
sometimes appear to the superficial observer to have an idea of
what is right, as such ; but there is not the slightest evidence
that they really have any such knowledge.
41. In view of these endowments of man, it is wrong to
consider him merely as being at the head of the animal king-
dom. He is something more than this. He is so much and
so distinctly more, that the accepted classification of him, on
the ground of mere difference of organization, gives a most
inadequate idea of his true position in the scale of being. It
leaves entirely out of view the essential distinctions; and it
separates man from other animals, as you will see, by a distinc-
tion of organization which is of rather a trivial, perhaps ques-
tionable, character.
42. The force of this view of the subject is enhanced, if we
take into consideration that great fact, revealed to us by God
in his Word, that man is destined to immortality. It may be
objected that, as this fact is learned only by revelation, and not
by observation, it is not to be regarded as a scientific fact.
But, granting that there is truth in the objection, it certainly
is allowable to allude to the revelations of Scripture, as con-
firming or enforcing views developed by scientific observation.
This is all that I have done in this case. The view which I
have presented is based upon endowments that are recognized
by the scientific observer, without the aid of revelation ; and I
appeal to the revealed fact of man's immortality, as adding
force to this view, and not as being at all necessary to the
establishment of its truth.
43. Let us look at this subject in another point of view.
The grand essential distinction between animals and plants lies,
as you have seen in the last chapter, in the fact that animals
have a nervous system. Now, with this system, as you have
also seen, appear certain mental manifestations. These differ
widely in different animals, and are most prominent in those in
which this system is most prominent and complicated. As we
trace upward these complications, when we come to man, we
find certain mental manifestations, which separate him by " an
impassable chasm" from all other animals. Till we arrive at
him, the difference is one of degree, for the most part. But in
his case it is a difference of kind, and a very wide one. Of
such a difference the naturalist should certainly take very dis-
tinct cognizance ; and, if it be not consistent for him to do so
in his classification, great force and prominence should be given
to these views in his instructions on this subject. As the super-
MAN IN HIS RELATIONS TO NATURE. 29
The hand of man. No other animal really has such a member.
adding of the nervous system separates the animal from the
plant, so, also, as Professor Guyot very justly maintains, the
superadding of such endowments as we find in man separates
him, by a chasm quite as " impassable," from other animals.
44. The distinction commonly received as the ground of
classification for man, I have said, is a trivial, perhaps a ques-
tionable one. He is said to have two hands, and so makes the
order Bimana ; while apes and monkeys are said to have four
hands, and are, therefore, considered as making the order
Quadrumana. Now, if we observe carefully and fully the won-
derful endowments of the human hand, we shall hardly be
willing to allow that monkeys and apes have four such mem-
bers. With a full view of the capabilities of the human hand,
those members can not be considered as hands, but as members
possessing some of the properties of both hands and feet.
They are given to these animals to enable them to climb with
facility, and to grasp their food ; and they have none of that
infinite variety of motion, which is so striking a peculiarity of
the hand of intelligent man. The ground upon which they
are said to have four hands is that which is thus stated by
Cuvier. " That which constitutes the hand, properly so called,
is the faculty of opposing the thumb to the other fingers, so as
to seize upon the most minute objects." No animal besides
man has this arrangement, except the Quadrumana. It is
claimed, therefore, that they have hands, although they are
very imperfect when compared with the hand of man. The
imperfection is indeed so great, as to make us at least reluc-
tant to admit the claim set up by the naturalist. " While,"
says Carpenter, " the thumb in the human hand can be brought
into exact opposition to the extremities of all the fingers, whe-
ther singly or in combination, in those Quadrumana which most
nearly approach man, the thumb is so short, and the fingers so
much elongated, that their tips can scarcely be brought into
opposition, and the thumb and fingers are so weak, that they
can never be opposed to each other with any degree of force.
Hence, although admirably adapted for clinging round bodies
of a certain size, such as the small branches of trees, &c., the ex-
tremities of the Quadrumana can never se:ze any minute object
with such precision, nor support large ones with such firmness,
as are essential to the dexterous performance of operations for
which the hand is admirably adapted." Indeed, what is called
the thumb of the Quadrumana is so short and slender, that Eus-
tachius, the anatomist, very properly said that, regarded as an
30 HUMAN PHYSIOLOGY.
Other peculiorfties. Chin. Erect posture. Weeping nnd laughing.
imitation of the thumb of man, it is a ridiculous affair. I
then, we take into view the extensive and varied capabilities of
the human hand, we must agree with Sir Charles Bell, when
he says that " we ought to define the hand as belonging exclu-
sively to man." This view of the subject has always impressed
itself upon the minds of acute observers in all ages. Aristotle
said, that man alone possesses hands deserving of the name.
Anaxagoras said, that " man is the wisest of animals, because
he possesses hands." And the opinion, thus uttered by these
philosophers some centuries before the Christian era, is fully
echoed at the present time.
45. It would seem, then, that, if mere organization be ad-
hered to, as the basis of classification, it is desirable that some
ground of distinction in relation to man be fixed upon, which
is more definite than the commonly received one. It is to be
remembered, however, that, in classification, some one very ob-
vious peculiarity that presents itself to the eye is ordinarily
made use of as a mark of distinction, while accurate and full
discriminations are followed out entirely separately from the
mere classification. This is done in the case of man. His
structure differs in many respects from that of the inferior ani-
mals. It would make this chapter too long to point out all
the differences. Some of them are important, while others are
not. As an example of the latter, I will mention the fact, that
no animal but man has a chin. Every other animal has its
lower jaw retreating from the teeth, instead of projecting for-
ward below, as in man. One of the most important and strik-
ing peculiarities of man's structure is that general arrangement
which enables him to be in the erect posture. No other animal
naturally assumes this posture, or is able to maintain it for any
length of time; and most animals assume one which is en-
tirely the opposite of this. Even the monkey, when taught by
man to stand and walk, is by no means erect ; but his lower
limbs are crooked, and the moment that he escapes the neces-
sity of being an imitator, he is on all fours. There is a distinc-
tion of an interesting character, which concerns both the ner-
vous and muscular systems. I refer to the fact, that no animal
tout man can shed tears, or perform those muscular motions
which are necessary to the acts of weeping and laughing. In
view of this marked distinction, man has sometimes been desig-
nated as " a laughing and crying animal."
46. But the great essential distinctions, to which all the rest
are really tributary, are, as I have before stated, of a mental or
MAN IN HIS RELATIONS TO NATURE. 81
Tendency to skepticism. Robinet's doctrines.
spiritual character. And these should always be made peculi-
arly prominent, whenever the distinctions between man ant!
the inferior animals are treated of by the naturalist. This
should be done, not only because they are essential, but also
because, as I have just hinted, all other distinctions are subor-
dinate and tributary to them. It is the mental peculiarities of
man, for the most part at least, that render necessary those
peculiarities which distinguish his organization from that of
other animals. I will not dwell on this point, as I shall speak
of it in another part of this book.
47. In view of this whole subject, it may be said, that the
classification upon which I have commented is not of itself of
very great importance, provided that the definite distinctions,
which have been pointed out as existing between man and
other animals, be clearly recognized by the naturalist. The
tendency, however, evidently is, to lose sight of these distinc-
tions in the exclusive regard which is paid to mere material
organization. This tendency, it is true, is effectually counter-
acted in the case of the great majority of scientific men, by
the comprehensive and Christian views which they take of the
whole subject ; but, still, it manifestly exists, and gives rise to
many sceptical notions, especially in superficial and theorizing
observers. Great care, then, should be taken to oppose this
tendency in all public teaching on this subject, whether it be
done by books or lectures.
48. There is a disposition, on the part of some writers, to
obliterate the grand distinction between man and the inferior
animals, and other distinctions which are stamped by the Cre-
ator upon his works. Some go so far as to maintain, that there
is not only no line to be drawn between the animal and the
vegetable kingdoms, but none even between organized and un-
organized substances. Robinet, and many other European
authors, teach that all matter has living properties, and that
every object that we see, whether mineral, vegetable, or animal,
is the result of repeated and progressive efforts of nature. The
ultimate aim of these efforts is considered to be the formation
of man, who is looked upon as the perfection of organization
evolved by these efforts. In advocating this theory, they make
great use of resemblances and analogies, and even represent
the fantastic shapes which minerals sometimes assume, from
their slight resemblance to parts of the human body, " as so
many proofs," in the language of Carpenter, " of this long and
bungling apprenticeship of nature to man-making." Although
32 HUMAN PHYSIOLOGY.
Gradations in nature. Wrong ideas of perfection.
such ridiculous doctrines are seldom formally advanced, there ia
a disposition in many scientific men to indulge in speculations
which have more or less resemblance to them. They seem dis-
posed to confuse with the veil of mystic scepticism the clear
characters which God has imprinted upon the manifestations
of his power. It is well, therefore, to fix these characters
definitely in the mind, in order to guard against the fascinating
and bewildering speculations of a false science. A true science,
forsaking the mazes of speculation, and inquiring only for the
facts, reads with admiration and reverence the clear lines of
God's handiwork, and attributes to no imaginary agency, termed
Nature, what bears the marks of exquisite design and Almighty
power.
49. An idea, somewhat akin to that of Robinet, is sometimes
entertained, viz., that the varieties in the mineral, vegetable,
and animal kingdoms are mere gradations in nature. There
would be some plausibility in this notion if it were difficult to
distinguish the minerals of the most perfect kind from the lowest
plant, and then the plants of the highest order from the lowest
animal. But the difficulty lies in other quarters. The most per-
fect in the three kingdoms are distinguished from each other in
the most marked manner ; and it is only when the character-
istic qualities are the least developed that there is any difficulty.
One kingdom is a no more perfect formation than another.
The < crystal, with its exact lines and angles the plant, with
its curvilinear and less definite shapes and the symmetrical
animal, are equally perfect in their kind. Each is made for
a definite purpose, and is perfectly adapted to that purpose.
In none is there any imperfection which could be remedied by
endowments taken from another kingdom of nature. In the
vast variety of forms which nature presents, there is to be seen
no vain struggling after a higher and better state. There is no
progressiveness, aiming at an ideal perfection. Neither are there
gradations leading to it. All the works of the Creator are per-
fectly adapted to the spheres which they fill. They were all,
from " man, made in His image," down to the humblest ani-
mal or plant, pronounced to be "very good," as they came
from His hand.
50. Let me not be understood to say that there are no gra-
dations in nature. There are some of a very interesting char-
acter ; but they do not obey any such laws as those which are
indicated by Robinet and other fanciful theorizers. There are
gradations in both the animal and vegetable world. You ob-
MAN IN HIS RELATIONS TO NATURE. 33 *
Man inferior to other animals in some respects.
serve them as you go from the simplest plant up to the most
complicated. And so of animals. But these two kingdoms
of nature are separate in their gradations, and are not in one
series together, as is represented by Robinet. And the grada-
tion in each kingdom is by no means an unbroken and regular
one, going up, step by step, from the lowest to the highest.
For example, in the animal kingdom, there are not constant
and regular additions made, as you trace the gradations up-
ward. And though man stands at the top of the series, it is
not as a compound, made up of all the excellencies found
below him, with additional excellencies peculiar to himself.
Superior as he is, as a whole, to all other animals, yet in some
respects he is inferior to many of them. He is inferior to them
in the wonderful capabilities of instinct. Some animals can do
some things better than he can. The monkey is a better
climber. Some animals can do what he can not. Birds and
winged insects fly, but he can not. These points could be
illustrated to any extent, but this will suffice.
51. Man is often spoken of as being the most perfect of ani-
mals. This, as you will see from what was said in a previous
paragraph, is not true in the strict sense of the word. His
organization is more complicated, and he has more and higher
endowments than any other animal ; but the perfection of struc-
ture, and of adaptation in contrivance to the purposes aimed
at, is as manifest in all the varieties of animals as it is in
man.
52. In one respect, there is a gradation existing through the
three kingdoms of nature. It is in regard to formation or nu-
trition. All the elements which are found in the composition
of animals exist in the mineral world. But these elements,
with very few exceptions, can not be transmitted directly to
animals, but they are transmitted indirectly through vegeta-
bles. No animal, therefore, can live on mineral substances,
although these substances contain all the elements found in its
composition. But vegetables draw their nutriment from the
mineral world, and then furnish nutriment to animals. There
is, therefore, in relation to formation, a gradation running
through the three kingdoms, from the mineral up to the ani-
mal.
53. At the summit of the last step in this gradation stands
man. To him, not only is the animal kingdom tributary, but
so, also, are the mineral and vegetable kingdoms. They are all
made for him, to beautify and gladden this his temporary home,
34 HUMAN PHYSIOLOGY.
All nature tributary to man. Imperfectly so.
and to sustain him in it. The subjection of them to him was
undoubtedly perfect in his primeval condition of innocence in
the garden of Eden. But now, we see this tributary subjection
manifested only as a general fact, with many exceptions. These
mark this life as the imperfect state, and this world as the
temporary home of man, in which he can prepare himself
for the perfect and everduring state and home of another life
beyond.
PART SECOND.
CONTAINING,
CHAPTER IV. GENERAL VIEWS OF PHYSIOLOGY, WITH A BRIEF ACCOUNT OF SOME OF TH
STRUCTURES IN THE BODY. CHAPTER V. DIGESTION. CHAPTER VI. CIRCULATION.
CHAPTER VII.-RJCSPIRATION. CHAPTER VIlI.-FoRMATiON AND REPAIR. CHAPTER
CHAPTER IV.
GENERAL VIEWS OF PHYSIOLOGY, WITH A BRIEF ACCOUNT OF SOME
OF THE STRUCTURES IN THE BODY.
54. THE contents of the previous chapters are preliminary
to the consideration of the real subject of this work, the Physi-
ology of Man. But they were necessary, in order to accomplish
a very prominent object which I have in view. It is my wish
that the student, as he examines the functions of the human
system, should at the same time observe the analogies existing
between man and other living beings, in the processes of life.
He will, in this way, get an enlarged view of man in his rela-
tions to the world around him, and will be prompted to observe
the phenomena of life, in whatever department of nature they
may be presented to his view. And, in order to promote this
object effectually, I shall, as I proceed with the development of
the physiology of man, refer occasionally to the analogous phe-
nomena in other animals, and also in plants. This will serve
to fix more definitely in the mind of the student the main facts
that are to be communicated, at the same time that the bound-
aries of his knowledge will be extended over fields full of in-
terest.
55. This is a work on Physiology, and not on Anatomy.
Physiology treats of the offices or functions of the different
parts of the structure, while Anatomy has regard to the struc-
ture itself. In the following pages, I shall introduce the anat-
omy of the system only so far as it is necessary to elucidate its
physiology.
Before proceeding to an examination of the individual sub-
jects which will claim our attention, it will be proper to present
some general views of them in their relations as a whole.
36 HUMAN PHYSIOLOGY.
Natural division of the subject. Interest of the study.
56. You have seen, in the preliminary chapters, that organ-
ized living beings have much that is common to them all. This is
true so far as nutrition is concerned. You have seen that the
animal grows very much as the plant does, and that the
arrangements for its growth vary from those of the plant only
so far as the difference of the source of its nourishment, and of
the circumstances under which it is obtained, require. The
grand distinction, as you have seen, between animals and
vegetables is to be found in the functions belonging to the
nervous system. These functions are wholly separate from the
nutritive functions, which animals perform in common with
plants.
57. This view of the subject suggests a natural division of
the physiology of man into two parts, viz., the nutritive func-
tions, and the animal functions, or those connected with the
nervous system. In other words, the first division will com-
prise all those subjects which relate to the building and repair-
ing of the human structure ; and the second will comprise those
which relate to the uses for which the structure is made. The
first class of subjects includes digestion, circulation, respiration,
formation, and excretion. The second class includes locomotion,
sensation, the five senses, the voice, instinct, thought, &c.
58. The student will see at one glance, that a wide range of
exceedingly interesting subjects opens before him. Contem-
plated as a mere mechanism, the human system is full of won-
ders. The principles of common Mechanics, of Hydraulics, of
Pneumatics, of Optics, of Acoustics, are abundantly illustrated
in the human body, by contrivances of the most exact and ex-
quisite adaptation. But this congeries of beautiful mechanisms
is all regulated by a nervous system, making it, by its minute
fibrils, to be alive with feeling in every part. Sensation and
sympathy govern, through the nerves, in a wonderful manner,
the ever-varying adjustments of all the parts of the complicated
system. It is not only mechanism, but living mechanism, that
develops to us its wonders, so numerous and diversified. And
then, when we look at the soul "that side of our nature
which is in relation Avith the Infinite" connected as it is by
the nerves with every part of this mechanism, the interest of
the study before us appears exceedingly great, and its variety
never ending. The study is a peculiar one. It is not the body
merely that you are to study in these pages ; but it is the body
and spirit united. The study differs from all others in this
-3spect. In other studies, you look at either matter alone, or
GENERAL VIEWS. 37
Bones. Two parts, animal and mineral. Cartilages.
spirit alone ; but here you look at them both, as brought to-
gether in mysterious union.
59. It will be proper, here, to say something in general of
the structure of the human frame, before proceeding to a par-
ticular view of individual subjects. I do this in order to avoid
a frequent turning aside for explanation, which would not only
be inconvenient, but would mar the interest of the study. It
will not be necessary to go into a full description of the nume-
rous and diverse textures, or tissues, (as they are commonly
called,) of the body. I will notice only some of the principal
of them.
60. From the osseous or bony tissue, the solid part of the
framework of the body is made. Bone is composed in part
of animal matter, and in part of mineral. The mineral
part is mostly phosphate of lime. These two parts of bone
are in different proportions to each other in the different
periods of life. The mineral part in the child is about one-
half of the bone ; in the adult, four-fifths ; and in the old,
seven-eighths. The bones are therefore very brittle in old age,
while they are somewhat yielding in childhood. The mineral
and the animal portions of bone can be separated from each
other. If a bone be put into diluted muriatic acid, the mineral
part will after a time become united with the acid, and the
animal part will be left, having the perfect shape of the bone.
Thus separated from the mineral part, it is so flexible, that it
can be tied into a knot without affecting its shape. On the
other hand, by subjecting a bone for some time to the action of
heat, the animal part can be removed, and the mineral part be
left by itself.
61. The animal part of bone is cartilage, or gristle. This
part is formed first, constituting a sort of mould, in which the
bone is to be formed. The mineral matter is gradually depos-
ited in the cells of the cartilage. In the very young child, you
can see that this process is not completed, especially if you ob-
serve the bones of the head. The bones are not united to-
gether, as they are in the adult; and there is so little of mineral
matter near their edges, that they can be bent with a very
slight pressure. The proportion of mineral matter which is
deposited in the cartilaginous bones varies much in different
animals. In many fishes, there is almost none of this deposit,
the skeleton retaining its cartilaginous character throughout
life.
62. Besides the cartilaginous portion of bones, there are car-
4
38 HUMAN" PHYSIOLOGY.
Ligaments. Muscles. Tendons. Cellular tissue.
tilages which are destined to remain so, instead of having
mineral deposits made in their cells. The ends of the bones
are tipped with them. They are placed between all the twenty-
four bones of the spinal column. They form the connecting
links between the breastbone and the ribs. Cartilage consti-
tutes the body of the outer ear, of the eyelids, and of the
lower part of the nose. The transparent part of the eye is
formed of cartilage. This substance is placed wherever firm-
ness and tenacity are required without hardness.
63. The bones are united together by ligaments of various
degrees of strength, according to the necessity of the case.
They are moved by muscles, which, in man, are bundles of
reddish fibres. Muscular substance is what is commonly called
the meat in animals. It is of various colors in different ani-
mals, or in the same animal at different periods of life. All
motion in animals is produced by muscles. I will not go into
an explanation of their action now, any further than to say,
that they act by contracting or shortening their fibres. Com-
monly there are tendons united with the muscles. These ten-
dons are composed of strong white fibres, and have no power
of contraction themselves. They serve merely as the cords
by which the contracting muscles move the bones and other
pails.
64. The most common tissue in the body is what is called
by the names, cellular membrane, cellular tissue, and areolar
tissue. This last name is most commonly used by physiologists
at the present time. The word areolar comes from the Latin
word areola, meaning a small open space. The term is appro-
priate, because this tissue is filled with minute spaces or cells.
The word cellular is quite as appropriate ; and, as this will be
more familiar to you, I shall make use of it whenever I shall
have occasion to speak of this tissue. That you may under-
stand what this tissue is, I will refer you to its appearance as
you see it in different meats. It is the delicate white substance
that you see between the different layers of muscle in a piece
of meat. If you notice particularly, you will see that it is
also between all the different fibres of the muscles. As the
spaces or cells communicate together, butchers sometimes " blow
up " this tissue in veal, in order to make the meat look more
plump. This tissue is the universal packing material of the
body. It is to be found almost everywhere. It surrounds
every thing, vessels, nerves, muscles, organs, &c. It enters
into their composition, uniting together different tissues, and
GENERAL VIEWS.
39
Communication between cells of cellular tissue. Shown in dropsy.
also the fibres of the same tissue. It varies much in its com-
pactness in different parts. It is very fine and compact where
it is necessary that it should be so ; while in other cases it is
loose and delicate, allowing a free motion of the parts which it
envelops and connects together. It is abundant and loose
among the muscles, and between them and the skin. Fig. 2
represents a portion of cellu-
lar tissue, inflated and dried, FIG. 2.
exhibiting the arrangement
of its larger meshes. This
ia magnified twenty diame-
ters. The free communica-
tion which exists between
the interstices or cells in this
tissue is exemplified in drop-
sy. These cells are bathed,
in the healthy state, with a
small amount of a watery
fluid ; and when this in-
creases largely, forming the
disease termed dropsy, it
obeys the force of gravity in
the cells, and accumulates
most in the lowest parts of
the lower extremities. This
tissue is very elastic in health,
so that if you press on the
skin, there is no indentation left when the pressure is taken
away, for the elastic cellular tissue at once rises from its state
of compression, pushing the skin before it. But in dropsy it
loses its elasticity by over distension ; therefore there is pitting,
as it is termed, after removing the pressure. We sometimes
have an opportunity of seeing the communication between the
cells manifested by the introduction of air into them. This has
occurred in some cases in which an opening has been made, by
disease or accident, from the air tubes in the lungs into the cel-
lular tissue in the walls of the chest. The whole body has
been seen largely swollen, from the air which has from this
cause accumulated in this tissue directly under the skin.
Among the many tricks of impostors, the inflation of the cel-
lular tissue of the head has been practised ; and as it produces
a frightful appearance, and therefore excites pity, the trick is a
very successful one.
CELLULAR TISSUE.
40 HUMAN PHYSIOLOGY.
Deposits of vat. Its uses. How kept in its cells. Mucous tissue.
65. There are here and there in the cellular tissue deposits
of fat. Various purposes are answered by these deposits. They
are sometimes of use in promoting a free motion of the adja-
cent parts. The eye has, intervening between it and the bony
socket, a cushion of fat, on which it rests, and against which
it is pressed when any violence is offered to it. Fat, as a non-
conductor, is a protection against the cold, and it is therefore
deposited largely in the cellular tissue under the skin, in ani-
mals that inhabit cold climates. Fat, also, sometimes serves as
nourishment to the system when its necessities require it. In
diseases in which food cannot be taken in any amount, the
fat is absorbed into the system. The heat of the body is
maintained also, in part, by this process. This occurs in the
torpid condition of hybernating animals. They commonly be-
come very fat in autumn, as a preparation for the winter, and
in the spring they come forth very lean, their store of fat having
been used up for the purposes of nutrition and heat during
their confinement. The fat thus deposited in the cellular mem-
brane or tissue is not diffused merely in the interstices, but it is
confined in cells of its own, which lie in these interstices. Mi-
nute blood-vessels pass from the fibres of the cellular tissue to
these fat cells. The fat, which is an oily fluid, is kept from
oozing through the pores of the cells that hold it by the blood,
which is very nearly four-fifths water, and by the watery fluid
which I have spoken of as bathing all the interstices of the
cellular tissue ; for oil, you know, will not pass through any
porous substance that is wet with any watery fluid. If a por-
tion of cellular membrane containing fat be dried, the fat, which
in the moist state is wholly confined to its cells, now oozes
through their pores. This is the reason that a lump of fat, as
it is called, feels so oily after it has been exposed for a while to
the air.
66. The mucous tissue is that which lines all the cavities of
the body that have outlets. It lines the mouth and the cavities
of the nose, and descends into the lungs, the stomach, &c. It
takes its name from the fluid called mucus, which is constantly
secreted by innumerable minute glands, that are situated in the
substance of this membrane. The chief object of this viscid
fluid is to protect the membrane from the substances which
come in contact with it, which would otherwise produce some
irritation. This membrane is continuous with the skin, shading
off into it insensibly, as you may observe on the lips.
67. The serous tissue or membrane forms the outer coat or
GENERAL VIEWS. 41
Serous membranes. Compound character of the organs.
lining of nearly all those organs the inner coat of which is mu-
cous membrane. This is the case with the lungs, the stomach,
and the intestines. The serous membranes are white, smooth,
and shining, and are lubricated with a watery fluid, called
serum. Every serous membrane forms a cavity or sac without
.an outlet, differing in this respect entirely from the mucous
membranes. Thus, in the case of the lungs, the serous mem-
brane lining the outside of each* of these organs passes from
the lungs to the walls of the chest, lining the inside of them,
arid thus makes a sac without an outlet for each lung. This
sac could be dissected off, and taken out whole. When the
fluid which lubricates the inside of this sac increases to any
extent, the disease called dropsy in the chest is produced. The
membrane which thus lines the outside of the lungs and the
inside of the walls of the chest is called the pleura, and it is the
seat of the disease termed pleurisy.
68. I have thus described some of the principal of the tis-
sues which make up the human structure. The other tissues
will be spoken of in the proper connection as we proceed. Be-
fore dismissing this subject, I will call your attention to the fact,
that the organs of the body are generally composed of several
tissues united together. Thus, the stomach has three coats, as
they are termed, the mucous as the inner coat, the serous as
the outer, and the muscular between them. And then we have
the cellular tissue uniting these together. Besides these, there
are arteries, and veins, and nerves, so that the stomach, which
looks like a simple pouch, is really quite a composite thing.
And the same can be said of the other organs.
69. Before entering upon the particular consideration of the
functions by which the system is built up and kept in repair,
it will be well to take a general view of them, that you may
see them in their connection and mutual dependence. Each
of these functions has its special and appropriate part to play,
in effecting the formation and repair of the structure. The
material from which all parts of the body are formed and
repaired is the blood. There are organs whose special duty it
is to make this material ; organs which distribute it ; and or-
gans which use it after it is distributed. There are also organs
whose duty it is to receive the blood after it has been used, and
fit it to be used again. This common building material of the
body is made out of the food ; and the succession of processes
by which it is done I will describe in the next chapter. After
it is made, it is distributed by the complicated apparatus of the
4*
42 HUMAN PHYSIOLOGY.
Summary of nutritive functions. Processes of digestion.
circulation. This apparatus is therefore the common carrier of the
building material of the system. It is the numberless little form-
ative vessels, so small as to be invisible to the naked eye, that
use the blood thus brought to them, and make and keep in
repair all the various structures that we see in the body. When
the blood has been used by these formative vessels, it is not fit
to be used again until it is submitted to a purifying process by
exposure to air ; and to this particular object the lungs are de-
voted. And besides all this, as there are continually some par-
ticles which, in the wear and tear of the machinery, become
useless, and even injurious, they must be got rid of in some
way; and so there are organs for this purpose organs of
waste, as they are termed. It is also to be remembered, that
the processes to which I have now alluded are so carried on,
that the heat of the body, as will be fully explained hereafter,
is steadily maintained. In the following chapters of this part,
I proceed to a particular examination of the functions of which
I have now given a brief summary.
CHAPTER V.
DIGESTION.
70. I SHALL include, under the term digestion, all those pro-
cesses which are necessary to effect the separation from the
food of its nutritious portion, and the introduction of it into the
circulation. A summary of these processes may be thus given.
The food is broken up and ground in the mouth, and it is at
the same time mixed with the saliva. It is then taken into the
stomach, where it is kept in constant motion, and is under the
solvent action of a fluid of a peculiar character. When it is
brought into the right condition, it is passed from the stomach
into the intestines. Here it is acted upon by two fluids, the
bile, the secretion of the liver, and the secretion of another
gland, the pancreas or sweet-bread. These secretions have
some agency in separating from the mass its nutritious portion,
and this is taken up or absorbed, in the form of a milky fluid,
by little vessels lying on the surface of the inner membrane of the
intestine. These vessels unite together to form a large tube,
and through this the milky fluid is poured into the circulation,
to replenish the blood.
DIGESTION. 43
Mastication. Teeth various, according to different kinds of food.
Having given this summary of the processes which make up
digestion, I proceed to speak of them more particularly in the
Border of their succession. In doing so, I shall notice some of
the points in which other animals differ from man, in regard to
these processes and the arrangements of the apparatus of diges-
tion.
71. Mastication is an important part in the process of diges-
tion. The teeth, which perform this act, are very hard bodies.
The body of a tooth is composed of two substances. The in-
ner part is called the ivory, and the outer is called the enamel,
which is exceedingly hard. The teeth are of different shapes
for different modes of action. There are long and pointed
teeth, for tearing; others, for cutting, which have a sharp edge;
and others, for grinding, having for this purpose a broad and
irregular surface. The teeth are differently shaped in animals,
according to the kinds of food which they eat. Thus, the her-
bivorous, or vegetable-eating animals, have grinding teeth to
bruise their food ; while the carnivorous, or flesh-eating animals,
have sharp-edged teeth and long-pointed teeth, by which their
food is torn and cut in pieces. And it is to be observed, that
the movement of the jaws always corresponds with the char-
acter of the teeth. In the carnivorous animals, the motion of
the lower jaw upon the upper is a mere up-and-down, or hinge-
like motion. As they have no grinding teeth, there is no
need of any lateral or grinding motion. But in the animals
that have grinding teeth, there is a lateral motion, to enable
them to grind. You see this difference very plainly, if you ob-
serve the dog and the horse while they are eating. In Fig. 3,
you see represented the teeth of a carnivorous animal. The
front teeth are long and pointed, for rending, while the back
FIG. 3.
FIG. 4.
TEETH OF HERBIVOROUS
ANIMAL.
TEETH OF CARNIVOROUS ANIMAL.
44 HUMAN PHYSIOLOGY.
Man an omnivorous animal.
teeth have a sharp edge for cutting. In Fig 4, you see repre-
sented the broad and irregular grinding surfaces of the teeth of
herbivorous animals. In animals that live on insects, the teeth
present conical points, which press into corresponding depres-
sions in the opposite jaw, as represented in Fig. 5, In those
that live on soft fruits, the teeth are rounded, as in Fig. 6.
These are quite in contrast with the tearing teeth of the carniv-
orous, and the grinding teeth of the herbivorous.
FIG 5. FIG. 6.
TEETH OF INSECTIVOROUS ANIMAL.
TEETH 01' FRUGIVOROU3
ANIMAL.
*72. There is an arrangement of the enamel and the ivory in
the teeth of the herbivorous which ought not to pass unnoticed.
Instead of having the enamel cover the ivory, as in the teeth
of the carnivorous, the two substances are arranged in upright
layers, as seen in Fig. 4. The object of this is plain. The
ivory wears away faster than the harder enamel, and, therefore,
the surface of the tooth always presents projecting hard ridges,
fitting them for grinding thoroughly. A miller would say, that
these are stones that never need picking.
73. So perfect is the correspondence of the teeth with the
kind of food on which the animal lives, that the skillful natural-
ist can infer very correctly, from the examination of the teeth
of an animal alone, the character of the food on which it lives,
and even the general arrangement of its structure. As man
has the three kinds of teeth which I have noticed, he is said to
be omnivorous, or an eater of all kinds of food In him, the
front teeth are the cutting ones ; what are called the stomach
and eye teeth are the tearing ones ; and the large back teeth
are shaped for grinding. It will be observed that the tearing
teeth, as they have not a very sharp point, and are no longer
than the other teeth, have but little power when compared with
the long and sharp tearing teeth of a carnivorous animal, as
seen in Fig. 3. As man can make use of instruments to cut
DIGESTION. 45
Wliales have no teeth. Substitute for teeth in birds
his food in pieces, he does not need such power in his teeth as
carnivorous animals have. Allowance should be made for this
in estimating the amount of carnivorous adaptation in man.
74. There are a few of the Mammalia that have no teeth.
This is the case with the common whale. In his case, instead
of teeth, there hang down from the upper jaw, as represented
in Fig. 7, plates of a fibrous substance, called whalebone, which
have their fibres separated at their free extremities, so as to
make a sort of sieve. This is intended to catch the little gela-
tinous animals, which the whale devours in great numbers.
FIG. 8. FIG. 7.
WHALEBONE. SKULL OF WHALE.
For this purpose, he draws in the water, making it to pass
through this sieve, and then expels it from the nostrils or blow-
holes. Birds, too, have no teeth. Their place is supplied
by a contrivance in the stomach itself, for the breaking up of
the food. This will be described in another part of this
chapter.
75. While the food is cut and ground by the teeth, it is at
the same time thoroughly moistened by the saliva, which is
poured forth from certain glands in the neighborhood. There
are three pairs of these glands. Fig. 9 shows the glands on
one side. The parotid gland, 1, is the largest. This is situated
in front of the lower part of the ear. It is the seat of the
swelling in the disease called mumps. Its duct, 2, passes over
one large muscle and between the fibres of another, and pours
its contents into the mouth opposite the second small grinder of
the upper jaw. If you press on this part of the cheek, you can
46
HUMAN PHYSIOLOGY.
Formation of the saliva. Three pairs of salivary glands.
FIG. 9.
SALIVARY GLANDS.
feel in the mouth an increased flow of the saliva. The sub-
maxillary gland, 3, is situated inside of the lower jaw at its
lower part ; and its duct, 4, opens into the mouth at the side
of the framum of the tongue. The sublingual gland, 5, lies
under the tongue, and discharges its secretion by a duct at the
side of that organ. These saliva factories, as we may term
them, are in much more active operation at some times than
at others. They are especially active when we are eating ; and
it is commonly estimated that, during an ordinary meal, about
eight ounces of saliva are poured into the mouth. This large
amount is wanted to moisten the food thoroughly before it is
swallowed ; and it is supposed, also, that it has some chemical
influence in preparing the food for the action of the gastric
juice in the stomach. More saliva than usual is needed, also,
when we are speaking, in order to keep the parts properly lubri-
cated, for the passage of the air in and out during speaking
dries up the saliva by evaporation. And, accordingly, the mo-
tion of the parts at such times stimulates a larger flow, just as
pressure on the cheek will do it, as before remarked. This
result is favored by the arrangement of the duct of the parotid
gland, which, as you have seen, passes over one large muscle, and
then through the body of another. Chewing any thing excites
DIGESTION. 47
Flow of saliva affected by sympathy. Swallowing.
an increased flow of the saliva ; and the tobacco chewer does a
real injury to the salivary glands, by keeping them constantly
in excessive operation, in addition to the ruinous effects of this
drug on the system at larg'e. When he eats, these over- worked
factories can not turn out as good an article as they should, nor
will it be in sufficient quantity.
76. It is supposect that, besides the mere mechanical stimu-
lus of the motion of the parts, the stimulus of sympathy is also
concerned in exciting these glands to increased action. The
glands are supposed to be affected in this way by the stimula-
tion of the food on the surface of the mouth, about the orifices of
their ducts. That sympathy does have an influence on their
secretion is evident from the very familiar fact, that the thought
of food will often, as it is expressed, cause the mouth to water.
77. The fact, that these glands do not all secrete the same
kind of fluid, has led to an interesting discovery in relation to
them. The submaxillary glands secrete rather a viscid fluid,
while that which is poured forth by the parotid and sublingual
glands is perfectly limpid. Now, it has been found, by various
observations and experiments on animals, that while the teeth
are cutting and grinding the food, and the parotid and sub-
lingual glands are pouring out the saliva to moisten it, no secre-
tion comes from the submaxillary glands. But these gland?
pour out their viscid fluid the moment that the tongue thrusts
the food back towards the throat, in the beginning of the act
of swallowing. The special object of this viscid fluid is then to
cover the food, so that it may, to use a common expression, slip
down easily into the stomach ; and it has nothing to do with
the moistening of the food, this being the particular office of
the other two pairs of glands.
78. When the food has been ground by the teeth, and
moistened by the saliva, it is carried by the act of swallowing
into the stomach. This act, simple as it appears to you, is a
very complicated one, and is performed by the conjoined and
agreeing action of many different muscles. The food is first
thrust back over the surface of the tongue into the large cavity
in the back of the throat, called the pharynx. In the pharynx
are the openings of two tubes the oesophagus or gullet, which
is the passage into the stomach, and the trachea * or windpipe,
the passage to the lungs. As the oesophagus lies behind the
* This term is sometimes used, as here, to mean the whole of the tube conducting to
the lungs, including the larynx, which is ut the top of this tube, and sometimes it it
eutricted to that part of the tube which is below the larynx.
48 HUMAN PHYSIOLOGY.
Parts employed in swallowing. Office of the epiglottis.
trachea, the food, in passing to it, must go directly over the
opening into the trachea. To prevent the food from entering
the trachea, therefore, there is a little tongue -shaped body,
called the epiglottis, extending back from the root of the tongue,
and acting as a lid to the glottis, the opening into the trachea.
When we are swallowing, this lid is shut down ; but it is always
raised up when we are breathing or speaking. When we swal-
low, not only does the lid shut down, but the larynx rises to
meet the lid, as you may readily perceive, if you place your
fingers upon what is called Adam's apple while you are swal-
lowing. With the aid of Figures 10 and 11, all this will be
very clear to you. In Fig. 10, you have - side view of the
parts engaged in swallowing, as if the head were divided into
two halves by a vertical section. At i, is the cavity of the nos-
tril ; at A, are the lips ; a is the divided bone of the chin ;
b is the tongue, between which and the spinal column, /, is the
large cavity of the pharynx. In front of this cavity hangs the
FIG. 10.
f/
a-'
e
VERTICAL SECTION OF THE THROAT.
palate, <7, as a door or valve, to direct the air coming from the
trachea, d, either through the mouth or through the nostrils,
according to its position. The oesophagus, e, is behind the tra-
chea, and the epiglottis, c, shuts down when we swallow, to let
DIGESTION.
49
Mode of action of the oesophagus in swallowing.
the food pass over it into the
oesophagus. In Fig. 11, you
have a view of the same parts
from the rear. At 1, is a sec-
tion of the bones at the base of
the skull ; 3, 3, are the cavities
of the nostrils ; 2, 2, the walls
of the pharynx spread apart ; 5,
the pendulous palate ; 6, 6, the
arch of the palate ; 8, the root
of the tongue ; 9, the epiglottis,
and 10, the glottis, or opening
into the larynx; 13, the oeso-
phagus; 14, the trachea. The
pharynx, you see, is a funnel-
shaped cavity, tapering down to
the oesophagus, the opening of
which is considerably below the
opening of the trachea.
79. When the food enters the
oesophagus, it is carried through
that tube into the stomach by the ac-
tion of muscular fibres. These fibres
are represented in Fig. 12. The cir-
cular fibres are seen at a and b. These
are removed at c, so as to show the
longitudinal fibres. It is by the con-
sent of action between these different
sets of fibres that the food is propelled
through the oesophagus. As the food
descends, a dilatation of the circular
fibres must everywhere take place
where the food is, and a contraction
of them immediately behind it the
dilatation making the way for it, and
the contraction forcing it along. And
in animals that chew the cud, these
actions must be reversed when the ball
of food is forced up through the esoph-
agus into the mouth.
80. The food being introduced into
the stomach, is here subjected to the
action of the gastric juice. This is a
5
FIG. 11.
VIEW OF THE THROAT FROM
BEHIND.
FIG. 12.
a
CESOPHAGUS LAID OPEN.
50 HUMAN PHYSIOLOGY.
Gastric juice. Chemical in its action.
peculiar fluid, somewhat acid in its character, which is secreted
by very minute follicles, or bag-like cavities, situated in the sub-
stance of the mucous membrane. Ordinarily there is none of
this fluid in the stomach when there is no food there. Dr.
Beaumont made some very interesting observations on this, as
well as many other points, in the remarkable case which fell
under his care. The individual, Alexis St. Martin, received a
wound in his left side by the bursting of a gun. The wound,
which opened into the stomach, never entirely closed, but an
orifice remained, after the healing process had done all that it
could. Through this orifice, Dr. Beaumont could look into the
stomach, and observe what was going on there. He describes
the mucous membrane, in its healthy state, as having a velvet-
like appearance, with a pale pink color, and as being covered
with a very thin, transparent, viscid mucus. On introducing
some food, or irritating the mucous membrane mechanically,
he saw, by the aid of a magnifying glass, "innumerable lucid
points " projecting on the surface, and from these there exuded
a pure, limpid, colorless fluid. These points were the follicles
which secrete the gastric juice, now rendered turgesceut by
being stimulated to action.
81. The amount of gastric juice secreted is generally about
in proportion to the amount of food which the necessities of the
system require. When the quantity of food taken is very
much more than is required, there can not be a sufficient
amount of gastric juice secreted to digest all of the food ; anc
some of the food must therefore remain undigested, and will prove
a source of irritation to the stomach. If the amount of food
taken from day to day is not very excessive, but is only a little
above the proper quantity, there will be enough of the gastric
juice made to digest it ; but the daily overtaxing of the pow-
ers of the secreting follicles will, after a while, produce derange-
ment in the stomach, and perhaps permanent disease.
82. The action of the gastric juice upon the food is of a
chemical nature. In order that it may act effectually on all
portions of the contents of the stomach, this organ is kept in
constant motion by the fibres of its muscular coat. These fibres
are so arranged that, as they contract and relax, they keep up
a sort of churning of the contents, and thus effect a thorough
mixture of them with the gastric juice. In Fig. 13, you see
these fibres represented. At 1, is the opening of the oesopha-
gus into the stomach ; and at 4, is the part which opens into
the intestine. The fibres are in different layers, running i
DIGESTION.
51
Churning of the food in the stomach. The chyme.
FIG. 13.
MUSCULAR FIBRES OF THE STOMACH.
different directions. The outer peritoneal coat, 5, 5, is dissected
off and turned back, showing some of the fibres that run length-
wise of the organ, 6 ; and some of them transverse, 7 ; and
others, 8, that run obliquely. You can readily see what effect
the contraction of these different fibres will have on the shape
of the stomach. The contraction of the longitudinal fibres, 6,
brings the large, bulging end of the stomach, 2, and the small
end, 3, nearer together. The transverse fibres, when they con-
tract, diminish the capacity of the stomach transversely. And
the oblique fibres modify these two motions by their oblique
action.
83. By the combined chemical and mechanical action of the
stomach, its contents are, after a little time -in three or four
hours reduced to an uniform, greyish, semi-fluid mass, called
chyme. While this process has been going on, the communi-
cation between the stomach and the intestines has been entirely
closed by a valve, called the pylorus. This is represented at 5,
in Fig. 14, which presents a view of the inside of the stomach.
This valve is made of a fold of both the mucous and muscular
coats of the stomach. It is a very faithful sentinel, as is indi-
cated by its name, which is derived from two Greek words, sig-
nifying to guard the gate. It wil-1 not ordinarily permit any
undigested food to pass it. While the process of digestion is
52
HUMAN PHYSIOLOGY.
The pylorus. A sentinel. On duty only during digestion.
FIG. 14.
INTERIOR OF THE STOMACH AND SMALL INTESTINE.
going on, the motions produced by the muscular fibres causa
the contents to move about, and of course they are thrown
against the pylorus, as well as any other part of the stomach.
But the valve remains closed, until some portion comes against
it that is thoroughly changed to chyme, and is therefore fit to
pass on into the intestine. It then opens to let this pass, and
it does so for any other portions that have become chyme.
Toward the conclusion of the digestion of a meal, small quan-
tities pass at first, and after a while, the contents pass quite
rapidly through the valve.
84. Although this sentinel-valve thus performs its duty so
faithfully in relation to nutritive substances, it seems to let other
substances pass very readily. Solid substances, swallowed by
mistake, as buttons, pieces of money, the pits and skins of vari-
ous fruits, often pass the valve without any trouble. The vaive
seems to be on duty as a sentinel only during the process of
digestion ; and, if the attempt to go through with this process
prove unavailing, the pylorus, though it let such hard sub-
stances as I have mentioned pass without difficulty, resists the
passage of the undigested food, sometimes causing much un-
easiness, and even perhaps pain, by so doing. In such a case,
either the valve after a time gives over its resistance, or, hold-
DIGESTION. 53
Theories of digestion. Eating between meals. Eating fast.
ing out, the action of the stomach is reversed, and the offending
matter is thrown off by vomiting.
85. It is not a little amusing to read the different theories
which were formerly broached to explain the process of diges-
tion. Some supposed it to be a concoction, heat being, in their
view, the chief agent ; some, a kind of putrefaction ; some, a
chemical solution; some, a trituration ; and some, a process
dependent upon the action of the nerves. Of these various
theories, the celebrated Hunter playfully remarked: "To ac-
count for digestion, some have made the stomach a mill ; some
would have it to be a stewing-pot, and some, a brewing-trough ;
yet, all the while, one would have thought that it must have
been very evident that the stomach was neither a mill, nor a
stewing-pot. nor a brewing-trough, nor any thing but a sto-
mach" All these theories are now done with ; and it is pretty
well ascertained, that digestion is a chemical process in part a
solution, and in part a fermentation and that mechanical
agency is employed only for the purpose of thoroughly exposing
the food to the action of the gastric juice.
86. The process of digestion, as it has been described, is a
regular process, requiring a certain average period of time for
its completion. If, during the progress of it, fresh food be in-
troduced, its regularity is broken in upon, and the process fails
to be well done. Then, too, if, immediately after the completion
of the process, a new supply of food be taken, harm is done,
because the organ has not its needed interval of rest. For
these reasons, the practice of eating between meals is a very
injurious one. Eating fast does harm, because, 1st, the food is
not sufficiently ground ; 2d, it is not mixed thoroughly with the
saliva ; and, 3d, more food is taken than would be sufficient to
satisfy the hunger if the individual ate slowly, and, therefore,
more than can be easily digested. Great variety in food stimu-
lates the appetite unduly, and too much is consequently eaten.
Exercise facilitates digestion, if it be not violent. An experi-
ment was once tried upon two dogs, which was thought to
prove that exercise hindered digestion. Two dogs were fed
freely, and while one was left to lie still, the other was made to
run about violently. Both dogs were kiPed after an hour or
two, and it was found that, while digestion had gone on thor-
oughly in the dog that was allowed to remain quiet, in the
other the food was undigested. This only proved that violent
exercise, taken immediately after eating, impedes digestion. It
has been found, on the other hand, that light exercise pro-
5*
64 HUMAN PHYSIOLOGY.
Cause of hunger, state of the system. Its seat in the stomach.
motes the process ; and daily experience, among laborers, shows,
that very strong exercise does not interfere with it, if a little
interval of rest be allowed, so that the process may be fairly
begun.
87. The sensation of hunger has been attributed to various
causes, as the empty state of the stomach, the presence of the
gastric juice irritating the mucous membrane, &c. It cannot
arise from emptiness ; for, if it were so, it should occur sooner
than it does after eating, and it should not be absent in dis-
ease, as it often is for a long time, when the stomach is almost
entirely empty. It can not arise from the irritation of the gas-
tric juice ; for it was found by Dr. Beaumont, in his observa-
tions of the stomach of Alexis St. Martin, that this fluid is not
secreted till after food is introduced into the stomach. The
cause of hunger is evidently in the state of the system. It is
a state of want. Nutriment is needed by the formative vessels,
the builders and repairers of the system, of which I shall speak
particularly in the chapter on Formation and Repair. And
they make their wants known as distinctly as the bricklayer
does, when he calls for more brick and mortar. Through the
nerves, an impression is communicated from these to the sto-
mach, and the sensation of hunger is the result. That the sen-
sation is seated there is evident from the fact, that it can be
temporarily relieved by putting indigestible substances into the
stomach. These produce the effect by causing other sensations
there, which take the place, for the time being, of the sensation
of hunger. After, however, the momentary effect is over, the
sensation of hunger returns again in its full force. The cause,
then, of the sensation is in the system at large, but its seat is
in the stomach. Its degree of urgency depends upon this
general state that causes it. If eating be delayed ranch beyond
its usual time, or if the system has been exhausted by the wear
and tear of severe labor, the sensation of hunger is very urgent.
So, too, if disease has impoverished the system, as soon as the
stomach is in a condition to respond to the call of the forma-
tive vessels that set themselves to work to repair the waste, the
hunger is often excessive. Observe, here, that in order to have
the sensation of hunger, not**bnly must there be a want in
the system at large, but the stomach must be in a state fitted
to receive the notice of this want. And fortunately it is seldom
in this state except when in a condition to do its work. If it
were otherwise, food would often be introduced into it when it
could not be digested. The stomach is sometimes incapacitated
DIGESTION. 55
Sensation of hunger affected by the mind. Thirst.
for receiving the notice of the want of the system by mental
impressions. In this case, an impression is communicated from
the brain to the stomach, through the nerves, which counteracts
the impression conveyed from the system to this organ, and so
neutralizes the sensation of hunger. Grief tfcus often destroys
the appetite for food. One thing more is to be observed in
relation to hunger. Although this sensation is caused by the
want of the system, it is removed long before the nutriment
reaches its final destination, and supplies the want. How is
this ? It is either because the new sensations produced in the
stomach, by the commencing process of digestion, take the
place of the sensation of hunger, or an impression is sent all
over the system from the filled stomach, which, so to speak, stills
the clamor of want with the immediate prospect of a supply.
88. Nearly the same remarks can be made in relation to
thirst, that have been made in regard to hunger. The seat of
this sensation is in the fauces or throat. Its cause is evidently
not there ; for the mouth and throat may be very dry, and yet
there may be little or no thirst; while, on the other hand, there
may be much thirst, although the mouth and throat are moist.
The cause of the sensation is like the cause of hunger, in the
system at large ; and, therefore, no local cause, producing a
dryness of the throat, can cause thirst independent of a general
condition.
89. Before describing the remainder of the process of diges-
tion, I will call your attention to the arrangement of the sto-
mach, and the other organs of the abdomen engaged in this
process. Fig. 15 exhibits them as they present themselves in
a front view, except that they are somewhat separated from
each other, instead of being as closely packed, as they are in the
abdomen. The large end of the stomach, you see, lies to the
left side,* and at this end is the spleen. The pancreas is be-
hind the right end of the stomach. Above the stomach, and
mostly to the right side, is the largest organ in the abdomen,
the liver. It is represented as turned upward in the Figure.
The stomach is directly connected with the small intestines at
the pylorus. At the end of this long and winding tract begin
the large intestines. The duct of the gall bladder, and that of
the pancreas, empty their contents into the small intestine at its
beginning. The office of the spleen has not yet been ascer-
tained. Neither has that of the worm-like appendage at the
* As this is a front view, the right side of the Figure is the left side of the body.
56
HUMAN PHYSIOLOGY.
Arrangement of the digestive organs.
FIG. 15.
GALL BLADDER.'
LARGE INTES -
TINES.
BEGINNING OF
LARGE IN-
TESTINES.
WORM-LIKE AP-
PENDAGE.
-SPLEEN.
LARGE INTES-
TINES.
SMALL INTES-
TINES.
8MALL INTESTINES.
DIGESTIVE ORGANS.
beginning of the large intestines. The omentum, or caul,
which hangs like a curtain from the front part of the sto-
mach down in front of the intestines, is not represented in the
Figure.
90. There is one arrangement in the abdomen which must
not pass unnoticed. If the intestines were left to lie loose in
this cavity, they would constantly be subject to displacement
and injury. They are therefore fastened to the backbone by
an arrangement, which secures them from any such accident,
and at the same time allows of a sufficiently free motion of differ-
DIGESTION. 57
The arrangement of the mesentery. Its offices.
ent parts of this tube. It is this. The intestinal tube makes
the margin of a broad sheet of membrane, the other edge of
which is gathered up and fastened to the spinal column. The
arrangement is like a ruffle with a puffed edging. The mem-
branous sheet is called the mesentery. As the intestinal tube,
the puffed edging, is much longer than the ruffle itself, the
mesentery, it is gathered on to the ruffle, as a seamstress would
express it. Now, the mesentery is composed of two folds of
the peritoneum, the smooth, shining, outer covering of the in-
testines. The arrangement will be easily understood by the
diagram in Fig. 16, which represents a section of the intestine
with the mesentery. The cav-
ity of the intestine, a, is lined FIG. 16.
by the mucous membrane re-
presented by the inner circle.
Next comes the muscular coat,
and next the peritoneal, the
outer, which, instead of making
a circular tube, as the other two
coats do, passes backward on
both sides of the intestine, to
make the mesentery, b. After
being attached to the spine by PLAN OF THE MESENTERY.
means of cellular tissue, it is re-
flected off to pass over other portions of the intestine, as seen at
c, c. Between the two layers of the peritoneal membrane, in the
mesentery, is considerable space, as seen at b. This space is
rilled up with blood-vessels, nerves, lacteals with their small
glands, soon to be described, all bound together by the com-
mon packing material of the body, the cellular tissue. You
see, therefore, that the mesentery subserves more than one use.
Besides fastening the whole tract of the intestinal canal to the
spine, so as to guard it against accident, it acts as a secure
medium for the communication of the blood-vessels and nerves
with the intestines. And, besides, as you will soon see, it con-
tains the little tubes which convey all the nutriment into the
blood for the growth and repair of the body.
91. I now go on to describe the remainder of the process of
digestion. The chyme, ( 83,) as it passes into the small intes-
tine from the stomach, has mingled with it the -bile-~and the
secretion of the pancreas.- These are poured into the intestine
at the point represented at 6, in Fig. 14. These secretions un-
doubtedly have some agency in separating the nutritious part
58
HUMAN PHYSIOLOGY.
Chyme. Chyle. Lacteals. Thoracic duct.
of the chyme from that which is not so. When thus separat-
ed, it is absorbed by the innumerable small vessels, called lac-
teals, which are situated in the mucous membrane. This nutri-
tious part of the chyme is a milky fluid, called the chyle. The
lacteals which absorb it are little tubes or ducts. These enter
certain glands, called the mesenteric glands, for the purpose of
having some effect, we know not what, produced upon it. They
then pass on, as seen in Fig. 17, to pour their contents into the
*>' ORIGINS
OP
LACTEALS.
SECTION OF INTESTINE SHOWING THE LACTEALS.
thoracic duct. This duct, which is about the size of a common
quill, running up on the left side of the aorta, the great artery
of the heart, pours its contents into the junction of two veins
at the top of the chest. As the circulation of the chyle in the
DIGESTION. 59
Mechanical contrivance of the thoracic duct. Chyle makes blood.
thoracic duct needs all the mechanical help that it can have, the
mode of the joining of this duct with these veins is calculated
to facilitate the freeness of the discharge of the chyle. As
the two large currents in the veins, v and v, v, in Fig. 18,
FIG. 18.
JUNCTION OF THE THORACIC DUCT WITH THE VEINS.
unite, there is created, by the forward motion of these cur-
rents, a tendency to a vacuum at the angle at which they
meet, the point where the thoracic duct, T, D, opens. There
is, therefore, a suction power, as it is termed, exerted upon
the fluid in this duct. The chyle, thus mingled with the
blood, becomes a part of it. Or rather, I should say, that the
blood is made from the chyle, and, as it is constantly used for
formation and repair in all parts of the system, it is thus as
constantly replenished. The material by which all the textures
of the body are made and are kept in repair, is furnished to
the system through this small duct, in the form of a milky
fluid. You observe in Fig. 17, certain lymphatic vessels. These
are trunks of absorbents, hereafter to be spoken of particularly,
which bring a fluid called lymph, to be mingled with the chyle,
and to be poured with it into the circulation.
92. The extent of surface on which the absorbent lacteals
open can not be appreciated, if you look merely at the outside
of the small intestines. It can be done only by looking at the
inner mucous coat. This coat is really much more extensive
than the outer coat, or the middle one, the muscular, arid it is
full of folds, as represented in Fig. 14, on page 52. The ob-
60 HUMAN PHYSIOLOGY.
Extent of absorbing surface in intestines. Alimentary canal in different animals.
ject of this is to offer a very large absorbing surface to the
chyme as it passes, and also to prevent its passing along as
rapidly as it would if the mucous surface were perfectly smooth,
instead of having folds. Before leaving this subject, I would
again call your attention to the analogy which exists between
absorption in animals and in plants. The lacteals do for the
animal in its stomach, what the absorbents do for the plant in
the extremities of its roots. Both absorb and assimilate nutri-
ment. The function is the same. It differs in the two cases
only in the circumstances under which it is performed.
93. The digestive apparatus varies much in different animals,
according to the kinds of food on which they live. As a gene-
ral rule, the more the food differs in character from the animal
itself, the more complicated and extensive is the apparatus.
Thus, the herbivorous animals have a very long alimentary
canal, and the beginning of it, the stomach, is a complicated
organ. While, on the other hand, in the carnivorous, the flesh
which they eat being very much like their own flesh, and, there-
fore, not requiring very much of a process of assimilation, the
stomach is a simple organ, and the alimentary canal is very
short. In the sheep, for example, the alimentary canal is about,
twenty-eight times the length of the body, but in the lion it is
only three times its length. In man, who lives on a mixed
diet, the alimentary canal is about six times the length of the
body.
94. The stomach is more complicated in animals that chew
the cud than in any other animals. It has four distinct cavities,
and, as you will see, a singular mechanism is called into opera-
tion in managing the food as it passes through them. In Fig.
19, you have a representation of the stomachs of the sheep, as
they appear exteriorly. The course which the food pursues is
this. As the animal crops the food, it passes into the first sto-
mach, which is little else than a great reservoir to hold it and
to soak it. Then it passes into the second stomach, from which
it is returned into the mouth. On being swallowed again, it
passes from the oesophagus into the third, and thence into the
fourth stomach. In Fig. 20, you see the interior of these four
stomachs ; and by the aid of this I will describe the process of
digestion in the sheep more particularly. You see the very
large first stomach, or paunch, in which the food is accumu-
lated. It is not yet masticated thoroughly, for the animal has
swallowed it as fast as he could, and packed it away in this
reservoir. From this it is passed, in small quantities at a time,
DIGESTION".
Digestion in the sheep.
OESOPHAGUS.
ORIFICE OF
STOMACH.
3D STOMACH.
FIG. 19.
STOMACHS OF THE SHEEP.
FIG. 20.
INTERIOR OF THE STOMACHS OF THE SHEEP.
into the second stomach, the honey-comb, so called from the
peculiar network of folds in it. Here the food is rolled up into
balls by the action of the muscular fibres in this network.
6
62 HUMAN PHYSIOLOGY.
Digestive apparatus in birds. Different in the grain-eating and the flesh-eating.
Each ball of food is passed up through the oesophagus into the
mouth, where it is chewed and thoroughly mixed with the saliva,
in doing which the animal seems to have great enjoyment.
Then it is swallowed, and, as it passes from the oesophagus, in-
stead of going into the paunch, as it did when swallowed the
fhst time, it is directed through the groove seen in the Figure
into the third stomach, the manyplies. This has many folds,
like the leaves of a book, so that the food is exposed to a large
surface in this cavity. It passes from this to the fourth sto-
mach, the reed. Here, and here only, it is acted upon by the
gastric juice. This, therefore, is the true stomach, all the other
cavities furnishing only preparatory steps to the true process of
digestion. It is from this fourth stomach that what is called
the rennet is taken. When fluid matter is swallowed, it goes
directly into the second stomach, and not into the first, the
paunch ; so that, in the case of the sheep, the drink goes one
way, and the solid food another. And, what is still more singu-
lar, while the animal is a suckling, the milk passes directly into
the fourth stomach through the third, which has its folds so
closed together as to form a mere tube to conduct it to its des-
tination. And the great paunch and the honey-comb are
wholly useless until the animal begins to crop its food for
itself.
95. In birds, the digestive apparatus is necessarily very
peculiar, from the fact that they do not masticate their food.
They have, on this account, an arrangement in the stomach
itself for grinding the food. In the cavity called the gizzard
are two opposing surfaces, made very hard, so that by rub-
bing together they bruise the grains ; and while they are
thus ground, as between two millstones, the gastric juice
is poured down upon them from above. This arrangement is
seen in Fig. 21, which represents the digestive apparatus in the
turkey laid open. At b is the gizzard, showing the two hard
surfaces, which are rubbed together by the stout muscles that
make the great bulk of the organ. Above, at a, are the
glands which pour forth the gastric juice. And above this
part of the stomach there is, in all grain-eating birds, a large
sac bulging out from the oesophagus, called the crop, which is
a reservoir for the food, just as the paunch is in the ruminating
animals. In those birds that live on flesh or fish there is no
such grinding apparatus; and the walls of the stomach are
quite thin, and it presents no hard surfaces.
96. It would be interesting, were it consistent with the plau
DIGESTION.
63
Pigestion in the turkey. Digestive apparatus in different animals.
FIG. 21.
STOMACH OF THE TURKEY.
of this book, to go into a further examination of the varieties
in the digestive apparatus in different animals. They have a
very wide range, being according to the wants of the animal in
each case. The kind of food, the mode of life, and the pur-
pose which the animal is designed to fulfill, are the circumstances
which govern these variations. The proportion which the di-
gestive apparatus bears to other parts varies very much ; and
in some of the lower orders of animals, the body seems to be
all stomach. In such cases, the only appendages are those which
seize the food and direct it into the orifice of this organ. This
64 HUMAN PHYSIOLOGY.
Apparatus of the circulation. Heart, arteries, veins, capillaries.
is the case with the hydra, represented in Fig. 1. And, what
is very singular, the outside of the body of this animal is just
as capable of acting as a stomach as its inside. For you may
turn it inside out, as you can a stocking, and yet it will go on
to catch and digest its food as usual. But, wide as the varia-
tions are in the digestive apparatus of animals, the same com-
mon object is aimed at in all the assimilation ( 10) of nu-
trient substances to the animal, to produce a material from
which its structure can be built and kept in repair. There is,
therefore, much that is common to them all in the modes in
which this object is accomplished. And even the analogy
which exists between the animal and plant, in regard to assimi-
lation, does not relate to the fact alone, but in some measure to
the modes in which the process is effected.
CHAPTER VI.
CIRCULATION OF THE BLOOD.
97. IN the last chapter I described the manner in which the
blood is made from the food. The blood, thus prepared, is
circulated in every part of the body, that it may be used for
the purposes of construction and repair. The apparatus by
which this is done acts, as I have before said, as the common
carrier of the material which is used everywhere in the body
by the laborers, the builders, to whom it is thus brought.
98. This apparatus consists of several parts a great central
organ, the heart, situated in the chest; the arteries, the tubes
by which the blood is conducted to all parts of the body ; the
veins, other tubes, which bring the blood back to the heart ;
and capillaries, a network of exceedingly minute vessels, through
which the blood passes as it goes from the extreme arteries into
the beginnings of the veins. The blood goes from the heart
through a large artery, called the aorta, which sends forth
branches ; and these divide and subdivide, so that the extreme
arteries, through which the blood flows into the capillary net-
work, are very minute. And the veins which receive the blood
from this network to carry it back to the heart, are equally
minute ; but joining together more and more, as they proceed
THE CIRCULATION. b'5
Heart n forcing and suction pump. Arteries firm tubes. Why.
toward the heart, they are at length all united into two great
venous trunks, one from above and the other from below, which
pour their contents into this organ. The capillaries, taking
their namev from the Latin word, capilla, a hair, are so small
that the) 7 " can not be seen by the naked eye. In any small
cut, the blood which oozes out comes from multitudes of these
vessels. They serve to hold the blood, while the formative ves-
sels, that construct and repair the body, may select from it such
materials as they need for their purposes.
99. The heart is a great central forcing and suction pump, in
the midst of this circulating apparatus. When it contracts, it
forces the blood out through the aorta and its branching ar-
teries into all parts of the system. And when it enlarges or
dilates itself, it, by suction, as it is termed, receives the blood
returning from the system through the veins. The blood never
ceases to go these rounds. The necessity for this continual
motion you will perceive as I proceed with the development of
the subject.
100. The arteries differ from the veins in their structure and
arrangement. The arteries are firm tubes, while the veins are
lax in their structure. The object of the difference is obvious.
As the blood is forced into the arteries by the powerful action
of the heart, it is necessary that they should be strong and
firm, else, they would be liable to dilatation and rupture, and
death would frequently result. As it is, it is not a common
event to have an artery dilate and burst, though it does occa-
sionally happen. When dilatation does occur in an artery, it
is called an aneurism. But the arteries need to be firm, not
only for the sake of security against rupture, but also that the
force of the heart may propel the blood to the extremities of
the arterial system. If the arteries were lax tubes, like the
veins, the impulse would soon be lost in the yielding tubes, and
the blood would move very sluggishly in the small arteries at a
distance from the heart. What we call the pulse, is caused by
this impulse. If the arteries were lax tubes, the pulse would
not be felt at any great distance from the heart. Instead of
being distinct, as it now is, w^h every beat of the heart almost
to the very extremities of the arterial system, it would be ren-
dered confused by the yielding of the tubes, even quite near
the heart, and at a distance from that organ it would be en-
tirely lost.
101. Besides the firmness of the arteries, there is another
circumstance which favors the freeness of the flow of blood
6*
66 HUMAN PHYSIOLOGY.
Different arrangement of arteries and veins.
through them. It is their mode of division. The branch of
an artery leaves the main trunk at a sharp angle, making thus
only a slight deviation from the direction of the current ; while,
on the other hand, in the veins where the current flows in an
opposite direction, the branch unites with the trunk at nearly a
right angle. This difference is represented in Fig. 22 ; 1 being
the artery, and 2 the vein.
FIG. 22.
ARTERY AND VEIN.
102. The venous system has a much greater capacity than
the arterial. That is, all the veins of the body are together ca-
pable of holding more blood than all the arteries are. And the
blood moves very rapidly and directly from the heart through
the arteries, but it conies back to the heart quite slowly through
the veins. Every thing is arranged to promote this rapid cir-
culation through the arteries, while the venous system is calcu-
lated for a slow but sure progress of the blood back to the
heart. To secure this, valves, made of folds of the inner lining
of the veins are so arranged as to prevent the blood from flow-
ing in the wrong direction. Fig. 23 represents a vein cut open
so as to show these valves. A shows the valves as they appear
when the vein is laid open and spread out ; B, as they appear
when the vein is simply laid open ; and C represents the ap-
pearance of the outside of the vein where there are valves.
THE CIKCULATION.
67
Valves in veins. Dangerous to wound an artery. Therefore well guarded
VALVES IN THE VEINS.
The need which there is of this help to the circulation through
the veins is obvious. The suction power of the heart is not
competent, unaided, to move the blood throughout all the lax
venous system. These pocket-like valves, therefore, are made
in the veins to assist the circulation there. They do so in this
way. Every motion of the muscles or other parts about the
veins tends to keep the blood in motion, and the valves serve to
prevent this motion from being in the wrong direction. The
difference in force and velocity with which the blood moves in
the arteries and in the veins, is made manifest when they are
wounded. The blood flows from a wounded vein in a slow
and steady stream. From an artery it flows rapidly, showing
the impulse of the heart in its jets, which correspond exactly
with the pulse. Hence comes the danger in wounding an ar-
tery, while the wound of a vein is ordinarily attended with no
danger. Accordingly, we find that the "Maker of our bodies"
has so placed the arteries that they cannot easily be wounded,
while many of the veins are quite freely exposed. The arteries
are deeply seated, except in some few cases where this is im-
possible ; but the veins are often superficially situated. You
can see this, for example, in the bend of the arm. Some large
veins appear there just under the skin, while the artery which
supplies the arm is imbedded among the muscles and tendons.
In every part of the body, the most secure spot is chosen for
an artery. Thus, at the knee joint, the artery, instead of run-
ning over the surface of bone, where it would be liable to be
68 HUMAN" PHYSIOLOGY.
Few arteries superficial. Mode of stopping the bleeding of an artery.
wounded, lies deep in the ham at the rear of the joint The
same is true of the elbow joint, just alluded to, and of other
parts of the body. Although there are arteries everywhere,
they are so uniformly deeply seated, that it is only in a few lo-
calities that you can readily find one. You can feel one pul-
sating at the wrist, and also on the temple. Here the arteries
are superficial, only because it is impossible that it should be
otherwise.
103. When the physician bleeds a patient, he commonly
does it at the bend of the arm, as being the most convenient
place for the operation. A ligature of some sort, as a ribbon, is
tied around the arm above the elbow, with sufficient tightness
to interrupt the flow of blood toward the heart in the super-
ficial veins, but not so tightly as to prevent the free supply of
blood to the arm by the artery. It is commonly tied as tightly
as it can be without stopping the pulse at the wrist. An open-
ing is then made in one of the veins ; and, as the blood flows
freely into the arm from the heart through the artery, on its
return, so much of it as passes through the opened vein is dis-
charged at that point.
104. It will be proper here to give some practical instruc-
tion, in regard to stopping the flow of blood from a wounded
arterv, as many lives have been lost from the ignorance of by-
standers when such accidents have happened. Enveloping the
part in cloths, which is so commonly done at such times, does
no good, but only serves to catch and conceal the blood as it
flows. Pressure upon the artery, on that side of the wound
which is toward the heart, will of course interrupt the supply of
blood from this organ to the wound. Firm pressure with the
thumb will do it. But the pressure must be made at the right
point, that is, directly upon the artery. You may not, in all
cases, press upon the right spot at once. If you do not, the
blood will continue to flow. In this case, press at different
points, until you find the point at which you see that pressure
stops the flow of blood from the wound. But you may not be
able to find the right spot. If you can not, you can *ie a slip
of strong cloth or a handkerchief around the limb, above the
wound, and twist a stick in it until the bleeding stops. In one
or the other of these ways, you can prevent the loss of blood
until the surgeon arrives to take charge of the case.
105. Although there is no such free communication between
arteries as exists between the capillaries, there is some amount
of communication, and particularly in certain parts of the body.
THE CIRCULATION. 69
Aneurism. Communication between arteries.
And it is well that it is so, for it sometimes helps the surgeon
to save a lirnb, when he could not do it if there were no com-
munication. I have already alluded to a disease of the arteries
called aneurism. An artery has three coats, one of which is a
strong fibrous one. When this is thinned or ruptured, the
other two coats bulge out, forming a pulsating tumour. And,
as the blood is constantly pumped into this by the force of the
heart, it enlarges, and at length it may burst, and the life of
the patient will be destroyed by the loss of blood. When an
aneurism formed in a limb, as for example in the ham, the sur-
geon, in former times, used to save the life of the patient by
amputating the limb above the aneurism. Putting a ligature
round the artery above the aneurism would of course stop the
flow of blood into it ; but it was supposed that the limb would
die, in that case, from the want of a proper supply of blood.
But it was found, at length, that this was not so ; and surgeons
now, in such cases, cure the disease, and save the limb too, by
tying the artery. Immediately after the operation the limb is
cold, and there is plainly very little circulation in it. But in a
few hours the circulation becomes free, and in a little time it is
as well established as ever. This is effected by the communi-
cations which exist between the branches which go off from the
artery above the aneurism, and those which go off below it.
It is obvious, however, that this would not be thoroughly
effected if no change took place in the size of the communicat-
ing arteries. But this change does occur. Some of them be-
come enlarged to meet the necessity of the case. This is a
most interesting fact ; and so is also the fact, that these commu-
nications between branches of arteries are very common in the
neighborhood of those places in the body, where aneurism,
from strains produced by violent and sudden motion, is peculi-
arly apt to appear. This same provision avails, of course, when
aneurism is cured by pressure made upon the artery above it,
a measure which modern surgery has found in many cases to
be as effectual as tying the artery.
106. There have been great differences of opinion among
physiologists, in regard to the proportionate amounts of agency
that the different parts of the apparatus have in carrying on
the circulation. The heart manifestly exerts the chief agency,
both by its forcing and its suction power. You can get a clear
idea of the manner in which it exerts these two forces in this
way. Fill a ball of India rubber, to which a tube is attached,
with water, and immerse the tube in water in a vessel. If you
70 HUMAN PHYSIOLOGY.
Action of the heart illustrated. Agency of the capillaries in the circulation.
press the sides of the ball together, some of the water is forced
out into the vessel. This represents the contraction of the
heart. If, now, you allow the ball by its elasticity to resume
its round shape, the water rushes into it from the vessel. Tnis
represents the dilatation of the heart. The dilatation of the
ball results from its elasticity ; and so it is supposed by some
that the dilatation of the heart results from the same cause, its
contraction alone being produced by muscular action. Whether
this be so or not, the dilatation is an active one, and the blood
rushes into the heart from the veins by suction, as it is termed.
The dilatation is so active that, as has been shown by experi-
ments on animals, even a great amount of pressure is not able
to prevent its taking place.
107. But, great as the agency of the heart is, it is not true
that it is the only moving power, and that the arteries and veins
are mere passive conducting tubes. There are various phenomena
which show that the arteries, the capillaries, and even the lax
veins, exert a considerable agency in circulating the blood. I
will merely allude to some of these phenomena. Determina-
tions of blood to particular parts show that the blood-vessels
have an active agency in the circulation. In inflammation of
any part, there is an increased activity of the particular portion
of the circulating apparatus supplying that part. In the act of
blushing, there is a local activity of the circulation somewhat
independent of the heart. This is also true of the circumscribed
flush of hectic.
108. There is one portion of the circulation in which the
active agency of the capillaries is especially manifest. The
veins, as I have told you, receiving the blood from all parts of
the body, at length are all united into two veins, which empty
their contents into the heart. But there is a very remarkable
exception to this. The veins which collect the blood from the
viscera in the abdomen unite in one large trunk, called the vena
portae ; and this, instead of pouring its contents into the large
vein that goes up to the heart, divides, like an artery, into
branches, which take all this blood to the liver for the manufac-
ture of bile. Fig. 24 represents this circulation of the vena
porta3. 1, 1, are the veins coming from the intestines ; 2 is the
trunk of the vena portse ; and 3, 3, are the branches of it dis-
tributed in the liver. Now, it can not be pretended that the
suction power of the heart extends its influence through the veins
that bring the blood from the liver, then through the capillaries
of this organ, and then through all the veins that bring the
THE CIRCULATION. 71
Circulation in the liver. Why the veins are full and the arteries empty after death.
1
CIRCULATION OF VENOUS BLOOD IN THE LIVER.
blood to the liver, even to the capillaries of the abdominal vis-
cera. There must be, in this case, some propelling power in
the capillaries, and some, too, also in the veins. If there were
not, another subordinate heart would obviously be needed in
the vena portae, to pump up the blood from all the veins of the
abdominal viscera, and then to send it through all its branches
into the capillaries of the liver.
109. The veins have a less active agency in the circulation
than any of the other parts of the apparatus. It is for this
reason that commonly after death the veins are found quite
full of blood, while the arteries are nearly empty. The appa-
ratus of the circulation may be regarded as forming a circle of
organs in this order the heart, the arteries, the capillaries, and
the veins. The blood is constantly going the rounds of this
circle. It is plain that, as the apparatus is about to stop, there
must be an accumulation in the weakest, least active, and most
relaxed of this circle of organs. The arteries and capillaries force
the blood into the veins to the last moment of life. This effec*
72 HUMAN PHYSIOLOGY.
The blood changed in the capillaries from red to dark.
probably extends no further than the smaller veins ; but the heart,
by its active dilatation, draws the blood from them into the larger
veins. And as these two forces, at the two ends of the venous
system, are at work up to the last moment, the whole of this
system is filled with blood.
110. The fact, that the larger arteries are commonly found
nearly empty of blood after death, gave the ancients the idea
that air circulated in arteries, while blood circulated in veins.
Hence, the name, artery, is derived from two Greek words, sig-
nifying to hold air. And hence, also, by long established cus-
tom, in common language, the blood is spoken of as running in
our veins; and it would sound strangely, if, in common, and
especially in poetical language, we should speak of it as running
in our arteries also. Although there were from time to time
some glimpses of the true idea of the circulation, it was not
really developed and demonstrated till about two hundred
and thirty years ago. Harvey spent eight years in maturing
his ideas on the subject. When he published them, they en-
countered much opposition ; but he lived long enough to see
them almost universally received by the medical world, although
the profession was in a much less enlightened state than it is at
the present day.
111. I will now take you a step farther in the development
of the plan of the circulation. I have said that the office of
the arteries is to conduct the blood to the network of capil-
laries, and that in the capillaries the blood has reached its
place of destination where it is to be used. The formative ves-
sels, appended to the capillaries, take from the blood what they
need for their various purposes, and at the same time there is
added to the blood refuse matter from the waste of the tissues.
The blood, then, is changed while it is in the capillaries. You
see the change in its color. In the arteries it was red ; but,
after passing through the capillaries, it appears in the veins of
a purple color. It is also as much changed in other properties.
It is no longer fitted to nourish the body. It would even prove
a poison to any organ if it should flow into its capillaries. If it
should, for example, be sent to the brain, instead of bright ar-
terial blood, that organ would cease to do its office ; insensibility
would ensue, and life would soon be destroyed, if the flow of
red blood could not be established.
112. This purple blood, which comes back to the heart from
the capillaries by the veins, must, therefore, be in some way
changed to red blood, before it is again sent all over the system
THE CIRCULATION. 73
Change in the blood in the lungs. Course of the circulation
through the arteries. This change is effected in the lungs. As
the purple blood returns to the heart, it is sent by the heart to
the lungs, in order to be exposed to the air before it is sent
again over the system. For this purpose there are two circula-
tions, and the heart is a double organ ; or rather, there are in
effect two hearts for the two circulations, for the two sides of
the heart have no communication with each other. The appa-
ratus for all this is very complicated, but I think it can be made
clear to you.
113. I present, first, a diagram, which is intended to repre-
sent merely the course of the circulation, without regard to
proportionate size, or to minutiae in the arrangement of the ap-
paratus. Let a represent the right side of the heart, c the left
side, b the lungs, and d the general system of the body. The
arrows show the direction in which the blood flows. In all the
shaded part the blood is venous or purple, and in the part not
shaded it is arterial or red. We will now take some point of
beginning, and trace on the Figure the course of the circulation.
PIG. 25.
DIAGRAM SHOWING THE COURSE OF THE CIRCULATION".
We will start at a, the right side of the heart. The blood re-
ceived here, of a purple color, from the whole body by the
veins, is sent by the heart to ft, the lungs. Here it changes to
red blood, and passes by veins back to the heart but, observe,
it is to the left side of the heart, c. It is now sent by this left
half of the heart to all parts of the system, represented by d.
Here, in the capillaries, it is changed to purple blood, and goes
back by veins to the right side of the heart, a, the place where
we started.
7
74 HUMAN PHYSIOLOGY.
Two circulations and two hearts. Arrangement of valves.
114. You see, then, that there are two separate circulations,
one through the general system, and the other through the lungs
alone. In both circulations the blood is sent from the heart
by arteries, and is brought back to it by veins. But notice that,
while in the general circulation the red blood is in the arteries,
and the purple in the veins, in the circulation through the lungs
it is reversed the red blood is in the veins, and the purple is
in the arteries. So, also, while the change of the blood in the
capillaries of the general system is from red to purple, in the
capillaries of the lungs it is from purple to red.
115. There are not only two sides or halves of the heart,
separated entirely from each other, but each of these sides has
two apartments, with valves or folding doors between them, so
arranged that the blood can pass one way through them, but
not the other. There are also valves at the beginning of the
great artery of the heart, the aorta. These are so arranged
that the blood can go freely out of the heart into the artery,
but not a drop can get back from the artery into the heart.
There are similar valves, also, at the beginning of the great ar-
tery, by which the purple blood is sent from the heart to the
lungs.
116. In Fig. 26, is represented a section of the right side of
the heart, for the purpose of giving you an idea of the arrange-
ment and the relative size of the two apartments. The auricle,
a, so called because a part of it has some resemblance to
an ear, receives the blood from the whole system by two
large veins, 6, b, called the venae cavte.
From the auricle it passes into the ven- FIG. 26.
tricle, v, which by its contractions sends a
it to the lungs through the pulmonary
artery, /. The valve between the au-
ricle and ventricle is composed of three
membraneous sheets, which are held at
their edges by small tendinous cords, o?,
just as a sail is held by the ropes at its
corners. This valve permits the blood
to pass from the auricle into the ventri-
cle ; but when it attempts to pass back
from the ventricle to the auricle, it SECTION OF THE RIGHT
pushes back the sheets of the valve, they SIDE OF THE HEART.
being prevented from going too far back
by the tendinous cords. There are also valves at e, the beginning
of the pulmonary artery, which allow the blood to pass through
THE CIRCULATION. 75
Relation between the auricles and the ventricles.
them into the artery, but no blood can pass through them from
the artery back into the ventricle. I shall soon call your atten-
tion again to these different valves, that you may see more par-
ticularly their structure and arrangement.
117. The auricle and ventricle act in this way in propelling
the blood. When the auricle contracts, the ventricle dilates *
to receive the blood from the auricle. The valves between them
are open while this is taking place. But the next moment the
ventricle contracts and the auricle dilates. You at once see,
that if now the valves between them should be open, the blood
would be forced back into the auricle. But the membranous
sheets of these valves shut upon each other as the ventricle
contracts, and thus prevent the blood from going back. It
therefore is discharged through the pulmonary artery, /, the
valves there being open. And when the ventricle dilates, you
can see that the blood would, from suction, enter it from the
artery as well as from the auricle, if the valves at the orifice of
the artery should remain open. They are accordingly shut
when the ventricle dilates. You see, then, that when the
auricle dilates and the ventricle contracts, the valves between
the auricle and ventricle are closed, and the valves at the mouth
of the pulmonary artery are open ; and, on the other hand,
when the ventricle, dilates and the auricle contracts, the valves
between them are open, and the valves of the pulmonary artery
are closed.
118. Dr. Carpenter has a very good illustration of the rela-
tion of the actions of the auricle and ventricle, in a representa-
tion given in Fig. 27. The apparatus which is represented
consists of two pumps, a and 6, the pistons of which move up
and down alternately. These are connected with a pipe, c, /,
in which there are two valves, d and e, opening in the direction
of the arrows. The portion c of the pipe represents the venous
trunk discharging its blood into the heart, and the portion /,
the artery which is the outlet for the blood. The pump, a,
represents the auricle, and the pump, 6, the ventricle. When
the piston in a is raised, the fluid enters through c to fill it by
suction, as it is termed. When, now, its piston is lowered, the
fluid is forced through the valve d into the pump 6, (which re-
presents the ventricle,) whose piston is at the same time raised
to receive it. And when the piston in b is lowered in its turn,
* This dilatation is an active one, as was stated in 106, when speaking of the heart
as a whole. The ventricle does not dilate because the blood is forced into it, but the
blood rushes into it because it dilates.
76
HUMAN PHYSIOLOGY
Ventricles larger and stronger than the auricles. Valves of the aorta.
FIG. 27.
a
db
the fluid being prevented from returning into a, by the closure
of the valve d, is forced through the valve e into /, representing
the discharging tube, the artery. At the same time, a fresh
supply of fluid is received into a by the raising of its piston.
119. I have described the auricle and ventricle of one side
of the heart, the right side. The left side is constructed very
much in the same way. You will observe, in Fig. 26, that the
ventricle is much more capacious than the auricle. The auricle
is indeed the antechamber to the ventricle. The ventricle,
too, you see, is much thicker in its walls. It is made very
strong, because it does by far the principal part of the work.
I remark here, in passing, that the size of the whole heart is
about that of the closed hand of the individual.
120. I will now call your attention to a more particular view
of the valves of the heart. We will take, first, the valves
which are at the beginning of the aorta, the great artery of the
body, going out from the left ventricle. These are very much
like the valves of the veins seen in Fig. 23. There are three
of them. They are like little pockets arranged around the ori-
fice of the artery, and looking toward the tube of the artery.
Of course, when the ventricle contracts, and forces the blood
into the artery, these pockets are pressed by the blood flat
against the sides of the artery. But when the ventricle dilates,
and the blood attempts to go back from the artery into the
ventricle, it gets into these pockets, and bulges them out toward
the heart, and thus the mouth of the artery is closed. But you
can see that if these pocket-like valves had plain curved edges,
they would not effect a perfect closure. There would be a
THE CIRCULATION.
77
Peculiar provision in the valves of the aorta.
FIG. 28.
little space in the very middle of the orifice of the artery which
would be left open. This is made plain by Fig. 28, which pre-
sents the orifice of the artery with
its closed valves, as it would appear
seen from the interior of the heart,
if the three valves had plain curved
edges. There would be a space left
between them. But this difficulty is
remedied by a very simple contriv-
ance. A little fleshy projection is
placed upon the middle point of the
edge of each valve, of such a size
that the three projections together
just fill the space A. When, there-
fore, the valves are closed, no blood
can go back from the artery into the
ventricle. This arrangement is shown in Fig. 29, in which the
aorta, a, is laid open and spread out, so as to show the three
valves with their projections on the edges. At 6 and c, are the
openings of the two arteries that supply the walls of the heart
FIG. 29.
VALVES OF THE AORTA.
with blood for their growth and repair, tor the heart is con-
structed and repaired from its own blood. The valves at the
orifice of the pulmonary artery are arranged in the same man-
ner as those which are at the orifice of the aorta.
121. The valves which are between the auricles and the
7*
78 HUMAN PHYSIOLOGY.
Arrangement of the valves between the auricles and ventricles.
ventricles I have already partially described. They are folds
of strong white membrane, their edges being held by numerous
small tendinous cords. And these cords are manned, as we may
express it, by muscles attached to the walls of the heart. The
office of these muscles is to hold on to the cords that are fast-
ened to the edges of the valves, and prevent these sheets of
membrane from flapping back too far when the powerful ven-
tricle contracts. It is by a nice adjustment of forces that these
valves act with such exactness. They are of greater extent
than the valves which are at the mouth of the aorta and the
pulmonary artery, and, therefore, it would not do to leave them
to act alone, as those valves do, upon simple mechanical princi-
ples. The living muscular fibre must be introduced as the
agent to control and regulate these principles in their applica-
tion here. If it were not done, the consequence would be, that
when the ventricle contracts with prodigious force, as it some-
times does when the circulation is in a great state of excitement,
the light tendinous fastenings would be ruptured by the pres-
sure of the blood upon the valves. As it is now, the strong
but yielding muscular bundles, to which these tendons are
attached, regulate with great exactness the closing of the valves.
Even if there were no need of any regulation, by muscular
action, of the movement of these valves if the tendons would,
in all cases, let the valves go back to just the right point as
they are not extensible, and have no elasticity, it is manifest
that there would be more danger of rupture than there is with
the present arrangement. The tendons cannot be stretched, and,
therefore, under great pressure they might break. In Fig. 30
is a representation of a portion of this valvular apparatus. The
engraving was made from a drawing of the part taken from
the heart, and pinned upon a board for the purpose. At m,
you see the sheet of membrane ; o, o, are two of the muscles
attached to the inside of the ventricle, to hold on to the ten-
dons, A, that are fastened to the edge of the membrane. This
membrane is now in the position that it is when the valves are
open, that is, lying in a line with the little tendons and their
muscles. But when the ventricle contracts, the blood, pushing
against the membrane m, carries up the free edge to which the
tendons are fastened, which, meeting the free edges of the other
valves, closes with them the communication between the auricle
and ventricle.
122. In looking at Fig. 26, you observe that, while there are
valves between the auricle and ventricle, and at the mouth of
THE CIRCULATION. 79
No valves at the openings of the venae cavse. Why this.
FIG. 30.
PART OF THE VALVULAR APPARATUS BETWEEN THE AURICLE
AND THE VENTRICLE.
the artery going out from the ventricle, there are none at the
openings of the two ven<# cava, the veins that pour their con-
tents into the auricle. Why is this ? Why is there no need
of valves here to prevent a regurgitation into these veins when
the auricle contracts ? It is because that, as the auricle con-
tracts, there is at the same time the dilatation of the strong
ventricle, making, of course, a suction in that direction so
powerful as to counteract most fully any tendency to regurgita-
tion into the veins. You readily see, that if the arrangement
were reversed, and the auricle were stronger than the ventricle,
then, when the auricle contracted, there would be regurgitatior
into the vena? cavge, if there were no valves there to prevent it.
The same remarks could be made in regard to the pulmonary
veins, that pour their contents into the left auricle.
123. Having thus examined the heart in detail, you are now
prepared to look at it as a whole. For this purpose, I present
to you, in Fig. 31, a front view of the heart, in which a is the
right auricle, receiving the purple blood from the whole body
by the two large veins, h and i, called the ve nee cav<z j b is the
right ventricle, that receives the blood from the right auricle,
and sends it to the lungs by the pulmonary artery, f ; c is the
left auricle, which receives the red blood from the lungs, by
the pulmonary veins, g, g, a; d is the left ventricle that re-
ceives the blood from the left auricle, and sends it all over the
body through the aorta, e. You observe, that you see but a
part of the left auricle and ventricle, they lying partly behind
Mie right ventricle. You do not see the very beginning of the
80
HUMAN PHYSIOLOGY.
General view of all the parts of the heart.
FIG. 31.
FRONT VIEW OF THE HEART.
aorta, for, as it rises from the left ventricle it is at first con-
cealed behind the top of the right ventricle and the beginning
of the pulmonary artery. It then forms an arch, from which
it sends forth branches to the head and upper extremities ; and
it afterwards passes down behind the heart, to supply with its
branches the trunk of the body and the lower extremities. In
the line of division between the two ventricles, b and d, you
see one of the coronary arteries, as they are called, which,
coming from the beginning of the aorta, as describedjn 120,
supply the walls of the heart with blood. '4|p
124. To make you quite familiar with the relations of the
different parts of this complicated organ, and with the course
of the blood through its different apartments, I give vou, in
THE CIRCULATION.
81
Course of the blood through the different cavities of the heart.
Fig. 32, a map of the heart, with the names pHiced upon the
parts. I will describe the circulation with this map before you.
The dark blood is received from all parts of the body by the
venae cav<e from the parts above by the descending cava, and
FIG. 32.
MAP OF THE CIRCULATION.
from the parts below by the ascending cava. These veins pour
the blood into the right auricle. From this it passes into the
right ventricle, wl^h sends it by the pulmonary artery to the
lungs. Fr^tffflfllmgs it returns by the pulmonary veins to
the left B^^ ^ nen P asses m t t ne left ventricle, from
which itiBMBby the aorta to all parts of the body.
125. In Fig. 33 is represented the heart, situated between
the two lungs, with the arteries which carry blood from it, and
82
HUMAN PHYSIOLOGY.
Situation and connections of the heart. Its harmonious action.
the veins whic^i pour their blood into it. The lungs are repre-
sented as being drawn apart to the right and left in front, so
as to expose fully the heart and its vessels. The sac containing
the heart, and the packing cellular tissue are removed, so as to
lay the heart and its vessels bare. At a is the trachea or wind-
pipe ; on either side of it are the two arteries, the carotids,
which go to the head ; c is the artery which goes to the arm ;
6, 6, are the jugular veins coming from the head, d, c?, the veins
e f g h i
LUNGS, HEART, AND PRINCIPAL BLOOD-VESSELS.
from the arms, all empting their contents, as you see, into the
descending cava; e is the right auricle, receiving the blood
from the two cavae ; / the ascending cava ; g the right ventri-
cle, i the left ventricle, and h the descending aorta.
126. I have been thus particular, and have led you through
some repetitions in the description of some of the, figures, in
order that you may get a clear idea of the c^jft^Hcated mecha-
nism of the circulation. And now, perhaps^BJ iiunqiiire,
in what way all these four apartments of thew((Hfrcontract
and dilate, so as to have the organ act as one harmonious
whole. You have seen how the auricle and ventricle of one
THE CIRCULATION. 83
The causes of the two sounds of the heart. Its forward impulse.
side act in relation to each other the auricle contracts when
the ventricle dilates, and the ventricle contracts when the auri-
cle dilates. Now, the harmony of action between the two sides
is preserved by having the two auricles act together, and
the two ventricles act together. And this action produces
two sounds, which may be heard by applying the ear to the
chest of any one on the left side. The first sound is rather
a prolonged and heavy one, the second is light and quick.
They are very well represented by the syllables lub-tup. The
first sound occurs when the strong action of the heart is per-
formed, that is, when the ventricles contract. It is owing
to several causes. One of these is the impulse of the heart
against the walls of the chest; the cause of which I shall
speak of soon. Another is the flapping together of the
valves between the auricles and the ventricles, to prevent the
blood from regurgitating into the auricles, when the ventricles
contract to force out their contents. The light and quick
second sound is caused principally by the flapping together of
the valves at the mouths of the aorta and the pulmonary
artery when the ventricles dilate. The pulse (which I have
already remarked upon in 100) is produced by the impulse
given to the blood by the contraction of the ventricles. There
is, therefore, a pulse in the arteries of the circulation through
the lungs, as well as in those of the circulation through the
general system. Wherever there is an artery there is pulsation.
127. The impulse of the heart against the front wall of the
chest on the left side is easily explained. The heart is so en-
veloped by the lungs, that only a small portion of it comes
near to the front wall of the chest, and such is the situation of
the heart, that this portion comes to the left of the middle line
of the chest. The position of the heart is an oblique one, its
upper part being both farther back and more to the right than
its lower part. Keeping in view this position of the heart, you
will readily see how the impulse is produced against the front
of the chest at its lower part. The aorta, in going from the
heart, makes an arch upward and backward, to go down in
front of the spire ; and it is the tendency to straighten out,
produced in this arch by the force of the blood thrown into it
by the ventricle, that causes the throwing of the heart forward
by a spring. This is easily seen as illustrated by Fig. 34, in
which a is the spinal column ; 6, the front wall of the chest ;
d, the heart ; and c, the arch of the aorta. When the heart
throws the blood inio this arched tube it tends to straighten it;
84
HUMAN PHYSIOLOGY.
Arrangement of the sac of the heart. Its lubrication.
but, as the aorta is fastened to the
fixed spine behind, there can be no
impression made in that direction. FIG - 34 -
The straightening of the arch must
therefore occur in the other direction,
to the front ; and therefore the heart
is thrown a little forward, as represent-
ed by the dotted lines. The change
of position thus produced is indeed
but slight, but it is sufficient to cause
the impulse. The entrance of the
blood into the pulmonary artery per-
haps aids in the result, but not very
materially.
128. The heart, as I have already
hinted, is inclosed in a sac, called the
pericardium, which, at its upper part,
is fastened all around the vessels that proceed from the heart.
This sac is lined on the inside by a serous membrane, which also
lines the outside of the heart, being reflected over upon it from
the pericardium. This membrane forms, therefore, a sac without
any outlet. This is made plain by Fig. 35. In this diagram,
showing the plan of the serous membrane of the pericardium,
a, a are the auricles ; v, v, the ventricles ; 6, c, the vessels pro-
ceeding from the heart ; p the serous membrane lining the out-
side of the heart ; j/, the same membrane reflected from the
FIG. 35.
V....-
PLAN OF THE PERICARDIUM.
CIKCULATTOtf. 85
Action of the heart involuntary. Number of its beats.
upper part of the heart on to the inside of the pericardium.
The arrangement of this membrane, as it fits on to the heart,
is much like the common double nightcap, as it fits on to
the head ; and if it were dissected off whole from the outside
of the heart and the inside of the pericardium, it would be
like such a nightcap when taken off from the head that is, a
sac without an outlet. Now, this sac is kept moistened by a
fluid exuding from its whole surface, so that, as that part of it
which lines the outside of the heart, in the motions of that
organ, rubs against that part which lines the pericardium, the
lubrication prevents any injury from the friction. This lubri-
cating fluid is continually renewed, the exhalents and the absorb-
ents balancing each other in their action. When the exhalents
secrete more fluid than the absorbents can take up, it accumu-
lates, making what is cafled dropsy of the heart.
129. The heart, as you have seen, is a complex arrangement
of muscles. And these muscles are wholly involuntary ; that
is, they are not at all under the direct control of the will. No
one can by an exercise of the will make his heart beat slower
or faster. As I shall show you in another chapter, this organ
is kept at work by its nervous connection with the spinal mar-
row. It has no repose, as the voluntary muscles have, unless
you call the intervals between the contractions and dilatations
of its several parts intervals of repose. The amount of work
which it does is enormous, if we calculate it for a lifetime.
The heart of an adult beats, that is, each one of the four cham-
bers of this organ dilates and contracts, about 70 times in
a minute. This would make 100,800 times in 24 hours,
36,792,000 times in a year, and 2,575,440,000 times in a life
of 70 years. In children, the action of the heart is much more
rapid, and in disease it sometimes reaches in them to 160 or
even 200 beats in a minute. It is thus that this organ, situ-
ated in the centre of the complicated apparatus of the circula-
tion, labors continually, by night and by day, in keeping the
blood in motion. The two circulations of the general system
and of the lungs are ever going on. The blood is ever moving
in all the cavities of the heart, in every artery, and vein, and
capillary. It never stops till it is arrested by death.
86 HUMAN PHYSIOLOGY.
Apparatus of respiration. Air-ceils in the lungs. Their size.
CHAPTER VII.
RESPIRATION.
130. You saw, in the last chapter, that the purple venous
blood is sent to the lungs to be changed into arterial blood.
The great object of the apparatus of respiration is to introduce
the air to the blood, so that it may act upon it, and produce
this change. Another object is effected at the same time, viz.,
the production of the voice, by the striking of the air upon
the vocal chords in the larynx, as it is forced out from the
lungs. This will be made the subject of a future chapter, and
I propose now to show how the chief object of respiration,
which is so immediately essential to the continuance of life, is
secured.
131. The lungs are spongy bodies, filling up a large part of
the chest, and surrounding the heart. They are in common
language, the lights ; and you can see what they are in man
by observing the lights of other animals. They are composed
chiefly of air-tubes, air-cells, blood-vessels, and nerves, packed
together with the common packing material of the body, cellu-
lar membrane. The spongy lightness of the lungs is owing to
the air-cells or vesicles. You can get some idea of the propor-
tion of these cells to the solid part of the organs if you
inflate the lungs of some animal, as the sheep or calf, by blow-
ing into the windpipe. These cells are exceedingly minute.
It is in them that the change is effected in the blood. The
capillaries holding the blood branch out on the walls of the
cells, and the blood is acted upon by the air through the pores
of the vessels. The object, therefore, of respiration is to in-
troduce the air freely into these cells. The air enters through
the windpipe, and this branches out into tubes called bronchi,
which divide and subdivide, till they become very minute, and
then end in the air-cells. These cells are estimated to be about
the To~oth of an inch in diameter. Some calculations have
been made in regard to the extent of surface which they would
all make if they could be spread out in one sheet. There is of
course no great accuracy in such calculations ; but we can readily
see that the aggregate surface must be immense, and, therefore,
the blood is thus very extensively exposed to the action of the
RESPIRATION. 87
Air-tubes. Relative situation of the lungs and the heart.
air. In Fig. 36 is represented the lung of one side, d ; the
branches of the bronchi of the other lung, c, at the lower part
of which, <?, they are represented as they branch put minutely
to open into the air-cells ; b is the trachea or windpipe, and a
LUNGS AND AIR-TUBES.
is the larynx at the top of it. It is through a chink called the
glottis, in the larynx, that all the air passes as it goes into and
out from the lungs. This will be particularly described here-
after.
132. In Fig. 33, in the last chapter, you see represented the
relative situation of the heart and lungs, the lungs being some-
what separated, however, from the heart, to the right and left,
in order to show that organ fully. In their natural position
they are close to the heart, and cover up all of it, except a
small portion in front and to the left side, where its beating is
so plainly felt. Both the heart and the lungs are suspended in
the chest to the upper part of the walls of this cavity, and are
fastened also to the spinal column in the rear. The large vessels
of the heart, and the bronchi of the lungs, serve as the princi-
88 HUMAN PHYSIOLOGY.
Pleura. Mechanism of breathing. Provision for expansion of the chest.
pal means of suspending these organs, as you can readily see
by the Figure. The lungs are covered by a white, shining
membrane, which also lines the inside of the walls of the chehw
( 67.) called the pleura. This is always kept lubricated by
a watery fluid, so that, as the lungs expand and the chest
moves, the friction will be attended with no inconvenience or
injury. You may perhaps ask why, as the lungs follow the
walls of the chest in its expansion, they could not have been
fastened to these walls throughout their whole surface. The
principal reason probably is that, if this were the arrangement,
the intimate vascular connection, which would in this case
exist between the walls of the chest and the lungs, would ex-
pose the delicate texture of these organs more frequently to
injury from external violence. As it is now, the eifusion, or the
inflammation, consequent upon a blow on the chest, is not
apt to affect the lung in the neighborhood, because it has
no direct connection with it by nerves and blood-vessels.
133. You are now prepared to see by what mechanism the
air is alternately introduced to and expelled from the lungs. The
chest incloses a large space, which can be made much greater by
certain movements of its walls. It is this expansion of the cav-
ity of the chest, effected by certain muscles, which, by creating a
vacuum, causes the air to rush into the chest through the tra-
chea, just as air rushes into the bellows when the space within
is expanded by the separation of its walls. That you may un-
derstand how the expansion of the chest is effected, I now
proceed to describe the chest. In Fig. 37 you see the frame-
work of the chest. At 6, 6, is the spinal column, the grand
pillar supporting the walls of this cavity. The ribs, c, c, go
from this with a large curve round to the breastbone, a, in
front. The ribs, however, do not join directly with the breast-
bone, but there are cartilages intervening, as you observe in
the Figure. The collar-bone goes from this breastbone across
to the top of the shoulder. The ribs are twelve on each
side. The lowest two are attached only to the spine, and are
called floating ribs. The whole is so constructed as to allow a
very considerable expansion of the cavity. As, in effecting this
expansion, the ribs are carried upward and forward with the
breastbone, the ends of the ribs at the spine move but very
slightly. As the chest is kept in constant motion, lightness in
its walls is an object of some importance ; and, at the same
time, it is necessary that the structure should be a strong one,
in order to guard effectually the lungs from injury. Both of
RESPIRATION. 89
Framework of the chest. Bones. Cartilages. Muscles.
FIG. 37.
these objects are secured, by having the walls in front and at
the side composed of so many bones, well bound together by
the muscles which move them. If these bones were all in one,
it would be necessary that it should be quite thick, to answer
as a defence, and then it would be a heavy and unwieldy thing
to move. The cartilages which connect the ribs to the breast-
bone are a great safeguard. They give elasticity to the struc-
ture as a whole, and the ribs are not very liable to be broken,
because of the yielding of the cartilages with which they are
connected.
134. This framework is filled out with connecting material,
chiefly muscles, which effect the expansion of the chest in in-
spiration. First, there is a large expanse of muscle and tendon
stretching across the lower part of the chest, separating its con-
tents from the contents of the abdomen below. The edge of this
muscle, which is called the diaphragm, is fastened to the spine
behind, to the end of the breastbone before, and all around the
lower ribs. It is arched upward ; and against its concave sur-
face press upward the liver and stomach, while the lungs and
8*
90 HUMAN PHYSIOLOGY.
Diaphragm. Its action in inspiration and expiration.
the heart press downward against its convex surface. The dia-
phragm is represented in Pip-. 38. The ribs are cut away in
front, so as to give a front view of the cavity of the chest, C, c,
the lungs and heart being entirely removed. D D is the
diaphragm, very high in the central portion, which is tendin-
ous, but descending very low at its edges at the sides and in
the rear.
FIG. 38.
DIAPHRAGM.
Front View.
135. You can see that, if all the muscular fibres in the dia-
phragm contract, the arch will be flattened, and thus the room
in the chest will be enlarged. To occupy this new room thus
made, the air rushes in through the windpipe. This is inspira-
tion. In expiration, the reverse movement takes place the
arch of the diaphragm rises, and, compressing the lungs, forces
the air out of them through the trachea. In inspiration, as
the diaphragm is flattened, it pushes down before it the
stomach, liver, &c., and hence the pressing out of the abdomen,
which is so sensibly felt, if the hand be placed upon it during
the act of inspiration. In expiration, on the other hand, the
RESPIRATION".
91
In expiration little muscular action. Elasticity the chief agent.
abdomen retreats inward. These two opposite states of the
arch of the diaphragm, and of the walls of the abdomen, are
represented in Fig. 39. It is a side view, the ribs being cut
away. C c is the cavity of the chest, and C a, the cavity of
the abdomen. The diaphragm and the abdomen are represented
FIG. 39.
DIAPHRAGM.
Side View.
as they are in expiration. The dotted line marks the flattening
of the arch of the diaphragm, and the projection of the ab-
domen, as they occur in inspiration. It is supposed that in
ordinary expiration, there is little, if any, muscular action
that, as the diaphragm, which in inspiration pushed down the
stomach and liver, and thus thrust out the walls of the ab-
domen, ceases to contract and relaxes, the mere elasticity of
the parts below, and especially of the abdominal walls, restores
the former condition of things, and so the diaphragm is car-
ried upward, and expiration results. When, however, the ex-
92
HUMAN PHYSIOLOGY.
Other muscles, besides the diaphragm, act in inspiration.
piration is at all forcible, it is produced in part by the action
of the muscles of the abdomen and some of the muscles about
the chest.
136. While this dome-shaped muscle, the diaphragm, is the
principal agent by which the chest is enlarged, there are other
muscles which do the same thing in another way. In Fig. 40,
a is the spine ; c, c, c, the ribs ; 6, the breastbone ; c?, the col-
lar-bone ; g, the diaphragm. You observe, on the right side
c a h
WALLS OF THE CHEST.
of the chest, certain muscles, *, extending from the spinal
column in the neck to the first rib. When these contract, the
effect will be to raise this first rib, and all the others, being
attached to it, of course follow. And, as the ribs, as you see
in Fig. 37, slant downwards from the spine toward the front,
the result will be, that all the ribs will be carried together for-
ward and upward. This result is the more effectually secured
by muscles which pass from rib to rib, as seen at e, e, e, e. In
this Figure, the ribs, c, c, c, are left bare on the left side, to show
RESPIRATION. 93
Arrangement of muscles between the ribs.
the arch of the diaphragm, #, the dotted line indicating it on
the right side.
137. There are two layers of muscles connecting the ribs,
the fibres of which cross each other, as represented at M, in
Fig. 41. R R are parts of two ribs. The spaces between the
FIG. 41.
ribs are filled with muscular fibres, arranged as represented in
in the Figure. If the fibres were straight, as at L, they could
not bring the ribs as near together as the oblique fibres do.
For, as muscles can not shorten themselves, at the farthest, more
than one-third of their length, the straight fibres could bring
the ribs only one-third nearer together, while it is obvious that
the oblique fibres, with the same contraction, can do much
more than that. These muscles between the ribs not only,
then, help to raise all the ribs as a body, as mentioned in 136,
but they bring each rib nearer to the one above it. This in-
creases the expansion of the chest, especially as the ribs are so
joined to the spine, that if a rib be moved upward, it must be
carried outward as well as forward. You can see, then, that
by the operation of these muscles in the neck and between the
ribs, the diameter of the chest will be increased from front to
rear, arid also from side to side.
138. The chest is expanded, then, in two ways by flatten-
ing the arch of the diaphragm, and by raising the ribs. In
ordinary quiet respiration, this expansion is effected chiefly by
the diaphragm. But when there is a call for more active
respiration, as in violent exercise, the muscles which raise the
ribs act strongly, and hence the heaving of the chest, as it is
called. Their action is violent when from disease, as in asthma
for example, it is difficult to introduce sufficient air into the
lungs.
139. The lungs, heart, &c., accurately fill the chest in all the
variations of size to which its cavity is subjected in respiration.
94 HUMAN PHYSIOLOGY.
Change in the blood effected in the air-cells.
For, when the chest is expanded, the spongy lungs swell out to
follow its walls, and the air rushes in through the trachea to
fill the expanding air-cells. If, now, there were an opening
through the walls of the chest, communicating with the out-
side of the lung, when the chest expanded, the air would rush
in at this opening as well as through the trachea, and the lung
would be compressed in proportion to the freeness of the open-
ing. This has sometimes occurred from disease and from
wounds. If a free opening were made at the same time in
both sides, both lungs would be compressed, and death would
be produced by suffocation, as really as if some obstruction in
the windpipe prevented the air from entering the lungs.
140. I have said that the change in the blood, from purple
to red, is effected in the air-cells. The blood and the air are
brought very near together for this purpose ; and yet they are
kept entirely separate, except when, from disease, the blood
escapes into the air-cells and air-passages, and is then expecto-
rated mingled with air. It is supposed that the air in the cells
acts upon the blood through the pores of the vessels containing
it, which branch out on the walls of the cells ; for if dark
venous blood be inclosed in a bladder, the air will act through
the pores of the bladder, and gradually change the outer por-
tion of the blood to a red color.
141. These air-vesicles, then, do an important work. The
change which is effected in them is immediately essential to the
continuance of health, and even of life. If the air be in any way
shut out from them death occurs at once. And so important
is it that they should do their work well, that extraordinary
provisions are made to secure an abundance of room for them
under all circumstances. For the cavity of the chest, as you
have seen in this chapter, can be expanded to a very great ex-
tent. It would indeed be difficult to conceive how a greater
range of expansion could be sec^^d. As the air-cells are
called upon to do more work at some times than at others,
there are special provisions for a larger dilatation of the chest
than is required in ordinary quiet respiration. Thus when,
from violent exercise, the blood is coursing rapidly through the
lungs, and more air is therefore needed to change it to red
arterial blood, the chest is largely expanded by calling into
action muscles, which do but little, if any thing, in ordinary
breathing.
142. As the apparatus of res] -ration is so especially ar-
ranged to secure room for the lungs under all circumstances,
RESPIRATION. 95
Injury done to the air-cells by compression of the chest.
it must be very deleterious to the health of the body to inter-
fere with this arrangement. If the expansion of the chest in
breathing be limited by any pressure, every air-cell must be
embarrassed in doing its part in changing the blood. Either
all of them must be unduly contracted, or some of them must
become obliterated, so that there will not be as many vesicles
as there should be. In either case, the organ is disabled in
proportion to the amount of the compression. The blood is
not as good as it would be if there were enough vesicles, and
they could perform their work without constraint. The vigor
of the system is therefore lessened. And, besides, the lungs
themselves are especially liable to disease from this unnatural
confinement.
143. Much injury is undoubtedly done to the lungs that are
thus confined, when any strong exercise is taken. If the chest
be left free to expand to its fullest extent when occasion re-
quires, this injury is avoided. For when the strongly and
rapidly contracting heart pumps the blood in such quantities
into the lungs, the widely expanding chest draws in the due
amount of air to change the extra amount of blood. All the
air-vesicles are ready to do their duty, and, therefore, no violence
is done to the delicate texture of the lungs. But if these or-
gans be compressed, the dilatation of those vesicles that are not
obliterated, in the midst of the commotion of the .difficult res-
piration, is very unequally effected, and some of them are
stretched beyond their proper dimensions. At the same time,
the blood must be here and there obstructed in its passage
through the lungs, producing what is termed congestion. And
if this violence be repeated from time to time, permanent dis-
ease will after a while be the result.
144. From the considerations in the two last paragraphs it
is manifest, that the interference with the due expansion of the
lungs, which so commonly results from the modes of dress in
the female sex, must be one of the prominent causes of con-
sumption, to say nothing of other diseases arising from this
cause. This interference is effected in two ways chiefly by
compression of the chest directly, but also by the pressure
which the load of clothing hanging from the girt waist must
make upon the upper part of the abdomen. This latter cause
interferes with that forward movement of the abdomen which,
as you saw in 135, is necessary to the flattening of the arch
of the diaphragm in the act of inspiration. The extent to
which compression of the chest is sometimes carried is seen by
96 HUMAN PHYSIOLOGY.
Change of the form and capacity of the chest by compression.
comparing the two outlines in Fig. 42. One is an outline, of
the Venus de Medicis, the universally recognized beau ideal
of beauty of form in the female, and the other is an outline
FIG. 42.
of the form of a lady with an artificially small waist. In Fig.
43 is represented the framework of the chest of its natural
size, and as it is sometimes contracted by fashion. The Figures
FIG. 43.
representing the contraction of the chest may appear at the
present time as caricatures, for a very small waist is not con-
sidered now to be as essential to beauty in the female form, as
it was twenty-five years ago. The truth, as uttered by medical
men, has had some effect. But the evil is remedied only in
RESPIRATION. 97
Cause of death in drowning. Singular provision in the whale.
part. The chest of the female is still too much begirt, in obe-
dience to the tyranny of fashion, to allow of the free expan-
sion, to secure which such special pains are taken by nature.
The evil begins in childhood. The chest is moulded during
its growth to the shape which fashion prescribes. It could not
be done after the chest has attained its full size. The torture
of the compression necessary to do it could not be endured.
In childhood, therefore, while the boy's chest is left to grow
in its natural shape and dimensions, the girl is begirt so tightly
as to embarrass her respiration, because nature is too ungen-
teelly large in her patterns to suit her case. The subject is
an important one ; but as this book is not designed to treat of
hygiene, I can not go into it further.
145. It is the interruption of the change which is effected
by the air upon the blood in the lungs, that produces death in
drowning. The very common supposition, that considerable
water gets into the lungs in drowning, is erroneous. Very
little water ordinarily gets in not enough to occasion any em-
barrassment. The difficulty is, that the air is kept out, and
not that the water gets in. The drowning person makes at-
tempts to inspire, but the moment that the water reaches the
epiglottis, the door of the windpipe, it causes at once, by its
irritation, a spasmodic closure of the epiglottis, so that almost
no water is introduced. In the mean time, the purple blood
continues to be thrown by the right ventricle of the heart into
the lungs. But the little air contained there soon parts with
its oxygen ; and then the change in the blood ceases to occur,
and dark blood is sent from the lungs to the heart, and thence
to all the organs. These can not go on to do their duty with-
out the stimulus of arterial blood. The brain, therefore, gives
out, and there is insensibility. The muscles cease to act, and
all motion is gone. If a good supply of arterial blood could
be furnished to all the organs until breathing could be again
commenced, life would be preserved. And there is provision
for such a supply in certain animals that can remain under
water for some time. For example, in the whale there are
large reservoirs for containing arterial blood, which can be used
for the supply of the organs while he remains under water.
"When the supply begins to be exhausted, the animal of course
has those uncomfortable sensations which a predominance of
purple blood is so apt to produce. He manifests his uneasbess
by his puffing and blowing, as he rises to the surface, to get a
fresh supply of air, and with it a fresh supply of arterial blood
in the reservoirs. 9
98 HUMAN PHYSIOLOGY.
Respiration in fishes. Arrangement of the gills.
146. The apparatus of respiration varies in different animals,
It appears in three forms lungs, gills, and tracheae or air-
tubes. The gills of the fish are arranged in fringed laminae, in
order to present by all its minute divisions a large surface ; and
these delicate organs are covered with a lid to protect them
from injury. The blood-vessels which contain the blood to be
changed branch out on the surface of the fringes of the lami-
nae, just as the blood-vessels in lungs branch out on the surface
of the air-vesicles. The air which is to change it is mingled
with the water. It acts upon the blood, as the
water containing it, after being taken into the
mouth of the fish, passes out through these la-
minae, as through a sieve. That the air in the
water is the cause of the change can be proved
by experiment. If a fish be placed in a vessel
with its orifice closed, so that no air can enter, it
will soon die from suffocation, because the air in
so small a portion of water is soon used up.
Although the fish can not with his gills use air
that is not mingled with water, it is supposed
that it is merely because the gills soon become
dry when exposed to the air, and that the air
would act on the blood in the gills if they were
only kept moist. Indeed, in the land crab, that
has the power of living for some time out of the
water, it has been found that there is a gland in
the gill-chamber which furnishes a secretion to
keep" the gills moist. Gills differ much in their
shape and arrangement in the various aquatic
animals. In Fig. 44 is represented the arenicola
or lob-worm. Here, the gills are in the form of
tufts arranged along the outside of the body.
They take a somewhat similar form in the larvae
of many aquatic insects, as seen in Fig. 45. A
large surface is presented to the air contained in
the water by the delicate and beautifully arbor-
escent gills of these animals. In insects, we find
the respiration effected by tracheae or air-tubes.
These go into all parts of the body, and the air
contained in them acts upon the blood in the ves-
sels which branch out upon their walls. The in-
sect, therefore, has no distinct respiratory organs
situated in any one part of the bqdy, but the LOB-WORM.
RESPIRATION.
99
Respiration in insects. Tracheae. Stigmata.
air is carried into every part. This seems to
be necessary on account of the feeble circula-
tion in the insect. The tracheae which, as
Cuvier says, conduct the air in search of the
blood, as the blood has no means of travelling
in search of air, open on the surface by stig-
mata, as they are called, which are of various
shapes and number in different insects. In
the grasshopper there are twenty-four, ar-
ranged in four rows. You can kill an insect
by suffocation by simply covering the stigmata
with varnish. In Fig. 46 are represented the
tracheae in an insect, the nepa or water-scor-
pion. The tracheae, as you see, send branches
out in every direction, so that air is introduced
FIG 46.
FIG. 45.
WING CUT OFF
LARVA OF TUB
MAY-FLY
- AIR-SACS.
RESPIRATORY APPARATUS OF THE WATER-SCORPIOW.
100
HUMAN PHYSIOLOGY.
Respiration in birds. Apparatus for it extensive.
into ev 7 ery part of the body. There are lungs, so to speak,
everywhere in the insect.
147. The apparatus of respiration is largely developed in
birds for two objects to provide for the extensive change in
the blood which is required by their great activity, and to give
lightness to the body. To secure these objects there are air-
sacs connected with the lungs, and located in different parts of
the body ; and in birds that fly rapidly and are long upon the
wing, these sacs are very extensive, and even many of the
bones are made hollow, and are connected with the air sacs.
By this arrangement, the air is introduced extensively to the
biood in the capillaries on the walls of these sacs> and at the
same time the body is made very light. And the heat gener-
ated by the effort of flying must expand the air in the air-sacs
and swell them out, and thus make the body lighter. In Fig. 47
is seen this arrangement of air-sacs in the ostrich. The lungs,
/, , are quite small, but the air-sacs, c, c, c, are very large.
The orifices by which they communicate with the lungs vou see
FIG. 47.
LUNGS OF THE OSTRICH.
KESPIRATION. 101
Changes produced in the air in the lungs.
in the Figure. In birds of great powers of flight, the air-saca
are much more extensive. This arrangement of air-sacs in
different parts of the body of the bird bears some analogy to the
tracheae distributed in the bodies of insects.
148. You have seen that the object of the apparatus of re-
spiration is to change venous blood into arterial, and you have
also seen how the air is introduced to the blood in order to
effect this change. And now the interesting inquiry arises,
what are the actual changes which occur, both in the blood
and in the air, in the lungs. If you take a tumbler filled
with lime-water, and breathe into it through a tube, the lime-
water will become turbid, and will soon deposit a sediment.
This is chalk, or carbonate of lime, formed by the union of
the carbonic acid gas exhaled from the lungs with the lime
in the lime-water. Whence comes this carbonic acid gas,
and how is it formed ? In order to answer this question satis-
factorily, we must look at the chemical constitution of the air
which we breathe. It is composed of two gases, oxygen and
nitrogen. In every 100 parts of common air, there are 79
parts of nitrogen and 21 of oxygen. It is found that the
oxygen is that constituent of the air which is necessary to
life. If an animal be placed in a closed jar filled with com-
mon air, he will soon die, and the oxygen will be found to have
disappeared, while the nitrogen remains very nearly the same
in amount. If, now, you place an animal in a jar of nitrogen,
and another in a jar of oxygen, the one in the nitrogen will die
immediately, while the other will be very lively until the oxy-
gen is mostly used up by his lungs. The animal in the pure
oxygen will breathe at first more rapidly than the animal in
the jar of common air ; and it is thought that oxygen is too
stimulating for the lungs, and therefore needs to be diluted
with the nitrogen, as it is in the air that we breathe.
149. In the case of both the animal in the jar of air, and
that in the jar of oxygen, carbonic acid is found to have taken
the place of the oxygen which has disappeared. This gas is
made by a union of oxygen with carbon or charcoal. It was
formerly supposed that this union is effected in the lungs
that carbon is thrown off from the venous blood in the lungs,
and that the oxygen of the air there unites with it, and so car-
bonic acid appears in the air expired from the chest. But it has
been discovered that the exchange is made in a different man-
ner. It is not made in the lungs. The oxygen is absorbed by
the blood, and goes with it to the heart to be sent all over the
9*
102 HUMAN PHYSIOLOGY.
Changes produced in the blood by the air.
system. And it is in the capillaries that the oxygen unites
with carbon to form carbonic acid. The union takes placa
while the blood is changing from arterial to venous, and is an
essential part of the change. The carbonic acid thus formed
in the capillaries, is brought back to the heart in the venous
blood, and is discharged from the system in the lungs. That
the change takes place as stated has been abundantly proved
in various ways. It has been found by experiments which I
will not detail, that carbonic acid exists in considerable amount
in venous blood ; while, on the other hand, there is much oxy-
gen in arterial blood. The plain inference from this is, that
oxygen unites with the blood as it passes through the lungs,
goes with it to the capillaries, and there unites with the carbon,
giving us the carbonic acid which we find in the blood in the
veins, after it has passed into them from the capillaries. It has
been found, also, that if frogs or other cold-blooded animals
be placed in hydrogen or nitrogen, (gases which produce no in-
jurious effect on them,) they will give off for some time nearly
as much carbonic acid as they would have done in common
air. In this case, as no oxygen is introduced into the lungs,
the carbonic acid can not come from any union effected in
these organs between carbon and oxygen, but it must be dis-
charged by exhalation from the blood as it is passing through
the lungs. Of course the discharge of the carbonic acid ceases
after a little time ; for, there being no new supply of oxygen by
way of the lungs, as there is when the animal is breathing com-
mon air, there can be no new formation of carbonic acid. But
even cold-blooded animals can not live in these gases for any
great length of time, although they are not positively deleterious
to them, for oxygen is needed for the continuance of their func-
tions. And in the warm-blooded animals, a constant supply
of it is necessary they will die if cut off from this supply
even for a short time.
150. The change which takes place in the blood, as it passes
through the lungs, occurs to some extent when the blood is ex-
posed to the air in any way. Thus, if blood be drawn from a
vein into a bowl, the surface of it becomes red by the action
of the air upon it. Carbonic acid is discharged from it, and
the oxygen of the air takes its place, uniting with the blood,
just as the process occurs in the lungs. A larger part of the
blood will be thus changed, if it be shaken so as to expose
more of it to the air. The change takes place to some extent
even if a membrane be interposed between, as when the blood
KESPIKATION. 103
Quantity of carbonic acid given out by the lungs. Necessity ol ventilation.
is inclosed in a bladder. The oxygen of the air, in this
case, is introduced through the minute pores of the bladder,
and the carbonic acid gas escapes through them. Precisely in
this way is the change effected in the lungs, as already stated
in 140. The blood is separated from the air by being con-
fined in blood-vessels, and the air in the vesicles acts upon it
through the minute pores of these vessels. Arid, as the blood is
divided into innumerable little streams, every part of it is acted
upon by the air in the vesicles. Though the texture of the
lungs is exceedingly delicate, and the separation between the
air and the blood is almost as nothing, yet the blood is confined
to its limits, even though it courses through these organs with
great, rapidity, and it never mingles with the air except as 9
consequence of actual disease.
151. The quantity of carbonic acid gas discharged from the
lungs in the course of twenty-four hours is very great. Many
experiments have been tried and calculations made to ascertain
its -amount, and I am within bounds when I state, that there is
at least three-quarters of a pound of charcoal in the carbonic
acid thrown off from the lungs of a common-sized adult in the
course of twenty-four hours. This gas is a deadly poison.
When accumulated in a considerable amount, as when char-
coal is burned in an open furnace in a close room, it may prove
immediately destructive to life. And in the very prevalent
neglect of ventilation, the frequent accumulation of this gas
from the respiration must prove more or less injurious to the
health. Whenever the proper amount of oxygen gas is with-
held from the lungs, and carbonic acid takes its place, the
quality of the blood is impaired from incompleteness in the
change effected in the lungs, and the vigor of the body must
in this way be lessened, to say nothing of the deleterious influ-
ence of this gas upon the nervous system. Though the results
are not immediate and palpable, great injury is continually
done to the health of multitudes by the accumulation of this
gas, in small close apartments, and in crowded assemblies. A
congregation of twelve hundred people in two hours throw off
from their lungs an amount of carbonic acid that contains
seventy -five pounds of charcoal. And yet little pains is com-
monly taken to carry off this vast quantity of poisonous gas,
and replace it with pure air.
152. As so much oxygen is absorbed in the lungs of all ani-
mals, and so much carbonic acid is thrown out from them, the
inquiry arises how the air is replenished with oxygen, and is
104 HUMAN PHYSIOLOGY.
Carbonic acid exhaled from the lungs of animals absorbed by plants.
cleared of the carbonic acid which is thus so largely mixed with
it. It is found that this is done, to a great extent at least, by the
leaves of plants. The process which goes on in these lungs, as
they may be called, of the plants, is quite the reverse of that
which is going on in the lungs of animals. The carbon of the car-
bonic acid which is thrown off from the lungs of animals is ab-
sorbed by the leaves of plants, and the leaves replenish the air
with the oxygen, which is so constantly and abundantly ab-
sorbed in the lungs of the animal creation. Thus, the animal
and vegetable kingdoms are sources of supply to each other.
But it may be thought that there would be apt to be a surplus
of oxygen in the atmosphere in warm climates, where the vege-
tation is so luxuriant ; while, on the other hand, there would
be an accumulation of carbonic acid gas in the colder regions.
This would be so, if the air were not so movable that the equi-
librium is readily secured in either case.
153. It is an interesting fact, that the presence of light is
necessary to the process which I have described as going on in
the leaves of plants. Each leaf may be considered as a labor-
atory, and the light as the chief agent in effecting the chemical
changes that occur in it. And it is found that no artificial
light can do the work. It is only the light of the sun that is
competent to this chemistry. And as these innumerable labor-
atories are everywhere at work, absorbing the carbon and ex-
haling the oxygen, to purify the air rendered noxious by the
laboratories of the animal creation, we must confess it to be a
mystery as to how the chemistry of the lungs of animals, and that
of the leaves of plants should be kept so nicely balanced. The
balance is so strictly maintained, that the chemical composition
of the air is always found to be almost exactly the same.
154. The heat of the body is maintained by the union
which takes place in the capillaries between the carbon and
hydrogen of the system, and the oxygen which is introduced
into the blood through the lungs. It is a process analogous to
combustion. When carbon or charcoal is burned in a ves-
sel containing air, the oxygen disappears, for it unites with
the carbon, and carbonic acid gas, therefore, appears in its
place. The same union occurs in this case between carbon and
oxygen, as we find occuring in the capillaries. A sort of com-
bustion, then, is going on in every part of our bodies. And, as
heat is evolved in the one case, so it is in the other. The same
can be said of the burning of hydrogen and oxygen together.
Heat is caused by the union thus produced between them, and
RESPIRATION. 105
Animal heat. Produced by a sort of combustion. Three sources of fuel.
so it is when they unite in the body. The water which is ex-
haled from the lungs comes from this union of oxygen and
hydrogen. It was formerly supposed that the union between
the oxygen and the carbon and hydrogen takes place in the
lungs, and that the heat is made there, and then is distributed
over the whole system. But it was objected to this supposi-
tion, that it made the lungs a sort of furnace for the rest of the
body, and that, if the supposition were correct, there ought to
be a much higher degree of heat in these organs than any-
where else, which is not the case. Ingenious theories were
broached to get over this difficulty ; but it was at length dis-
covered that the union between the oxygen and the carbon and
hydrogen occurs in the capillaries of the body, instead of the
lungs, and that the combustion, therefore, that produces the
heat is everywhere, instead of being in one locality.
155. The fuel for this combustion comes from three sources.
One of these is the waste of the tissues. This furnishes a con-
siderable amount of the carbon and hydrogen for the union
with the oxygen, in all animals that are subjected, from their
activity, to much wear and tear of the system. I barely al-
lude to this now, and shall enlarge upon it soon. Another
source of the fuel for combustion is food. The oily, sugary,
and starchy kinds of food are devoted in a great measure to
this particular purpose. These furnish a sort of floating fuel,
as we may express it, which is carried about in the blood.
Hence, we see, that our diet must necessarily be varied accord-
ing to the weather and the climate. In cold weather, the heat
of the body is more rapidly abstracted than in warm weather,
and, therefore, we need then more of that food which affords a
supply of carbon and hydrogen. And so as to climate. The
enormous quantity of oily food often consumed by inhabitants
of very cold climates is used up by being burned, as we may
say, in the capillaries to keep up the animal heat. Of course,
keeping the body warm by fire and clothing relieves from the
necessity of taking any large quantities of fuel-making food.
Still, under the most favorable circumstances in this respect,
there is a need of variation in diet to suit the weather and the
climate, and we make this variation for the most part instinct-
ively. Indeed there is a marked provision in nature for it. I
will mention but a single example of this provision. While
there is a large amount of fat in the bears and seals and whales
which afford food for the Esquimaux and Greenlander, there is
very little in the animals which furnish a part of the diet of the
106 HUMAN PHYSIOLOGY.
Animal heat differs in cold and warm-blooded animals. Why.
inhabitants of tropical climates. Another source, still, of ani-
mal heat is the store of fat which is laid up in the body. Ona
design of this accumulation of fat in different parts of the
body seems to be to provide for the heat when other sources
fail. Thus, when disease destroys the appetite, and thus cuts
off the supply of food, the fat wastes away, or rather is burned
up, to keep up the temperature of the body. The fat is the
great means of maintaining the requisite temperature when hi-
bernating animals become torpid for the winter. They become
very fat in the autumn, before crawling into their winter quar-
ters, and in the spring they come out very lean, their fat having
been consumed in keeping up the low degree of temperature re-
quired during this time.
156. As the amount of heat produced, when charcoal is
burned in air, or when oxygen and hydrogen are burned
together, depends upon the quantities of carbon and hydrogen
that unite with the oxygen, so, also, the degree of animal heat
depends upon the quantities of carbon and hydrogen that unite
with the oxygen in the capillaries. This may be illustrated by
referring to the effects of exercise on the heat of the body.
When the circulation is quickened by exercise, the blood passes
more rapidly than usual through the lungs, the respiration is
consequently quickened, more air is introduced into the lungs,
and therefore oxygen is more rapidly absorbed by the blood.
At the same time, the action of the muscles effects a waste in
their structure by the wear and tear, so that more carbon and
hydrogen are ready to be released to be united with the in-
creased oxygen. Hence comes the heat produced by exercise.
So, too, those animals which are the most active, ordinarily
have the most animal heat, and have the most extensive respi-
ratory apparatus, so that there may be a free supply of absorbed
oxygen to unite with the carbon and hydrogen of the changing
tissues. It is in birds and insects that this union takes place
most largely, and in them, therefore, the respiratory apparatus
is very largely developed. This is to be attributed to their mus-
cular activity, which produces so much waste matter that must
be removed from the system. Cold-blooded animals, on the
other hand, are very inactive. There is not, therefore, much
wear and tear of the tissues. There is comparatively little
waste, therefore, to be thrown off. And so but little oxygen
needs to be introduced into the lungs, and consequently little
heat is generated. To realize fully the contrast between the
warm and the cold-blooded animals in these respects, observe, a*
KESPIRATION. 107
Uniformity of animal heat in the warm-blooded. Interesting experiments.
the representative of the one class, a canary bird, and a frog ai
the representative of the other. The frog is generally quiet,
and only now and then takes a leap or croaks ; but the bird
is ever in restless motion, and sings much of the time with
all his might. The bird is warm with the heat generated by
the constant union of oxygen with carbon and hydrogen in its
capillaries ; but the frog is nearly as cold as the water in which
he is immersed. The bird breathes rapidly, to let the oxygen
of the air largely into his lungs ; but the frog scarcely seems
to breathe at all, so scanty is the supply of oxygen which he
needs.
157. Cold-blooded animals are very nearly of the same tem-
perature with the substances that are around them ; but warm
blooded animals have a certain degree of temperature, which
they maintain with considerable uniformity under all variations
of temperature in the atmosphere. This in man is about ninety-
eight degrees of Fahrenheit. This, you observe, is above the
temperature of the surrounding air, except in exceedingly hot
weather. The human body is therefore always giving off heat.
Indeed it is essential to comfort that it should part with con-
siderable heat, for any near approach of the atmosphere to
ninety-eight degrees produces an uncomfortable sensation of
heat. But the amount of heat which the human body can
bear for a short time is much greater than the facts above
alluded to would lead us to suppose. It was long taken for
granted, that it could not safely bear, even for a short time,
a heat much higher than that which is endured in hot climates.
The truth on this subject was at length discovered by accident.
Two Frenchmen were employed by government, in 1760, to
devise some method of destroying an insect which infested the
grain at that time. The result of their experiments was the
discovery, that by subjecting the grain to a certain degree of
heat in an oven the insect was destroyed, and the grain not
injured. While they were trying their experiments, a girl
offered to go into the oven and mark the height of the mer-
cury in the thermometer. It stood at 260 ; and, after remain-
ing there for ten minutes, which she found that she could do
without any great inconvenience, she marked it at 288, that
is, 76 above the boiling point of water. These facts led to the
famous experiments of Dr. Fordyce and Sir Charles Blagden,
in England. With wooden shoes, tied on with list, they went
into a room in which the thermometer showed the air to be
at 260. Their watch chains were so hot that they could scarcely
108 HUMAN PHYSIOLOGY.
Different degrees of torpor in hybernating animals.
touch them, and eggs were roasted hard in twenty minutes, and
beefsteak was cooked in thirty-three minutes. And yet tha
same air that produced these results was breathed by them with
impunity, and it raised the heat of the body but very little.
The air which was breathed out from the lungs was so much
cooler than the air of the room, that it was refreshingly cool to
the nostrils, and to the fingers as they blowed upon them. In
such cases, the evil effects of the heat are prevented chiefly by
the great amount of perspiration that occurs, the vaporization of
this abstracting the heat, which would otherwise accumulate in
the body and produce disastrous results. The exhalation from
the lungs, also, has some influence.
158. In the state of hibernation, to which I have several
times referred, the torpidity varies in degree in different ani-
mals. In cold-blooded animals, respiration and circulation may
cease altogether in this state. In them the movements of life
are often, perhaps we may say generally, as fully suspended as
they are in the seed that is kept from heat and moisture. They
may be preserved in this state for a long time and yet revive.
Serpents and frogs have been kept in an ice-house for three
years, and then have been revived on being brought out into a
warm atmosphere. In the warm-blooded animals that hiber-
nate the torpidity is less deep than in those which are cold
blooded. In them the respiration and the circulation become
very slow, but never entirely cease. Indeed some species take
food with them into their winter quarters, and occasionally wake
up sufficiently to eat. But most of them are in a quiet, deep
sleep, from which they do not arouse at all till the winter is
past. In this state, as life is nearly, sometimes quite at a stand,
there is no wear and tear, and therefore no change in the tissues,
and so there is no need of the introduction of oxygen by the
respiration. Dr. M. Hall, in his experiments and observations,
found that the bat, when completely torpid, consumed no oxy-
gan, and discharged no carbonic acid from the lungs, although
its circulation was not entirely suspended.
159. The more active is the respiration of animals, the less
able are they to bear a deprivation of air. A warm-blooded
animal will die if it be under the water only a few minutes ;
but a cold-blooded animal can live under the water for some
time, because it is not in so urgent need of oxygen. And, for
the same reason, a warm-blooded animal, in a state of hiberna-
tion, may be kept under water for a long time without destroy-
ing life, although when in its active state it would die on being
FORMATION AND REPAIR. 109
Formative vessels appended to the capillaries.
kept under water for only a few minutes. And this suggests a
probable explanation of those cases, in which individuals hava
been restored, after having been under the water longer than
the usual time that suffices to destroy life in drowning. In such
cases, the condition is not simply that of a drowned person.
A blow, or the shock of body or mind, or both, may have in-
duced a suspension of active vitality, like that which we see in
the animal in a state of hybernation. The bare fact of immer-
sion in the water may have but little or even nothing to do
with the actual condition. Such a state of things is especially
to be suspected in those cases in which the countenance does
not exhibit the usual dark and full appearance of drowned per-
sons.
160. I have thus shown the extensive play which the respi-
ration has in the vital operations of the system. I have shown
what the chemical changes are, which it effects directly in the
lungs, and indirectly in the system. And you have seen how
the animal heat is produced by these changes, and how unac-
countably it is so regulated, that it seldom varies to any ex-
tent from ite fixed standard. But it is to be remembered that,
while the lungs, and even the capillaries, everywhere are thus
chemical laboratories, the nervous system exerts a constant
influence upon this chemistry of the body. This is especially
seen in regard to the production of heat, but it is true of
the whole range of the chemical operations. The laboratories
would all cease their work if their nervous connections were
destroyed.
CHAPTER VIII.
FORMATION AND REPAIR.
161. THE building and the repairing of the various struc-
tures of the body are done by vessels appended to the capil-
laries. The capillaries having received from the arteries the
blood, the building material, the formative vessels select from
it, while it is in these capillaries, whatever they need for their
purposes. The selection is made according to the tissue or
structure to be formed. Those vessels which, for example, form
bone, select from the blood very different constituents from those
which make nerve or muscle.
10
110 HUMAN PHYSIOLOGY.
Selecting power of the formative vessels. Their concert of action.
162. It is wonderful that the blood can be formed from such
a variety of food as is often taken into the stomach. But it is
far more wonderful that from the blood can be made so many
and such different structures. How different are the teeth from
the gums which surround them ; and yet both are made from
the blood. Observe, in some particular part of the body, how
many different structures there are which are all made from the
same common material. Take, for example, those which are
in and around the eye. There are, the skin of the eyelids ; the
eyelashes ; the vascular lining on the inside of the lids ; the
cartilages of the lids ; the firm, white coat of the eye, giving
to the eyeball its firmness ; the thin, transparent window in
front, setting into the firm, white coat, like a watch-glass into
the case ; the beautiful iris, a round moving curtain with a cen-
tral opening ; the lens behind this opening ; the optic nerve ex-
panded on the inside of the cavity of the eye ; the muscles
that move the eye, with their tendons; the tear-gland; the
cushion of fat on which the eye reposes ; the bone which forms
the socket, &c. All these various textures are formed from the
blood ; and the different workmen are as unerring in their se-
lections from this common material, as if they were intelligent
beings. Indeed, no ordinary intelligence could accomplish such
a selection. It is effected, inscrutably to us, under the direction
of an all-wise Intelligence, and by Almighty power.
163. But these builders of the body not only have the power
of selecting their building materials from the blood, but they
work in concert. Each company of builders work together in
harmony, as if they were under intelligent leaders. And
though different companies may be in close proximity, there is
no disagreement nor interference. For example, the builders
of a tooth and the builders of the gum around it, do not en-
croach on each other ; but each do their appropriate work with-
in their assigned limits. Even when different structures are
intermingled, as when tendon and muscle mingle together at
their place of union, there is no confusion- in the work of the
two sets of laborers. In Fig. 48 you see the difference in struc-
ture between the transparent cornea in the front part of the
eye and the white coat, the sclerotic coat, into which the cornea
is set like the crystal of a watch. It is represented as seen
magnified 320 times. The dotted lines mark the place of
union. The cornea, a, is a much more open structure, you ob-
serve, than the sclerotic coat, b. The builders of these two
structures, though some of them are in such near neighborhood
FORMATION AND REPAIR.
Concert of action shown in producing different shapes.
FIG. 48.
never encroach on each other, but each set adheres strictly to
its own kind of work. The sclerotica-makers never go to mak-
ing the open work which you see in the cornea. If they should
do so at any point there would be a little transparent window
at that point in the white of the eye ; and if the cornea-makers
should at any point make close work like that in the sclerotica,
here would be a white spot in the cornea.
164. The concert of action which we observe in the different
sets of formative vessels is to be looked at in another point of
view. It is such that they give a definite and peculiar shape to
the structure which they make. Each bone differs in shape
from every other bone, each muscle from every other muscle ;
and so of other parts. There is very great variety of shape in
the structures of the body ; and each shape can be determined
only by a certain concert among the builders. That you may
realize in some measure the extent of this variety, observe
again the numerous different textures which I have mentioned
as making up the eye. Each of these has its own peculiar
shape, and its definite limits. Its builders work after a fixed
plan, and within fixed bounds.
165. This concert of action may be looked at in still another
point of view. If the different structures in the body were
made, as a crystal is, by layer after layer of particles deposited
upon the outside, wonderful as the concert among the little
builders would be in that case, it would not be any thing like
as wonderful as it is now. In the growth, that is the construc-
tion of any part, the addition is made by the formative vessels at
every point of the part, and not upon the outside merely. As
these builders are at work enlarging the part in the growth
from infancy to childhood, they must so act in concert, as to
112 HUMAN PHYSIOLOGY.
Change of action. The teeth. Tadpole and frog.
preserve the same general form in the part during all the suc-
cessive stages of growth. And, as all the different stiuctures
of the body enlarge together, there must be agreement between
different sets ; else there would be encroachment and confusion.
Thus in the growth of the tiny arm of infancy to the sturdy
arm of manhood, each set of builders must during all this time
keep within its proper limits, so that there may be just the right
proportion, and the right position of bone, and muscle, and
tendon, and ligament, and cellular membrane, and skin, and
nail, &c., that make up the arm.
166. But this concert of action appears the most wonderful
when a new action, or change of action is called for. In the
transition from childhood to youth, for example, the builders
of the apparatus of the voice, the larynx, all at once become
unusually active in their work, and a great enlargement of this
musical instrument, for such it is, takes place, so that it may
now utter the grave notes of manhood. Soon, too, the beard-
builders begin their new work upon the face. And during the
period of childhood new operations have been continually insti-
tuted among the builders of the teeth, as one tooth after
another has made its appearance, and as the new set have re-
placed the old. To produce in the enlarging jaw a new set of
teeth to take the place of the smaller and less numerous first
set, and to bring them out in a symmetrical arrangement, re-
quire a very complicated series of operations. To effect each
one of these, there must be concert of action among the forma-
tive vessels ; aiid there must be a most wonderful concert
among the different successive sets of builders, to make
all tliese series of operations work out at length the general
result.
167. This change of action in the formative vessels is
strikingly exemplified in some animals. I refer to those that
so entirely change their forms during the period of their exist-
ence. I will give two examples. The first is the common
frog. He is at first what is termed a tadpole, and goes through
many successive changes to become a complete frog. Tliese
changes are represented in the following figures. The relative
sizes are not preserved, the tadpole state being represented re-
latively much too large, for the purpose of showing more
clearly the development of the legs. The young tadpole is
represented in Fig. 49. It has a large head and body, and a
long flat tail by which it swims easily. There are no promi-
nences to indicate the putting forth of any thing like limbs. It
FORMATION AND REPAIR.
113
Change of action in the silk-worm. Concert preserved in these cases.
FIG. 50.
has gills, which are loose fringes on each side of the head.
These gills after a time disappear, and it has another set of
gills arranged under a fold of skin very much like the gills of a
fish. The form is then as in Fig. 50. The next change is
this. The hind legs begin to grow out as seen in Fig. 51.
Next, the fore legs appear as seen in Fig. 52. The tail is still
very large. This now gradually disappears while the legs grow
as represented in Fig. 53. In Fig. 54, representing the perfect
frog, the tail has entirely disappeared. With these exterior
changes interior ones have been going on also. The animal,
which was at the first a real fish, breathing with gills
and swimming in water, has lost its gills, and has now a pair
of lungs ; and it is no longer able to remain long under water,
without coming to the surface to breathe the air.
168. The other example is the silk- worm. It is represented
in Fig. 55. When it has attained its full growth, it passes into
what is termed its chrysalis state, Fig. 56, it having previously
woven for itself from its silken thread a case or cocoon.
While it is in this state of inactivity great changes are going
on in its structure, and it at length becomes a perfect winged
insect, as represented in Fig. 57.
In the two cases which I have described, in each successive
change, the concert of action in the formative vessels is pre-
10*
114
HUMAN PHYSIOLOGY.
Change of action to meet new exigencies.
served, but it is after a new plan. This change of plan makei
the concert of action exceedingly wonderful.
FIG. 55. FIG. 56.
FIG. 57.
169. The change of action in the formative vessels, which is
sometimes called for by accident and disease, exhibits in an in-
teresting manner the concert between these vessels as in-
fluenced by circumstances. When a bone is broken, these
formative vessels set themselves to work to repair the injury,
by forming new bone between and around the two ends of
bone, which new bone we call callus. In this case, the bone-
builders extend their range of operations to meet the new
necessity ; and in doing so they maintain the same concert
which marked their usual operations before the bone was
broken. I stated in 105, that when an artery is tied, to
cure an aneurism, the circulation in the limb is kept up by the
small arteries that go off from it above the ligature, communi-
cating with those that branch off below ; and that, in order to
make the circulation perfect, some of these communicating
arteries gradually enlarge, to meet the necessities of the case
Now, this enlargement is not a mere dilatation produced tr-
ibe distending blood. The arteries grow in thickness as wel.
as in capacity. The artery-builders are awakened to a new ac-
tivity, and make the arteries in this quarter after a larger pat-
tern than the one originally designed for them.
170. Concert of action under successive changes is strikingly
exhibited in the processes of inflammation. The following ac-
count of these processes is from a work published by the
author, entitled " Physician and Patient." " You see a swelling.
FORMATION AND REPAIR. 115
Illustration from processes of inflammation.
It after a while begins to soften. There is matter in it, but it
is not yet very near the surface. But soon, at some point, it
comes nearer and nearer to the surface, the wall of the abscess
thus becoming constantly more thin, till, at length, it opens
and discharges. The discharge continues till the swelling is
nearly all gone, and the remainder is absorbed, and the part
is restored to its natural state. Just look for a moment at
the complicated character of this apparently simple operation.
Here is quite a large deposition of substance which is to be re-
moved; and this is the object to be effected. Observe how it
is done. The softening of the swelling is not a mere change
of solid substance into a fluid, as if by decay, but it is the re-
sult of an active process, which we call suppuration. When
this process is properly performed good pus is made, or as
the old writers in medicine rather quaintly expressed it, laud-
able pus. This process of suppuration, when it is well done,
does not go on here and there in the swelling, making it like a
honeycomb with a multitude of little abscesses ; but there is a
consent, an agreement of action by the vessels of the part, as
really as if they worked intelligently. It is this consent
of action which not only makes the line of movement
in the abscess, but points it towards the surface, instead of
giving it some other direction, laterally or inward, upon some
of the internal organs. But it is further to be observed, that
in this agreement of action, the vessels of the part do not all do
one thing. Three different offices are performed by them in
the different quarters of the abscess. While some of these
little workmen are forming the pus, there are others thinning
the wall of the abscess in the direction of the surface, by
absorbing or taking up the substance there ; while there are
others still, in the rear, and at the sides of the abscess, deposit-
ing substance, in order to make a barrier to prevent the pus
from being diffused in the surrounding parts. Each class of
these workmen perform their particular work with even more
exactness and harmony, than would be expected of any com-
pany of intelligent laborers under the direction of a leader.
The absorbents absorb together, the wall-builders build together,
and the makers of pus make pus together, and deposit it in a
common reservoir.
171. But observe farther, and you will soon see an entire
change come over the whole scene of operations. When the
absorbents have completed their passage for the pus through
the skin, the pus is gradually discharged from its reservoir, and
116 HUMAN PHYSIOLOGY.
Formative vessels and absorbents act in concert.
the " occupation " of the pus-makers is soon " gone." The wall
builders also cease their work, and while the vacancy becomes
filled up by contraction and deposition, the wall of defense, so
carefully maintained so long as was needed, is now taken up
by the absorbents, workmen which seem to know just when, as
well as how, to do their duty."
172. Here you have concert of action exemplified in a
complicated set of associated actions, to accomplish a tempo-
rary purpose. These actions, as you see, change in the
different stages of the process, each one being performed just at
the time, and during the period that it is wanted. And when
the temporary purpose aimed at is accomplished, the vessels of
the part resume at once their ordinary duties. It is to be ob-
served also, that the concert of action is not confined to the
formative vessels ; but it appears also in those vessels called
absorbents, of which I shall speak soon more particularly.
And these two sets of vessels do not interfere with each other,
but have a sort of agreement together in accomplishing the
general result. This concert of action is plainly seen among
the absorbents, not only in this case, but in all the cases that I
have cited as exhibiting it among the formative vessels. For
example, in the case of the frog ( 167) while the formative
vessels are constructing the legs, the absorbents are removing
the tail. So in the case of the teeth ( 166) while the
formative vessels are constructing the second set, the absorbents
remove the ends of the fangs of the teeth in the first set, so
that they are loosened in their sockets, and are thus taken out
of the way of the coming teeth. And indeed, wherever there
is formation, there is absorption ; and the same concert of
action always appears.
173. I have spoken of the great variety of structures, which
are made out of the same material, the blood. Besides this,
all the different secretions are also formed from the same
material. This appears wonderful when we look at the differ-
ence between such secretions as the tears, the ear-wax, the
gastric juice, the bile, <fec. And it appears more wonderful still,
when we consider that these various glands, or factories, as we
may call them, are built from the same material out of which
they make their products. There is one curious exception to
this. It is in the case of that large gland, the liver. This
gland is built {.nd kept in repair, like all the other glands, by
arterial blood. But while they make their secretions out of
this arterial blood, the liver makes its secretion out of venous*
FORMATION AND REPAIR. 117
Formation of all parts from the blood. Waste. Lymphatics.
blood, which is brought to it for that purpose as described in
108.
174. Thus, all *he solids and fluids in the body are made
from the blood. Even the heart itself is made from the blood
which it pumps out into the aorta ; for from this aorta go out
some small arteries, to carry blood to the walls of the heart for
its growth and repair. These arteries are represented in
Fig. 31.
175. There is not only construction going on in every part
of the system, but there is waste also. The wear and tear of
the ever-moving machinery continually makes some of the par-
ticles useless, and these must in some way be removed. I pro-
pose now to show how this is done.
176. There are two kinds of waste particles; and for the dis-
posal of them two different plans are pursued. Some of the
waste particles, though wholly useless where they are, can be
rendered tit to be used again by being subjected to certain pro-
cesses. These, therefore, are not thrown out of the system, but
are taken up by absorbents, and are carried where the neces-
sary processes can be applied to them ; and then they are in-
troduced into the blood, to make again a part of the building
material. But there are some waste particles that can not be
used again ; and these are so managed as to be got rid of at
various outlets of the system. These two kinds of particles are
taken up by two different sets of absorbents. The selecting
power which they thus exert is as unerring as if they were pos-
sessed of intelligence ; and it is wholly unaccountable, although
some physiologists have attempted to explain it.
177. The particles which can be used again are taken up by
absorbents, which are termed lymphatics. These vessels are
much like the lacteals, the absorbents in the intestines. They
unite together, as they come from all parts of the body, into
two trunks. One of these is the thoracic duct (described in
91), which is the common duct, both of the lymphatics
and the lacteals, (Fig. 17,) and in which the chyle and the
lymph, as the fluid in the lymphatics is called, are mingled to-
gether. The other trunk, which receives the lymph from but a
small part of the body empties its contents into a large vein at
the right side of the top of the chest. The largest part of the
lymph, therefore, unites with the chyle, and is poured with it
into the circulation, and the rest reaches the same destination
by another way. It all becomes with the chyle a part of the
blood. But before this is done it passes, like the chyle, through
118 HUMAN PHYSIOLOGY.
Two kinds of waste particles. Excretion and secretion. .
glands, in order to fit it to become again a part of the building-
material of the body. These glands are every where in the
track of the lymphatics. They are often enlarged from disease,
and then they can be readily felt. This is often the case with
these glands in the neck. In relation to this appropriation of
waste particles, which I have thus described, it may be truly
said that man lives in part upon his own flesh.
178. Those waste particles which are entirely useless are
taken up by the veins directly into the circulation. They then
travel the rounds with the blood, and are thrown off from the
system by organs appropriated for that purpose. These organs
are the lungs, the skin, the liver, the kidneys, <fec. Each of
these excretory organs is fitted to throw off its particular part
of the waste. Thus the lungs, excrete a kind different from
that which the skin does ; and so of the rest. The lungs, as
you saw in the chapter on respiration, throw off in the form of
carbonic acid gas, large quantities of the carbon evolved in the
wear and tear of the system. The liver, the skin, &c. throw
off parts of the waste which differ from that which is thrown
off by the lungs. Why it is that the waste matter is thus in-
troduced into the circulation to be carried to the excretory or-
gans, instead of having special channels appropriated to the
particular office of carrying it to its outlets, we know not. And
how it can thus be mixed with the blood, and be carried about
the system without proving noxious, is a mystery. That it can-
not be long retained in the blood without doing injury, is shown
by the evil results, which come from a suspension of excretion
from any of the organs that I have mentioned.
179. It is interesting to observe that some of the excretory
organs perform other functions besides that of mere excretion.*
Thus the lungs, while they excrete carbon, absorb oxygen,
without which life could not go on. At the same time, too,
they act as the bellows for the organ of the voice, the larynx,
as you will see in the chapter on that subject. So also, the
liver, while it excretes what would be noxious if it remained in
the blood, puts its excretion into such a form, that it proves, as
you saw in the chapter on digestion, an auxiliary in some of
the processes of the digestive organs.
* The words excretion and secretion, are often applied to the same thing. Excretion,
rtrictly speaking, should be applied only to something to be thrown off, and not to some-
thing formed to be used. But sometimes an excretion is so formed, that it can be used,
and then the word secretion is also applicable to it. Thus the bile, while it is an ex-
cretion containing noxious particles to be thrown off from the system, is put to use
and so it is as often called a secretion as an excretion.
FORMATION AND REPAIR.
119
The skin. Cuticle. True skin. Papillae.
FIG. 58.
180. The skin, while it is an extensive excreting organ, per-
forms other important offices. It serves as a firm yet very
flexible and soft covering to the body, protecting its internal
parts from injury. It is highly endowed with nerves for two pur-
poses the one, that it may act as a sentinel to warn of danger ;
and the other, that it may be the seat of the sense of touch.
That you may see how well it is fitted
to perform these various functions,
I will describe here its structure.
What is very commonly spoken of as
the skin, is not really the skin, but
only a covering for it. When the
skin is rubbed off, as it is expressed,
it is only this covering of the skin, or
cuticle, which is removed. The skin
which is raised by a blister is this cu-
ticle. The great object of the cuticle
is to protect the true skin, which is
very highly endowed with nerves for
the purposes mentioned above, and
which therefore, if uncovered, would
prove a source of severe suffering. As
it is, the cuticle protects the skin effec-
tually, and yet does not interfere with
its functions as the organ of the sense
of touch. It is of so slight and so
soft a texture, that the nerves of touch
may readily receive impressions
through it. It is composed, as you
will see in the next chapter, of many
layers of minute round cells, the
outermost layers being made up of
these cells broken, and emptied of the
fluid which they contained. The
true skin, which the cuticle covers, is
of a fibrous texture, with a good
supply of both nerves and blood ves-
sels. On the surface of this true skin
next to the cuticle are eminences called
papillae. In these are seated the ex-
tremities of the nerves of touch.
Fig. 58 'represents a highly magni- Vertical section ofthe
fied section of a bit of the skin from SOLE OF THE FOOT.
120 HUMAN PHYSIOLOGY.
Tubing in the skin. Insensible perspiration. Sebaceous glands.
the sole of the foot ; a is the cuticle ; c is the true skin ; b re-
presents the papillae. You observe that the deepest layers of
the cuticle, next to these papillae, are more colored than the
outer ones. The coloring matter of the skin is situated here.
You observe also a tube which runs up through the cutis or
true skin and the cuticle, and in the latter part of its course
has a sort of cork-screw arrangement. This is the discharging
tube of the sweat-gland, d, lying within the true skin, and sur-
rounded with globules of fat. These glands are more numer-
ous in some parts of the skin than in others. They are par-
ticularly numerous on the palms of the hands, and on the soles
of the feet. Mr. E. Wilson counted, with the aid of the mi-
croscope, 3528 of them in a square inch on the palm of the
hand. Reckoning the length of one of these at one quarter of
an inch it gives 882 inches or 73 feet of tubing in this small
space. He calculated the amount of this tubing in the skin of
the whole body as being 48,600 yards, or nearly 28 miles.
The amount of excretion from the seven millions of these tubes,
which open on the surface of the skin, is very great. Many
experiments have been tried to determine what the amount
is in 24 hours, but approximations only to the truth, of course,
could be obtained, and the results of the experiments have
differed much. While the excretion is great in amount, it is
very important. It is, as you have seen in the chapter on
Respiration, a great means of regulating the temperature of
the body. It is also the means of discharging from the body
a portion of its waste. This waste is dissolved in or mingled
with the water or vapor of the perspiration. The perspira-
tion is ordinarily insensible, as it is termed ; that is, it is in the
form of vapor. But sometimes, as in vigorous exercise, when
the sweat glands are rendered very active, chiefly to prevent too
great an accumulation of heat, the perspiration becomes sensible.
181. There is another set of glands in the skin called
sebaceous glands, which secrete an oily fluid. They have
also thin "tubes like the sweat glands. They are most
abundant where the skin specially needs an oily lubrica-
tion, as where there are folds in the skin or hairs, or
where the skin is exposed to friction, or to the drying atmos-
phere. They are very abundant on the face and head. The
amount of the oily secretion of these glands is very great in
the skin of races fitted to inhabit warm climates. Every hair
has sebaceous glands connected with it, as represented in
Fig. 59 ; in which 6 is the hair emerging from the skin ;
FORMATION AND REPAIR.
121
Influence of labor on wear and tear, and on absorption.
HAIR
and sebaceous glands.
a a are the sebaceous glands pouring their
secretion by thin tubes into the tube or
canal in which the hair grows ; c the root
of the hair surrounded with fat globules.
From all this you see that the skin, with
its two sets of glands and tubes, its nerv-
ous papillae, and its layers of constantly
renewed cells, making the cuticle, is a
complicated organ, and is thus fitted to
perform its functions as an organ of sen-
sation, and at the same time of excretion,
while it is also a pliable but firm cover-
ing for the body.
182. You have seen in the facts de-
veloped in this chapter, that there is con-
stant change going on in all parts of the
body. Particles which have become use-
less are taken up by the absorbents, while
the formative vessels deposit others to take
their places. The rapidity with which
this change occurs, depends mostly upon
the activity of the individual. The busy
laborer, whether the labor be bodily or mental, requires more
nourishment than the indolent man, because there is more
waste in his case, from the wear and tear occasioned by motion
or thought, and there is therefore a necessity for a larger sup-
ply of repairing material. The difference, it is true, is not as
great in regard to mental labor, as in regard to that of the
body ; but still it is very apparent. This dependence of the
amount of change in the system upon the degree of activity is
very manifest, if we compare different animals together in this
respect. I have already contrasted the frog and the canary
bird in regard to respiration ( 156,) and they can be con-
trasted in this respect also. As the frog makes but little
exertion either of body or mind, there is but little change in his
body, and but little nutriment is required to supply the small
waste that occurs. But in the ever active canary there is
much waste from this action, and therefore there must be much
eating to supply the material of repair. As he sings and hops
from perch to perch, his mind as well as his body is vastly
more active than that of the frog ; and so the particles in his
brain and nerves, as well as in his muscles, are oftener changed.
You see the same thing still more strikingly, if you contrast
11
122 HUMAN PHYSIOLOGY.
Change varies in different parts of the body, and in the same body at different times.
the torpid state of the hibernating animal in winter, with his
active state in the warm weather. In his torpid state life is
dormant, almost at a stand still, sometimes entirely so. And
the more perfect the quiescence, the less is the change, and the
less, therefore, the need of nutrition. The fat which he lays
up in the autumn ( 65) answers all his necessities both for
nutrition and for heat.
183. The proportion, thus seen to exist between the amount
of change and the degree of activity, is exemplified in a com-
parison between different parts of the body. In those which
are most actively used the change of decay and repair is going
on most constantly. The active muscles and nerves are con-
tinually changing ; while the bones, which are only passive in-
struments of motion are changed very slowly. And it is a sig-
nificant fact, that in the case of the muscles and nerves, the
waste particles are to a large extent of the entirely useless kind
( 176), for they are mostly absorbed by the veins, there
being in them but few lymphatics. That is, whenever we
think, or feel, or move, we render entirely useless quantities of
the particles which make up the structure of the muscular and
nervous systems, and these are got rid of at the proper out-
lets, while other particles immediately take their places.
184. It is a very prevalent notion in the community, that the
human body changes throughout once in every seven years.
But you have seen that the change is very unequal in different
parts of the body, and is dependent to a great extent on cir-
cumstances. Sometimes very rapid changes occur. Thus,
when one has been much reduced by sickness, and then on re-
covery quickly regains his usual bulk, the body is very exten-
sively changed in a short period of time. Ordinarily the cir-
cumstance which most influences the change is, as you have
seen, the degree of activity which exists, whether we look at
an animal as a whole, or at the tissues separately.
185. In this constant change going on in the body, life and
death may be said to be brought into very near companionship.
Every act of the mind, and every movement of the body breaks
down some of the structure ; and the particles, which are no
longer fitted to maintain the living functions, must be taken
away as refuse dead matter, and new particles endowed with
vital affinities must take their place. Action, destruction,
repair, are the successive events which are ever occurring in
in every part of our frame. Action is followed by destruction,
and in proportion to its intensity ; and repair is necessary to
CELL-LIFE. 123
The formative vessels shown by the microscope to be cells.
fit for further action. And so through life the nutritive func-
tions are thus struggling against the tendency to decay and
death, till at length at the appointed limit the struggle is given
over, the vital affinities release their hold, the common laws of
dead matter take possession of the body, and the soul passes to
a world where decay and change are unknown.
CftAPTERIX,
CELL-LIFE.
186. IN previous chapters, in treating of the construction of
the body, I have spoken of the formative vessels in accordance
with the common language of physiologists. The common
idea has been hitherto, that the work of construction is per-
formed by vessels appended to the capillaries. The capillaries
were considered as the repositories of the blood, they receiving
it from the arteries, and holding it in readiness for the use to
which it is to be put by the formative vessels. These formative
vessels, it was supposed, exercised in some way a power of se-
lection in regard to the constituents of the blood, and also a
power of uniting the constituents thus chosen into particular
forms. In this way physiologists accounted for the formation
of all the different structures in the bddy. What shape these
formative vessels had, or how they were arranged no one pre-
tended to know. But of their existence no one had a doubt,
for there seemed to be an absolute necessity for supposing some
apparatus of vessels appended to the capillaries for the per-
formance of this function.
187. But the microscope has of late years revealed pheno-
mena which have changed our ideas on this subject, and
which must to some extent change our modes of expression in
relation to it also. It has showed us agencies which differ
from those which we had supposed to exist. The subject is an
interesting one, and I propose in this chapter to give you some
glimpses of this interior life, as it may be termed, of the body.
188. It is found by the aid of the microscope, that all the
minute operations of the system are performed by the agency
of cells. They are not such cells as I described in 64 as
existing in the cellular tissue, which are mere interstices, com-
municating together. But they are bladders or sacs, and ar
124
HUMAK PHYSIOLOGY.
Cells when first formed globular. Seen in the blood and in most other parts.
filled either with a fluid alone, or with a fluid containing some
grains of solid substance, termed molecules. The usual form of
the cell when it first appears is globular or spheroidal. It is
seldom, however, seen in this form ; for, besides the change of
form from the pressure of neighboring cells, the cells them-
selves often change into various shapes, as you will see in
another part of this chapter.
189. Cells can be seen in the blood. If the web of the foot
of a live frog be placed under the microscope, you can see
them sweeping along in the blood vessels, like so many little
bladders, varying their shape, according as they press on each
other, or on the sides of the vessel. This is very well repre-
sented in Fig. 60, in which a portion of the web of a frog's foot
is seen as magnified 110 diameters. The dark irregular spots
which you see, as at 3,3, are pigment cells, which give the
<>lor to the part.
FIG. 60.
CAPILLARIES IN THE WEB OF A FROG'S FOOT.
1 90. Cells may be seen in most of the fluids besides the
blood, and also in the solids. The solid parts of animal bodies,
CELL-LIFE.
125
Character and color of tissues dependent on the contents of cells.
are composed either of cells, or of structures produced by cells,
or of a mixture of these structures with cells. The same can
be said also of plants. Cells, therefore, are the real formative
vessels in both classes of organized beings.
191. We have very striking exhibitions of the FIG. 61.
cells in the lower orders of animals. The Hydra,
a representation of which is given in Fig. 1,
seems to be made up of little else than cells.
If you observe under the microscope one of its
arms, as it moves about, the motion appears to
be a motion of the cells upon each other.
There are no fibres to be seen, to which the mo-
tion can be attributed. Fig. 61 represents one of
these arms highly magnified. The cells, as you
see, have somewhat of a spiral arrangement.
192. The character of many of the tissues
in the body depends on the contents of the
cells. The cell itself, or the cell -wall, as it is
termed, is considered to be always the same.
But the contents vary, and this variation makes
generally the variation in the character, and in
the color also, of the various textures. For ex-
ample, all the glands are constructed essentially
on the same plan ; and their difference depends
upon the contents of the cells in them. Thus
the liver differs from the tear-gland, chiefly be-
cause the former has cells which fill themselves
from the blood with the components of bile, while
the other has cells which fill themselves with the components
of the tears. The color of various parts, as the iris of the eye,
the skin of the dark-colored, the hair, &c., depends upon a
coloring matter, which constitutes either a part or the whole of
the contents of particular cells. So in plants the various colors
displayed result from the various coloring matters which cer-
tain cells contain. Some contain yellow coloring matter, others
red, &c. When various colors appear together in any flower,
there are, where the colors bound upon each other, cells lying
side by side which contain different coloring matters. And in
the shading off of the colors, the effect is produced wholly by
the variation in the quantities of the coloring matter in the cells.
193. It is clear from the facts which have been stated, that
the cells have a selecting power. In the body they take from
the common pabulum or material, the blood, such constituents
CELLS
In the nrm of ths
Hydra.
126 HUMAN PHYSIOLOGY.
Cells absorb and select. Cells real laboratories.
or substances as they need for their particular purposes. I
have already given illustrations of this, in speaking of the
difference in the glands. This selecting power is seen in the
cells everywhere. Every cell contains its own peculiar consti-
tuents, which it has taken from the blood. For example, there
are fat-cells which receive fatty matter from the blood, rejecting
every thing else ; pigmentary cells receiving nothing but color-
ing matter from the blood, &c. The same thing appears too
in plants. There are cells which receive from the sap volatile
oil ; others, fixed oil ; others, starch ; others, coloring matter,
&c.
194. Fluids, and sometimes gases enter the cells continually.
The pores through which they enter are not visible even
through the microscope, but of course such pores must exist.
Their entrance is controlled by the selecting power to which I
have alluded.
195. This selecting absorption thus performed by cells, as
revealed by the microscope, is one of the most wonderful and
mysterious phenomena in the material world. There is here
a power in these cells which is unaccountable. The selection
is made by the little cell as unerringly, as if its pores were con-
trolled by an intelligence residing there. It has been said that
this selection is a mere result of affinity ; that a certain affinity
exists between the contents of the cell, or the cell itself, for the
constituents which are absorbed. But if it be so, the mystery
comes no nearer to being solved than before. For how are
these affinities, so numerous and various, established, and what
are the principles by which they are governed ? In either
case the wisdom and power of the Creator may be considered
as making, in this minute interior life of all organized sub-
stances, some of their most wonderful manifestations.
196. There is not only a selecting power in the cell, but there
is often a converting power, by which new compounds are
formed from the constituents introduced into it. The cell in
this case, though so small as to be seen only by a microscope
of considerable power, is a real laboratory, effecting chemical
changes in its contents. There can often be seen quite a brisk
movement in the molecules in the cell while these changes are
going on.
197. Some cells produce other cells. This is the sole office
of some of them. In some cases new cells are made by a
separation of a cell into two or more. A sort of hourglass
contraction takes place at the middle, by an inflection or fold-
CELL-LIFE. 127
Different offices of cells. Office of red cells in the blood.
ing in of the inner cell-wall, for the cell has two walls. At the
tame time the cell becomes elongated. An entire separation
into two cells is thus, after a little time, effected ; and then each
of these cells becomes two more, and so on. In other cases
cells are formed within cells. When this takes place, the
nucleus, that is an aggregation or mass* of solid matter in the
cell, separates into two different parts, each of which has a cell
formed around it.
198. Cells, as you have already seen, do not all perform the
same office, but there are cells for a great variety of purposes.
A consideration of these will develope to you still greater won-
ders in the cell-life, and show you in the most interesting man-
ner how great the Creator is in the minute operations of nature,
as well as in those which are large and obvious to the naked
eye.
199. There are different kinds of cells in the blood. There
are colored and colorless ones. The office of the colorless ones
has not yet been satisfactorily determined. But we know more
about the colored ones. These give the red color to the blood.
They are not red when looked at singly, but are of a yellow
cast ; and the red color appears only when several are together.
One office of these colored cells is to carry oxygen to all parts
of the system, and return the carbonic acid to the lungs to be
thrown off. By carrying these cargoes back and forth in the
circulation, these little cells perform a very important office.
A very valuable part of the cargo of these cells is iron. In low
states of the system, when the red cells are deficient, the ad-
ministration of iron in some form is often found to be very
effectual, in connection with a good diet, in remedying the defi-
ciency. The proportion of these red cells varies much in
different animals. It is largest in those which are the most
active, and which, therefore, as you saw in the chapter on
Respiration, consume the largest quantity of oxygen. The
proportion is greater generally in birds than in the mammalia,
and it is much greater in the latter than in reptiles or fishes.
In man it varies much in different individuals. These cells
are abundant in the ruddy, strong, and active ; while it is other-
wise in the inactive, pale, and feeble.
200. There are cells for absorption, and cells for secretion
* To the common ear the word mass, which is ordinarily used in relation to aggregates
of some size, sec:ns out of place when applied to a collection of molecules which is so
small, that it c .. only be seen by a microscope of high power ; but though fco small, it is
to the little . jntaining it a mass.
128 HUMAN PHYSIOLOGY.
Manner in which absorption is performed by cells.
and excretion. Of these I will give some examples. I have
said in the chapter on Digestion, that the vessels called lacteala
absorb chyle from the contents of the intestine. It was formerly
supposed that they did this through their open mouths on the
surface of the mucous membrane. But the microscope has
shown that this is not so. The absorption is accomplished by
cells, which are developed for this purpose at the extremities
of the lacteals. They take up the chyle and discharge it into
the lacteals, and they are dissolved away in the very act of
emptying themselves. A new crop therefore of cells appears
eve Y time the process of absorption is to be performed. And,
wha: is still more curious, every time that absorption is to take
place, ihere is cast off, as a preparatory step, a sort of pavement
of cells f rom over every point in the mucous membrane where
there is n extremity of a lacteal. The absorbing cells are
thus uncovered, so that they can perform their duty. All this
can be made clear by the following diagram. I must premise
that the surfac of the mucous membrane of the intestine is not
a perfectly smo( h surface, but examined by a microscope it is
seen to be covered with eminences and depressions. Absorp-
tion takes place on the eminences, while the depressions are
the seats of secretion. In the diagram. Fig. 62, you have a
FIG. 62.
DIAGRAM SHOWING ABSORPTION IN A MUCOUS MEMBRANE.
representation of the arrangement of one of the eminences
highly magnified. A, represents it as it is in the intervals
of digestion when absorption is not going on, and B as i-t is
during absorption ; a a are the absorbent vessels or lacteals ;
b b basement membrane, as it is termed, an exceedingly thin
membrane acting as a basement to the pavement cells c c ; d d,
CELL-LIFE. 129
Manner in which secretion is effected by them.
the absorbing cells. When absorption is not going on, the
prominence is somewhat shrunken, and the pavement cells
cover it. There are some granules or small grains, c?, in A,
which are, it is supposed, the germs of the absorbing cells,
which you see developed in B. When absorption is taking
place, the prominence is swelled out as represented, the lacteal
vessels are full, and the absorbing cells appear at their ex-
tremities, while the pavement cells have been thrown off, so
that the chyle may have free access to the absorbing cells
through the pores or interstices of the basement membrane.
201. While absorption thus goes on in the eminences,
secretion takes place in the depressions. The diagram, Fig. 63,
FIG. 63.
DIAGRAM SHOWING SECRETION IN A MUCOUS MEMBRANE.
represents one of these depressions, or follicles, as they are
termed, in two opposite states, when secreting, and when not
secreting. In A, secretion is not going on, and the cells e, in
the follicle remain quiet. In B, on the other hand, secretion
is taking place, and it is done by the casting off of cells, as
represented. These cells discharge their fluid contents into
the cavity of the intestine, and disappear, while other cells take
their places. These follicles are really little glands. And the
various glands, the salivary glands, the liver, the pancreas, &c.,
are made up essentially of such follicles arranged in different
ways. You see, therefore, in this diagram, the manner in
which secretion is effected everywhere. The secreted matter
is received by the absorbing cells, through the interstices of the
basement membrane, from the blood in the capillaries which lie
under this membrane.
202. The pavement cells, of which I have spoken, cover
every part of the mucous coat or membrane, and answer as a
protection to it. There is a similar arrangement over the
whole outer surface of the body. Next to the true skin is a
130
HUMAN PHYSIOLOGY.
Muscles made up of cells. Their tontraction nnd relaxation.
basement membrane, and upon these, as in the case of the
mucous coat of the alimentary canal, lie pavement cells. These
cells, constituting the cuticle or scarf-skin, are much more
numerous than in the alimentary canal. There are many
layers of them. The outer cells dry by exposure to the air,
and become scales. As these are rubbed off. the cells below
take their places ; and there is a constant supply of fresh cells
from the basement membrane.
203. There are some cells which are devoted entirely to the
production of motion, for an ordinary muscle is composed of
great numbers of chains of cells included in sheaths bound to-
gether. A muscle appears to the naked eye to be made up of
fibres. Each one of these fibres is found by the miscroscope to
be composed of from 500 to 800 fibrillce, or minute fibres.
And each of these fibrillse is a series or chain of cells. In Fig.
64, a, is represented a fibre as seen under the microscope,
FIG. 64.
a
FIG. 65.
FIBRE OF A MUSCLE.
showing the fibrillse of which it is com-
posed. They are separated at the broken
end by the violence in tearing the fibre.
In 6, you see one of the fibrillae very highly
magnified, showing that it is a chain of
cells. In the diagram, Fig. 65, is repre-
sented the condition of a fibrilla in the
two states of contraction and relaxation.
In a it is relaxed. In 6 it is contracted,
the cells being shortened, and at the same
time widened. And as all the cells in the
muscle are thus widened when the muscle
contracts, we see the cause of the well
known swelling out of muscles when they
are in action. That you may form some
idea of the size of these cells in muscles, I
will state that in the space of the square
of a tenth part of an inch, thus, there
are over 100,000 of these cells. M When
MUSCULAR FIBRIL;
a relaxed ; 6 contracted.
CELL-LIFE.
131
Hoofs, horns, nails, and teeth made by cells.
a large muscle contracts what an innumerable multitude of
these cells are set in action !
204. There are cells whose office it is to make certain solid
deposits. Hoofs, horns, nails, and teeth are made in this way.
Even the hard enamel of the teeth is constructed by cells.
They deposit it in the form of prisms of hexagonal shape as
seen in Fig. 66, which represents a vertical section of enamel
as seen under the microscope. Their shape is more plainly seen
in A, Fig. 67, which represents a transverse section of enamel.
The line of these prisms is generally wavy, but they are for the
most part parallel to each other. At B are some of these prisms
separated. They are more magnified here than in Fig. 66.
FIG. 66.
VERTICAL SECTION OF ENAMEL.
FIG. 67.
ENAMEL.
A, Transverse section. B, Separated prisms of it
205. Perhaps the most wonderful exhibitions of the functions
of the cell are presented to us in the nervous system. The
nerves are bundles of tubes of exceeding fineness. They vary
from TsVoth to i o.oouth of an inch in diameter. Now, each
of these little tubes, or tubuli, as they are called, was once a
chain of cells. The cells in each chain or row, as the micros-
132 HUMAN PHYSIOLOGY.
Nerves composed of tubes made from cells. Cells in the gray substance of the brain.
cope has shown, gradually became incorporated together to be-
come a tube, and in this tube is contained the true nervous
matter. And it is supposed that each of these tubuli preserves
itself separate and distinct, from its origin in the brain, or some
other of the central organs of the nervous system, to its ter-
mination in some fibre, or on some surface. For no communi-
cations between the tubuli have ever been foun,d by any micros-
copist. The manner in which these tubuli are made from cells
may be illustrated by the diagram
in Fig. 68, in which the steps by FIG. 68.
which the row of cells A becomes A B
the tube B are represented.
206. It is these tubuli, thus
formed from cells, that constitute
the means of nervous communica-
tion between all parts of the sys-
tem. Thus, when a muscle con-
tracts in obedience to the will,
an impression is conveyed through those tubuli that connect the
brain with the fibres of the muscle, or rather with the cells of
which these fibres are composed. These tubuli exist in all the
nerves, and in the white parts of the brain and spinal marrow.
They transmit, but they have nothing to do with originating
what is transmitted. This is done by another part of the nervous
system, the reddish gray substance, which is seen in the brain
and spinal marrow, as entirely distinct from the white portion.
This gray substance, in which all nerve force, as it is termed, is
produced, is made up chiefly of cells. These cells, which have
a nucleus or central particle, are originally globular, but many
of them assume various shapes, and often shoot out branches.
Some of the shapes are very fantastic as represented in Fig. 69.
These are magnified 200 diameters.
207. In the views which I have given of cell-life, I have not
attempted to describe all the phenomena which have been dis-
covered, but only enough of them to give the student a general
view of this interior unseen life, that is at work so busily at
every point of every living substance. The cell, you have seen,
performs a great variety of functions. It is the agent by which
all vital operations are carried on. The very beginning of life,
so far as we can see, is in the cell which the microscope reveals
to us. Its first manifestation is here. We can suppose a germ
as the origin of a cell, but we do not see it if it exist.
208. All animated nature is built up by cells. The first
CELL-LIFE.
133
All organized substances built up by cells.
FIG. 69.
NERVE CELLS IN THE GRAY SUBSTANCE.
thing which comes from the supposed germ is a cell. And
this single cell is the parent of all the cells which build up the
whole structure, whatever it be. It is by these cells thus pro-
duced, that all plants and animals are constructed. "A globu-
lar mass," says Carpenter, " containing a large number of cells
is formed before any diversity of parts shows itself; and it is
by the subsequent development, from this mass, of different
sets of cells, of which some are changed into cartilage, others
into nerve, others into muscle, others into vessels, and so on,
that the several parts of the body are ultimately formed. Of
the cause of these transformations, and of the regularity with
which they take place in the different parts, according to the
type or plan upon which the animal is constructed, we are en-
tirely in the dark ; and we may probably never know much
more than we do at present."
209. A beautiful exemplification of what has just been stated
is seen in the development of the animal in the interior of an
egg, and, particularly- in the egg of the bird tribe. By an ex
12
134 HUMAN PHYSIOLOGY.
Arrangement of the parts of the egg.
animation of different eggs at different stages of the process of
hatching, the various steps in the development of the animal
have been observed and noted. It is a series of most wonderful
processes, that go on concealed from our view by that sym-
metrical inclosure of lime. Of these I will present the general
outlines. In the middle of the egg is the yellow yolk, com-
posed of albumen and oil globules. It is surrounded by an ex-
ceedingly thin sac, which keeps it separate from the albumen,
the white of the egg that envelopes it. The yolk, 6, Fig. 70, is
SECTION OF A BIRDS' EGG.
lighter than the white, and it therefore always seeks the highest
point in the egg. But there is a particular contrivance which
prevents it from actually touching the shell. It is held down
by two very delicate ligaments e,e, connecting it with the white
lining of the shell. And you will observe, too, that the cica-
tricula, or germ-spot, a, which is a collection of cells beginning
the process which is to form the animal, being lighter than the
yolk is always at the top of it, in order to receive the warmth
from the body of the bird as it sets upon its eggs. Besides all
this, there is at the blunt end of the egg, /, a bubble of air
which is intended as an invigorating draught for the lungs
of the young bird, preparatory to its bursting its shell.
210. When the processes preparatory to the formation of the
animal commence, the yolk itself is composed in part of cells,
as represented in Fig. 71, A. In the midst of it there is a
germinal spot, a, with a vesicle in it, b. This vesicle produces
CELL-LIFE.
135
Succession of cells in the yolk before the animal is formed.
FIG. 71.
B ?
DEVELOPMENT OF CELLS IN THE YOLK DURING INCUBATION.
a cluster of cells. But these cells, and those which in part
compose the yolk are temporary, and all disappear. Before,
however, the cluster of cells in the germinal spot disappear,
there are seen in the midst of them two twin cells. These
multiply ; and what is singular, they do it by doubling, so that
there are successively 4, 8, 16, 32, &c. At length there is a
mass of them, like a mulberry, as at e, in B. This mass then
sends off cells at its edges which makes a layer,/, all round
the yolk as represented in C. A second layer, ^, is formed
inside of the first as seen in D. In the case of the higher
animals a third layer is added.
211. There is no formation of the animal yet. But now a
single large cell appears in the centre of the mulberry-shaped
mass of cells, and from this begins the formation of the animal.
All the other parts of the egg the cells, the yolk, the white
are tributary to the action which proceeds from this cell.
Within its wall is a ring-like nucleus. This takes the shape of
a pear, and then it is afterward very much like a violin.
From this nucleus are produced cells which form all the
various parts of the animal, the heart, lungs, stomach, brain,
limbs, <fec. And these are made out of the yolk and the white
of the egg.
136 HUMAN" PHYSIOLOGY.
Office of the allantois. All animals and plants come from simple cells.
212. There is one contrivance made use of during this de-
velopment of the animal, which must not pass unnoticed. A
very delicate bag, called the allantois, is formed, which is attach-
ed to the embryo, and at length almost envelopes it. The office
of this is to expose the blood of the embryo to the air. This is
accomplished through the pores of the shell, against which the
allantois with its minute blood-vessels presses. This organ is
in fact the temporary breathing apparatus of the developing
animal. The development can be arrested by smearing over
the egg with some substance that will prevent the entrance of
air through the shell. When the animal is fully developed,
and is ready to come forth from his prison, he inhales the air
provided for him, as before described, and with the strength
given to him by the stimulus of the air in his lungs, he bursts
the crust of lime that incloses him.
213. I have described these processes which take place in
the egg, in order that you may see the mysterious connection
between the simple cells that form in the beginning, and the
full development of the complete and diversified organization.
In the formation of all animals, and we may say plants also,
there is a similar connection, varied of course according to the
circumstances of each case. As we observe the various steps
of the process, the mind is filled with wonder. As we look at
the egg, containing nothing but a yolk surrounded by albumen,
with its little cell of air at the end, and see it wholly separated
from every living organization, shut up entirely by itself in a
wall of lime, we can hardly believe that the mere application
of heat will cause in the contents a series of processes, which
will result in an animal so complete, that it can burst its own
prison walls, and, as is the case with some of the tribe, at once
walk forth into the open air. The processes by which all this
is effected have been narrowly watched by the eager eye of
scientific inquiry ; but the mystery remains unsolved, and pro-
bably to man it will always remain so.
214. From the views which I have presented in this chapter
it is manifest, that the grand distinction between organized and
unorganized substances is to be found in this cell-life of the
organized. In unorganized substances particles or molecules
are the only things which we know of as being concerned in
their formation. But in the construction of organized sub-
stances or beings, every thing is done by the agency of cells.
And in this cell -life of the living world we have another beauti-
ful example of the divers and almost numberless results, which
CELL-LIFE. 137
The power of the Deity shown in the minute operations of Nature.
the Creator works out by simple and single means. As gravi-
tation holds atoms together in masses of every size from the
minutest to the largest, and keeps the mighty orbs in their
appointed circuits, so the cell-organization constructs and moves
all living things, however small, however large, and however
diversified.
215. As we examine the various workings of this cell-life, wa
can not but perceive the truth of the old adage, Natura in
minimis maxima est nature is greatest in its smallest things.
The power of mere bulk or mere force we can comprehend by
mental addition, however great that power may be. We can
imagine a power which we see, to be indefinitely multiplied,
and thus can form the idea of immense power. But when
with the microscope we see minute cells working out such
results as we have contemplated in this chapter, and inquire
how it is done, we see that there is a hidden power here that
utterly defies our conception. The mechanics and the chemis-
try of the cell, who can understand them ? From the inscruta-
ble movements of this hidden power, at work wherever life is,
in the cells, its laboratories, we get a higher idea of Omnipo-
tence than we can get from the grandest and most terrific ex-
hibitions of mere force. We get from them the idea of an all-
pervading, as well as an all-wise power, working not merely in
every locality, but at every point of the universe. And the
revelations which the microscope makes to us seem to draw us
very near to the Infinite. As we gaze with wonder and delight
at the secret operations of his power thus opened to us, we seem
almost to be admitted to his presence ; and even our awakened
curiosity, amid the wonders now brought into our field of vision,
does not suffice to remove the awe which almost oppresses us.
216. How great is the inner beauty of the living world
around us ! We admire the symmetrical forms, and the beau-
tiful colors which nature presents to us in such variety ; but
there is an inner world of beauties throughout nature, still more
perfect and resplendent, which is hidden from the naked eye
of man, though it is all open to the Omniscient. If you would
get some idea of the beauty of this inner world, take the most
delicately beautiful of all the specimens of man's workmanship,
and examine it with a microscope ; and then compare it with
some living texture or coloring. Compare in this way, for
example, the most perfect painting of a flower with the flower
itself. The painting loses all its beauty as it is magnified ; but
in the bosom of the flower the microscope developes to you
12*
138 HUMAN PHYSIOLOGY.
The inner beauty developed by the microscope.
beauties far transcending those which are seen by the unassisted
eye. Even such living structures as are unattractive to the
naked eye, present under the microscope wonderful beauty in
the delicate lines of their textures. It is true of every one who
has used this instrument in his observation of nature, that he is
impressed with the fact, that great as is the beauty of nature,
as we look out upon it, it is vastly inferior both in kind and in
amount to that inner beauty seen so completely by the all-
seeing Eye, and now developed to us in part by the skill and
ingenuity of man. And it suggests to us the hope, that in a
new state of being, and with higher faculties, we shall be able
to look farther into these inner beauties of the universe, than
we now can with all the aids which our ingenuity can devise.
PART THIRD,
CONTAINING
CHAPTER X.-Tmc NERVOUS SYSTEM. CHAPTER XL-Tint Boras. CHAPTER Xri.-Tmi
MUSCLES. CHAPTER XIII.-THE LANGUAGE OP THE MUSCLES. CHAPTER XIV.- -Tin
VOICE. CHAPTER XV.-THE EAR. CHAPTER XVI.-THE EYE. CHAPTER XVII.-THB
CONNECTION OF THE MIND WITH THE BODY. CHAPTER XVIII. DIFFERENCES BETWEEN
MAN AND THE INFERIOR ANIMALS. CHAPTER XIX.-VARIKTISS OF THK HUMAN RACK.
CHAPTER XX.-LiFK AND DKATH.
CHAPTER X.
THE NERVOUS SYSTEM.
217. THUS far we have contemplated man merely as a struc-
ture. We have observed the means by which the body is
built and is kept in repair. We have seen that in regard to
these functions of nutrition, man and all animals have much in
common with plants. So far as these functions are concerned,
they vary from plants only in the modes by which the nutrition
is effected. The difference in this respect is not an essential
one. The absorbents in the root of the plant do for the plant
what the lacteals in the digestive organs do for the animal,
the difference between them being only according to the
differing circumstances. So also, circulation and formation are
in all essential points the same in these two different depart-
ments of animated nature. The microscope has in the most
striking manner shown this to be true of formation, for vegeta-
bles and animals are alike constructed, as you have seen, by
cells.
218. The functions of which I have treated in the previous
chapters, as being common to plants and animals, are called the
functions of organic life, because they concern merely the struc-
ture, the organization. But there are other functions. The
body, with all its complicated parts, is constructed and kept in
repair for certain uses. These uses are secured by the nervous
system, a system, which I have spoken of in 32, as being
superadded to what the animal has in common with the plant,
and which, therefore, constitutes the essential difference between
the animal and the plant. This system furnishes the means
of the relations of the animal to the world around him. He
receives his impressions from external things through this
140 HUMAN PHYSIOLOGY.
The nervous system and its subordinate instruments.
system ; and through it he acts upon external things. He
feels through the nerves, and by the nerves excites those
motions by which he acts on both material and immaterial
existences. The functions, therefore, which are performed
through this system, are called functions of animal life, in dis-
tinction from the functions of organic life, which are common
to vegetables and animals. They are sometimes also called
functions of relation, in view of the relations which it estab-
lishes between sentient and moving beings, and all external
things.
219. But there are intermediate instruments, through which
the nervous system exercises its functions. The nerves do not
themselves move, but they excite motion in muscles, and these
move bones and other parts. Neither is sensation performed
by the nerves alone. The different senses, for example, have
different organs, with arrangements differing according to the
kind of sensation. Mere nerves do not alone see, or hear, or
taste, or smell, or touch. There are special organs constructed
for these purposes ; and through these the nerves receive im-
pressions. Thus the nerve of sight cannot of itself see ; but
the eye being there, so formed as to have pictured on a mem-
brane the images of objects, the nerve receives an impression
from these images, and this impression is transmitted through
the trunk of the nerve to the brain, where the mind takes cog-
nizance of it ; and this constitutes seeing.
220. While then the nervous system is the great essential
means of connection between the mind and external things,
there are other subordinate means, as we may consider them.
They are organs of various kinds, through which the nerves act
and are acted upon. The nervous system, therefore, may be
viewed as presiding over the sentient and moving machinery, in
the complex structure of the human system, which we have
been examining in the previous chapters.
221. The nervous system in the lower orders of animals is
very simple, and forms an exceedingly small part of the animal.
But, as we rise in the scale, we find that, as the limits of rela-
tion to external things enlarge, this system becomes more
prominent ; till, in man, in whom these relations, both mental
and physical, are much more extensive than in any other
animal, it is very prominent and greatly complicated.
222. The interest of the class of subjects, now to be opened
to you, much transcends that of the subjects which we have
already gone over. If you look at a child as it first opens its
THE NERVOUS SYSTEM. 141
All knowledge acquired and communicated by nerves.
eyes upon this world, you see a being, whose senses are com-
mencing their work as inlets of knowledge to the soul within.
Nothing is known at the outset, of shapes, or colors, or dis-
tances, or any other relations of things. This is all to be
learned, through the nerves and their subordinate organs. And
as all knowledge is acquired through the nerves, so it is com-
municated through nerves to others. It is communicated by
the motions that are excited in the muscles by the nerves the
motions of the countenance varying its expression ; the motions
of the limbs, or gestures ; but especially by the motions which
produce and articulate the voice. Thought and feeling can be
communicated in no other way than by muscular motion.
223. From what has now been said, you readily see, what
will be the subjects of the third part of this book. They are
those which relate to the nervous system and its connections or
dependencies. They are, the nervous system itself; the organs
of locomotion, the muscles, and the bones ; the voice ; the ex-
pression of the countenance, and the language of the muscles
generally ; the senses, with their organs ; instinct ; thought ;
reason.
224. As preparatory to a particular view of these subjects, I
will give you a general view of the nervous system, with the
functions performed by the various parts of it. I shall reserve
for another chapter a particular view of some of the higher
functions of this system, and a consideration of some subjects,
which we can better examine after we have considered the
organs of locomotion and the senses.
225. The nervous system may be considered as having
three parts ; 1, certain central parts, as the brain and spinal
marrow ; 2, nervous trunks, which going from these central
parts divide and subdivide, as the arteries do, till they become
exceedingly minute ; and 3, the nervous expansion in the
organs, having a relation to the nervous trunks similar to that
which the capillaries bear to the arteries. In what we call sen-
sation we suppose that an impression is produced in the nerv-
ous expansion, that the trunk serves to transmit it, and that
through the nervous centre, the brain, it is communicated to
the mind.
226. Let us see now what is necessary to this compound act,
termed sensation. First, it is necessary that the organ where
the nerve is expanded be in a condition to let the nerve receive
the impression. If the eye be so injured in its textures, that
the impression can not be made on the nerve, there can be no
142 HUMAN PHYSIOLOGY.
Necessary conditions of nervous action in sensation and motion.
vision. So, too, of the other senses. Taste and smell are often
impaired, sometimes even destroyed for a time, by an inflam-
mation of the mucous membrane, on which the nerves devoted
to these senses are expanded. This is sometimes the case in a
common cold. It is necessary also, that the trunk of the
nerve be in a proper condition. If the nerve of vision be
pressed upon by a tumor, there will be no impression trans-
mitted from the images formed in the eye. So, too, if a nerve
going to any part of the body be cut off, there can be no trans-
mission of impressions to the brain from that part. Again, it
is necessary to sensation, that the brain should be in a state to
communicate the impression to the mind. If the brain be
pressed upon strongly by a depression of the skull from
violence, or by effusion of blood by the rupture of an artery, as
sometimes occurs in apoplexy, there can be no sensation.
Excitement of mind, too, sometimes prevents the occurrence of
sensation, by its action upon the connection between the mind
and the brain. The pain of a wound received in battle is often
unfelt, until the excitement of the battle is over. The aching
of a tooth is often stopped by the excitement consequent upon
going to the dentist to have it extracted. I once burned my
hand in the beginning of a chemical lecture, but felt no pain
till I had finished it, and then the pain was at once very
severe. In these cases the cause of the pain is acting all the
while upon the nervous extremity, and the trunk of the nerve
is capable of transmitting the impression, but the state of the
mind is such, and such is the consequent condition of the
brain, that the sensation does not occur one link in the neces-
sary chain is defective.
227. The same can be said, in regard to the necessity of
each of these links of the chain, in relation to voluntary mo-
tion, as well as sensation. The brain must be in a condition
to be acted upon by the mind ; the nervous trunk must be
capable of transmitting the impression ; and the muscle must
be in such a state, and in such connection with the extreme
nervous fibres, that it can respond to the call of the brain.
228. Before going further, I will give you some idea of the
proportions and arrangement of the central organs of the
nervous system. In Fig. 72 you have presented a general
view of this system, the central organs with the nerves going
out from them. At a is the cerebrum, the upper large brain,
filling up a considerable portion of the skull; at b is the
cerebellum, the lesser brain, lying beneath the cerebrum at its
THE NERVOUS SYSTEM.
143
General plan of the nervous system.
FIG. 72.
NERVOUS TRUNKS IN MAN.
144
HUMAN PHYSIOLOGY.
Hemispheres and lobes of the brain.
back part : at c is the great facial nerve, the chief nerve of the
face ; the spinal marrow, c?, sends off branches on either side
in its whole length ; at e is the brachial plexus, a bundle of
nerves coming from the spinal marrow, which here unite
together, and are then distributed to all parts of the arm ; at i
is a similar plexus from which are distributed nerves to the
lower extremity ; /, #, and h point to different nerves in the
arm, and I, m, n, and o to different nerves in the leg. You
observe that the whole of this nervous system is divided into
exactly similar halves. The cerebrum and the cerebellum are
both double organs, and the nerves of one side are just like
those of the other.
229. Having thus observed the general arrangement of the
nervous system, I call your attention next to the arrangement
and structure of the brain which are seen in Fig. 73. This
h i k m e
BRAIN AND NERVES.
Figure presents to view a perpendicular section of the brain, as
made from front to rear, dividing it into two halves. You
have here a view of the inner surface of one hemisphere, as it is
THE NERVOUS SYSTEM. 145
Cerebrum. Cerebellum. Convolutions. Membranes.
termed, of the cerebrum, the large upper brain, which is com-
monly described as having three lobes or divisions, a, the
anterior ; 6, the middle ; and c the posterior. At / is the
broad band of white fibrous matter, which unites the two
halves or hemispheres together, of course divided in the
section ; at d is the cerebellum showing a peculiarly beautiful
arrangement, called the arbor vitce, or tree of life ; at g is the
beginning of the optic nerve which goes to the eye ; I is the
nerve of smell ; e is the commencement of the spinal marrow.
The many nerves which you see, are distributed to various
parts of the face ; the nerve at h goes to the tongue ; at i to
the throat, and at m to one of the muscles of the eye. From
the beginning of the spinal marrow go forth many nerves, one
of which, &, is a very important one, as it sends off branches to
the lungs, the heart, and the stomach. It is this part of the
nervous system, the top of the spinal cord, that it is most im-
mediately essential to the continuance of life. For it is by
their nervous connections with the top of the spinal marrow,
that the heart and lungs continue to perform their duty. It
has been ascertained, by experiments upon animals, that the
cerebrum, and even the cerebellum, can be destroyed, and yet
the animal will continue to breathe, and the circulation will go
on for some time. But the moment that this part of the
spinal cord, from which the heart and lungs are supplied with
nerves, is destroyed, the breathing and the circulation stop
and the animal dies. So, too, in apoplexy, if the effusion of
blood take place at the top of the spinal marrow, death will
occur more certainly, and in much shorter time, than if the
effusion take place in the cerebrum or cerebellum.
230. You observe that the cerebrum has deep irregular
furrows on its surface, and that it presents undulating tortuous
projections. These are called the convolutions of the brain.
Into the furrows between them dips down the membrane, in
which branch out the arteries that supply the brain with blood,
and the veins that return it from this organ. This membrane
is from its soft and delicate texture, called the pia mater (pious
mother), while the stout fibrous membrane, which lies outside
of this next to the bony covering is called the dura mater, or
hard mother. The names are entirely inappropriate, for the
latter serves as a protection to the brain, and the former is
merely a vehicle or medium for the entrance of the blood
vessels into the brain. There is another membrane lying
between these which is called the arachnoid membrane, be-
13
146
HUMAN" PHYSIOLOGY.
Gray and white substance. Proportions and arrangement.
cause in its tenuity and delicacy it resembles the spider's
web. It is one of the serous membranes, and it serves as a
protecting envelope to the brain, and at the same time by its
serum, keeps this organ bedewed with moisture over its whole
surface.
231. The substance of which the brain is composed is very
soft, something like blanc-mange. It is the softest organ in
the body. It is not uniform throughout in color. All around
the white inner part of. the brain there is a thick layer of gray
substance. In Fig. 74 you have a horizontal section of the
FIG. 74.
SECTION OF THE BRAIN.
brain, showing the proportions and arrangement of the gray
and the white substances. As the gray substance dips down,
as you see in the figure, into all the furrows, its extent is
greater than you would suppose at the first view. In the
middle is represented the broad connection which exists
between the two hemispheres of the brain. You observe in
THE NERVOUS SYSTEM.
147
The gray substance made of cells, the white of tubes.
Fig. 73, and Fig. 74, that there is no apparent arrangement of
the external parts of the brain, which would give countenance
to the idea of the phrenologist, in relation to a division into
particular organs. The convolutions, so far from presenting
any well defined arrangement, are exceedingly irregular.
232. The gray substance, which is sometimes called the
cortical (bark-like) substance, because it surrounds the white
central part of the brain, is made up, as I said in the Chapter
on Cell-Life, 208, of cells, while the white part is composed of
exceedingly minute tubes. These tubes are continued into the
nerves, and as they hold the nervous matter, they constitute the
medium of communication between the brain and all parts of
the body. This function of communication is the sole function
of the white nervous matter. In the brain this white matter is
a mere collection of tubes, and these branching out in bundles
form the nerves. These tubes are supposed to be entirely
separate from each other, from their beginning in the brain to
their termination in the various parts of the body, for the
microscope, as stated in 205, has never discovered any union
between them at any point. The brain then is a great central
organ of communication, where innumerable minute tubes are
brought together, each of which is connected with some one
moving fibre, or some one sensitive point in the body. Those
which are connected with mus-
cular fibres transmit impres-
sions from the brain, and
those which are connected
with sensitive points transmit
impressions to it. Of the
size of these tubes you can
judge by Fig. 75, which
shows some of them as they
appear magnified 350 diam-
eters. They vary much in
size, but the cause of this
variation has not been dis-
covered.
233. The office of the gray
substance, it is quite well
ascertained, is very different
from that of the white sub-
stance, as the difference in
its structure would lead us to suppose. It is more nearly
FIG. 75.
NERVOUS TUBULI,
Magnified 350 diameter*.
148 HUMAN PHYSIOLOGY.
Office of the gray substance. Proportioned to the amount of intelligence.
connected with the mind than the white substance. When,
for example, motion is produced in obedience to the will, the
impression producing the motion is transmitted through the
white matter, but the cause of this impression does not act
directly on this matter. The impression is caused by the
action of the mind on the gray matter, and the white substance
only serves to transmit it. The gray matter, therefore, has a
more active agency than the white in the phenomena of the
mind and the nervous system. It is the first link in the chain
of connection between the spiritual and the physical in our
nature. Hence, in examining the brains of animals, we find
that the higher is the intelligence, the more abundant is the
gray substance ; and it is especially abundant in man, by the
large development of the convolutions.
234. The question arises here, whether, as in motion the
active agency is on the part of the gray matter in the brain,
there is also gray matter at the extremities of the nerves of
sensation, exerting an active agency there. It would seem that
it should be so. When voluntary motion is produced, the
action of the mind is on the gray substance, and the white sub-
stance of the brain and the nerves transmits the impression of
this action. But in sensation the first step in the process is not
in the brain, but in the nervous extremities. Now in this first
step, in the actual production of the impression to be trans-
mitted to the brain, we should suppose the gray matter as
necessary as in the production of the impression to be trans-
mitted from the brain in effecting voluntary motion. Else we
must conclude, that, while the white substance can have no
active agency in the brain, but serves only for transmission, at
its other extremity, expanded in the organs, it serves for both
transmission and production. Dr. Carpenter supposes, there-
fore, that there is a sort of gray matter in the expanded extrem-
ities of all nerves of sensation. But the microscope has never
discovered the existence of this matter in any nervous expan-
sion, except in the nerve of the eye, in the retina, and in some
parts of the internal ear. And some facts seem to militate
against Dr. Carpenter's view of the subject. If, for instance,
you hit the trunk of a nerve, as the little nerve so often hit at
the elbow, a sensation is produced, which is in some measure
referred to the part to which the nerve is distributed. From
such facts it would appear, that in sensation the white nervous
matter does not merely transmit impressions, but has an
agency also in originating them. There is then probably
THE NERVOUS SYSTEM.
149
The gray substance well supplied with arterial blood. Ganglions and plexuses.
no gray matter ordinarily in the expanded extremities of a
nerve, but they are merely terminations of the tubes which
make up its trunk.
235. The cells which form the peculiarity of the structure of
the gray substance are often, as you saw in Fig. 69, of very
singular appearance from their prolongations. They lie in the
interstices of a vascular network. A due supply of arterial
blood is absolutely essential to the vigorous performance of the
functions of the gray substance. If the supply be cut off in
any way, as by the failure of the heart's action in fainting,
insensibility and the loss of the power of motion are the conse-
quence. While the gray substance is on the outside of the
brain, it is on the inside of the spinal marrow. It is also on
the inside of the little bodies called ganglions, scattered here
and there, as depositories of nervous force, or as little brains, as
we may term them. These ganglions are not merely a part of
the apparatus of communication. They are different from
plexuses, which are mere combinations of nervous trunks, as
seen in Fig. 77, t t being the trunks, which, after uniting with
FIG. 76.
each other in various ways, again separate to go to their
different destinations. At g, in Fig. 76, is a ganglion into
which the fibres / of the nerve n run. It then divides again
into branches b. These ganglions produce nervous force, and
therefore are composed like the brain in part of gray substance.
The spinal marrow, too, produces as well as transmits, and so
13*
150 HUMAN PHYSIOLOGY.
Changes in the nerve-cells. Termination of the nervous fibres.
this substance forms a part of it. This gray substance, as it is
in constant operation, is subject to much wear and tear, as we
may express it, and therefore the changes of repair are con-
stantly going on in its structure. Hence, the necessity for so
large a supply of blood, as is secured by the network of vessels,
among which the cells peculiar to this substance are scattered.
The microscope has fully demonstrated the reality of these
continual changes, for it shows us, whenever a portion of this
substance is examined by it, the cells in all the various stages
of development mingled together. The freshly made simple
cells are seen among those which have been formed for some
time, and which have put forth their long off-shoots, as seen in
Fig. 69.
236. The extremities of the fibres, or rather of the tubuli
(Fig. 75) of the nerves terminate variously. The most common
termination is in loops, as seen in Fig. 78, which represents the
FIG. 78.
NERVES OF TOUCH IN THE SKIN OF THE THUMB.
termination of the nerves as seen through the microscope in
a thin perpendicular section of the skin in the thumb. The
three eminences in this figure are those of the papilla, as they
are termed, which you can see are arranged in curvilinear rows,
if you look at the ball of the thumb. In Fig. 79 you see this
same loop-like arrangement in the nervous tubuli, as seen
through the microscope, on the sensitive sac that lines the
cavity of a tooth, the entrance for the nerves and bloodvessels
of this sac being at the end of the root,
237. One very singular termination of the nervous tubuli, is
in what are called Pacinian corpuscles, after Pacini, the first
microscopist that discovered them. They are found attached
to the nerves in the hand and foot more often than any where
THE NERVOUS SYSTEM.
151
Pacinian corpuscles. Their office not known.
FIG. 80.
FIG. 79
NERVES IN A TOOTH.
PACINIAN CORPUSCLES.
else. Their structure, which is seen in Fig. 80, A, highly
magnified, is very curious. They are attached to the branches
of the nerves on which they cluster by little peduncles or
stalks. At a is the peduncle; 6 is the nervous fibre or
tubulus ; / is its termination in the corpuscle. The corpuscle
itself is composed of layers of a very delicate fibrous membrane
inclosing each other like the coats of an onion, to the number
of sometimes sixty, the inner ones, d, being closer together than
the outer ones, c, are. In B is represented a portion of a
nerve of a finger, with clusters of these corpuscles of about the
natural size. Of what use these singular bodies are we know
not. But the fact that they are always found in certain
regions of the body shows that they are placed there for some
definite purpose. It has been supposed by some that they are
minute electrical batteries, because they bear some resemblance
to the electrical organs found in some fishes.
238. There is a wonderful fact in regard to the healing of
wounded nerves which must not pass unnoticed. You know
152 HUMAN PHYSIOLOGY.
Healing of nerves. Nice fitting of the tubuli.
that if a nerve be divided, all communication between the part
that it supplies with branches and the brain is cut off. No
impressions can be transmitted through it to and from the
brain. But the two cut ends of the nerves can grow together,
and the communication can thus be more or less restored.
Sometimes it is as perfect as before. Now, if you call to
mind the structure of a nervous trunk, you will see that this is
passing wonderful. It is made up, you will recollect, of tubuli
which are entirely separate from each other, and each one
of these goes from its origin in the nervous centre to its
destination by itself. It is difficult to conceive, therefore, how
the nerve can be healed without creating confusion. For to
avoid this it would seem to be necessary, that each little tube
at its cut end must unite with its corresponding end, and not
with the end of some tube with which it has no relation. For
example, if the nerve distributed to the hand were cut, it
would not do, as it seems to us, to have tubuli which go to the
thumb unite with those which go to a finger. And besides, as
I shall soon show you that the tubuli, through which the
impression that produces motion is transmitted, are separate
from those which transmit the impression that causes sen-
sation, it would not do for a tubulus of one kind to unite
in the healing with one of the other kind. We can not
conceive how a confusion in sensations and motions can be
avoided, unless the end of each fibre or tubulus is united
with its corresponding end ; and such an accurate union
of the multitude of tubuli in a nerve ^seems an impossibil-
ity. That there is, however, a very accurate union effected, is
manifest from the observations of M. Brown Sequard. He
examined in animals nerves which were divided twelve months
before, and could not discover the point of division even with
the aid of the microscope. If the tubuli were not all made as
perfectly continuous as before the nerve was divided, the
microscope would have revealed the defect. But it takes time
to effect this adjustment of the tubuli, for it was found by Dr.
Haighton in his experiments nearly fifty years ago, that after
dividing nerves, their functions were not restored till some
time after they were apparently healed. This shows most
clearly, that the arrangement of the tubuli, which is required
for the communication of impressions through them, is gradu-
ally effected after the union takes place.
239. Taking this view of this interesting point, the difficulty
is greatly enhanced, when we look at the union of parts that
THE NERVOUS SYSTEM. 153
Nerves of the spinal morrow compound.
did not originally belong together, as, for example, when a
piece of skin is dissected from the forehead, and is twisted
down so as to be made to grow on to the nose to supply
a deficiency 4here. Here new relations entirely are established
between the nerves of the divided parts, and, as we should
expect, there is confusion in the sensations. The patient, at
first, whenever the new part of his nose is touched refers the
sensation to the forehead. But this confusion of the sensations
is after a while removed. And it is curious to observe, that
while the old nervous connections are breaking up, and the
new ones are becoming established, there is an interval of
partial, sometimes entire, insensibility in the part. How these
new relations can be established consistently with the known
arrangement of the tubuli in the nerves is a mystery.
240. As I have already hinted, there are different nerves for
different purposes. The nerves through which the mind sends
its messages to the muscles, are not the same with those
through which it receives impressions in sensation. In and
about the face, the nerves of motion and sensation are, for the
most part, entirely separate from each other. But in other
parts of the body, the fibres or tubuli for motion and sensation
are mingled together in the same nervous trunk, inclosed in
one sheath. It is found that each of the nerves, coining out
from each side of the spinal marrow, has two roots, which
unite together and are inclosed in one sheath.
This arrangement is represented in Fig. 81,
in which a is a portion of the spinal cord ;
d the anterior root ; 6 the posterior root ; e
the trunk formed by the union of these two
roots ; and / a branch of the nerve. At c,
on the posterior root is one of the ganglions, or
little brains, of which I spoke in 235.
Why they are placed on these posterior roots,
and not on the anterior, or why they are
placed here at all, we know not. It has
been ascertained by many experiments on
animals, that the posterior roots are composed
of tubuli, which bring impressions to the -spinal marrow ; while
the anterior are composed of tubuli which carry impressions
from the spinal marrow. For, if the spinal cord of an animal
be laid bare, and a posterior root be irritated, pain is produced ;
but if an anterior root be irritated, violent motions are caused
in the parts to which the nerve is distributed. That is, the
154 HUMAN PHYSIOLOGY.
Different nerves for different offices.
posterior root is a nerve of sensation, and the anterior a nerve
of motion. It is a mere matter of convenience that they unite,
and are mingled together in the same sheath, for they are to
be distributed in the same parts. In and about^he face the
nerves of motion and sensation are kept for the most part
separate, as before stated, merely because it would be no con-
venience in any case to put them together in one sheath.
241. But not only are there different nerves for sensation
and for motion, but there are also different nerves for different
kinds of sensation. Thus, in the eye, the optic nerve which
transmits the impressions from the images formed on the
retina, as will be shown in the Chapter on the Eye, is wholly
separate from the nerve by which any pain or irritation is felt
in this organ. The latter is called a nerve of common sen-
sation the former a nerve of special sensation. So in the
nose, the nerve that takes cognizance of odors is a different
one from that by which irritation on the same membrane is
felt. The snuff-taker smells the snuff with one nerve, and feels
its tingling with another.
242. The nerves devoted to one kind of sensation can not in
any case perform the function of those of any other kind.
Each nerve is fitted for its own peculiar office, and has for this
its own peculiar susceptibility. Thus, the nerve of touch is
insensible to light, and, on the other hand, the nerve of vision
is insensible to touch. If, therefore, the nerve of vision be
paralyzed, but the nerve of common sensation in the eye be
unimpaired, although there is no seeing, the eye is as sensible
to irritation as ever. On the other hand, if the nerve of vision
be unimpaired, and the nerve of common sensation be par-
alyzed, as sometimes happens, the individual can see, but he
has lost the sentinel that stands guard over the eye, and by its
warning of pain keeps it from injury. What, therefore, is
flying in the atmosphere may lodge in the eye, and though it
produce no pain, it will excite inflammation by irritating the
capillaries. The eye in some of these cases is destroyed,
by the inflammation which thus arises from the loss of sensi-
bility to the touch. When the nerve of common sensation is
in a healthy state, the moment any thing gets into the eye
great pain is produced, and the tears flow and the eyelids are
in constant motion ; and if by these instinctive means, as we
may term them, the irritating substance is not removed, other
means are at once resorted to. But when this nerve is par-
alyzed, although the irritating substance produces no pain, it
THE NERVOUS SYSTEM. 155
Different degrees of sensibility in the various parts of the body.
gradually causes inflammation in the delicate vascular texture
of the eye. Pain, then, in this case, as well as in every other,
is a safeguard against danger. The part is endowed with an
acute sensibility to touch, because it is needed as a sentinel in a
part so delicate and yet so exposed.
243. This leads me to remark, that the different parts of the
body are endowed with different degrees of sensibility, accord-
ing to their necessities, in relation to the warning of danger.
Accordingly, the skin is the most sensitive part or organ of the
body, that it may warn at once of the approach of danger ;
while the internal parts have much less sensibility, some of
them none. In the performance of operations, therefore, the
great suffering is in the cutting of the skin. There is very
little sensibility in the muscles, and there is none in the bones.
The following fact illustrates the use of the sensibility of the
skin in the prevention of injury. A man who had lost all
sensibility in his right hand, but retained the power of motion,
lifted the cover of a pan when it was burning hot. Although
he was not aware of any effect at the moment, the consequence
was the loss of the skin of the fingers and of the palm of the
hand, laying bare the muscles and tendons. If the sensibility
had not been lost, that is, if the nervous tubuli which transmit
sensation had not been paralyzed, the warning of pain would
have been instantly given to the brain, and orders would have
been sent to the muscles to relax their grasp of the cover ; and
so rapid are these transmissions, that the cover would have
been dropped soon enough to prevent any great amount of
injury from being done.
244. Although there is so little sensibility in the internal
parts in their healthy condition, yet when they become inflamed
they become sensible of pain, sometimes acutely so. Thus, an
inflamed bone is the seat of severe pain ; and the tendons,
although nearly insensible ordinarily, become very painful
when inflamed, as any one that has a deep-seated felon can
testify. The question as to the cause of this change of sen-
sibility I will not stop to discuss, but that there is a benevolent
object in it is very manifest. If inflammation caused no pain
in such parts, it might go on to a destructive extent without
the person's being aware of the danger, and therefore without
his applying for medical means.
245. It was formerly supposed that a nerve must of course
have an exquisite sensibility. But there is no sensibility in
nerves devoted to motion. Neither is there any in the brain
156 HUMAN PHYSIOLOGY.
Insensibility of the heart to the touch. Respiratory nerve of the face.
itself. Portions of it can be cut off without producing any
pain. The heart, too, is insensible to the touch. A case
proving this fell under the observation of Harvey, the dis-
coverer of the circulation of the blood. A young nobleman,
from an injury received in a fall, had a large abscess on the
chest, which occasioned such a destruction of the parts, as to
leave the lungs and heart exposed. Charles L, on hearing of
the case, desired to have Harvey see it. "When," says
Harvey, "I had paid my respects to this young nobleman, and
conveyed to him the king's request, he made no concealment,
but exposed the left side of his breast, when I saw a cavity,
into which I could introduce my fingers and thumb ; aston-
ished with the novelty, again and again I explored the wound,
and first marveling at the extraordinary nature of the case, I
set aboiit the examination of the heart. Taking it in one
hand, and placing the finger on the wrist, I satisfied myself
that it was indeed the heart which I grasped. I then brought
him to the king, that he might behold and touch so extraordi-
nary a thing, and that he might perceive, as I did, that unless
when we touched the outer skin, or when he saw our fingers
in the cavity, this young nobleman knew not that we touched
his heart!" This absence of sensibility in the heart is not
because it is not well endowed with nerves. It is well
endowed, but it is with nerves which are devoted to another
purpose. They are nerves of sympathy, which establish a
connection with every part of the body, making this organ to
be so easily affected by motion, by disease, and by every pass-
ing emotion in the mind.
246. In the face we have an example of different sets of
nerves for different classes of motions. All those motions that
are used in the expression of the countenance are associated
together by a certain nerve. This nerve has nothing to do
with other motions, as mastication. Other nerves are provided
for them. Sometimes this nerve of expression is paralyzed on
one side. The result is, that while the individual can masti-
cate equally well on both sides, he can laugh, and cry, and
frown, only on one side, and he can not close the eye on the side
affected. In Fig. 82 is a representation of this condition of
things. The left eye can not be closed by any effort, and the
left side of the face is wholly devoid of expression. This nerve
of expression is often paralyzed by itself, the other nerves in the
neighborhood, both nerves of sensatioti and of motion, being
entirely unaffected. This nerve has been called the respiiatory
THE NERVOUS SYSTEM.
157
Paralysis of the respiratory nerve of the face.
FIG. 82.
PARALYSIS OF THE NERVE OF EXPRESSION
on one side of the face.
nerve of the face, because it controls motions which are con-
nected with the, movements of respiration. If you observe how
the various passions and emotions are expressed, you will sea
that there is a natural association between the muscles of the
face and those of the chest in this expression. This is very
obvious in laughing and in weeping. But this association can
be effected only through nervous connections. And these con-
nections in this case are very extensive and intimate. When
the nerve of expression, or facial respiratory nerve, is par-
alyzed, all the motions of the face connected with the respi-
ration are absent. Though the individual may sob in weep-
ing, or send forth the rapid and successive expirations of
laughter, yet the face on the side where the nerve is par-
alyzed will be perfectly quiescent. So, too, those movements
of the nostrils which are sometimes used in expression, can
not be performed. Sneezing and sniffing up can not be dono
14
158 HUMAN PHYSIOLOGY.
Nerves of the eye. Paralysis affecting different nerves.
on the affected side. Neither can the individual whistle,
because a branch of this nerve goes to the muscles at the
corner of the rnouth, which are therefore disabled. Sir
Charles Bell, in cutting a tumor from before the ear of a
coachman, divided this branch of the nerve. Shortly after, the
man thanked him for curing him of a formidable disease,
but complained that he could no longer whistle to his horses.
247. The eye has six different nerves, each for a different
service. 1. The optic nerve. This has nothing to do with the
motions or the common sensations of the eye. Its sole office is
to transmit impressions from the images formed in the eye to
the brain. 2. A nerve of common sensation, by which any irri-
tation in the eye is felt. 3. A nerve which is distributed to the
muscles of the eye generally, and to no other parts of this organ.
4. A nerve which goes to one particular muscle, one of the oblique
muscles of the eye. It is an involuntary muscle which performs
the insensible rolling motions of the eyeball, and is associated
with the muscles of expression in the countenance by means of
nervous connections. 5. A nerve which goes to another single
muscle, which turns the eye outward. 6. A branch of the
respiratory nerve, which regulates the motion of the eyelids,
and has much to do, therefore, with the expression of the coun-
tenance. To this small organ, then, are distributed six different
nerves, each having its distinct office, and its separate origin in
the brain. How various are the transmissions through these
nerves, and how nicely adjusted must all the parts of this
complicated apparatus be, that each may perform its office
without interference with the rest !
248. I have already alluded incidentally to the fact, that one
nerve may be paralyzed, and others distributed to the same
parts may be entirely unaffected. Thus the nerve of expression
in the face may be paralyzed alone, the face retaining its usual
sensibility and its power of performing other motions than those
of expression, as mastication, because the nerves of common
sensation and of common motion are untouched by the disease.
So, too, in the nerves which go out from the spinal marrow,
composed of tubuli of motion and sensation mingled together,
one set of the tubuli may be affected while the other is not ;
for in paralysis it is often the case that the sensibility remains
while the power of motion is gone, and vice versa. Sir Charles
Bell relates an interesting case, in which the paralysis was
different on the two sides of the body. A mother was seized
with a paralysis, in which there was a loss of muscular power
THE NERVOUS SYSTEM. 159
Nerves, though having different offices, all alike in structure.
on one side, and a loss of sensibility on the other. She could
hold her child with the arm of the side which retained its
power of motion but had lost its sensibility. But she could do
it only when she was looking at it. She could not feel her
child on the arm, and therefore when her attention was drawn
to any thing else, and she ceased to have her eyes fixed on the
child, the muscles having no overseer, as we may say, to keep
them at work, were relaxed at once, and the child would fall
from her arm. In this case, bound up in the same sheaths were
two sets of tubuli, one set of which were useless in the nerves
on one side of the body, and the other set were useless in the
nerves of the other side.
249. We should suppose that there would be a difference in
the construction of the nerves, corresponding with the different
uses to which they are devoted. But it is not so. The micro-
scope shows us that the nerves of motion and of common and
special sensation are all alike in their structure, and chemistry
shows us that they are alike also in their composition. The
question arises, then, why the impression producing motion can
not be transmitted by the same nerve with the impression
causing sensation. The reason is evidently not to be found in
the nervous trunk itself, as this is the same in all cases. It is
in the circumstances of the two ends of the nerve that which
is in the nervous centre from whence it arises, and that which
is expanded in some part of the body. You can see at once
that the nervous tubuli which end in the fibres of a muscle
can not transmit sensation to the brain from the skin over the
muscle, because they do not go to the skin at all. There are
other tubuli that are distributed there for that purpose, mingled
indeed in most cases with the tubuli for motion, but yet kept
entirely distinct from them. And besides, there is probably
something in the mode of arrangement of the extremities of a
nerve of sensation, which differs from that which exists in the
distribution of a nerve of motion, so as to make it impossible
for a nerve of motion to receive the impression producing sen-
sation, even where the impression is made directly upon the
muscle itself. There is also probably a different ending of the
nerves of sensation and motion in the nervous centre, the brain,
or spinal marrow, that makes the one kind incapable of
performing the duties of the other kind.
250. There have been many hypotheses in regard to the
action of the nerves. The most common theory, even up to
modern times, was this that the brain is not only the great
160 HUMAN PHYSIOLOGY.
Nerve-force not electricity. Proved by facts and experiments.
centre of the nervous system, but its central workshop, as \re
may express it, and that in it is secreted a nervous fluid, which
is distributed through all the body by the nerves, they being,
as it was supposed, bundles of conduit-pipes. This fluid was
supposed to move back and forth in the nerves, going outwards
towards the extremities of the nerves to excite motion, and
going inward to the brain to convey the sensation of external
impressions. This theory has been exploded by the researches
of Sir Charles Bell and others, and during the last half century
important and numerous discoveries have been made, in rela-
tion to the functions of different parts of the nervous apparatus.
And though there are many things in this system, which links
the spiritual with the physical, that we shall never understand,
the bounds of our knowledge in regard to it are undoubtedly
to be largely widened by future researches.
251. It is a favorite idea with some physiologists that nerve-
force, as it is termed, is identical with electricity, and that the
nervous system is therefore a system of electrical batteries, with
an apparatus for a sort of telegraphic communications. They
ground their opinion upon the fact, that a current of electricity
passed along nerves may produce motion or sensation, accord-
ing to the character of the nerve through which it is passed,
and also upon the analogy which exists between nerve-force
and electricity in the instantaneousness of their transmission.
But facts and experiments have wholly disproved this alleged
identity. Some of these I will briefly relate. Mechanical and
chemical stimuli produce the same nervous action that elec-
tricity does. This shows that the electricity acts merely as a
stimulus to wake up the nerve-force, instead of being that force
itself. Experiments have been tried, to detect, if possible, the
existence of an electrical current in a nervous trunk while the
parts to which it is distributed were in action, but in vain.
Thus, Prof. Matteucci laid bare the large nerve of the leg of a
horse, and although by irritating its roots he excited powerful
action of the muscles of the leg, the instrument in connection
with the nerve was entirely unaffected, though it was so ex-
tremely delicate that it would indicate an infinitesimally small
disturbance of the electrical equilibrium. Again, a ligature put
around a nerve will by its compression prevent nervous trans-
mission through it, but will not hinder the passage of an elec-
trical current. Still again, if a piece of a nerve be cut out, and
some good conducting substance be introduced in its place,,
electricity will pass, but there can be no transmission of nerve
THE NERVOUS SYSTEM. 161
Products of nervous action sensation, motion voluntary and involuntary.
force to the parts below the division. Besides all this, nerve-
force differs from electricity in the fact that it can be confined
to the nervous trunk, or even to a small portion of the trunk, as
when a motion is very limited in extent ; while electricity not
only passes through the whole trunk, to all the parts to which
the nerve is distributed, but is diffused in the parts around it.
Thus, if an electrical current be passed through the main nerve
of the limb of an animal, it will go through every branch
of that nerve, and cause all the muscles of the limb to contract ;
but nerve-force may be so insulated in a small portion of the
nerve, that a single toe may be moved alone. And some of the
electricity will be diffused at once in the muscles and other
parts around the trunk of the nerve before it reaches any of the
branches that go off from it. Indeed, the muscles are much
better conductors of electricity than the nerves, which should
not be if the nerves were particularly designed for its transmis-
sion, as the hypothesis would claim. And both muscles and
nerves are nothing like as good conductors as a common copper
wire.
252. We have thus far contemplated nervous action, for
the most part, only in two forms as producing sensation
and voluntary motion. In sensation the action is from the
extremity of the nerve to the nervous centre ; but in motion it
is from the centre to the extremities of the nerves, as they are
expanded among the fibres of the muscles. This voluntary
motion, you see, may arise in consequence of sensation, as
when you withdraw the hand from the fire, if the heat be
painful; or it may occur without a preceding sensation, as
when the thinking mind wills to perform certain motions for
effecting some purpose. In either case it is supposed that the
gray vesicular or cellular substance of the brain is in immediate
connection with the mind, and that the white tubular matter
of the brain and the nerves serves only for transmission. That
is, both in sensation and motion the effective physical agency is
in the vesicular gray substance. This is the working part of
the telegraphic apparatus of the mind, while the innumerable
tubuli of the white matter of the brain and nerves are the
communicating wires.
253. Much of the muscular motion of the body is produced
without the agency of the will, and sometimes even in oppo-
sition to it. This is true of the motions caused by emotions in
the mind. For example, the muscular motions in sobbing and
in laughing often occur in opposition to the strong action of the
14*
162 HUMAN PHYSIOLOGY.
Involuntary motion. Excitor and motor nerves.
will. In this case, the emotion produces its effect upon the gray
vesicular substance, and from this the impression is transmitted
through the nerves to the muscles.
254. There are some common motions which are performed
to a greater or less extent without the agency of the will. The
muscles which perform them are called involuntary muscles.
The muscles of respiration, for example, ordinarily act without
our willing them to do so. If they did not, respiration would
stop when we sleep, or become stopped from disease. But the
will can quicken these muscles in their action. They are
therefore not wholly involuntary. But there are some purely
involuntary muscles. The muscular coat of the stomach, which
I spoke of in the Chapter on Digestion, as being constantly in
motion when the stomach is filled with food, is of this char-
acter. No effort of the will can quicken or retard the action of
this muscle. That exceedingly compound muscular engine,
the heart, is a collection or arrangement of purely involuntary
muscles. No effort of the will can directly influence its
motions, though it may do it indirectly, by so directing the
thoughts as to awaken emotions calculated to produce this
effect. That beautiful circular curtain in the eye, the iris, has
the size of its circular opening, the pupil, controlled, as you will
see in the Chapter on the Eye, by an involuntary muscle.
By what agency, you will inquire, are these involuntary
motions produced ? The answer to this question will open to
you a new view of the nervous system.
255. I have already alluded to the two roots which unite to
make up each nerve that comes from the spine. One of these
roots is composed of tubuli through which impressions are
transmitted to the spinal marrow ; and the other contains
tubuli, through which an impression is transmitted from the
spinal marrow to the muscles, causing them to contract. Each
nerve, then, coming from the spine, is made up of two distinct
nerves, or two distinct sets of tubuli. One of these is called an
excitor nerve, the other a motor nerve. In the case of the
muscles of respiration, every time that they act, the process is
this an impression is transmitted from the lungs through an
excitor nerve to the spinal marrow, the gray vesicular substance
there responds to this impression, and sends in consequence an
impression by a motor nerve to the muscles. So in the case
of the iris, which contracts to prevent too much light from
entering the eye, the light as it strikes the retina produces an
impression, which is transmitted through an excitor nerve, an(J
THE NEKVOTJS SYSTEM. 163
Reflex action of nerves. Sometimes sensation with it, and sometimes not.
in consequence another impression is transmitted through a
motor nerve to the iris. So also, the presence of food in the
stomach produces an impression which is transmitted through
the excitor nerve, and another impression is returned through
the motor nerve, exciting the muscular coat to action. And in
the act of swallowing an impression is transmitted from the
food thrust back into the throat, and then impressions are
returned to the many muscles engaged in this compound act,
( 78). The action of the nerves illustrated by these examples
is termed their reflex action, because the impression transmitted
by one nerve to the spinal marrow is reflected from it by
another.
256. You see that I use the rather indefinite word, impres-
sion, in relation to the transmissions through the nerves. It is
the best word that can be employed, because although some-
thing is transmitted, we know not what that something is.
The result of the transmission is different in the excitor nerve
from what it is in the motor nerve. The result differs also in
the excitor nerves according to circumstances. In some cases
it is accompanied with actual sensation, while in others it is
not. That is, the brain sometimes participates in the result,
and sometimes it is confined to the spinal marrow. Thus, in
the act of respiration, the impression carried from the lungs by
the excitor nerves comes from the presence of dark blood in the
lungs. Ordinarily, a mere impression, and nothing like sen-
sation, is transmitted. The respiratory muscles, most of the
time,' go on to do their work, in obedience to the impres-
sions communicated from the lungs, without the process being
recognized by the mind. But when there is embarrassment
in the lungs, the quiet process, carried on through the agency
of the spinal marrow alone, is not adequate to meet the exi-
gency. In some way, the brain becomes a party in the ope-
ration. The act of breathing is now accompanied with pos-
itive sensations, and there is a mixture of voluntary and
involuntary muscular action. So, also, the ordinary movements
of the stomach are attended with no positive sensations. That
is, there is no transmission to the brain of any impression of
which the mind takes cognizance. But if there be disturbance
there, and extraordinary movements are produced, then cogni-
zance is taken of them, and sensations of various kinds result.
257. The spinal marrow, in relation to the involuntary
muscles, seems ordinarily to be in a great measure independent
of the brain ; while on the other hand, in relation to voluntary
164 HUMAN PHYSIOLOGY.
The spinal marrow performs two separate functions.
motion and sensation, it forms the chain of communication be-
tween the brain and the moving and sentient parts. In this
respect the dependence is perfect. In injuries of the spine,
therefore, the extent of the loss of the power of motion and of
sensibility depends on the nearness of the injury to the brain.
The higher up the injury is, the larger is the number of nerves
whose connection with the brain is cut off, and therefore the
greater is the extent of body rendered insensible and motionless.
258. The spinal marrow then performs two separate functions
one, in producing involuntary motion, as an organ by itself;
and another, as an organ in connection with the brain, in the
production of voluntary motion and sensation. The arrange-
ment, by which it does two things which are so different from
each other, will be clear to you, if you bear in mind the fact
that the spinal marrow, like the brain, is composed of the two
nervous substances, the white tubular, and the gray vesicular sub-
stance. When the spinal marrow acts as a mere medium of
communication for the brain, the transmission is made directly
through the tubes of the white substance to and from the brain
to the brain in sensation, and from it in voluntary motion.
Thus, when a sensation is felt in the foot, the impression made
there is transmitted through the nerve to the spinal marrow,
and up through the white part of this organ to the brain. It
touches none of the gray substance of the spinal marrow, but
goes to the gray substance of the brain. And when the foot is
moved, an impression is returned from the brain through the
white part of the spinal marrow, and then through the nerve
which goes from it to the muscles that move the foot. But, on
the other hand, when the spinal marrow acts by itself, inde-
pendently of the brain, producing what is called reflex action,
( 255,) the impressions that are transmitted, some of them
begin, and some end in the gray substance of the spinal
marrow. The impression on an excitor nerve ends there, and
the impression on a motor nerve begins there, the latter result-
ing from the former, except when motion is produced by dis-
ease in the spinal marrow itself. Thus, in breathing, as de-
scribed in 255, an impression goes from the lungs through
excitor nerves to the gray substance, and that is the end of it ;
but another impression begins there as a result of it, and is
transmitted to the involuntary muscles moving the chest.
259. One marked distinction between the brain and spinal
marrow is, that the . brain has its intervals of rest ; but the
functions of the spinal marrow never cease for a moment as
THE NERVOUS SYSTEM. 165
The brain rests. The spinal marrow does not. Convulsions.
long as life continues. In sleep the brain is more or less at
rest, and it is in a state of entire torpor when the sleep is pro-
found. But during sleep the heart beats, the respiratory-
muscles work the chest, and the muscular coat of the stomach
churns the food if there be any there. For these motions, with
many others, are dependent upon the spinal marrow, and not
upon the brain; and so, while the brain sleeps, the spinal
marrow keeps up the operations of the system that are essential
to the continuance of life, in the manner described in 255.
So, also, in apoplexy, when the brain is torpid from the
pressure of blood, the spinal marrow, being unaffected, keeps up
the functions of those organs which are dependent upon it.
But besides the motions that I have mentioned, as being kept
up by the spinal marrow, when the brain is torpid from any
cause, there are other motions which can be excited by stimu-
lating nerves that are connected with the spine. For example,
the act of swallowing can be produced by pouring a liquid into
the mouth, and motion can be produced in the muscles of a
limb by irritating the limb at different points. If you cut off
the head of a frog, and thus destroy all sensibility, you can
produce movements in his limbs by irritating them. You
can, indeed, make the whole body to move together, by
producing irritation at many points at the same time. So, too,
if a man be paralyzed in his lower limbs by a blow upon
the spinal column, these parts, which he cannot move by his
will, can be excited to motion by irritation with electricity
or other agents.
260. The motions of the muscles in convulsions are pro-
duced by the agency of the spinal marrow. The irritation
causing them sometimes exists in the spinal marrow itself,
being the result of disease there. But commonly the irritation
is in some other part of the system, and it produces the con-
vulsive movements by sending an impression through excitor
nerves to the spinal marrow, to be reflected back through the
motor nerves, as described in 255. The brain during the
convulsion is in a torpid state, the individual being uncon-
scious. That the brain is involved to some extent in the con-
vulsion is very clear, and sometimes the cause of the convul-
sion is in this organ. But it is probable that the convulsive
movements are directly dependent on the spinal marrow, and
that even when the cause is in the brain, it is by the action of
the spinal marrow, sympathizing with and affected by the
diseased brain, that the convulsion is produced. And when
166 HUMAN PHYSIOLOGY.
Involuntary action of voluntary muscles. How produced.
the cause is in some other part, as in the irritation of teething
or indigestion, the impression is sent directly to the spinal
marrow, and is reflected from it to the muscles, the brain being
only secondarily affected.
261. It is worthy of remark, that in convulsions there is a
purely involuntary action of muscles, that are ordinarily under
the control of the will. How is this ? How are they taken
away from the usual control of the will so suddenly and so
entirely ? It is not possible that any temporary new connec-
tions can be established all at once by the disease, that there
is, to use illustrations of a familiar character, a sort of unship-
ping of the usual connection, and a hitching on of another for
the time being, or a switching off from one track on to
another. These voluntary muscles must have all the time a
connection with the gray substance of the spinal marrow, just
as the involuntary muscles have, only it is not as intimate and
extensive. If it were not so, they could not act occasionally a9
involuntary muscles. Being thus connected with the gray
substance, both in the brain and spinal marrow, when they
act in obedience to the will, the impression exciting their ac-
tion comes to them from the gray substance in the brain
through the white part of the spinal marrow ; but when they
act involuntarily, the impression comes from the gray sub-
stance in the spinal marrow, and not from the brain.
262. I may remark farther, that the voluntary muscles act
involuntarily more often than is commonly supposed. As
already stated, (259) in animals, from which the head has
been removed, the voluntary muscles can be excited to involun-
tary action, resembling voluntary movements, although of
course with the removal of the head were destroyed all sensa-
tion and all exercise of the will. And in the case of the man
paralyzed by injury in the back, alluded to also in 259, in-
voluntary movements can be excited in the voluntary muscles.
A pigeon, whose cerebrum had been removed, would fly when
thrown into the air, would run when it was pushed, and would
drink when its beak was put into water. There was no sensi-
bility and no will in this case, for they can not be without the
cerebrum. The movements were involuntary, though per-
formed by voluntary muscles. Now as these facts prove that
voluntary muscles are, through their connection with the spinal
marrow, capable of acting as involuntary muscles also, the
question arises, whether they do not much of the time act in
part as involuntary muscles, and sometimes wholly so. That
THE NERVOUS SYSTEM. 167
Walking. Reverie. Brain not directly essential to life.
this is the case, a little reflection will show. When we are
walking we use voluntary muscles. But manifestly a distinct
act of the will is not put forth for every motion performed
in walking. The mind may be at the same time fixed upon
something else ; and there seems ordinarily to be only an oc-
casional action of the will, as when we change our course, or
when some obstacle is in the way, requiring a variation from
the regular consecutive series of movements. There is a dis-
tinct action of the will when the movements begin ; but after
this the motions seem for the most part almost automatic, and
are probably produced by the reflex action of the spinal mar-
row, the will interfering only when occasion requires. This is
more manifestly the case when one is walking in a reverie, and
perhaps finds himself on awaking from it, in a different place
from that to which he had willed to go. It is as if the brain
set the machinery of the limbs to work, and then delivered it
over to the care of the spinal marrow, interfering only when it
needs to do so to meet some difficulty, or when it wishes to
give a new direction to the movement, or to stop it. And in
a reverie, the brain occupied with other things, neglects even
to exercise this superintendence, and leaves the machinery
wholly to the guidance of the spinal marrow. The same re-
marks can be made in regard to other motions, as in speaking,
singing, playing on an instrument, &c. In all these cases the
voluntary muscles act in some measure involuntarily, being
governed by an association in their action which is far from
being wholly dependent upon the brain, and the direction of
the will. I shall recur to this point again, when I come to
treat of the connection between the mind and the body.
263. Many experiments have been tried upon animals in
reference to the functions of the brain, and of the spinal mar-
row. I have already alluded to some of them. It was
formerly supposed, that the brain was the only centre of nerv-
ous power, and that it was immediately essential to the pre-
servation of life. But these experiments have shown that this
is far from being the truth. The brain, it has been found, has
nothing to do directly with the maintenance of life. Animals
live for some time after the brain is destroyed. A pigeon was
kept alive for some months after its cerebrum was removed.
Its condition was very much like that of a man, the functions
of whose cerebrum are suspended by the pressure of a frac-
tured portion of the skull. Although, like him, the animal
had lost all sensation and voluntary motion, yet, like him, it
168 HUMAN PHYSIOLOGY.
Upper part of the spinal cord directly essential to life.
continued to breathe, and its heart continued to beat. Of
course so extensive an injury of so important an organ will at
length cause death ; but life continues long enough in such
cases to show, that this organ is not immediately essential to
its continuance. The functions most essential to life, the
respiration and circulation, are, as you have seen, "kept up by
the spinal marrow. The very upper part of this organ is espe-
cially devoted to this purpose. You may take out the brain
of an animal, and destroy all its spinal marrow, except this
upper portion of it, and the animal will still breathe, and its
heart will beat. But if you destroy just this small portion of
the spinal marrow, though you leave the rest of it and the
brain untouched, the animal will die at once from the cessa-
tion of the respiration and the circulation. In the Spanish
bull-fight, when the matadore at length kills the animal, by
adroitly piercing the spine in the back of the neck, he inflicts
his wound upon this upper part of the spinal marrow.
264. If after cutting off the head of a frog, you divide the
spinal marrow in the back, you can produce involuntary mo-
tions in both the upper and lower extremities. But you can not
produce them at the same time in both together, for the divi-
sion of the spinal marrow in the back separates it into two
independent parts. When, therefore, you irritate the upper
extremities, the motion is confined to them, and the lower ex-
tremities are quiescent. And if you irritate the lower extrem-
ities, the motion produced there does not extend to the upper.
The division can be carried much farther with similar results.
If the spinal marrow be divided above and below where a pair
of nerves is given off, so as to separate this point wholly from
the rest of the nervous system, the reflex action can be excited
in the nerves connected with this point. That is, an irritation
of the parts supplied by the excitor nerve of this little segment
of the spinal marrow will produce an impression in that seg-
ment, which will be reflected by the motor nerve to the
muscles. The gray substance of the spinal marrow may, there-
fore, be regarded as a chain of little brains, in some measure
separate from each other. But while there are thus many
centres of reflex action, there is only one centre of sensation
and voluntary motion, and that centre, the brain, is connected
with the mind. Some physiologists have maintained that
there is sensation independent of the brain; but it may be
considered as most abundantly proved, that it is through the
brain alone that the mind feels and acts, or rather that we
THE NERVOUS SYSTEM. 169
Two systems of nerves, cereoro -spinal and sympathetic.
know nothing in this world of a sentient and acting mind
existing without a brain.
265. The system of nerves which we have been examining
is termed the ccrebro-spinal, from its two great central organs,
the brain and spinal marrow. But there is another nervous
system, the functions of which are involved in much mystery.
It is called the system of the great sympathetic, or the sympa-
thetic system. Sometimes it is called the nervous system of
organic life, because it is so intimately and extensively con-
nected with the nutritive processes ; while the system that we
have been considering is called the nervous system of animal
life, because it regulates the functions peculiar to animals in
distinction from plants, sensation, and spontaneous motion.
While the sympathetic system is thus connected with the
nutritive processes, it is also supposed to be the means of effect-
ing the sympathetic connection between different parts of the
body, and to act as the medium by which the passions and
emotions of the mind produce their effects upon the functions
of the different organs. In this system there are many gang-
lions or little brains, which communicate with each other by
nerves. There is a chain of them along in front of the spinal
column, and there are two quite large ones in the abdomen.
This system has connections everywhere with the cerebro-spinal.
The purposes aimed at in the particular arrangements of this
system are as yet but little understood, and we probably never
shall know as much about it as we shall about the cerebro-
spinal system. The arrangement of the sympathetic system
differs very materially from the cerebro-spinal. It is a single
system, and has no symmetrical arrangement, while the
cerebro-spinal has throughout two halves which are precisely
alike.
I have thus described the arrangements and functions of the
nervous system to such an extent, as will prepare you for the
consideration of those subordinate organs, by which the pur-
poses of this system are accomplished. After treating of the
organs of locomotion, the voice, and the senses, I shall call your
attention again to this system, presenting some views of its
uses and connections, which you will then be better prepared
to understand.
15
170 HUMAN PHYSIOLOGY.
Bones the framework of the body. Composition of bone.
CHAPTER XI
THE BONES.
266. THE bones furnish the points of support and attach-
ment for the muscles which move the different parts of the
body. They are, therefore, the passive instruments of loco-
motion. I treat of the bones before the muscles, because you
will then better understand the action and the arrangement
of the muscles.
267. The bones, forming the framework of the body, not
only furnish points of support and attachment to the muscles,
but in many cases serve to defend important organs from in-
jury. Thus, the soft brain is thoroughly secured from harm
by being inclosed in the skull ; and the lungs are surrounded
by walls of bone so arranged, as you saw in the chapter on
Respiration, that, while they defend the lungs from external
violence, they secure a wide range of motion for the necessary
expansion of these organs.
268. The bones are composed of two parts, the earthy or
hard portion, and the animal portion which is soft. Each of
these portions, as was stated in 60, can be obtained separate
from the other. These two portions of bone exist in different
relative proportions in the different periods of life. In the
child the animal portion predominates, while the mineral
does in old age. It is a wise provision in regard to the
child, for if his bones were as brittle as those of old age,
or even as those of middle life, they would be often broken
in the falls to which the child in its feebleness and carelessness
is subjected.
269. There are some points of interest in relation to the
structure of bone and its growth. I stated in 61 that bone is
generally formed in cartilage, the cartilage being formed first as
a mould for the bone. Bone is deposited in two forms, solid and
cellular. In the flat bones, as in the skull, the cellular struc-
ture lies between two plates of solid bone. In the long bones
the cellular part is at the two ends, and is covered with a
thin plate of solid bone, while the shaft is a hollow tube
vith the bone very much condensed. This arrangement
THE BONES.
171
Structure of bone. Long bones hollow. Marrow.
is seen in Fig. 83, representing
the thigh-bone and the bone of the FIG. 83.
arm. Certain well known mechanical
principles are observed in this arrange-
ment. The bone would be unneces-
sarily heavy if it were solid through-
out. Lightness in a moving limb is
of considerable importance. At the
same time strength is to be carefully
provided for in a bone which is to
sustain the weight of the body, and
to which the large muscles of the
thigh are attached. By having the
bone hollow, both of these objects,
lightness and firmness, are secured.
The principles involved are recognized
by the architect in the construction
of pillars, and we see them exemplified
in the hollow stalks of plants. The
hollow pillar has more strength than
the same quantity of matter would
have if in one compact mass ; and
the stalk which supports the full clus-
ters of grain, would break under its
load as it moves back and forth in
the wind, if it were solid instead of
being hollow. But the round cavity
of the shaft of the bone does not
extend to the ends. These are ne-
cessarily large, in order to present broad surfaces for articu-
lation with the neighboring bones ; and strength and light-
ness are secured in this case by a cellular arrangement of the
bony matter, the outer plate of solid bone being comparatively
thin. There is obviously more firmness in the resistance to
shocks or pressure, secured in this way, than there would be if
the bony matter were all consolidated into a shell containing a
cavity.
270. The round canal in the shaft and the cellular structure
at the ends are filled with an oily substance called marrow.
This, like all other fatty substances, is contained in fat cells, as
described in the chapter on Cell-Life. The marrow is also
present in the cellular structure between the plates of the flat
bones. The cavities and the cells in bones have branching
172
HUMAN PHYSIOLOGY.
Mode of nutrition in bones. No bloodvessels in their solid parts.
about in them bloodvessels, which are branches of arteries and
veins that enter the body of the bone at some particular points,
in the long ones near the middle of the shaft. It is from these
bloodvessels, together with those that come from the mem-
brane investing the bone, called periosteum, that the bone is
nourished. But, although an artery runs through the body of
the bone, to branch out upon the walls of its cavity, none of its
branches enter the very substance of the bone. How then is
the bone nourished, that is, constructed and kept in repair?
The manner in which the material for this purpose is carried
to every point of the solid bone has been developed by the aid
of the microscope, and I will describe it to you. If we cut
across the solid portion of a bone, and examine it with a
microscope, we see here and there orifices of certain minute
canals that run lengthwise of the bone. These canals are
found to communicate with the cavity of the bone and receive
therefore blood, or some of the constituents of the blood, from
the bloodvessels which are situated there. These orifices, as
seen under the microscope, are represented in Fig. 84. Around
these orifices a a, you see little dark spots arranged in rings,
with lines running to them from the orifices. By magnifying
the section of bone still more, we see what these spots and lines
are. The dark spots are small cavities, and the lines are
minute tubes running to them. In Fig. 85 is a representation
of this arrangement as seen in a little portion of the section of
bone, more highly magnified than it is in Fig. 84. The
FIG. 84.
SECTION OF BONK.
THE BONES. 173
No sensibility in bones. Variety of shape.
tubes pass out from the canals to the rows of cavities which
are around the canals, and thus a circulation is kept up at
every point of the solid bone. It is supposed that the blood
itself does not circulate in these little channels and cavities
in the solid bone, but a fluid containing the constituents of
bone. For these channels are too small even to admit the
cells which the microscope shows us as swimming in the blood.
The fluid that circulates in them is selected from the blood,
which is contained in the bloodvessels in the cavity of the
bone, and in the periosteum that envelopes it.
271. It is a very common popular notion, that the bones are
endowed with great sensibility, and especially the central part,
the marrow. The surgeon is very often asked if the sawing of
the bone in amputation is not very painful, and if when the saw
reaches the marrow it does not produce agony. But the
'hones have in their healthy state no perceptible sensibility, as
I have before stated, and the sawing of the bone in amputation
occasions no suffering. When, however, a bone becomes in-
flamed, severe pain is one of the symptoms. And it is well
that it is so ; for if it were not, disease might go on to pro-
duce disastrous results in a part so covered up by others, with-
out any warning of the danger of the case.
272. The bones are of every variety of shape, to suit the
various offices which they are to fulfill. You will see this to be
true, as you cast your eye over the skeleton as represented in
Fig. 86. You first observe the somewhat round box of bones,
which contains the brain, and at the same time furnishes
sockets for the eyes, extended irregular surfaces for the appara-
tus of smelling, and for that of the taste, a place for the organs
of hearing, and at its lower part, in connection with the lower
jaw, a mill for grinding the food. Then you observe the many
bones of the thorax or chest, containing and protecting the
heart and the lungs. The spinal column, k, composed of
twenty-four bones, you see as a firm but movable pillar, ex-
tending the whole length of the body, and having its base
firmly planted upon that stout thick bone, the sacrum, which
is wedged in so tightly like the key-stone of an arch, between
the broad spreading bones on either sida. To this pillar are
strongly fastened the walls of the chest ; and from the chest
thus supported by the spine hang the lax front and lateral
walls of the abdomen. Then below you see the pelvis, as it is
called, a set of large bones so arranged in a bowl-form, as to
offer a broad surface of support to the contents of the abdomen.
15*
174
HUMAN PHYSIOLOGY.
The bones of the skeleton.
FIG. 86.
SKELETON.
THE BON*,S. 175
Bones of the cranium and the face.
The bone called the ilium, m and I, on either side, with its
flaring upper surface, is especially serviceable in this way.
The pelvis also furnishes a socket for the round head of the
thigh bone s, and points of attachment for the large muscles
that move the lower extremity. You observe the large bones
of the thigh and leg, intended to give firmness to the lower
extremity, and the lighter bones of the arm and forearm, fitted
for extent and quickness of motion. And finally, you notice
the numerous bones of which the hand and foot are made up,
giving them with the intervening cartilaginous coatings, great
elasticity, and vast variety of motion, especially in the hand.
273. I will notice with some particularity some of the
bones, of which I have given a general description, as they are
united together to form the whole skeleton. I can not notice
them all, nor dwell upon every point of interest, for this would
require much more space than I can devote to the subject. I
shall, therefore, select those points which can be made most
clear and interesting.
274. I first call your attention to the bones of the head, as
you see them in Fig. 87. There are twenty-two bones in the
whole head. Fourteen of these belong to the face, while eight
belong to the cranium, that is that part of the skull which in-
closes the brain. Of these, notice particularly the large bone
in front called the frontal bone, a, making the forehead, and
below forming the upper portion of the orbits of the eyes ;
the parietal bone, b, the upper lateral part of the dome of the
FIG. 87.
BONES OF THE HEAD.
176 HUMAN PHYSIOLOGY.
Why so many bones in the skull. The two tables, and the sutures.
skull ; and c the temporal bone on which the parietal bono
rests. There is a large bone in the rear forming the back of
the cranium as the frontal bone does the front. There are
also two bones in the base of the cranium which are out of
sight in this view of the skull. You may, perhaps, be disposed
to inquire why this box for holding the brain, should be made
of so many bones. One reason is, that the enlargement of the
skull from infancy to adult age is effected more easily and
better than it would be if the cranium were one bone. Another
reason is, that even in the adult, in whom these bones are at
length so tightly united, violence is less apt to produce injury,
from the giving, as it is expressed, of the bones upon each
other, than it would be if one bone made the whole structure.
And this is especially true of the child, in whom the bones are
very imperfectly united. Hence it is that the frequent falls of
children upon their heads so seldom do any injury.
275. The principal bones of the head are composed of two
solid plates, while the bony matter between these plates is ar-
ranged in a cellular or sponge-like form. The outer table or
plate (for both of these terms are used in relation to it) is
rather rough, and in some parts has ridges for the attachment
of muscles. But the inner plate is very smooth on account of
the soft delicate organ that is contained in the cranium. It is
so brittle that it has been called the vitreous table, from its re-
semblance to glass in this respect. The modes of the joining
of the bones differ in the two tables. In the outer table the
joining is by a minute dovetailing, called a suture. Numerous
little projections from one bone fit accurately into correspond-
ing spaces in the edge of the other. This is very well repre-
sented in Fig. 88, in which you see the sutures on the top of
the skull ; b being the suture which is formed between the
two parietal bones ; a a, that between the parietal and the
frontal bone in front ; and c c, that between the parietal and
the bone which forms the back of the cranium. A better
joining for bones of such a shape as these have can not be con-
ceived of. But the inner table is joined differently. It is so
brittle that the small projections of the dovetailing mode of
joining would not answer here, for they would break very
easily. The joining accordingly is in this case by smooth
accurately fitted edges, somewhat beveled, so that one slightly
overlaps the other.
276. The upper part of the cranium is in the shape of a
dome, and is constructed upon the same principles that such
THE BONES. 177
The cranium a dome. Contrivances for giving it strength.
FIG. 88.
SUTURES IN THE SKULL.
structures are in regard to resistance to pressure or violence.
Just as in the domes that are built by man, so in this dome
of the cranium, great strength is secured around the lower
part, so as to resist outward lateral pressure. In the dome
of St. Paul's there is a double iron chain around its base
for this purpose, of course concealed from view. In the head
of man the dome may be considered as composed of the
frontal bone in front, the parietal bones at the side, and the
occipital bone in the rear. In front you see the base of
the dome strongly fortified, in the heavy arches that form the
upper part of the sockets of the eyes, and on the jutting edges
of which are the eyebrows. In the rear the base of the occi-
pital bone is very thick, and is fortified with ridges which
furnish attachment to the large muscles in the back of the
neck. But the most marked and interesting contrivance for the
strengthening of the base of this dome is at the side. It is where
the parietal bone 6, as seen in Fig. 87, is joined by the temporal,
c. The joining here is not by suture, for that would afford no
resistance to lateral pressure, either outward or inward. To
secure this object, the lower bone, the temporal, laps over the
upper, the parietal, with a beveled edge. It abuts upon or
against it It has the relation to the parietal of a buttress to
178 HUMAN- PSYSIOLOGY.
Defenses of the brain. Many and efficient.
an arch. You can readily see that when great pressure is
made on the top of the head, as when a heavy load is carried
there, there must be a tendency to outward lateral pressure at
the base of the dome of the cranium, and that this is effectually
resisted by the temporal bones acting as buttresses. The same
thing is true, also, when a blow is inflicted on the top of the
head. And if a blow be received at the side of the head, on
the temporal bone, it is evident that the bones will not be so
apt to be fractured and pressed inward upon the brain, as they
would be, if they were united by suture.
277. You are now prepared to see, to what extent the brain
is guarded against the effects of violence inflicted upon the
head. These effects come either from fracture of the bones,
or from concussion without fracture. In either case the vibra-
tion of the parts concerned is the cause of these effects. The
guards of the brain defend it from injury by lessening or dif-
fusing this vibration. And it is to be observed, that when
vibration passes from one texture to another, it loses some of
its force in the change. No two substances vibrate just alike ;
and when a vibration in one is communicated to another, it is
modified, and is therefore lessened. Some substances modify
and lessen vibrations communicated to them more than others
do. If you apply these principles to the effects of violence on
the head, you at once see that the brain would be much more
apt to receive a dangerous shock from the vibration occasioned
by a blow, if its coverings were condensed into one firm and
thick layer of substance, than it is now. So also, if the bones of
the head were in one solid layer, instead of having two layers, or
plates, with the spongy structure between, and the integuments
were all consolidated into one thick substance, there would be
much more liability to fracture than there is with the present
arrangement. Observe now how many, and how various are
the textures, through which the vibration of a blow must pass,
before it reaches the brain. Outside of the bone there is first
the hair ; next comes the skin ; then there is the cellular mem-
brane containing some fat; then a muscular coat; and lastly,
the lining membrane over the surface of the bone. These
various textures must deaden very much the force of a blow,
and especially the outer cushion of hair, and those inner
cushions, as we may call them, of fatty cellular membrane and
of muscle. Then, when the vibration reaches the bone, it is
lessened by the two plates with the intervening cells, and
there is diffused largely among the many bones that unite with
THE BONES. 179
Skull especially guarded at some points.
the one on which the force comes. Then as the shock goes
into the brain, it is still farther lessened by the membranes
which cover that organ. These greatly diminish the vibration,
precisely as a coating of leather on the inside of a bell would
deaden its vibration when produced by a blow upon the out-
side. With all these provisions the result is, that comparative-
ly few of the blows received by the head do harm. The skull
may be considered as a sort of helmet for the brain, its effect-
iveness as a defense being very much increased by its cover-
ings and linings.
278. There are some ^special guards at particular points in
the cranium, where there is much liability to exposure to
violence. Thus, as the lower part of the frontal bone, where
the eyebrows are, is especially exposed, the distance from the
surface to the brain is made considerable by an intervening
chamber in the bone, called the frontal sinus. This sinus,
which varies much in size in different individuals, is lined with
a membrane, and communicates with the nose. You can see
that this arrangement is a great protection to the bone at that
point. The outer plate could be broken, while the inner is not
injured. But the protection which this arrangement affords,
is not confined to that single point ; it serves also to deaden
the vibration of a blow received by any part of the forehead,
or by the forehead as a whole. The side of the head, too, is
peculiarly exposed to blows. And, therefore, the skull is
peculiarly guarded at this point. Beside the overlapping of
the temporal bone upon the parietal, to which I have before
alluded, the parietal bone is made thicker at its lower part,
where it is most liable to be struck, than it is in most of the
other parts of it. Then, too, the place of joining of the
temporal and parietal bones is covered over by a thick muscle,
the contractions of which you can feel if you press your
fingers upon the temple while moving the lower jaw as in eat-
ing. This cushion of muscle is of great use in breaking the
force of a blow received in that quarter. Other points might
be specified where there is arrangement for special protection,
but, those to which I have alluded will suffice.
279. The cranium not only contains and protects the brain,
but it at the same time serves various other purposes, and pro-
tects other important organs. The tender and delicate eye has
there a bony socket with jutting prominences all around it, to
guard it against violence. The exceedingly minute and com-
plicated apparatus of the hearing is also carefully protected fry
180 HUMAN PHYSIOLOGY.
Complicated and extensive cavities in the nose.
the skull, and the most important part of it is furnished with
winding and intricate apartments, halls of audience, in that part
of the temporal bone which is so hard, that it is called the
petrous or rock-like bone. To the bones of the cranium are
attached in various ways, the fourteen bones of the face. All
these, with the exception of the lower jaw, are immovable.
The two principal of them are the upper jaw bone, and the
cheek bone. The former makes with its mate of the other
side the forward portion of the roof of the mouth, the palate
bones making its rear portion ; and it furnishes the sockets for
the teeth. It also at its upper part nmkes nearly the whole^of
the floor of the orbit of the eye. Trie cheek-bone forms the
outer lateral part of the socket of the eye, and sending back a
process or projection to unite with one from the temporal bone,
c, Fig. 87, forms the zygoma or arch, inside of which the tempo-
ral muscle passes down to be fastened to the lower jaw. The
bones of the nose make quite a complicated series of cavities,
for the purpose of presenting, in the mucous membrane, which
lines them, a large surface, over which the nerve of smell is
expanded. A representation of these cavities is given in Fig.
89 ; in which a is the mouth ;
6, the opening into the nos-
tril ; c?, a part of the base of
the skull ; c, the communica-
tion of the nostril with the
back of the throat ; e, the cur-
tain of the palate ; /, the front-
al sinus ; m, another large si-
nus ; ^, i, A, spongy bones pro-
jecting into the cavity of the
nostril. There is a large sinus,
that is not seen in this figure,
which lies over the teeth in e a
the jaw-bone. The different INNER BONES OF THE NOSE.
sinuses are lined with the mu-
cous membrane extending into them from the nose. These, with
the spongy bones make a very large extent of surface in the
cavities devoted to the sense of smell. The branches of the
nerves of smell enter these cavities, to be distributed over
thin walls, through many small openings in a bone in the
r oof of the nose, giving it a sieve-like appearance.
280. The lower jaw is a bone shaped something like ahorse
shoe, with its ends turned considerably upward. It has two
THE BONES.
181
Structure of teeth. Three different kinds of texture.
smooth projecting surfaces which articulate with two corres-
ponding shallow cavities in the temporal bone. Its prominence
at the lower part in front, the chin, is peculiar to man, there
being no such prominence in any other animal. The lower
jaw has sockets for the teeth, and it is so constructed, and is
so arranged with muscles, that these teeth can be brought to
bear against the teeth of the upper jaw in cutting and grind-
ing motions.
281. The teeth are very nearly like the bones in their
structure, but they differ from them in some particulars which
it will be interesting to notice. Every tooth has in it three dis-
tinct structures, which differ in hardness, for reasons which will
appear clear to you as I proceed. The dentine or ivory consti
tutes the body both of the tooth and of its fangs. In the body
of the tooth there is a coating of that very hard substance, the
enamel, over the whole surface of the ivory. This is thickest
over the top of the tooth, and grows thinner on the sides till
it is entirely gone where the gum begins. The ivory in the
fangs has a coating of a very different character, called the
cementum. It is not hard like the enamel. This arrangement
is represented in Fig. 90. This is a tooth with two fangs or
roots; 1, is the enamel; 3, the den-
tine or ivory : 2, and 7, the cement-
um ; 4, an unnatural enlargement of
the cementum, making an excres-
cence ; 5, the cavity of the tooth
supplied with bloodvessels and nerves
which come through the channels
that you see running up the middle
of each fang. This cavity is analo-
gous to that which is found in the
shafts of the long bones as seen in
Fig. 83. The ivory and the cement-
um are seen b^the microscope to be
very differentmextures. The ivory
is traversed by innumerable branch-
ing tubes running from within out-
ward towards the cementum, as
represented in Fig. 91. This is a
section of a small portion of the
dentine anc 1 cementum in the fang of a tooth, very much mag-
nified, a, a, btaiig the dentine, and c, c, the cementum, evidently
a different structure. The structure of the enamel as exhibited
16
FIG. 90.
Vertical
SECTION OF A TOOTH.
182
HUMAN PHYSIOLOGY.
How teeth are different from bones, and why.
FIG. 91.
by the microscope is represented in Fig. 66 and 67, in the
chapter on Cell-Life. I have been thus particular in the
description of the parts of a tooth, that you may see how
compound even so apparently simple a part of the body is.
The three different structures in it are built by cells, and the
cells of each part select from the blood such constituents as
are needed for their purpose.
282. A tooth differs from a common bone in one import-
ant particular when once formed it is never altered in its
size. A bone grows with the growth of other parts of the
body ; but a tooth, when it first protrudes through the gum is
as large as it ever will be. The reason of this is, that so
hard a substance as enamel can not be made changeable as
bone is. Its hardness is inconsistent with any thing like cir-
culation in it, and without circulation there can be no change.
If the enamel were not needed, and the teeth could be com-
posed only of dentine, they could grow as other bones do.
And if they could grow, one set of teeth might be made to
answer the purpose. As it is, the second set ar.e needed, be-
cause as the jaws grow, the first set are neither ISrge enough in
proportion to the size of the jaws, nor numerous enough to
fill up the whole space. If the first set were to be the only
set, when the jaws became of their full size, the teeth would be
altogether too small, and would be quite separated from each
other. Twenty small teeth (the number of the first set) in the
jaws of an adult, in place of the thirty-two large teeth of the
second set, would present a very odd appearance, besides being
incapable of doing the service required of them.
THE BONES. 188
Hyoid bone. Patella. Spinal column. Its firmness and flexibility.
Under the lower jaw is a, little bone, called from its resem-
blance to the Greek letter v, the hyoid or u-like bone. Its
round end is towards the root of the tongue, and its two ends
reach backward towards the spine. The larynx is suspended
from it as from a frame, and the muscles that draw up thig
bone, draw up the larynx with it. It is one of the few bones
in the body that are not directly connected with any other
bone. The patella, or kneepan, is one of these bones. The
four little bones in the ear, of which I shall speak particularly
when I come to treat of the sense of hearing, are not connected
with any other bone.
283. I pass now to the bones of the trunk of the body. I
shall speak first of the spinal column, or the backbone, as it is
called in common language, as if it were all one bone. In
some respects it does act as one bone, although it is made up
of twenty-four distinct bones. It is the great pillar of the
body. As such, it has the head resting on its top, and it fur-
nishes support for the walls of the chest, and for the muscles
which make up the most of the walls of the abdomen. To it
also are fastened, as you have seen in the chapter on Digestion,
the mass of intestines in the abdomen, and indeed to some ex-
tent all the viscera both of the abdomen and the thorax. Sus-
taining, therefore, as it does so much weight in so many ways,
it stands firmly planted on its great pedestal, the strong broad
bone of the pelvis, the sacrum. And this pedestal is supported,
as I have before said, after the manner of a keystone, between
the lighter spreading bones of the pelvis on either side. But
while the spinal column acts as a strong and firmly supported
pillar, it is necessary that it should loe flexible for the different
motions of the body. It is therefore composed of twenty-four
bones called the vertebra, so that, as in any considerable motion
of the column as a whole, there is but little motion between
any two of them, the motion does not interfere with its office as
a firm pillar. It is most free in its uppermost part, the neck ;
it is considerable in its lower part, the small of the back ; and it
is least of all in that part to which the ribs are joined. You
readily see the reasons for this difference in motion in different
parts of the column. For the varied motions of the head there
is need of a free movement between the vertebrae. Then for the
twisting and turning motions of the body, you have the free
movement between them at the lower part of the column,
which is easily provided for there, because there are attached to
that portion of it nothing but parts that are pliable. It is not
184 HUMAN PHYSIOLOGY.
Vertebrae. Processes for locking strongly together.
so with that portion of it that forms the supporting pillar of the
framework of the chest. There is little motion here between
the vertebrae, because the joining of the ribs to the column
forbids it.
But besides serving as a firm pillar, and as a flexible chain,
the spinal column also forms a canal or tube in which the
spinal marrow, one of the most delicate and important organs
in the body, is securely lodged. This canal extends through its
whole length, and from the spinal marrow included in it there
pass out the nerves to go to all parts of the body.
284. Having thus presented a general view of the spinal
column, I will now give a particular description of the form
and arrangements of the bones of which it is composed, so that
you may understand how the various objects of this wonderful
structure are secured. In Fig. 92 you see a representation of
A SIDE VIEW OF A VERTEBRA.
A VERTEBRA.
one of the vertebrae ; a, being the body of the bone ; 5, the hole
which forms this vertebra's part of the canal for the spinal
marrow ; and c, the spinous process. It is these spinous pro-
cesses that make the row of projecting points seen down the
length of the back. There are six other processes, only four of
which you can see in the figure. Four of these processes serve
to lock the vertebra with its two adjoining ones above and
below, which they do so strongly, that there can be no disloca-
tion of them without a fracture. Fig. 93 gives a side view of
a vertebra. Strong ligaments bind these bones together, and
there are very numerous muscles attached to the processes, so
THE BONES.
185
Spinal column. Canal through it. Cartilages.
that this jagged column of bones is very thoroughly enveloped
in softer substances.
285. In Fig. 94. you see the whole FIG. 94.
spinal column with the sacrum on which
it stands. It is laid open by a verti-
cal section dividing it into two halves, so
as to show the manner in which the bones
form the tube that contains the spinal
marrow. The darkly shaded strip through
the length of the figure represents this
tube. It extends, you see, down beyond
the limits of the column itself through the
sacrum. It is bounded in front by the
bodies of the vertebrae represented as sawn
through from front to rear, and by the
spinous processes behind also sawn in the
same way. In this canal you see there
is a row of little openings, arranged just
behind the bodies of the vertebrae.
Through these openings, each of which
is between two of the vertebrae, the nerves
go out from the spinal marrow. The ar-
rangement is such, that the nerves are
very securely guarded against the hazard
of pressure in the movements of the verte-
brae upon each other. You see also that
there are spaces between the bodies of all
the vertebrae. These are filled with car-
tilages, which vary in thickness in differ-
ent parts of the column, from one quarter
even to three quarters of an inch, being
thickest in the lower part of the back,
where the backward and forward motion ~*
of the vertebrae upon each other is the SPINAL COLUMN.
greatest. Each cartilage is firmly fas-
tened to the two vertebrae, between which
they are situated, by the rough surface of the body of the bono
which you see represented in Fig. 92. This arrangement of
cartilages is an important provision for the motion of the spinal
column. It contributes greatly to its flexibility. When you
stoop forward, all of the cartilages are compressed, and when
you rise up they return to their usual size by their elasticity.
And besides this, they serve to diminish any shock which
186 HUMAN PHYSIOLOGY.
Spinal column shaped so as to guard against shocks.
iniglit otherwise be transmitted through the column of bones
to the head with too great force. There is another guard
against the injurious transmission of shocks to the brain, in the
shape of the spinal column, the twenty-four bones being ar-
ranged, not in a straight line, but in a double curve. The
vibration, communicated upward through the spinal column, is
thus not only lessened by the elasticity of the cartilages, but is
also distributed in different directions by the curved arrange-
ment of the bones. If the column had been made straight,
the head would have been subject to frequent jars in the
movements of the body, which would be disagreeable and
often injurious.
286. You have thus seen how three different objects, ap-
parently incompatible with each other, are accomplished in the
arrangement of the spinal column. To put twenty -four bones
together in such a way, that they shall form a strong firm
pillar for the whole frame, and yet they shall make a column
or chain flexible enough for the various motions of the trunk
of the body, and at the same time provide in this column a se-
cure canal for the rod of nervous matter which moves all the
muscles of the body, is to produce a piece of mechanism which
far transcends any thing that has ever been contrived by the
ingenuity of man.
287. There remains to be noticed one especial contrivance
in the spinal column. It is at its summit, and it is for the
purpose of providing for the free motions of the head in various
directions, and at the same time securing the spinal marrow at
that part from all hazard of pressure from these motions.
These two objects are accomplished in this way. The head in
moving backward and forward rocks on two smooth surfaces on
the first vertebra. But when the head moves to the right and
left, this first vertebra moves along with the head on the second
vertebra. And there is a tooth-like process that projects up
from the second vertebra inside of the first, around which this
rotary motion is performed. In Fig. 95 is represented the first
vertebra. J. J. are the two surfaces on which the head rests,
and rocks backward and forward. A is the opening for the
spinal marrow. L is the strong ligament which confines the
tooth-like process that projects upward from the second verte-
bra. In Fig. 96 is the second vertebra. P is the tooth-like
process, around which the first vertebra rotates, carrying the
skull with it. You see it is smaller at its root than at its top.
This smaller part is bound firmly by the ligament in the first
THE BONES.
187
Arrangement of first and second vertebras.
vertebra. It is shaped thus to prevent its slipping out from the
ligament. J, J, are the two surfaces on which the first verte-
bra moves as it rotates around the tooth-like process. Fig. 97
shows the two bones together, the tooth-like process being con-
fined in the ring of the upper bone. Special painsaretaken to
make this arrangement secure, that the process may not be
in danger of pressing upon the spinal marrow at this important
point. It is thus that the lateral rotary motion of the head and
the forward and backward motion are secured by two joints,
just as is done in the mounting of a telescope. The difference
between the two cases is, that in the mounting of the telescope
there are no difficulties to overcome, while in arranging the
FIG. 95.
FIRST VERTEBRA.
FIG. 96.
FIG. 97.
First and Second
VERTEBRAE TOGETHER.
SECOND VERTEBRA.
188 HUMAN PHYSIOLOGY.
Snecial defense of spinal cord in neck of birds.
mounting of the head, as we may term it, a peculiar contrivance
and a nice adjustment are needed to prevent injury of a very
important organ. It is a wonderful contrivance, by which so
much and so varied motion can be effected in the very walls that
contain the soft and delicate spinal marrow, without injuring
it. You will fully appreciate this, if you observe the extent and
variety of the motions of the head and neck, executed chiefly
with the two bones that I have described.
288. In the neck of birds there is a contrivance of a different
character, for the arrangement which answers for the motions
required by man, obviously could not secure the very free mo-
tions which the bird executes with its neck. As the bird bends
its neck at such abrupt angles in all directions, a peculiar ar-
rangement of the vertebrae is necessary, to prevent the spinal
marrow from being pressed upon. The arrangement is a sim-
ple, but effectual one. I can make this plain
to you by the rough diagram in Fig. 98. A, A,
are two of the vertebrae of the neck laid open.
B is the spinal canal, and C is the spinal mar-
row. You observe that each vertebra is larger
at its ends than in the middle, allowing at the
joinings of the bones, where the motion is, a
considerable space between the bone and the
spinal cord. Now if each of these bones were
of equal size throughout, and the spinal mar-
row filled up the canal, you can readily see
that when any two of these were much bent SPINAL COLUMN
upon each other, there would be pressure upon
the spinal cord ; and pressure would produce palsy, and often
destroy life. But with the simple arrangement above described,
free motion, almost to a right-angle in some directions, can be
executed without pressing on the cord. And besides this, you
can see that the cord by this arrangement will not be bent at
an angle, as the vertebrae are, but in a curve, for the spaces in
the spinal canal at the joinings allow of a lateral movement of
the spinal marrow at these points.
289. It would be interesting to consider in full the variations
in the spinal column in different classes of animals. But I will
only allude to a few of them. In quadrupeds, as they have
their heads suspended, instead of being supported, as in man,
upon a column of bones, the spinous processes in the neck are
very large, and project much, for the attachment of strong
muscles which hold up the head and move it. There is also
THE BONES.
189
Spinal column in fishes, reptiles, and in neck of giraffe.
FIG. 99.
attached to these processes, a very stout fibrous ligament, com-
monly called the paxy-waxy, to assist in sustaining- the head.
In fishes the spinal column is so arranged as to
give it a great flexibility. In Fig. 99 is repre-
sented one of the vertebrae of a fish. If you
compare it with a human vertebra, as seen in
Fig. 92, you will see that it differs very widely
from it. It has no transverse or side processes.
While the human vertebra has one spinous pro-
cess that projects behind, this has two /,/, one
in front and one in the rear, or rather, according
to the usual position of the fish, one above and
one below. The body of the vertebra has a cup-
like cavity on each side towards its neighboring
vertebra. When, therefore, two of these vertebrae
are joined together, their two cup-like cavities make
one cavity of the shape of a double cone, as seen in Fig. 100.
This is a representation of a section
of a portion of the spine of a fish.
The division is made so as to cut
the vertebrae into two halves, and
thus show these cavities. Each
one of these contains a sac which
is filled with a gelatinous fluid.
FIG. 100.
This arrangement, Avhich secures
very great flexibility of the spinal
column, you can examine at any
time when you have fish on the
table. The long spinous processes
make the broad frame-work of the SPINAL COLUMN OF A FISH.
animal, to which its muscles are
attached. In reptiles there is still greater flexibility of the
spine than in fishes. This is secured in two ways, by the
great number of the vertebrae, and by a peculiar arrangement
of them. There are three hundred and four vertebrae in the
boa constrictor, over three hundred in the common ringed
snake, and over two hundred in the rattle-snake. The articu-
lations of the vertebrae in reptiles are with a ball and socket
arrangement. The forward part of each vertebra has a deep
cup-like depression, in which plays a round smooth ball from
the back part of the next vertebra. And as these joints are
firmly bound together by ligaments, the spinal column is very
strong as well as flexible. In the gracefully flexible neck of the
190 HUMAN PHYSIOLOGY.
Arrangement of collar-bone, shoulder-blade, and breastbone.
giraffe we have the same ball and socket articulations of the
vertebrae.
290. The framework of the chest I have already described
sufficiently in the chapter on Respiration. The breastbone,
which is flat and of simple form in man, is much larger and
less simple in its form in some animals. In birds it is not only
broader, but it has a keel-shaped projection for the attachment
of the large muscles used in flight. The clavicle, g, Fig. 86 (so
called from its resemblance to a key,) and commonly called
the collar-bone, is attached at one end to the top of the breast-
bone, and at the other unites with a process of the scapula, or
shoulder-blade at the top of the shoulder joint. It is a prop to
the shoulder, pressing it outward ; and accordingly it is large in
those animals, the movements of whose superior extremities
tend to bring the shoulders towards each other, while it is very
slender, or absent even, in those the tendency of whose move-
ments is to keep the shoulders apart. Thus in birds the
drawing down of the wings by the strong muscles would bring
the shoulders towards each other, were this not prevented by
stout clavicles. Sometimes a second bone is added for the
same purpose. But in the horse and other similar animals, the
pressure of the body downwards between the shoulders tends
to separate them, and here we find the clavicle deficient because
it is not needed. The scapula, or shoulder blade is a thin bone
with a stout raised spine or ridge running across it, and ending
in forming the top of the shoulder joint. It is situated differ-
ently from any other bone in the body. It is imbedded in
muscles and has a very free motion. Its design is to give free-
dom of motion to the arm. It is directly connected with the
skeleton only by its union with the clavicle. In Fig. 101 you
see the arrangement of the clavicle, scapula, and breastbone.
C, C, are the scapulae or shoulder-blades. A, is the upper part
of the breastbone. B, B, are the clavicles fastened to the
breastbone at one end, and to the shoulder-blade at the other
end at E, which is a process of the shoulder-blade, making the
projecting top of the shoulder-joint. D, is another process of
the shoulder which serves for the attachment of muscles and
ligaments. It is called the coracoid process, from its resem-
blance to the beak of a crow.
291. The upper extremity is divided into three parts, the
arm, the forearm, and the hand. The arm has but one long
bone, the humerus, i, Fig. 86. This has a round head which
moves in a shallow cup formed bv the shoulder-blade. The
THE BONES.
191
Collar-bones. Shoulder-blades. Bones of the forearm.
FIG. 101.
THE COLLAR-BONES AND THE SHOULDER-BLADES.
FIG. 102.
192 HUMAN PHYSIOLOGY.
Arrangement of the bones of the forearm for rotary motion. Bones of the hand.
shallowness of the socket is the cause of the frequent disloca-
tion of the shoulder. But if there were a deep socket like that
in which the head of the thigh-bone is, the arm could not have
any thing like the freeness of motion that it now has. Such an
arrangement would involve too much of a sacrifice of necessary
uses for the sake of security. At its lower part the humerus
makes a hinge joint with the forearm. The forearm has
two bones, the radius, b, Fig. 102, and the ulna, a. The par-
ticular arrangement of these two bones is worthy of notice.
The hinge-like motion of the forearm upon the arm is per-
formed by the ulna alone. This bone has a beak-like process,
which works over a smooth round surface at the end of the
humerus. It is the outside of this process which you feel at
the point of the elbow. The other bone, the radius, has
nothing to do with this motion. This only rolls on the ulna
in the rotary motions of the forearm. But at the other end of
these bones, at the wrist, the arrangement is reversed. Here, it
is the radius on which the hand moves in a hinge-like manner,
while the ulna at c rolls on the radius, as the radius does on the
ulna at the elbow. You can readily see that as the radius rolls
on the ulna at the elbow, and the ulna on the radius at the wrist,
a very free rotary motion of the forearm is provided for. The
combination of this motion with the motions at the wrist, the el-
bow, and the shoulder, secures that almost endless variety of move-
ment, which is so striking a peculiarity of the upper extremity,
as compared with the lower. The hand is divided into three
parts, the carpus, p, Fig. 86, composed of eight smaif bones,
the metacarpus, q, composed of bones which are like the bones
of the fingers, r. The eight bones of the carpus are firmly
packed together, but they have a slight motion upon each
other, and this, together with the motion of the metarcarpal
bones, makes the hand a more easy, light, and springy instru-
ment than it would be, if these bones were all consolidated into
one. The metacarpal bones are the framework of the flat part
of the hand, and to them are joined the first row of the bones
of the fingers. The metacarpal bone of the thumb has a very
free motion upon the carpus, differing in this respect altogether
from the metacarpal bones in the body of the hand. The
bones in the wrist and hand are bound together by very strong
ligaments. Those which are seen in the palm of the hand are
represented in Fig. 103. Those which you see at a, b, and c
bind the small bones of the wrist together, and also tie them
strongly to the bones of the forearm, the ends of which you see
THE BONES.
193
Ligaments of the wrist and the hand.
FIG. 103.
in the Figure. The bone at 6, to which so many of these liga-
ments are attached, is the prominent bone which you feel at the
beginning of the palm of the hand on the side towards the
body. The ligament g connects this bone with the metacarpal
bone of the little finger. At c?, df, are ligaments which running
across the hand bind the metacarpal bones together at their
beginning. At e, e, are similar ligaments where the bones of
the fingers join them. The bones of the fingers and thumb are
strongly held together by lateral ligaments, as seen at /,/.
The various ligaments of the wrist and hand permit a slight
motion between the bones ; and thus the hand has freedom
and ease in its motions while it is also a very strong and firm
instrument.
292. The lower extremities have some resemblance to the
upper in their structure and arrangement, but they differ from
them in some important respects. Here firmness is the chief
object, while freedom of motion is the great thing to be secured
in the structure of the upper extremities. The lower extremi-
17
194
HUMAN PHYSIOLOGY.
Bones of the leg and the foot. Arranged for firmness.
ties are chiefly for locomotion, but the upper are fitted for a
variety of purposes. The body is supported upon the lower
extremities, and, therefore, the thigh-
bones have sockets in the broad flar- FIG> 104>
ing bones of the pelvis m and /, Fig. 86.
In Fig. 104 is represented a rear view of
the thigh-bone. Its head, a, is round,
and fits into a deep socket in the
pelvis. At b is a depression in which
one end of a stout short ligament is
fastened, its other end being attached
to the bottom of the socket. At c is
the neck of the bone; at d and e are
two projections to which are attached
large muscles to move the limb.
Along the shaft of the bone, #, there
is a rough ridge, A, to which muscles
are fastened ; i and k are two smooth
surfaces for articulation with the leg
below. At t, Fig. 86 is the bone
called the patella or kneepan, which
answers as a defense to the joint,
and at the same time affords a
mechanical advantage to the muscles
which throw the leg forward. These
muscles are fastened to the upper
part of the patella, and then a con-
nection is formed by a strong tendon
between its lower part and the large
bone of the leg. You see at once
that the leg can be thrown forward
with more, force by this arrangement,
than it could be if the tendon of the
muscles passed over the front of the
joint without any patella. I shall
refer to this again in the Chapter on the Muscles. The leg,
like the forearm, has two bones, v and u, Fig. 86 ; but unlike
them they are constructed and arranged for strength, and not
for freedom of motion. The foot, like the hand, is divided into
three parts. The tarsus, a, Fig. 105, is that part of the foot
which extends from the heel to the middle of the foot. It is
composed of seven bones, the largest of which makes the body
of the heel. The metatarsus, p ? has .five long bones reaching
THE BONES.
195
Elasticity of the foot. Arrangement for oiling the joints.
FIG. 105.
from the tarsus to the toes. The toes, c, have fourteen bones*
The object of having so many bones in the body of the foot is
to give a certain springiness to it, which guards against shocks,
and facilitates motion. Its arched form also tends to secure the
same object. In every movement of the foot there is a slight
motion between all these bones. Thus in walking, when the foot
first touches the ground, it does so at the heel, as represented in
Fig. 105. Then as the body moves forward, the fore-part of the
foot is brought down, the weight of the body at length press-
ing upon the ground at the ball of the foot, b. In executing
this movement, elasticity is given to the tread of the foot by
the very slight motion which occurs between these many
bones. If the body of the foot were all one 'bone it would
manifestly be a very stiff and awkward affair, and ease and
grace in walking would be an impossibility. With such a foot
we should not walk much better than one does with a wooden
leg.
293. Before leaving the subject of the
bones, I will call your attention to the
provision which is made for the easy
movement of their joints. The ends of
the bones are tipped with cartilage, so as
to afford a firm but smooth surface for the
motion of the one bone upon the other.
Besides this provision, the ends of every
two bones that move upon each other are
lined with a membrane, so arranged as to
make a blind sac. This is illustrated in
Fig. 106, in which a and b are the ends
of two bones, the sac, c, lying between
them represented here as detached from
the bone, in order that the arrangement DIAGRAM
maybe clear to you. It is as if a small .bowing Aiming of j
FIG. 106.
196 HUMAN PHYSIOLOGY.
Each fibril of a muscle supplied by a nervous tubulus.
bladder were introduced between the two ends of the bones,
and were fastened all over the surfaces that press together.
The inside of this sac is kept lubricated with a bland fluid re-
sembling the white of egg, so that the joint may work easily.
This fluid is secreted by the membrane itself, and the moving
machinery of the human system may therefore be said to oil
its own joints. In the knee-joint, the broad surfaces of which
are subjected to so much pressure, there are two flat pieces of
cartilage loose in the joint, which operate like friction wheels in
lessening the friction. There is a similar provision in the
articulation of the lower jaw. This member does so much
work in talking, and such heavy work in mastication, that each
of its joints has a movable cartilage for the diminution of
friction. Sometimes when the lubricating fluid is deficient, or
becomes too thick, a disagreeable crackling noise is produced
by these cartilages in the motions of the jaw.
CHAPTER XII.
THE MUSCLES.
294. HAVING described the bones, I now proceed to speak
of the muscles, which move them and other parts of the frame.
I have already described the structure of muscles in 203 in
the chapter on Cell-Life. Each fibril, you there saw, is a chain
of cells, and it is the shortening of all these chains of cells in a
muscle that produces its contraction. The action of a muscle
is dependent upon the nerves. Each fibril has a nervous fibril
or tubulus, ( 232.) by which its connection with the brain or
spinal marrow is established. And each fibril is in this respect
probably wholly separate from every other fibril. When, there-
fore, the mind wills that a certain motion shall be performed,
an impression ( 232) is sent to each fibril of every muscle en-
gaged in that motion, through the tubulus devoted to that
fibril. When the action is a very compound one, calling into
operation many muscles, a multitude of these impressions are
communicated through a multitude of distinct channels or
tubuli. The individual is not at all conscious of the compound
nature of muscular action, and he knows nothing of the muscles
THE MUSCLES. 197
Relation of muscles and tendons. Their relative size.
which produce any particular movement, unless he has studied
anatomy and physiology. He wills the movement to take
place, and at once the requisite impressions are sent along the
appropriate channels or tubuli to their destination. These im-
pressions must differ in degree or intensity in producing differ-
ent amounts of motion ; and they must differ in some cases in
different parts of the same muscle, as some fibres are put in
motion while others are not, or as some act with more force
than others. I will not dwell here on this point, as I shall
recur to it in another part of this chapter, when I come to
speak of the compound character, and the varieties of motion.
295. Muscles commonly end in tendons, which, as they are
white and shining, are quite in contrast with the red muscular
fibres. The tendons have in themselves no power of contrac-
tion, but are mere passive cords. They have the same relation
to the muscles, that ropes have to the men that pull them.
They are of various shapes, according to circumstances. Long
and slender tendons may be seen on the back of the hand in
thin persons, the muscles that pull them being in the full arm
above. The tendons are not bounded by a distinct line where
they join the muscles, but tendinous and muscular fibres inter-
twine, so that they appear to run insensibly into each other.
Tendinous fibres also mingle in the same way with the fibres of
bone, making so strong an union, that a great force exerted in
pulling on the tendon will sooner effect a rupture of the tendon
or the bone, than a separation of the connection between them.
The tendons are very strong, being made of very condensed
fibrous substance. The tendon of a muscle is, therefore, much
smaller than the muscle itself. This is a circumstance of much
importance in the arrangement of the moving apparatus of our
frames. The bulky muscles and the slender tendons, are so
arranged, for example, in the limbs, as to give them both free-
dom of motion and beauty of form. The muscles that move
the fingers help to make up the full part of the arm, while
their slender tendons occupy but little space as they play over
the bones of the wrist. If there were no tendons, and the
muscles were extended to the parts which they move, the hand
would be a large cumbrous mass, instead of the light and agile
thing that it is now. For the muscles would of necessity be
continued of their full size, and, therefore, the bones would of
course be very large in order to afford an attachment to the
muscles.
296. In the action of the muscles upon the bones, we havo
17*
198
HUMAN PHYSIOLOGY.
The three kinds of lever exemplified in the action of muscles.
examples of the three kinds of levers treated of in natural phi-
losophy. Some of these I will now notice. The first kind of
lever has the fulcrum between the weight and the power, as
represented in Fig. 107. F is the fulcrum, W the weight, and
FIG. 107.
FIRST KIND OF LEVER.
P the power. You have examples of this lever in the common
pump handle, the beam of a pair of scales, the crowbar, as
commonly used, scissors, <fec. You have an example of this form
of lever in the human body, in the action of the muscles in
moving the head back and forth on the top of the spinal
column. In this case, when the head is moved forward, the
top of the spine is the fulcrum, the weight to be moved is the
back of the head, and the power is the contraction of the muscles
that bow the head forward. When the head is bent backward,
the power is the contraction of the muscles behind 4 , and the
weight is the front part of the head. The muscles that move
the head backward are stronger than those that move it for-
ward. It is necessary that it should be so, for there is more of
the head in front of the point of support or fulcrum than there
is behind it. Hence, when sleep relaxes the muscles, if we are
sitting up the head falls forward.
297. In the second kind of lever the weight is between the
fulcrum and the power, as represented in Fig. 108. The com-
mon wheelbarrow is an example of this form of lever. You
have an example of it in the body in the raising of the heel
FIG. 108.
SECOND KIND OF LEVER.
THE MUSCLES.
199
Motion of the foot in walking.
from the ground in walking. In doing this the weight to be
raised is the whole body, the foot being the lever, and the
forward part of the foot being the fulcrum. This will be made
slear by Fig. 109. W is the large bone of the leg sustaining
FIG. 109.
the weight of the body ; F, is the fulcrum, the forward part of the
foot that presses on the ground as the heel is raised ; and P, is
the large muscle in the calf of the leg, the power that raises
k the heel, the end of the lever.
298. In the third form of lever the power is between the
weight and the fulcrum. A common example of this is seen
in the raising of a ladder. The fixed foot of the ladder is the
fulcrum, the ladder itself is the weight, and the power is ap-
plied as far from the fulcrum as it can be. Fig. 110, represents
FIG. no.
THIRD KIND OF LEVER.
a lever of this kind. This form of lever is more frequently
used than the other forms in the human body. We have an
example of it in bending the forearm upon the arm as seen in
Fig. Ill, in which 1 is the bone of the arm; 2, the tones of
the forearm ; 4, the muscle which bends the forearm upon the
arm ; 5, its double headed attachment above ; and 6, its at-
200 HUMAN PHYSIOLOGY.
Tw, objects aimed at in muscular action ; quickness and power.
no. 111.
tachm-mt to the radius, one of the bones of the forearm. In this
case the fulcrum is at 8, the joint of the elbow, the weight is
the hand with whatever it holds, and the power is applied at
the point where the tendon is fastened to the ulna, that is, as in
the case of the ladder, between the fulcrum and the weight.
The muscle which straightens the forearm upon the arm is
represented at 7. I shall remark upon this in another con-
nection.
299. In the management of the three kinds of levers there,
are two different objects aimed at under different circumstances.
One object is to move a great weight with a small power.
Here quietness* is not aimed at, but the weight is moved slowly.
The other object is to move the weight quickly, an object in-
consistent with the moving of any very heavy weight. When
the object is to move a heavy weight slowly, the lever is so
managed as to get a good purchase, as it is expressed. Thus
in the case of the lever of the second kind, Fig. 108, if the
weight be a heavy one, the power is commonly applied at some
distance from the weight. The nearer the power is to the
weight, the greater must it be to move the weight. The smaller
the power, the further must it be from the weight in order to
raise it. But though a small power if at a distance from
the weight answers to raise it, yet in this case the power must
move through a considerable space to move the weight but
little ; while to raise the weight to the same height, a power
nearer to it passes through but little space. This will be made
clear to you by Fig. 112. F is the fulcrum, and W the weight.
If the lever, A, be raised to the line, B, the dotted lines will
show the different spaces which the power passes through, ac-
cording to its distance from the weight. If the power be at P,
THE MUSCLES. 201
Quickness more often important thun power.
FIG. 112.
A
it passes through the space indicated by the dotted line a in
moving the weight W to c. But if it be at p, it passes through
a much shorter space, 6, in raising the weight to the same
height. The more important, therefore, in this form of lever
quickness of movement is, the nearer to the weight is the
power applied. Let us look at the application of these prin-
ciples to the example of this kind of lever, which I cited from
the human body, represented in Fig. 109, the raising of the
weight of the body on the foot in walking. The power is here
applied quite near to the weight, for quickness in raising the
heel in walking and running is of great importance. By hav-
ing the heel project farther behind, the muscle could be at-
tached farther from the weight, and thus act with more power.
But there would in this case be a sacrifice of quickness of move-
ment, and besides this, the lengthened heel would present a
very awkward and ugly appearance.
300. But it is in examples of levers of the third kind that
we find these principles best illustrated. This form of lever is
much more often used in the mechanism of the muscles than
the other forms. I refer you to the example given of this lever
in the action of the biceps muscle in bending the forearm, as
shown in Fig. 111. In this case it is of much more importance
to move small weights quickly, than to move heavy ones slowly.
Therefore the power is applied quite near to the fulcrum. The
tendon of the biceps, as you see, is fastened to the main bone
of the forearm near the fulcrum, the elbow. You can readily
see that the point where the power is applied would pass
through but a little space, in moving a weight through a con-
siderable one. The lower jaw, in its upward motion, is a lever
of the same kind. In this case, force rather than quickness is
required in breaking and grinding the food. Here, therefore,
the power, the action of the muscle, is applied farther from
the fulcrum than in the case of the biceps muscle of the arm,
202
HUMAN PHYSIOLOGY.
Force most important in the case of the lower jaw.
and nearer to the weight to be moved, or the point where the
resistance is which is to be overcome. It is applied also in a
different direction, a point which I shall however speak of in
another connection. The muscles which move the lower jaw
upward can be seen in Fig. 113. One is the large spreading
FIG. 113.
MUSCLES OF FACE AND NECK.
muscle &, the swelling of which, in its contraction, we can feel,
if we place the fingers on the temple while moving the lower
jaw upward. The other is the short strong muscle c, the front
edge of which is so far forward, that one-third at least of the
lower jaw-bone is embraced by this muscle. Now, if you com-
pare this bone as a lever with the forearm as acted upon by
the biceps, you will at once see that the power is applied much
nearer to the weight, or the resistance to be overcome, in the
case of the jaw, than in the case of the arm. It is so even when
the resistance to be overcome is at the front teeth ; and it is
much more so when the resistance is at the back part of the
mouth, as when we are grinding our food. Here, indeed, a por-
tion of the muscular force is brought to bear upon the resistance
in a direct line. It is not merely because the back teeth aro
THE MUSCLES. 203
Mechanical disadvantage in muscular action.
stronger than the front ones, but also because the power is nearer
the resistance, that we can crack a nut more easily with the
back, than we can with the front teeth.
301. It is clear that the biceps muscle acts, as it is expressed,
at a mechanical disadvantage, if we regard mere power or force,
and leave out of view quickness of motion. If it were inserted
further down on the forearm, nearer the hand, it could raise
much greater weights than it now can. And the same can be
said of most of the other muscles of the body. But force is
sacrificed for the sake of quickness in most cases, because the
latter is more important. In the few cases in which force is
more important, as in the case of the lower jaw just cited, the
reverse arrangement is provided. The gain in quickness in the
arrangement of the biceps muscle can be illustrated on Fig. 114.
FIG. 114.
/\ P P
F being the fulcrum, the power in raising the weight, W, to c,
if acting at P, passes through the space indicated by the dotted
line a. But if it act at jo, it will pass through all the space 6,
and of course raise the weight more slowly than when acting at P.
302. Most of the muscles work at a mechanical disadvantage
in another way. I refer to the direction in which the muscle
acts on the bone to be moved. This is seldom at right angles,
and therefore a considerable part of the force exerted is lost.
This can be made clear to you by Fig. 115. Let b represent
the bone of the arm, and r its fulcrum, or point of support in
the shoulder. You readily see that if the bone be acted on by
a muscle, ra, at right-angles to it, it will require less force to
move it to a given point than would be required if the same
muscle were placed in the position represented by n. For the
204: HUMAN" PHYSIOLOGY.
When loss in power, gain in quickness.
FIG. 115.
muscle W, acting obliquely on the bone would expend a part of
its force in pressing the end of the bone upward against the
socket of the joint at r.
303. But in this case also, what is lost in power is gained in
quickness of movement. This can be shown on the figure.
We will suppose that the muscle contracts or shortens itself the
half of the length of the teuton. If the muscle were placed as
at ra, the bone would be earned to the line , c. But if the
muscle be placed as at n, the same degree of contraction would
raise the bone to the line a, rf, the point of the bone where the
tendon of the muscle is attached moving in the curved line as
marked. The resistance to be overcome, of course, requires
much more power for the obliquely placed muscle, n, to raise
the bone to the line a, rf, than for the muscle m to raise it to
a, c ; and therefore a much larger muscle is needed than there
would be if it acted at right-angles to the bone as at m. And
the muscle which raises the arm at the shoulder, acting as it
does at so great disadvantage, is a very large muscle. The
muscle, w, in the figure represents only the line of its action,
and not at all its shape. If you observe the various motions of
the arm in which this muscle has a part, you will appreciate
the necessity of so arranging it as to secure quickness of move-
ment. This was the chief object to be aimed at in its arrange-
ment; and the second and less important object, power, is
secured, so far as it is needed, by simply making the muscle a
large one.
304. The mechanical disadvantage, which I have noticed as
resulting from the oblique action of the muscles, is in part ob-
viated by a very simple contrivance. It is done by making the
THE MUSCLES.
205
Contrivance to change the direction of force.
FIG. 116.
i J
FIG. 117.
-o
tendon of the muscle work over an enlargement of the bones at
the joints. The operation of this contrivance can
be made clear by Figs. 116 and 117. Let r and
o (Fig. 116) be the two bones of a joint, and let
the muscle m be attached to the bone o at i. As
it contracts, almost all its force will be spent in
drawing the bone o upward against the bone r,
because it acts almost entirely in a line with the
bones. But let the ends of the bones be en-
larged as in Fig. 117, and you can see that the
direction of the tendon of the muscle m is so
changed where it is attached to the bone, that the
muscle can now very easily make the lower bone
turn upon the upper. The enlargement then of
the bones at the joints, which is needed to give
the requisite extent of surface for working them,
answers also another good purpose in thus alter-
ing the direction of force in the muscles. In the
case of the knee-joint there is an additional contrivance for
making this change of direction still greater. A movable bone,
the patella or kneepan, besides acting as a protection to the
joint, effects also the purpose referred to. The manner in which
it does this can be made plain by Fig. 118, in which a represents
the end of the thigh-bone ; 6, the end
of the large bone of the leg articulat-
ing with it ; c, the patella ; rf, the large
tendon which comes from the muscle
above, and is fixed into the patella ;
and e, the tendon which goes from
the patella to the large bone of the
leg below. The dotted line shows
how much the direction of the force
of the muscle is changed by this ar-
rangement. The movement performed
by this muscle is throwing the leg and
foot forward, which it is by the above
arrangement of the patella enabled to
do with great ease in walking, and
with great force in the act of kicking.
305. The pulley is used in the ar-
rangement of the muscles, though by
no means as often as the lever. It
serves, whenever it is used, to give the force a different direction
18
FIG. 118.
206 HUMAN PHYSIOLOGY.
The pulley-arrangement in muscles.
from what it would otherwise have. I will cite but a few
examples. At the wrist and the ankle there are broad liga-
ments, which bind down the tendons of the muscles, and sus-
tain to them the relation of pullies. If it were not for these
ligaments the tendons at these joints would fly out continually
when the muscles are in action, making projecting cords under
the skin. And if the skin were removed, the tendons would
be in a position similar to that represented at A, in Fig. 119.
FIG. 119.
In this Figure, C is the tendon of the great toe in its position as
bound down by ligaments. Now if the muscle were in the
position represented by A, it is plain that it would act at a
greater mechanical advantage than in the position C ; but the
toe would not be moved as quickly ; and besides, if the tendons
projected in this way, the foot would be a very cumbrous piece
of machinery, compared with what it is now, with the tendons
bound down around the slender ankle. So that both beauty
and use are secured by the arrangement.
306. There is a beautiful application of the pulley in the
case of the muscle that draws down the lower jaw, called
the digastric muscle. It is represented in Fig. 120, in which
a is one end of the muscle attached behind the ear, and b is the
other end attached to the inside of the lower part of the chin.
THE MUSCLES. 207
Manner in which the lower jaw is drawn down.
FIG. 120.
DIGASTRIC MUSCLE.
It is muscular at the two ends, and tendinous in its middle
part. This middle part runs through a loop or ring in a small
muscle as represented in the Figure. This little muscle is
fastened above to a small process of bone under the ear, and
below to the hyoid, or U-shaped bone, c, which is situated just
above the larynx. Now when the jaw is to be drawn down,
the two fleshy ends of the digastric muscle contract, and the
middle tendinous part works in the ring provided in the little
muscle. This muscle is so slender, that its loop is of itself alone
hardly strong enough, as we should suppose, for the tendon of
so large a muscle as the digastric to work in. And we accord-
ingly find that there is an additional security in a strong liga-
ment, which fastens the tendon of the digastric muscle to the
hyoid bone. This ligament (which I have not represented in
the figure, because it would confuse your view of the pulley-
action of the parts) is sufficiently long to allow of all the
freedom of motion necessary to drawing the jaw downward.
You see at once that one object of this arrangement of the di-
gastric muscle is to secure beauty of form in the neck. A
muscle extending from the top of the chest to the chin in a
straight direction would very effectually draw down the lower jaw,
but it would be a great deformity. This is avoided by the pulley-
arrangement of the digastric .muscle. But this muscle answers
another purpose besides drawing down the jaw. If while the jaw
be held fast by muscles which draw it upward, the digastric
contracts, it will draw up, as you can readily see by the Figure,
the hyoid bone, c, and with it, of course, the larynx which is at-
^^^"^iv^^
OF
208 HUMAN PHYSIOLOGY.
Straight and oblique muscles of the eye.
tached to it. Now precisely this set of motions occurs when we
swallow. The mouth is shut by the drawing up of the jaw,
and then the contraction of the digastric muscle draws up the
larynx, as you can perceive if you place your fingers on the
larynx, or Adam's apple, as it is called, when you perform the
act of swallowing. The little muscle in which the loop is,
renders some assistance to the digastric in thus drawing up the
hyoid bone and the larynx, as you can see by the Figure.
307. I will notice one more example of the pulley- ar-
rangement. It is in the eye. There are six muscles that
move the eye-ball. Five of them are represented in Fig. 121.
There are four straight muscles, three of which are marked
FIG. 121.
o, &, c; the fourth is behind 6, the upper edge of it only
being seen in the Figure. These muscles are at their origin in
the back part of the socket of the eye arranged round the optic
nerve, and passing forward are attached to the sclerotic coat,
the firm white coat of the eye. The two lateral muscles, ft, and
its opposite, move the eye to the one side and the other, and
the two muscles, a and c, perform the up and down motions.
But there are certain oblique rolling motions of the eyeball
which can not be executed by these straight muscles. For these
motions two muscles are provided, one of which has a pulley-
arrangement, as represented in the Figure. This muscle, s, has
a long tendon which passes through a ring in cartilage in the
roof of the socket, and then turning back is fastened as you see
to the upper pail of the eyeball. This muscle, as stated in the
chapter on the Nervous System, is under the direction of one
nerve alone. It is an involuntary muscle which performs the
insensible rolling motions of the eyeball, and like the other in-
voluntary muscles of the body, is at work while we are asleep,
as well as when we are awake. It is the muscle which rolls
about the eye tremulously when it is open in the insensible
state sometimes produced by disease.
THE MUSCLES. 209
Opposing muscles. Compound muscular action.
308. Every muscle performing a motion has its opposing
muscle or muscles, which perform the opposite motion. In the
case of any two opposing muscles the one must be in some
measure relaxed while the other is in action. Thus in alter-
nately bending the elbow, and straightening it, there is alternate
action and relaxation in the two opposite muscles 4 and 7, as
represented in Fig. 111. So in moving the head back and
forth the muscles in front and rear are alternately contracted
and relaxed. Paley very aptly compares this to the action of
two sawyers in a pit, as they move the saw back and forth.
The comparison, however, is not strictly true, because the re-
laxing muscle is never wholly relaxed. There is indeed in every
muscle some amount of contraction which is independent of
action through the nerves, whether it be reflex, or produced by
the will. For this reason the muscles cut off in amputation
of a limb retract. So also if the muscles on one side of the
face be palsied, the muscles on the other side draw the mouth
to that side. The mouth is held in the middle of the face by
the equal action of pairs of muscles. The head, too, is held in
equilibrium in the same way. In what is called wry-neck, this
tonic contraction, as it is sometimes termed, is greater in the
muscles on one side than it is on the other. In some cases a
cure can be effected only by dividing the contracted muscles.
In strabismus, or squinting, one of the straight muscles of the
eyeball contracts too strongly for its opposing muscle, and as
in wry-neck, dividing the contracting muscle is often necessary
to remedy the difficulty.
309. Most motions are not performed by single muscles, but
by the joint and agreeing action of several, and sometimes
many muscles. And as these muscles may vary to a great
extent in their degree of contraction, the motions produced by
them are not only compound, but are exceedingly varied. To
illustrate this compound and varied character of motion, I will
refer to a single example in which only two muscles are con-
cerned in the motion. In Fig. 113 you see a pair of muscles,
one of which is marked A, which extend from the large protu-
berances behind the ears to the top of the breast-bone. In the
neck of a thin muscular person these muscles are very promi-
nent. When they contract equally, the head is bent straight
forward in the middle line between the muscles, and a line
drawn from the middle of the forehead down to the breast-
bone would strike exactly at the point where these two muscles
unite. But if one muscle contracts more strongly than the
18*
210 HUMAN PHYSIOLOGY.
Variety in muscular action. Exemplified in the tongue.
other, the head as it bows forward bows towards the side on
which is the strongest contraction. And as the degrees of
contraction in these two muscles may be endlessly varied, so
there may be an endless variation in the degree of inclination
of the head to one side or the other, as it is bent forward. If
then so great a variety in the direction of motion may be pro-
duced by variation in the degrees of action in two muscles, you can
readily see that an almost infinite variety of motion must result
from this variation, where many muscles are called into action.
310. I know not any part of the body, which exemplifies in
so palpable a manner the compound and diversified character
of muscular motion as the tongue. It is mostly a bundle of
muscular fibres, apparently mingled together in confusion, but
really arranged in perfect order, so that it can be moved with
great definiteness in all directions, forward, backward, upward,
downward, to either side, and in all intermediate directions. If
you stand before a glass, and opening your mouth, move the
tongue rapidly about in all these directions, you think of a har-
lequin performing his antics. But all this wonderful variety of
movement is produced in obedience to the definite action of
nerves, whose fibres are mingled with the muscular fibres of the
tongue. And in order to produce each motion there is an agree-
ment of action not between merely many of these fibres, but
between multitudes of them.
311. With the view which I have given you of the compound
and varied character of muscular motion, you are prepared to
take a general survey of the muscular system. For this pur-
pose I call your attention to a side view of the muscles of the
body as presented in Fig. 122. I must premise, that you can
get no idea from this Figure of the number of the muscles in
the body, for you see here only the outer layer of muscles, and
there are many muscles concealed by them. You observe that
they are of various shapes and sizes, according to the motions
which they are designed to produce, and the circumstances
in which they are placed. They are round, long, short, flat,
fan-shaped, circular, serrated, &c. I will point out some
of them. At a is the very large muscle that makes the
fleshy prominence at the upper part of the arm, and the
office of which is to raise the arm, carrying it out from the
body. You observe that its fibres are not all arranged alike
but lie in different directions. The result is, that while the
arm is raised by the muscle as a whole, it may be carried at
the same time forward or backward by the varying action of
THE MUSCLES.
211
External layer of the muscles of the body.
FIG. 122.
MUSCLES OF THE BODY.
212 HUMAN PHYSIOLOGY.
General description of the muscles in various parts.
these different fibres. There are many of the muscles of the
body which are made thus to produce various results by
variation of the action of different parts of the same muscle.
And the regulation of this variation by the nerves is one of
the most wonderful and mysterious things which we find in
our study of the nervous system. For each fibre in the cases
referred to is told, as we may express it, just how much it must
do in order to produce the requisite general motion of the
muscle. It is manifestly much more wonderful thus to pro-
duce various but accurately graduated contraction in different
parts of the muscle, than to produce an uniform contraction in
all its fibres.
312. I go on with my notice of the particular muscles. At
b is the biceps muscle, which bends the forearm upon the arm,
and at c is another muscle that assists the biceps. At e is the
large muscle in the back of the arm, which acts in opposition
to the biceps, and straightens the forearm upon the arm. At
d is a muscle which rolls the radius outwards, and thus turns
the palm of the hand upward as seen in the Figure. At g is a
very large broad muscle coming from the whole length of the
back, and at the axilla or arm-pit, its fibres are collected,
twisted, and folded upon each other. The muscle is fastened
by a stout tendon to the upper and back part of the bone of
the arm, and its office is to pull the arm backwards and down-
wards. At h is a serrated muscle, which rising from the ribs,
goes to the shoulder-blade, and serves to draw the shoulder-
blade forwards. At i is one of the broad muscles of the ab-
domen. At I and k are two large muscles that move the
thigh. At o and jt?, as seen on the right thigh, and at w, as
seen on the left, are three large muscles, which are fastened to
the kneepan, and serve to throw the leg forward as described
in 304. At q is the tendon that forms the outer hamstring,
and at r are the two tendons which form the inner one. The
muscles to which these tendons belong, serve to bend the leg
upon the thigh, drawing it upward and backward. At 5 is
the muscle which makes the bulk of the calf of the leg. It
lifts the heel upward and backward, and it is seen in action m
the right leg of the Figure. Its strong tendon which is at-
tached to the top of the heel bone is called, on account of its
strength, the tendon of Achilles. This muscle is in Fig. 109,
the power P which raises the weight of the body, W, on the
fulcrum, F, as the heel is raised from the ground in walking.
313. In Fig. 123 you have a rear view of the muscles. At
THE MUSCLES.
213
Rear view of the external layer of the muscles.
FIG. 123.
c....
REAR VIEW OF THE MUSCLES.
214 HUMAN PHYSIOLOGY.
Some muscles are very small. Symmetrical arrangement of the muscles.
a is a very broad muscle, which rising from the back is attached
to different parts of the shoulder-blade. You can see that
this irregularly shaped muscle, will move the shoulder-blade
variously, according to the various action of the different fibres
of the muscle, which run in so different directions. At c you
see the rear part of the muscle that raises the arm. At b is
the extensive muscle that you saw in Fig. 122 at </, which
draws the arm backward. At e is a large muscle that draws
the thigh backward. At g, h, and / are the muscles whose
tendons form the two hamstrings. At i is the muscle that
forms the calf of the leg, and raises the heel.
314. I have thus described to you a few of the principal
muscles in the body, that you may have some idea of the modes
in which they act, and the manner in which they are arranged.
Those which I have described are all muscles of considerable
size. But there are some exceedingly small muscles in the
body, producing some very delicate motions. For example, all
the variations in the note of the voice result, as you will see in
the Chapter on the Voice, from the variation of tension of
the vocal ligaments, which is regulated by certain very small
muscles. As the laborer sings over his work, great is the con-
trast between the delicate action of these little muscles, and the
strong action of the muscles of his stalwart arm. A variation
of less than a hair's breadth in the contraction of the muscles
of the vocal ligaments suffices to produce an appreciable differ-
ence in the note of the voice.
I have thus far spoken of the bones especially as being
moved by the muscles. But other parts are moved by them
also. In the case of the voice, just alluded to, the little muscles
move cartilages to which the vocal ligaments are attached.
The tongue and the palate are moved by muscles. Muscles
move the skin. In man- this is generally very much confined
to the face. The mouth, the eyelids, the eyebrows, &c., are
moved by muscles. In many animals the skin is moved ex-
tensively by muscles, as for example when the horse shakes his
skin to get rid of the biting flies.
315. In the arrangement of the muscles great regard has
been paid by the maker of our bodies to convenience and sym-
metry, and not merely to mechanical advantages. Thus, the
muscles moving the fingers are mostly placed in the forearm,
while the slender tendons pass over the surface of the bones in
the wrist. The flowing outline of the arm is thus secured, and
the hand is made a light, and at the same time, a strong ap-
THE MUSCLES. 215
Contrivances in muscles and tendons of the hand and foot.
paratus. The same can be said substantially of the arrange-
ment of the muscles and tendons in the leg and foot. There
is one arrangement in the foot which is worthy of especial no-
tice. There is a muscle in the fleshy part of the leg, which by
a long tendon, divided in the foot into four tendons, bends the
last joints of the toes. There is also a short thick muscle in
the bottom of the foot which joins the tendons of the first
named muscle, and assists it in bending the toes. It is as if
two different sets of men were placed in two different positions,
with ropes arranged so as to pull in the same direction. The
question arises, why the toes are not bent by a single muscle,
lodged conveniently in the fleshy part of the leg. The reason
probably is, that the muscle placed in the sole of the foot is
needed there as a filling up in the arch of the foot, and so the
force necessary to bend the toes is divided between the two
positions.
316. There is another contrivance in this muscle that bends the
toes which I will notice here. Its four tendons pass to the last
bones in the toes, and in doing so they go through the tendons
of the muscle that bends the second joints. These latter divide
at their ends where they join the bones for this purpose. A
similar arrangement also is made in the fingers for the tendons
of the second and third joints. This is represented in Fig. 124,
FIG. 124.
in which e is the tendon which goes to the last bone c through
the division in/, which goes to the second bone b. It is mani-
fest that this is the best way of packing the tendons, as we may
express it. Any other conceivable arrangement would add to
the bulk of the finger. As they are represented in the figure
they are raised up, instead of being closely packed down upon
the bone, as they are in reality.
317. I have already alluded to the fact that many muscles
unite in producing most of the movements of the body, and
that, as they vary in the degrees of their contraction, the
variety of motion resulting from both these causes, is exceed-
216 HUMAN PHYSIOLOGY.
Complicated action of associated muscles.
ingly great. I will now call your attention more particularly
to these points, as you can more readily appreciate them after
the general view which you have taken of the muscular system.
Even when only a part of the body is put in motion, there are
often many muscles engaged in the act. Take, for example,
the act of swallowing, which I have described in 78 in the
Chapter on Digestion. In this compound act the muscles of the
jaw close the mouth, the tongue thrusts the food back into
the throat, the digastric muscle .( 306), pulls up the larynx,
and the epiglottis is at the same time shut down by muscles
upon the opening into the larynx, to let the food slide over it.
In speaking and singing the action of the muscles is much more
complicated than in the act of swallowing. The muscles of the
chest work the bellows of the organ (for such is the relation of
the chest to the musical instrument, the larynx,) the muscles of
the vocal ligaments put them in the state of tension required
to produce the note intended, the muscles of the epiglottis raise
it to let the sound out, and the muscles of the throat, palate,
tongue, and lips, give articulation to the sound as it comes from
the larynx. And observe, that some of the same parts are en-
gaged in the act of speaking that are engaged in that of swal-
lowing, but are put in different positions for the two acts.
Thus, the epiglottis is raised up when we speak, and is shut
down when we swallow, and the larynx is raised up when we
swallow, and is drawn down again when we speak. And how
quickly we pass from the one act to the other, as we mingle
our talking and eating together ! And we do it with such
facility and precision, that it is a very rare accident that a crumb
or a drop slips into the larynx. Observe farther, that when we
take a breath, as well as when we speak, the epiglottis must be
raised, the air passing in, instead of passing out as in speaking.
The parts, therefore, are often engaged in these different acts,
not only distinct from each other, but inconsistent with each
other also, and they change from one of these acts to another
so readily, that as we eat, and breathe, ana! talk, we are con-
scious of no disturbance, and scarcely ever of any effort in the
change. No change of action in any machinery of man's in-
vention can be at all compared with this in the precision and
facility of the change, much less in its complicated character.
318. But if there be complication and variety of action when
but one part of the body is put in motion by the muscles, there
will be vastly more when the muscles of the body as a whole
are brought into action. If you look at Fig. 122, you see the
THE MUSCLES. 217
Constant change in complicated muscular movements.
muscles generally in more or less action, and the action of each
one has its particular relation to the attitude assumed. If now
the attitude be varied, this particular relation of each muscle
must be varied also. If, for example, the right foot be carried
forward so as to bring the weight of the body on to that foot,
instead of the left, on which it now rests, as represented in the
Figure, all the muscles of the frame will have a different rela-
tion in their action. And not only this, but while the body is
changing from the one attitude to the other, there will be a
continual change of this relation. At no one moment during
the act or motion, which changes the attitude, will the state of
contraction in each muscle be precisely the same, that it is at
any other moment. Thus, the state of the muscles in the be-
ginning of the change of attitude is altogether different from
what it is when the movement is half accomplished. And the
same can be said of any other two points in the progress of the
movement. The same is true of any other general action
of the muscles. Thus, if one is pulling with his feet braced, the
muscles do not remain in the same relative condition all the
time, but as the body which is pulled yields, the relative tension
of the muscles is changed every moment. But there is no
movement which exemplifies this change of relative condition
of the muscles so well as that of balancing. If with the views
which I have presented in your mind, you observe some one
who is skillful in balancing, you will be impressed with the ever
changing but precisely regulated degree of tension in the differ-
ent muscles, and with the variety of combination in their
action.
319. I will not comment to any extent upon the general
movements and attitudes of the body. But I
will here simply call your attention to one
mode of action, in which a large number of
the muscles are called into play, on account of
its analogy to an expedient often used in me-
chanics. I refer to what is called the toggle-
joint. This I will explain. Let c, a, and c, 6,
represent two bars connected together, like a
carpenter's folding rule, by a hinge or joint at
c. Suppose the two ends, a and 6, to be fitted
into the two blocks represented in the Figure.
If now the block at b is fixed, and the block at
a is movable, and force be applied to the joint
c carrying it towards c?, the block at a will be TOGGLE-JOINT.
19
c carr
218 HUMAN PHYSIOLOGY.
Examples of the toggle-joint in muscular movements.
pressed upward with considerable power. If on the other
hand, the block at b is movable, and that at a is fixed, the block
at b will be pressed downward. We see this latter form of the
contrivance applied in printing presses. In the human body
this toggle-joint is used in both ways. When one stoops to
take a heavy weight upon his back or shoulder, he puts both
the knee and the hip-joints into the condition that the toggle-
joint is when it is bent ; and then as he straightens up, the
weight is raised by an action of the joints precisely similar to
that of the toggle-joint in machinery. In the case of the knee,
the straightening of the joint is done by the muscles on the
front part of the thigh, that draw up the kneepan with the
tendon attached to it. This is using the principle of the toggle-
joint in pressing upward. It is also sometimes used in pressing
downward. In crushing any thing with the heel, we give great
force to the blow on the principle of the toggle-joint, by flexing
the knee and straightening the limb as we bring down the heel
upon the thing to be crushed. In pushing any thing before us,
we bend the elbow as preparatory to the act, and then thrust
the arm out straight, thus exemplifying the toggle-joint. The
horse gives great force to his kick in the same way. The great
power exerted by beasts of draught and burden is to be referred
very much to the principle of the toggle-joint. When a horse
is to draw a heavy load, he bends all his limbs, especially the
hinder ones, and then as he straightens them, he starts the
load. In this case the ground is the fixed block of the me-
chanism, the body of the horse to which the load is attached is
the movable one, and his limbs are so many toggle-joints. By
this application of the principle we see draught horses move
very heavy loads. "So, (admitting fable to be fact,") says Dr.
Griscom, " when the farmer, in answer to his petition for assist-
ance, was commanded by Hercules to exert himself to raise his
wagon from the pit, he placed his shoulder against the wheel,
and drawing his body up into a crouching attitude, whereby all
his joints were flexed, and making his feet the fixed points, by
a powerful muscular effort, he straightened the toggle-joints of
his limbs, and the wheel was raised from its bed of miry clay.
His horses at the same moment extending their joints, the
heavily laden wagon was carried beyond the reach of farther
detention."
320. The hand is the most wonderful of all parts of the
body, in regard to variety and complication of movement
There are over lifty muscles, which are engaged in the various
TIIK MrrVM-lS. 219
Great vnrioty of notion in tlie muncloi of tho hnnd.
motions of tho upper extremity, all of which, of course, have
more or less reference to (In- hand. Indeed the hand is the
part, of (lie upper extremity to which all ils oilier parts are
tributary, and therefore we, may properly consider all these
muscles as in :i great measure belonging to the hand. 1C now
you call to mind the fad, that each one of these muscles can
vary the (tinoiint of its contraction in all decrees, from the most
powerful action down to the slightest movement, you cau
readily sec that fifty muscles with this power of variation can
produce an almost endless ^number of combinations of motion.
The variety would be exceeding I y great, even if every muscle,
whenever it acted, had always the same amount of contraction.
l>ut the power of varying the amount, of contraction multiplies
the variety to an inconceivable extent.
321. If you watch the movements of the hand with its fingers,
as you exercise, it in a great variety of motions, yon cau get
some idea of its capabilities in this respect. If, too, you ob-
serve its movements in different individuals in all kinds of labor
and handiwork, vou will be still more impressed with the ex-
treme variety of its movements. It is capable of performing tho
heaviest and rudest, work, and at the same time the most deli-
cate. How wide the difference between wielding the ax or the
sledge-hammer, and moving the engraver's tool in some of the
finest, productions of his art! How firm is its grasp of the
hammer, and yet how gentle is its pressure upon the graver, as j(,
moves it, in almost, invisible lines! The shape of the hand, with
its fingers of unequal length, and its thumb opposite to them,
capable of touching the. tip of each of the fingers, or all of them
ton-ether, enables it to accommodate itself to a vast, variety of
shapes and sixes of objects; and its delicate papilhe, tilled with
nerves and arranged in rows, as you can see, on the tips of the
fingers under the skin, endow this wonderful instrument with a
sensibility which guides its muscular movements. When,
therefore, we OOMUier the almost endless variety of its motions,
the delicacy and accuracy of its sense of touch, and besides
these, the force and grace with which it acts in the expression
of thought, and feeling, we hardly wonder that some have fixed
Upon tin- hand as man's distinguishing characteristic, and we
are impressed with the thought, that it is a fitting instrument,
>f work and expression for that mind, which is tho image of
<Jod in man.
^'J'2. Having thus taken a survey of the muscular system, let
iis look fora moment at the whole machinery, aa it works when
220 HUMAN PHYSIOLOGY.
Nice adjustment of the muscular movements. How effected.
it is engaged at the same time in some general movement, and
in some special movements of some departments of it. Look,
for example, at some one who is busied in conversation while ho
is walking, and is perhaps at the same time twirling something
in different directions in his fingers. Here you have a general
action of the muscles as described in 318, and with it a par-
ticular action of two sets of muscles in two different parts of the
body ; and yet so well do the nerves regulate these various
movements, that there is no disturbance or confusion in the
complicated machinery. While the muscles of the arm and
fingers are at work executing their diversified motions, the little
muscles of the larynx are ever varying the notes of the voice,
and the muscles of articulation are putting that voice into every
variety of shape. And while these movements are going on in
these particular parts of the system, the machinery as a whole
is executing one of its grand general movements. And besides
all this, the muscles of respiration are at work all the while, in-
troducing air into the lungs to change the blood, and forcing it
out through the trachea to make th* vocal ligaments vibrate ;
and that compound muscle the heart is pumping at the rate of
seventy times a minute sending the blood through its tubes
every where ; and if there be any food in the stomach, the mus-
cular fibres of that organ are at work churning the food to
make more blood. How complicated is the machinery that per-
forms all these operations, and yet with what precision every mus-
cle, nay, every individual fibre works in obedience to the nerves !
323. The question arises, how in all the diversified action of
the muscles their nice adjustment is effected. How do the
muscles know, as we may express it, just how much to do in
each movement? When, for example, you reach your hand
up to touch some object, how does each muscle know just what
degree of contraction is necessary to make the hand go with
precision to the particular point arrived at ? And so when one
is playing on an instrument with the fingers, as the piano, vary-
ing their pressure continually in accordance with the desired loud-
ness of the sound, how does each muscle know just what amount
of contraction is required of it in each movement ? Though the
senses of vision and touch afford some assistance in the guidance
of muscular action in such cases, something else is manifestly
necessary. Sir Charles Bell, therefore, supposes that there is
what he calls a muscular sense, which acts as a guide to the
muscles, in connection with the senses of sight and touch. In
some cases it is the sole guide. On this subject, Sir Charles
THE MUSCLES. 221
Sir Charles BelPs description of the muscular sense.
says, " When a blind man, or a man with his eyes shut, stands
upright, neither leaning upon or touching aught ; by what
means is it that he maintains the erect position ? The sym-
metry of his body is not the cause ; the statue of the finest pro-
portion must be soldered to its pedestal, or the wind will cast it
down. How is it, then, that a man sustains the perpendicular
posture, or inclines in due degree towards the winds that blow
upon him ? It is obvious that he has a sense by which he
knows the inclination of his body, and that he has a ready ap-
titude to adjust it, and to correct any deviation from the per-
pendicular. What sense then is this ? for he touches nothing,
and sees nothing ; there is no organ of sense hitherto observed
which can serve him, or in any degree aid him. Is it not that
sense which is exhibited so early in the infant, in the fear of
falling ? Is it not the full development of that property which
was early shown in the struggle of the infant while it yet lay in
the nurse's arms ? It can only be by the adjustment of muscles
that the limbs are stiffened, the body firmly balanced, and kept
erect. There is no oth* source of knowledge, but a sense of
the degree of exertion in his muscular frame, by which a man
can know the position of his body and limbs, while he has no
point of vision to direct his efforts, or the contact of any exter-
nal body. In truth, we stand by so fine an exercise of this
power, and the muscles are, from habit, directed with so much
precision, and with an effort so slight, that we do not know
how we stand. But if we attempt to walk on a narrow ledge,
or stand in a situation where we are in danger of falling, or rest
on one foot, we become then subject to apprehension ; the actions
of the muscles are, as it were, magnified and demonstrative of
the degree in which they are excited."
324. It is obvious then that this muscular sense informs the
mind of the changing postures of the body, and guides the
muscles in effecting these postures. And it has a particular set
of nervous fibres devoted to it, separate from those fibres which
excite the muscles to action, though they are ordinarily in-
closed in the same sheath. This sense, it may also be remarked,
is a source of pleasure, as well as the other senses. The mo-
tions of the body are attended with a senso of enjoyment, which
lightens labor, and adds zest to our active sports. The enjoy-
ment of the muscular sense we see constantly exemplified in the
gambols of animals. It may be still further remarked, that this
sense is capable of being educated like the other senses. But
of this I shall speak in another place.
19*
222 HUMAN PHYSIOLOGY.
All thought and feeling communicated by muscles.
CHAPTER XIII.
LANGUAGE OP THE MUSCLES
325. As THE nerves of sensation are the inlets of all know-
ledge to the mind, the nerves of motion are the outlets by
which all knowledge is communicated. Thought and feeling
are expressed only by muscular motion. It is true that there
are some accompanying and subordinate modes of expression,
as the flowing of tears, the action of the capillaries producing
blushing, and the paleness occasioned by fear. But these
could not of themselves alone communicate thought and feel-
ing, and can do so only by being associated with other signs.
They only add force to the expression already produced by
muscular action. Indeed they are signs which can not be un-
derstood, unless muscular action interpret them. Thus if tears
flow, we know not whether they are tears of joy or sorrow, e-x-
cept as the expression of the countenance informs us ; and ex-
pression, as I shall show you in this chapter, is wholly the
result of the action of muscles. So too, the muscles of the face
tell us, whether the blush that mantles there is the blush of
shame, or of modesty. And when we see paleness caused by
fear, we know that this is the cause, only from the expression
of the countenance and the attitude of the body, which may
very properly be called the expression of the body, though it is
much less marked than the expression of the countenance.
326. It is by the voice chiefly that thought and feeling are
communicated. And every variation of note, or of articulation,
is caused, as I shall show you in the next chapter, by the action
of muscles. When the muscles of the hand communicate to
others thought and feeling by writing, they merely translate
the language of the muscles of the vocal organs into conven-
tional signs. Leaving the language of these vocal muscles for
another chapter, I shall in this notice the language of the other
muscles of the body and especially of those of the foce.
327. As we watch an animated speaker, we see that it is not
the face alone, that adds force to his utterances by its corres-
ponding expressions. Various parts of the body in a measure
do the same thing. The head is nodded or shaken, the shoulder
is shrugged, the foot is stamped, and above all, the hand exe-
THE LANGUAGE OF THE MUSCLES. 223
Extent of range of the language of the muscles.
cutes a great variety of motions, in correspondence with th
thoughts and feelings which the mouth utters. Sometimes too,
the whole frame is brought into action. The gestures and the
attitudes, which are but gestures of the whole body, are im-
portant aids to the orator in conveying his thoughts and feelings
into the minds of his auditors.
328. This language of the muscles is used to a greater ex-
tent than we are conscious of in our ordinary intercourse. We
are not aware how much we communicate in this way. This
language is by no means confined to those palpable acts which
this subject suggests at once to the mind, the broad laugh
of merriment; the sighing, and sobbing, and weeping of grief ;
the stamping of the foot in anger ; the pointing of the finger in
calling attention to any particular subject ; the gesture used in
beckoning one to come to you, &c. But it includes numerous
little and scarcely observed motions, which in great variety
add to the significance of the words which we utter. And in
the case of the countenance, far more is communicated in the
aggregate by the constant gentle play of the muscles, than by
the broader and more palpable expressions, which are occasion-
ally produced by their stronger action. The deaf mute can
gather from the language of the muscles, as it accompanies the
voice that he can not hear, much more information as to the
passing conversation than one would suppose that he could.
And the full capabilities of this language we can only learn, by
observing to what wonderful extent the deaf and dumb can
communicate with each other by the use of natural signs, with-
out any aid from those which are artificial.*
329. While in man the muscles of the face are the chief
agents of expression, in other animals the very limited expres-
sion of which they are capable, is chiefly effected by other parts
of the body. For example, the dog wags his tail, the cat puts
up her back, the game-cock spreads out his ruff of feathers on
his head, &c. Rage is almost the only passion which can be
expressed by animals in the countenance. They can snarl, but
* I wns much struck with an illustration of the great range of the language of natural
signs, in an exhibition made many years ago by the lamented Gallaudet before the legisla-
ture of Massachusetts. Previous to exhibiting the attainments of his pupils, he requested,
that if any deuf and dumb person who had not been educated in an asylum were present,
his friends would bring him forward, thut he might show how much could be communi-
cated by natural signs. A man came forward, and Mr. Gallaudet learned from him by
natural signs alone such facts as these, the place of his residence, the fact that his parents
were living, the number of his brothers and of his sisters, the fact that he had seen Mr.
G. before in a certain place, ficc. Any one, it may be remarked in this connection, who
has been engaged in teaching the deaf and dumb, and who has, therefore, become skilled
in the use of sign-language, can converse quite readily by signs with foreigners from any
purt of the wort.
224 HUMAN PHYSIOLOGY.
Principal muscles used in smiling and laughter.
they can not laugh or cry. Hence it has been said, that man
can be very properly distinguished from other animals by
calling him " a laughing and crying animal."
330. Though the variety of expression in the human coun-
tenance is very great, it is ordinarily produced by the action
of very few muscles. The principal muscles are these the
muscle that wrinkles the eyebrow, causing frowning; the
muscles which draw down the corners of the mouth ; and
those which draw them up. When a smile occurs, it is pro-
duced by the muscles which raise the corners of the mouth.
When sadness is expressed, it is done by the muscles by which
the corners of the mouth are drawn down. Hence the origin
of the common expression, " down in the mouth." In laughter^
the muscles which raise the corners of the mouth act strongly,
wrinkling the cheek, simply because the corner of the mouth is
carried up so far as to push up the cheek before it. One other
muscle is brought into some action the circular muscle which
closes the eyelids for the eyelids are brought nearer together
in laughter, though in mere smiling they are not. In Fig.
126, representing broad laughter, you see the two effects
spoken of above, the wrinkling of the upper part of the chetk,
FIG. 126.
THE LANGUAGE OF THE MUSCLES.
225
Muscles used in the expression of grief.
and the partial closure of the eyelids. In weeping, the
muscles that draw down the corners of the mouth, which in
the mere expression of sadness act slightly, now act strongly.
At the same time the frowning muscle wrinkles the eyebrow.
In ordinary weeping it does so but slightly, but in weeping
from pain this muscle is strongly contracted. So it is also
when there is crossness mingled with the grief. Fig. 127,
FIG. 127.
which is the face of a faun weeping from pain, illustrates these
points. Sir Charles Bell, from whose work on the Anatomy
of Expression most of the figures in this chapter are taken,
says that he represents the expression of weeping in the face
of a faun, because it is mean and ludicrous as seen in the
countenance of man.
331. It is very commonly supposed that the eye has muck
226
HUMAN PHYSIOLOGY.
Prominent agency of the mouth in expression.
to do with the expression of the countenance, and hence such
phrases as these are in universal use a speaking eye ; a wild
eye ; the witchery of the eye ; the eye flashed, &c. But the eye
of itself has no active agency in expression. The muscles
which move it have, but not to any great extent ordinarily.
Of them I shall speak in another part of this chapter. The
apparent expression which the eye has is merely apparent, and
not real. It results altogether from the position of the parts
about the eye. This can be proved to you by any portrait
painter. It is related of an artist that, when a royal visito..
was admiring a sketch of the face of a weeping child, he said
to him, " has your majesty a mind to see how easy it is to
make this very child laugh ?" As the king said that he should
like to see it, the artist rubbed out a little at the corners of the
mouth and on the eyebrows, and added a few strokes to represent
the corners of the mouth as raised, and the eyebrows as with
out wrinkles, and the face, which was the moment before the
very picture of grie now exhibited a merry laugh. Afterward
he as readily restored the original expression. Now in this
case there were the same eyes in the two expressions. The al-
terations were made only in the neighboring parts, and the
same eyes were apparently weeping eyes at one time and
laughing ones at another.
332. In Fig. 128 and 129 you can see how much the
mouth alone affects the expression of the whole countenance.
The apparent expression of the eye is wholly altered by the
FIG. 128.
FIG. 129.
THE LANGUAGE OF THE MUSCLES. 227
The eye has little active agency in expression.
change about the mouth. If we could add at the same time
a change at the eyebrows, the expression of the eye would be
much more affected.
333. The language which is ordinarily used, in relation to
the agency of the eye in the expression of the countenance,
implies that the eye itself, apart from any motion, changes in
the changing expression. How this is done is not inquired ;
but there seems to be an ill defined notion that the animal
spirits, as it is expressed, flow into the eye more or less freely
with the changing feelings, or that a nervous influence is
exerted in some way upon the eye, altering its appearance.
These notions are so universal, and are so inwrought into our
language, and especially the language of poetry, that scientific
men even are apt to use the expressions to which they give rise,
in their descriptions of the language of the passions. Even Sir
C. Bell, in his celebrated book on the Anatomy of Expression,
in describing the expression of the emotion of joy, uses the
phrase, the eye is lively and sparkling. Let me not be under-
stood to mean, that I would have the expressions, in such uni-
versal use in common language and in poetry, given up. I
would as soon claim that the expression, the sun rises, should
be abandoned in common language. But as the astronomer
would have it understood, that the apparent fact, that the sun
rises, is only apparent, not real, so as a physiologist, I would
have it understood, that the apparent active agency of the eye
in the expression of the countenance is not real. And as it
would be objectionable to speak of the sun as rising, in a book
on astronomy, so in a professional book on the Anatomy of
Expression it is objectionable, in a description of the physical
signs of an emotion, to use the common phrases in regard to
the agency of the eye in expression.
334. Having thus noticed the principal muscular motions
that are concerned in the expression of the countenance, I pro-
pose now to go more extensively into the subject, and show
you how other muscles, besides those to which I have alluded,
228 . HUMAN PHYSIOLOGY.
Description of the muscles of expression in the face.
335. I will first call your attention to the particular muscles
of expression in the face, and indicate their mode of action.
They are represented in Fig. 130. There is a thin flat muscle
FIG. 130.
MUSCLES OF THE FACE.
covering the whole top of the head, represented at 1, 2, and 3 ;
3 being its thin tendinous part. It is fastened to the large
bones behind, and in front its fibres end in the skin of the fore-
head and the eyebrows, and in the circular muscle of the eye-
lids, 4. When it contracts, therefore, it raises the skin of the
forehead and the eyebrows ; and if it contract strongly, it
wrinkles the forehead. The circular muscle of the eyelids, 4,
when it contracts closes the eye. This and the large frontal
muscle just described, you can see, must have much to do with
the expression of the countenance. There is a very important
though small muscle which is not seen on this figure. You
see it on Fig. 113, at a. It is attached to the bone at the side
of the top of the nose, and is inserted into the skin of the eye-
brow. It is called the corrugator supercilii, or wrinlder of the
eyebrow. From the agency which this muscle has in the ex-
pression of certain passions and emotions, comes the word in
so common use, supercilious. Though a little muscle, it is
THE LANGUAGE OF THE MUSCLES. 229
Muscles of the face continued.
truly a supercilious one. It lias, as you will see as we go en,
a large play in many varieties of expression, produced by
combinations of action in the muscles of the face. There are
two muscles on the nose, 5 and 6, which compress the nose,
and wrinkle its skin. They have some agency in certain ex-
pressions of the countenance. At 7 is the circular muscle of
the mouth. When this contracts it closes the lips, and if it
act strongly it pushes them out. This is the muscle with which
in part pouting is done. At 8 is a muscle which is fastened
above to the bone of the nose, and runs down, its fibres ending
in the wing of the nose, and in the upper lip. When it con-
tracts, therefore, it moves the wing of the nose outward, and
draws up the lip. You see this muscle in action in some
emotions, the nostrils appearing spread out. At 9 is a muscle
which raises the lip, and at 10 and 11 are two muscles, that
raise the corner of the mouth, carrying it a little to one side.
At 13 is the muscle which acts in opposition to the two last.
It pulls the corner of the mouth down. At 12 is the muscle
which pulls down the lower lip. At 18 is the muscle in the
side of the mouth, which draws the corner of the mouth
backward, and also serves to press the cheek inward, and thus
prevent the food from getting outside of the teeth when we are
chewing it. This muscle also, by its compressing power, forces
out the air from the mouth when the cheeks are distended, as
in blowing a horn or a trumpet. Hence it is called buccinator,
from buccinare, to blow a trumpet. At 15 is a large muscle
which closes the lower jaw against the upper, and although its
chief use is to masticate the food, it has some agency in
the expression of the countenance, in fixing the teeth firmly
together, as in the expression of rage. There are three muscles
which move the ear; 19, moving it upward; 17, forward;
and 21, backward. These have but little power in man, but
in some animals they move the ear considerably, and are
prominent agents of expression.
336. In Fig. 131 the muscles about the mouth, which have
so much to do with the expression of the countenance, are very
distinctly showft. At a is the muscle which draws up the wing
of the nose and the lip ; b raises the lip ; c raises the corner of
the mouth ; d and e raise the corner of the mouth, and at the
same time carry it outward ; n draws it outward ; m draws it
downward and outward in which it is assisted by a broad thin
muscle, o, which situated just under the skin comes up from
the neck ; I draws the lower lip downward ; and i is the cir-
20
230 HUMAJ* PHYSIOLOGY.
Muscles of expression about the mouth.
I TW
MUSCLES ABOUT THE MOUTH.
cular muscle which closes the lips, and thrusts them out in
pouting. At A is a short muscle which is fastened to the sockets
of the teeth, and has its fibres ending in the skin of the chin. It
therefore draws the chin up when it contracts. It has so much
agency in the expression of scorn and contempt that it has been
called the superbus. It is by the action of this muscle, together
with the circular muscle i, that the expression termed pouting
is produced. The muscles which I have thus described are all
in pairs ; and in every pair both muscles contract always
exactly alike, unless affected by disease. We laugh and frown
and weep on both sides alike. All of these muscles of ex-
pression in the face are governed in their action by the
branches of one nerve, the respiratory nerve of the face.
When this nerve, therefore, is paralyzed on one side, and not
on the other, as is no uncommon occurrence, thfese muscles on
the paralyzed side, are motionless, and the individual can laugh
and frown and weep on only one side of the face. In Fig. 82
you have illustrated the result of this partial paralysis, the
face being perfectly quiescent on the left side. The contrast
would have been still greater if the face had been repre-
sented as in more decided action, as laughing, for example.
THE LANGUAGE OF THE MUSCLES. 231
Action of particular muscles in passions and emotions.
337. Having thus described the muscles of the face which
are the agents of expression, I will now show their action in the
expression of different passions and emotions. And I remark,
that you will see, as I proceed, that so far from there being any-
one muscle devoted to the expression of one emotion or passion,
expression is commonly the result of the combined action of
many muscles. And you will also see that, by virtue of this
combination, the same muscle often takes a part in the ex-
pression of various emotions.
338. When the frontal muscle (1, 2, 3, Fig. 130) contracts
it raises the eyebrows. This motion expresses either doubt or
surprise, and the observer determines which it is, by the ex-
pression of other parts of the countenance accompanying it, or
in other words, by the action of other muscles in the face.
When this muscle contracts very strongly, it draws up the eye-
brows so much, as to push up the skin of the forehead, and
wrinkle it. This, as you will soon see, is one of the many mo-
tions of the face which make up the expression of great bodily
fear. In joy this muscle acts moderately, raising the eyebrow,
therefore, but a little. This muscle often acts in connection
with the corrugator supercilii, the wrinkler of the eyebrow.
This may be seen in Fig. 132, respresenting a testy, peevish,
jealous melancholy. Here the corrugator and the frontal
muscles are both in strong action. You see also in this face
certain muscles about the mouth acting forcibly. The muscle
which draws the corner of the mouth down is in action while
the superbus (A, Fig. 131,) is drawing up the chin which
pushes up the lip before it. At the same time the muscle
which draws up the wing of the nose and the lip, (a, Fig. 131,)
contracts to some extent, producing an arching of the mouth,
and a peculiar shape of the wings of the nose. The upper lip
is arched by the action of this muscle in such a way, as to fit
the arching upward of the lower lip, produced by the superbus
and the muscle which draws down the corner of the mouth.
339. In the expression just described, and illustrated by the
figure, you see that the muscle which draws down the corner
of the mouth has. a considerable agency. Now, this muscle is
the chief agent in the expression of sorrow, as you saw in the
first part of this chapter. The difference in the" two cases lies
in the combination of action of the muscles. Thus, in sorrow
the muscle which draws down the corner of the mouth, does
not have the superbus to act with it, as in the case of the
passion, or rather compound feeling, represented in Fig. 132.
232
HUMAN PHYSIOLOGY.
Action of the muscles in fretful melancholy.
FIG. 132.
So also, in some forms of grief the corrugator supercilii acts
quite strongly, as seen in Fig. 127, where the grief is repre-
sented as caused by bodily pain. It performs a different office
in this case from what it does in the case of the expression re-
presented by Fig. 132, simply through the accompanying action
of other muscles, thus illustrating the effect of combination in
muscular action in varying the character of the expression. I
have already alluded to the different degrees of action in this
muscle in different forms of grief in 330. In quiet sorrow
this muscle is not in action, but there is a general languor re-
laxing the muscles of the face, while the corners of the mouth
THE LANGUAGE OF THE MUSCLES. 233
Action of the muscles in calm pleasure, and in admiration.
are slightly depressed. It is a state of the muscles directly op-
posite to that which exists when there is a calm quiet pleasure.
Then most of the muscles are in a state of gentle action, and
the corners of the mouth are a little raised, giving the radiance
of a light smile to the whole countenance. The frontal
muscle, slightly raising the eyebrows, adds to the effect.
340. The attitude, for so we may call it, of the countenance
in admiration, is quite nearly allied to that which I have just
described. The brow is expanded by the action of the frontal
muscle, and there is a slight smile produced by the raising of
the corners of the mouth. But the expression differs in some
respects from that of mere pleasure. The frontal muscle acts
rather more strongly in the former than in the latter, the eye
is more wide open, and is fixed upon the object of the admira-
tion, and the mouth is apt to be open, the jaw falling a little,
so that we can see the edge of the lower teeth and the tip of the
tongue. In both pleasure and admiration the expression varies
much in different individuals, according to their temperaments,
being characterized by activity in some, and in others more by
relaxation or even languor.
341. Let* me now call your attention to an expression of the
countenance, in which many of the muscles are in a state of
strong action. I refer to the expression of rage represented in
Fig. 133. The combination of muscular action here is quite
extensive. The corrugator super cilii acts forcibly, but un-
steadily, as is the case with the action of all the muscles in the
expression of this passion. The frontal muscle acts at the same
time, raising the eyebrows. The eyes are opened widely,
showing the rolling eyeballs. The muscle that raises the upper
lip, 6, Fig. 131, and the muscle that raises the wing of the
nose and the lip, are in strong action. The nostrils are there-
fore spread out to the utmost, arid the upper lip is drawn up-
ward. But as the circular muscle of the mouth also acts
strongly, there is only that part of the upper lip to which
the muscles, a and 6, Fig. 131, are attached, that can be drawn
up. This point is just where the sharp eye-teeth, or canine
teeth, as they are sometimes called, are situated. They are
therefore seen laid bare. This allies man to the snarling
brute, that shows his sharp teeth in his rage. Cooke, the tra-
gedian, is said to have had great power in the use of these
muscles. " In him," says Sir Charles Bell, " the ringentes (the
snarling muscles) prevailed ; and what determined hate could
he express, when, combined with the oblique cast of his eyes,
20*
234
HUMAN PHYSIOLOGY.
Complicated muscular action in expressing riige.
FIG. 133.
he drew up the outer part of the upper lip, and disclosed a
sharp angular tooth !" In rage the teeth are firmly closed by
the muscles which move the lower jaw, and when utterance is
given to it by the voice, these muscles but slightly relax to let
the words out through the almost closed teeth, and are rigid
again as soon as the words are finished.
342. The expression of mere bodily fear, represented in Fig.
134, is very different from that of rage, although some of the
muscles act in the same way in both. The frontal muscle acts
very forcibly, raising the eyebrows to their utmost extent, and
the eyeballs are largely uncovered, giving to the eyes a broad
stare. The corrugator supercilii is perfectly relaxed, while in
rage it is strongly contracted. The lip is raised and the nos-
trils are spread out by the same muscles, a and 6, Fig. 131,
which act so forcibly in rage. But the circular muscle of the
mouth, t, is relaxed, so that the whole lip is raised, instead of
THE LANGUAGE OF THE MUSCLES.
235
Movements of the eye in expression.
FIG. 134.
a part of it, as is the case when rage is expressed. The lower
jaw is fallen, while in rage it is in the opposite condition. The
hair is raised up by a general action of the whole frontal
muscle, 1, 2, 3, in Fig. 130.
343. The muscles of the eye, that is, those which move the
eyeball have some agency in certain expressions of the counte-
nance. Thus, in admiration, the fixing of the eye upon the ad-
mired object makes a part of the expression. In the expression
of devotion the eye turns instinctively upward. There are cer-
tain involuntary motions of the eyeball, which have much to
do with expression in certain states of the body, and in certain
emotions. These motions are performed by the oblique mus-
cles ( 307.) When the straight muscles which ordinarily con-
trol the motions of the eye lose their power from a state of
general insensibility, the eye is given over to the action of
these oblique muscles, which are involuntary, and therefore is
236 HUMAN PHYSIOLOGY.
Muscles of expression peculiar to man.
rolled about in its socket, being turned upward all the time, so
that the white of the eye only is seen. This occurs in sleep, in
fainting, in the stupor of disease, and in the approach of death.
344. The loss of power in the voluntary muscles of the eyeball
and eyelid is often seen ludicrously exhibited in the intoxicated
man. He squints and sees double from deficiency of action in
the straight muscles of the eyeball. The oblique involuntary
muscles of course roll the eye in proportion to the deficiency of
these straight muscles. The voluntary muscle too, which holds
up the upper lid, fails to do its duty, and the lid is constantly
disposed to fall over the eye. The frontal muscle is therefore
called upon to aid it. Hence, in the effort of the drunkard to
keep his eyes open, you see him raise up the eyebrows, the
eyelids being of course dragged up after them to a little extent.
" It is," says Sir Charles Bell, " the struggle of the drunkard to
resist, with his half-conscious efforts, the rapid turning up of the
eye, and to preserve it under the control of the voluntary
muscles, that makes him see objects distorted, and strive, by
arching his eyebrows, to keep the upper lid from descending.
The puzzled appearance which this gives rise to, along with the
relaxation of the lower part of the face, and the slight paralytic
obliquity of the mouth, complete the degrading expression."
345. I have thus pointed out the agency of the several mus-
cles that are engaged in the expression of the countenance.
Most of them are peculiar to man, being found in no other
animal. The inferior animals are variously endowed in regard
to muscles of expression. But even those that have the most
expression, have but few of those muscles which we find in the
face of man devoted to this purpose. They have the muscles
that move the eyes, those which raise the upper lip and thus
expose the teeth, and to some extent those which distend the
nostrils. The horse is especially endowed in regard to this
latter motion. In that glowing and beautiful description of the
horse in Job it is said, " the glory of his nostrils is terrible."
But most animals, even of the higher orders, have but a limited
motion of the nostrils compared with man. In him they have
much more to do with the expression of the countenance than
is commonly supposed. Their chief agency is in the expression
of the nobfer passions, and Sir Charles Bell remarks, that the
great tragedians, Mrs. Siddons and Mr. John Kemble, exhibited
their power in this respect in a remarkable manner.
346. None of the inferior animals have the corrugator super-
cilii. Indeed they have no eyebrows to move. The eyebrow
THE LANGUAGE OF THE MUSCLES. 237
Muscles of expression in animals.
is a strong peculiarity of man, and in view of its agency in the
expression of the countenance, varied as it is by the frontal mus-
cle and the corrugator, it has been said by some one, that it is
" the rainbow of peace, or the bended bow of discord." So also,
the muscles that raise and depress the corners of the mouth
are wholly peculiar to man. It is sometimes said that the dog
smiles. But if you observe him closely, you will see that as he
separates his lips or opens his mouth, at the same time that he
wags his tail, there is no raising of the corners of the mouth,
and therefore no true smiling. The idea that he smiles has
come from mere association with other motions by which he indi-
cates pleasure. The same can be said of the expression of sorrow
in the dog and other animals. There is little of it in the face
itself, amounting to nothing more than a mere downcast look,
if even that ; and we connect the idea of sorrow with the face,
by the force of association, from hearing the cries and witness-
ing the movements which distress produces. The grand peculi-
arities of human expression are in the muscles whose action I
have noticed in this paragraph, viz., the muscle that wrinkles the
eyebrow, the muscle that raises it, and those muscles which
move the corners of the mouth up and down. No animal but
man can frown, or weep, or laugh, for it has not the muscles by
which these acts are done.
347. Fear and rage are almost the only passions that are
expressed in the faces of animals. And in some of them there
are special provisions in muscular endowment, for the expression
of these mere brutal passions, particularly for rage. Thus, in
beasts of prey the ringentes, or snarling muscles have great
power. They raise the lip strongly, and display the sharp long
teeth which are to rend their prey in pieces. The eye too is
made terrible by certain muscles which are not found in man.
They are muscles which draw the eyelids backward upon the
prominent eyeball, thus producing a fixed staring of the eye,
and exposing its brilliant white coat, which by reflecting the
light gives the eye a sparkling appearance. These muscles Sir
Charles Bell calls scintillantes, from the apparent scintillating
effect which they produce. In the cat tribe light is reflected
from the bottom of the eye, when the pupil is dilated so as to
admit the light over a large portion of the retina. This occurs
in an obscure light simply because the pupil is then so much
dilated. The light is not created in the eye, and it is no indi-
cation of passion, as has been supposed.
348. You have seen the fact most fully illustrated in this
238 HUMAN PHYSIOLOGY.
Variety of combination in muscular action in expression.
chapter, that it is from combinations of action among the mus-
cles, that the various expressions of the countenance result.
To produce each one of these combinations, there must be a
consent of action between the muscles. Some are relaxed, while
others are contracted ; and those which are contracted are in
different degrees of contraction. Sometimes this harmony of
action is sportively destroyed by one who has great command
over the muscles, of the face, and the most incongruous expres-
sions result, mingled together in the same countenance, giving
it a very ludicrous appearance. And I may remark, that the
portrait painter is not always true to nature, but sometimes fails
to depict the full harmony of muscular action in the expression
of the countenance. I have noticed some of the combinations
of muscular action in expression ; but the view which you thus
get of them gives you but a faint idea of the infinite variety
of expression of which the human countenance is capable, as the
result of these combinations. In order to obtain some adequate
idea of this variety, keeping the views presented in this chapter
in your mind, watch some one engaged in speaking or in conver-
sation, in whom the play of the muscles of expression is peculi-
arly free. By so doing you will acquire new views of the capa-
bilities of the countenance in communicating thought and feeling,
and you will learn a lesson in this respect which the deaf mute
from necessity learns every day.
349. But we do not get a full view of the combination of
muscular action in expression, if we confine our observations to
the countenance. As I remarked in the first part of this chap-
ter, the muscles of other parts of the body, and sometimes of
the whole frame, are brought into action in connection with the
muscles of the face, in expressing thought and feeling. The
attitudes and motions of other parts of the body correspond
with the attitudes and motions of the countenance, so as to
produce an harmonious effect. The hand is more used than
any other part in aid of the countenance in expression ; but the
whole body is often brought more or less into action. The
character of a passion can sometimes be inferred from the atti-
tude merely, or from the mode of walking, as you see one at a
distance.
" You may sometimes trace,
A feeling in each footstep, as disclosed,
By Sallust in his Cataline, who, chased
By all the demons of all passions, showed
Their work even by the way in which he trode."
THE LANGUAGE OF THE MUSCLES. 239
Action of the respiratory muscles and the circulation in expression.
350. But it is the muscles of the respiratory organs which
sympathize most with the muscles of the face in expression.
This sympathy is the result of a nervous connection, and the
nerve of expression in the face is therefore, as before stated,
sometimes called the respiratory nerve of the face. Observe the
prominent agency which the muscles of the chest have in the
decided expression of the passions and feelings. In laughing
the individual draws in a full breath, and then lets it out in
short interrupted jets, the muscles of the throat, neck and chest,
especially the diaphragm, being convulsively agitated. And if
the laughter be strong and continued, he holds his sides, which
become really sore, from the violent action of the respiratory
muscles in this expression of his emotions. In weeping too,
these same muscles are affected. The diaphragm acts spasmod-
ically, the breathing is cut short by sobbing, the inspiration is
quick, and the expiration is slow, and often with a melancholy
note. But it is not alone in these marked cases that the respi-
atory muscles are seen to act, but you can observe their action
in many of the slighter expressions of feeling.
351. There are certain effects produced by emotions upon
the circulation, which heighten the expression resulting from
muscular action. I have already referred to the blush of mod-
esty, and the paleness of fear. In both laughter and weeping
the spasmodic action of the muscles of respiration impedes the
flow of blood through the lungs ; and hence the countenance
becomes flushed or suffused with the blood of the impeded cir-
culation. This is very different from common blushing, which
has nothing to do with the state of the general circulation, but
is entirely a local effect, confined to the capillaries of the part,
where it occurs. These capillaries are affected by the emotion
through nervous connections, just as the minute secreting vessels
in the tear glands are excited to unusual action.
352. From the views which I have presented of the capabil-
ities of the human countenance in expression, you must be as
much struck with its adaptation to the mind that moves it, as
you were with the hand in this respect. Both are instruments
of the mind, by which it accomplishes its purposes; and they
would be out of place in any other animal, even one of a higher
order, because he has not a mind capable of using such instru-
ments to advantage. Man needs the face, with all its endow-
ments, to express his thoughts and feelings, and the hand to do
the handiwork which his mind designs ; and the Creator has
240 HUMAN PHYSIOLOGY.
Training of the muscles of expression. Beauty depends much on their action.
proportioned the capabilities of these instruments to the necesi-
ties and the mental powers of man.
353. As the muscles of the face perform such high functions,
as the instruments of the mind in expression, it is important
that they should be well trained in these functions. Much is
often said about the importance of grace in the attitudes and
movements of the body, while seldom is a thought given to the
attitudes and movements of the countenance. Muscles are at
work in the one case as well as in the other, and the muscles
of the face can be trained to work skillfully and gracefully as
well as the muscles of any other part of the body. Indeed,
grace of action is much more important in the face than in the
body generally, because the muscles there are used so much
more for expression than in any other part. And yet the
speaker, who aims to gesture gracefully with his arms, is often
very careless in regard to the gestures, for so we may call them,
which are made by his face. So too the parent, who takes
unwearied pains to make the gait and attitudes of her child grace-
ful, often allows most uncouth attitudes of countenance to grow
into a habit. Many a child that has been drilled most faithfully,
in order to overcome awkwardness of movement, is suffered to
become incurably awkward in the face, as some one has aptly
expressed it. Sometimes even a habit of making grimaces is
unconsciously contracted, which utterly prevents the countenance
from accompanying the words that are uttered with any thing
like appropriate expression.
354. Beauty depends much upon the attitudes and move-
ments of the face, and not alone upon the shape of the features.
We often see a face which is beautiful in repose, that becomes
ugly the moment that it is in action, because the movements of
the muscles are so ungainly. And, on the other hand, we often
see faces which are quite at fault in the shape of the features,
display great beauty when in action, from the movements which
play so easily and gracefully among the muscles. It is a great
triumph of the spiritual over the physical, when the mind within
thus puts its impress of beauty upon a material form which is
destitute of symmetry. When it does this, there is more to
challenge our admiration, than when the sculptor chisels the
marble into beauty. And if he were to undertake, in imitation
of what we often see in living nature, to put beauty into ill-
shapen features, he would signally fail. This can be done only
by the active mind within, moving plastic features by the subtle
agency of nerves and muscles. In relation to the inadequacy
THE LANGUAGE OF THE MUSCLES. 241
Skill in the use of the muscles of expression.
of mere symmetry of form to meet our ideas of beauty in the
living countenance, Addison has justly said, "No woman can
be handsome by the force of features alone, any more than she
can be witty only by the help of speech."
355. There is nearly as much difference in skill in the use of
the muscles of the face, as in the use of those of the hand. And
we need not go to the accomplished orator or actor, as furnish-
ing us alone with the higher examples of this skill. It is often
seen exhibited in the ordinary intercourse of life, in those who
have great capacity of expression, together with a mind uncom-
monly refined and susceptible. In them every shade of thought
and feeling is clearly and beautifully traced in the countenance.
While this is the result of education of the muscles of expres-
sion, an education of which the individual is for the most part
unconscious, no direct attempt in the training of these muscles
will succeed, unless the mind itself be of the right character.
Intelligence and kindness cannot be made to beam from the
countenance, if they do not exist in the moving spirit within.
They are often awkwardly counterfeited, the one by the bustling
air assumed by the face of the shallow pretender, and the other
by the smirk of him who smiles only to get favor or profit from
others. The counterfeit is often mistaken for the reality ; and
in relation to the truly intelligent and kind, there is often much
error in the estimate put upon their intelligence and kindness,
from the different degrees in which these qualities, when exist-
ing in the same amounts, are exhibited in the expression of the
countenance. In some, the muscles of expression respond more
readily and aptly to the thought and feeling within, than they
do in others.
356. I know not of any more beautiful and striking exempli-
fication of the influence of the mind and heart upon the expres-
sion of the countenance, than is to be seen in those institutions
where juvenile outcasts from society are redeemed from their
degradation by the hand of benevolence. You can often note
most clearly the progress of the mental and moral cultivation
in the lineaments of the face, as lively intelligence takes the
place of stolid indifference, and refined sentiment that of brutal
passion. Sometimes a few weeks suffice to change the whole
character of the expression. The dull eye becomes bright, not
from any change in the eye itself, but from the intelligence and
sentiment which now play upon the muscles in its neighborhood.
Those muscles which impart a lively and pleasant cast to the
countenance when they are in action, are awakened from their
21
242 HUMAN PHYSIOLOGY.
The habitual expression of the countenance after death.
long continued dormant state by the magic wand of benevolence,
and thus give outward expression to the thoughts and feelings,
which genial influences are producing in the mind and the heart.
.The change is often as great in a little time, as it would be in
the face of an idiot, if he could be suddenly brought into the
full possession of the mental faculties.
357. The habitual expression of the countenance, depending
as it does upon the habitual condition of the muscles, is seen
after death. In the state of relaxation which immediately
ocelli's at death the face is very inexpressive, because its muscles
are, together with those of the whole body, so entirely relaxed.
But very soon they begin to contract, and they assume that
degree of contraction to which they were habituated during
life, and therefore give to the countenance its habitual expres-
sion. It is when this has taken place when the muscles, recov-
ering from the relaxation of the death-hour, resume their accus-
tomed attitude, as we may express it, that the countenance of
our friends appears so natural to us, and we are held, as if by a
charm, gazing upon the intelligence and affection beaming there
amid the awful stillness of death, till it seems as if those lips
must have language. And this expression is retained through
all the period of rigidity, till it is dissolved by the relaxation
which succeeds- this state and ushers in the process of decay.
It is thus that the soul, as it takes its flight, leaves its impress
upon the noblest part of its tabernacle of flesh ; and it is not
effaced till the last vestige of life is gone, and the laws of dead
matter take possession of the body. The state of countenance
which I have described is thus beautifully alluded to by Byron.
He who hath bent him o'er the dead,
Ere the first day of death has fled,
The first dark day of nothingness,
The last of danger and distress,
(Before decay's effacing fingers
Have swept the lines where beauty lingers),
And mark'd the mild angelic air,
The rapture of repose that's there,
The fix'd yet tender traits that streak
The languor of the placid cheek,
And but for that s;id, shrouded eye,
That fires not, wins not, weeps not, now,
And but for that chill, changeless brow,
Where cold obstruction's apathy
Appals the gazing mourner's heart,
As if to him it could impart
The doom he dreads yet dwells upon ;
Yes, but for these, and these alone,
THE VOICE. 243
Superiority of the vocal apparatus to musical instruments.
Some moments, aye. one treacherous hour,
He still might doubt the tyrant's power ;
So fair, so calm, so softly sealed,
The first, last look by death revealed !
CHAPTER XIV.
THE YOICE.
358. THE apparatus of the voice is truly a musical instru-
ment. We can see therefore, in its construction and arrange-
ment, the application of those principles, which usually regulate
the production of musical sounds, and which man observes in
making the various instruments which his ingenuity has invented
to delight the ear. It is, however, a much more perfect instru-
ment than any which man has invented. Almost every musical
instrument, it is true, has a greater compass than that of the
human voice ; but it is by no means the chief excellence of an
instrument that it can command a great extent of the scale.
The apparatus of the voice can execute enough of the scale for
all common purposes. It is wonderful that its compass is so
great as it is, for it is a very small instrument, occupying a space
of less than an inch square where the vibrating ligaments are
situated. In every respect besides compass this instrument far
excels all others. Listen to a good voice which has been
well educated. Its transitions have an ease and a grace which
the workmanship of man can not equal ; the richness and sweet-
ness of its tones are above all imitation with the most perfect
instruments ; and utterance is given to its various notes with so
little apparent effort, with so little show of machinery, in com-
parison with the instruments made by man, that we are tilled
with wonder at the effects produced by so simple, delicate, and
beautiful a piece of mechanism. But the most important cir-
cumstance to be noticed is, that there are parts connected with
this apparatus, which give articulation to the voice as it
comes from the vocal chords, thus making it the principal me-
dium of communication between man and man. This distin-
guishes it from every other musical instrument, and constitutes
244 HUMAN PHYSIOLOGY.
Voice of conversation and song. Voices of the brute creation.
its crowning excellence. When I come to speak particularly
of the articulation of the voice, you will see how really compli-
cated is the apparently simple mechanism that produces the
varied articulations, and thus makes the voice the chief medium
of mental communication. And if you try to measure, with
the utmost stretch of conception, the endless variety of thought
and feeling, which this apparatus conveys daily, hourly, every
moment from heart to heart in the intercourse of life, you will
be able to estimate in some good degree the value of those or-
gans, which, though we seldom spend a thought upon them, are
so constantly ministering to our enjoyment.
359. Such being the high uses for which the voice is designed,
when it possesses a rich and flowing melody, and its articulation
is graceful and easy, its powers of fascination are wonderful.
Such a voice is a fit medium of communication for " thoughts
that breathe and words that burn." This is more often true of
the voice of conversation than that of song. It is in the hourly
intercourse of life that melody of voice is most valuable to us as
a source of enjoyment, and here its influence is often astonishing.
It will sometimes give a charm, not to say beauty, to an ordinary
face ; while on the other hand, the fascination of beauty is often
destroyed by the utterance of a voice harsh and without melody.
And it may be remarked that a rich and finely modulated voice
of conversation, and a melodious voice of song, do not always
go together. The voice which has delighted the ear of multi-
tudes at the public concert, may be divested of all its charms,
when used in conversation ; and on the other hand, there are
many who sing unskillfully, and yet in conversation give utter-
ance to genuine and varied melody.
360. There is music not only in the human voice, but in the
voices also of the brute creation. And the varied forms of the
apparatus by which it is produced show the impress of the same
power. What variety there is in the sounds which come from
the multitudes of different animals on our globe, and how diversi-
fied is the handiwork exhibited in their vocal organs ! The pow-
er from which springs this endless variety is the same as that
which gives such diversity to the human countenance, and I
know riot which is the most wonderful display of it. And it
may be remarked, that although the voices of some animals are
harsh and discordant, those which we most frequently hear are
melodious. Even some of those which are unpleasant to the
ear, become in some degree pleasant when occasionally heard
at the right time and in the right place, from the addition which
THE VOICE.
245
. 135.
Two kinds of wind instruments reed, and those having an inflexible mouthpiece.
they make to the variety of sounds that we hear, and from the
associations which become connected with them. A goose on a
common, says Cowper, is no bad performer.
With these preliminary remarks I proceed to the investiga-
tion of the subject. I shall speak first of the voice as it is pro-
duced in the larynx by the vibration of the vocal chords or
ligaments, and then treat of the articulation of the voice.
361. As the apparatus of the voice is really a wind instru-
ment, I will first develope the principles on which wind instru-
ments produce the various musical notes, and
then show you the resemblance between these
instruments and the set of organs which are
engaged in producing the notes of the voice.
Wind instruments are of two kinds those
that have an inflexible mouthpiece, and those
in which the sounds are produced by a vibrat-
ing reed. The horn, trombone, trumpet, flute,
fife, flageolet, flute-stop and other stops of the
organ, <fec., are instruments of the first kind.
The cause of the variation of notes produced
in these instruments may be thus explained.
The column of air contained in the tube is the
vibrating body from which proceeds the sound.
Any thing then that affects the column of air
affects the note. The length, the breadth,
and the mode of producing the vibrations are
the causes of the variation of the note. The
holes which are in the side of a flute are for
the purpose of altering the length of the con-
fined column of air. In the trombone this is
done by sliding one part of the instrument
upon the other. The general rule is, the
longer is the column of air the more grave is
the note. Thus in the flute, the lowest note
that can be produced by the instrument is
made by covering all the holes, so that you
have a column of confined air the whole length
of the tube. The highest note, on the other
hand, which the instrument is capable of pro-
ducing is made by so arranging the fingers as
to allow the air to escape at the first hole.
In this case the length of the confined vibra-
ting column of air extends only from the mouth
24:6 HUMAN PHYSIOLOGY.
Size and width of vibrating column of air affecting the note.
hole to the hole from which the air escapes. I take another
illustration from the organ. Fig. 135 is a representation of one
of the pipes of the flute-stop of the organ, which is a wooden
box, made very much after the manner of a boy's chesnut
whistle. At a is the passage for the introduction of the air ; 6
is the inclosed column of air, the vibration of which produces
the sound ; c is the place of escape for the air ; and d is a mov-
able plug, by means of which the vibrating column of air can
be made longer or shorter, according to the note desired. In
tuning the organ, if the pipe gives too low a note the plug is
moved downward, thus shortening the column of inclosed air,
but if too high a note, the plug is raised up.
362. The same rule applies to the width of the vibrating
column of air. The wider the column the graver the note, and
vice versa. I would observe, that in a long, slender column of
air, as in the trombone, by giving the current of air from the
mouth a great velocity a high note may be produced ; but
where, as in the ophicleide, the column is both wide and long,
it is difficult to do this, because it is difficult to produce a quick
vibration in so large a body of air, with all the suddenness and
force with which we can move it.
363. In those instruments which have no expedient for alter-
ing the length of the column of air, such as the common horn,
the various notes are produced by narrowing or widening the
orifice by the agency of the lips, as the case requires, at the
same time giving, by the varied velocity with which the air is
forced into the instrument, a quicker or slower vibration to the
air. Grave sounds are produced by a wide, and acute by a
narrow opening. . In playing the flute the opening of the lips
is thus varied in order to produce a vibration which shall cor-
respond with the length of the column of air. If the flute
player, with his fingers arranged for a high note, should blow
into the mouth hole with his lips forming a large orifice, he
would not produce the desired note. To produce the proper
vibration in a short column of air, the orifice from which the air
issues to move this column must be small enough to corres-
pond, and with it there must be the requisite velocity in the air
as it comes from the mouth. You have a good illustration of
the influence of size of orifice on the note of sound in common
whistling. The higher the note produced the more narrow is
the outlet from the mouth. The size of it is regulated by both
the lips and the tongue.
364. In reed instruments the variations in note are produced
THE VOICE. 247
Reed instruments. Principles. Tube connected with the reed.
in a different manner. The clarionet, hautboy, bassoon, the
reed stops in the organ, &c., are instruments of this sort. It is
the vibration of the thin plate called the reed that causes the
sound. The longer this plate is, the slower are the vibrations,
and therefore the graver is the note, and vice versa. The prin-
ciple can be well illustrated in the reed stops of the organ. The
reeds in the different pipes are made of different lengths, accord-
ing to the notes which they are to produce. In a reed instru-
ment played by the mouth, as the clarionet for example, the
rapidity of the vibrations is regulated by the pressure of the lips.
In producing a high note the lips press firmly on the reed and
leave but a small portion of it to vibrate ; while in producing a
low note the lips press less firmly on the reed, and leave a large
portion of it to vibrate.
365. You see that the same principles apply to the reed as
to the column of air in the other kind of wind instruments. In
both cases the longer and thicker the vibrating body the coarser
is the vibration, and the graver the note. This same principle
also applies to stringed instruments. Thus in the piano, the
grave notes come from long and large strings, while the higher
notes come from slender and short ones. In the violin the
strings are all of the same length, the larger strings giving the
graver notes, and the smaller the higher ones. The notes are
varied also in the case of each string, by varying the tension.
They are varied too while playing on the instrument by varying
the length of the vibrating strings by the pressure of the fingers.
366. The reed is always connected with a tube. Has this
any influence upon the note produced by the reed ? It contains
a column of air through which the sound caused by the vibra-
tion of the reed must pass. Unless, then, the vibration of this
column of air corresponds with the vibration oF the reed, it will
alter the note. It does alter the note to some extent always.
It never raises it, but always makes it more grave. That is,
the vibration, in passing from the reed to the column of air,
becomes less rapid and coarser, as is always the case when vi-
bration passes from any substance to another. But the tube is
so arranged that there may be as little change in this respect
as possible, and yet have the combined effect of a reed and wind
instrument secured. Holes are therefore properly placed in the
side of the tube, so that with the fingers the column of confined
air may, in the case of every note, be placed in correspondence
with the vibration of the reed. Suppose the tube to be long
and without holes ; in this case low notes could be easily pro-
248 HUMAN PHYSIOLOGY.
Description of the organ of the voice. Hyoid bone. Lnrynx. Trachea.
duced, but attempt a high note arid you would fail. The reason
is obvious. The low note is caused by a low and coarse vibra-
tion of the reed, for the transmission of which a long column
of air is fitted. But if a high note be attempted, the slow
vibration of the long column of air disagrees with the quick
vibration of the reed, and flattens very much the sound after it
comes from the reed, as it passes through the tube. As I have
already hinted, the object of the tube is to secure in the instru-
ment the combined effect of a reed and a wind instrument.
The tube makes the reed speak, as it is expressed ; that is, it
gives intensity and an agreeable character to the sound. If
you disconnect the reed of the hautboy or bassoon, for example,
from its tube, and blow upon it, you can produce all the variety
of notes, but the sound is disagreeable ; but by connecting the
tube with the reed you produce a compound sound, as we may
call it, which has a sweet and rich melody.
We will now examine the apparatus of the voice, and see how
far the principles which I have developed in relation to common
musical instruments are applicable to this instrument.
367. Just at the root of the tongue, as described in the Chap-
ter on the Bones, 282, is a small bone, shaped so much like
the Greek letter v that it is called the hyoid or U-like bone.
The round end of this bone is towards the root of the tongue,
and its two ends point backward toward the pharynx. To
this bone is connected a long cartilaginous tube extending to
the lungs, called the trachea, or windpipe. It is through this
tube, as you have already learned, that the air goes back and
forth from the lungs in respiration and speech. It is not one
solid tube, but is composed of a great number of rings of carti-
lage connected together by membranous parts. The rings are
not perfect circles. They are deficient behind, and this deficiency
is supplied by a membrane. The object of this arrangement is
evident. The part of the tube where the rings are deficient is
Jirectly in front in its whole length of the oesophagus or gullet,
the tube through which the food passes. If the rings had been
made entire, it is manifest that their pressure would interfere
somewhat with swallowing. But it is the upper part of the
windpipe, that part which is immediately below the U-like bone,
rtrhich claims our attention as the seat of the formation of the
voice. This part is called the larnyx. It is formed of five car-
tilages, the arrangement of which I will now show you. The
largest of these cartilages, the one which forms the most of the
body of this music-box, as we may call it, is the thyroid. It is
THE VOICE.
249
Thyroid, cricoid and arytenoid curtilages.
the pomum Adami, or Adam's apple, which is so easily felt in
the top of the neck. This cartilage forms the front and sides
of the larynx, but it is open behind. The cricoid cartilage is
shaped very much like a seal ring, and this resemblance gives
it its name. The narrow part of it is situated directly under
the thyroid cartilage, in its front and at its sides, but the broad,
seal-like part of it. is behind, projecting upward and filling up a
part of the open space left by the deficiency of the thyroid in
in its rear. A side view of these parts
is given in Fig. 136, in which 1 is the FIG 136>
the U-like bone ; 4 is the thyroid car-
tilage; and 6 the cricoid. At 8 is
the back part of the cricoid, filling up
a part of the space in the open rear
of the thyroid ; 3 is a horn shaped
projection of the thyroid, and 5 is a
smaller one below, projecting over on
to the outside of the cricoid ; 2 is a
strong membrane or ligament connect-
ing the hyoid or U-like bone with
the top of the thyroid ; 9 is the epi-
glottis, drawn up by a hook ; and at
V are the rings of, the trachea. The
epiglottis is composed in part of car-
tilage. It is, as I have already told
you, in the Chapter on Digestion, 78,
the lid of the music box, the larynx,
shutting down when we swallow, so side view of
that the food or drink may pass over THE LARYNX.
it, and being raised up when we
breathe or speak.
368. There are two small cartilages which are not seen in
this figure, called arytenoid cartilages, from two Greek words,
meaning ladle and shape, because they bear some resemblance
in form to a ladle. They stand in the open space in the rear
part of the thyroid, on the top of the cricoid cartilage. They
are the pillars to which the vocal chords or ligaments are attached
behind. These two cartilages are movable, having a regular
joint with the upper edge of the cricoid. There are small mus-
cles which pull them in different directions, and thus change
the degree of tension and the position of the vocal ligaments,
and of course vary the note of the sound produced by their vibra-
tion. That you may understand how this is done, I give you
250
HUMAN PHYSIOLOGY.
Vocal ligaments. Mode of their action.
Diagram showing the action of the
VOCAL LIGAMENTS.
FIG. 138.
in Fig. 137 a diagram showing the arrangement of these liga-
ments. It represents a view of them as you look down into
the larynx, in which a is the front of the thyroid cartilage, and bb
are the two arytenoid cartilages. To
these you see are attached two sheets
of membrane, which are also fastened
all around to the inside of the thy-
roid. If these movable posts, as we
may call them, to which the ligaments
are thus attached, be drawn back-
ward, it is obvious that it will make
the ligaments more tense. If they
are separated from each other, the
opening between the ligaments will
be widened. If they are brought
nearer together, this opening will be
narrowed, and the forward part of the free edge of each liga-
ment will be prevented from vibrating, because it is here brought
in contact with the other ligament.
Now there are small muscles which
are attached to the arytenoid car-
tilages for the purpose of moving
them as I have pointed out. The
figure which I have presented is a
mere diagram, to show the arrange-
ment of the ligaments for the pro-
duction of the various notes of the
voice. In Fig. 138 is represented
the actual appearance of the liga-
ments and the arytenoid cartilages,
as you look down upon them. The
ligaments you observe are thicker at
their free edges than any where else.
369. In Fig. 139 you have a view of the larynx and trachea
irom behind, in which are shown two of the muscles that move
the arytenoid cartilages. At h is the hyoid bone ; t t, the
posterior margins of the thyroid cartilage; between these
stands the broad rear part of the cricoid cartilage, the
middle line of which you see at c; at r are the rear ends
of the rings of the trachea ; I is the membranous part of the
trachea, which lies in front of the oesophagus or gullet; a
marks the top of one of the arytenoid cartilages, and you see
also the top of the other ; e is the epiglottis represented as
THE VOCAL LIGAMENTS.
THE VOICE.
251
Muscles regulating the tension of the vocal ligaments.
FIG. 139
BEAR VIEW OF THE LARYNX AND THE TRACHEA.
raised up as when we are speaking ; b is a muscle, which, be-
ginning at the middle line of the cricoid cartilage, runs forward,
and is fastened to the outside of the arytenoid cartilage, there
being one like it on the other side, as you see ; s is another
muscle going from the cricoid to the arytenoid cartilage, which
also has its fellow on the other side. You can see that the muscle,
s, and its fellow, if contracted would bring the arytenoid cartilages
nearer together, and so diminish the opening between the vocal
membranes which are fastened to these pillars. The muscle, 6,
and its fellow, on the other hand, when they act, so draw upon
the outer edges of the arytenoid cartilages as to separate these
cartilages from each other, and therefore enlarge the openings
between the ligaments. There are other muscles not seen in
the figure, that alter the size of the orifice between the vocal
ligaments and their degree of tension, and thus affect the notes
of the voice.
370. I have described the true vocal ligaments. But there
252
HUMAN PHYSIOLOGY.
Interior view of the larynx and epiglottis.
is another pair of ligaments directly above them, the space
between which is the real opening into the larynx, upon which
the epiglottis shuts down when we swallow. You will get a
good idea of the arrangement of the two pairs of ligaments from
Fig. 140. This is a representation of an inner view of one
FIG. 140.
INTERIOR OF THE LARYNX.
half of the larynx, the division being made directly down, and
from front to rear. At t is the front of the thyroid cartilage
with its cut edge ; at c c, are the two cut edges of the cricoid,
showing how narrow is its front part compared with its broad
rear portion ; a is the left arytenoid cartilage, c showing the
place where it is united by a joint to the top of the cricoid ; / is
the trachea ; r is the true vocal ligament or chord ; v is the
space between this and the upper ligament ; and e is the epig-
lottis which is shut down upon the upper ligaments as a cover
by the contraction of the muscle 6, just when this is needed.
THE VOICE.
253
Upper and lower ligaments. The lower the true vocal chords.
FIG. 141.
In Fig. 141 is a diagram represent-
ing the plan of these two pairs of
ligaments, as shown by a perpendic-
ular section from side to side. B B
represents the vocal ligaments, C C
the upper ligaments, and V V, the
two recesses between them.
371. We know that it is the
lower ligaments that are the true
vocal chords, because the parts
above these, even the upper liga-
ments, may be all cut away, and yet
a vocal sound may be produced ;
while if an opening be made into
the larynx below the lower liga-
ments the voice will be destroyed.
Magendie, a French physiologist,
speaks of a man, who on account of
an opening in the larynx was never
able to speak without pressing his
cravat tightly against this opening,
in order to prevent the air from escaping through it. Many
experiments have been tried with the larynx after death to
verify the results above stated. The lower ligaments are then
the vocal chords, by the vibration of which all the different
notes of the voice are produced. And the other parts of the
vocal apparatus serve only to modify the sound caused by the
ligaments. The lungs act merely as the " wind-chest," to hold
the air which being forced out strikes on the ligaments, and
makes them to vibrate.
372. Let us now apply to this apparatus the principles
which I have developed in the beginning of this chapter, as
regulating the variation of note in common musical instru-
ments. The size of the aperture, through which the sound is
thrown out, influences the note, of which we have a familiar
example in whistling. And as you have seen that the size of
the opening between the vocal ligaments is varied by the
muscles moving the arytenoid cartilages, this must have an
influence upon the note of the voice. But this is not the only
cause of the variation of the note. As I showed in relation to
the reed, and to the strings of stringed instruments, so also
here the larger and less tense are the vibrating bodies, the vocal
chords, the graver is the note, and vice versa. You have seen
22
254 HUMAN PHYSIOLOGY.
Principles of musical instruments applied to the vocal apparatus.
how these chords or ligaments are varied in tension by the
action of the muscles that move the arytenoid cartilages. You
have also seen that, as these cartilages are brought near to-
gether by the muscles, the extent of the free vibrating edges of
the ligaments is shortened, because their edges are brought to-
gether in their anterior part (Fig. 137). Magendie verified
this by observation. He opened the throat of a noisy dog in
such a way that he could look directly upon the vocal ligaments.
When the sounds were grave, he observed that the ligaments
vibrated in their whole length, and that the air passed out in the
whole length of the chink between them. But when the
sounds were on a high note, the ligaments did not vibrate in
their anterior part, but only in the posterior, and the air passed
out only at the open vibrating part. It is manifest that in pro-
ducing the various notes, the muscles that move the arytenoid
cartilages act upon the ligaments just as the lips do upon the
reed of the hautboy or bassoon, regulating the extent and the
rapidity of the vibrations.
373. There has been much discussion as to the kind of
musical instrument the larynx most resembles. From the facts
above stated it appears clear that it most resembles reed instru-
ments, though its analogy to stringed instruments is also quite
apparent. There is also a resemblance to some small extent to
common wind instruments, as the size of the orifice between the
vocal ligaments must have some influence upon the note.
Whatever we may think as to the degrees in which these
analogies exist, we can see that the great principle of musical
sounds is regarded in all the arrangements of the vocal appara-
tus, viz., that coarse and slow vibrations produce grave notes,
while rapid and fine vibrations produce high ones.
374. I will trace the resemblance between the instrument of
the voice and common musical instruments still farther. The
sound as it comes from the larynx passes through a tube, just
as the sound coming from a reed does in a reed instrument.
In other words there is a body of inclosed air extending from
the larynx to the outlets of the mouth and nose, which vibrates
in transmitting the sound from the larynx. This body of air is
not as simple in its form as that is which is inclosed in the tube
of common reed instruments. It has three outlets, the mouth
and the two nostrils. The sound of the voice, however, seldom
comes out from the orifices of the nostrils, but almost always
from the mouth. In humming it comes altogether from the
nostrils. In ordinary speaking and singing the cavities of the
THE VOICE. 255
Tube of the vocal apparatus like that of a reed instrument.
nose act as reverberating cavities, the sound which reverberates
there issuing from the mouth. This fact will be illustrated
when I come to speak of the articulation of the voice. The
curtain of the palate answers as a sort of swing door between
the cavity of the mouth, and the cavities of the nose, to direct
the air the one way or the other. When a sound is to be
reverberated in the cavities of the nose, it hangs in such a way
that the communication between the mouth and these cavities
is open.
375. You have seen that the tube connected with the reed
in the reed instrument is so arranged, that the length of the
confined column of air can be changed, in producing the
different notes, the vibration of the air thus being brought into
correspondence with that of the reed. How is the same thing
effected in the vocal apparatus ? It is done in two ways.
First, the length of the tube is altered. If you place your
finger on the front of the larynx, and then sound various notes,
you will feel the larynx rise when you sound a high note, and
fall when you sound a grave one. The object of this move-
ment is to alter the distance from the larynx to the outlet of the
mouth, in other words, to alter the length of the column of air
in the tube, so that it may correspond in its vibration with the
vibration of the vocal chords. But the size of this column of
air is altered in another way. It is altered in its width, which,
as I have remarked in relation to musical instruments, 362, is
quite as effectual in changing the vibration as an alteration of
length. The tube of the vocal instrument you readily see can
be altered in its width by the muscles of the throat and
mouth.
376. The object of the tube of the reed instrument is, I have
stated in 366, to make the reed speak, as it is termed ; that is,
to give intensity and an agreeable character to the sound. The
tube in the instrument of the voice undoubtedly does the same
thing. If the voice should come directly from the larynx with-
out passing through the tube attached to it, it would be as dis-
agreeable as the sound of a reed when separated from its tube.
The voice gets most of its melody after it is made in the
larynx, as it passes out through the column of air in the throat
and mouth. And it is the variations of this tube produced by
the muscles that surround it that give to the voice its variety
of tone as well as its melody, thus constituting one of the
great excellencies of the vocal instrument in comparison with
all common musical instruments. If the voice of Jenny Lind
256 HUMAN PHYSIOLOGY.
' ' *
Seat of hoarseness. Influence of the epiglottis on the voice.
could be made to come directly from the larynx, notwithstand-
ing its great compass, it would lose all its charm, and would be
better fitted for the performances of Punch and Judy, than for
the public concert.
377. It is a very common popular notion, that a hoarseness,
or a loss of voice, indicates disease in the lungs. But y6u have
seen that the lungs are the mere bellows, or the " wind-chest " of
the organ of the voice, and that the voice is produced by the vi-
bration of the vocal ligaments as the air forced from the wind-
chest strikes them, and is modified by the tube which extends
from the larynx to the outlet of the mouth. Any alteration of
the sound therefore, as hoarseness, must be caused by difficulty
either in the ligaments, or the tube, or in both, and an en-
tire loss of the voice can be caused only by an affection of the
ligaments. Disease in the lungs, it is true, is very apt to affect
the larynx and the throat by extension or by sympathy, and
thus alter the voice ; but it often does not. Consumptive per-
sons sometimes have a clear voice almost to the last.
378. The epiglottis, besides acting as a lid for the larynx, for
the food to pass over it into the oesophagus, also has an in-
fluence upon the voice in two ways. First it can be made to
narrow more or less the passage of air from the larynx. And
secondly, some experiments of M. Grenie on reed instruments
show, that it has an influence upon the intensity of the voice.
When experimenting on some reed instrument, he wished to in-
crease the intensity of sound without changing the reed. For
this purpose he gradually increased the force of the current of
the air ; but this not only augmented the sound, but raised its
note. He at length obviated the difficulty, by placing obliquely
in the tube, just under the reed, a supple elastic tongue. He
could now give greater intensity to the sound without raising
its note. The epiglottis seems to perform the same office in
our vocal tube, for it is elastic and supple like the little tongue
which M. Grenie placed in the tube of his instrument. Its
situation is similar also, it being directly over the double reed
of the larynx, as we may call its ligaments. There are muscles
to move it, so that it maybe at the right inclination in all
cases. One of these is seen in Fig. 140 at b.
379. I have thus traced the analogy between the apparatus
of the human voice, and musical instruments. How nicely ad-
justed are all its parts ! With what precision must the muscles
that move them act in those who are able to produce the most
delicate, as well as the most striking variations of note ! Every
THE VOICE. 257
Delicucy of the action of the vocal muscles. Gliding from note to note.
modulation of the voice, however slight, requires muscular ac-
tion to effect it. The vocal ligaments must be put in just such
a state, or the wrong sound will be produced. So too, the
muscles of the mouth and throat must put the tube of the
vocal instrument into the right shape, in order to have the con-
tained column of air correspond in vibration with the vocal
ligaments. To have some conception of the variety of the
motions of the muscles concerned in the modulation of the
voice, listen to some singer whose voice can command with ease
and freedom a great extent of the scale. For every note that
you hear there is a distinct and particular adjustment of the
vocal ligaments, and of course a particular degree of contrac-
tion of the little muscles that move them. Let us see how deli-
cate the action of these parts is. U is calculated that the liga-
ments vary in length only about the of an inch in producing
all the notes of the voice. Now the natural compass of the
voice (that is its range from its lowest to its highest note) in
most singers is about two octaves or 24 semitones. Within
each semitone a singer of ordinary capability can produce 5 or
6 distinct notes ; so that for the whole number of notes that he
can sound distinctly 120 is a moderate estimate. He therefore
produces 120 different states of tension in the vocal ligaments.
Arid as the variation in their length for passing from the lowest
of these 120 notes to the highest is only the -J-th of an inch, the
variation required to pass from one note to another will be only
the -rJrrth of an inch. A very expert singer can produce a
much more delicate action than this, and distinctly appreciate
the result by his ear. How great the contrast between the
minute contractions of the little muscles that move these vocal
ligaments, and the contractions of the large muscles in the arm
that wield the ax and the sledge-hammer!
380. It is proper to notice here one very marked difference be-
tween the vocal apparatus and common musical instruments. I
have spoken in the previous paragraph of distinct notes as exe-
cuted by the voice. Most instruments execute only these distinct
notes. But the voice can also glide from one note to another
with a continuous sound. In this respect the vocal instrument
is superior to common musical instruments. There is one
instrument, however, the violin, in which this gliding movement
can be to a great extent imitated. It is done by sliding the
finger on the string, as it vibrates under the bow. A peculiar
use of this gliding movement distinguishes tjie voice of speech
from that of song, as I shall show you in another part of this
22*
258 HUMAN PHYSIOLOGY.
Training of the muscles of the voice. Importance of keeping the chest full of air.
chapter. It is by an imitation of this, by sliding the finger on
the string, that the violin can be made to imitate so well the
tones of conversation.
381. The muscles, by which all the variations in the tension of
the vocal ligaments are effected, receive nerves from the brain, and
are under the guidance of the will. When the mind therefore
wills to produce a certain sound, these muscles immediately
place the parts in such a state as to cause that sound. This is
true of the muscles that put the tube in correspondence with
the larynx, as well as of those which produce the right state of
tension in the ligaments. It is also true of the muscles which
articulate the voice, of which I am yet to speak, and of those
which work the chest, the bellows or "wind-chest" of the organ
of the voice. The muscles of this apparatus are in the same con-
dition with other voluntary muscles; and therefore, like them,
the more they are trained in the exercise of their powers, the
more perfect will be their action. The muscles in the arm and
hand of the infant learn to execute the motions of which they
are capable gradually. Just so it is with the muscles of the
voice from our infancy they are trained under the ear as an
instructor. The muscles which regulate the adjustment of the
vocal ligaments, in producing the different notes, cannot do it
accurately without the education of exercise, any more than the
lips of one just beginning to play on the hautboy or clarionet,
can regulate their pressure on the reed, so as to sound the dif-
ferent notes correctly. The analogy is perfect, for it is the
muscles moving the vocal chords that vary the note of the voice,
and it is the muscles moving the lips that vary their pressure
on the reed, and of course vary the note of the instrument.
382. The skillful singer or speaker exhibits much skill in
managing the muscles of the " wind-chest." He keeps it all
the time well supplied with air, so that but a comparatively
slight action of the expiratory muscles will suffice to throw the
air against the vocal ligaments with the requisite force. But
an unskillful singer or speaker much of the time has his chest
poorly supplied with air, and so speaks or sings, as it is expressed,
from the top of the chest. It costs him, therefore, so much labor
to throw out the air with sufficient force, that he is soon tired
out. The necessity of keeping the chest full of air, in order to
work the vocal apparatus easily, may be illustrated by reference
to the bagpipe. If the bag containing the air be well filled, a
slight pressure of the arm upon it will force the air through the
pipe with sufficient rapidity to produce the sound. But if the
THE VOICE. 259
Tiring out the vocal muscles. Vocul apparatus in birds.
bag be flaccid, from the little quantity of air in it, a very strong
pressure of the arm will be required to produce the same effect.
383. But it is not the muscles of the chest only that are tired
out in the unskillful singer or speaker, but also the muscles of
the larynx and the throat. And a frequent tiring of these
muscles weakens the force of the parts, and often at length
produces disease. Much of the throat-disease of public speakers
comes from this cause, and is a nervous disease, the affection of
the lining membrane of the throat being often a mere accompa-
niment. This result is more apt to occur when the nervous
force of the system generally is impaired, than when there is a
state of vigor. It is also more apt to occur in those who speak
in a uniform and somewhat monotonous manner, than in those
who have much variety in their mode of speaking. A continua-
tion of precisely the same muscular effort for any length of time is
apt to produce painful exhaustion, while a much greater amount
of varied muscular effort may be put forth without weariness,
or even with pleasure.
384. It would be interesting to trace the differences in the
arrangement of the vocal apparatus in different animals, but I
will only notice the arrangement which we find in birds. The
voice of birds is formed not, as in us, at the top of the wind-
pipe, but at its lowest portion. Like the human voice, it is
produced by the vibration of sheets of membrane. These are
placed just at the division of the trachea, where its two branches
go off to supply the two lungs with air. The voice is formed
by these ligaments, and is then transmitted through the column
of air contained in the whole length of the windpipe. This
column of air must have some influence on the note of the voice,
according to its length and diameter. Birds, therefore, in sing-
ing different notes change its length in some measure. This is
easily done, as the windpipe is composed of rings of cartilages,
connected together by membranous substance. There are mus-
cles indeed up and down the tube, for the purpose of shortening
it by approximating these rings to each other. As the turkey
gobbles he throws his head up and down, and thus shortens
and lengthens the trachea. This movement is quite obvious
also in the canary bird.
385. Having thus treated of the formation and the mod-
ulation of the voice, I come now to its articulation, which
makes it the grand medium of intercourse between man and
man. I will first describe the parts engaged in articulation, and
then speak of the agency of each of them.
260 HUMAN PHYSIOLOGY.
Parts engaged in the articulation of the voice.
386. The vocal tube, which I have described as extending
from the larynx to the outlets of the mouth and the nostrils,
produces all the variety of pronunciation in all the different lan-
guages of our globe. It is all one cavity, though it is partially
divided by partition walls. If you recur to Fig. 10, on page
48, you will see a representation of this compound cavity. At
the top of the trachea d you see the epiglottis c, which shuts
down upon its orifice when we are swallowing. Above this is
a large space called the pharynx. It is the back part of the
throat, which we can see behind the arch of the palate on
looking at it through the open mouth. Its communication with
the mouth and the cavities of the nose is regulated by the palate
g, which is moved by muscles into the different positions required.
The cavities are very complicated, having several partitions par-
tially dividing them, as seen in Fig. 89, and they communicate
with cells in the bones by small orifices. That very movable
organ, the tongue, and the teeth and lips, I need not describe.
387. We will now observe the agency which the different
parts of this compound vocal tube have in the articulation of the
voice. Every letter, whether it be a vowel or a consonant, re-
quires a particular position of the different parts of the vocal tube.
In some letters the tongue is the chief agent in articulation, in
others the lips, in others the teeth, in others the palate, and there
are some in the formation of which the cavities of the nose have
an important agency. I will notice the different parts separately.
388. The tongue has been considered so essential to speech,
that tongue and language are often used synonymously. But
though it does perform an important part in articulation, it is
not absolutely essential. Though it assists in the formation of
many of the alphabetical elements, it is the principal agent in
but two of them, I and r. The loss then of this busy little
organ does not necessarily produce dumbness, nor even impair
to any great extent, in some cases at least, the power of speech.
To prove this I will cite a few facts which appear to be well
authenticated. The Emperor Justin says that he had seen ven-
erable men who, after their tongues had been cut off at the root,
"complained bitterly of the torture they had suffered." He
says also in another place that some prisoners, who were pun-
ished in this barbarous manner by Honorichius, King of the
Vandals, " perfectly retained their speech." But there are cases
more thoroughly attested, having been examined and reported
upon by scientific observers. A boy, who lost his tongue by
disease at the age of eight years, was exhibited publicly because
THE VOICE. 261
The tongue less essential than commonly supposed. Dentals.
he could talk without a tongue. At the request of the members
of the University of Saumur, the boy was brought before them
by his friends. After a strict examination they were perfectly
satisfied as to the facts in the case, and recorded their official
testimony to that effect. A very interesting account is given
of another case in the Philosophical Transactions, in several
papers published from time to time between the years 1742
and 1747. It is the case of a girl who lost from disease the
whole of her tongue, together with the uvula, (the little round
body which hangs down from the middle of the arch of the
palate,) and yet could talk and swallow as well as any one.
So perfect was her articulation, that she could pronounce with
exactness those letters which commonly require the agency of
the tip of the tongue. She could sing finely, articulating with
the same clearness as when she talked. The sockets of the teeth
too were so much injured, that there were few teeth, and these
rose so little above the gums, that they could not render much
assistance, if any, in articulation. This case was investigated
very thoroughly. The account was giveiito the Royal Society,
attested by the minister of the parish, a physician of repute,
and another respectable person. The Society, not wishing to
give too easy a credence to so strange a case, requested another
report from another set of witnesses appointed by themselves,
arid they gave them a series of questions to guide them in their
investigations. The report which they made out coincided very
minutely with the account first given. The case excited so
much interest that the young woman was at length brought to
London, and appeared before the Royal Society to satisfy them
that she could really talk and sing, although she had no tongue.
389. Some of the letters are formed principally by the teeth,
as c, t, s, z. They are therefore called Dentals. It is the too
frequent and bungling employment of some of these which con-
stitutes lisping. Those who have a tongue too large for the
mouth are apt to lisp. In advanced age, when the teeth are
lost, we find this defect of lisping. The reason is obvious.
When the teeth are gone, the sockets gradually become oblit-
erated, and that part of the jaw-bone where the teeth were, of
course diminishes in size, making the mouth too small for the
tongue.
390. The letters, in the articulation of which the lips take
the lead are 6, p, m,f, v,w, &c, and are called labials. Chil-
dren, when they first begin to talk, use labials freely, because
they can see in others the motions necessary for their pronunci
262 HUMAN PHYSIOLOGY.
Labinls. Reverberation in some letters in the nasal cavities.
ation, and then imitate them. Hence the endearing terms used
by the child to the parent are, I believe, in all languages, or
nearly all, composed of labials and vowels. And too, it is from
the delight which the child takes in repeating over and over
these terms, that we have the word papa and mama, instead
of pa and ma. The same thing can be observed in other lan-
guages as well as the English. If we teach a child to say
father instead of papa, he finds little difficulty in articulating
the first syllable, because it begins with a labial,/; but in the
last syllable he will at first substitute for th the labial v, making
it faver. Intoxicated persons, their lips being weak and trem-
bling, are apt to make an awkward use of the labials, as well as
of those letters in which the tongue has much agency. Per-
sons with large lips also are apt to use the labials unskillfully.
Sometimes one labial is used for another, as / for v, and p for
b. This is very common among the Welsh. Shakspeare gives
us an amusing case of this sort in Sir Hugh Evans in the Merry
Wives of Windsor. "Ferry goot," says he, "I will make a
prief of it in my note book." And so he says prains for brains,
peings for beings, petter for better, &c. The labial w is some-
times used for v, thus, winegar, indiwisible, werry wigorous.
391. The nasal cavities, it is obvious, must have a great
influence in articulation. The letters m and n are partly nasal.
In pronouncing m at the end of a syllable, as am, em, or om,
we close the lips, and the sound issuing from the larynx rever-
brates in the cavities of the nose. You can perceive this rever-
beration by pressing gently upon the nostrils with the fingers
while pronouncing this syllable. The same can be said of n,
except that in pronouncing it we press the tip of the tongue
against the roof of the mouth just behind the front teeth, pre-
venting the passage of the air out through the mouth in this
way, instead of doing it by closing the lips, as in articulating
m. When m and n begin syllables, as in mo and no, the mouth
is opened after the m or n is pronounced, in order to give utter-
ance to the next letter. These are two distinct acts, but the
one succeeds the other so quickly, that they appear to be a
single act. The nasal sound ng is the one which we employ in
humming. Hence, the mouth is kept closed and the sound issues
from the orifices of the nostrils.
392. A reverberation of sound in the back part of the mouth
and the cavities of the nose constitutes a distinguishing peculi-
arity of many of the consonants. Thus, in pronouncing b arid
p. the lips are placed precisely in the same manner, and the
THE VOICE. 263
This reverberation in some consonants and not in others.
only difference between them is that 6 has the reverberation
spoken of, but p has not. If you pronounce these two letters
in the syllables op and ab, for example, while you press on the
nostrils with your fingers, you can feel the vibration occasioned
by this reverberation in pronouncing 6, but there is obviously
none in pronouncing/). This reverberation is heard in the follow-
ing alphabetical elements, B, D, G, V, Z (the sound of s in the
word as), Y, W, Th (as in thou), Zh (the sound of z in azure),
Ng, L, M, N, R. Those which have not this reverberation are
P, T, K, F, S (as heard in sun), H, Wh (as heard in which),
Th (as heard in thing), Sh (the sound of s in sure). That you
may contrast these two sets of alphabetical elements individually,
I place them here in two rows. B is like P, except that it has
a reverberation, and so on through.
B, D, G, V, Z, Y, W, Th, Zh, Ng, L, M, N, R.
P, T, K, F, S, H, Wh, Th, Sh.
393. In what is commonly called speaking through the nose
the reverberation mentioned above is disagreeably strong. The
popular idea of it is incorrect, for this fault occurs in those who
have some obstruction to the free passage of the air through
the nose. This obstruction acts like the pressing of the nostrils
with the fingers, confining more or less the body of air con-
tained in the nasal passages. It is the vibration of this air thus
partially confined in tortuous passages that produces the nasal
twang. Any thing therefore which prevents the free outlet of the
air from the nose will occasion it. Pressing the fingers on the
nostrils while speaking, as already hinted, will produce it. A
common example of it we have in what is called a cold in the
head. The snuff-taker has this twang, because by such constant
stimulation of the lining membrane it becomes thickened.
Those who have this fault of " speaking through the nose," do
not like others breathe ordinarily through the nose alone, but
you see them sitting with their mouth constantly open, showing
that there is so much obstruction in the nasal passages that
they are not able to transmit sufficient air to the lungs.
394. I have thus far spoken of articulation as employed m
ordinary speech, that is with a vocal sound. But when no
sound is produced by the ligaments of the larynx, as is the case
in whispering, the noise produced by the passage of the air
through the cavities of the vocal apparatus can be so articulated,
as to be heard distinctly at a considerable distance. Persons,
therefore, who have entirely lost the voice can converse. In
264
HUMAN PHYSIOLOGY.
Variation of note in whispering. Contrivances to imitate articulation.
whispering the vocal ligaments are relaxed as they are when we
simply breathe. But the sound of whispering has its high and
low notes like the vocal sound. The variation of note is caused
by variation of the size of the column of air contained in the
vocal tube. This is effected chiefly by the tongue. In the high
notes of whispering the tongue is nearer the roof of the mouth
than in the low notes. The distinction between many of the
letters as to reverberation noticed in 392 holds in whispering
as it does in ordinary vocal speech.
395. You can observe the mechanism of the parts that is
necessary for any one of the alphabetic elements, by pronoun-
cing some syllable which it ends, prolonging the sound of the
letter in question. And in doing this you will readily see the
incorrectness of the common definition of consonants, viz., that
they are letters which cannot be sounded without the aid of a
vowel. Take, for instance, the lettter m in the syllable am.
After getting an idea of the mechanism necessary for it by
sounding it with a, you can readily sound it alone. It is proper
to remark here, that in observing the distinctions between the
alphabetical elements, you must bear in mind that the names
w^hich are given to the letters in the alphabet do not represent
their sounds. For example, -H (aitch) and W (double-u) are
nothing like the sound of these letters in have and wave.
396. Various attempts have been made to imitate the artic-
ulation of sounds by mechanism, but with very limited success.
In 1779 a prize was offered by the Academy of Science at St.
Petersburg, for the best dissertation on the theory of vowel
sounds, and it was awarded to G. R. Kratzanstein, an account
of whose experiments was published in the Transactions of the
Academy. He found that the sound of the four vowels, A, E,
and U, might be produced by blowing through a reed into
tubes, the forms of which are represented in Figures 142, 143,
144 and 145, and that the sound of I, as pronounced by the
FIG. 142 FIG. 143.
FIG. 144.
FIG. 145. FIG. 146.
THE VOICE. 265
Accurate adjustment of vocal and articulating muscles.
French and other European nations can be produced by blowing
into the tube, Fi<. 146, by blowing at a without using the reed.
M. Kempelen, of Vienna, the inventor of Maelzel's automaton
chess-player, carried the imitation of the human voice still
farther. He produced an instrument capable of uttering certain
words and short phrases in Latin and French. But it is not
known exactly how he accomplished this, as he kept the matter
secret. A gentleman of Cambridge, England, investigated this
subject, and among other things found that by blowing through
a reed into a conical cavity, the vowel sounds could be pro-
duced by altering the size of the aperture for the passage of the
air from the cavity, by means of a sliding board. I have alluded
to these attempts to imitate the voice, to show by contrast
the wonderful completeness and perfection of the vocal appa-
ratus. Kempelen's instrument, a box three feet long, could
produce only a few words, but the instrument of the voice,
although it occupies so little room in the body, can utter all
words in all languages.
397. We have now examined the whole of the vocal appa-
ratus. You will observe that I have spoken of it as having two
parts, the larynx, which is the reed of the instrument, and the
vocal tube, which you have seen is quite complicated, for the
purposes of articulation. Every action in both parts of the in-
strument is produced by muscles. You have seen that the
action of muscles is requisite to cause any, even the slightest,
variation of note. So it is with the articulating apparatus, as
it may be called. Every alphabetical element, (and in our lan-
guage Rush makes 35 in the whole,) requires a particular ad-
justment of the articulating apparatus. This adjustment is
effected by muscles that move the tongue, lips, palate, &c. As
these muscles then perform such varied movements, to produce
this variety of note and articulation, it is no wonder that they
require such long and diligent training.- The child begins this
long course of education the moment he utters an articulate
sound. Observe him as he pronounces the syllable pa or ma,
the first which children generally learn. He looks at his mother's
lips, and imitates the motion as well as he can. Cheered by
his success, and by her approving smile, he is constantly repeat-
ing these first lessons in pronunciation to every one that comes
"near him. Being as yet without skill in the use of these organs,
he gives much more force than is necessary to the mechanical
motions of articulation. For example, in pronouncing the word
pa, he closes his lips strongly, and not slightly as we do, and
23
266 HUMAN PHYSIOLOGY.
Training of the muscles in speech. Skill in their use.
when he opens it for the utterance of the word he does it with an
explosive force, at the same time quickly bowing his head. The
energy of his whole frame seems to be concentrated upon the
effort. Day after day he strives to add to his stock of words,
but his progress is slow ; and as a sort of compensation for the
leanness of his stock he repeats those which he has learned, and
so of his own accord he says papa and mamma instead of using
the words of a single syllable. In this education of the organs
of the voice the ear is the principal instructor, but the eye, as
you see, is also of great assistance. The little pupil, on hearing
a sound which he wishes to utter himself, tries to imitate the
motion which he sees is used in producing it, and he continues
to try till his ear assures him that he has actually mastered
the sound. Soon he is able to utter two different articulate
sounds in succession ; and he goes on learning year after year,
till at length he can command all the sounds of his native
tongue. And I may remark that it is in childhood and youth
alone, that we can learn accurately and thoroughly the pronun-
ciation of a language that is at all difficult in this respect.
Hence a foreigner, however long he may live in a country, to
which he goes in adult life, cannot wholly conceal his native
accent. And we know how much such sounds as that of th
trouble the German and the Frenchman, unless they begin to
learn the English language early in life.
398. If we observe different persons while speaking or sing-
ing, we shall see that some manage the vocal apparatus, or play
on the vocal instrument, as we may express it, with more skill
than others. Listen to two persons in conversation, the one
modulating and articulating his voice with a graceful melody,
the other having an utterance harsh and awkward ; and the
contrast is as great as that between two instruments, one of
which is well and the other badly played. In some you can al-
most imagine that you hear the creaking of the machinery ; while
in others you do not once think of the mechanism of the voice,
but your "ear feasts upon its richly modulated and gracefully
articulated sounds. It is as true of the muscles of the vocal
apparatus as of those of any other part of the body, that skill in
the management of them can be very much increased by exer-
cise. The rope-dancer, by training his muscles, gives them a
wonderful precision of action. The same thing can be done
with the muscles that regulate the modulation and articulation
of the voice. And in the most noted singers the little muscles
which move the vocal ligaments and those which adjust th>
THE VOICE. 267
Stammering. The ear the instructor of the voice.
parts of the vocal tube, must have a precision of action incom-
parably more accurate and delicate than the large muscles in
the limbs of the rope-dancer. If we compare the limited and
bungling operations of the vocal apparatus in a little child just
beginning to talk, with its infinitely varied but precise move-
ments in a 'voluble speaker, or a skillful singer, we shall have
some conception of the delicacy of motion, of which the muscles
of this apparatus become capable by long continued exercise.
399. There is a defective action of the muscles of the vocal
apparatus, called stammering or stuttering, which I -will just
notice. It is an irregular spasmodic action of these muscles, very
much like that which we see in the muscles of other parts of
the body in the disease called St. Vitus' dance. It is very much
influenced by habit, and mental agitation aggravates it. Shak-
speare gives the following accurate description of it. "I would
thou wouldst stammer, that thou mightest pour out of thy mouth,
as wine comes out of a narrow mouthed bottle, either too much
at once, or none at all." It is a singular and instructive fact,
that many who stutter in ordinary conversation can read and
sing as well as others. Dr. Good remarks that one of the worst
stammerers he ever knew was one of the best readers of Paradise
Lost that he ever heard. Such facts suggest some valuable
principles in the treatment of this difficulty, which can be more
easily overcome than is commonly supposed.
400. Not only is the ear the educator of the muscles of the
voice, but the dependence upon the ear is entire. The deaf and
dumb therefore are in almost every case dumb because they
are deaf. Their vocal organs are in a good condition, and the
muscles are all there with their nervous connections. But the
machinery does not work, for there is no guiding power to
direct it. That this is the true view, is proved by those cases in
which hearing has been restored, for such restoration is followed
by that of the power of speech. Magendie relates an interest-
ing case of this kind. It was the case of a young man deaf
and dumb from birth, who had his hearing restored by M. Itard.
He first heard the sound of the neighboring bells, which not
only caused very lively emotions, but even headache and dizzi-
ness. The next day he heard the sound of the small bell in
the room, and shortly after he could hear the voice of persons
speaking. His delight was then extreme, and he was so ab-
sorbed in his new enjoyment that, says Professor Percy, " his
eyes seemed to search the words even on our lips." His voice
was soon developed. The muscles of the vocal organs, so long
268 HUMAN PHYSIOLOGY.
Absolute dependence of the voice upon the hearing. Seen in the denf and dumb.
inactive, began to wake up under the tuition of their instructor,
the ear. Only vague sounds were formed at first, and, although
after a while he could pronounce some words, he did it awk-
wardly as children do when they are beginning to talk. He
learned to talk very slowly. It would have been very interest-
ing to have watched this case in its progress, but this was pre-
vented by a disease which proved fatal.
401. Few cases occur like that which is related above, but
there are many cases in which the dependence of speech upon
hearing is proved in another way. I refer to those cases in
which the loss of the power of speech is obviously the conse-
quence of the loss of the hearing. This is the case with children
that become entirely deaf after they have made some progress
in learning to talk. They cease to talk, and very soon forget
the motions which they had learned to make in articulation.
Sometimes some of these motions are remembered, and the
individual can pronounce some words. But he does it very
awkwardly, and the consciousness of this makes him very averse
to trying it. A friend mentioned to me the case of a man who
became deaf just after he had learned the alphabet. He re
membered the mechanical effort necessary to produce each letter,
but he had no control over the loudness or note of the voice, so
that some of the letters he sounded very high, others low, some
very loud, and others soft, making of course some laughable
contrasts. It is undoubtedly possible to teach deaf and dumb
persons to talk to some extent, if we begin early enough ; but
the power of speech, after the most persevering training, must
be awkwardly mechanical, and exceedingly limited. Accord
ingly all such efforts have been very soon given up.
402. The question has probably arisen in your minds as to
what the difference is between the voice of speech and the voice
of song. The common notions on this subject were very indefi-
nite until recently. But Dr. Rush, in his admirable work on the
voice, has developed the true principles in regard to it. He
has shown that we use the same notes in speech and song, and
that the difference lies in the mode of using them. I will en-
deavor to place before you the most prominent and material
points in his view of this subject.
403. If you pronounce the sound a as heard in day, you will
observe that it ends in another sound, that of e. The voice in
pronouncing it rises through the interval of a tone, the sound
at the same time gradually diminishing. So of other letters
Thus, a as sounded in awe, ends or vanishes in e as heard in err; o
THE VOICE. 26S
Voice of speech and of song. Explanation of emphasis.
as heard in old vanishes in oo as heard in ooze; and ou as heard
in our vanishes also in oo. The vanishing sounds are of course
rather obscure and feeble. The first sound he calls the " radical
movement of the voice," and the subsequent diminishing sound
its u vanishing movement." The rise of the voice during the van-
ishing movement is not always through the interval of a tone,
but it may be only a semitone, or it may be even through the
interval of an octave. In singing the movement is very differ-
ent. We pass " quickly and faintly through the radical move-
ment to dwell with greater time and fullness on a note or level
line of sound at the extreme place of the vanish." Both in
song and speech there is also a downward as well as an upward
movement on the scale. The gliding of the voice on the scale,
and its gradual vanish cannot be imitated on instruments. They
may be imitated to some extent however on the violin if the
finger moves along the string while the bow is drawn. The
difference between the voice of speech and song is thus repre-
sented by Dr. Rush :
VOICE OF SPEECH. OF SONG.
At 1 is represented the vanish on the interval of a tone ; at 2
on that of a third ; at 3 on that of a fifth, and at 4 on that of
an octave.
404. I will notice very briefly the use of the vanishing move-
ment in speech. In simple narrative the vanish never rises
above the interval of a tone, as at 1. Whenever it rises higher
it is either for emphasis or interrogation. The vanish on the
interval of a fifth, as at 3, is the most common mode of interro-
gation. That of the octave, 4, is used when the question is
asked with great vehemence, or is accompanied with sneering,
mirth, contempt, or raillery. Thus when the Jew in the Mer-
chant of Venice asks,
Hath a dog money ? Is it possible
A cur can lend ten thousand ducats ?
there is a rise through the interval of an octave on the words
cur and dog. You observe that the rise is on the words which
are emphasized. Thus we can make four entirely different
23*
270 HUMAN PHYSIOLOGY.
Use of the semitone in speech. Difference in capability of singing.
sentences of the question, do you ride to town to day ? accord-
ing as we make the rise on you, or ride, or town, or day. By
the use of this rising vanish we can make a question of the
most positive assertion, even of the blunt negative, no.
405. The vanish on the interval of a semitone gives the voice
a plaintive character, and it is therefore used for the expression
of love, grief, supplication, &c. It is sometimes used so much
as to give a general character of plaintiveness to one's whole
conversation. As a very clear and striking illustration of the
power of the semitone we will take the cry of fire. Divide the
word into two syllables, fi-yer, and ascend the scale thus :
Fi-yer. Fi-yer Fi-yer. Fi-yer.
The two places of the semitones, indicated by the braces, will
give the cry of fire as we commonly hear it. Sometimes we
hear it cried in sport upon one note, and the sound is discordant
and ludicrous. So also, the two words, "0 dear," sound like a
mere mockery of grief, if uttered on one note, or any other
interval than the semitone.
406. Every one learns to talk, but there are many who do
not learn to sing. Now as the same notes are used in the two
cases, what is the reason of the difference? The reason is not
in an absolute inability to appreciate the variations of note in
sound, for these are practically appreciated in the use of the
vanishing rise in conversation. There are two reasons for the
difference. One is this. As the transitions of the voice from
one part of the scale to another are much more varied in song
than in speech, and are made by leaps instead of slides, song
requires greater skill than speech does in the action of the mus-
cles. Another reason is, that speech is a necessity, and song
is not. We learn to speak therefore as a matter of course, but
singing is a mere accomplishment. If it were learned as uni-
versally as speaking is, there would be nearly aL much good
singing as good speaking. We can realize the truth of this
assertion, when we observe the results of very early training in
singing. And we should realize it still more if singing were
universally considered, as it should be, as an essential part of
THE EAR. 271
Ventriloquism. Difference between a sound and a noise.
the education of children. And I may remark in this connec-
tion, that all have some measure of musical talent, though in
some it is exceedingly small in amount. The difference in this
respect in different persons is the same as the difference in re-
gard to any other talent, as that of drawing for example. Skill
is acquired in the same way in both cases, and its degree de-
pends to the same extent, and in the same manner upon natural
endowment.
407. Some persons possess extraordinary powers in the use
of the vocal organs. I refer to ventriloquism. This is a purely
imitative art, and is not to be attributed to any peculiar forma-
tion of the parts in the individual who possesses the power.
The ventriloquist must have the faculty of appreciating with
great accuracy the almost infinite variety of tones, articulations,
and inflections of the voice, and must be able to imitate them
with but little motion of those parts of the articulating apparatus
which appear in view. He at the same time makes skillful use
of those circumstances, which will favor the false impressions
in the minds of his audience, in relation to the locality of the
source of the sounds. This is the simple explanation of this
wonderful power.
CHAPTER XV.
THE EAR.
IN the last chapter I treated of the production of sound by
the vocal apparatus. In this chapter I propose to show you
how the impression of sound is transmitted to the brain, in
order to produce the sensation of hearing.
408. That you may the better understand the arrangement
of the apparatus of hearing, I will first notice some of the
principles that govern the transmission of sonorous vibrations.
Sound may be produced by the vibration of any substance;
though some are better fitted to produce it than others, and are
therefore called sonorous bodies. When the vibrations which
cause sound are equal, a musical sound results ; but if they are
272 HUMAN PHYSIOLOGY.
Reflection of sound. Speaking tube. Ear trumpet.
unequal, we have a discordant sound, or what we ordinarily
call a noise. Sound is transmitted from the point where it
originates, in all directions. And its vibrations gradually les-
sen, just as the ripples lessen which are produced by dropping
a stone into the water. The vibrations of sound are reflected
by objects against which they strike. For this reason the voice
can be heard at a much greater distance if it be transmitted
along a wall than when it is uttered in an open space. This
may be illustrated on Fig. 147. Let A B represent a wall, and
FIG. 147.
C the position of the ear. If the bell at D be rung, besides
the vibrations which come to the ear at C in the direct line
C D, a vibration striking the wall at F will come to the ear in
the line F C, and the same can be said of other points along
the wall. An accumulation of vibrations, therefore, comes to
the ear at C, which therefore receives a louder sound from the
bell than it would if the bell were rung in a perfectly open
space. For the same reason a speaker can be heard much more
easily within walls than he can be in the open air. The sound
is reflected, and, therefore, in some measure concentrated by the
walls. In speaking tubes this reflection and concentration are
carried to a still greater extent. Sound can in this way be
heard at a great distance from its source. M. Biot found that
when he spoke in a whisper at one end of a tube, over three
thousand feet in length, he was distinctly heard at the other
end; so entirely do the walls of the tube prevent the diffusion
of the vibration in the air around. Speaking tubes are there-
fore used to a great extent in large manufactories, where direc-
tions need to be given continually to workmen in different parts
of the establishment. The flexible tube, now so commonly
made use of by deaf persons, furnishes another illustration.
The vibrations of the voice received by the trumpet -shaped end
are transmitted through the tube to the ear.
THE EAK. 273
Difference in the transmission of sound through solid, liquids, and guses.
409. Sound may be transmitted through any substance^
whether it be solid, liquid, or gaseous. It cannot be trans-
mitted through a vacuum, for there is nothing there to vibrate.
Sound differs in this respect from light, which passes as readily
through a vacuum as it does through any transparent substance.
The fact that sound cannot be transmitted through a vacuum
is often illustrated by an experiment with the air-pump. If a
bell be put under the receiver, and be set to ringing, ?. the air
is exhausted by the pump, the sound becomes more and more
faint, and at length it is not heard at all. For the same reason,
a pistol fired on the summit of a mountain, gives nothing like
so loud a report as when it is fired in the valley below. The
more solid the medium is for the transmission of sound, the
more readily is it transmitted. The scratching of a pin at the
end of a long log may be heard by the ear applied to the other
end, although it cannot be heard through the air, at even the
distance of a few feet. Savages are in the habit of putting
the ear to the ground to hear the step of their enemies when
they apprehend their approach. A deaf gentleman, resting
the bowl of his pipe on his daughter's piano-forte as he smoked,
found that he could hear the music with great distinctness; and
many deaf persons can hear conversation, by holding a stick
between their teeth, while the other end rests against the teeth
of the person speaking. A knowledge of the ready transmis-
sion of sound through solids suggested the examination of the
chest in disease by the ear. If the ear be applied to the chest,
the various sounds produced by the air, as it passes through
the bronchial tubes into the air cells, can be heard through the
solid walls of the chest, and thus the state of the lungs can be
discovered. Water is a much better conductor of sonorous
vibration than air, though it is not as good an one as a solid
substance. The force of the vibration is lessened more gradu-
ally in water than in air, and its rate of progress in water is,
according to Chladni, 4,900 feet in a second, or between four
and five times as great as in air.
410. Sonorous vibration does not pass readily from one
medium to another. Thus, although the scratch on the log is
heard so easily by the ear at the other end, if the ear be
removed a little from the log, it does not hear the sound,
because the vibration is so much lessened in passing from the
solid wood to the air. It is clear that the more unlike the two
substances are, when sound passes from one to the other, the
more will the vibration be lessened ; for the more unlike they
274 HUMAN PHYSIOLOGY.
Hearing a compound process. Only in part mechanical.
are, the less easily will the one take the vibration from tho
other. For this reason, a sonorous vibration, produced in a
solid body, may be transmitted to water with much less loss of
intensity or force, than occurs when it is transmitted to air.
Arid it may be remarked in this connection, that when vibra-
tions are transmitted to a fluid, from air or from a solid, the
intervention of a membrane is of essential service, for it pre-
sents a firm surface upon which the vibrations can be received.
411. The principles which I have thus noticed will be seen
to apply to the arrangement of the apparatus of hearing, as
we proceed in the examination of it. It has various parts for
the different portions of the process which we call hearing. I
will premise a mere general description of this process, before
entering upon the examination of the apparatus in detail. The
vibrations of sound, passing into the ear by a tube, strike at
the bottom of that tube upon a drum. The air can go no far-
ther, for this drum is perfectly air-tight. It communicates its
vibrations, however, to the drum, which transmits them to a
chain of four little bones, the last of which transmits them to
another drum, covering an opening into various winding pas-
sages in solid bone. In these passages is contained a limpid
fluid, which is put in motion by the vibrations of the drum last
mentioned. So much for the mere mechanical part of the pro-
cess. In the winding passages are spread out the minute fibres
of the nerve of hearing. The vibrations of the liquid in these
halls of audience, as we may call them, make an impression
upon these nerves, which is communicated to the brain through
the trunk of the nerve, and this completes the whole process
necessary to the production of the sensation of hearing.
412. The parts of the apparatus of hearing may be seen in
Fig. 148. The internal portions are made rather larger than
natural, in order that the arrangement may be more clear. At
a b c is the external ear; at d is the entrance to the tube of
the ear f; g is the drum of the ear at the end of this tube,
called the membrane of the tympanum ; h is the cavity of the
tympanum, the chain of bones which it contains being left out,
so that the plan of the apparatus may be more clear to you;
k is the Eustachian tube, which makes a communication be-
tween the back of the throat and the cavity of the tympanum;
n is a part of the winding passages, shaped like a snail's shell,
and is therefore called the cochlea; at m are three other wind-
ing passages, called, from their form, semi-circular canals; and
at / is the vestibule, or common hall of entrance to all these
THE EAB.
275
The parts of the apparatus of hearing described.
FIG. 148.
..-a
VERTICAL SECTION OF THE ORGAN OF HEARING.
winding passages. In the cavity of the tympanum, on the side
opposite to the drum of the ear, you see two holes. These
open into the winding passages, the larger one into their vesti-
bule or entrance hall. Both of these holes are covered by a
membrane, and to the membrane of the larger one is attached
the last of the chain of bones. At o is the trunk of the nerve
of hearing, and at e e is the bone that incloses these parts,
which is so hard that it is called the petrous, or rock-like bone.
Having given you this general view of the apparatus, I shall
now speak of each part more particularly.
413. The object of the external ear is to collect the waves of
sound, and direct them into the tube of the ear. There have
been many speculations in regard to the use of the prominences
and ridges of the external ear, but they are fanciful and ground-
less; and its surface is thus diversified, probably for the sake
of making this organ a comely one. If the object were to give
it the best shape and arrangement for collecting the vibrations
of sound, it would have had a different shape altogether, and
276 HUMAN PHYSIOLOGY.
External ear. Tube. Ear-wax. Drum and bones.
would have been arranged with muscles which could turn it in
different directions, as is the case with many animals. The
shape of the external ear is much better in many animals than
it is in man, if we consider its object to be merely the collec-
tion of the waves of sound. The endowment is in this case, as
well as in every other, according to the necessities of the case.
The bat is guided so much in its movements by the sense of
hearing, that it has of necessity very large ears, and they are
so shaped as to collect, in the best possible manner, the vibra-
tions of the air. With proportionably large, and similarly shaped
ears, man could hear much better than he now does, but he has
no need of such ugly appendages. In regard to the motions
of the ears in animals, it is worthy of remark, that animals of
prey can turn their ears forward with the most facility, while
timorous animals turn their ears backward to keep warned of
danger.
414. The tube of the ear is about an inch long in the adult.
It is formed of cartilage like the external ear, and ends at the
drum. At its entrance are hairs which afford some protection
against intruders. But the chief protection is the bitter wax,
which is secreted by little glands, situated in the skin of the
tube. The odor from this secretion so effectually keeps out the
insects from this open entrance, that it is quite a rare occurrence
to have an insect get into the ear. And when one does get in,
the wax envelopes him, and commonly soon destroys him.
415. The drum of the ear, which makes the closed end of
the tube above described, as seen at g, Fig. 148, is very thin
and transparent. On the other side of it is the cavity of the
tympanum h. In this cavity are the four bones. These are
represented in Fig. 149, enlarged
so that you can see their shape F1G -
distinctly. They are named from
their shapes. They are the mal-
leus or hammer m; the incus
or anvil ij the os orbiculare, or
round bone o, the smallest bone
in the body ; and the stapes or
stirrup-bone. The long handle
of the hammer k is fastened to
the middle of the drum of the ear. The little round bone is
fixed between the slender end of the anvil, and the top of the
stirrup-bone. In Fig. 150 you have a representation of these
bones, together with the drum of the ear. While the end of
THE EAR. 277
Eustachinn tube. Winding passages of the internal ear.
the handle of the hammer is fastened to FIG - 150>
the middle of the dram, the base of the
stirrup is fastened to another drum, cover-
ing the hole or window, opening into the
vestibule of the winding passages. There
are three very delicate muscles which move
these bones. One of them relaxes the
drum of the ear, and another makes it
, , , , . . DrtUAl Or 1 ralti &An
more tense; and thus the drum is put into whh ^^^
the right states of tension, to accommodate
it to the various kinds of vibration that come to it. This is a
matter of some importance, for it is plain that while a relaxed
drum can vibrate properly to grave sounds that enter the ear,
it must be tense, in order to respond properly to the vibrations
of the air in the higher notes.
416. The cavity of the tympanum (h Fig. 148) in which the
little bones are, and which is beyond the drum, communicates
with the mouth by the Eustachian tube k. If you shut your
mouth, and close the nostrils with the fingers, and then perform
the action of blowing, you will feel the air enter the Eustachian
tubes, and fill the cavity of the tympanum. The chief object
of this communication is to have air on the inside as well as
the outside of the drum, so that it may vibrate freely. The
cavity of the tympanum might indeed have been a closed
cavity, containing air. But it would then have been very much
like a common drum, with the hole in its side closed. This
would very much impair the vibration.
417. We now come to another part of the apparatus of
hearing the winding passages. These are inclosed, as I have
already stated, in the most solid bone in the body. They are
called together, very appropriately, the labyrinth, sometimes
the internal ear. This is really the essential part of the appara-
tus. Here are the true halls of audience, where the nerve is
posted, which receives the messages from without, and trans-
mits them to the brain. The drum of the ear and the chain of
little bones may be destroyed, and yet, if these winding pas-
sages remain entire, with the membranes over the two windows
that open into them, the hearing will not be lost ; though it
will be less perfect than it is when the whole of the apparatus
is there, and in good order. Sir Astley Cooper relates the case
of a gentleman, who lost the drums of both ears by disease.
By shutting his mouth, he could blow the air out through his
ears, with such force as to make a whistling noise, and to move
24
278
HUMAN PHYSIOLOGY.
FIG. 151.
Description of the winding passages. Their importance.
the hair that hung from his temples. Yet he was not only able
to hear with ease all common conversation, but he had a nice
appreciation of musical sounds. Sir Astley says that " he
played well on the flute, and had frequently borne a part in a
concert ; and he sung with much taste, and perfectly in tune."
418. The labyrinth is represented much magnified in Fig.
151. The middle part of it, v, is the vestibule. From this go
out the semi-circular canals,
fc, y, z, on the upper side, and
on the lower the winding pas-
sages of the cochlea, k. At o
you see the opening called the
fenestra ovalis, or oval win-
dow. This is covered by a
membrane, on which presses
the base of the stirrup-bone.
You see another opening r,
which is called the f en.es tra
rotunda, or round window.
This is covered with a mem-
brane. Both of these open-
ings you see in Fig. 148, in
the cavity of the tympanum,
Opposite to the drum of the
ear. In these winding pas-
sages is a watery fluid, the vibrations of which, acting upon
the branches of the nerve distributed there, cause the sensation
of hearing. Of course, if either of the membranes covering the
openings into these passages be destroyed or broken, the fluid
will run out from the ear, and there can be no more hearing,
although the rest of the apparatus is perfect. The drum wili
continue to vibrate as sounds strike upon it, the little chain of
bones will repeat the vibration, but it will stop at the end of
the chain, the stirrup-like bone. So too, although the mem-
branes may be entire, and the whole apparatus may be perfect
a* a piece of mechanism, so that the succession of vibrations
from the air without through the drum and the chain of bones,
to the fluid of the labyrinth, is uninterrupted, if the nerve of
hearing be paralyzed, so that it cannot be impressed with the
vibration of the fluid that bathes its branches, there can be no
hearing. Partial deafness is undoubtedly often owing to a
thickening of the fluid in these passages, or to a partial failure
of the nerve distributed in them.
THE EAR. 279
Principles of transmission of sound observed in the arrangement.
419. It will be proper to say a word here in relation to the
choice of a fluid, instead of a solid or an aeriform substance, as
the medium through which the impression of the vibration of
sound is communicated to the nerve. It is better than a solid
would be, so far as we can see, because no arrangement of a
vibrating solid with the minute fibres of the branches of the
nerve could be effectual, and at the same time so little liable
to derangement, as the arrangement of nervous fibres immersed
in a liquid, and the whole inclosed in solid walls of bone. It
is better than air would be, for at least two reasons. 1st. The
vibrations of sound, as stated in 409, are communicated with
much more ease and rapidity through water than through air.
This we see to be a consideration of some importance, when we
look at the complicated and winding passages that contain the
fluid. 2d. There is not as much loss in the force of the vibra-
tion in the transmission from the solid stirrup-bone through the
membrane to the fluid, as there would be if the transmission
were to air.
420. The whole arrangement in regard to material we can
see to be admirable, if examined in relation to the known prin-
ciples of the transmission of sound. We can see the object of
the chain of bones. If these were left out of the arrangement
we could hear, but not so well as we do now. For it has been
ascertained by experiment, that the transmission is much more
perfect when the vibration passes, as in the case of the ear,
through a tense membrane, then through a chain of solid sub-
stances, and from them through a second membrane to the
fluid, than it is when the chain of solid bodies is omitted, and
air is made to take their place. And when the vibration has
arrived at the fluid in the labyrinth, there is a contrivance there
for increasing its intensity. There are two little chalky con-
cretions suspended in this fluid by nervous fibres. These are
found in all mammalia, and in fishes they are quite large and
hard. This being the case, it was inferred that these bodies
have some important influence upon the transmission ; and it
has been found by experiment that hard bodies thus situated
in a fluid increase the sonorous vibrations in their neighborhood.
421. You will remember that there are two openings into
the labyrinth, from the cavity of the tympanum. Both are
covered by membranes, one of which is pressed upon by the
stirrup- bone, while the other is free. It was formerly supposed
that the second opening was absolutely essential to the vibra-
tion of the fluid in the labyrinth. For, as fluids are incoin-
280 HUMAN PHYSIOLOGY.
Mode of vibration of the fluid in the winding passages.
pressible, it was inferred that, as the stirrup-bone communi-
cated its vibration to the membrane of the fenestra ovalis, the
fluid in the labyrinth would not vibrate, unless there was another
opening some where, the membrane of which would yield to
pressure. This, however, has been ascertained to be not strictly
true. It has been proved by experiment that a sonorous vibra-
tion can be transmitted through a confined fluid. Indeed there
are some animals in which there is only one opening into the
labyrinth. But, although this second opening is not essential to
the vibration of the liquid, it undoubtedly makes that vibration
more perfect. Although the second opening is so near the
first, as seen in the cavity of the tympanum, (Fig. 148) yet in
relation to the arrangement of the winding passages of the
labyrinth, as you will soon see, it is really quite at the other
end of it. The vibration then may be considered as communi-
cated through a long tube, which has a membrane at both
ends. And it is obvious that a vibration communicated to the
membrane at one end, will more readily move the fluid through-
out all the tube, from the yielding of the membrane at the
other end. This will be more obvious, as I describe more par-
ticularly the arrangement of the passages in the labyrinth,
which I will now do.
422. To recur to Fig. 151, the vestibule v, into which the
fenestra ovalis o opens, is, as before stated, a sort of common
entrance hall to all the passages of the labyrinth. I have
spoken of the semi-circular canals #, y, and z, that lead out
from this. These are simple canals. But the passages of the
cochlea, k, are very complicated, and it is this fact that has
given the name of labyrinth to the whole of the internal ear.
The vestibule opens into the cochlea at its base. Now, the
cochlea is so divided, that the passage into which the vestibule
opens, runs around the pillar in the middle of it to its top,
making just two turns and a half. It there opens into another
passage, which makes two turns and a halfback to the base of
the cochlea. This passage does not end in the vestibule where
the other began, but it ends in the round hole r, which opens
into the cavity of the tympanum. This disposition of the
parts of the cochlea may be seen in Fig. 152, which represents
it as opened to show the arrangement of the walls of the two
winding galleries. The pillar in the middle, around which
these dividing walls are fastened, expands in the top into what
is called a cupola, where the two spiral galleries communicate
together. With this description, you can understand in what
THE EAR. 281
Distribution of the nerve of hearing in the cochlea.
FIG. 152,
THE COCHLEA OPENED.
directions the vibration is transmitted, when it is received from
the stirrup-bone, at the door of the labyrinth, by the membrane
which covers it. It travels one way up the fluid in the three
semi-circular canals. It travels another way through one spiral
gallery in the cochlea to the cupola, and then down the other
spiral gallery, reaching at length the membrane of thefenestra
rotunda, or round window.
423. I will now describe to you the arrangement of the
branches of the nerve of hearing in these passages. The ar-
rangement is different in the vestibule and the semi-circular
canals from what it is in the cochlea. In all the cavities of the
labyrinth, there is a thin, delicate lining of membrane, which
secretes a watery fluid. In the vestibule and semi-circular
canals, there is a second membrane. This is separate from the
first membrane, and lies loose in the cavities. It makes a close
sac, and as it extends from the vestibule into the semi-circular
canals, it is very irregular in its form. This sac contains a fluid,
and the fluid secreted from the membrane which lines the bone
bathes the outside of the sac. Now, it is on the delicate mem-
brane which forms this sac, that the fibres of the nerve are
distributed, so that they may receive the impression of the
vibration of the fluid. In Fig. 153, is a representation of this
sac, with the distribution of the nerve. At 1, 2, and 3, you
see the parts of this sac which line the semi-circular canals.
At 4 is a junction of two of these canals, for what purpose we
know not. At 6, 9, 10, and 11, are seen the terminations of
branches of the nerve. At 8 and 13 are two of these branches
24*
282
HUMAN PHYSIOLOGY.
Distribution of the nerve in the semi-circular canals.
FIG. 153.
and at 14 is the branch of the nerve which goes to be distrib-
uted in the cochlea. In Fig. 154 is represented one of the parts
FIG. 154.
THE EAR. 283
Beautiful arrangement of the nervous fibrils in the cochlea.
where the nerve terminates, as at 10 in Fig. 153, much more
highly magnified. You see the loop-like termination of th,j
nervous fibrils. You can readily see that every vibration of
the fluid would make an impression upon these nervous fibrils
thus distributed upon this delicate membrane, which has the
fluid upon both sides of it.
424. The distribution of the nerve is after a different man-
ner in the cochlea. Here there is no loose membrane, with the
nerve distributed upon it, and the fluid each side of it, as in
the vestibule and the semi-circular canals. But the nerve is
distributed upon the division wall of the galleries in a very
beautiful manner. This is represented in Fig. 155, in which 2
FIG. 155.
is the nerve, and 3, 3, 3, show its distribution. These fibrils
lie in little channels in a lamina, or leaf of solid bone. But the
bone extends only to 4, 4, and the remainder of the division
wall is made of membrane, represented at 5, 5, 5. At 7 is the
opening in the cupola, by which the two spiral galleries com-
municate. At 1 you have these parts of the natural size. We
know not exactly how this mechanism works, but the proba-
bility is, that the nerve receives impressions from the vibrations
of the fluid in two ways directly from the fluid itself, and also
from the vibration of the membrane to which the extremities
of the nerve are attached, this membrane being shaken of
course by the vibrating fluid.
425. Having thus described the parts of the organ of hear-
ing, I will trace for you, with some particularity, the steps of
284 HUMAN PHYSIOLOGY.
Steps of the process of hearing given in their order.
the process of hearing, as it must occur in the case of every
sound that produces that sensation. The vibrating air enters
the tube of the ear, and, reaching the drum, produces a vibra-
tion there. This vibration is communicated to the chain of
bones, which, as Dr. Paley very aptly says, like a repeating
line of frigates pass it on. It is transmitted from the last of
this chain of bones, the stirrup-bone, to the membrane covering
thefenestra ovalis, and from this to the fluid contained in all
the passages of the labyrinth. The vibration goes through all
the semi-circular cr.nals in one direction, and in another up one
gallery of the cochlea, and down the other. In all these cavi-
ties, are spread out in various ways, the filaments of the nerve
which receive the impression of the vibration. This impression
is transmitted from the extremities of the nerve, through its
trunk, to the brain, where the mind receives it. All this to-
gether constitutes hearing ; and all of it occurs in the case of
any sound which we hear, however closely it may follow any
other sound.
426. Most of our hearing is done precisely in the way
described, but not all. We sometimes hear directly through
the bone surrounding the labyrinth. If you place a watch
between the teeth, you hear the ticking ; and it gives a very
different sound from what it does when held to the ear, be-
cause the sonorous vibration is transmitted directly through
the solid bones of the skull from the teeth. In the same way
was the sound transmitted in the case of the deaf old gentle-
man, ( 409) who heard his daughter's music through tho
stem of his pipe, as he rested the bowl of it on the piano.
The fact thus illustrated is often made use of by physicians, in
detecting the nature of the difficulty in cases of deafness. Thus,
if a watch held between the teeth communicate a very distinct
and loud sound to the ear, we infer that the internal ear is in a
good condition, and that the difficulty is in some of the other
parts connected with it, the drum, or the cavity of the tym-
panum, or the Eustachian tube.
427. I have described the apparatus of hearing as we find it
in man. But it varies in different animals, according to the
circumstances in which they are placed, and their necessities.
Animals that live in water of course have a different appa-
ratus of hearing from those that live in air. In most fishes the
semi-circular canals exist, but there is nothing like a cochlea.
As sounds are transmitted so easily through water, ( 410,)
fishes have no need of so complicated and perfect an apparatus
THE EAR. 285
Hearing in other animals. Only a part of the process of hearing understood.
as animals that live in air. They are fitted to hear in their own
element, and probably the moment that a fish is taken out of
the water he becomes quite deaf, because his hearing apparatus
is so poorly fitted to receive and transmit vibrations from the
air. But in many animals that live in air the ear differs from
that of man in its arrangements. The cochlea in birds is nearly
straight instead of being spiral. Such facts lead to the infer-
ence, that the peculiar arrangements in the hearing apparatus
of man have regard, not merely to the medium in which he is
placed, but to peculiar uses which are necessary in his case, as
the determination of the direction of sound, the appreciation
of its pitch and its character, the power of hearing very slight
sounds, &c. The simplest form of apparatus found in animals,
is a cavity excavated in bone, with a fluid shut in it by a mem-
brane, and nervous filaments distributed so as to be impressed
by the vibrations of the fluid. And this is all that is absolutely
essential to hearing.
428. Many speculations have been broached in regard to the
special offices of particular parts of the labyrinth. Thus, it has
been supposed that the semi-circular canals have an agency in
informing us of the direction of sounds ; for it is observed that
they are always arranged in the same relative angle to each
other. It has been supposed also, that the cochlea gives us the
idea of the note of sounds, because it is noticed that the devel-
opment of this part in different animals is in proportion to the
variety of note which they produce. These suppositions, though
quite probable, require farther investigation in comparative anat-
omy to test their truth.
429. In the process that makes up the sensation of hearing,
there is one part which we can in some measure understand,
and to which we can apply the known principles which govern
the transmission of sonorous vibrations. But there is another
part, that which links the process to the immaterial mind, that
we cannot understand. We can trace the vibration received
from the air through the several parts to the fluid in the laby-
rinth, but here we come to a stand in our knowledge. The
vibration stops here, and what is transmitted through the nerve
to the mind we know not. We call it an impression; but this
is only an indefinite word, implying simply that something is
transmitted, without defining what it is. Neither do we know
how the transmission is made. All that we do know is, that
the nerve is essential to the completion of the sensation of hear-
ing, and that it spreads out its minute fibrils or tubuli in the
286 HUMAN PHYSIOLOGY.
Ear equal to the eye in delicacy, beauty, and complication of structure.
halls of audience, in order to receive impressions from the vi-
brations that come there, and transmit them to the brain where
the mind takes cognizance of them. Every part of the appa-
ratus may be mechanically perfect, so that the vibrations
may be transmitted to the fluid which bathes the nervous
fibrils, but if the nerve be paralyzed, or if the communication
between its extreme fibrils and the brain be in any way inter-
rupted, the mind knows nothing of the vibration, and there is
no hearing.
430. The eye has generally been spoken of as being more
wonderful than any other organ in the body, in view alike of
the delicacy, the beauty, and the complication of its structure.
But the apparatus^ of hearing presents a combination of these
qualities quite as wonderful. There is nothing more delicate,
and beautiful, and complicated than the arrangement of the
nervous fibrils in the winding labyrinthic passages of the halls
of audience. And as we trace the steps of the process of
hearing, from the drum of the ear where the sound strikes, to
the gray substance of the brain where the mind receives the
impression, and think of each sound as sending a vibration
through membranes and a chain of bones to the fluid in which
the nervous fibrils are immersed, and of these fibrils as catching
from every vibration of the fluid a definite impression and
transmitting it to the mind, we see a mingling of the purely
mechanical with the spiritual, which greatly enhances our ad-
miration of the mechanism. Though the apparatus is compli-
cated, the mechanical result is a simple one it is a mere
trembling of a fluid inclosed in winding cavities of bone. But
simple as the result is, it is made, through the beautiful nervous
connections of the ear with the brain, one of the chief inlets of
knowledge to the mind, coming to it from nature's multitudinous
voices, and is a constant medium of communication for thought
and feeling between man and man. Thus intimately in the
human body are the simplest mechanical results connected with
the complicated and diversified operations of the mind. In the
process of hearing the drum of the ear is to be considered one
end of the apparatus, and the gray portion of the brain the
other. The drum simply vibrates ; and instantaneously the
mind receives a distinct impression from the vesicles of the gray
matter. And thus is the communication established between
the immaterial mind, and the vibrations of the material sub-
stances with which it is surrounded.
THE EYE. 287
Seeing a compound process. Refraction of light.
CHAPTER XVI.
THE EYE.
431. THE sensation of sight is the result of a compound
process, which may be divided into two distinct parts, as I re-
marked in relation to the sensation of hearing, in 429. The
one part is purely mechanical, and the apparatus for it is con-
structed according to the common principles, which we find
illustrated in optical instruments. The object of its arrange-
ments is to form distinct images of objects in the back part of
the eye. The other part of the process is executed by the nerve
of vision, called the optic nerve. This nerve, expanded upon
the membrane where the images are formed, transmits impres-
sions from these images to the brain, just as the nerve of hearing
transmits to the brain the impressions which come from the
vibration of the fluid of the labyrinth.
Before proceeding to an examination of the eye as an optical
instrument, I will call your attention to certain principles, which
we shall find illustrated more beautifully and perfectly in the
eye than in any optical instrument which man has ever con-
structed.
432. The rays of light coming from any luminous point go
in straight lines in all directions, just as the vibrations of sound
do, and, like them, become less intense the farther they are
diffused. But they move in straight lines only so long as they
remain in the same medium. When they pass from one me-
dium into another they are bent out of their straight course,
or refracted, as it is termed, unless they pass from one to the
other in lines perpendicular to the
surface of the medium which they FIG. 156.
enter. This may be illustrated by
the following experiment. Place
a coin, a, in the bottom of a basin,
as represented in Fig. 156, and then
withdraw from it so far that the
coin may be hidden from your eye
by the edge of the basin, as repre-
sented in the figure. Keeping your
eye fixed in that position, pour some
288 HUMAN PHYSIOLOGY.
Refraction as light passes from a rarer into a denser medium, and vice versa.
water into the basin up to the level, c. The coin will again
become visible to your eye. The reason is, that the rays of
light, as they come from the water into the rarer medium, the
air, are refracted or bent downwards, that is from the perpen-
dicular. The effect of this may be seen in the figure. A ray
of light, coming from the coin in the direction a, d, does not
pass to d, but is bent downward, and so passes to the eye at
e. And so of other rays coming from the object. The coin,
therefore, is seen by the eye at e, but it is not seen in its true
direction from the eye which is in the line e, c, a. The only point
in which the eye can see the coin in its true position is when
the eye is at >, in a perpendicular line directly over it. A ray
that passes from one medium to another in a line perpendicular
to the surface of the medium into which it passes is not bent
out of its course. All other rays are, and the more so the
farther they are from the perpendicular.
433. While rays that pass from a dense medium into a
rarer, as from water into air, are bent from the perpendicular,
those on the other hand, which pass from a rarer medium into
a denser, as from air into water, are bent towards the perpendic-
ular. Thus if in Fig. 156 a be the position of the eye of a
fish, and where the eye is, at e, there be an insect, the fish can
see it, because the ray that strikes the surface of the water, c,
is refracted or bent towards the perpendicular line, 6, a. And
so of other rays. He does not see the insect, however, in its
true direction, a, c, e, but it appears to him to be at d. For we
always judge of the place of an object by the direction in
which the rays from it strike the eye.
434. When light passes from one medium into another which
presents a convex or concave surface, instead of a flat one, a
very great change is produced in the direction of its rays.
Thus suppose, as represented in Fig. 157, three diverging rays
coming from a point, a, through the air, enter a convex surface
of glass, 6, 6'. The central ray a, c enters the glass in a direc-
tion perpendicular to its surface, and therefore does not bend
from its course. But the ray a, d enters very obliquely, and is
bent towards the perpendicular at that point, e, and passes on
in the direction /. So likewise the ray, a, <7, is bent towards
the perpendicular A, and passes on in the line i. These rays
diverging in the air have become converging in the glass, and
the point at which they meet is called the focus. To this point
all the other rays entering the convex glass converge also.
435. But if the surface of the glass be concave, as represented
THE EYE.
289
Refraction by convex and concave lenses.
in Fig. 158. the diverging rays which enter it will be made to
diverge still more. The ray, a, c, being perpendicular to the sur-
face is unchanged in its course ; but the ray, o, c?, is bent towards
the perpendicular, e, into the line/, and the ray, a )t /, is bent to-
wards the perpendicular h into the line t. In the case of both
FIG. 158.
the concave and the convex lens, the greater the curvature, the
greater is the change of direction in the rays. The greater the
curvature, therefore, the sooner are the rays brought to a focus
in the case of the convex lens.
There are other optical principles illustrated in the apparatus
of vision, that will be brought out in the description of the
eye, which I will now proceed to give.
436. The arrangement of the different parts of the eye you
can understand by Fig. 159, which is a mere map of a section
of the eye, through its middle part from front to rear. It is
intended merely to represent the arrangement of the parts dis-
tinctly, without strict regard to proportion. The eye has three
25
290 HUMAN PHYSIOLOGY.
Description of the parts of the eye.
FIG. 159.
CL I
DIFFERENT PARTS OF THE EYE.
coats, as they are called. At a is the thick strong white coat,
called the sclerotic coat, from a Greek word meaning hard,
This, which is commonly called the white of the eye, gives to
the eyeball its firmness. Into it the cornea, e, fits, like a watch-
glass into its case. The sclerotic and cornea then make one coat
of the eye, the o\iter one. Next comes the choroid coat, b. This
is a very vascular coat, containing the minute branches of blood
vessels which nourish other parts of the eye. It is of a dark
color, for reasons which I will state in another place. Its color
is owing to coloring matter contained in pigment cells, which
lie. along on the inner surface of this coat, next to the inner
coat of the eye, the retina, c. The retina is a thin membrane,
being principally composed of the expansion of the optic nerve,
d. The eye has three humors, as they are termed. The first
is the aqueous or watery humor,/", which is in a chamber be-
tween the transparent cornea, e, and the crystalline humor, or
lens, h. This chamber is divided into two parts by the iris, g,
<7, the pupil being the circular communicating door between
them. The part of the chamber which is in front o^f the iris
is much larger than that which is behind it. The crystalline
humor, or lens, as it is more often called, has the consistency
of half dissolved glue. At i is the vitreous humor, filling up
a large part of the cavity of the eye. It is called vitreous from
its glassy appearance. It is a clear, jelly-like substance, having
about the tenacity of white of egg. It is contained in an ex-
THE EYE.
291
Arrangement of the front part of the eyeball.
ceedingly thin and delicate sac, and this is divided into cells
which contain the liquid.
437. Fig. 160 is a map of the front part of the eye, in which
the parts are more minutely delineated than in Fig 159. At 2
is the sclerotic coat ; 3, the cor-
nea ; 6, the crystalline lens ; a, a,
a, the aqueous humor; 7, 7, the
iris ; 4, the choroid coat ; 8, the
retina; c, c, the vitreous humor,
and 9, the sac containing it.
Around the inside of the cham-
ber containing the aqueous hu-
mor is a very thin membrane,
(represented as you see by a line,)
which secretes the humor. In
this membrane, as in the case of
every other closed sac in the body,
there are both exhalents and ab-
sorbents, so that the fluid may be
changed as necessity requires.
There is another thin membrane
of the eye which I have not yet
described. It is represented by a
line, 1, in the figure. It is the
conjunctiva, so called because it
unites or conjoins the ball of the
eye with the eyelids. It covers
the cornea, passes back a little way on the white of the eye,
and then turns forward to line the eyelid. It is the seat of the
most common form of inflammation in the eye. It is very vas-
cular, as is shown by its distended vessels when it is inflamed.
It is exceedingly sensitive, and hence the great pain which is
occasioned by any thing, even the smallest mote, that gets into
the eye. The object of having it so sensitive I have spoken
of in the Chapter on the Nervous System, 242.
438. At 6 in Fig. 160, is one of the ciliary processes, as they
are called, from their resemblance to the eyelashes. There is a
circular row of them, numbering from sixty to eighty, so ar-
ranged as to resemble the disk of a radiated flower. In Fig.
161 they are represented as they appear in looking at them
from behind, the back part of the eye being removed. At 1
is the divided edge of the three coats ; 2, the pupil ; 3, the iris ;
4, the ciliary processes. At 5 is the anterior edge of the retina,
292 HUMAJST PHYSIOLOGY.
Object of the apparatus to form images of objects on the retina.
FIG. 161.
CILIARY PROCESSES.
which stops at the beginning of these processes, presenting, as
you see, a scalloped appearance. The processes, however, do
not arise from the retina, but come from the choroid coat, and
are united at their origin by a ring of ligamentous substance
to the sclerotic coat. The exact operation of this beautiful
arrangement is not known, but it is pretty well ascertained,
that muscular fibres are so connected with these processes, that
when they contract they draw the crystalline lens forward.
This, as you will see in another part of this chapter, is a very
important movement in the adaptation of the eye to seeing at
different distances.
439. The object of all this apparatus, which I have de-
scribed, is to have images of objects formed in the back part
of the eye upon the retina, so that the optic nerve expanded
there may carry impressions from them to the brain. This is
done in this way. The rays of light coming from an object
pass through first the cornea, then the aqueous humor, then
the crystalline lens, and lastly the vitreous humor to the retina,
where they, so to speak, daguerreotype the object. The fact
that such an image is formed has been often proved by obser-
vation on the eyes of animals. If the eye of a rabbit be
cleansed from the fat and muscles at its back part, and a candle,
be held in front of it, you can see the image of the candle
through the sclerotic coat, formed upon the retina. So if you
take the eye of an ox, and carefully pare off the back part, so
THE EYE.
293
Images on the retina inverted. Camera Obscura.
as to leave it very thin, a distinct image of any thing placed in
front of the eye may be seen at the back part. The image
however will be inverted, as represented in Fig. 162. For the
FIG. 162.
sake of clearness two rays only are represented as coming from
each of the two ends of the object, a, c. These rays cross each
other in the middle of the eye, those from a being brought to
a focus at 6, and those from c at d. As all the other rays,
coming from other points in the object, are refracted in the
same manner, a complete inverted picture of it is thus formed.
The same thing is seen in the instrument called the camera ob-
scura. If light be let into a darkened room through a small
aperture in a window shutter, an inverted picture of objects
without can be seen on a screen, as represented in Fig. 163.
FIG. 163.
This experiment, which can be performed by any one, illustrates
in a rude way the principle of the camera obscura. The real
instrument has a tube with a double convex lens, so as to collect
together the rays from objects, and concentrate them upon a
small space, thereby making a very distinct small image of
them. The eye is a very beautiful and perfect instrument of
this sort. The space filled by the vitreous humor is the dark-
ened room ; the pupil answers to the hole in the window shut-
25*
294 HUMAN PHYSIOLOGY.
Cornea. Iris. Its radiated and circular muscular fibres.
ter, or the tube of the more perfectly constructed camera ; the
crystalline humor is the lens ; and the retina is the screen on
which the images are formed.
We will now attend to the agency which the different parts
have in producing the result, for which the apparatus is con-
structed, observing the perfect adaptation of each of them to
the particular part which it performs in the process.
440. The cornea, as it lets in the light, requires to be trans-
parent, and, as it is very much exposed to injury, it also re-
quires to be very firm and hard. Both of these objects are
secured in an admirable manner. Its transparency is secured
in this way. It is made of different layers, which are kept
moist by a delicate transparent fluid. It is this which in health
makes the eye so clear and sparkling. Disease often so lessens
it, as to give this window of the eye a dull appearance. The
cornea is, as you see by Fig. 159, more convex than the sclerotic
coat, so that it may act with some power as a lens in making
the rays converge.
441. The iris is a circular curtain with a round opening in
its centre, the pupil, which can be varied in size to a consider-
able degree. On the iris depends ,vhat is called the color of
the eye, which is various, as blue, nearly black, grey, hazel, &c.
The color is owing to the pigment which is in cells on its inner
surface. The chief office of the iris is to regulate the quantity
of light that enters the eye. When the light is obscure the
opening in the iris is widely dilated ; but when there is much
light it is contracted ; and if the light be excessive, it is con-
tracted almost to a point. Its motions, therefore, considering
irig its small extent, have a very wide range. You can realize
this if you look at the eye of some one in a dim light, and then
suddenly bring a lighted candle very near to it. These motions
are effected by a peculiar arrangement of muscular fibres, of
which the iris is in part composed. There are
two sets of fibres, the circular and radiated, as
represented in Fig. 164. When the circular
fibres contract, the pupil is contracted ; and when,
on the other hand, the radiated fibres contract,
the pupil is dilated. There must be a very nice
adjustment of the fibres, to enable them to di-
late the pupil as widely as they sometimes do,
without producing any puckering of the surface of
the iris. The opening in the iris is always round in man ; but
in animals whose range of vision requires to extend widely in
THE EYE. 295
Crystalline lens. Seat of cataract. Choroid coat. Why dark.
a korizontal direction, (as the herbivorous animals,) it is in the
form of an ellipse, with the long diameter horizontal. In ani-
mals, on the other hand, that leap up and down in pursuit of
their food, as the cat and other carnivorous animals that seek
their prey in the same manner, the pupil has the elliptical
form, but with the long diameter vertical.
442. The crystalline lens is the chief agent in the eye in con-
centrating the rays of light by refraction. In Fig.
165 you have a side view of it. Its anterior part, FIG - 165>
1, is less convex than its posterior, 2. In Fig. 166
is a magnified view of the lens hardened in spirit
and cut open, so as to show the different layers of
which it is formed. The layers are more and more
hard as you go towards the centre. The object of
this arrangement and of the peculiar shape of the Cr y stalline Len -
lens, is not as yet understood.
This lens is the seat of the disease ^ G - 166 -
called cataract. In this disease
the lens becomes opake so as to
prevent the rays of light from pass-
ing to the retina. There are three
ways of getting rid of the difficulty.
One is to introduce an instrument
shaped like a needle into the side
of the eyeball, with which the opake
lens is pushed off one side in the
vitreous humor, so as to be out of
the way of the rays of light. An-
other is to break up the lens with the needle, so that its frag-
ments may be absorbed. The third method is to make an
opening in the cornea, and to extract the lens through it.
443. The choroid coat (6, Fig. 159) contains quite a large
share of the minute bloodvessels, and nerves of the eye, and
serves for a medium by which they pass to other parts of this
organ. But it serves another important purpose by means of
its dark pigment. It makes a dark chamber of the back part
of the eye where the optic nerve is expanded. The object of
this is to secure distinctness in the images formed upon the
retina. If the choroid coat were of a light color, there would be
so much reflection of the rays of light back and forth in all
directions in the eye, that the pictures formed upon the retina
would be confused. There would be a glare of light, such as
we experience in a room where the walls are all of a very lighl
296 HUMAN PHYSIOLOGY.
Want of pigment in the choroid of the albino. The retina.
color. There is the same reason for having the chamber of
the eye of a dark color, as for having that of the camera ob-
scura so. In the albino there is a deficiency of the pigment of
the choroid ; and, therefore, in a bright light there is in his cas(
a defect of vision, from the cross reflection to which I havt
alluded. During the day his vision is very indistinct ; and it is
only when twilight appears that he can see well, or with com-
fort. The pigment is also deficient in the iris of the albino ;
and the bright red or pinky hue of the iris in his case is owing
to the blood in the minute bloodvessels, with which this part
is so well supplied. Those animals that use their eyes mostly
in daylight have the pigment of the choroid of the darkest
color ; while, on the other hand, those that need to see most
clearly at night, as the owl, either have none of this pigment,
or have it of a very light color.
444. The retina is a soft greyish delicate membrane, formed
chiefly of the expansion of the optic nerve. Here the images
are formed, and the minute fibres of nerve in this membrane
receive impressions from these images, which are transmitted to
the brain by the trunk of the nerve. This nerve has the same
relation to light that the nerve of hearing has to sound, the
nerve of smell to odors, or the nerve of touch to the qualities
of bodies that we feel. And it is curious to observe that the
termination of the nerve of sight on the surface of the retina
is arranged in papillce, just as the terminations of the nerves
of touch are. In Fig. 167 is represented
a portion of the retina of a frog magni- FIG. 167.
fied three hundred times. The upper
rows of papillae, which are without dots,
are seen sideways.
445. The superiority of the eye, as an
optical instrument, is seen in a striking
manner in several particulars, in which
difficulties and defects to which all opti-
cal instruments are liable are removed. There is, for example,
a defect in the operation of lenses in optical instruments, which
is termed spherical aberration. This can be explained on Fig.
168, which represents a lens, L, I/, with some of the rays as
they pass through it. Now the rays R, R", R'", are brought
to a focus at F ; while the rays R, L and R"", L' come to a
focus much nearer, at L It was found by experiment, that if the
central portion of the lens be covered, so that the rays R', R"
R'", cannot pass, a distinct image will be formed on a screen
THE EYE. 297
Spherical and chromatic aberration. How remedied in the eye.
B-
put at I. And, on the other hand, if the outer portion of the
lens be covered, so that the outer rays are intercepted, then the
middle rays, R' R" R r// will form an image on a screen at F.
But if the whole lens be used, no distinct image is formed, wher-
ever you may place the screen. If you place it at /, it will
receive with the rays that come to a focus there, rays that have
their focus at F. And so of other points.
446. It is in view of such experiments, that a contrivance
has been adopted in the construction of telescopes and micro-
scopes, for the purpose of remedying the difficulty above de-
scribed. What is called a diaphragm, or stop, is put in against
every lens. It is a perforated partition which permits the light
to pass only through the central portion of the lens. The lines
D, D', in Fig. 168, cutting off all rays in the neighborhood of
R and R"", show the operation of the stop. In the eye the
iris acts as the diaphragm or stop to the crystalline lens which
is behind it, as you can see by recurring to Fig. 159. Ordina-
rily, by means of this stop, the rays pass through only the
central part of the lens.
447. Another difficulty attending the operation of a common
lens is what is termed chromatic aberration. Every ray of white
light consists of a mixture of rays of seven different colors.
Some of these colors are more easily refracted than others, and
therefore on passing through a lens will come to a focus sooner.
This of course is apt to make some confusion in the color and
the distinctness of objects, when seen through a single lens, or
through several if they are alike. The difficulty has been rem-
edied, although Sir Isaac Newton thought that it never would
be. And it is said that the hint of the remedy was taken from
the arrangement of the eye. At any rate, the defect is avoided
298 HUMAN PHYSIOLOGY.
Adjustment of the eye to objects at different distances.
by having lenses made of different materials, just as is the case
in the eye. Thus if two lenses be used, one of which is made
of flint and the other of common glass, the difficulty disappears.
In the eye it is perfectly avoided by the passage of the rays
through so many different materials, before it reaches the retina.
The stop has been found a partial remedy in the case of optical
instruments ; and the iris, the stop of the eye, of course acts in
the same way. But the full remedy was not found, till another
step was taken in imitation of the eye, the most perfect of all
optical instruments.
448. There is another arrangement in the eye, which the
optician can imitate only in a comparatively bungling manner.
It is that by which the eye adapts itself to different distances in
looking at objects. If we look through a telescope at a near
object, and then turn it towards one at a distance, we cannot
see it distinctly until we adjust the lenses to suit the distance.
But in the eye how quickly the adjustment is made ! It is
done ordinarily, without any effort on our part of which we are
conscious. It is done so easily that we do not think of the
change. We look at an object at a few inches distance, and in
an instant turn the eye and see an object afar off with almost
equal distinctness. There has been much discussion in regard
to the means by which this adjustment is effected. One of the
means undoubtedly is, a change in the relative position of the
crystalline lens, which is effected by the muscular fibres spoken
of in 438. These fibres when they contract, draw the lens to-
wards the front of the eye, and away from the retina. This is
done whenever we look at a near object. If it were not, the rays
which come from the object, as they diverge considerably, would
not be brought to a focus when they reach the retina. The
iris also has some agency in adjusting the eye for seeing at
different distances. When the eye is turned to a near object
the pupil always contracts, thereby shutting out those rays
coming from it which are the most divergent.
FIG. 169.
THE EYE. 299
Difficulty in the near-sighted and the far-sighted.
449. In some cases this power of adjustment is counteracted
by defect in the arrangement of the eye. Thus, in the near-
sighted, either the cornea or the crystalline lens, or both, are
too convex ; or, the crystalline lens is too far from the retina.
The result is, that the rays of light coming from a distant ob-
ject come to a focus before they reach the retina, as represented
in Fig. 169. All objects, therefore, are seen indistinctly except
those which are brought near to the eye. This defect is rem-
edied by the use of a concave lens, which counteracts the effect
of the too highly refractive power of the eye by making the
rays divergent, instead of parallel, before entering the eye. By
an habitual adjustment of the eye for seeing near objects, near-
sightedness may be produced. Hence it is that engravers,
watch-makers, students, <fec., are so liable to become near sighted.
450. In the far sighted the difficulty is of an opposite char-
acter. The refractive power of the eye is too feeble. This is
owing either to too little convexity of the cornea, or of the
crystalline lens, or of both ; or, to too great nearness of the
crystalline lens to the retina. In this case the rays coming
from a near object do not come to a focus soon enough. The
focus of the rays coming from any point of the object is behind
the retina, as seen in Fig. 170, in which the rays from two
FIG. 170.
points are represented as prolonged till they meet at their focus
behind the retina. This defect is palliated by the use of convex
glasses. It is quite common in persons who have passed middle
age ; while near-sightedness appears mostly in younger persons,
the full compliment of the humors of the eye in their case
making the front part of the organ prominent.
451. There has been much discussion of the question why
we see every thing in its real position, while the images of ob-
jects are, as you have seen in 439, reversed on the retina. It
has been supposed by some that we really see every thing re-
versed, and that our experience with the sense of touch, in
connection with that of vision, sets us right in this particular.
300 HUMAN PHYSIOLOGY.
Why we see things erect, though their images on the retina are reversed.
And this, it is supposed, is the more readily done from the fact,
that our own limbs and bodies are reversed as pictured on the
retina, as well as objects that are around us, so that every thing
is relatively right in position. But if this be the true explana-
tion, those who have their sight restored, after having been
blind from birth, should at first see every thing wrong side up,
and should be conscious of rectifying the error by looking at
their own limbs and bodies. But this is not so. In the case
related by the anatomist Cheselden, of the boy who was blind
from birth, and who at about the age of thirteen had his sight
restored by an operation, there was no complaint that he did not
see things erect at the first. If this difficulty had existed, he would
have complained of it quite as readily as he did of the difficulty
in estimating the size and the distance of objects. The above
explanation of erect vision, and other explanations of a similar
character, are based upon a wrong idea of the office which the
nerve performs in the process of vision. It is not the image
formed upon the retina which is transmitted to the brain, but
an impression produced by that image. The mind does not
look in upon the eye and see the image, but it receives an im-
pression from it through the nerve ; and this impression is so
managed that the mind gets the right idea of the relative position
of objects. Of the way in which this is done we know as little
as we know of the nature of the impression itself.
452. It is an interesting and wonderful fact, that as we look
at an object with both eyes, although there are two images
formed, and therefore two impressions are carried to the brain
by the two nerves, yet a single impression is produced in the
FIG. 171.
THE EYE. 301
Correspondence of action between the two eyes.
mind. To produce this single effect at the end of the process
of seeing, it is manifest that there must be a very exact corres-
pondence in the two eyes as optical instruments. The two
images must be similar, and must be formed on corresponding
parts of the retina in both eyes. Thus, if there be a range of
objects, as at A, B, C, in Fig. 171, the impression will be a
single one in the mind, because the picture of these objects is
on the same part of the retina in both eyes, a, 6, c, and a', &', c r .
But if you press with your finger one of the eyes a little out
of its place, all these objects will appear double, because their
images occupy different parts of the retina in the two eyes.
453. It is essential, therefore, that the muscles which move
the eyes, as we direct them towards different objects, should
harmonize in their action. They must move together with
great exactness, or there will be disarrangement of vision. If the
want of correspondence be slight, the vision will be merely
confused. But if it be considerable, so that the images are
formed on quite different parts of the retina, in the two eyes,
every object will be distinctly double. You can verify this, by
pressing one of your eyes with the finger with different degrees
of force, while you look at the objects. The intoxicated man
often sees indistinctly, and sometimes even double, from this
want of correspondence in the action of the muscles moving
the eyes. This is one of the causes of double vision, as we see
it occurring in disease. I will cite a case which has recently
come under my care, in illustration. The patient could see as
usual, so long as he looked directly in front, or towards the
left. But when he turned his eyes to look towards the right,
he saw every thing double, and the farther he looked in that
direction, the farther apart were the two images of every ob-
ject. The reason was obvious. In looking to the right, the
left eye turns towards the nose, while the right eye turns from
it outward. The failure in this case was in the action of the
muscle that turns the right eye from the nose. The conse-
quence was, that as he attempted to turn his eyes to look to
the right, the right eye did not correspond in its motion with
the left, but remained nearly stationary, presenting therefore a
squinting appearance. In common squinting, there is a per-
manent contraction of one of these straight muscles, similar to
that which we see in wry-neck, as stated in 308. When
this difficulty exists, the images of objects are formed in two
different parts of the retina in the two eyes, as in the case which
I have just related. We should therefore expect that there
26
302 HUMAN PHYSIOLOGY.
The two images of an object in the two eyes not always exactly alike.
would be double vision, but ordinarily there is not. Why is
this ? It is because the mind acquires the habit of attending
to the impression that comes from one eye alone, the sound one.
If the squinting occur suddenly there is double vision at first,
because it takes a little time for the mind to acquire the habit
referred to. But it generally comes on gradually, and there-
fore there is no difficulty in the acquisition of this habit, to
meet the exigency of the case.
454. While it is necessary to single vision when both eyes
are used, that the image of the object should occupy corres-
ponding portions of the retina in the two eyes, it is not true
that these two images are in all cases exactly alike. They are
so when the object presents a plane surface, or one, every line
of which can be seen equally well by both eyes. But if the
object be such that some lines or surfaces of it are seen by one
eye alone, while other lines and surfaces of it are seen only by
the other eye, two different images are obviously formed in the
two eyes. You can verify this by a simple experiment. If
you hold a book before your eyes, with its back in a vertical
direction, you see the back of the book and its sides at once, as
a single object. If now, still holding the book in the same
position, you shut one eye, you see but one side of the cover of
the book that one which is on the same side with the open
eye. And so with the other eye. The plain inference is, that
when you look at the book with both eyes, the image formed
in the right eye is composed of the back of the book and the
cover of the right side, while the image in the left eye is com-
posed of the back of the book and the cover of the left side.
From these two distinct images, of course, two distinct impres-
sions are sent to the brain ; and yet but a single impression is
recognized there by the mind, for the book is seen as a single
object. This single impression must, therefore, result in some
way from a mingling of the two impressions transmitted along
the two optic nerves. Were it not for this mingling of the two
impressions, we should see double, that is, see two things, when-
ever we look at any solid projecting object, and should see
single only when we look at plane surfaces. Indeed, one who
has but one eye can not acquire from sight alone any idea of
solidity. Every thing would appear to him to be on a plane
surface, till he finds it to be otherwise by the use of the sense
of touch, in connection with that of sight.
455. The statements in the last paragraph are beautifully
illustrated by the instrument contrived by Professor Wheatstone,
THE EYE.
303
Explanation of the stereoscope.
which he calls the stereoscope. In using this instrument, you
look at two pictures of the same object with the two eyes, and
yet you see but one thing that is, but one impression is pro-
duced in the mind, although two different pictures are made in
the two eyes, and of course two different impressions are con-
veyed to the brain. Suppose the object represented is a book,
as described in the experiment alluded to, in 454. In the
right half of the instrument is a representation of the book, as
seen by the right eye, and in the left half is a representation of
it as seen by the left eye. As you look at them you see but
one book, just as you do in holding the book before your eyes.
The two different images formed in the two eyes are the same
in the two experiments. The same thing is done with other
objects. Thus, the two representations of a dog, seen in Fig.
172, are seen in the instrument as a single dog. You observe
FIG. 172.
that they are shaded differently. They are representations of
the two pictures, which a dog in this position would make on
the retina in both of the eyes of a person looking at him.
When you look at them in the instrument, the single dog that
you see stands out more than either of the two representations,
as seen when they are not in the instrument. The reason is
obvious. In the two, images formed in the eyes, as you look
into the instrument, are all the lines of light and shade, which
304
HUMAN PHYSIOLOGY.
Rude imitation of the stereoscope.
you would see in looking at a real dog with both eyes ; while
either one of these representations contains only a part of these
lines. You can imitate in some good degree the effect of the
stereoscope, by placing the end of a small book between these
figures, and letting the other end rest against the nose and fore-
head, thus separating the eyes from each other. If now you
look intently at the two figures, you will in a few moments find
them approximate each other, till at length they mingle to-
gether, and you will see but a single dog standing out like a
statue. The same thing can be shown by mathematical figures.
Thus, if two figures a a, represented in Fig. 17$, be placed in
FIG. 173.
\
\
/
I
/
\
the two apartments of the instrument, on looking into it you
will see a single figure, shaped like b. You can imitate the
stereoscope here also, by placing the end of a book in such a
way as to cover the middle figure, the other end being between
the eyes. The two figures will run together, and the union
will represent the figure of a truncated, four-sided figure, stand-
ing out in bold relief. But such experiments afford only a rude
imitation of the stereoscope, for in this instrument the separa-
tion between the eyes is entire, so that the effect is produced
at once. There is no running together of the two figures, but
the moment that you look into the instrument they are blended
in one.
456. The harmony which we have seen to exist in the action
of the eyes is very wonderful. It must be remembered the.t
the eyes are optical instruments, endowed with self-adjusting
powers, to accommodate the different distances of objects, and
the varying degrees of light. And thus must both be just
alike in all these diversified adjustments, that the images in
both may correspond. And besides all this adjusting machinery
inside of the eyes, so delicate and so correspondent in its action
in both, there is muscular machinery outside, to move the eye-
THE EYE. 305
Correspondence not only between the two eyes, but also between their nerves.
balls in all directions ; and in these movements also, as you
have seen, there is an exact correspondence. All these motions
for adjusting this complicated machinery within and around the
eyes, are regulated by the nerves. How astonishing the accu-
racy with which they do this ! How exact are the different
impressions transmitted through them, in producing the various
degrees, and multiplied combinations of action, in the little
muscles of these organs !
457. There is correspondence not only in the machinery of
the eyes, as optical instruments, but also in that portion of the
process of seeing which is not mechanical. The nerves of vis-
ion must be exactly correspondent in the two eyes, that similar
impressions may go from the retina to the brain in both. And
the correspondence is in this case the more wonderful from the
fact, that the impressions transmitted are, as you have seen,
not always precisely alike. How the harmony is preserved in
connection with this variation is a great mystery. We can
readily conceive how a single impression can result in the mind,
from two impressions transmitted to the brain from two images
which are exactly alike. But we cannot conceive how confu-
sion can be avoided when the images and the consequent impres-
sions are in some measure different. In this connection I will
notice a peculiarity in the arrangement of the optic nerves.
They are not entirely separate as they go from the eyes to the
brain. At one point in their course they unite together, and
then separate again. In doing so, some fibres from both the
nerves communicate together, and some cross each other, so
that a portion of each nerve passes over to the other before
they go to the brain. Undoubtedly this arrangement has some
reference to the harmony of action of the two nerves, but we
know nothing of the way in which it exercises its agency in
this respect.
458. The power of perceiving the size, distance, and figure of
objects, is wholly an acquired power. The case already referred
to, in which Cheselden restored the sight by an operation, shows
this to be true. " When he first saw," says Cheselden of his
patient, " he was so far from making any judgment about dis-
tances, that he thought that all objects whatever touched his
eyes (as he expressed it,) as what he felt did his skin, and
thought no objects so agreeable as those which were smooth
and regular, though he could form no judgment of their shape,
or guess what it was in any object that was pleasing to him.
He knew not the shape of any thing, nor any one thing froxn
26*
306 HUMAN PHYSIOLOGY.
Power of perceiving the size, distance, and figure of objects acquired.
another, however different in shape or magnitude; but upon
being told what things were, whose form he before knew from
feeling, he would carefully observe, that he might know them
again ; but having too many objects to learn at once, he forgot
many of them ; and (as he said), at first he learned to know,
and again forgot a thousand things in a day. At first he could
bear but very little light, and the things he saw he thought
extremely large ; but upon seeing things larger, those first seen
he conceived less, never being able to imagine any lines beyond
the bounds that he saw ; the room he was in, he said, he knew
to be but part of the house, yet he could not conceive that the
whole house could look bigger." Every infant, if it could ex-
press its ideas, could give us a narrative of a similar experience,
in its first lessons in seeing. It is obvious that seeing is a pro-
cess which we learn to do, as really as we learn to talk or walk.
The confused vision of the infant bears the same relation to
the accurate vision of the adult, that its uncouth noises and
awkward motions bear to the adult's harmonious utterances and
graceful movements. In order to acquire definite and correct
ideas of objects, we are obliged to learn how to use those opti-
cal instruments, the. eyes. The infant manifestly does not know
how to use them to any great advantage. He does not at first
know how to use the muscles that direct the eyes towards any
object, and there is, therefore, an obvious awkwardness in their
movements. As he reaches out his hands towards objects, it
is plain that he does not appreciate their distances. He reaches
out for the moon, or any other distant object, just as he does
for the toy that is held before him. It is by a continued com-
parison of experiences that he learns the sizes, shapes, and dis-
tances of objects. And in doing this, the sense of touch acts
as the educator of the vision, very much, as the ear educates the
voice. And even the adult, with all the training wmch he has
bestowed upon his eyes, often makes mistakes, especially in rela-
tion to magnitude and distance. There are various degrees ot*
skill in seeing; and he is the most skillful seer wno makes the
fewest of the mistakes referred to.
459. Let us look now at the means by which we gain the
experience that is necessary to correct vision. One means is
the appreciation of the space occupied by objects in the field
of vision. This is measured by what is termed the visual
angle that is, the angle which is formed by two lines corning
from the extremities of an object, and meeting in the eye, as
represented in Fig. 1 74. In this way we get the idea of mag-
THE EYE. 307
Visual angle. Distance of objects estimated by their distinctness.
FIG. 174.
nitude. But it is manifest that it cannot alone give us this idei
correctly. It would do so, if all objects were at an equa\
distance from the eye. But you can see by the figure, that if
they are at different distances, you must know something of
those distances, to estimate the magnitude of the objects by
the visual angle, which they subtend. The arrow at A, B will
appear just as large as the larger one at A', B', because it will
occupy the same space a, b on the retina, and subtend the same
angle. But if you know that the one is nearer to you than
the other, you make allowance for this in the estimation of the
size. Your hand, held up to keep the rays of the sun from
your eyes, would look to you as large as the sun itself, if you
did not know how near it is to you ; and the sun and moon
appear to us to have about the same magnitude, because we do
not keep in mind the fact that the sun is ninety-six millions of
miles from us, while the moon is only two hundred and forty
thousand.
460. Another means which we use in getting a correct idea
of objects by vision, is the degree of distinctness in their lines,
and shadows, and colors. The fact is learned very early by
the child, that the nearer objects are, the greater is their dis-
tinctness ; and he makes use of this fact continually in estim-
ating both their distance and their magnitude. He estimates
the latter less directly than he does the former by this means.
He makes use of his notion of the distance of an object, gained
by its degree of distinctness, in forming an idea of its magni-
tude. Many mistakes are made in the use of this means of
judging of objects. Thus, a very bright light will often appear
to be nearer than one that is less bright. When the atmos-
phere is very clear, mountains and other objects appear nearer
to us than they do when the atmosphere is thick and hazy.
461. Another means of making a correct estimate of the
distance and magnitude of objects is, comparison with other
308 HUMAN PHYSIOLOGY.
Size of objects estimated by comparison. Muscular sense in the eye.
objects which are familiar to us. Thus, we get our ideas of
the size of animals from objects in their neighborhood. The
artist makes use of this means of communicating ideas of size
in pictures and engravings. Figures of men are placed near
large buildings for this purpose. A notion of the great size of
the elephant is given by placing his keeper at his side. I need
not multiply instances of this sort. We are not ordinarily
aware how dependent we are upon such comparisons, in esti-
mating the magnitude of objects. An occasional mistake re-
minds us of it however. For example, I once turned my eye
suddenly from a giddy height, upon some huts below at a river's
side ; they appeared to me to be dog kennels, till a man issued
from the door of one of them, and thus dispelled the illusion,
by affording me a means of comparison. So complete was the
illusion, and so sudden was the dissipation of it, that it seemed
as if there was an instantaneous swelling of dog kennels into
huts. Every one must have noticed how large the full moon
appears as he sees it rising, while the higher it rises the smaller
it becomes to the eye, although it is really at no greater distance
than it was when it first rose. The reason is, that when it first
rises you see it in a range with other objects, with which you
instinctively compare it. And, therefore, it appears larger when
you see it rising in the direction of some distinct object, as a
large building, or a high hill, than it does when you see it rising
over a level plain.
462. Another means of judging of the magnitude and dis-
tance of objects is, the muscular sense ( 323) exercised in
adjusting the eyes in seeing them. Thus, consciousness of
the amount of muscular action, in passing the eye up and down
a tall object, helps to give us an idea of its height. So too, in
looking at near objects, consciousness of the amount of effort,
in turning the two eyes towards the point looked at, helps us
to estimate the distance of the object. Commonly we do not
distinctly think of this effort, because it is so easily made ; but,
if after looking at an object held at some distance from the eyes,
we suddenly bring it very near, the effort to make the axes* of
the eyes converge enough to see it distinctly is very manifest,
producing a straining effect, which, if it be repeated many times
successively, wearies the eyes. You can discover how very
dependent you are upon this sense of the convergence of the
* The axis (plural axes) of the eye is a line drawn through the centre of the cornea
and pupil backward through the eye to the central point of the retina. In Fig. 171 UM
axes are B b, and B b'
THE EYE. 309
Seeing is in part a mental process. Really complicated and difficult.
eyes, in accurately estimating comparative distances in near
objects, by attempting to thread a needle, or nib a pen, or
snuff a candle with one eye shut. The change in the converg-
ence of the eyes, on looking at objects at different distances, is
very manifest to us when we observe the eyes of others. We
perceive thus not only the direction, but the distance of the objects
at which they are looking. We do this so continually from our
infancy, that we very early acquire great accuracy in judging,
at what distance the point is towards which the eyes are turned,
or in which, in other words, the axes of the eyes meet.
463. From the facts presented in the few last paragraphs, it
is obvious that what we include in the word seeing is, to a great
extent, a mental process. That is, there are certain mental
efforts which are absolutely essential to correctness in vision.
Without these mental efforts or processes, we could not see
things as they are, as it is expressed very properly, but we
should see them as the boy operated upon by Cheselden did,
when he first began to see. Seeing is cojnmonly supposed to
be a very simple process. The idea is, that one has merely to
open his eyes, and he sees. But, as you have seen, the whole
process is both a complicated and a difficult one; and in order
to be able to do it, the eyes have to go through a course of
training in the case of every infant, just as was the case with
the boy whose sight Cheselden restored. We should be con-
scious of this, if we could recollect the experiences of infancy.
But not being able to do this, it is only when we make some
extraordinary effort in vision, that we are at all sensible that
there is any acquired skill in the process. After the training
which the eyes have in infancy, ordinary seeing is done with
so much facility, that we are not conscious of any effort either
bodily or mental. This appears very wonderful, when we con-
sider that the eyes are two optical instruments, which need, as
you have seen, a most careful and nice change of adjustment
continually, to see in different directions, and at different dis-
tances, and that there is also considerable and complex mental
effort in getting the right impressions from the objects which
are pictured upon the retina.
464. But there is another view in which the mental part of
the process of vision appears strikingly prominent. When it is
said that images of objects are formed upon the retina, and that
impressions are transmitted from them to the brain, this is far
from stating all that is true on that point. Many of the
images pictured upon the retina do not transmit impressions to
310 HUMAN PHYSIOLOGY.
All images on the retina do not produce impressions in the mind.
the mind. The sensation of seeing is, therefore, in relation to
them incomplete the beginning only of the process is effected.
This you have seen to be true in the case of strabismus or
squinting. The faulty eye in this case is not used the mind
takes no cognizance of the images formed in it ( 453). But
it is true of ordinary vision also, that the mind takes no cogni-
zance of many of the images formed on the retina. This can
be verified by a simple experiment. If you hold a finger near
the eyes (at some ten or twelve inches from them), and a fin-
ger of the other hand at a greater distance, but in the same
direction, and then look at the near finger, you will perceive
that the other finger appears double. So, on the other hand,
if you look at the distant finger, the near one appears double.
The reason of this can be made clear to you by Fig. 175. The
two eyes, L and R, being direct-
ed so that their axes converge FIG - 175>
on the object A, the middle
points of the two wages cor-
respond with the middle points
of the retina in the two eyes, a
and a'. The images thus cor-
responding in their place on the
retina, the impressions carried
from them by the two optic
nerves to the brain correspond
also, and so the vision is single.
But the image of the object B
is formed in the two eyes, in
parts of the retina that do not
correspond, b and b'. They are
both on the inside of the mid-
dle points, a a 1 , that is towards
the nose; whereas the outward
part of the retina in one eye
corresponds with the inward
part in the other eye, and vice versa. This you will see to be
true by recurring to Fig. 171, in which is shown the way in
which a row of objects is pictured on the retina in the two
eyes. There you see that the image of the object A, for ex-
ample, is in the left eye, L, on the inner side of the middle point,
b of the retina; while in the right eye, R, it is at the outer side
of the middle point, b'. In the case of the object B, then, in Fig.
175, it is clear to you that the images of it in the two eyes are-
THE EYE. 311
Some of the images on the retina are not attended by the mind.
formed in parts of the retina that do not correspond, and there-
fore it appears double.
465, The application of all this to the point in hand you
can readily see. As the images of all objects in the field of
vision of the two eyes are pictured on the retina, it is plain,
according to the facts developed above, that whenever the eyes
are directed together to any one object, other objects in the
same direction, but at a different distance, must make images
on the retina in the two eyes that do riot correspond. We are
therefore continually seeing double, so far as that part of the
process of seeing, which consists in the formation of the im-
ages, is concerned. But we are not ordinarily conscious of
seeing double. How is this ? How is the difficulty (for it is a
real difficulty in the eyes, as a pair of optical instruments, aris-
ing from the non-corresponding images) remedied ? It is dona
obviously in the other part of the process of seeing, the mental
part. The mind regulates vision by the varying degrees of
attention it bestows on objects. Ordinarily it does not attend
to non-corresponding impressions that come from the non-cor-
responding images, but it attends only to those which are corres-
pondent. As in squinting, it disregards, as you have seen, the
impressions that come from the faulty eye, so in ordinary vision
it disregards many of the impressions that come from both of
the eyes. By an effort of the will it can attend to the impressions
which it ordinarily disregards. When this effort is not made,
it disregards them, as we may say, instinctively. To make this
obvious, I will recur to the experiment with the two fingers,
held at different distances. W T hen you first attempt the experi-
ment, you do not for the moment perceive that you see one
finger double, because you change the direction of your eyes
from one finger to the other, so easily and so unconsciously,
that you seem to see them both singly at once. But by a little
mental effort you fix your eyes on one, at the same tim attend-
ing to the images and consequent impressions produced by the
other, and then the experiment succeeds. From all this it is
obvious that the reason that you do not see very near objects
double, when looking beyond them to distant ones, or see distant
ones double when looking at near ones in the same direction,
is simply that the mind ordinarily attends only to those images
and impressions which are correspondent, while it with an ha-
bitual instinct disregards those which are not so.
466. In connection with this subject of the influence of mental
attention on vision, it is proper to notice the fact, that vision is most
312 HUMAN PHYSIOLOGY.
Point of distinct vision. Minuteness of the images on the retina.
distinct at the central part of the retina that part where the axis
of the eye strikes, as seen in Fig. 171, b, b'. This is commonly
called the point of distinct vision. The mental attention makes
use of this point continually. Thus, if we are looking intently
at a minute object, the eyes are so directed, that their converg-
ing axes meet on the object. So when we are reading, although
the whole page may be pictured on the retina of each eye, only
the letter on which the axes of the eyes meet is seen with per-
fect distinctness. And the point of union of the axes moves
from one letter to another along the lines, so that each letter is
successively pictured on the central part of the retina. The
process is so rapid that we are not conscious of it, until
we take pains to observe what the process is. So, in looking
at a prospect, the eyes at each moment see some one point
more distinctly than any other part of all that fills the field of vis-
ion. We are unconscious of this, just as in the case of read-
ing, because the axes of the eyes are so continually moved by a
slight but exceedingly quick motion from one point to another.
We in this way take into the central part of the retina so many
points with such rapidity, that, by a mingling of the impres-
sions upon the mind, we seem to see the whole prospect at the
same moment, with nearly equal distinctness. The successive
impressions from the images on the retina, occupy so little time,
that they appear to be simultaneous, unless we watch the process.
467. But although some one letter on a page, or some one
point in a prospect, is at each moment seen with much more
distinctness than what is all about it, yet there is some vision
of the page and of the prospect as a whole, of course being
less distinct the farther it is from the central point. It is pic-
tured as a whole on the retina, and the impression from it as a
whole goes by the nerve to the brain. The picture is a very
minute one, as it occupies a small space, and yet it is very dis-
tinct in all its lines, and shades, and colorings. On this point
Dr. Paley remarks that " in considering vision as achieved by
the means of an image formed at ',he bottom of the eye, we
can never reflect without wonder upon the smallness, yet correct-
ness of the picture, the subtility of the touch, the fineness of
the lines. A landscape of five or six square leagues is brought
into a space of half an inch diameter ; yet the multitude of
objects which it contains are all preserved ; are all discriminated
in their magnitudes, positions, figures, colors. The prospect
from Hampstead Hill is compressed into the compass of a six-
pence, yet is circumstantially represented."
THE EYE. 313
Our judgment of the motion of objects often erroneous.
468. We form a judgment of the motion of bodies, in part
by the movement of the images of them upon the retina. The
perception of this movement must be exceedingly delicate, for
even when a body passes over a considerable space, its image
moves over a very small space on the retina. "A stage-coach,"
says Dr. Paley, "traveling at its ordinary speed for half an
hour, passes in the eye only over one-twelfth of an inch, yet is
this change of place in the image distinctly perceived through-
out the whole progress ; for it is only by means of that per-
ception that the motion of the coach itself is made sensible to
the eye. If any thing can abate our admiration of the small-
ness of this visual tablet, compared with the extent of vision,
it is the reflection which the view of nature leads us every hour
to make, viz : that in the hands of the Creator, great and little
are nothing."
469. Many of our impressions in regard to motion, as we
look at objects, are erroneous. When we are moving ourselves,
for example, stationary objects appear to move. As we ride
rapidly, the objects that we see seem to fly by us. This is
especially the case, if the motion to which we are subjected be
an even one, as when we ride in a rail-road car. And if we
look at distant and near objects at the same time, while the
near objects seem to fly back, the distant seem to go along with
us. This is owing to their relative change of position, as can
be made clear by Fig. 176. Suppose that when at a you see
FIG. 176.
27
314 HUMAN PHYSIOLOGY.
Rapidity of succession of images on the retina. How measured.
two objects, c and d, in the same direction. If you pass rap-
idly to 6, the object c appears to have moved backward in rela-
tion to the object, d, while the object, d, appears to have moved
forward in relation to c ; and the line, d, e, represents the rela-
tive change of positions in the images of the two objects upon
the retina.
470. As every object that we see is daguerreotyped, as we
may say, upon the retina, the rapidity with which these pic-
tures change, and the distinctness with which the nerves trans-
mit impressions from them to the brain, are very wonderful.
The time required for each transmission is very small only the
fraction of a second. The length of time has been estimated
by experiment. Thus, if it is found that a burning coal, whirl-
ing around at the rate of six times in a second, produces a
continuous circle of light, but that the circle is broken when it
whirls round only five times in a second, we know that the
length of time required for a distinct and separate impression
is the one-fifth of a second. The same experiment can be
tried with a wheel. In this case we observe what is the largest
number of revolutions in a second, that can be made without
blending the visual impressions of the spokes into one con-
tinuous impression. By such experiments, it has been found
that the time required for a distinct visual impression varies in
different individuals, and in the same individual at different
times, from one-fourth to one-tenth of a second. This differ-
ence in the rapidity of succession of the impressions is of course
not owing to any difference in the rapidity of the formation of
the images ; for they are formed by the light, and light always
moves with the same velocity. It must be owing manifestly to
a difference of facility on the part of the mind, in receiving
impressions from the images. In other words, the mental ac-
tivity in the use of the optical instruments, the eyes, differs in
different individuals, and in the same individual at different
times. If one sees more quickly than another, it is a mental
quickness. It is a difference analogous to that which we see in
relation to the use of other instruments of the mind, the mus-
cles for example. Some use these instruments much more
readily and rapidly than others. We see this in the motions
of the eyes themselves, and the eyelids also. Some wink more
quickly than others, and there was wisdom in the decision of
the blacksmith who dismissed a workman, because he did not
wink quick enough, and was therefore always getting sparks in
his eyes.
THE EYE. 315
Thaumatrope. Defenses of the eye. Bones. Cushion of fat.
471. The blending of impressions in vision, produced by
rapid motion, has been made use of in the contrivance of an
amusing optical toy, called the Thaumatrope. In making this,
you cut a circular card, and make two different figures on its
two sides. If you attach two silken strings to opposite points
in its diameter, and then twist the strings, so that when the
card is left to go free, it will revolve with considerable rapidity,
the two figures will be mingled together as seen by the eye.
In Figs. 177 and 178, are represented the two sides of a card,
FIG. 177. FIG. 178.
prepared in this way. In this case, the figures as they mingle
together appear to the eye as a cross. If a bird be drawn on
one side of the card, and a cage on the other, the mingling of
the two figures, as the card revolves, will show you the bird in
the cage.
There are many other points in regard to the phenomena of
vision, which it would be interesting to notice. But it would
make this chapter too long.
472. The means by which so delicate an organ as the eye
is protected from injury, are worthy of notice. Observe first
its situation. Parapets of bone surround it, and receive the
force of most of the blows that come upon that part of the
face. Above is the strong arch of bone, forming the lower
part of the forehead. Then there are the cheek bones, and the
bones of the nose. Thus, walled in, in all directions by these
prominences, the eye is seldom hurt, except by a direct thrust.
And besides being thus protected by surrounding bones, it re-
poses upon a soft cushion of fat, which yields, if the eye be
pushed backward by violence. Indeed it is thus pushed back-
ward effectually by the muscle that closes the eyelids, whenever
an impending blow is seen, and it is thus sunk farther back in
its cushioned recess, amid the projecting parapets, and of course
receives less of the force of the blow than it otherwise would.
This muscle, also, by its instantaneous action, prevents many
316
HUMAN PHYSIOLOGY.
Eye defended by the eyebrows, eyelashes, and lids. The tears wash it.
light articles from flying into the eye. Such articles are also
often prevented from entering the eye, by being intercepted by
the eyelashes. The eyebrow, beside being an ornament, pro-
tects the eye from harm, by preventing the salt perspiration
from running down into the eye, and irritating it. It acts as a
thatched roof, projecting from the arch over the eye, and letting
the perspiration from the forehead evaporate from it, when it
is small in amount, or drop from it down upon the cheek, when
it is abundant. The eyelashes also serve to keep the perspira-
tion of the eyelids from entering the eye. The structure of the
eyelids is such, that the freest motion is allowed, while they
afford by their firmness considerable protection to the organ.
They derive their firmness from a fibrous cartilage, which makes
the body of each lid. You can readily see that this cartilage,
making an even pressure on the surface of the eye, must often
prove an effectual defense against direct thrusts. If the weapon
hit this cartilage, it acts as a firm shield, to ward off the blow
from the eye behind it. And even that part of the lid which
is intended* by its laxness to allow free motion to the lid, the
skin, is often an effectual defense. If an impending blow be
seen, and the eye be instantaneously and forcibly shut, the
wrinkled skin forms a soft cushion over the eye, and thus not
only covers it up, but serves materially to deaden the force of
the blow.
473. The tear apparatus
affords the eye material
protection. The bland tears
keep the organ properly
lubricated, so that its con-
stant motions occasion no
irritation. And if any thing
gets into the eye, the tears
are manufactured abund-
antly, for the purpose of
washing out the intruding
substance, which is generally
effected. Fishes have no
need of a tear apparatus, as
their eyes are washed con-
stantly by the water in
which they live. In Fig.
179 is represented the tear-
apparatus. The tears are TEAR APPARATUS.
FIG. 179.
THE EYE. 317
Tear apparatus. Oiling the eyelashes.
secreted by a small gland, called the lachrymal gland, situated
at a, in the orbit under the arch of the forehead, and near the
outer angle of the eye. At b are the ducts which empty the
tears in upon the surface of the eye on the inside of the upper
lid. By the constant motions of the organ the tears are diffused
over its whole surface, and thus continually wash the eye. The
arrangement for carrying off the fluid is this. It flows through
a tube, c?, e, into the nose. This tube has at its beginning in
the eye two branches, c, c, which open on the edges of the two
lids at the inner corner of the eye. These open mouths, that
drink up the tears as they flow to them, you can very readily
see. The drain of the eye, which thus conveys the lachryma.
fluid to the nose, is ordinarily capable of taking care of all the
tears that the gland makes. But when an uncommon amount
is made, as in weeping, it cannot receive all the tears, and they
therefore overflow their banks, the edges of the eyelids. And
sometimes there is a constant overflow from obstruction of the
drain by disease. The continual weeping of the eye, when this
obstruction exists, will give you some idea of the amount of fluid
which the lachrymal glands make.
474. Along on the edge of each eyelid are some very small
glands which secrete an oily substance. This serves two pur-
poses. It oils the eyelashes. It also prevents the tears, when
they are only in ordinary quantity, from being diffused over
the edges of the eyelids in the constant motions of the eye.
This exceedingly small quantity of oily substance suffices to
keep the tears in the eye where they are needed. There i?
also a curious provision for directing the tears
to the mouths of the ducts when the lids are FIG< 18 -
closed. When brought together their edges
unite in such a manner as to form with the
surface of the eye a triangular channel for the
tears to run in. This is made clear by the
diagram in Fig. 180, in which the line b rep-
resents the surface of the eye, and a the edges
of the lids, showing a section of the canal be-
tween them.
475. I had intended to notice some of the
peculiarities of the eyes of different classes of
animals, but this chapter is already so long that I will notice
but one the nictitating membrane in the eyes of birds.
When not in use it is gathered up in the inner corner of the
eye. When it is stretched over the organ it is a thin translu-
27*
318
HUMAN PHYSIOLOGY.
Nictitating membrane in the eyes of birds.
cent membrane. It is very elastic, so that
as soon as the muscles that sweep it so
quickly over the eye are relaxed, it flies
back at once to the corner where it is so
snugly folded. In Fig. 1 8 1 it is represented
as half way over the front of the eye. In
Fig. 182 are seen the curiously arranged
muscles that move it. One of the muscles,
g, arises from the ball of the eye at its up-
per part, and running back forms by the
trunk of the optic nerve a tendon with a
loop, through which the tendon of the other
muscle, p, works. This muscle arises from
the lower part of the ball of the eye, op-
posite to the origin of the first muscle. Its
tendon, t, is fastened into the edge of the
nictitating membrane. It acts through
the loop as a pulley, and you can see that
the muscle, y, assists it materially in effecting
the very quick motions of the membrane.
FIG. 181.
FIG. 182.
CHAPTER XVII.
CONNECTION OF THE MIND AND THE BODY.
476. IN the Chapter on the Nervous System I gave you a
general view of its functions and its arrangements. You saw
that it is to the mind the grand means of communication with
the world of material and immaterial things around it. In the
Chapters on the Senses and the Organs of Locomotion, we have
considered the modes in which this communication is maintained,
through organs subordinate to the nervous system. And you
have seen that through the senses all knowledge of external
things is communicated to the mind, where it is used as the
material of thought and reflection and feeling ; while, on the
other hand, through the muscles the mind produces all its im-
pressions upon the things and beings on which it acts. You
CONNECTION OF THE MIND AND THE BODY. 319
The brain the organ of the mind. Facts which prove this.
are now therefore prepared to look more thoroughly into the
connection which the nervous system establishes between the
mind arid the body, and to observe some of the higher and more
intricate phenomena which result from it. It is to views upon
these points that I shall devote this and the following chapter.
477. The brain is the organ of the mind. In this life there
can be no mental manifestations except through the agency of
this organ. The rnind and the brain always act together as one
thing. This is manifest in regard to motion and sensation. It
is equally true of thought. The mind can think and excite
motion in the muscles only through the brain. The proofs of
this are various and abundant. If a man by a blow upon his
head have a portion of the skull driven in upon the brain, so as
to press upon it considerably, all sensation and power of motion
are suspended. His mental connection with the world around
him is completely cut off. And not only so, but all mental ac-
tion is arrested. The mind, thus shut in from the world around
by the suspension of sensation, does riot go on to act indepen-
dently of the compressed brain. The man does not think ; for
if thinking did occur in such cases, there would occasionally be,
as after dreaming, some recollection of what passed through the
mind, after the pressure is taken off from the brain by the tre-
phine and elevator of the surgeon. He lives, because the invol-
untary muscles, connected by their nerves with the top of the
spinal marrow, ( 229,) which is uninjured, carry on the breath-
ing and the circulation. But though he lives, he is not now a
moving, or a sentient, or a thinking being. His mind is as
dormant as life is in a state of hibernation.
478. The same state of things occurs in apoplexy, and in the
senseless state which accompanies most convulsions. And it
may be remarked, that the degree of the suspension of the
mental functions depends upon the degree of effect produced
upon the brain. If, for example, in the case of injury, the
pressure of the bone driven in upon the brain be not very great,
the suspension will be partial ; but if the pressure be considera-
ble the suspension will be complete.
479. The dependence of the mind upon the brain is mani-
fested in a great variety of diseases. The delirium of fever and
of inflammation of the brain, and insanity resulting from chronic '
disease in this organ, show this absolute and inseparable con-
nection of the mind with the material organization in our present
state of being. We sometimes see the mind gradually blotted
out by the progress of disease in the brain, so that a man of
320 HUMAN PHYSIOLOGY.
Insanity a disease of the organization. Situation of the brain.
even high mental powers becomes a drivelling idiot. So, too,
a bad formation of the brain, or early disease of this organ
often prevents mental development. Insanity is always the re-
sult of disease in the organization. This is so even when it is
produced by moral causes acting directly upon the mind. The
insanity in such a case is an indirect effect the organization
affected by the mind is thrown into a diseased state and reacts
upon the mind, influencing its manifestations. "If the mind
thus acted upon were a spirit, separated from the body, the
result would be merely the feelings, which the motives applied
would naturally produce, and not the unnatural feelings of
insanity. It is not strictly proper then to speak of a 'mind
diseased.' Let me not be understood to mean that mental de-
rangement in every case is to be attributed to disease that leaves
such palpable traces, that the dissecting knife would reveal it if
death were to take place. There are diseased operations of the
body, that are hidden from our view so hidden, that they not
only leave no traces, but often develop no characteristic bodily
symptoms."* I shall recur to this subject of the dependence
of the mind upon the brain in another part of this chapter, and
shall endeavor to point out definitely what are the teachings of
physiology, of our consciousness, and of revelation respectively
in regard to it.
480. Observe for a moment the situation and the immediate
connections of the brain, the organ of the mind. Its situation
in the human structure is appropriately a commanding one. It
is fitly placed at the summit of the structure, inclosed by that
noble dome which I described to you in the Chapter on the
Bones. And then observe that in its immediate neighborhood
are the organs of four of the senses, sending their messages
continually to the mind. Especially you notice that under the
jutting arches of the front of the dome are the ever-moving
eyes, looking out from their elevated place of observation ; and
at the sides of the base of the dome are the halls of audience,
ever open and ready to transmit the messages that come to the
soul through the vibrations of the air. And there, too, in the
very front of this habitation of the mind is the face, indicating
by the delicate, quickly changing play of its muscles the thoughts
that are at work within. And lastly, there is the mouth, the
outlet for the voice, the chief agent of the outward manifesta-
tions of the mind. Here then are clustered together in this
* "Physician and Patient," page 292.
CONNECTION OF THE MIND AND THE BODY. 321
Rapidity of communication between the mind and the body.
small space, in the immediate neighborhood of the mind's hab-
itation, its principal instruments of communication with the
world around. When we are listening to eloquence, whether
it be in the public assembly, or in the social circle, or in the
more private intercourse of friendship, and observe, as the rich
tones proceed from the mouth, the elevated and changeful ex-
pressions of the countenance, we are impressed with the idea,
that, if it be the mind which constitutes the image of God in
man, the face of man thus situated in the front of the mind's
habitation, is the fitting outward emblem of that image.
481. It is interesting to observe how exceedingly rapid are
the communications of the mind with the different parts of the
body. Notice what the process is, or rather what the processes
are, when you withdraw your hand from any thing that hurts it,
as heat for example. An impression is produced upon the ex-
panded nerve in the part this impression is sent along the
nervous tubuli to the brain the mind there receives the im-
pression the mind in return communicates an impression to
the brain this impression goes by another set of nervous tubuli
to the muscles they act, and the hand is withdrawn. If it
took as long to do all this as it has for me to describe it, the
hand would be very thoroughly burned before it is drawn away.
The same set of processes is gone through with, when in ex-
ecuting music, either with the voice or an instrument, a mis-
take is immediately heard and corrected. And so of other
cases.
482. In the Chapter on the Muscles I spoke of the great va-
riety in the motions of the body. In executing these motions
the individual commonly knows nothing of the muscles with
which he does it. Even the anatomist, who is familiar with the
situation and arrangement of the muscles, seldom thinks of
them while he works them in the production of different mo-
tions ; and if he does think of them it affords him no assistance
in their use. Great skill can be acquired in the use of the
muscles, without any knowledge in the individual of the fact that
he has such organs. In muscular action men commonly move
a machinery of which they know nothing. They have only to
will any particular motion, and the nerves are so arranged at
one end with the muscular fibres that will do it, and with the
brain at the other, that the message from the mind goes to
exactly the right fibres, and the result is produced. For the
infinite variations of motion in the body what complicated and
intricate arrangements are needed ! These variations, it is to
322 HUMAN PHYSIOLOGY.
Skill in the .use of the muscles. Variety in their action.
be remembered, do not result merely from combinations of
movements, but are rendered vastly more extensive from the
varying degrees of contraction in the muscles. If each muscle
always acted just so much and no more, there would be even
in that case great variety of motion, from its combination in
various ways with other muscles. But the variety is made to
be endless from the endless variation in the degree of their con-
traction. And for each one of these variations, both in degree
and combination of action, there must be a different message
sent from the mind along the nerves. In every motion the
muscles that produce it must, so to speak, be told to act, and not
only so, but they must be told just how far to act. In motions
that are very compound, and at the same time exceedingly del-
icate in their variation, the accuracy and variety of the mes-
sages thus sent from the brain along the nerves are not only
wonderful, but are beyond our conception. We realize this
fully, when with the views above expressed in the mind, we
watch a skillful balancer, as he executes his endlessly varied but
exact movements. So, too, when we hear from Ole Bull's one
violin such a mingling of sounds, that we feel that there must
be a half a dozen violins played upon at once, how inconceivably
rapid and numerous and complicated must be the messages that
fly from his brain along the nerves to the muscles, and yet there
is not a failure in one of them not a fibre that does not con-
tract at the right moment, and in the right degree !
483. The use which the mind makes of all the machinery of
the senses and of the organs of locomotion does not come to it
at the outset. It comes by training, and in some cases by very
long training. The child at first uses its muscles bunglingly.
It does not see or hear skillfully. It knows nothing at the first
of the colors, or shapes, or distances of objects. It knows nothing
of the direction or distance of sounds. It has all these things
to learn. And for this purpose the organs of sense and the
muscles are put into exercise at once, and the child begins its
long process of learning on the day of its birth. Few have any
conception of the amount of knowledge which is acquired in
the first of the child's life. He is born not only with absolutely
no knowledge of the world of things around him, but he has
no skill in the use of the instruments, the muscles and the
senses, by w r hich he is to obtain his knowledge. These give
him at first no very definite information ; but by the constant
exercise of them, and by comparisons between the reports of
the different senses he soon adds rapidly to his stock of knowl-
CONNECTION OF THE MIND AND THE BODY. 323
Learning to use the muscles. Their action at first njtnle?s and awkward.
edge, and becomes skillful in the use of his means of gathering
it. But let us see a little more particularly how this is done.
484. I will speak first of the progress of the child in learning
how to use his muscles. When he first puts them into action
you see that he has no skill in using them. The action is aim-
less and awkward. You see in his movements none of that
native grace of which so much is said. This is to be acquired,
and all that is native about it is the power of acquiring it. He
learns to execute very many motions before he comes to that
complicated movement of so many muscles, creeping, and then
the no less complicated but more difficult one of walking suc-
ceeds. How awkwardly he does this in his first attempts to
preserve his balance, and how many failures must he encounter
before he can perform this motion even decently well ! The
same thing can be said of learning to talk or to sing, for this is
but a training of the muscles. It is thus gradually that all the
voluntary muscles become educated. It is true even of the
muscles of the face. At the first how expressionless ordinarily
is the face of a child. You see nothing of those delicate move-
ments of the muscles which in after years express every varying
shade of thought and feeling. When he cries there is an awk-
ward over action of the muscles, as represented in Fig. 183.
FIG. 183.
He learns to use these muscles partly at least, by imitation.
His first lesson ordinarily is in smiling, which he soon learns
by imitating the smile of his mother. But even this, simple
324 HUMAN PHYSIOLOGY.
Skill in the use of the senses and the muscles. Comes later in man than in animals.
as it is, he does awkwardly at first, and he must go through it
long process before he can master all the capabilities of ex-
pression in these little muscles.
485. Skill in the use of the muscles varies quite as much as
any other acquirement in different individuals. It is wonderful
in the juggler, the rope dancer, the skillful player on a musical
instrument, and the accomplished singer. You will have some
conception of what education can do for the muscles, if you
contrast the awkward balancing of the child in walking with
the agile and delicate balancings of the rope dancer, or the
aimless and uncouth movements of the infant's hands with the
rapid and varied execution of the player on an instrument, or
the monotonous and coarse sounds uttered in a child's first
attempts at singing with the varied melody of a skillful singer.
486. The senses are educated as well as the muscles. As
you see an infant reaching out his little hands awkwardly with
his unskilled muscles towards an object, it is manifest that he
knows not at what distance the object is from him, and that
he does not readily adjust his eyes to its distance, so as to see
it clearly. He after a while by practice acquires the power of
doing this. The same may be said of hearing. The little
muscles which I described to you as so nicely adjusting the
eye for seeing at different distances, and the ear for hearing
various notes of sound, require training, just as the muscles do
with which we walk or talk.
487. It is a singular fact that most other animals are born
with so much more skill in the use of the muscles and the
senses than man. While man is " in the nurse's arms," the
chicken, for example, walks about as soon as it is hatched.
He does it at first awkwardly, it is true, but he soon learns all
that is to be learned about it. He is assisted materially, it is
to be remarked, by the fact that his feet spread out over so
large a space, that he has no hard lessons to learn in balancing
as the child has. But this is evidently not all the difference.
If it were, the child should be able to creep at the first, or even
walk on its hands and feet, for in performing these motions
there is no difficulty in supporting the centre of gravity. The
same difference exists also in regard to the senses, for the
chicken seems to understand distances at once. As it runs
about to pick up its food it makes no mistakes on this score.
But while man is thus at the first the most helpless of animals,
in regard to both his muscles and his senses, by his process of
learning he ultimately acquires vastly greater range and va-
CONNECTION OF THE MIND AND THE BODY. 325
The senses and the muscles mutual teachers. Exemplified.
riety of motion than other animals. And the same thing can
be said of his acquirements through the senses.
488. The senses and the muscles are mutual teachers in
this education which I have described. Thus, in singing, tha
accuracy of the sense of hearing in estimating sounds is ac-
quired through the action of the muscles of the voice while
the ear is listening. And on the other hand, skill in executing
sounds is acquired by these muscles under the tuition of the
ear. The dependence of the senses upon the muscles is not as
absolute, however, as that of the muscles upon the senses.
The ear can be trained in the accurate appreciation of sounds
without any corresponding exercise of the muscles of the
voice, though the two processes are ordinarily to a greater or
less extent connected, and are corrective of each other. But
even when the ear is trained without any aid from the mus-
cles of the voice, the training is in some measure a train-
ing of muscles. For, as you saw in the Chapter on the Ear,
415, there are certain little muscles that regulate the tension
of the drum of the ear, which undoubtedly go through a pro-
cess of training when we are learning to distinguish accurately
between different notes of sound. While the dependence of
the senses upon the muscles is thus a partial one, the depen-
dence of the muscles upon the senses is, on the other hand,
complete. Although the muscles have a sense of their own,
a muscular sense, as Bell cahs it, this is not adequate to be
their sole guide in action, but it serves as a mere auxiliary in
this respect. This absolute dependence of the muscles upon
the senses is very strikingly s'lown in the fact, that the deaf
and dumb are dumb simply because they are deaf. The voice
in them has no teacher. The muscles which regulate the ten-
sion of the vocal ligaments, and those which articulate the
voice do not act, because, as stated in the Chapter on the Voice,
400, they have no guide in their action.
489. Although I have spoken of the education of the mus-
cles and the senses, this language is not strictly correct. For
the education is an education of the mind that operates through
these muscles and senses. It is the training of the mind in
the use of these instruments. This is very clearly shown in
cases of idiocy. In these cases the defect in talking is pro-
portioned to the mental deficiency. It arises from an inca-
pacity on the part of the mind in using its instruments, the
muscles and the apparatus of the senses, and not from any
defect in the construction of these instruments. The larynx
28
326 HUMAN PHYSIOLOGY.
The involuntary muscles not educated. Why.
and the articulating organs of the voice are perfectly well
formed in the idiot, as I have stated that they are in the deaf
mute. While, in the case of the deaf mute they are not used
at all as vocal organs, because the mind, through the absence
of hearing, has no power of regulating them ; in the case of
the idiot they are used to a limited extent, and in a very
bungling manner, because the capability of regulating them is
limited by the deficiency of the directing intellect. And what
I have said of the muscles of the voice in the idiot is equally
true of the muscles of the face. There is no defect of con-
formation, nor is there any lack of lustre in the eye, as is
commonly supposed. The limited range of expression and its
awkwardness arise from an incapability on the part of the
mind of using the muscles of expression with facility and skill.
The muscles have an incompetent teacher, and so learn to do
but little, and do that little bunglingly ; or, to speak more
correctly, the deficient mind is not capable of learning to use
them properly.
490. The education of the muscles does not extend to those
which are involuntary. Though respiration, for example, is a
very complicated act of many muscles, these muscles require
no education to do their part skillfully. We have no need to
superintend them, for their constant action is secured by an
arrangement for nervous influence which is independent of the
mind, as stated in the Chapter on the Nervous System. So,
while the mind sleeps, or when it is locked up in the stupor
of disease, these muscles continue to perform their duty, as
well as when we are awake. The same substantially can be
said of the muscles which perform the act of swallowing. Al-
though this is a very compound, and, mechanically considered,
a very difficult act, as shown in the Chapter on Digestion, 78,
it is performed as well in the first hour of the child's life as it
is at any future period. The muscles that execute it need no
training. And yet it is only after long and diligent training
that the purely voluntary muscles, as for example those of the
hand, execute movements which are no more complicated and
difficult. The reason for this difference is obvious. The move-
ments which are performed by the involuntary muscles, such
as breathing and swallowing, are immediately essential to the
preservation of life, and it is therefore necessary that they
should be well executed from the first. Their perfect action is
therefore secured by a nervous arrangement, which is indepen-
dent of the mind. The voluntary muscles, on the other hand,
CONNECTION OF THE MIND AND THE BODY. 327
Association of action in the muscles without mental action.
instead of being devoted, like the involuntary, to the main-
tenance of life, act as the instruments of the mind, and there-
fore the mind acquires the power of using them skillfully by
dint of long-continued training.
491. In the education of the muscles, it is to be observed,
that although during the process of learning the mind takes
distinct cognizance at first of every movement, it after a while,
as the education becomes complete, takes little or no notice of
many of the movements, except when some error occurs, or
some obstacle arises. Thus, when one is learning to sing or
play a tune, the mind at first through the ear takes a definite
and distinct notice of every sound, and makes a palpable ex-
ertion in every movement. But after the tune is learned, this
ceases to be the case, and the movements seem to be associated
together, in some measure independently of mental action. So
in learning to walk the child notices each of his movements
very distinctly. But when he has fully learned, but little
thought seems to be expended upon the motions, except when
some obstacle appears which interrupts their regular succession.
When one walks in a reverie, the mind is most of the time
wholly abstracted from the associated movements which make
up the compound act of walking. In learning to read the
child makes a distinct mental effort in regard to each letter,
resorting to every aid which will help to make the effort a
successful one, even to the putting the finger on each letter as
he looks along the line. But as he becomes more and more
skilled, the association of action of which I have spoken comes
more and more into play. I will refer you to a partial expla-
nation of the facts above alluded to, given in 262, in the
Chapter on the Nervous System.
492. It has been stated in 325 and 476 that the mind
receives impressions only through the senses, and imparts
them only through the muscles. These act as the instruments
of the nervous system, the senses being the inlets and the
muscles the outlets of communication. And it has been gen-
erally considered as a settled point, that these are the sole
channels through which the interchange of thought and feeling
is effected in our present state of being. But it has been pre-
tended that other mysterious modes of communication have in
these latter days of progress been discovered. The phenomena
presented by animal magnetism, as it is called, are claimed by
some to demonstrate, that there is in some cases a peculiar
means of communication, distinct from those which are usually
828 HUMAN PHYSIOLOGY.
Animal magnetism. Simple tests expose it.
employed. It has been fancied that something analogous to
magnetism is the medium of connection in such cases, and
hence the name of animal magnetism. Through this medium,
it is asserted, that thoughts and sensations pass from one person
to another, independent for the most part at least, of the ordi-
nary conditions on which communication depends. The phe-
nomena have been presented at different times under different
phases, and the theory framed to account for them varies
somewhat from time to time, according to the varying char-
acter of the phenomena, and the tastes and imaginations of
the believers in this so called science. Amid all the various
forms which it has thus assumed, with its corresponding di-
versity of names, one thing has always been true of it, viz.,
that whenever any efficient tests have been applied, it is shown
to be a large superstructure of falsities built upon a very few
facts. And in view of the uniform results of these tests, we
may confidently say, that as yet there has been no satisfactory
proof, that there are any other channels of mental communi-
cation, than the ordinary ones furnished by the senses and the
muscles. Most minds are bewildered by the strange, and some-
times inexplicable things, which appear in the exhibitions
which they witness, and are ready to adopt any plausible ex-
planation which may be offered. But some simple yet search-
ing tests have thus far, whenever applied, always sufficed to
expose the delusion.
493. In illustration of the manner in which these tests de-
molish the lofty pretensions of this so called science, I will
give a single example. The exhibitor asserted that whatever
was in his mind, realized distinctly and vividly, had its image
in the mind of the subject whom he magnetized, by means of
the peculiar connection thus established between them. Any
decided sensation, therefore, which he felt, the subject felt also ;
and if he fixed his thoughts upon any thing, the subject thought
of the same thing. I observed that whatever was said by the
subject, in relation to any sensations or thoughts in the opera-
tor, was generally in reply to questions on the part of the
operator himself. And as these questions were sometimes
repeated in various forms before correct answers could be ob-
tained, I suspected that the information requisite for the answers
was communicated to the subject in this way. I, therefore,
proposed to the exhibitor to try some experiments without
questions, as these, according to his theory, were clearly not
necessary ; for, if there were such a channel of communication
CONNECTION OF THE MIND AND THE BODY. 329
Mental phenomena of animal magnetism.
between his mind and that of his subject as he asserted, the
aid of the voice was not required. The proposition was man-
ifestly so fair an one that he could not refuse to comply with
it. But his experiments performed in this way failed altogether,
and the audience, caring less for a strict search for truth than
for the continuance of their amusement, showed little relish
for the interruption, and the pseudo-scientific exhibition wen!
on. I applied other tests as I had opportunity, which developed
the evidence of imposture here and there in the exhibition, and
though many sober and intelligent citizens were deluded with
the belief that they had enjoyed a rational and truly scientific
amusement, I had no doubt that the whole was a piece of
jugglery. There was one feature in the exhibition, which of
itself was enough to condemn it as a ridiculous imposture. The
operator claimed to have a sort of absolute control over the
subject, so that at will he could hold him in a connection with
himself so insulated that no impressions could be imparted to
him by any other person, and yet could dissolve this connection
and put him into connection with some one else, with as much
facility as a locomotive can be switched off from one track on to
another. And ridiculous as this shifting of mental connections
is, this was quite as successful with the audience as any part
of the exhibition.
494. Some of the phenomena presented in the exhibitions of
animal magnetism afford interesting illustrations of the influ-
ence exerted upon the body through the mind. The mental
influence, exerted by the operator upon his subject, often causes
a condition of the nervous system, which is analogous to som-
nambulism, or to some of the forms of hysteria. The manip-
ulations practiced, the looking the subject intently in the eye,
the holding of a piece of metal in the hand with the eye fixed
upon it, and other expedients, help to produce the impression
in the mind of the subject, that a mysterious and resistless in-
fluence is coming from the operator upon him, and is stealing
over his system. It is not strango that this should occasion
such physical results as we often see, when the mind and the
nerves are very susceptible. This is the simple explanation of
all that is positive in what such exhibitions present to us. There
is no such thing as a magnetic influence, and animal magnetism
is a misnomer.
495. The state of nervous system often produced is not in-
consistent with imposture any more than hysteria is. As in the
nervous states exhibited by this disease there is often a strange
28*
330 HUMAN PHYSIOLOGY.
Alliance to hysteria. Suggestive influences.
perversion of the moral mingled with that of the physical, so
there is also in the state produced by the mental influence of
the magnetizer. Accordingly his most available subjects are
women found here and there in every community, who, through
this mingled moral and physical perversion, have acquired a
permanently morbid state of mind, that makes them like to be
thus petted, and to be the wonder of a gaping multitude. There
is often in the exhibitions of animal magnetism self-imposition
at the same time that there is imposition upon others. In the
case of travelling exhibitors there has always been collusion
enough to stamp the character of jugglery upon the exhibition.
And in other cases, where both the operator and the subject
are honest, there is delusion in both, and they impose not only
upon themselves, but upon each other, as well as upon those
that witness the performance.
496. One of the peculiarities of the state of somnambulism
which is induced by the magnetizer, is the ready obedience of
the mind of the subject to suggestive influences. It is alive to
any suggestions which come from the mind to which it supposes
itself bound by a magnetic spell, and is often in fact shut up to
influences from that source alone, so as to be insensible to in-
fluences from any other quarter. The somnambule is possessed
with one idea, and that an all-absorbing one, because invested
with such mystery. His insensibility to all that is not in ac-
cordance with this idea is to be accounted for in the same way
that we account for the fact, that a wound received in battle
is often unfelt till the excitement of the battle is over, and other
similar facts, as alluded to in 226. This state is often quite
successfully imitated by impostors ; and sometimes there is a
mixture of a partial real somnambulism with imposture, similar
to that which occurs in the case of the hysterical condition.
Of course when this mental connection is so easily shifted from
the operator to bystanders as was described in 493, there must
be sheer imposture. Whether there be full somnambulism alone,
or this in a partial degree and mingled with deception, the in-
fluence of the principle of suggestion is very apparent. Nothing
can be done without questions. Leading questions suggest
ideas to the mind of the subject, and an audience led on by
love of the marvellous and the exciting, are readily satisfied by
the coincidences that occur in the exhibition, while the failures
are disregarded and forgotten.
497. In the state of somnambulism induced artificially by
the so-called magnetizer, as well as in that which occurs from
CONNECTION OF THE MIND AND THE BODY. 331
Clairvoyance a false pretension. Little that is true in so called animal magnetism.
other causes, there is often an exaltation of the powers of the
senses. Thus, sometimes a somnambule can read through en-
velopes of even many thicknesses, from an exaltation of tha
sense of vision.* But all pretensions to reading through bodies
that have no pores or interstices, as metallic substances, or to
reading from other parts of the body, as the pit of the stomach,
or the back of the head, are impostures. So too are all the
pretensions to seeing what is going on in other places, or inside
of the body. This clairvoyance, as it is called, has precisely
the same claim upon our confidence that fortune telling has,
and no more. Real searching tests have always sufficed to ex-
pose its imposture.
498. I have introduced the above views of what is generally
called animal magnetism, in order that you may be prepared to
apply the proper tests, whenever such popular delusions claim
your confidence. I have introduced them, also, because, what-
ever real phenomena do appear in the exhibitions presented to
us under this name, afford some interesting illustrations of the
influence of the mind upon the body. They add another chap-
ter to our view of the mysterious connection of the physical with
the spiritual, secured by means of that wonderful apparatus, the
nervous system. It is from this consideration merely that they
claim the attention of the physiologist. The so-called animal
magnetism, when thoroughly sifted is dissipated, and there are
left as a residuum only a few phenomena, which offer nothing
particularly new, but are chiefly interesting from their analogy
to phenomena with which we were already familiar. And its
boast of the discovery of a new medium of mental communica-
tion is, as you have seen, entirely groundless.
499. In the Chapter on the Nervous System I spoke of the
different offices of the different central organs of this system.
The brain, as you have seen, is more especially connected with
the mind, and is the great instrument through which mental
* Many of the statements, however, of such cases, could have been found to be
lse if the proper tests had been applied. The failure in testing, so common in these
cases, I will exemplify by a single case, which made some noise in its time. It is a
false if the proper tests had been applied. The failure in testing, so common in these
cases, I will exemplify by a single case, which made some noise in its time. It is a
case reported by Col. Stone in his famous pamphlet. He gave the clairvoyant a
sealed packet with a very odd sentence in it, which she read, as the Colonel sup-
posed, wilhout opening it. But how did he know that she did not open the packet?
Simply because she returned it to him a day or two after apparently in the same
state as lie gave it to her, accompanied with a copy of the sentence contained in
it. This he considered good proof, but it is defective in its most essential point.
If she could read the packet without opening it, why did she not do it in his pres-
ence ?- There is not a particle of evidence that any one saw her do it. The true
test was an easy one. but it was not applied. There is such a thing as skill in open-
ing seals and replacing them so as to avoid detection, and until we have proof that
this was not done we are not called upon to believe that the clairvoyant read through
the envelopes.
HUMAN PHYSIOLOGY.
Offices of the cerebrum and cerebellum.
manifestations are made. But it is only a certain part of the
brain, the cerebrum, a, Fig. 72, that has this special connection
with the mind. The cerebellum, 6, Fig. 72, it is supposed, is
especially devoted to the motions of the body, for it is found in
animals that it is developed in proportion to the range and va
riety of motion. From extended observations on this point in
comparative anatomy there seems to be good reason to conclude,
that the cerebellum is the great central apparatus for combining
the various compound motions of the body. It is uniformly
found to be larger in those animals that have great complica-
tion in their muscular movements, than in those in which these
movements are of a simple character. Thus, in animals whose
most complicated motion is walking, as the hoofed quadrupeds,
the cerebellum is much smaller, than in those animals that climb
and that take hold of things with their paws. In man it is
much larger than in any other animal, for he walks erect, and
thus brings into action a very large number of muscles in this
delicate balancing movement (for such it is), and then, in the
individual parts of the body, especially the hand, he executes a
great range of very complicated movements. It is more devel-
oped in monkeys and apes than in any other of the inferior
animals, because, with their capability of extensive variety of
posture, and their power of seizing objects with their extremi-
ties, they obviously come nearer to man than any other animal
in the varied combination of their muscular action.
500. The conclusions, thus arrived at by comparative obser-
vations in animals have been confirmed by experiments. It has
been found by physiologists, that if the cerebellum be removed
in an animal, with as little disturbance as possible to other parts,
although the sensibilities remain, and motions are performed,
the power of combining muscular actions in definite compound
movements, such as flying, walking, <fec., is lost.
501. These conclusions have also been to some extent con-
firmed by observation of the phenomena of disease. The testi-
mony from this source, however, has not as yet been very decided
for two reasons. First, because disease in the brain is not apt
to be confined to one portion of the organ. And secondly and
chiefly, because we have not had a sufficient number of observa-
tions of cases on this point. It has been observed, however, in
some interesting cases of chronic disease in the cerebellum, that
deficiency in the performance of the compound movements of
the body was a prominent symptom. An unsteadiness of gait
was remarked in these cases. The negative testimony which
N OF THE MIND AND THE BODY. 333
Gray part of the cerebrum proportioned to the intelligence.
disease gives us in regard to the office of the cerebellum is very
conclusive. The mental phenomena of disease, when it is fast-
ened upon this particular portion of the brain, show that this is
not that part of the organ where the thinking is done.
502. It is chiefly, as you see, by observing the different de-
velopments of the nervous system in various animals, in con-
nection with the different functions performed by this system,
that we can discover the uses of its different parts. In pursuing
observations of the animal kingdom in this way, we find a more
and more complicated nervous apparatus, as we proceed from
the lower animals up to man. We find part after part added,
and with every addition of a part we find new functions. And
as we study any particular part in relation to the functions
which appear as connected with it, we see that these functions
are prominent in proportion to the amount of the development
of the part. Thus, as before stated, we find the size of the
cerebellum is in proportion to the variety and complication of
motion in the animal, while that of the cerebrum is in propor
tion to the amount of intelligence. And in relation to the
cerebrum itself we find that the amount of intelligence depends
on the amount of its gray portion, the vesicular substance. In
man, therefore, this part of the cerebrum is very much greater
than it is in any other animal. It is the difference in the amount
of the gray substance which constitutes the grand distinction
between the brain of man, and that of any of the higher orders
of animals, for in all other respects his brain differs very little
from theirs.
503. In looking at representations of the brain, as in Fig. 74,
it would seem at first view that the gray substance, the working
part of the cerebrum, is much less in amount than the white
portion, which serves only for transmission. But this is not so.
The eye is deceived, because the white substance is all together
in one central mass, while the gray substance is spread out in
an external layer. This is very plainly illustrated by Fig. 184.
Here the area, a, contained in the inner circle, strikes the eye as
being larger than the area, 6, included between the two circles,
and yet these areas are precisely equal.
504. Observe for a moment in this connection the concurrent
evidence, by which we determine what the function of the gray
substance of the brain is. It comes from two sources. The
first is that which is furnished to us by the structure of the cere-
brum. As stated in 206 and 232, the gray portion is
made up of cells, while the white portion is composed of tubuli.
334
HUMAN PHYSIOLOGY.
Quantity of the gray substance. Phrenology considered.
FIG. 184.
These tubuli are such as we find in the nerves, and in fact are
continuous with them. We very properly infer, therefore, that
as the nerves serve only for transmission, the white part of the
brain does the same. Is has, therefore, nothing to do with the
thinking, and yet this we know from other facts, ( 477 and
499,) is done in some part of the cerebrum. So we infer
necessarily that it must be done in the gray substance. And
here, to confirm the truth of this inference, comes in one other
source of evidence, viz., the comparison between different ani-
mals in regard to the correspondence between the amount of
the gray substance and the amount of intelligence. This I re-
marked upon in 502, and need not dwell upon it farther.
505. This dependence of the mental faculties upon the gray
substance, the outer part of the brain, seems to give some coun-
tenance to the doctrine of phrenology. But there is no evidence
from an examination of this substance that it is arranged at all
in separate organs, as instruments or seats of different faculties.
And all the facts which have been collected in regard to the
external conformation, as indicating the comparative prominence
of different organs with their faculties, go to show, when properly
examined, that the mapping out of the brain which phrenology
does so definitely is altogether a fiction. The question in re-
gard to this is wholly a question of evidence. For although
we can see no division of the cortical substance into organs, yet
CONNECTION OF THE MIND AND THE BODY. 335
Observations opposed to phrenology.
if the pretensions of phrenology in regard to the results of the
external examination of heads are well founded, we must ac-
knowledge such divisions to exist, though even the microscope
cannot reveal to us their boundaries.
506. It would lead me into too long a discussion to examine
fully the evidence in regard to these pretensions of phrenology.
Besides stating the general fact, that the failures in describing
mental and moral character from external examinations of the
head are such, when the examination is conducted fairly, as to
exhibit the falsity of these pretensions, I will only allude to one
or two particular facts, and dismiss the subject. In the phre-
nological map of the cranium there are located some half a
dozen organs along in the region of the eyebrows. Now, you
will remember that the frontal sinus extends along in this lo-
cality. This sinus varies very much in size in different individ-
uals. It is obvious, therefore, that an external examination
can give us no accurate idea of the quantity of brain in that
locality. Take another point. Phrenologists have always in-
sisted that there was the most positive evidence, from examina-
tions of the head in man and in animals, that certain faculties
or propensities have their organs in the locality where the
cerebellum lies. But all this mass of vaunted evidence is swept
away by the discovery stated in 499, that the cerebellum is
chiefly concerned in effecting the compound motions of the body.
I might go on to examine in this way the rest of the evidence
adduced in favor of the truth of phrenology, and show that
there is no satisfactory evidence of the correct localization of any
one of the organs paraded with such definiteness on the cranial
map of this so called science. But it would occupy too much
space.
507. The only fact which seems to give any countenance to
phrenology is that general fact, which is matter of common ob-
servation, that the front and upper portion of the brain that
which occupies the forehead is commonly developed in pro-
portion to the development of the intellect. This would seem
to show that the intellectual faculties have their seat in this
part of the brain. But it is far from proving this to be so.
For it may be, that a general enlargement of the cerebrum is
for some reason accommodated by having the forehead enlarged,
in preference to other portions of the cranium. For it is evident
that a brain which is larger alike in all its parts than usual,
can, as it is a soft yielding organ, be equally well accommodated,
whether the cranium be made of unusual size in only one direo-
336 HUMAN PHYSIOLOGY.
Size of the front part of the brain. Facial angle.
tion, or in all directions. The fact that in the child the forehead
is more prominent than in the adult, is inconsistent with the
supposition that the intellect has its seat especially in the front
part of the brain, for the child has more of the instinctive and
less of the intellectual than the adult. I may remark in this
connection, that the phenomena presented by injuries and by
disease in this part of the cerebrum, have not, as thus far ob-
served, seemed to show that it is the peculiar seat of the intel-
lectual faculties.
508. The size of the anterior portion of the brain, above re-
ferred to, may be estimated by the measurement of the facial
angle, so termed, proposed by Camper, a Dutch naturalist.
This angle is formed by drawing two lines as represented in
Figures 185 and 186. " The line, a, 6, is drawn from the most
FIG. 185.
prominent part of the forehead to the front of the upper jaw.
The line, c, rf, is intended to represent the line of the base of the
brain, and runs from the orifice of the ear along on the floor of
the cavity of the nose. It is manifest that the less prominent
is the forehead, that is, the less brain there is in the front part
of the head, the more acute will the angle be that is formed by
these lines. In Fig 186, which represents the skull of a negro,
this angle is more acute than in the skull of the European, Fig.
185. In animals this facial angle is much more acute than in
man. In the monkey tribe it varies from 65 to 30, while in
man its average is about 75. The ancient Greeks, wishing to
give the aspect of great intellectual superiority to their statues
of deities and heroes, made it in them as high as 90.
509. It is proper to remark here, that while it is clear that,
as a general rule, the amount of intelligence is to some extent
proportioned to the amount of the cerebrum, both in man and
in animals, the rule is not an invariable one. Size is far from
CONNECTION OF THE MIND AND THE BODY. 337
Mental difference between man and animals. Little difference in the brain.
being the only measure of power in this case. What differ-
ences there may be in intimate structure, to compare with the
mental differences, we know not. Even where the rule stated
above holds good, the difference in mere bulk is far from being
proportionate to the mental difference. The mind of a Newton
or a Shakspeare is gigantic compared with any common mind,
but the brain in such cases is not very much larger than ordi-
nary brains.
510. In relation to the evidence drawn from a comparison
between different animals, in regard to the functions of the
nervous system, there is one significant fact which must not pass
unnoticed. Though, as we rise in the scale of animal life in
our observations, we find every new addition of functions coupled
with some new additions of structure, until we come to the
higher animals, we do not find this to be so when we pass from
them to man. The brain, it is true, is larger in man than it is
in them, and has much more of the gray substance ; but there
are no essential differences of structure in his brain, to corres-
pond with the added mental qualities which so decidedly dis-
tinguish him from the brutes. These qualities constitute some-
thing more than a difference of degree. It is a difference of
kind. And, therefore, it is a great and a significant fact, that
there is no corresponding difference of kind in the organization
of the brain.
511. The qualities to which I refer I have alluded to in the first
part of this book ( 40). They are possessed by every hu-
man being to some extent, however debased he may be;
and, on the other hand, they are never possessed by any of the
inferior animals, however high their mental manifestations may
be, and however much they may be improved by training.
Though there be so wide a distance between such minds as
Newton, and Milton, and Shakspeare, and the lowest representa-
tive of our race, yet in him are contained the elements of the
excellence to which they arrived. But no one dare assert thi
to be true of the very wisest of the inferior animals.
512. The distinction between man and animals is a definite
one. It is as definite as it would be if it were based upon differ-
ence of organization. The barrier is fixed ; and not a step over
it has any animal advanced, with all the training which may
have been expended upon him. No animal, however intimate
has his intercourse been with man, has ever acquired man's
habit of abstract reasoning, or manifested any real knowledge
of the difference between right and wrong. Prof. Guyot does
29
338 HUMAN PHYSIOLOGY.
Intimate connection of the mind and the body.
not speak too strongly when he says, "I will even go farther
than is ordinarily done, and I will say, that there is an impassa-
ble chasm between the mineral and the plant, between the plant
and the animal ; an impassable chasm between the animal and
man" Surely if the impassable chasm between minerals and
vegetables, and that between vegetables and animals, are worthy
of note when we take a comprehensive view of the material
world, so also is that which is much more manifest as existing
between animals and man. When, therefore, the comparative
physiologist, in his examination of mental manifestations in con-
nection with physical developments finds, as he comes to man,
that in him are peculiar and distinctive mental manifestations
with no corresponding physical developments, he should deem
it to be an important fact in science, which should not be slurred
over, or passed unnoticed, as is often the case. I shall allude
to certain bearings of this fact in another part of this chapter.
513. In looking at the facts presented in this chapter and
in that upon the Nervous System, you must have been contin-
ually struck with the intimacy of the union between the mind
and the body. On this subject I thus remark in another work.
" There are various figures used to illustrate this connection.
The most common one is that in which the mind is spoken of
as dwelling in the body as a habitation. In a certain sense
this is true. This tabernacle of flesh, as the Bible aptly terms
it, is in its present state a habitation, which the mind is to leave
in a short time, to return to it, however, at length, rebuilt and
refitted in a more glorious, an incorruptible form, to dwell in it
then forever. But this illustration of the mysterious connec-
tion of the mind with the body is but a partial one it does
not express the extent nor the intimacy of that connection.
The mind is not a mere dweller put into this habitation. Its
union with it is not thus loose and easily severed. It is bound
to its every nerve and fibre, so that the least touch of the body
at any point affects the mind. Instead of being put into the
body, it has, being thus interlaced, as we may say, fibre with
fibre, grown with its growth and strengthened with its strength.
In the feebleness of infancy the mind is just as feeble as the
body, and they both grow together up to the vigor and firmness
of manhood, and both decline together in old age. So close is
their union through all the stages of life, and so equally is each
affected by the joys and sufferings of the other, that we might
justly conclude that at death, when the tabernacle crumbles
into dust, the mind falls with it never to rise again, had not a
CONNECTION OF THE MIND AND THE BODY, 339
Sources of evidence in regard to the nature of the connection.
divine revelation told us that, indissoluble as this connection
appears during life. Almighty power will dissever it, and release
the soul from the thousand ties that bind it to its habitation, at
the very moment of its destruction. Were it not for this assur-
ance of our immortality, we could look forward in the uncertain
future to nothing but blank, drear annihilation, as awaiting our
minds, just as it does the minds of the brutes that perish.
514. In our carefulness to avoid materialism, we are too apt
to look upon the mind and the body as two separate and inde-
pendent things. At death they do indeed become so, but who
of us knows that they would, were it not for the fiat of the Al-
mighty ? Who knows that there is not a necessity for the
putting forth of his power in each individual case at the time
of death, to prevent the mind of man from dying with his body,
just as the mind of the brute does with his? The very preva-
lent notion that the mind is essentially indestructible, and that
it is put into the body as a separate thing, having the power
of itself to leave the body whenever it dies, rests on no sub-
stantial proof. That it is destined thus to leave the body is
quite another thing."*
515. The nature of the connection of the mind and the body
is a great mystery. Still, there are many things which we can
know in relation to it. The sources of our knowledge on this
subject are three, viz., the investigations of Physiology, the tes
timony of Consciousness, and that of Revelation. Each of
these kinds of evidence throws light upon the others. If,
therefore, we use all of them, giving to each its due limits and
force, we shall come to some certain and valuable conclusions.
But if we take any one of them alone, we shall be liable to be
led into gross error.
516. There is in some physiologists a disposition to rely upon
physiology alone, to the exclusion of the other sources of evi-
dence, in the investigation of this subject. In doing this they
are driven to this alternative. Either they must be content
with a very limited knowledge of the subject, or they must rely
upon mere presumptive evidence for many of their conclusions.
And commonly the latter is the course which they pursue.
They are not content with the very limited conclusions to which
they are shut up by the absolute proof furnished by physiology,
They boldly reason, therefore, upon what they deem to be
'"Physician and Patient," from the Chapter entitled " The Mutual Influence oJ
the Mind ami Body in Disease."
340 HUMAN PHYSIOLOGY.
Endowments of matter. Is intelligence one of them?
probable. And they are invariably led into error. This I pro-
pose now to show.
517. In order to get definite ideas of the manner in which
the erroneous conclusions are arrived at, let us view matter in
its various states and connections. Unorganized dead matter
you see to be entirely different in some important respects from
living organized matter. The distinction is a definite one. It
is easily recognized, and none but dreamers in science have
failed to see it. Though Robinet and others of his class have
sought to obliterate it, in carrying out their fanciful notions,
( 48,) and though some have supposed that there was a latent
life in all unorganized matter, ready to be called into action on
the application of the appropriate excitants, it is considered by
all rational observers as a settled point, that there is an essential
distinction between common dead matter and living matter.
The latter is endowed with certain properties that the former
has not. They are termed vital properties. They control to a
certain extent the mechanical and chemical properties which
both forms of matter have in common. Some suppose that
what we call life is a single principle ; but others suppose the
endowment to be compound, made up of different principles or
properties. But this question we need not discuss. All that
concerns the view I am presenting .is the mere fact of the en-
dowment.
518. Let us go a step farther. Some living beings have more
endowments than others. All have those of organic life in
common ( 32). But there is an animal life also, which by
means of the nervous system is superadded to the organic.
And, as we trace the animal kingdom from the lowest animal
up to man, we find the endowments connected with this system
multiplied as we advance, till in him they are more complicated
and extensive than in any other animal. This is especially true
of intellectual endowments, those which are merely instinctive
being more developed in many, perhaps we may say most, of
the inferior animals. And in man we find special mental
endowments, of which other animals present not the faintest
trace.
519. Now the question arises, whether intelligence is like
life, a mere endowment of matter, or whether it is in some
measure independent of it. In other words, whether it is a
principle or set of principles with which matter is endowed, or
an immaterial something which acts through matter as its in-
strument. How much does bare physiology teach us on this
CONNECTION" OF THE MIND AND THE BODY.
Reliance on evidence from physiology alone leads to materialism.
question ? It has often been claimed that it can teach us much,
and the most bold conclusions have sometimes been ventured
from this quarter. But mere speculation has in all such cases
been deemed to be proof. Physiology does show us, as I have
before said, that the spiritual is in this world always connected
with the material, and that mind never acts independently of
the matter with which it is connected in the brain. But it
gives us no light upon the nature of this connection. It is
well for us to know how deficient are its teachings on this point.
For all that it can teach us, we know not but that the mind
may be a mere result of action in matter. It neither tells us
that it is so, or that it is not. It leaves us entirely in the dark
on this point. Indeed so far as it affords presumptive evidence,
it appears to teach, that mental phenomena are results of mat-
ter, acting in consequence of certain endowments or tendencies
imparted to it, just as secretion is in living substances, or chem-
ical action in those which are not living. Accordingly those
who have relied upon physiology alone on this subject, have
adopted various forms of materialism. Some have supposed
that thought is a mere product of matter, and that the brain
secretes it as the liver secretes bile. Others have taught that
the mind is " a bundle of instincts," each residing in some par-
ticular part of the brain as its organ. This has been the doc-
trine of some prominent phrenologists.
520. Let us look at living matter in another point of view,
and see to what physiology alone, if at all venturesome in draw-
ing conclusions, will lead us. Let us look at the origin and
growth of the thinking animal. Take, for example, an animal
the formation of which we traced in the Chapter on Cell-Life,
210. The beginning of the bird as it forms in the egg is a
simple cell filled with a fluid. This produces other cells, and
soon the organs and the limbs of the animal are formed. At
length the animal bursts the shell, and comes out not only a
living and sentient being, but a thinking being. It has a mind
which feels desires and emotions, and prompts the muscles to
action to effect its purposes. Organization here precedes the
development of mind so far as we can see, and therefore it would
seem that mind is a result of organization. Especially does
this appear to be so, when we find that the amount of mind in
different animals is proportioned to the amount of a certain part
of the organization, the brain. All this is as true of man as it
is of other animals. And besides, we see in man that as the
organization becomes perfected, the intelligence is proportiona-
29*
34:2 HUMAN PHYSIOLOGY.
Action of formative vessels like instinct, and even intelligence.
bly increased. In infancy, when the organization of the brain
is imperfect, the intelligence is small in amount, and grows with
the growth, and strengthens with the strength of the brain.
And as the mind thus grows with the body, it appears to perish
with the dissolution of the organization, and in the case of the
inferior animals undoubtedly does so.
521. But it may be said, that the physiologist observes that
the mind designs, and devises means to carry out its designs, and
this shows that there is an immaterial principle that moves the
machinery of the material organization. This is a plausible
view of the subject, but it is only plausible. Physiology alone
cannot prove it to be a correct view. For, if we limit ourselves
to her teachings alone, it can be made to appear by the same
line of argument, that mind is at work in all the phenomena
that we see in living beings. In the formation of any part, as
you saw in 163, in the Chapter on Formation and Repair,
the formative vessels work after a fixed plan, and cooperate to-
gether to accomplish the object. They seem to act intelligently,
as if they had a mind by which they designed, and devised
means for carrying out their designs. And the formative and
other vessels thus act together, proportioning means accurately
to ends, not only under fixed and regular circumstances, but they
do so under varying circumstances, to meet exigencies. Thus,
when an artery supplying a limb is tied, 169, the formative ves-
sels enlarge the arteries in the neighborhood, in order that the
blood may be supplied to the limb in suitable quantity. That is,
they construct after a larger pattern to meet the new want, just
as if they were informed of it and acted accordingly. Take
another example afforded by the formation and discharge of an
abscess, as described in 170. In this case, as the abscess
forms, various operations are going on, with different sets of
vessels cooperating together to effect a common purpose. And
when the abscess has made its way to the surface, and dis-
charged itself at an outlet, a change comes over the operations,
in order to restore the part to its usual state. The different
vessels accommodate themselves to this change, as if they were
intelligent workmen, acting in conformity to a design or plan
of their own, upon which they had agreed. Other examples
might be cited, both from vegetable and animal life, all showing
design and cooperation in effecting purposes.
522. In such phenomena we see a striking analogy to those
of instinct, and even to those of intelligence also. It is this
analogy which has led some in their speculations to adopt the
CONNECTION OF THE MIND AND THE BODY. 343
Conflicting evidence of Physiology.
idea that life and soul are the same thing. Hence, too, many
phenomena in vegetable life are in common language often
called instinctive. Thus, it is said, that when a seed sprouts,
the roots instinctively seek the ground, and the stalk and branches
instinctively seek the air and the light. This is even the case
sometimes when the seed is placed at some little distance from
the ground. So, too, if a plant that naturally grows in wet
ground is put into dry soil, but in the neighborhood of a wet
spot, it shoots forth roots abundantly towards this spot, rather
than on the other side.
523. But the evidence from physiology does not all tend to
materialism. There is some negative evidence which has a
different bearing. I refer to the fact stated in 510, viz., that,
while man differs in his spiritual nature so widely and so spe-
cifically from the inferior animals, his brain exhibits no corres-
ponding specific difference in structure, but only a difference in
amount. The difference in degrees of intelligence in the animals
below man is marked by a corresponding difference in the
amounts of the gray substance. And if it were true that man,
as some think, differed from them only in having a higher de-
gree of intelligence, we should expect to find in him a mere
increase cf this substance. But as his mind differs from theirs
not merely in degree, but in kind also, we should have reason
to expect, if mind were wholly dependent on organization, that
the anatomist would find not only an increase in the quantity
of the gray substance, but also a difference in its structure.
524. But strong as this evidence is, it appears to be strongly
rebutted, perhaps almost overborne, by the other evidence which
I have cited from physiology. And the physiologist might
perhaps say that, although as yet no difference of structure has
been found that corresponds with the mental difference, future
investigations with the microscope may discover some subtle
difference of structure which now escapes our notice. But this
it must be allowed is not at all probable. On the whole it may
be remarked, that the fact of which I have been speaking, although
significant and valuable as being coincident with evidence drawn
from the other sources, yet considered simply in connection with
the physiological evidence, the evidence from the other sources
being wholly shut out, it is doubtful how much weight it ought
to have. The physiological evidence, taken by itself is con-
flicting, and looking at the whole scope of it, the preponderance
must be acknowledged to be towards materialism.
525. It is quite clear then, that the physiologist cannot well
344 HUMAN PHYSIOLOGY.
Physiologist needs other evidence. Consciousness.
avoid materialism, if, in examining the connection between the
mind and the body, he rejects all evidence beside that which
physiology furnishes. He can be saved from this result only by
being content with the narrow limits, to which he is shut up, if
he confine himself to absolute proof. As we have already seen,
the positive knowledge that physiology gives us on this subject
is exceedingly narrow. We soon come to the line that divides
between the known and the supposed. And if we attempt to
go beyond that, our conclusions as to what is probable will
quite certainly lead us to the result which I have pointed out.
The need, therefore, of the evidence drawn from the other
sources that I have mentioned is most palpable. The physiol-
ogist must confess himself to be under the necessity of going
out of his physiology, in order to learn all that can be learned
upon this subject. At the best, there is much mystery in rela-
tion to it which we cannot penetrate, with all the light that we
can bring to bear upon it. And the mystery is deep indeed,
when we call to our aid only the dim light of physiology. It
needs some other light to deliver us from the confusion of ideas,
into which we are introduced by the analogy existing between
the phenomena of life and instinct and intelligence, in relation
to their connection with the organization of matter. Let us
look then at the evidence which comes from the other two
sources, viz., our consciousness, and revelation.
526. Every individual is conscious that, as he feels and thinks
and acts, he, that is his mind or spirit, acts upon the structure
of his body, and is acted upon by it. It is not a consciousness
that he as a material body does all this. He feels that it is a
power within that does it, and he instinctively separates in his
ideas the power from the different parts of the body, and from
the body as a whole. He is conscious too of a responsibility in
relation to the thoughts and acts of the spirit within. He has
a knowledge of right and wrong, and has self-reproach on doing
wrong, and self-approbation on doing right. It is this conscious-
ness of a self-acting immaterial spirit in this material body, that
constitutes the basis of all character, and of all the moral rela-
tions of man to his fellow man, and to his Maker. Every body
acts upon the testimony of this consciousness as being valid and
certain testimony. And, however the physiologist may reason
about matter and mind, as if the latter were a mere product or
endowment of the former, yet as a man, as a member of society,
as a subject of government and law, he cannot avoid acting
upon the ground, that mind in a certain sense controls matter,
CONNECTION" OF THE MIND AND THE BODY.
Evidence from consciousness confirmed by Revelation.
and is responsible for its acts independently of the matter with
which it is connected.
527. Now the evidence which this consciousness affords us
should suffice to keep us from the materialism, into which phys-
iology taken alone would be apt to lead us. It shows us that,
although the mind is developed with the material organization,
and can act only with it, it is not its mere product, nor one of
its endowments. It shows us, on the other hand, that it is in
some measure independent of matter, and that its dependence
upon it is only a dependence of connection, matter being the
instrument of mind, through which it acts on external things^
and is acted upon by them. The evidence from this source is
of a positive character. We are driven by it to the alternative,
of believing that the mind is an immaterial, self-acting agent,
in some measure independent of matter, or of harboring the
impious and monstrous belief, that the Creator has implanted
in the bosom of man a lie, and that he is living a horrible farce,
acting in view of moral relations and responsibilities that have
no existence.
528. This positive testimony of our consciousness is confirmed
by the testimony of revelation. This is not done by any formal
array of proof. The existence of the spiritual part of man as
a self-acting responsible agent is assumed as a fact that needs
no proof. All the statements, and teachings, and appeals of the
Bible recognize it as a fact known to the consciousness of every
man. The Bible, therefore, may be considered as simply affirm-
ing that the testimony of our consciousness on this point is
valid testimony. But the Bible goes farther than this. It
gives us one great fact of which neither physiology nor our con-
sciousness could assure us. I refer to the mind's immortality.
Our consciousness could, it is true, give us presumptive evidence
to show that the soul with its high powers and aspirations is to
live after the death of the body. But it could furnish us no
absolute proof of the fact. And its presumptive evidence would
be effectually rebutted by the presumptive evidence from physi-
ology, which, as you have seen, points in another direction.
We are so familiar with the mind's immortality as a known fact,
and we so uniformly think of it in connection with the death
of the body, that we are not aware how absolutely dependent
we are upon revelation for all that we know in relation to it.
If there were no revelation, and death were to us an unknown
event, and we were now for the first time called upon to witness
the death of a friend, how little should we know, and how con-
346 HUMAN PHYSIOLOGY.
Immortality revealed only by revelation.
fused would be our thoughts in relation to the great mystery
before us! "What is it?" we should ask. "Is it sleep?"
No. We never saw any one sleep thus. What is it ? Who
can tell us ? " And we should wonderingly watch to see some
signs of awakening, not giving up all hope till decay begins its
ravages on the loved form before us. Then, as we should from
the dictate of nature, consign to the earth the friend who was
so recently among us a breathing, moving, speaking man, now
a mere mass of decaying matter, we should feel that we bury
there not the body only, but all that belonged to that body
during life the whole man. Thought and feeling, as well aa
life and motion, would appear to us, untaught of God, to be
extinguished in the grave. Even if some one should utter all
tremblingly the hope, that there might be a subtle spiritual
part of our friend, that would some time in some form return
again to our society, that hope would at once be crushed by
the reflection that whatever it was in our friend that thought
and felt, it came into existence with the body, was infantile
when the body was, grew with the growth of the body, and
strengthened with its strength, and therefore now, so far as we
can see, has perished with it. Nature utters no voice to tell us
otherwise. She emits no light to illumine the grave. Dark-
ness and silence rest there, till the light of revelation shines
upon it, and God proclaims man's immortality.
529. I have thus spoken of the three sources of evidence in
regard to the connection of the mind and the body, and have
indicated the character of the evidence furnished by each. I
have shown particularly that if the attention be confined to that
which is furnished by physiology, the mind is apt to be led into
materialism. But the attention should not thus be confined.
All the three kinds of evidence should be employed and should
be brought to bear upon each other. If this be done, the dis-
crepancies in the evidence from physiology are cleared up by
the evidence afforded by consciousness and revelation, and we
see the true value and bearing of the fact, that the specific men-
tal difference between man and animals is not attended with a
corresponding structural difference. Though this fact operates
merely as conflicting evidence, when taken simply in connection
with the rest of the facts developed by physiology ; when, we
come on the other hand, to take the whole range of evidence
from the three sources spoken of, it is exceedingly satisfactory as
concurring with the testimony of consciousness and revelation.
At the same time, those physiological phenomena, which taken
MAN AND THE INFERIOR ANIMALS. 347
Evidence from consciousness and Revelation positive.
by themselves seem to show so strongly that the mind is wholly
dependent upon organization, are so interpreted by the evidence
from the other sources, that the dependence is seen to be for
the most part a dependence of connection only, the brain being
the instrument of the mind.
530. The evidence from consciousness and revelation is of the
most positive character, and cannot be set aside by evidence
from any other source. Other evidence may serve to interpret
it, but cannot nullify it. The attempt is sometimes made to set
it aside by urging the presumptive evidence of physiology, as
if it were absolute proof. But most physiologists engage in no
such futile and unchristian efforts, but give due weight to the
testimony of consciousness and revelation in all their investiga-
tions of the mysterious connection of the mind and the body.
The influence of Carpenter, an English physiologist, whose works
are more extensively used by students than those of any other
physiologist, is especially to be commended in this respect. And
although skepticism occasionally utters its plausible falsities, de-
ceiving the superficial and the speculative, we have no fears
from present indications that the votaries of physiological science
will, as a body, be arrayed in opposition to Christianity.
CHAPTER XVIII.
DIFFERENCES BETWEEN MAN AND THE INFERIOR ANIMALS.
531. I HAVE already treated somewhat of the differences be-
tween man and the interior animals in different parts of this
book, and especially in the preceding chapter. But it has been
done only incidentally, and the subject demands at our hands a
more thorough and systematic investigation. This I propose to
do in the present chapter.
532. Lord Monboddo maintained that man is only an im-
provement on the monkey, occurring as a result from the general
tendency to advancement claimed to exist in nature. He seemed
to think that man bore a relation to the monkey somewhat like
348 HUMAN PHYSIOLOGY.
Lord Monboddo. Nature of instinct a mystery.
that which the frog bears to the tadpole, as described in 167,
and that as the tadpole becomes the frog, so the race of man
was produced by a change at some remote period of the crea-
tion, of the monkey into a man. This ridiculous notion of the
erudite but fanciful Scotch philosopher is really but another
phase of the more recent theory of gradation, or development,
as it is sometimes called, which in different forms is now advo-
cated by so many European philosophers. And, although few,
comparatively, adopt this theory definitely and fully, there is
quite a disposition among many to obliterate the distinctions by
which the Creator has in so marked a manner separated man
from the inferior animals. It is well, therefore, that we should
have a clear idea of these distinctions.
533. It is often very loosely said that while man is governed
by reason, instinct rules in the animal.* If it be meant by this
that, as a general rule, reason predominates in man, while in-
stinct does so in animals, the statement is a correct one. But
if it be meant that animals are wholly governed by instinct, and
that man is distinguished from them as a reasoning animal, it
is not correct. For some animals do reason, that is, if making
inferences be considered as reasoning. In tracing out the differ-
ences between man and animals I shall not attempt to show
what the nature of instinct is. This is a great mystery, and all
attempts to solve it have utterly failed. I shall content myself,
therefore, with pointing out some of the differences between in
stinct and reason. In doing this it is not always easy to say
just where the one begins and the other ends, so intimately are
their phenomena often mingled together.
534. The actions of instinct are more unaccountable than
those of reason. In the operations of reason we see something
of the processes by which results are reached. But it is not
so with instinct. For example, as a man travels over an unex-
plored country, we can understand by what means he obtains a
knowledge of the country, in order to guide him on his journey.
The processes of his reasoning in regard to this we can com-
prehend. But when an insect travels with unerring certainty
to its place of destination without any guide marks that we can
* Some explanation may be well here in relation to tbe different uses made of the word
animal in different connections. Here it is used in contra distinction to man. So it is
used in the expression, man and animals. But as man is in certain senses an animal,
whenever we wish to recognize this fact we speak of other animals as the inferior oni-
mals. And thus in regard to animals, we speak of their higher and lower orders, the
higher of course being those that approximate nearest to man.
MAN AND THE INFERIOR ANIMALS. 349
Instinct governed by invariable rules. Mysterious in its operations.
see,* or when a swarm of bees or a flock of birds wing their flight
to distant places, or when bees construct their honey-comb with
the exactness of mathematics in obedience to the best principles
for such a structure, we cannot understand the processes which
lead to the result. It seems to be produced by an impulse from
a cause extraneous to the animal, guiding it as if it were a mere
machine. The little intelligence of the animal seems to have
only an incidental connection with this impulse. It, therefore,
merely controls somewhat the circumstances under which the
instinct acts.
535. So little has the intelligence to do with the instinct, and
so nearly mechanical therefore are the actions of the latter, that
they are governed by an invariable rule. It is as invariable
almost as are the movements of a machine. For this reason
there are no improvements or alterations in the acts of instinct.
The bird and the bee, for instance, have no change of fashion
in their architecture from age to age. The honey that fed
John the Baptist, or that which was found by Samson in the
carcase of the lion, was deposited in the same hexagonal cells
* I will introduce here as an illustration, a little incident recorded in my note book
many years ago. The account of it runs thus : I was much entertained to-day in watch-
ing the movements of a very small winged insect about one-third of the size of a com-
mon fly. He was dragging a dead spider across the road. Every now and then he would
drop his load, and run forward a little, springing about here and there, and then would
go back and take up his load again. His movements in this way were so quick and ap-
parently so irregular, that they seemed to be without an object. But I observed, that
although he thus ran about here and there, his course in its general bearing was a very
straight one. Soon a waggon passed along directly over where the insect was, separating
him from his load, and disturbing the whole surface of the ground. He, however, soon
found his toad, and then with a good deal of apparent reconnoitering he went on again in the
same general course. In the latter part of his journey he travelled over and amidst a heap
o f stones. Here he would occasionally leave the spider and disappear, and then return
again to take his load. Again a little farther on I would see him emerge from his con-
cealed pathway, and so on to the end of his journey. His place of destination was a hole
in the sand beneath a flat stone. Now, how did this insect in his journey to his home,
(which to him was a long one, though only three rods,) manage to keep so straight a
course? Was it in the same way that men manage in their journeys, guided by way-
marks, and by information obtained from others ? Following out this idea, suppose then
a man to be at the same distance from his home in proportion to his size that the insect
was from his home. According to this supposition he must be over three thousand miles
from home. Suppose the direct line to his home lay across an uninhabited country, so
that he can get no information from others. This makes his case parallel with the in-
sect's, for we saw him meet no other insects on the road. Now, if he knew the exact
direction in which his home lay, he could not, without his compass, move with any pre-
cision towards it. And if he had wandered away from it without a compass, as the in-
sect did from his home, how would he know in what direction it lay ? And yet the insect
travelled towards his home as if he preserved exactly amid all his wanderings the points
of the compass. The surface over which he went was very irregular. He had to cross
or wind around eminences, which were to him as large as hills and mountains are to man,
and yet he was not embarrassed ; and when he went among the stones he hod more and
greater difficulties to encounter than man meets with in passing through the wildest coun-
tries. Again, suppose that the travelling man should meet with some whirlwind or some
convulsion of nature, which should separate him from his burden, and disarrange in some
measure the face of the country about him, just, as the travelling insect was served by the
commotion of the horse's feet and the wheels of the waggon. Would he find his load as
easily as the insect did, and go on his way with as little hesitation 1
850
HUMAN PHYSIOLOGY.
Contrivances in the nests of birds.
which are constructed by the bees of the present day. And
each bird builds its nest "precisely in the same way that its an-
FIG. 187.
NEST OF THE BAYA.
cestral birds have ever done. Most birds'
nests are constructed after the same general
pattern. But sometimes we observe strik-
ing peculiarities to subserve some special
purpose. Fig. 187 represents the nest of
the Baya, a little bird of Hindoostan. It
is in the shape of a bottle, and is made of
long grass. It is suspended from a slen-
der branch of a tree, so that monkeys,
serpents, &c., cannot reach it. The en-
trance to the nest is made on the under
side, so that these animals cannot enter,
while the bird itself can readily fly in. It
is divided into apartments, in one of which
the female sits upon the eggs, while in the
other the male bird " solaces his companion
with his song whilst she is occupied in ma-
ternal cares." In Fig. 188 is seen the nest
of another little eastern bird, which with
filaments of cotton taken from the cotton
plant, sews leaves together with its beak
and feet, so as to conceal th inclosed nest
from its enemies.
FIG. 188.
NEST
of th Tailor Bird.
MAN AND THE INFERIOR ANIMALS. 351
Contrivances in the honey-comb. Mathematical principles exactly applied.
536. While there is no change in the acts of instinct they
are marked by perfection. That is, they are perfectly adapted
to the purposes to be effected and to the circumstances under
which they are performed. The Creator, who directs the im-
pulse that governs the animal, in this case as well as in all
others, accurately fits the means to the ends to be accomplished.
There is nothing in which this perfection of instinct is better
shown than in the construction of the honey-comb. The cells
are made hexagonal, because in this way all the space is occu-
pied there is no waste of room. If the cells were made cir-
cular, there would not only be a waste of room, but a large
quantity of material would be needed to fill up the spaces be-
tween the cells. The difference can be seen in the two Figures
189 and 190. Each comb, it is to be observed farther, has two
FIG. 189. FIG. 190
sets of cells, the ends of one set being arranged against the ends
of the other in a peculiar manner. These ends are not flat, but
each one has three plane surfaces, forming with each other a
particular angle soon to be noticed, and uniting together at the
centre in a point. In the arrangement of these cells, therefore,
a cell of one set does not lie end to end with a cell of another
set. Its three surfaces form a part of
the bottom or end of three cells of FIG - 19L
the other set. This is made clear by
Fig. 191, in which a cell of one set is
represented as it abuts against a cell
of the other set by one of its surfaces,
its other two surfaces forming a third
part of the ends of two other cells. Now it has been found
that the angle formed at the edge of these surfaces between the
two sets of cells is such as to secure the greatest strength with
the least amount of material. It was at one time thought that
.../;--
352 HUMAN PHYSIOLOGY.
Wonderful operations of instinct in communities among animals.
this was proved to be not exactly true. The variation from the
correct angle, made out by the calculations of the mathemati-
cians, was indeed a slight one, but still it was variation enough
to show, if the calculations were correct, that the workings of
instinct were not perfect in this case. But the investigations
of Lord Brougham have satisfactorily shown that the mathe-
maticians were wrong in their calculations, and that the bees
are right.
537. The perfection of the operations of instinct is shown in
the most wonderful manner in the regulation of communities of
animals. Here we see cooperation to produce results effected
through an irrational, and therefore in some measure a blind
instinct. This social instinct is most extensively exemplified
among the insect tribes, as for instance the bee and the wasp.
The structures, resulting from the cooperation of multitudes of
little laborers guided by this instinct, are very interesting. I
shall allude to but a single familiar example, the construction
of the nests of wasps. These insects make their building ma-
terial from the fibres of old wood. These they convert by mas-
tication into a pulp, which made into a thin layer, becomes firm
like paper. It is indeed a process very much like the common
process of paper-making invented by man, and the first rude
inventor may have got his idea from the insect. With this
substance the wasps build several ranges of cells, which are
hexagonal, like the cells in the comb of the bee. These ranges
of cells are placed parallel to each other, at regular distances,
with little supporting columns between them, as seen in Fig.
192,
The number and variety of instincts of the ordinary hive bees
are very wonderful, but it would occupy too much space to de-
scribe them.
538. The wonderful cooperation of animals in obedience to
social instinct, in the building of habitations and other struc-
tures is seen in several of the mammalia. But it is most won-
derful in the beaver, the following description of whose habits
in this respect I take from Carpenter. " During the summer it
lives solitarily in burrows, which it excavates for itself on the
borders of lakes and streams ; but as the cold season approaches
it quits its retreat and unites itself with its fellows, to construct,
in common with them, a winter residence. It is only in the
most solitary places that their architectural instinct fully devel-
ops itself. Having associated in troops of from two to three
hundred each, they choose a lake or river, which is deep enough
MAN AND THE INFERIOR ANIMALS.
353
Exemplified in the beaver community.
FIG. 192.
NEST OF WASPS.
to prevent its being frozen to the bottom ; and they generally
prefer running streams, for the sake of the convenience which
these afford in the transportation of the materials of their erec-
tion. In order that the water may be kept up to a uniform
height, they begin by constructing a sloping dam ; which they
form of branches interlaced one with another, the intervals be
tween them being filled up with stones and mud, with which
materials they give a coat of rough-cast to the exterior also
When the dam passes across a running stream, they make it
convex towards the current ; by which it is caused to possess
much greater strength than if it were straight. This dam i?
usually eleven or twelve feet across at its base, and is enlarged
every year; and it frequently becomes covered with vegetation
so as to form a kind of hedge.
539. When the dam is completed, the community separate*
30*
354 HUMAN PHYSIOLOGY.
Blindness of instinct exemplified.
into a certain number of families ; and the beavers then employ
themselves in constructing huts, or in repairing those of a pre-
ceding year. These cabins are built on the margin of the water ;
they have usually an oval form, and an internal diameter of six
or seven feet. Their walls are constructed, like the dam, of
branches of trees ; and they are covered, on two of their sides,
with a coating of mud. Each has two chambers, one above the
other, separated by a floor ; the upper one serves as the habita-
tion of the beavers, and the lower one as the magazine for the
store of bark, which they lay up for their provision. These
chambers have no other opening, than one by which they pass
out into the water. It has been said that the flat oval tail of
the beavers serves them as a trowel, and is used by them in
laying on the mud of which their erections are partly composed ;
but it does not appear that they use any other implements than
their incisor teeth and fore -feet. With their strong incisors they
cut down the branches, and even the trunks of trees which may
be suitable; and by the aid of their mouths and fore-feet, they
drag these from one place to another. When they establish
themselves on the bank of a running stream, they cut down
trees above the point where they intend to construct their dwell-
ings, set them afloat, and, profiting by the current, direct them
to the required spot. It is also with their feet that they dig up
the earth they require for mortar, from the banks or from the
bottom of the water. These operations are executed with ex-
traordinary rapidity, although they are only carried on during
the night. When the neighborhood of man prevents the
beavers from multiplying to the degree necessary to form such
associations, and from possessing the tranquillity which they
require for the construction of the works just described, they
no longer build huts, but live in excavations in the banks of the
water."
540. Instinct moves straight on to its result, and it does so
blindly. It exercises no intelligence in regard to the purpose
for which the result is intended, or the circumstances which
tend to defeat this purpose. It evidently in some cases never
knows any thing of the purpose aimed at by its acts, as, for ex-
ample, when an animal makes provisions for a progeny which
it is never to see. " It is scarcely possible," says Carpenter,
"to point to any actions better fitted to give an idea of the na-
ture of instinct, than those which are performed by various
insects, when they deposit their eggs. These animals will never
behold their progeny ; and cannot acquire any notion from ex-
MAN AND THE INFERIOR ANIMALS. 355
Results of instinct mingled with those of reason.
perience, therefore, of that which their eggs will produce ; never-
theless they have the remarkable habit of placing, in the neigh-
borhood of each of these bodies, a supply of aliment fitted for
the nourishment of the larva that is to proceed from it ; and
this they do, even when they are themselves living on food of
an entirely different nature, such as would not be adapted for
the larva. They cannot be guided in such actions by any thing
like reason; for the data on which alone they could reason
correctly, are wanting to them ; so that they would be led to
conclusions altogether erroneous if they were not prompted
by an unerring instinct, to adopt the means best adapted for
the attainment of the required end."
541. The results of reason are often mingled with those of
instinct in such a way that it is difficult to distinguish them
from each other. But instinct is of itself wholly irrational.
If it were not so, it would avoid acting whenever action would
evidently be useless. But instinct has not the eyes of reason
to see when this is the case. It leads the animal blindly on ;
so that, although under all ordinary circumstances the object
is accomplished definitely and in the best manner, yet there is
no capability of making provision for extraordinary circum-
stances. Therefore, actions are occasionally performed, which
do not at all answer the purpose which the instinct is designed
to effect. Instinct, though perfect in its action under the fixed
uniform circumstances under which it is destined to act, is a
kind of blunderer when irregular circumstances arise. Instinct
is a strict routinist, while reason readily accommodates itself
to endlessly varying circumstances. In illustration of the
above characteristic of instinct, I will cite a few examples.
The hen will sit on pieces of chalk shaped like eggs, as readily
as she will on the eggs themselves. Her instinct is so blind
as to be deceived by this general resemblance. The flesh-fly
often lays its eggs in the carrion-flower, the odor of which is
so much like that of tainted meat as to deceive the insect.
An amusing illustration of the blind disregard of circum-
stances in following out the promptings of instinct is given by
a gentleman, Mr. Broderip, in an account of a beaver which
he caught when very young. As soon as it was let out of its
cage, and materials were placed in its way, it began to build
after the fashion followed by these animals when they construct
their dam in a stream of water and build their habitations in its
banks. " Even when it was only half grown," says Mr. B., " it
would drag along a large sweeping-brush, or a warming-pan,
856 HUMAN PHYSIOLOGY.
Blindness of instinct illustrated in the beaver.
grasping the handle with its teeth, so that the load came over
its shoulder ; and would endeavor to lay this with other ma-
terials, in the mode employed by the beaver when in a state
of nature. The long and large materials were taken first ;
and two of the largest were generally laid cross- wise, with one
of the ends of each touching the wall, and the other ends pro-
jecting out into the room. The area formed by the cross-
brushes and the wall, he would fill up with hand-brushes, rush-
baskets, books, boots, sticks, cloths, dried turf, or any thing port-
able. As the work grew high, he supported himself on his tail,
which propped him up admirably ; and he would often, after lay-
ing on one of his building materials, sit up over against it, ap-
pearing to consider his work, or as the country people say, 'judge
it.' This pause was sometimes followed by changing the position
of the material judged ; and sometimes it was left in its place.
After he had piled up his materials in one part of the room,
(for he generally chose the same place,) he proceeded to wall
up the space between the feet of a chest of drawers which stood
at a little distance from it, high enough on its legs to make
the bottom a roof for him ; using for this purpose dried turf
and sticks, which he laid very even, and filling up the interstices
with bits of coal, hay, cloth, or any thing he could pick up.
This last place he seemed to appropriate for his dwelling; the
former work seemed to be intended for a dam. When he had
walled up the space between the feet of the chest of drawers,
he proceeded to carry in sticks, cloths, hay, cotton, &c., and to
make a nest ; and when he had done, he would sit up under
the drawers, and comb himself with the nails of his hind feet."
I simply remark in relation to this amusing narration, that you
can see at once that if the instinct of this animal had been at
all rational, it would not have impelled him to construct a dam
and a dwelling in a common room, where they would be of
no use to him. Reason would have dictated the building of
a nest and nothing more.
542. The care which animals exercise in relation to their
progeny seems to be governed to a great extent, perhaps wholly,
by a blind instinct. All care is given up when care is no longer
needed, and with it what appears to be affection is given up
also. In animals there is no such lasting affection of the pa-
rent for the progeny as there is in man; for in them it is
merely instinctive, and not rational and moral in its character,
and it, therefore, lasts only so long as it is needed to carry out
the purposes for which this particular instinct is designed.
MAN AND THE INFEKIOR ANIMALS. 357
Difference between the intelligence of man and that of animals.
Indeed, in some cases there can be no affection in all the care
which is instinctively exercised by the parent, for it is put forth
for progeny which, as stated in 540, the animal is destined
never to see. And in those cases among animals in which the
family state exists, it is a mere temporary affair, and as soon
as the offspring is able to take care of itself it is no more to
the parent than any other animal of the same tribe is.
543. But some animals have intelligence as well as instinct.
When 'this intelligence is shown in the mere power of imita
tion it is of a low order. The parrot that learns to imitate
man in speech is nothing like as intelligent as some animals
that have no such power. Some animals have really a reason-
ing intelligence that is, they make rational inferences. Their
reasoning is sometimes, as before remarked, so mingled with
the operations of instinct, that it is difficult to distinguish them
accurately. In the case of the beaver related in 541, who
labored so faithfully in obedience to a blind instinct, there was
some exercise of reason, as, for example, when he "judged "
his work. But it is difficult to point out definitely the line
between instinct and reason in such a case. There are some
animals, however, in whom the workings of a reasoning intel-
ligence are to be seen with perfect distinctness. But their
reasoning differs from that of man. The inferences which the
reasoning animal makes are individual ; while man goes be-
yond this, and makes general inferences, and therefore dis-
covers general truths. Newton's dog, Diamond, saw apples
fall to the ground, as well as his master. And he was capable
of making some inferences in regard to them ; but they were
individual inferences. For example, if an apple-tree were
shaken, and the dog were hit by a falling apple, whenever he
saw other apples falling he would infer that he might be hit
again, and would infer also that it was best for him to get out
of harm's way. This would be the extent of his reasonings.
But his master inquired into the cause of the fall of the apple,
and by considering this and other similar phenomena, he de-
duced general principles, which govern the movements both
of the atoms, and the worlds of the universe.
544. The inferences which are formed by animals are mere
results of the association of ideas, and the process, therefore,
really hardly merits the appellation of reasoning. Thus, in
the case of Newton's dog, supposed above, the idea of the fall-
ing apples was associated in his mind with the hurt experienced
hen he was hit, and prompted the getting out of harm's way.
w
358 HUMAN PHYSIOLOGY.
Reasoning in animals mere mental association. Exemplified.
When such associations are extended and complicated, it ap-
pears at first thought as if the animal acted in view of general
truths, arrived at by the same process of reasoning that man
employs. But it is a mere extension of mental associations.
Thus, Newton's dog probably associated the idea of being hit
and hurt with other falling bodies beside apples. And so, too,
various circumstances might come to be associated with the
falling of bodies, and thus complicate the mental process which
occurred when he saw any object falling near him.
545. To show somewhat the extent to which this mental
association operates in the brute mind, I will allude to some
examples. A wren built its nest in a slate quarry, where it
was liable to great disturbance from the blastings. It soon,
however, learned to quit its nest, and fly off to a little distance,
whenever the bell rang to warn the workmen previous to a
blast. As this was noticed, the bell was sometimes rung when
there was to be no blast, for the sake of the amusement in
seeing the poor bird fly away when there was no need of alarm.
At length, however, it ceased to be deceived in this way, and
when it heard the bell ring it looked out to see if the workmen
started, and if they did then it would leave its nest. In this
case the bird merely learned to connect in its mental associa-
tions two circumstances with the blasting, instead of the one
from which it at first took the warning. The operation of
this mental association is shown in a little different manner in
the following case. Some horses in a field were supplied with
water in a trough which was occasionally filled from a pump.
As the supply was not always sufficient, one of the horses, more
sagacious than the rest, whenever he, on going to drink, found
the trough empty, pumped the water into it by taking hold of
the pump-handle with his teeth, and moving his head up and
down. The other horses seeing this, would, whenever they
came to the trough and found it empty, tease the one that
knew how to pump, by biting and kicking him, till he would
fill the trough for them. In this case the horse that did the
pumping associated in his mind the motion of the pump-handle,
as he had seen it done by his master, with the supply of water.
And while they associated this supply with his pumping, he
knew what their teasing him meant, because he associated it
with their motions about the trough, indicating so plainly that
what they wanted was water. But I will give a still stronger
case. A dog belonging to a Frenchman was observed to go
every Saturday, precisely at two o'clock, from his residence at
MAN AND THE INFERIOR ANIMALS. 359
Relation between cause and effect learned from association.
Locoyarne to Hennebon, a distance of about three quarters of
a league. It was found that he went to a butcher's, and for
the purpose of getting a feast of tripe which he could always
have at that hour on Saturday, their day of killing. It is also
related of this dog, that at family prayers he was always very
quiet, till the last paternoster was commenced, and then he
would uniformly get up and take his station near the door, in
order to make his exit immediately on its being opened. The
narrator of these facts thinks that the first fact shows, that the
dog could measure time and count the days of the week. But
this cannot be so. The dog undoubtedly associated in his
mind the time at which he could get the tripe, with something
that occurred on Saturday at that hour at his master's house,
just as he associated the concluding of family prayers with
something that occurred as the last paternoster was read, per-
haps with some peculiarity in the manner of his master when
he came to that part of the service.
546. Animals learn the relation between cause and effect by
this mental association, and act upon the experience thus
gained. This is manifest in the examples I have cited. And
it may be observed in many acts that we witness occasionally
in the higher animals. Thus, for example, as my horse was
cropping some grass, he took hold of some that was so stout,
and yet so loosely set in the ground, that he pulled it up by
the roots, and, as the dirt which was on it troubled him, he
very deliberately knocked it across the bar of a fence till he got
all the dirt out, and then went on to eat it. Here was a
knowledge of cause and effect which was derived from previous
experience through mental association. You see the same
thing when you see a cat jump up and open the latch of a
door, or a horse unbolt the stable door to get out to his pasture.
But in all such cases the knowledge of cause and effect differs
from the same knowledge in man in one important particular.
In the animal it is always an individual knowledge, that is, a
knowledge of individual facts ; while in man it is often a knowl-
edge which has relation to general truths or principles.
547. From the facts stated in the last few paragraphs it is
clear, that Carpenter is not correct in saying, that " the mind
of man differs from that of the lower animals, rather as to the
deyree in which the reasoning faculties are developed in him,
than by any thing peculiar in their kind" While there is much
in common between them in their modes of mental action, es-
pecially if man be compared with other animals in the period
360 HUMAN PHYSIOLOGY.
Abstract reasoning source of language and of a belief in a Creator.
of his infancy and childhood, there is, as you have seen, one
attribute of the human mind which is wholly peculiar to it,
and never exists in any degree in any other animal. And this
attribute, the power of abstract reasoning, or in other words,
the power of deducing general truths or laws from collections
of individual facts, constitutes the great superiority of the hu-
man mind, in distinction from the mind of the brute.
548. It is this attribute which is the source of language in
man. This can be readily seen by observing what is the na-
ture of language. It is a collection of corresponding vocal
and written signs of an arbitrary character, arranged accord-
ing to certain general rules or principles. Other animals do
have a kind of language of a very limited character. It is
the language of natural signs. It is composed of cries and
motions, which vary in different tribes of animals, so that each
tribe may be said to have its own natural language. But an-
imals never invent and agree upon any arbitrary signs, as is
done continually by mankind in the construction and exten-
sion of language. This they cannot do, because abstract rea-
soning is required for such an invention. General principles
are observed in the construction and arrangement of arbitrary
signs, and, as I have shown, brutes know nothing of principles.
549. This attribute also is the source of man's belief in a
Creator. If he had not the power of deducing general truths
from individual facts, he could neither discover the truth that
there is a first great Cause, nor appreciate or even receive it,
if it were communicated to him. Not the faintest shade of
such an idea can be communicated to any of the inferior ani-
mals, however high their mental manifestations may be, and
simply because the structure of their mind is such that they
know nothing of general principles. Carpenter speaks of the
disposition to believe in the existence of an unseen but pow-
erful Being, which is found to be universal even among the
most degraded races of mankind, as a natural tendency, which
he seems to think is implanted in the human breast by the
Creator. But it appears clear, that it is a mere natural result
of the exercise of the power that I have just spoken of.
550. Man differs from other animals also in having a con-
science, or, a knowledge between right and wrong, and a sense
of obligation in relation to it. This moral sense is supposed
by some to be a mere result of the exercise of the power of
abstract reasoning. But others suppose that the sense is im-
planted as a distinct quality or power, and that the office of the
MAN AND THE INFERIOR ANIMALS. 361
Conscience. None in animals. Summary of mental distinctions.
reasoning power in relation to it is to bring the evidence before
it for its decision. I shall not discuss this point, but will merely
remark in regard to this subject, that there is no doubt as to
the existence of such a sense in man. Some attempt to throw
doubt over it by pointing to its perversions, maintaining that it
is a mere creature of circumstances, varying almost endlessly in
different parts of the world. But it would be just as rational to
attempt to show, that there is no such thing as a sense of the
beautiful in man, by appealing to the evidences of perversions
of taste, which ignorance, bad education, and foolish and nov-
elty-loving fashion have induced.
551. In those cases in animals in which this moral sense has
been supposed to exist, it is nothing but slavish fear. It has
been said by some one that man is the god of the dog ; but it
is sacred trifling to compare the attachment of an animal to its
master and its fear of his displeasure, with the intelligent regard
of man for his Creator as a holy and benevolent being. We
ordinarily recognize the distinction between man and animals,
as to the existence of a conscience, in the language we use.
We never attach the idea of moral character to the acts of an
animal except by the force of association, and then only slightly
and loosely. We are not apt to speak of punishing a dog, for
this word implies a moral fault as the occasion of the infliction.
We whip him, sometimes, simply to associate in his mind the
smart with the act done, so as to prevent him from doing it
again, and sometimes to vent our ill feeling for the harm done
us on the poor dog that has so innocently done it. It is related
of Sir Isaac Newton that he had a favorite little dog called
Diamond, who being left in his study, overset a candle among
his papers, and thus burnt up the almost finished labors of many
years, and yet the philosopher only said, "O Diamond! Dia-
mond ! thou little knowest the mischief thou hast done." New-
ton was both a wise and a good man, and while he saw that
whipping the dog would do no good in preventing any similar
accident in future, he had no ill feeling to vent on poor Diamond,
who certainly had a better arid more rational master than most
dogs have.
552. The mental distinction between man and animals may
be thus summed up. The animal is governed by instinct, and
in the higher orders by a kind of reasoning which is based upon
mental association. Man has, in addition to instinct and this
lower order of reasoning, the power of abstract reasoning. In
the lower orders of animals probably instinct rules alone. In
31
362 HUMAN PHYSIOLOGY.
Experience gathered by animals, but not transmitted.
them there is none even of the limited, reasoning which we see
in the higher animals. They have a nervous system with cer-
tain central organs, but have really no one great central organ
that we can call the brain. As we trace the animal kingdom
upward, we soon find that a brain appears, that is, such an
organ as may be considered the chief centre of the nervous sys-
tem. And then, as we continue to trace upward in the scale,
we find that the more intelligence or reasoning there is, the
more prominent is the brain in proportion to other parts of this
system. When we come to man the brain is much larger than
in any other animal, and his intelligence is not only greater,
but it is of a different character. Not only is the amount of
his reasoning by association greater than in other animals, but
there is also superadded, as his grand distinguishing mark, the
power of abstract reasoning.
553. Instinct, you have seen, cannot be improved by educa-
tion. It always acts in the same way throughout the life of an
animal, and through the succeeding generations of the tribe. It
has no accumulated experience, either individual or traditional.
But it is otherwise with the two kinds of reasoning power.
These can be educated, and they have an experience. But here
there is a marked difference between the two kinds of reason-
ing. The lower kind of reasoning, that of mere association,
which is the only kind possessed by animals, is altogether in-
dividual, and is not at all traditional. However wise an animal
may become, there is no transmission of his wisdom to his
posterity. No animal can start from a point of knowledge
gained by his ancestor, as a vantage ground, and thus make
greater advances than his predecessors. Each animal, in ac-
quiring experience as to the relations of cause and effect, has to
begin at the beginning, and learn every thing for himself. The
higher form of reasoning, that which man alone possesses, is
absolutely essential to the transmission of experience from one
generation to another. It is necessary to the transmission even
of that experience which is gathered by the other power of
reasoning, as well as that which is gathered by itself. The
amount of improvement which can be effected where there
is only the lower kind of reasoning to act upon, is very won-
derful in the case of some of the docile animals. The dog, the
elephant, the monkey, &c., are familiar examples. By the
skillful and persevering use of mental association in the training
of animals, results can be obtained, that resemble very closely
those which come from man's power of abstract reasoning.
MAN AND THE INFERIOR ANIMALS. 363
The power of generalization the basis of improvement in man.
And in some cases the animal accumulates quite a large indi-
vidual experience. But his race is none the wiser for it. It ia
none of it transmitted to another generation.
554. We see then the basis of improvement in man. It is
not his power of making inferences merely. The brutes do
this. It is his power of making general inferences, or, in other
words, deducing general laws or principles from individual facts.
And as this power distinguishes man from the inferior animals,
so a superior degree of it ordinarily constitutes the intellectual
superiority of one man to another. This is seen very readily in
inventions and discoveries. In the case of almost every inven-
tion or discovery, the individual facts upon which it is based
were known to many others, perhaps even a long time before
the invention or discovery was made. The merit of the in-
ventor or discoverer consists in having seen the available general
truth indicated by the facts, and traced out its application to
certain objects to be attained. Thus, to take a single example,
dairymen and dairywomen in great numbers knew the fact,
that a certain disease, derived from the cow accidentally by in-
dividuals, prevented them from taking the small pox; but
Jenner was the first to see, that here was developed a ^reat
general fact, capable of universal application. And thus seeing
the wide scope of the fact, he collected the proofs of it, and de-
vised the means by which it could be made available to prevent
the ravages of one of the great scourges of the race. It was
by the generalizing power of his reasoning that he went beyond
dairymen and dairywomen, and became the discoverer.
555. It is interesting to observe that while the capabilities
of instinct are developed rapidly, sometimes almost instantane-
ously, the capabilities of the reasoning power are developed
gradually. Especially is this the case with the higher reasoning
power, that distinguishes man from the brutes. The child is
governed at the first wholly by instinct ; and then as he gathers
knowledge of the world around him through his senses, mental
association comes into play. By the exercise of the lower kind
of reasoning, which he has in common with animals, he accumu-
lates experience of the relation of cause and effect. Thus far
he is on common ground with animals, that is, those of the
higher orders, except that he adds more largely to his experience
from mental association than they do. Meanwhile the power
of abstract reasoning is gradually developed, raising him up
from the level of the brutes, and introducing him into compan-
ionship with the whole intelligent creation, even with God him-
364 HUMAK PHYSIOLOGY.
The wonderful power of abstract reasoning. Slowness of development in man.
self, whose image he bears in possessing this attribute. This
power of generalizing facts is developed earlier than is generally
supposed. It is of course feeble at first, and has a narrow
range ; but it very early shows itself sufficiently to indicate to
us clearly, that the child's mind differs essentially from that of
the brute. And when disease or original physical defect pre-
vents its development, we see the mental deficiency, and the
consequent resemblance of the child in mental character to the
inferior animals.
556. When this characteristic power of the mind of man is
fully developed, its achievements are often so wonderful, that
they give us some realization of the great truth, that man is
created in the image of God. As we witness the demonstra-
tion of such facts as Newton discovered, or the unerring calcu-
lations of an eclipse, or listen to a perfect argument as it develops
grand truths, and leads us with a majesty of thought almost
divine, straight on to mighty conclusions, we take in the full
meaning of the assertion, that "the soul is that side of our na-
ture which is in relation with the Infinite," and we see the folly
of those dreamers in science, that look upon man as making
merely the highest order in the animal kingdom. We see that
the chasm between him and other animals is truly " impassable."
We see that we are in a mental region of which the most intel-
ligent of them know nothing that though they live like us,
having the same senses, seeing the same beautiful things, and
hearing the same voices of nature, and like us have thoughts
and emotions and desires, they are shut out from an upper region
of thought and feeling in which we freely roam, and from which we
look with aspirations unknown to them to another world beyond.
557. As the mental capabilities peculiar to man are slowly
developed, so it is with his physical frame, and the powers that
belong to it. Though man at length so excels all other animals,
that they are subject to his power as their master, he is at the
first the most helpless of all animals. He is a long time "in
the nurse's arms," and for years he is unable to obtain his own
food. He does not reach the full strength of his body and
mind till he is more than twenty years of age. He is in strong
contrast with other animals in regard to this slowness of devel-
opment, they generally reaching their full capabilities in a short
time. But even among them, it is to be observed, that there is
a difference in this respect, in obedience to a general law, that
the higher the capabilities are, the slower they are in their de-
velopment.
MAN AND THE INFERIOR ANIMALS. 365
Difference between man and animals in physical endowments.
558. The differences between the physical endowments of
man, and those of the higher orders of animals, are often very
minutely described. But though strongly marked, too much
prominence is ordinarily given to them. They should be con-
sidered as subordinate altogether to the mental differences.
Thus, much is often said of the superiority of man in regard to
the possession of a hand, on which I have remarked in various
parts of this book. But why should he have such an instrument
given to him ? Simply because he has a mind which is not
only capable of directing it, but which needs such an instrument
to produce suitable results in its action on the world around.
If other animals had a hand they could not use it properly.
1 bey have instruments of a different character, of less various
capabilities, but such as are suited to their wants and powers.
The same thing can be said of other bodily endowments. They
are always suited hi range and power to the wants and mental
capabilities of the animal. As we trace out this general idea,
we find that some animals have some bodily endowments which
far excel the same in man. Thus, some have greater powers
of vision and hearing than he has, because they need them.
So, too, some have endowments of which we find no trace in
man, as, for example, the power of flying. For the same reason
most animals have special natural means of defense against the
attacks of other animals ; but man has not, because he has no
need of them, as by his ingenuity he can contrive such means as
he may require.
559. The physical endowments of man in comparison with
animals are indeed wonderful, and correspond with his spiritual
endowments, so far as gross matter can compare with subtle
immaterial mind. We have looked at these endowments in
detail in various parts of this book. Let us glance at the prin-
cipal of them collectively. As the muscles are the organs by
which all communication between man and man, and indeed
all action upon the external world is effected, it is in the endless
combinations of muscular action that man is most signally su-
perior to animals in physical endowment. This is shown, as
you have seen, in the human hand, whether it be looked at as
an instrument for work or for expression. The same thing we
see exhibited almost as strikingly in the muscles of the voice
both those which by their delicate and accurate action regulate
the vocal ligaments, and those which by their complicated action
"ive the voice all its variety of articulation, especially the latter.
ut let us look at the body as a whole. Man walks erect, a
31*
366 HUMAN PHYSIOLOGY.
Beauty of the human form. Best shown when it is in action.
significant characteristic of him as differing from animals. And
though there be grace of movement in many animals, it is not
in any case to be compared with that which we see exhibited by
the erect human form. The extreme variety of combination in
the action of the muscles in man is one cause of this superiority.
But another and the chief cause is the impress of beauty given
to graceful action by the mind. Almost all muscular action
speaks to us a language that comes from the thought and feel-
ing at work within, even when it is unintended ; and this is the
source of a large portion of the enjoyment that we receive, for
the most part unconsciously, from the graceful movements that
we witness in our fellow men. And when in a beautiful and
graceful form we come to add to the ordinary movements of the
body, which are commonly, though improperly, considered as
'' meaningless, those movements which are distinctively expressive
of thought and emotion, we are filled with admiration of the
wonderful capabilities of the human frame in graceful action.
560. The human form in repose, when in its greatest perfec-
tion, far transcends, as a combination of varied beauty, any
thing that we see in the inferior animals. But its superiority
in this respect is best seen when the intelligent and feeling
mind puts it into action. And this is especially true of those
parts which are most engaged in expression the hand with its
endlessly varied movements, but most of all the face. It is in
this noblest part of the human frame that the soul of man,
through the subtle agency of the nerves, most strikingly imprints
its immaterial qualities upon a material form, and exhibits the
highest graces of motion in the delicate and ever varying play
of the muscles. And when in the impassioned speaker, while
the muscles of the voice and articulation are executing their
exceedingly rapid and complicated movements, we see the whole
frame in its motions and attitudes brought into consonance with
the burning words and the beaming countenance, we take in
the full idea of the adaptation of the human body to the mind
that tenants it. Though the hand is commonly spoken of as
affording the best illustration of man's superiority to other ani-
mals in muscular action, it is far from being as impressive an
exhibition of it as this action of the whole frame. It is when
the mind, through the numberless nerves that connect it with
every part of the body, brings them all into its service in ex-
pression, that we get the most exalted conception of the excel-
lence of the human organization.
VARIETIES OF THE HUMAN RACE. 367
Mankind all the same species, but presenting very marked varieties.
CHAPTER XIX.
VARIETIES OP THE HUMAN RACE.
561. ALTHOUGH, as we look at men of different nations, we
find that there is a general agreement in form and organiza-
tion, there are many points in which they strikingly differ from
each other. " With those forms, proportions, and colors," says
Mr. Lawrence, " which we consider so beautiful in the fine fig-
ures of Greece, contrast the woolly hair, flat nose, thick lips, the
retreating forehead, advancing jaws, and black skin of the negro ;
or the broad square face, narrow oblique eyes, beardless chin,
coarse straight hair, and olive color of the Gal muck. Compare
the ruddy and sanguine European with the jet black African,
the red man of America, the yellow Mongolian, or the brown
South Sea Islander ; the gigantic Patagonian to the dwarfish
Laplander ; the highly civilized nations of Europe, so conspicu-
ous in arts, science, literature, in all that can strengthen and
adorn society, or exalt and dignify human nature, to a troop of
naked, shivering, and starved New Hollanders, a horde of filthy
Hottentots, or the whole of the more or less barbarous tribes,
that cover nearly the entire continent of Africa ; and although
we must refer them all to the same species, they differ so re-
markably from each other as to admit of being classed into a
certain number of great varieties ; but with regard to the pre-
cise number, naturalists have differed materially." Cuvier ad-
mitted but three varieties, the Caucasian, Negro, and Mongolian.
The more commonly received classification, however, is that of
Blumenbach, who makes five varieties, viz., the Caucasian,
Ethiopwn, Mongolian, American, and Malay.
562. The chief characteristic of the Caucasian variety is the
fine form of the head, it being nearly oval, as you view it from
the front. It is also characterized by a great range of varia-
tions of the color both of the skin and the hair. There has
been more of civilization and improvement of every kind in this
race than in any of the others. It is mentally superior to the
other races. It is called Caucasian from Mount Caucasus, from
the vicinity of which, it is supposed, it originated. Even at the
present day it is said that the characteristics of this race are
368 HUMAN PHYSIOLOGY.
Blumenbach's classification most commonly received.
most perfectly developed in the Georgians and Circassians, who
live in the neighborhood of this range of mountains, and who
are considered the handsomest people in the world.
563. The Ethiopian variety is quite in contrast with the
Caucasian. The organization has not the perfection and ele-
gance which the Caucasian presents, and it shows an approxi-
mation to the higher orders of the inferior animals. The skull
is small. The forehead is retreating, while the face below is
projecting, the cheek bones being prominent, and the nose
broad. The apparatus of the senses is thus fully developed,
while the brain is less than in the Caucasian. The hair is black,
oily, and frizzled. It is commonly said to be woolly, but it is
really not so. Dr. Carpenter says that " microscopic examina-
tion clearly demonstrates that the hair of the negro has exactly
the same structure with that of the European, and that it does
not bear any resemblance to wool save in its crispiness and its
tendency to curl." The skin is generally black ; but not so in
all the race, for the Caffirs and the Hottentots are yellow.
564. The Mongolian variety, of which the Chinese race forms
the largest family, is characterized by prominent broad cheek
bones, flat square face, small oblique eyes, straight black hair,
scanty beard, and olive skin.
565. The American variety is characterized by high cheek
bones, a narrow low forehead, features large and bold, except
the eyes, which are deeply sunken in large sockets, hair gen-
erally black, stiff and straight, and complexion varying from a
crimson brown to a deep copper.
566. The Malay variety, which occupies the Islands south
of Asia, in the Indian and Pacific oceans, has not so well marked
characteristics as the other varieties. The complexion is brown,
varying from a light tawny to almost black, the hair is black
and thick, the forehead is low and round, the nose is full and
broad, the nostrils wide, and the mouth large.
567. Other classifications have been made, in some of vhich
the human race is divided into many more varieties. Any
classification must be in a great measure arbitrary, and must
be regarded rather as a convenience, than as having the defi-
nite and invariable character which belongs to truly scientific
distinctions. In each of the five divisions of Blumenbach
there is great diversity. Thus, in the Caucasian variety, the
English, the French, the German, the Irish, &c., are quite dis-
tinct from each other. And we sometimes see very striking
characteristic marks separating single families from others. The
VAKIETIES OF THE HUMAN EACE. 369
Differences in individuals, families and nations produced by similar causes.
varieties of the race are thus almost endless, the lesser differing
only in degree from the larger.
568. The national differences are evidently produced by
causes of very much the same character with those which pro-
duce differences in individuals and families. And the question
arises whether such differences as those which Blumenbach de-
scribes as marking the races, are not produced in a similar
manner. This question has been much discussed, and there is
great difference of opinion in regard to it. The great majority
of naturalists believe in the unity of the origin of the human
race, and hold that its varieties are the results of the various
circumstances by which man has been surrounded. But some
suppose that the different varieties come from separate pairs
created by God in different localities, and hold that the history
in Genesis is a history of the origin of only one of the varieties
of the race. Those who advocate this doctrine are few in num-
ber ; but it has acquired greater currency of late, because one
of the most eminent naturalists of the present day, Professor
Agassis, has espoused it. His doctrine on this subject I will
give as briefly as possible.
569. All animals, he asserts, like plants, have particular lo-
calities, for which they are fitted, and to which they belong.
These zoological provinces, as he terms them, are of unequal
extent, some animals having a wider range than others. From
this general law of distribution, which he illustrates with many
facts, he infers that the various animals on the face of the earth
were not created in one part of the earth and distributed from
this to other parts, but were created in the provinces to which
they belong. This view of the subject forces itself upon the
mind of the naturalist, as he observes the arrangement of the
various tribes of animals on the earth's surface. And besides,
there are apparently insurmountable difficulties in the way of a
diffusion of animals over the globe by means of migration. For
example, we cannot conceive how the polar animals could have
migrated over the warmer tracts of land, which they would
have to cross according to this supposition, for it is impossible
now to keep them alive under such circumstances with the
greatest precautions. And farther, some animals of the same
species, sometimes presenting varieties and sometimes not, are
found in different localities which are so cut off from all com-
munication with each other, that it is impossible that these ani-
mals could migrate from some one locality to all the rest. " To
assume," he remarks, "that the geographical distribution of
370 HUMAN PHYSIOLOGY.
Doctrine of the multiple origin of the human race.
such animals, inhabiting zoological districts entirely disconnected
with each other, is to be ascribed to physical causes, that these
animals have been transported, and, especially, that the fishes
which live in fresh water basins have been transported from
place to place to suppose that perches, pickerels, trouts, and
so many other species found in almost every brook and every
river in the temperate zone, have been transported from one
basin into another by freshets or by water birds is to assume
very inadequate and accidental causes for general phenomena."
Not only then were different species of animals created origi-
nally in different localities, but it is also true to a considerable
extent, that animals of the same species occupying different lo-
calities were created in those localities.
570. All this he claims to be consistent with scripture, and
with very good reason. The account of the preservation of an-
imals in the ark, interpreted according to the common license
of language, indicates really only such a preservation, as would
be necessary for the stocking of that part of the world where
Noah and his family were, after the waters should subside.
The number and the variety of the animals preserved for this
purpose would of course be very great, and would, according to
the common usage of language in narration, be spoken of in
the terms used in the Bible. This interpretation holds equally,
whether the deluge be considered as having been partial or
universal.
571. The case being thus quite clearly made out in relation
to animals generally, he proceeds to trace an analogy between
them and the races of man in this respect. He supposes that
there are certain zoological provinces for the different human
races, as there are for the different species and varieties of ani-
mals ; and that these races were separately created in these
provinces with organizations suited to their peculiar localities.
While he allows that climate and other influences affect the
varieties of the human race, he claims that they are not com-
petent to produce them alone; and he infers, therefore, that
there must have been, as in the case of animals, different original
creations in the different zoological districts. He accordingly
claims that the history given in Genesis is a history of the origin
of only one branch of the human family. He does not sup-
pose that the different branches constitute different species, but
are made varieties of one species.* He characterizes mankind
* The difference between species and varieties is this. The distinction of species rests
upon specific characteristics, that cannot be changed by those influences which tend tc
VAKIETIES OF THE HUMAN RACE. 871
Most naturalists believe that the race came from one pair.
as being every where essentially the same in mental character,
and alike the accountable subjects of God's kingdom, notwith-
standing their multiple origin. It is in this respect that ha
considers them as being of one brotherhood, and he looks upon
the expression in the Bible, " made of one blood," as being en-
tirely figurative, and as referring to " the higher unity of man-
kind, and not to their supposed connection by natural descent."
I do not propose to go into a thorough discussion of this
question. This would not be possible in the narrow limits of
a chapter. I shall only present a general view of the chief
facts and arguments that bear upon the point at issue. And
let us look at this subject first in the light of physiology and
natural history.
572. The great majority of physiologists and naturalists, as
I have before remarked, have thus far been of the opinion that
the human race came from one origin, and that the varieties of
it have been produced by the various influences to which man
has been subjected. These are commonly included in the gen-
eral expression, climatic and other influences. To be more par-
ticular, they are climate, situation, food, clothing, customs,
habits, way of life, state of civilization. Too great prominence
has been undoubtedly given to the influence of climate. Law-
rence very justly remarks in his general conclusions in regard
to the production of the varieties in man and animals, " that of
the circumstances which favor this disposition to the production
of the varieties in the animal kingdom, the most powerful is the
state of domestication." This word, as he uses it, includes all
those social influences, which as manifestly affect the animals
which man domesticates as they do man himself. The analogy
between man and animals in relation to the results of the influ-
ences referred to I shall soon speak of more particularly.
573. That climatic and other influences do have a very great
agency in producing the varieties both individual and gone nil,
that we see on looking over the human family, no one doubts.
The only question is, whether they have produced all tluse
differences whether, for example, they have occasioned that
produce the differences thnt make varieties. The characteristics of a species are orig-
inal, while those of a variety are acquired. "The term species," says Prichard, ''in-
cludes only the following conditions, namely, separate origin and distinctness of race,
evinced by the constant transmission of some characteristic peculiarity of organization.
A race of animals or of plants marked by any peculiarity which it has ever constantly
displayed, is termed a species; and two races are considered specifically different, if they
are distinguished from each other by some characteristic which the one cnmx.t he supposed
to have acquired, or the other to have lost, through any known operutu-n of pnysicul
causes."
372 HUMAN PHYSIOLOGY.
Color affected by climate. Circumstances affecting the form.
very wide difference that we see between the Caucasian and the
Ethiopian. My limits will not allow me to go into a full exam-
ination of the influence of these causes, and I can only touch
upon a few points in a very general way.
574. That climate has a great influence upon the color of the
race is proved by many clearly observed facts. Tropical heat
always has a tendency to produce a black skin. This is shown
very decidedly in the case of the Jews, who have preserved their
characteristic features amid varieties of climate, and yet have
their color altered. Thus, while the Jew of the interior of
Europe has a fair complexion and light hair, under the scorching
sun of India his hair is crisped, and his skin is black. The ev-
idence of the influence of climate is the stronger in this case,
because the change from the original color has been two-fold,
For the original Jew in Palestine had undoubtedly a dusky skin
and dark hair, upon which the temperate climate of the interior
of Europe, and the tropical climate of India have produced two
opposite effects.
575. But in the varieties of the human race there are differ-
ences of form as well as of color. That the various influences
to which man is subjected have a marked effect upon his phys-
ical form is universally acknowledged. We see this alike in
individuals, families, and nations. Intellectual and moral influ-
ences manifestly have some agency in moulding the shape of
the head in the individual. The differences, which we so com-
monly see in the shape of the head between the intellectual and
the ignorant, are not owing altogether to original difference
of capacity, but in part to education. The brain, like all other
organs in the body, is influenced in its development by the
degree of activity to which it is stimulated. It is not made an
exception to this general law of development. Accordingly we
find that depressing influences tend to make the top of the head,
tlia cerebral part, small, and the forehead retreating, while the
face, from the predominance of the sensual over the intellectual,
is rendered relatively too prominent. The tendency of elevating
influences is of an opposite character. And such influences, thus
operating in the individual, when repeated and accumulated
from generation to generation, produce great and lasting results.
It is thus that a race becomes either degraded or elevated. By
a continuance and accumulation of influences it acquires either
a good or a bad fixed character.
576. I have thus spoken of one class of causes effecting
changes in the physical form, the influence of which is manifest
VARIETIES OF THE HUMAN EACE. 373
Marked tendencies to three different forms of the head.
But there are changes seen, the causes of which we cannot
clearly make out ; and yet we know that they are occasioned
by the varying circumstances in which man is placed. By the
compound influence of many causes combined we continually
see differences in the shapes of various parts of the body intro-
duced. Family and national peculiarities are thus occasioned.
The influences to which I have thus referred, some of which are
little understood, are all those which Mr. Lawrence includes in
the term domestication, which, as I have before said, he applies
to man as well as to animals.
577. Dr. Prichard has pointed out three different types of
form in the head, occasioned by three distinct classes of influ-
ences. One he terms the prognathous, (a word derived from
two Greek words meaning before and the jaw,) in which the
jaws project very prominently forward. This formation is char-
acterized by the predominance of the sensual over the intel-
lectual, the apparatus of the senses being largely developed,
while the cerebrum is small, making the forehead retreating.
The tendency to assume this type is always in proportion to the
action of the degrading influences. " Want, squalor, and igno-
rance," says Carpenter, " have a special tendency to induce the
diminution of the cranial portion of the skull, and that increase
of the facial, which characterize the prognathous type." It is
seen most strongly marked in the negroes of the Gold Coast.
In the pyramidal type, as it is termed, the cheek bones are very
broad, and the bones above are so shaped as to give the top of
the head a sort of pyramidal form. This type we see in those
tribes that lead a wandering life the nomadic races, as they
are called. The oval or elliptical form, which is seen so well
marked in the Caucasian variety, is manifestly the result of ele-
vating influences. These types are convertible into each other.
Thus, the oval may be degraded into the prognathous, or the
prognathous may be elevated into the oval. The latter change
is seen in the Ethiopian, when in successive generations he is
subjected to elevating influences, in his intercourse with the
Caucasian. And it is interesting to observe that the form of the
head is more readily changed than the color. " Thus," says
Carpenter, " in some of the older West Indian colonies, it is
not uncommon to meet with negroes, the descendants of those
first introduced there, who exhibit a very European physiog-
nomy ; and it has even been asserted that a negro belonging to
the Dutch portion of Guinea may be distinguished from another
belonging to the British settlements, by the similarity of the
32
374 HUMAN PHYSIOLOGY.
Insensible gradations in diversity. Fixedness of the varieties.
features and expression in each, to those which peculiarly char-
acterized his master's. The effect could not have been produced
by the mixture of bloods, since this would be made apparent
by alteration of color." In the same way is the pyramidal type
convertible with the others. The pyramidal and the progna-
thous are often mingled together, by the influence of vagabond
habits and degrading causes.
578. The view thus given of the operation of influences in
producing the varieties of mankind is strengthened by the fact
that, as Humboldt says in his Cosmos, there are " many inter-
mediate gradations in the color of the skin and in the form of
the skull." If we look alone at the extremes in varieties of color
and form, we are of course disposed to regard such great differ-
ences as marking a distinction of species. But when we see
these varieties passing into each other by such insensible grada-
tions, and at the same time observe the manifest influence of
causes upon these gradations, as in the cases referred to in the
last paragraph, the evidence is clear to us that the varied influ-
ences brought to bear upon man are competent to produce the
varieties of the race.
579. But it is objected that although climatic and other in-
fluences have a great effect, yet, so far as we can see, they only
produce changes that approximate to those differences that
mark the grand divisions of the race. They cannot, for exam-
ple, be shown, from actual observation, to have effected the
entire change in any length of time of any portion of the Cau-
casian race into the Ethiopian, nor, on the other hand, of the
Ethiopian into the Caucasian. It is objected, farther, that the
peculiarities of the principal varieties of man existed in the early
history of the race. This appears in relation to the Ethiopian
variety in the figures found on Egyptian monuments. These
show that the peculiarities of the negro race were as strongly
marked nearly 5,000 years ago as they are now. This fixedness
of character under such a variety of influences continued so
long, it is claimed, indicates that the peculiarities were original,
and not acquired.
580. In reply to both of these objections, I will call your
attention to a general fact, which I deem to be very significant
in its bearing upon the great point at issue. It is the fact that
when a variety is formed by any influences, either among plants
or animals, it is apt to remain in spite of opposing influences.
It seems to be easier by far to produce a variety, than to bring
it back to the character of the original from which it came.
VARIETIES OF THE HUMAN RACE. 875
Influence of " domestication " both in man and in animals.
Domestication has been continually producing varieties in the
animals that man has so largely appropriated to his service, and
tne varieties once produced, commonly remain. And the same
thing is seen in the varieties resulting from the same class of
influences so continually in the human race. It is matter of
common observation that family and national peculiarities are
apt to be perpetuated. And it is not merely from a continu-
ance of the causes from which they result, for they are apt to
remain even when strong counteracting influences are brought
to bear upon them. Now the causes which tend to produce
varieties in the human race acted of course at the first, and
were competent to produce the most prominent varieties during
the first ages of the race. And the tendency to fixedness, which
we see exemplified in so many ways in the varieties of both
plants and animals, is sufficient to account for the perpetuation
of such marked characteristics as those of the Ethiopian and the
Caucasian.
581. The analogy then which is thus observed between man
and the domesticated animals is a much clearer and stronger
one, than that which Professor Agassis has attempted to make
out between man and animals generally in regard to zoological
districts. And the inference is a legitimate one, that the same
influences, that we see produce varieties in domesticated animals,
are competent to produce the varieties in the human race, which
are even less marked than some of those which we see in ani-
mals. Varieties are produced more readily and in greater
numbers in animals than in man, probably because they have
less power of resisting influences that act upon them. The va-
rieties of some of the domesticated animals are very numerous.
582. The analogy drawn between man and animals in regard
to zoological districts is weakened by the consideration, that
there was no necessity for man's being created in diiferent lo-
calities, because he can migrate so easily from one country to
another. The necessity existed in regard to plants and animals,
but not to the same extent in all. Migration is easier in the
case of some than in the case of others. And this difference
seems to have been acted upon by the Creator. Accordingly,
the evidence is quite conclusive, that those animals which have
been so universally appropriated by man to his service, have
been diffused from central points and have gone with man,
instead of being created in many localities. This being the
case, it is hardly to be supposed that man, who is capable >
through his ingenuity, and skill, and daring, of going every
876 HUMAN PHYSIOLOGY,
New causes occasionally introduced by the Creator. Facts showing thii.
where, would be unnecessarily created in different pairs at differ-
ent points on the earth's surface.
583. But suppose that in view of all the evidence we should
come to the conclusion, that the climatic and other influences
are not the sole causes of the differences in the races, are we of
course driven to the admission that, as Agassis and others teach,
there must have been created at the first, several, we know not
how many different pairs in different localities ? By no means.
We are not to forget that the Creator, besides using influences
of which we have no knowledge, (which he is continually doing,)
can effect new combinations of the causes already existing, or
introduce into operation entirely new causes. That he is from
time to time evolving new results in one or the other of these
ways, or both of them, is manifest. The very common notion,
that at the creation all the causes which have produced all the
phenomena that have been observed to the present time, were
then set in operation, and have been left to work out their
results, seems to be contradicted by many facts. Most of the
causes then set in operation, it is true, have been at work ever
since. Unless this were so, nature would not exhibit the regu-
larity which it now does, and calculations could not be made
with such definiteness as to its processes from knowledge gained
by experience. But changes and irregularities sometimes occur
which must have been the result of new causes. I shall allude
to but a few examples.
584. The age of man before the flood was much greater than
it has been since. A change was effected at that period. It
was not a mere arbitrary change, but such a change in the very
character of the human system, that its capability of resisting
the tendency to decline was greatly reduced in the period of its
continuance. It was not a change resulting from the influence
of deteriorating causes, for in that case it would have been less
suddenly induced. To effect this change some new causes must
clearly have been brought to bear upon the system, making it
in the post-diluvian a different system in some important respects
from what it was in the ante-diluvian. Take a fact of a differ-
ent kind, indicating a similar change of agency. New diseases
from time to time appear. This could not occur without either
entirely new causes, or new combinations of elements heretofore
existing. That very definitely marked disease, the small pox,
we have the best of evidence, was not known to the ancients,
and is comparatively a modern disease. It is impossible to
conceive of its being introduced without some new cause of a
VARIETIES OF THE HUMAN RACE. 377
Supposition of new causes more probable than Agassis' supposition.
very definite character. Take now another fact of a widely
different kind from either of those to which I have alluded.
The earth is marked all over with signs of great convulsions
that have occurred since its first creation. It has been supposed
till recently that these signs all refer to that great event de-
scribed in the Bible, the Deluge of Noah ; but geological
researches have demonstrated pretty clearly that they point in
part at least to other previous convulsions. Now these convul-
sions are not to be reckoned as a part of the regular order of
nature. They could not have resulted from the ordinary causes
that act continuously. New causes must have been introduced
at the time, to produce these unwonted results.
585. It matters not to the argument above indicated, whether
the new results that are occasionally developed, come from a
direct agency at the time, or come from a chain of causes set in
operation a long time before. The results are new results, and
come from causes or combinations of causes, which differ from
those that have produced the ordinary and regular results which
we witness from day to day or from year to year.
586. Now in like manner can we suppose, if it be necessary,
that the Creator produced the varieties of the human race, by
adding other and new causes to the ordinary influences to which
man is subjected. This is a much more probable supposition
than that of the advocates of the multiple origin of the race.
For besides accounting satisfactorily for the facts, and at the
same time being consistent with the record in Genesis, it is
more clearly supported by analogical facts than the supposition,
(for it is a mere supposition,) that the human race was created
in different localities. And farther, this supposition avoids diffi-
culties which attend the other. For, if we suppose that the
race came from different pairs, it would be difficult to decide
how many pairs there were. Such are the variations of the
race in different localities that there would be much disagree-
ment as to the number of the representative pairs, and their
distinguishing characteristics.
587. But it may perhaps be said in objection, that I am
supposing a miraculous interposition. Whether it may rightly
be termed such I will not stop to consider,' but will merely re-
mark, that it is just such an interposition, or rather, direct agency,
as is affirmed by the advocates of a multiple creation, differing
from it only in the time of its occurrence. They suppose the
direct agency of God to be put forth in creation at different
points, whether at different times they do not say, and this is
32*
378 HUMAN PHYSIOLOGY.
The testimony of the Bible to be received as evidence.
really quite immaterial ; and I suppose the same direct agency
to be put forth, but in a less marked manner, to produce a
change in what has been already created. In supposing the
direct agency of the Deity at all, we go beyond mere physics ;
and he surely has the power to put forth this agency at such
times as he pleases.*
588. But the supposition made above is not in my view
needed. I believe that the regular, continuous, natural causes,
which have ever operated upon man, have been competent to
produce all the varieties of the race. And I only suggest this
supposition, as a consideration for those who fail to see that
these causes have been thus competent; and I claim that
it is a more probable supposition than the one offered by
Agassis and others to meet the difficulty in the minds of such
persons.
589. Thus far I have treated this subject chiefly as one
of natural history and physiology. But is the testimony of
the Bible not to be received as a part of the evidence ? Is
the question to be decided wholly on considerations and facts
drawn from natural history and physiology ? This seems to
be the view of some naturalists, though the great majority of
them are disposed to admit the statements of Scripture as evi-
dence. It is true that the Bible does not purport to be a phi-
losophical book. Its language is based upon the principles of
common and not scientific usage, and is so to be interpreted.
And it should be thus interpreted in relation to the subject be-
fore us. Its statements on this subject are of the most explicit
character. It purports to give an account of the origin of the
race, and portions of its history. It ascribes the corrupt char-
acter of the race to a fallen parentage. This connection of the
general corruption of the race with the fall of its original pair,
however divines and philosophers may differ in accounting for
it, is recognized as a fact throughout the whole book of revela-
tion. The testimony is definite, and is not to be mistaken.
The question is, whether it be valid testimony. And if the
Scriptural record be established, as it is abundantly, by both
* There seems to be in the minds of some naturalists a great reluctance to admit at all
the direct agency of the Creator, whether it he exerted in consonance with, the order of
nature which he has established, or miraculously in opposition to it. And they would
smile skeptically at what they would deem the simplicity or superstition of Hugh Miller,
in referring some narrow escapes which he has had, in pursuing his geological researches,
to a particular Providence. The relation of the agency of the great First Cause to second
causes, it is true, is a mysterious subject; but it implies no disposition to fathom what is
unfathomable if we assert that the facts are far from warranting us in the belief, that this
agency has not been exerted since the period of the creation, but confined itself to that
time.
VAEIETIES OF THE HUMAN" RACE. 379
The unity of the race recognized by the whole scope of the Bible.
internal and coincident evidence, its testimony in regard to the
origin of the race is to be received by scientific men. It can
not be set aside by any mere presumptive and analogical evidence
drawn from physiology and natural history. If actual facts
be proved inconsistent with the Mosaic history, as properly
interpreted, they will of course bring discredit upon that his-
tory. No immunity against a strict investigation is to be
claimed for the Bible. But there is no fear of such an issue ;
and it is to be remembered that mere analogies are not facts,
and are not to be deemed as having much force, especially when
there is a question in regard to their value in comparison with
other analogies that point to an opposite conclusion.
586. If the account given in Genesis be a correct account,
as is generally allowed by the advocates of the multiple origin
of man, and if, as they claim, it is the account of the origin of
only one branch of the race, while other pairs were created in
other parts of the world, they are driven by the facts in the
case to this alternative. Either other pairs were created with
an original corrupt nature, or they were created innocent as
Adam and Eve were, and then were tempted in a similar man-
ner and with a similar result. To claim that the other pairs
were made so like Adam and Eve as to constitute with them
one species, alike physically, intellectually and morally, without
taking either of the suppositions just given, is to admit the
truth of only a small portion of the Mosaic account, and is also
inconsistent with the existence of the great acknowledged fact
of the general corruption of the race. So that it is evident
that the unity of the race, and the truth of the Mosaic history,
must stand or fall together. And it is not the truth of this
history merely that is involved in this question, but the truth
of the Bible as a whole. For the corruption of the race, which
the Bible seeks to remove, as before remarked, is throughout
this book distinctly referred to the fall of man as recorded in
the Mosaic history as its origin. The main facts of that record
are recognized as true by the whole scope of the Bible, what-
ever may be thought of the minute particulars of the narration.
It matters not then, you will observe, to the argument, whether
the Mosaic account be received as true in all its minutiae, or
whether it be considered, as it is by some, as a mere myth.
For the argument is based upon the recognition by the rest of
the Bible of the main facts contained in the history. And if it be
a myth or fable, it must be based upon these facts, or, in other
words, it is these facts that it is the object 01 this myth to convey.
380 HUMAN PHYSIOLOGY.
Distinction between man and the higher animals very definite.
587. I have thus presented a summary (for it necessarily is a
mere summary) of what I deem to be the proper view of this
subject In doing so, I have left out many facts and considera-
tions which are important, if we intend to go into a full and
thorough investigation. I have selected for your consideration
those points which are most prominent and important. I have
attempted to indicate as clearly as I can the value of the differ-
ent prominent arguments, that have been advanced on both
sides of the question. And from the views and facts presented
I think it very evident, that the true interpretation of the pre-
sumptive evidence, drawn from natural history and physiology,
is entirely in accordance with the teaching of the Bible, viz.,
that God " made of one blood all the nations of men for to dwell
on the face of the earth." We are all one brotherhood. And,
therefore, however debased our fellow man may be to what-
ever degree of degradation the unrestrained corruption of his
nature may have brought him we are to look upon him as
containing the elements of that moral and intellectual elevation
which is attained by the most gifted of men. It is this view
of the subject that imparts dignity, and interest, and hope, to all
philanthropic efforts to raise man from the moral, intellectual,
and physical degradation, to which sin has reduced him.
588. Although there are perhaps none at the present time
who distinctly advocate the doctrine, that the lower races of
men, as they are termed, are half way between man and such
animals as the monkey and ourang-outang, yet there is in some
minds an indefinite partial admission of this idea. There is a
disposition in some naturalists to make the most of any resem-
blances found between these races and animals. The attempt
has been sometimes made to show, that there is a decided re-
semblance between the form of the Ethiopian and that of the
monkey tribe. But it has always failed. It has been said that
the arm of the negro is longer than that of the Caucasian, and
that in this respect he approaches to animals of this class. But
the difference is so slight that the analogy fails entirely. And
besides, the hand of the negro, the most important part of the
upper extremity, bears no manner of resemblance to the imper-
fect hand of the monkey, but is essentially like that of the
European. It has been said, too, that the brain of the negro is
like that of the monkey. The brain in any race or family of
men that are debased and ignorant is smaller than in the ele-
vated, and in this respect alone does it approach to that of the
monkey and other higher orders of animals. And, as I have
LIFE AND DEATH. 381
Life, though various in its manifestations, in some senses always the same.
before said, there are certain mental characteristics in the most
debased which link them to the most exalted of our race, creating
an " impassable chasm " between them and the most intelligent
of animals.
CHAPTER XX.
LIPE AND DEATH.
589. LIFE is very commonly spoken of as being one thing,
although its manifestations are exceedingly various in their
character. In the simplest growths that we see, both in the
vegetable and the animal kingdoms, the operations of life are
in some respects very different from the complicated processes,
that we witness in the human structure, which has been the
subject of your study in this book. And yet, as you have seen
in the Chapter on Cell-Life, life in these apparently opposite
cases is essentially the same. It is the same in its origin. It
begins always in a single cell, whether the living being is to be
minute or monstrous, simple or complex, a plant or an animal,
a creature of a day, or a being destined to immortality. Why
it is that from a simple cell the vital force, as it is termed, can
evolve such a range of diversified results as we see in all ani-
mated nature, is one of the great mysteries of the Creator. As
we see in the spring time a bud upon a tree unfold itself grad-
ually, and develop to us successively leaves and flowers and
fruit, it fills us with wonder, when we reflect how much has
come from that little bud ; but when we go farther, and think
of the whole tree as having come from a single cell, so small
that it can be seen only by the microscope, the mystery appears
passing wonderful. And it is a still greater mystery, when a
complicated animal organization is looked at as having been
developed by the vital force, alike with all other living things,
through a single cell as its origin.
590. Life is not only always the same in its origin, but it
continues essentially the same in its processes. All the various
forms which it produces, both in the vegetable and animal
world, are built and kept in repair by cells. All the functions,
too, are carried on through the same agency. The secretions
382 HUMAN PHYSIOLOGY.
Difference between the vital force, and heat, light, and electricity.
and excretions, as you saw in 201, are effected by constant
successive creations of numberless cells. Even the intellectual
operations in the mind of man are dependent upon cells so lono-
as the mind is connected with the body. In thinking, as well
as in muscular motion, cells are worn out, and must be replaced
by other cells, which are continually supplied by the vital force.
591. Life being thus wonderful in its operations, the inquiry
arises, what can this mysterious agent be. With curious eye
we watch its workings, but although we can learn some of its
laws, its nature eludes our search. Then pressing the micro-
scope into our service, we trace it back to its hiding place in a
minute round cell containing a fluid ; but simple as this prison
is in which it is confined, it is more of a mystery than ever.
The vital force, which begins here, and, enlarging more and
more the sphere of its operations, developes gradually the simple
or the complicated living form, as the case may be, has been
classed by some with other forces, the nature of which we do
not understand, as heat, light, and electricity. But it differs
from them entirely in some important points. While they act
in connection with matter generally, both organized and unor-
ganized, vital force is only seen acting in organized substances.
While they diffuse themselves through all kinds of matter with
more or less rapidity, the vital force has no power of diffusion,
but is confined within certain limits. These limits differ in the
different living substances. The vital force has the power of
appropriating matter to itself within these limits. It does this
by assimilation, as described in 10. It has then the power
of extension to a limited degree ; while the other forces men-
tioned have the power of diffusion, in some respects limitless.
592. Another difference is this. While these forces, light,
heat, and electricity, are lessened in power by being diffused,
vital force is not lessened by extension. Heat, for example, if
diffused is lessened at the point of its diffusion ; but life is as
energetic at its starting point after its extension as before, and
even more so. It is, so to speak, self-generating, while the
other forces are mere products. The vital force stands peculi-
arly alone in this respect. The effects too, which this force
produces, as it lays common matter under contribution, and
fashions it in such diversified forms, have an infinitely wider
range of variety than the effects of the other forces.
593. We can thus trace the differences between the vital force
or principle and other forces, but we cannot, as I have before
said, discern its nature. We know not whether it be one thing.
LIFE AND DEATH. 383
Life in the blood. Vital laws control the chemical and mechanical.
It is convenient to speak of it as being so. But we know not
but that it may be a compound of endowments, or tendencies
imparted to matter, and varying with the various forms of living
substances. Some have supposed that the vital principle resides
chiefly in the blood, and that this is the meaning of the passage
in the Bible, " the life of the flesh is the blood." That the
blood has some vital properties is certainly true. These prop-
erties are communicated to it as it is made from the food, and
fit it to be the material for the construction and repair of the
organization. And it is simply the fact, that the blood is the
common material out of which all the diversified parts of the
living structure are made, that is recognized in the language of
Scripture on this subject. The same fact is embodied in an-
other form in the remark of the French physiologist, that the
blood is chair coulante, or running flesh.
594. When the vital force appropriates to itself common
matter in assimilation, it takes it away in part from the opera-
tion of certain forces which have had entire control over it. As
long as it is common dead matter, it is wholly subject to the
laws of mechanics, and of chemical action. But when it be-
comes organized living matter, the laws of life take possession
of it. The laws of chemistry and mechanics are not, it is true,
annulled in relation to it. They still exert their influence, but
under the control of vital laws. The force of gravity acts con-
tinually upon the body ; but the living muscles are much of the
time acting in direct opposition to it. The blood circulates on
hydraulic principles ; but the vital force furnishes the motive
power, and keeps the blood from becoming solid and stopping
up its channels. Chemical changes are going on in the stomach,
the lungs, and at every point in the capillary circulation ; but
they are modified, controlled, by the vital principle, and are
properly termed chemico-vital processes.
595. The human body is made of materials that are exceed-
ingly prone to chemical decomposition, and the degree of heat
which is maintained is such as to favor this result ; but the vital
force not only holds the chemistry of the system in abeyance,
but even presses it into its service. When life is destroyed, the
laws of chemistry assume their full sway, and the process of
decay begins. The very agencies which served, while under
the control of the vital principle, to maintain the living organi-
zation, now acting alone run riot, and work its destruction.
Thus, that powerful agent, heat, existing in the body at the
point of 98, is necessary to the carrying on of the processes of
384. HUMAN PHYSIOLOGY.
Change always attends life in action. Life sometimes dormant.
life ; but let life be destroyed, and the maintenance of this de-
free of heat would ensure a very rapid putrefaction. So too, a
egree of heat which would rapidly putrefy a dead egg by
quickening the chemical changes, would actively stimulate in a
living egg those curious vital processes that produce at length
the bird. During intubation the egg of the hen is kept for
three weeks at a heat of 105, and yet when the chicken is
hatched all of the yolk that is left is unchanged. A dead egg
would soon putrefy under such a temperature.
596. The vital force exhibits its controlling power in an ex-
traordinary manner in connection with that great force of nature
to which I have just referred. Heat is very diffusive, and is
exceedingly liable to change from varying circumstances. And
yet the vital force maintains the heat of the body quite uni-
formly at one point, although the agencies which tend to vary
it are very numerous and effective. The production of heat in
the system is a chemical operation, but the vital principle reg-
ulates the quantity in the body very accurately, by providing
for its escape in various ways, and perhaps by curtailing in some
measure its production.
597. Continual changes are effected by the vital force in every
part of the body. In one sense death may be said to be taking
place constantly, while life is as constantly generated, as the
useless particles are separated and taken away, and the new
ones are deposited in their place. While these changes are
going on the vital force so operates as to maintain the peculiar
shape and plan of every part, even during its growth. And as
we look abroad over all the diversified forms of animated na-
ture, the accuracy with which this force works in the prescribed
mould of each is very wonderful. This point I have commented
upon in the first chapter, page 18, and will not dwell upon it
here.
598. While the vital force is in action there is constant
change ; but sometimes it is dormant. A seed in its quiescent
state has life in it, ready to be waked into action by the proper
excitants, air, warmth, and moisture. Seeds that were found in
the excavations of Pompeii have shown that they retained their
life during all this time, by shooting forth their germs as soon
as they were exposed to these natural excitants of their growth.
One of the most interesting cases of this kind is related by Dr.
Lindley. " I have now before me," he says, " three plants of
Raspberries, which have been raised in the gardens of the Hor-
ticultural Society, from seeds taken from the stomach of a man
LIFE AND DEATH.
Mysterious connection of life with the soul.
whose skeleton was found thirty feet below the surface of the
earth, at the bottom of a burrow which was opened near Dor-
chester. He .had been buried with some coin of the Emperor
Hadrian, and it is probable, therefore, that the seeds were six-
teen or seventeen hundred years old."
599. A similar dormant condition of the vital force exists in
a greater or less degree. *\s you saw in 158, in the state of
hibernation. So also, m cold climates, life is throughout al-
most the whole vegetable world dormant during the period of
winter, to wake to greater energy from the stimulating warmth
of spring. In the human body, with the exception of some
few very rare cases, life is always in an active state. Some
portions, however, of the system are a part of the time dormant
for the purpose of rest and repair. The brain and the muscles
sleej) ; but during their sleep life is busy in the formative vessels,
repairing their energies, and we may say, their textures also,
which have been wasted by their labor. I will not dwell longer
upon this interesting subject, but in leaving it I remark, that it
is a very wonderful attribute of the vital force that it can, as
in the case of the hibernating warm blooded animals, stop all
its active operations, without damage to the machinery of life,
and with such facility resign itself into a state of temporary
inactivity.
600. The most mysterious of all the circumstances in regard
to the vital force is its connection in man with the immortal
soul. The life and the soul are so intimately connected that
some have considered them to be the same. But they are two
distinct forces. They are in some measure indeed antagonistic to
each other. For the soul, in using the machinery of the nerves
and muscles occasions a wear and tear of the structure, which
it is the office of life with its numberless cell-laboratories to re-
pair. The soul and the vital principle are both present in all
parts of the system, but not in the same sense. The vital
principle is seen equally at work every where. It has no great
central organ from which it sends forth its influence. But the
soul is especially connected with the brain, and by means of
the complicated nervous connections of this organ, it affects
and is affected by all parts of the system. Its influence is thus
an all pervading one. Every point of the living organization
has thus a sort of telegraphic communication with the imma-
terial soul.
601. But there is another view of this connection of the soul
and the vital principle. The soiil is developed in and with tta
33
386 HUMAN PHYSIOLOGY.
Natural limits of life. Decay.
living structure. It is not created by itself and put into the
body as a tenant. Its powers are developed while the vital
force developes the powers of the physical organization. The
two processes go on together. Nay more, the development of
the soul is in a measure dependent upon the development of
the body. The vital force exerts a manifest influence upon the
soul's growth. As it prepares the organs for the use of the
soul those organs by which it acquires knowledge from with-
out, and thus procures the stimulus and even the material for
its growth whenever the vital force fails to construct these
organs properly, the powers of the soul are not well developed.
This we see exemplified in the idiot. In this intimate connec-
tion of the soul with life we find a great mystery. Life, a force
belonging to mere matter, an endowment of it, or a compound
of its endowments life, that builds up all organized substances,
the humblest and simplest vegetable growth, as well as that
most complex of all living structures, man life, that so soon
perishes in the noblest of its works that it is likened to the dis-
solving vapor is made by the Creator an agent in developing
an immaterial principle or being, that is to survive the dissolu-
tion of the structure in which it is generated, and is to live
forever. Strange that the immortal should be thus produced
in the mortal that the unchangeable and imperishable soul
should be thus developed in such intimate connection with the
changeable and perishable body. It is a mystery which we
cannot fathom.
602. The vital force, that is so busy in building and repair-
ing so long as it lasts, has in all cases its natural limit ; and in
the case of the human system it seldom fully reaches this limit.
The diversified, and complicated, and beautiful structures which
it evolves, if saved from accident till the natural period of de-
cline comes, lose their vigor and beauty, and at length die and
are given up to the action of the common laws of chemistry,
which the vital force has so long resisted and controlled. The
structures then decay, and the particles are dissipated, perhaps
to be united again to other structures.
603. The death of the body is not ordinarily complete at
the moment when what we term death occurs. Though as a
whole, as a system of organs, the operations of life are at an
end, yet there is some degree of life in some parts, and there
may be in all parts of the body. The beard and nails even,
may grow. Some of the organs may secrete their fluids the
liver its bile, and the stomach its gastric juice. Some of the
LIFE AND DEATH. 387
Systemic and molecular death. Death beginning in the heart, and in the lungs
properties of life, too, manifestly still remain. The irritability
of the muscles, which is strictly a vital property, as it never
belongs to common dead matter, still appears on the applica-
tion of excitants. It was the contraction of the muscles in the
leg of a dead frog on the accidental application of a stimulus,
that led Galvani to his grand discovery. And it is through
this vital property that the culprit who has been hung can be
galvanized into apparent life. Death then may be said to be
of two kinds systemic, that is, the death of the body as a
whole, a system of organs and molecular, that is, the death
of the individual molecules or particles which compose the
body. Death can be said to be complete only when the laws
of life have resigned their power over these molecules, and the
laws of purely chemical action have taken their place. When
this change occurs, the process of decay, which is strictly a
chemical process, begins.
604. It will be interesting to notice here the modes in which
systemic death occurs. There are three great systems in the
body, each of which is immediately essential to the continuance
of life the system of the circulation, the respiratory system,
and the nervous system. And we may speak of death as be-
ginning in any one of these systems when the cause of death
acts primarily upon it. I will notice some examples under each
head.
605. If a large quantity of blood be lost, so large as to result
fatally, death in this case obviously begins in the circulation.
The heart not being supplied with the quantity of blood that
usually flows through it, becomes more and more feeble in its
action, till it at length ceases to beat. When a large aneurism
bursts, it is the sudden drain from the circulation that destroys
life.
606. Any thing which to any great extent prevents the air
from entering the lungs may cause death to begin in the respt
ratory system. This may be done by three classes of causes.
1st. Causes that act upon the large air passages. Example*,
of this class of causes are strangling, smothering, drowning,
&c. In croup the principal cause of death is the prevention
of the free passage of air through the windpipe into the lungs.
2d. Causes which act upon the walls of the chest. If a bank
of earth fall upon a man, though it leave his head clear, so that
the air passages are unobstructed, he cannot breathe, because
his chest is held as if in a vice. A man came near dying from
this cause, who was having a cast taken of the^upper part of
388 HUMAN PHYSIOLOGY.
Death beginning in the nervous system.
his body. If the muscles of respiration were to be paralyzed,
death would ensue, just as it does when they are prevented from
acting by other causes. 3rd. Causes acting upon the lungs.
Disease may occasion an amount of obstruction in the very
substance of the lungs sufficient to cause death. It does so by
preventing the introduction of the air into the minute air vessels,
where the air revivifies the blood. The obstruction is just as
effectual in this case as it is where it occurs in the large air
passages.
607. When death occurs from a blow upon the head as the
immediate result of the shock, we have an example of death
beginning in the nervous system. But the cause may act upon
this system in some other quarter. A blow at the pit of the
stomach, for example, may so shock the whole nervous system
as to stop at once the operations of life. Some poisons, too, as
opium, destroy life by their influence upon this system. Very
extensive burns give a shock to the nerves from which they do
not rally. The same can be said of other injuries when there
is no recovery from the first shock. Powerful medicines, im-
properly given in cases of disease disposed to prostration, may
depress the nervous system to a point from which it may never
revive. Cold destroys life mostly by the benumbing, paralyzing
influence which it exerts upon the nerves.
608. Though we thus classify the modes of death, in the
great majority of cases death is a complex event, resulting from
a concurrence of causes. It is so even when the disease is not
of a complicated character. Take, for example, a case of pure
uncomplicated consumption, in which all the organs but the
lungs are in a healthy state to the end. The whole system
becomes at length exhausted by the disease. If this exhaustion
alone be the cause of death, then we may say that it is an ex-
ample of death beginning in the nervous system. But if the
obstruction in the lungs to the admission of air in the air-cells
be the cause, it is a case of death beginning in the respiratory
system. Generally in such cases death results from the two
causes combined, and it is often difficult to determine which is
the more prominent cause.
609. The signs of death are so clear that there is, with very
few exceptions, no mistake in regard to the occurrence of the
event. The stories that are related about burying alive are
most of them unfounded. The apprehensions created by them
in the minds of some persons have led them to insist, that no
body ought to be committed to the grave, till the most infalli-
LIFE AND DEATH. 389
The signs of death. Death as viewed by the Physiologist, and the Christian.
ble sign of death, putrefaction, has appeared. That we should
wait for the appearance of this sign in all cases in which there
is a shadow of doubt, I will allow. But the cases are exceed-
ingly rare in which we cannot determine the reality of death
long before this sign shows itself. Our decision is not made
up, it must be observed, merely from the signs of death. All
the circumstances of the case are taken into view the disease,
its progress, its symptoms, and the events of the last hours of
the patient. With this evidence before us, we absolutely know,
in all ordinary cases, that death has occurred when the respi-
ration and the circulation have ceased. And in the exceed-
ingly few cases in which there is any reason to doubt on that
point, there is always something which will attract the attention
and excite the curiosity of some one, unless there be stolid in-
difference and the most absolute lack of intelligence. In such
cases there is always something strange the circumstances
attending the cessation of the respiration and circulation are
singular, and the signs of death are not complete and in their
proper order of succession. Whenever there is for these reasons
any doubt as to the reality of the apparent death, the strictest
watch should be maintained till the signs of commencing putre-
faction appear. With this simple rule of prevention burying
alive need never to occur.
610. The investigations of physiology, as you have seen, end
with the death of the body. It can give us no light on the
question as to what may be beyond this life. Although the
physiologist studies the human structure not merely as an or-
ganization instinct with life, but also as the wonderful machinery
through which a reasoning soul acts and is acted upon in this
state of being, yet, as a physiologist, he knows not that the
soul survives the death of the body. He knows not but that
it is a mere endowment of matter, as life probably is, and so
perishes in the hour of dissolution. He may indeed conjecture
that such exalted faculties which are in this world susceptible
of such high cultivation, instead of being destroyed with the
body, are destined to still farther development in another state
of existence. But what is mere conjecture 'to him as a Physi-
ologist, is made fact to him as a Christian. The eye of his
faith sees an immortal spirit rise from the dying body, and he
realizes the truth of the sublime declaration, that "death is
swallowed up of victory."
890 HUMAN PHYSIOLOGY.
Sources of our knowledge of hygiene.
CHAPTER XXL
HYGIENE.
611. IT seems appropriate that the concluding chapter of
this book should be on Hygiene. After having considered
the construction of the machinery of the human system and
the uses which the mind makes of it, one naturally inquires
what are the conditions on which the full development of
this complicated machinery and its daily repair depend.
612. The principles and rules of Hygiene are to be
learned from two sources. 1. They are to be learned from
Physiology. As we observe the functions of the different
organs, we can learn what those circumstances are which
favor their due performance, and what those are which in-
terfere with it. 2. They are to be learned, also, by observ-
ing the effects of those agencies which are known to
interfere with the functions and to produce disease. An
exemplification of these two modes of learning the principles
of Hygiene in relation to a single point will suffice. The
study of the physiology of the chest shows us that nature
has, in the construction of its framework, especially provided
for giving ample room to the lungs ; and so we deduce a
law of Hygiene, that the chest should not in any way suffer
compression. This is the first mode. But the same law
can be deduced by the second mode, that is, by observing
the results of compression of the chest.
613. Rules of hygiene generally have but little practical
influence, unless the physiological facts upon which they are
based are understood. Although the evil effects of their
violation may be vividly portrayed, and even illustrated, as
in the case of the chest, by engravings, the impression upon
the mind is by no means as thorough and practical, as when
the same lesson, is enforced by a clear knowledge of the
functions and arrangements of the organs and the conditions
necessary to their healthy action. Physiology, therefore,
should be studied as preparatory to a proper appreciation of
Hygiene.
614. Not only is a knowledge of Physiology essential to
a proper appreciation of the rules of Hygiene, but in many
HYGIENE. 391
Hygiene of digestion. Quantity of food to be eaten.
cases they cannot be fully understood in their varied appli-
cation without such a knowledge. With the very partial
and superficial knowledge of Physiology that is usually
communicated with Hygiene, these rules are for the most
part mere arbitrary rules. And just so far as the principles
on which they are based are not understood, is there a
liability to mistake their application under various circum-
stances.
615. In considering the subject of hygiene, the natural
division of Physiology, stated in 57, should be kept in
mind. There is a hygiene relating to the construction of the
machinery of the body, and there is also a hygiene relating
to the uses of this machinery. Besides, each organ has to a
certain extent its own hygiene. And yet, as all the organs
are connected more or less together in sympathetic action,
there is a general hygiene of the system. I shall observe
for the most part the same natural order that I followed in
developing the subject of Physiology. I shall first treat of
the hygiene of the construction and repair of the system
that is, the hygiene of digestion, circulation, respiration, and
formation and repair. You can recur to a summary of these
functions given in 69. I shall then pass to the considera-
tion of the hygiene of the uses of the machinery thus con-
structed and kept in repair.
616. Many of the points in the hygiene of the digestive
organs have been already noticed in the physiology of diges-
tion. I need say nothing more in addition to what is said
there of the importance of the thorough mastication of food,
and of its having a due amount of saliva mingled with it ;
of the evils resulting from eating too fast, from eating be-
tween meals, and from eating a great variety of food ; and
of the influence of exercise upon the process of digestion.
There are some other points, however, that remain to be
noticed.
617. No very precise rules can be given as to the quan-
tity of food that is proper to be eaten. But a consideration
of the physiological principles of digestion suggests rules
that are sufficiently definite for practical purposes. There
must be such an amount of food as will furnish sufficient
chyle to keep the blood, the building material of the body,
in proper quantity. The question arises, how we shall
know what amount of food is requisite for this purpose
Fortunately, the want of the system and its supply are com
392
HUMAN PHYSIOLOGY.
Mistakes as to quantity of food. Length of intervals between meala.
monly quite accurately indicated by the sensations as stated
in 87. The proper hygienic rule then on this point is,
that we should cease to eat when the sensations created bv
the want of the system are removed that is, when the
hunger is appeased, and the accompanying feeling of discom-
fort is succeeded by a feeling of agreeable ease.
618. But there are mistakes often made in regard to these
sensations. They may be prevented from making a true
report. Thus, when eating is done too rapidly, more food
than is needed may be introduced into the stomach before
the sensation of ease and satisfaction is experienced. It is
only when suitable time is given to mastication, and the
food is rather gradually introduced, that this sensation forms
the proper limit of eating. Again, there is a very common
mistake in substituting the feeling of fulness for the sensation
alluded to, as indicating the time for ceasing to eat. Those
who adopt this false rule generally make the stomach tc
bear as much as it can without absolute discomfort, and
many daily overreach this point. The result is, that this
organ soon gives out under this daily overworking ; or, if
the stomach be a strong one, an injurious repletion is pro-
duced in the system. Even in the latter case, the stomach
at length gives out, and becomes the seat of disease. But it
is astonishing how much labor, in the work of digestion, this
organ will perform in some cases.
619. Too little food is sometimes taken. Poverty is
commonly the cause. But sometimes it arises from false
notions ; as, for example, the notion that the quantity of
food should be regulated by weight, or the more common
notion, that we should rise from a meal with some amount
of appetite remaining. The result is, that there is not a
sufficient supply of chyle to meet the wants of the system.
The wear and tear create a demand which is greater than
the supply, and the body therefore loses its fulness and its
vigor.
620. In determining the length of the intervals between
the meals, we should have regard to the time required for the
completion of the process of digestion, and to the wants of
the system. Some articles are digested more rapidly than
others, but it commonly requires from three to four hours
to complete the digestion of a meal. When the system is
in a state of action, its want of food, as indicated by its
sensations, shows itself a little time after the completion of
HYGIENE. 393
Begularity of meals. Quality of food. Influence of the mind on digestioa
the process of digestion. The interval, then, between the
meals should not vary much from four hours. If it be made
longer than five hours, some degree of exhaustion results ;
and if it be less than three hours, disturbance of the diges-
tive process may occur, from having the digestion of one
meal begin before that of the previous one is fairly finished.
621. It is important that the meals should be eaten at
regular periods from day to day. For the stomach, with its
times of work and of rest, naturally contracts regular habits,
a disturbance of which is injurious. This obedience to habit
in this organ is manifest whenever any change is made in
the time of eating.
622. The question is often asked, whether such and such
an article " is healthy," as if there were essentially different
degrees of suitableness in different articles of diet. So far
as digestion is concerned, any article is healthy to any in-
dividual whose stomach can digest it without difficulty. An
article may be perfectly healthy to one, and unhealthy to
another. There are sometimes wide differences in this re-
spect, owing to unaccountable peculiarities. But even in re-
gard to ordinary differences, the question as to the propriety
of any article of food is wholly an individual question.
623. Our food should be varied in the different seasons
of the year to a greater extent than is commonly done. In
the warmer seasons it needs to be less stimulating, less heat-
producing than in the colder seasons. The fruits, each in
its season, should form regularly quite a large proportion
of our food in the warmer months. If used thus, and not
irregularly, as is commonly the case, they will tend to pre-
vent, rather than induce, the complaints peculiar to that
portion of the year.
624. The state of the mind has much influence on the
digestive organs. This is sometimes strikingly exhibited in
the loss of appetite on the sudden reception of bad news.
It is also seen in the influence of continued sorrow upon the
appetite and the digestion. It is not strange, then, that one
of the prominent causes of dyspepsia is mental disturbance
or depression. And a cheerful mind is very properly
deemed to be essential to easy and thorough digestion.
625. In order to understand fully the hygiene of respira-
tion, it must be borne in mind, that the great object of this
function, as stated in 131, is to bring the air into all the
minute air-oells of the lungs, that it may change the blood
394: HUMAN PHYSIOLOGY.
Compression of the chest. Importance of a good supply of pure air.
which is sent there for this purpose. Anything, then, which
interferes with the free introduction of the air into these
cells is a palpable violation of the laws of health. And yet
this interference is so commonly practised, that it is one of
the prominent causes of disease.
626. This interference is effected in two ways. It is done,
first, by mechanical compression of the chest. Although,
as I have shown in the chapter on the Respiration, there
are special pains taken by the framer of our bodies to pro-
vide, in the construction of the chest, for the free introduc-
tion of air into the lungs under all circumstances, this is
often prevented by certain prevalent modes of dress. It
must be observed that in the arrangement of the chest, a
free motion of its walls in the expansion of the lungs is con-
templa.ted. The dress, therefore, should always be so loose as
to admit of this free motion. If it is not, the air is not freely
admitted to all the air-cells, and therefore the blood is not as
fully changed, as nature requires ; and the health is impaired
just in proportion to the degree in which the due expansion
of the chest is prevented. I have said so much on the re-
sults of this compression of the chest in the chapter on
respiration, both in this book and in my " First Book on
Physiology," that I will only say here, that in this country
it is one of the most prominent causes of disease among
females. It not only produces disease in the lungs, but, by
preventing these organs from effecting fully the requisite
change in the blood, it impairs the quality and lessens the
quantity of this building material, and thus diminishes the
nutrition and the vigor of the system, and therefore renders
it liable to a great variety of diseases, especially those of
which debility is a prominent characteristic.
627. The free introduction of pure air into the lungs is in-
terfered with, secondly, by cutting off its supply. As you
learned in the chapter on respiration, the oxygen of the air
is used up in large quantities by the lungs, and the carbonic
acid gas thrown off takes its place. If, therefore, there be not
sufficient provision for the supply of fresh relays of pure air,
a mixture of air and carbonic acid gas will be introduced
into the lungs at every breath, so that there will not be
sufficient oxygen to effect thoroughly the change in the
blood. In this respect, therefore, the result is the same as
when too little air is admitted by reason of compression of
the chest. A portion of the requisite quantity of pure air
HYGIENE. 395
Bad results of defective aeration seldom appreciated. Hygiene of the circulation
is shut out, irf one case by diminishing the capacity of the
chest, and in the other by having the lungs in part occupied
by carbonic acid gas.
628. The influence which this defective aeration of the
blood, occasioned by these two causes, exerts upon the
health, is seldom appreciated. For unless the deficiency be
very great, no immediate obvious result is produced. But
though the deficiency may be comparatively small, if it be
continued from day to day for a long time, the aggregate
result of this steady depressing influence is a serious one.
The destruction of health and of life that comes from this
imperceptible agency in every community is vast in amount.
But most persons seem to be insensible to this fact. They
need a narrative of such a destruction of life as occurred in
the Black Hole at Calcutta, to convince them that a consider-
able quantity of fresh air is required by every pair of lungs.
And it is only by a description of an examination after
death of some one who has been killed outright by extreme
compression of the chest, that they can be made sensible of
the need that the lungs have of the room that nature has
given them. And even then the impression seems to be a
momentary one. If all the injury that is done by defective
aeration of the blood could be visibly traced out, we should
then realize the necessity of having just as many of the
air-cells, those little chemical laboratories, as nature de-
signed, and of keeping them well supplied with the fresh air
which they require for the life-giving work that they per-
form.
629. The hygiene of the circulation need not detain us
long. The office of the organs of the circulation is to circu-
late the blood, the building material, everywhere. They
never rest from their work. But they work more actively
when the muscular system is in action than when it is at
rest. As one lies in bed, the circulation goes on steadily,
but quietly. But on rising and moving about, the circula-
tion becomes more active. Not only does the heart beat
more quickly, but the capillaries in every part of the body
increase their action. And, as more blood is carried to
every part, there is more done everywhere. We see this
in the skin, in the increase of the perspiration on exercise.
When the muscular effort is very great, the excitement of
the circulation is violent and tumultuous. The heart beats
strongly and rapidly, and tbe flushed face shows how
HUMAN" PHYSIOLOGY.
Exercise necessary to health.
active is the circulation in its extreme vessels, the capil-
laries.
630. The occasional excitement by active exercise is
absolutely essential to the proper development of the body.
It may sometimes, indeed, maintain its proper bulk in a con-
tinued state of muscular inaction ; but its textures will not
have the requisite strength and tone. That they may have
these qualities, it is necessary that the blood be often pump-
ed into their capillaries with the force that is given to the
heart by active exercise. It is not the muscles alone that
are rendered stronger and firmer by exercise, but the same
effect is produced in all the textures, the bones, the liga-
ments, the veins, the skin, &c. The great internal organs
of the body are firmer, more fit to perform their duty, and
less liable to disease, if the circulation in them is excited
daily by this means. Active exercise makes the stomach
digest better, the lungs perform the work of aerating the
blood more thoroughly, and the brain serve the mind more
easily and effectually ; it therefore renders one less liable to
dyspepsia, to consumption and other diseases of the lungs,
and to apoplexy and other diseases of the brain and the ner
vous system.
631. But the activity of the circulation may be made sc
violent by exercise as to do some damage. Though its or
gans are capable of bearing much in this respect, there is
some need of caution. Harm is undoubtedly often done i
trials of strength when the effort is both violent and prolong-
ed. Vigorous action answers fully the purpose of developing
power and firmness ; but violent action is attended with some
hazard.
632. In considering the hygiene of formation and repair,
it must be borne in mind that there is constant change
everywhere in the system. Particles that have become
useless in the textures are continually taken up and carried
away in the veins or the lymphatics, and other particles are
put in their places, being taken for this purpose from the
blood in the capillaries. This change is going on during all
the period of growth, as well as afterwards. The health
and vigor of the textures, and therefore of the system as a
whole, are dependent upon the proper performance of this
constant process of removal and fresh supply.
633. There are two conditions necessary to the due per-
formance of this process. The first Vs, that the blood, the
HYGIENE. 897
Necessity of a free discharge of the -waste. Functions of the skin.
universal material for building and repairing, shall be of
good quality. This is secured when the digestive process,
which furnishes the blood, is well performed, and the lungs
and other organs, that purify the blood by discharging its
refuse matter, are in good condition. The second condition
is, that the blood shall be often quickened in its course
through the organs by the excitement of exercise. This I
have already mentioned in speaking of the hygiene of the cir-
culation.
634. The . necessity of having the waste matter that is
brought back from all parts of the body in the venous blood,
effectually discharged by the various organs designed for
this purpose (178), requires a particular notice. The lungs,
the skin, the liver, the kidneys, &c., must thoroughly eva-
cuate this waste, or its retention will impair the quality of
the blood, and thus interfere with the proper nutrition of
the body, or, in other words, with the process of formation
and repair. And the retention of this refuse in any consid-
erable amount is immediately productive of disease.
635. The lungs, while they take in oxygen from the air,
discharge carbonic acid gas, that part of the waste of which
it is their duty to rid the system. If this carbon be retain-
ed, the blood is impure in proportion to the degree of reten-
tion.
636. It is the duty of the skin to discharge some portion
of the refuse of the system in the sensible and insensible
perspiration (180). The skin is not a mere covering of
the body, but it is also an active organ, performing very
important functions. It continually discharges through its
numberless pores a large quantity of matter. Although
this matter is mostly in an insensible form, if from inactivi-
ty of this organ it fail to be discharged, its retention renders
the blood impure, and so does injury to the system. At
least two pounds of matter are discharged from the skin in
twenty -four hours. This being the case, it is not at all won-
derful that activity of this organ should be so necessary to
health, and that the suspension of its secretions should have
so much influence in the production of disease.
637. In the chapter on respiration, you learned that the
heat of the body is produced by the change that takes place
in the blood in the capillaries, as it receives the waste par-
ticles, and as the new are deposited in their places. This
change makes a real combustion in every capillary. The
34
398 HUMAN PHYSIOLOGY.
Animal heat. Conditions. Body comfortable only when giving off heat.
more rapid therefore is the change the greater is the com-
bustion, and of course, the greater is the heat. Hence comes
the increased heat of exercise. Exercise makes more wear
and tear, and so disengages in the waste more carbon and
hydrogen to unite with the increased amount of oxygen that
comes in the quickly flowing blood to the capillaries ; and
just as in combustion that is attended with flame, the great-
er the amount of fuel the greater is the heat. We have a
familiar example of the production of heat by exciting the
circulation, in the expedient often resorted to by laborers
for warming the hands, of striking them with a swinging
motion upon the shoulders.
638. The amount of heat produced in the body depends
also on the quality of the blood. The richer it is, the more
oxygen it contains, and therefore, the brisker is the fire in
the capillaries, and the greater is the heat. You see then why
it is that those who have a good state of the blood, and ex-
ercise much, maintain the heat of the system better, and so
need less clothing than those whose blood is weak, and who
exercise but little.
639. The heat of the body is maintained in all temperatures
of the atmosphere very nearly at 98 Fahrenheit. This is,
you observe, much above even the highest temperature that
is agreeable to us. You see then that it is essential to the
comfort of the body that it be giving off heat continually to
the surrounding atmosphere. If the atmosphere be at 98,
the same temperature with the body, there is great discom-
fort, from the fact that the heat is given off too slowly. It
would not be parted with at all if the skin were not an ac-
tive organ. It is by the evaporation of the perspiration
thrown off by the skin that the extra heat is got rid of when
the air is so hot. The temperature in which the body is
generally most comfortable is about 70. When the atmos-
phere goes below this, we need the ordinary expedients to
prevent a too rapid escape of the heat from the body. The
clothing and the heated air, with which we surround our-
selves to guard against the cold, do not act by communica-
ting heat to the body, but simply by retarding its escape.
640. Cold is a depressing agent, and exerts as such much
influence in the production of disease. Statistics show this
in a striking manner. The statistics of London, for example,
prove that the mortality of a severe winter is much greater
than that of a mild one. And this difference is found to be
HYGIENE. 399
Means of guarding against cold. Principles to be observed in using them.
chiefly among the very young and the very old, because in
them the power of generating heat is feebler than in other
classes. The greater is this heat-producing power in the
system, the better does the system resist the depressing in-
fluence of cold. All those means, therefore, which promote
the vigor of the body, are the best of the safeguards to be used
against this productive cause of disease and death. But,
besides thus fortifying the body internally against this
depressing agent, we have the means of outer defence alluded
to in 639, clothing and heated air. As there are many
errors committed in using these, they require a more parti-
cular notice.
641. Clothing serves, as I have before said, to shut in
partially the heat which is generated in the body. Its
amount and character should be regulated by two circum-
stances the degree of the cold, and the amount of heat-gen-
erating power in the system. The vigorous require less
clothing than the weak, because they have more of this power;
so, also, the body needs less clothing when it is in exercise
than when it is in a state of rest, because in exercise it gene-
rates more heat. And the same principles apply to heated
air, for this is an outer covering for the body, interposed
between it and the cold, like clothing, for the purpose of
preventing the too rapid escape of the heat generated
within.
642. These plain principles are violated in various ways.
Many, from carelessness or from mistaken notions, are often
unnecessarily exposed to the depressing influence of cold.
They are not sufficiently aware of the necessity of guarding
so much more thoroughly against the cold when at rent than
when exercising. And then, on the other hand, they add to
the effect by having too much clothing when in action, or when
in a warm place. When they thus suffer first from too
much heat, an after exposure to cold is exceedingly inju-
rious. The weak especially suffer from exposure to cold
when the body is at rest, and therefore, they should take
special pains to guard themselves against this depressing
agent. Any attempt on their part to harden themselves, as it
is expressed, by making use of as little clothing as the vigor-
ous wear, particularly when the body is in a state of inaction,
always does harm. The very thin coverings so commonly
seen on the feet of delicate females are palpably inconsistent
with this rule of hygiene, and are in ridiculous contrast with
400 HUMAN PHYSIOLOGY.
Cold sometimes a stimulant. Conditions on which reaction depends.
the stout coverings considered necessary for the feet of
rigorous men. Various opinions have been expressed in
regard to the warming of houses, so much in vogue at the
present day. On the principles developed above, this ex-
pedient for comfort is favorable to health if it be judiciously
managed, for when the body is at rest, as it commonly is in-
doors, an exposure to cold is depressing, that is debilitating
to the vital powers. Many other points might be noticed
in the application of the general principles mentioned, but
these will suffice.
643. The depressing influence of cold sometimes produces
a marked immediate effect. But this is not generally the
case. Commonly no harm is apparently done at the time,
and so little is thought of it. But if this influence be con-
tinued day after day, its effects accumulate and become estab-
lished. The vigor of the system is more or less destroyed,
and some local disease may make its appearance. The
debilitating influence of cold is in this way a fruitful cause
of disease, not only in the abodes of poverty, but even
among those who have ample means of guarding against it.
644. Although cold is generally a depressing agent, it is
often indirectly a stimulating one. It is so when, in conse-
quence of its impression upon the skin, it excites what is
termed a reaction. Several circumstances are necessary to
this result. 1. There must be the power of reaction in the
system. There may be so much debility that reaction can-
not be awakened. 2. If the system be in a state of rest, the
application of cold must be temporary. A continuous
application of it would be depressing, and would forbid reac-
tion. 3. In an active state of the body, reaction may be pro-
duced even when the application is continuous. Thus the
mere exercise of dressing may suffice to awaken reaction in
a degree of temperature which would chill one through if he
were sitting still.
645. The system may be accustomed to react under the
impression of cold in two ways. 1. By exercise in the
open air in cold weather. Those who have but little out-
door exercise in cold weather, have but little power of re-
action, and therefore feel the depressing influence of the cold
whenever they are exposed to it. 2. By a judicious use
of cold bathing. The object of cold bathing, aside from
purposes of cleanliness, is to accustom the system to react
under the influence of cold. It is only when reaction occurs
HYGIENE. 401
Cold bathing. To be used variously in different cases.
under its use that it does good. It does positive harm when
reaction does not occur ; and the harm done in this way
day after day, by depressing the vital powers, is sometimes
at length ruinous to the health.
646. There is a want of proper discrimination in many
writers on hygiene in regard to cold bathing. It is a mis-
taken ultraism to say, as is often said, that the preserva-
tion of health requires that the whole body should be bathed
every day in cold water. Neither cleanliness nor the other
purpose that I have mentioned ordinarily requires so frequent
and thorough bathing as this. The water may be applied
to only a part of the body at a time, and yet accomplish all
that we wish. Indeed, some persons of delicate constitution
cannot bathe the whole surface at once with cold water.
They may at first be able to apply it to only a small part of
the body. But they may, with the aid of friction, after a
while come to apply it over a considerable portion of the
surface, or perhaps over the whole. In some persons this
extension of the limits of the bathing from day to day must
be done very cautiously ; and there is occasionally one that
cannot bear it at ail over any considerable extent of surface.
It is necessary for some, in accustoming themselves to cold
bathing, to begin with using tepid water, making it from
day to day a little colder.
647. The best time for cold bathing is commonly in the
latter part of the forenoon, for the system is then in its
most vigorous state, and is therefore best prepared to re-
act. But in most persons reaction can be secured at the
hour of rising, and this is the most convenient time for
bathing. Few can use the cold bath with profit in the latter
part of the day, for the powers of the system are then more
or less exhausted, and full reaction is not easy. The sooth-
ing influence of the warm bath is appropriate at that time.
There are many other points in regard to bathing that might
be noticed, but my limits will not permit it.
648. Thus far I have spoken mostly of the hygiene of the
body as a structure. But digestion, the circulation, &c, are
engaged in constructing and repairing organs for the use of
the mind. In this use, there is wear and tear, and hence is
the necessity of seasons of rest, that the needed daily repaif
of the organs may be effectually done. The mind uses the
muscles and bones for motion, the various organs of the
senses in gaining a knowledge of the world around, and the
34*
402 HUMAN PHYSIOLOGY.
Exercise necessary to the development of both the muscles and the other organs.
brain in thinking, willing and designing. Any of these
organs may be overworked, and after a certain amount of
work has been done, there needs to be an interval of rest
for repair. The repair is going on continually, while the
organs are at work ; but it cannot be done thoroughly with-
out these intervals of rest. Most of the repairing is done
in these periods. This simple statement suggests the prin-
ciples of hygiene in regard to the uses which the mind
makes of the organs of the body. These I propose now to
develop briefly in regard to the muscles, the senses, and
lastly the brain.
649. There is a certain amount of muscular exercise
which is essential to firm health. While no one can fall
below this amount without impairing the healthy vigor, the
laborer goes much beyond it without injury. There is a
wide range, therefore, in the amounts of muscular exertion
that are consistent with health.
650. The exercise of the muscles is necessary to their full
development. When a limb fails to be used, as for exam-
ple in palsy, the muscles become small and lose their firmness.
When, on the other hand, the muscles of any part of the
body are much used, they become more developed than the
other muscles. For example, the labor of the blacksmith
develops the muscles of his arms largely. The same thing
is true of the muscles of the leg in the rope-dancer. It is
only a general exercise of all the muscles of the body that
develops them in all parts of the frame in their due propor-
tion.
651. But muscular exercise is also necessary to the pro-
per development of the other textures as well as the muscles.
I have already remarked upon this in another connection
( 630), and shall not dwell upon it here. There is, however,
one illustration of this influence of exercise which deserves a
particular notice. I refer to its influence in preventing de-
formity. In the universal vigor and firmness of the textures
which free exercise tends to produce, there is ordinarily a
precise equality between the two halves of the body : the
muscles on the two sides act with equal power; the spinal
column, the grand pillar of the trunk, is held between the
muscles that bind its twenty-four bones together with great
exactness, and there is a beautiful symmetry in the whole
frame. But when, from lack of exercise, there is want of
firmness in the textures, this symmetry is apt to be lost
HYGIENE. 403
Deformity of the spine why more common in females than males.
during the development of the frame, and the spinal column
is especially apt to become deformed.
652. There are two immediate causes of this deformity,
viz. : irregular muscular action, and irregular pressure.
Weakened muscles are prone to act irregularly ; and struc-
tures that have lost their firmness, readily yield to any
pressure that is laid upon them. When there is firmness of
texture, irregularities of pressure are not apt to produce de-
formity, because the elasticity prevents the permanent in-
fluence of such pressure. The moment the pressure ceases,
the elasticity of the part restores it to its usual shape. The
firm regular action of the muscles also tends to the same
result. Thus, in the case of the spinal column, if the
posture of the body be such that it is bent over to one side
for some time, the moment that the posture is altered, the
elastic cartilages resume their usual shape which has been
temporarily changed by the unusual pressure, and the mus-
cles also that lie along this pillar of bones bring them at
once to their right position. But if the cartilages have lost
in some measure their elasticity and the muscles are weak,
this righting up of the spinal column is not fully accomplish-
ed ; and a succession of slight failures in this respect will
after awhile, produce a permanent deformity in the direction
of the most commonly assumed posture.
653. You can see all this exemplified if you observe the
difference between males and females in regard to deformity
of the spine. This deformity is exceedingly common among
girls, while it is rare among lads. The simple reason is, that
lads have the invigorating influence of free out-door exercise.
Too much influence is attributed to posture in producing this
deformity. Posture is often spoken of as being the chief
cause of it, and this view of the subject is illustrated exten-
sively with cuts, showing how the deformity is- occasioned. If
this were the correct view, there should be much less deform-
ity among girls than among boys in our schools, for the form-
er sit in a crooked posture much less than the latter do.
So far as posture does have an influence, it is quite clear that
the prim, fixed posture enjoined upon the girl has a tendency
to produce deformity, by adding to one of the causes from
which it proceeds, viz., the weakness of the muscles. A fixed
uniform posture wearies the muscles, but variations of posture
relieve them, and so prevent an exhaustion of their power.
654. The muscles of the back in the female are not only
404 HUMAN PHYSIOLOGY.
Exercise should be varied and general. Gymnastics and Calisthenics.
weakened in common with the other muscles by a want of
stirring out-door exercise, but there is a special cause of
weakness in their case. The tight dress of the girl prevents
these muscles from having that free action which the loose
dress of the boy permits. You can see this in the difference
of movement in the two cases. In the boy, the spine is bent
and twisted in all directions freely ; but in the girl, both
custom and the stiff tightness of the dress require a move-
ment almost as if the spine were a single bone, instead of
being made up of twenty-four bones. The muscles in her
back, therefore, lose their power and fulness just as the un-
used muscles of a palsied limb do.
655. Variety should be aimed at in the action of the mus-
cles. A continuous action of any set of muscles is weari-
some and painful. This is well exemplified in the punish-
ment once much in vogue in schools, of making the of-
fender hold a book out at arm's length for some time. In
the management of the muscles of the voice, the weariness
caused by continued sameness of action is often experienced.
The monotonous speaker or reader tires out these muscles
much sooner than one who has great variety in his tones.
For remarks on this and some other kindred points, I refer
you to 382 and 383.
656. A general exercise of all the muscles is essential
both to symmetrical muscular development, and to the full
attainment of the invigorating effects of exercise. Gymnas-
tics and calisthenics, so called, are considered to be particu-
larly beneficial in this respect. This is true of them ; and
yet they are no better than any other exercises that are so
varied as to bring the muscles generally into action. The
varied exercises of walking, running, leaping, riding on horse-
back, dancing,.and active sports, are quite as good. And so
also are the varied labors of the garden, if they be pursued
with interest and pleasure. There is no especial benefit
in the extreme variety of exercise sometimes aimed at in
gymnastics. Variety that is sufficient to bring into general
action the muscles of the body is all that is requisite.
657. Gymnastics and calisthenics should always be con-
sidered as subsidiary to the common exercises that I have
mentioned, and should never be permitted to exclude them.
When they are made to do this, a temporary benefit is reap-
ed at the expense of a permanent injury. For after the
novelty of the round of exercises has passed away, they
HYGIENE. 405
Effect of too severe exercise. Hygiene of the Senses.
are given up, and the common and now despised exercises
are not apt to be resumed. Habits of inaction, therefore, are
often confirmed, instead of being removed, by a systematic
course of exercises under the high-sounding names of gym
nasties and calisthenics.
658. It is necessary that some of the exercise taken should
be such as to excite strongly the circulation. This I have
already remarked upon. Exercise should also be taken
daily. It should be habitual, and not occasional. The habits
of the English are much better than those of the Americans
in this respect. It is no uncommon thing for English ladies
to walk off on excursions of such length, that American
ladies could not possibly accompany them unless they rode.
659. But there may be too much exercise. The toil of
the laborer may be so severe and long continued, that the
reparative process in the intervals of rest is not competent
to effect a full repair of the muscles. A gradual exhaustion
of their power therefore results. Much harm is thus often
done by severe unremitting toil. Especially is this the
case when the excess of toil is exacted during the period of
growth, as it often is among the laboring poor.
660. It is necessary that exercise should be agreeable in
order to produce its best effect on the system, on account of
the genial excitement which then accompanies it. For this
reason exercise should commonly not be solitary, and there
should, if possible, be some object connected with it. If the
observation of nature were made from the beginning of edu-
cation as prominent as I claim in my Preface that it should
be, there would be no lack of objects in the rambles in
field and forest taken both for health and the pursuit of
science.
061. What has been said of the muscles may be substan-
tially said of the organs of the senses. They require inter-
vals of rest for thorough repair. And they may be so over-
worked that complete reparation may be impossible, and so
their power may be gradually exhausted. The office of the
senses is to receive impressions from things around. What-
ever gives an impression to any organ of sense may be re-
garded as a stimulus to it. If the stimulus be too great
or too long continued, injury is done. This is very obvious
in regard to the eyes. They are often injured by too much
light. A word of caution is needed in regard to the produc-
tion of near-sightedness. This is often caused in students
and others by holding objects too near the eyes.
406 HUMAN PHYSIOLOGY.
Necessity of seasons of rest to the brain. Overworking the brain.
662. I come now to the hygiene of the brain. This is the
great central organ or instrument of the mind, by which it
receives the impressions made upon the senses, compares
and arranges the knowledge thus gathered, and originates
those impressions that are made by it upon the world
around through the action of muscles. It is a very com-
pound instrument. It needs, like the muscles, seasons of
rest for the full repair of the wear and tear occasioned in its
daily use. It may be overworked, and then the repair will
not be complete, and gradual exhaustion of its powers will
result, occasioning disease in some form. A significant illus-
tration of the importance of seasons of rest for repair in the
case of the brain is furnished in the fact, that insanity is not
apt to result from mental disturbance, unless the subject of
it fail to have his regular sleep. If he sleeps well, the work
of repair is so well done in the brain in its nightly seasons
of rest, that the disease, which might otherwise occur, is
prevented.
663. With proper intervals of rest, the mind can perform
a large amount of labor without injury to the brain and ner-
vous system, if there be no undue excitement, and no wor-
rying and depressing anxiety. This is shown in the length
of life that so often accompanies the quiet but laborious
pursuits of science. While, on the other hand, the excite-
ment and anxiety of a life of business, especially as it is
ordinarily pursued in this country, it is well known, is not
favorable to longevity.
664. It is especially important that the brain should not
be overworked during the period of its growth. The reason
is the same as that which we have for the caution, so univer-
sally observed, in regard to putting too much labor upon
the muscles of a young horse. And yet there is buoyant
activity in the child, which is disposed to show itself in the
operations of the brain as readily as in the action of the
muscles. If this activity be turned into proper channels,
and be not too much stimulated, no injury will be done to
the delicate textures of the brain.
665. Although much is said of the danger of over-stimu-
lating the brain of the child, the difficulty does not so much
lie here, as in the manner in which the mind is led to act.
There is commonly too much of mere drudgery, and of
storing the mind with unintelligible, and therefore uninter-
esting matters. The mind, accordingly, is dissatisfied and
HYGIENE. v 407
Influence of quiet cheerfulness. The passions. Alcoholic stimulants.
wearied. The tedium of the labor exhausts, and so the
brain is essentially impaired. When early education shall
become in all respects what it ought to be, greater real ac-
quisitions will be made than we witness now, without any
injury to the growing brain.
666. It is well known that undue mental excitement and
the depression of anxiety are together apt to produce insanity.
Though they generally stop short of this result, they always
injure the health and shorten life. A firm and cheerful mind
is favorable to longevity, but the anxious and fretting are
seldom, if ever, long-lived.
667. As the passions must have much influence upon the
action of the mind, and therefore upon the state of the brain
and nervous system, the proper regulation of them is essen-
tial to health and longevity. Much of the positive disease
of the brain, and of the general nervous derangement so
common among the educated and refined, comes from the
bad management of the passions. I cannot dwell upon this
point, but remark, in passing, that the fictitious literature
of the present day exerts a considerable influence in this
way.
668. There are certain articles in common use in the
community, which produce so deleterious an influence upon
the system, that they demand a more extended notice than I
can give them in this chapter. I refer to alcohol and
tobacco. They act chiefly upon the brain and nervous
system, the former as a stimulant, and the latter as a seda-
tive. The use of opium is so limited compared with these
that I shall not dwell upon it, especially as it is never de-
fended.
669. No fact is more thoroughly demonstrated than that
the system has no need of alcoholic slimulants while it is in
a state of health. So far then as we look at mere necessity,
these articles are to be considered simply as medicines, re-
quired only in diseased conditions. But it is said by some
that they can be used in small quantities without injury to
health. This cannot be claimed with any shadow of reason,
unless in relation to very small quantities. Entire absti-
nence is at least safe, and there are so many other things
supplied by a bounteous Providence to gratify the taste and
the appetite, that we can easily forego the use of alcoholic
stimulants; and we ought to be willing to do so, if the good
of others require it. The common use of these articles as
408 HUMAN PHYSIOLOGY.
Tobacco an active poison. Coffee and Tea the propriety of their use not settled.
beverages is one of the most prolific of the sources of disease ;
and it is a significant fact, that the very moderate use, claim-
ed by some to be innocuous, has a strong tendency to pass
into a larger use, even so large that, its deleterious influence
upon health is palpable.
670. The evidence is quite as clear in relation to the inju-
rious effects of tobacco. This has sometimes been erroneous-
ly termed a stimulant. The error arises from the well-
known discomfort of the habitual user of it when he is depri
ved of the use of this drug. This discomfort has a depress-
ing influence, and when his system is brought again under
the influence of tobacco the depression is removed, not by
any direct stimulating effect, but by the relief given to the
uncomfortable sensations. Tobacco is really one of the
purest sedatives we have. It depresses vital action. It acts
chiefly upon the nervous system, and therefore, has a strong
tendency to produce nervous diseases. While it is injurious
to all, it is especially so to those who have a low vital action,
and are disposed to nervous complaints.
671. Tobacco is so active a poison that extreme caution
is required whenever it is administered, as it sometimes is,
as a medicine. The effects of even a small amount of it upon
one that is unaccustomed to its use are of the most decisive
character. And that must be an exceedingly artificial con-
dition of the system, in which, by continued use of this drug,
large amounts come to be borne with little apparent effect.
The evidence of the deleterious influence of tobacco upon the
system is as unequivocal as that which we have in regard to
the influence of opium, and wonderfully strong is that sla-
very to appetite that makes one persist in the use of this drug
in spite of such evidence.
672. Coffee and tea are often included in the same cate-
gory with alcohol and tobacco. Granting all that is claimed
in regard to the injurious effects of these articles, it is pre-
posterous to class them with such poisons. The evidence in
regard to them is conflicting, and all that is settled as yet is,
that in some persons they exert a bad influence upon the
nervous system. If this should be found to be true of a
very large proportion of all who use them, the evidence
would be conclusive against the propriety of their use as
common beverages. But as yet this has by no means been
proved to be true.
673. There are certain coisonous emanations, to which
HYGIENE. 409
Poisonous emanations. General view of the causes of disease.
the human system is often subjected, that are largely de-
structive of health and life. They arise from decomposing
filth of various kinds. Besides predisposing the system to
the action of contagious and epidemic causes of disease, they
also of themselves create disease. It is these emanations
that render the close air of a crowded city, especially in its
narrow lanes, so impure and fairly poisonous. And this
impurity of the air is one of the chief causes of the difference
in disease and mortality between the city and the country.
The difference is greater than is generally supposed. It has
been found by statistics in England, that there are 24 per
cent, more deaths from consumption, and 55 per cent, more
deaths from typhus, in cities than in the rural districts, and
the mortality from the diseases of childhood is twice as great
in the city as in the country. In what way these emanations
act we know not. But, although much is to be attributed,
to a mere want of ventilation, that is, to a lack of oxygen,
there is no question that these emanation? often act as posi-
tive poisons to the system.
674. In developing the principles of hygiene, I have
noticed many of the prominent causes of ili health and dis-
ease. They are chiefly these: 1. A disregard in various
ways of the rules relating to the digestive process. 2. Com-
pression of the chest, especially during the period of growth.
3. Deficiency in the supply of pure air to the lungs. 4. Fail-
ure to guard properly against the influence of cold and
heat, chiefly the former. 5. A lack of active exercise in the
open air. 6. Overworking the muscles. 7. Errors in the
management of the moral and intellectual powers. 8. The
influence of such articles as alcohol and tobacco. 9. Emana-
tions from decomposing filth. It is well thus to look at
these causes grouped together, endeavoring to give to each
its due prominence. For various and exclusive views are
often taken of this subject. Quite commonly some of these
causes are kept entirely out of view, while others are strong-
ly pressed upon our attention. Disease is generally a very
compound remit, produced by a concurrence of several of
these causes, and sometimes even of all of them.
675. These causes of disease, it will be observed, are more
or less under our control. Some of them are entirely so.
A knowledge of their operation, and an earnest endeavor to
remove them, would, therefore, vastly diminish the amount
of ill health and disease.
35
410 HUMAN PHYSIOLOGY.
Our control over the causes of disease. Preventive and curative measures.
676. It is true that there are some other causes of disease,
of which we know but little, and over which we have little or
no control. Such are the causes of various contagious and
epidemic diseases. But these really produce a much less
amount of disease than the causes which I have mentioned.
Their action is occasional, and confined to localities ; not
continual, and in all places. And besides, they may to a
great extent be shorn of their power, by guarding against
those causes of disease which are more or less under our
control. It is tho?e who neglect to do this that commonly
become most readily the victims of contagions and epide-
mics.
677. There is much interest in the community in regard
to the cure of disease, but there is a blind indifference to its
prevention. And yet vastly more can be done in the diminu-
tion of disease by preventive than by curative measures. The
ravages of consumption, for example, can undoubtedly be
greatly lessened by preventing the operation of its principal
causes ; and yet what is said about these causes is little
heeded, and the public attention is engrossed with the
delusions of consumption-curers. It is emphatically true
of this malady, that multitudes more can be saved by
preventive measures than by curative ones. Against no
disease can hygiene achieve greater victories than this.
The neglect to use preventive measures against this and
other diseases arises chiefly from an ignorance of the prin-
ciples on which these measures are based. The prevalent
indifference, therefore, on this subject can never be fully re-
moved, till the general introduction of Physiology as a study
into our schools shall make these principles familiar to the
mass of the community.
APPENDIX :
CONTAINING
DIRECTIONS TO TEACHERS FOR THE USE OF THE BOOK,
AND QUESTIONS.
IN order to be able to teach from this book properly, the teacher should
himself study all of it thoroughly before he begins his instruction. If
he merely keep a little in advance of his class, he will fail in his concep-
tions of the general scope and plan of the book. If the interest of the
subject awaken in him and in his pupils a spirit of inquiry, there will
be a continual looking forward to points which are explained and illus-
trated further on in the book. Now if the teacher has made himself
master of all the subjects treated of, instead of turning off the inquiry
of a scholar without an answer, or even the promise of an answer in the
future, or endeavoring to clear up the points about which inquiry is
made, which of course he can do, under the circumstances, in an imper-
fect manner at the best, he can satisfy the scholar by informing him that
these points will be found explained in their proper place at a future
stage of the investigation. I have aimed to have every topic treated of
in its right place in the development of the general subject, and the
teacher should be thoroughly master of the whole book at the outset, in
order that he may fully carry out my plan in the mode of developing the
topics to the minds of his pupils.
It must be obvious to any teacher that he can teach the minutiae of
the subject with more of interest, to say nothing of thoroughness, if,
while doing it, he takes in the general views presented, and has in mind
the relations of the particular topics in hand to other branches of the
subject. Indeed it will be profitable occasionally for the teacher to
afford the scholar some glimpses of the interesting fields to be explored
further on, taking care, however, not to anticipate so much, as to mar the
natural method and order of developing the whole subject, which I have
taken such especial care to observe in the preparation of the work.
The teacher should read the book through in course. If, instead of
doing this, he opens to some chapter in the middle or latter part of the
book, he may get the impression that too high matters are treated of,
and that the minds of his pupils are not competent to understand them.
They cannot be understood unless there be a preparation of mind for
them ; and just this preparation is aimed at ii; the first part of the
book. And besides, ii is quite important that the subjects treated of
412 APPENDIX.
should be developed to the mind of the teacher in the same order m
which they are to be developed to the minds of his pupils.
In the engravings clearness has been aimed at rather than beauty.
Yet I should not do the engraver justice if I did not say, that in beauty
they are generally quite equal to those which we find in our standard
professional works on physiology. It is to be borne in mind that wood-
cuts cannot represent correctly the beauty and delicacy of living struc-
tures. These can be realized only by seeing the structures themselves.
Another thing to be kept hi mind is, that parts which are represented in
engravings with definite lines for the sake of distinctness, are ordinarily
not thus distinct in the structures. To make them so, the dissecting-
knife must separate them, and take off the cellular substance, which, as
the general packing material of the body, everywhere connects adjacent
parts together.
The teacher can be aided very much in giving his scholars a correct
idea of different organs, by presenting to them organs taken from the
bodies of animals. Thus, in giving them an idea of the lungs, the
lungs of a calf or a sheep can be used. A pipe may be fastened into
the windpipe ; and by blowing into this, you can show how the lungs are
inflated. An idea of the appearance of the human brain can be given by
means of the brain of a calf, or any other animal of sufficient size.
An ox's heart may be used in showing the structure and arrangement
of the valves and other parts of that organ, for they are essentially the
same as in man. A very good idea of the arrangement of the cartilages
that make up the larynx, can be obtained from the larynx of an ox or
cow. The general shape and arrangement are the same as in man. It
is some trouble to clear the parts of -muscular substance, but the teacher
can get some physician or medical student to do it for him. When the
preparation is once made, it tan be dried for permanent use. I have one
which I made twenty-five years ago. In drying, it will be necessary to
keep the wings of the thyroid cartilage apart by a wedge, and the
supple epiglottis must be placed in such a position as not to interfere
with a view of the interior of the larynx. The large eye of the ox can
be made use of to show the various parts of that organ, and also to
show the formation of the images of objects on the retina.
One great advantage of thus using parts from different animals is,
that a taste is given for the examination of the phenomena of life, with
its wonderful mechanisms, wherever they may be seen. All living na-
ture thus becomes full of suggestive interest to the young student.
There are some things of which plates can give no correct idea.
Such, for example, is the cellular membrane. The attempt to represent
it is made in most books on physiology, but it is an entire failure.
I have a plate representing its cells as seen in a dried preparation under
the microscope ; but to give the scholar an idea of it as it appears to the
naked eye in its natural condition, I refer him to it as seen in any com-
mon piece of meat between the muscles and between the fibres of each
muscle. The teacher can use a piece of meat for this purpose. The
difference between muscles, tendons, and ligaments can be shown in the
same way.
Those figures which are mere diagrams it will be well for the scholar
to draw on the blackboard, and his skill in description and remark may
be exercised for his own benefit and for that of the class. He should
APPENDIX. 413
be trained in this exercise in such a way, that he will acquire the power
of giving well-proportioned and well-arranged descriptions, without the
aid of prompting by minute questions from the teacher.
It will be proper to say something of the use which should be made
of the questions that I have prepared. I have two reasons for not
placing them at the foot of the page. One reason is, that the book
is designed for general reading as well as for instruction. But the
chief reason is, that I wish to prevent a too free use of questions on the
part both of teacher and scholar. The marking with the pencil of parts
which contain the answers to the questions, so often done in our
schools, should never be permitted by the teacher, for reasons that I
need not stop to notice.
The scholar should read the text at first without reference to the
questions ; and then the questions can be made use of, perhaps with
profit, to fix definitely in the mind the principal points that are brought
out. It will be a useful exercise for the scholar, after reading a page or
two, to think over the main points, and then see by the aid of the ques-
tions whether any important point has escaped his recollection, or failed
to make the proper impression on his mind.
The questions that I have constructed will, I think, be found to be
fitted to the great majority of scholars. But of course the teacher will
vary them to suit the different capacities and mental attitudes which he
finds in his class.
It is best not to have an uniform mode of asking questions, even with
the same scholar. Variety should be given to the mode of hearing the
recitation. Sometimes the questions should be minute, and at other
times the mind of the scholar should be left to go on with as little lead-
ing as possible.
The scholar should be encouraged occasionally to give the substance
of a whole paragraph, or even of more than this. In doing so, any
failure in arrangement or proportion can be noticed by the teacher, for
the benefit not only of the scholar that is reciting, but also of the whole
class. The general scope of an argument may also be given in the
same way, and the manner of doing it be made the subject of criticism.
The numbers attached to the questions refer to the pages, this being
more convenient to the scholar than a numbering by paragraphs wuoiu
be, though of course it cannot be quite as definite in all cases.
35*
414 APPENDIX.
QUESTIONS.
CHAPTER I.
13. In what respect are a crystal and a plant alike 1 How do they
differ in the modes of their formation 1 What different offices do the
organs in a plant perform 1 What is meant when we call the plant an
organized substance, and the crystal an unorga?iizcd substance 1
14. Do the organs in the plant act wholly on mechanical principles 1
Or on chemical 1 What principles control the mechanical and the che-
mical 1 What two classes are there of organized living beings 1 How
do they differ as to the complex character of their organization 1 Under
what two grand divisions do you class all the substances of the mate-
rial world 1 How do plants and animals differ from minerals as to the
parts of which they are composed 1
15. What is assimilation 1 Explain it as it takes place: First, in
the plant, and secondly, in the animal. How do organized and unor-
ganized substances differ as to permanency 1 Point out the mode and
the extent of the change that occurs in the organized.
16. Why is there more change in animals than in plants 1 How
can minerals be changed 1 Are they productive, as animals and plants
arel Contrast organized and unorganized substances in regard to
change in the phenomena that you see in the world around you.
17. How do organized and unorganized substances differ as to regu-
larity in form 1 What does irregularity in the unorganized arise from ?
How does the law of regularity operate in organized substances ?
Does the exactness which it sometimes shows appear in straight or in
curved lines 1
18. In which is the regularity the most wonderful, the organized or
the unorganized, and why 1 Give the four reasons assigned : First, as
to change ; secondly, as to variety of form ; thirdly, as to its continu-
ance from age to age ; and fourthly, as to its preservation in the midst
of a certain range of irregularity.
19. Exemplify the last point by reference to the human countenance.
How is the law of regularity exemplified in the two halves of the body 1
Mention some organs which are destitute of this symmetry ; mention
also some animals that do not exhibit it. What is the distinction
between organized and unorganized substances as to limit of size 1
20. How do organized and unorganized substances differ as to their
structure 1 How do they differ as to the number of elements of which
they are composed 1 What are the four principal elements of organ
APPENDIX. 415
ized bodies 1 Which one of these is solid 1 In what form are the other
three 1 ? How many elementary substances are there in the material
world 1 How many of these are found in plants and animals 1
CHAPTER II.
21. Point out the difference between the plant and the animal as to
locomotion. How does this difference make it necessary that the ani-
mal should have a stomach 1 Trace the analogy between the stomach
in the animal and the roots in the plant. What is the difference
between most animals and plants as to central organs 1 What is their
difference as to the effect of mutilation upon them 1
22. What is the distinction between animals and vegetables as to sen-
sation and spontaneous motion 1 Have all animals consciousness and
thought 7 Name some exceptions to the distinction as to locomotion.
What is the difference between the motions of such plants as the sensi-
tive-plant and catch-fly, and those of animals 1 Make the comparison in
relation to the hydra, which describe.
23. Can the distinction as to a digestive cavity always be made out 1
If it could be, should it be considered an essential distinction 1 What is
the really essential distinction between animals and plants 1 What part
of the structure of animals is peculiar to them 1 Has this structure
ever been discovered in any plant 1 Why ought we to be able to dis-
cover it in the sensitive-plant and catch-fly, if it were the cause of their
motions 1
24. Is the nervous system necessary to the carrying on of nutrition 1
What are the functions of organic life 1 W T hat of animal life 1 W 7 hat
is the order of action in the nervous system 1 In what respect is this
order not observed in some cases 1 Give some examples of instinctive
and automatic motion. How does the heart differ from the muscles of
breathing as to the influence of sensation and of the will on its action 1
25. What is the office of the central organs of the nervous system
in sensation and motion 1 In proportion to what is the chief central
organ, the brain, found developed! Describe in general the difference
in development between the nervous system and the system of nutri-
tion in different animals. Does the nervous system undoubtedly exist
in those animals in which it cannot be found 1
26. What reason have we to attribute to such animals the exercise of
thought, will, and consciousness 1 Illustrate by reference to the Hydra.
27. What is the distinction between animals and plants as to their
chemical composition 1 In which is carbon the characteristic element,
and in which is it nitrogen 1 From what organs in animals is carbon
thrown off? In what organs in plants is it absorbed"?
CHAPTER III.
27. How is man commonly classed in the animal kingdom 1 ? On
what ground can the classification be claimed to be correct 1 Does this
classification recognize at all the essential distinctions between man and
other animals 1 What are those distinctions 1
28. Should the received classification be considered as giving man hie
true position in the scale of being 1 What bearing has man's immor
416 APPENDIX.
tality on this subject 1 Is the difference between man and other ani-
mals like that which we see between different animals 1 Is it a mere
difference of degree ? What notice should the naturalist take of the
difference 1
29. What is the distinction made in the common classification
between man and such animals as apes and monkeys '! Can these animals
be properly said to have four hands 1 How do the hands which they are
said to have resemble the hand of man, and how do they differ from it !
30. What is said by Sir Charles Bell about the hand ! What by
Aristotle, and by Anaxagoras 1 State some particulars in which the
structure of man differs from that of the inferior animals.
31. What relation have the peculiarities of man's organization to his
mental peculiarities'? Why is it important that the essential distinc-
tions between man and animals should be prominently taught 1 What
is the theory of Robinet ?
32. What is the teaching of a true science in regard to the Creator's
agency 1 What is the theory of gradations in nature 1 What are the
objections fatal to this theory, as stated in 491
33. What are the real gradations in nature 1 Are these gradations
in each of the kingdoms regular 1 Is man inferior to some animals in
certain endowments] Give some examples. Is it strictly true that
man is the most perfect of animals 1 In what respect is there a grada-
tion in the three kingdoms of Nature 1 Is all Nature wholly tributary
to man 1
CHAPTER IV.
35. Of what advantage is it to the student, in studying human physi-
ology, to observe the analogies in the processes of life between man and
other living beings or things 1 What is the difference between Anatomy
and Physiology'?
36. What functions distinguish animals from plants 1 Into what two
classes of subjects is Physiology naturally divided 1 Remark on the
wide range of subjects presented in Physiology. In what respect does
this study differ from all others 1
37. Of what two parts is bone composed 1 What are the propor-
tions of these parts in childhood in adult age and in old age 1 How
can you obtain these parts separate from each other 1 What is the
animal part of bone! What relation does this sustain to the mineral
part 1 What is the arrangement of the two parts of bone in the very
young child ! What is true of the skeleton of many fishes 1
38. Mention some cartilages that never have any mineral matter
deposited in them. With what are the bones joined together! By
what are they moved 1 How do muscles act 1 What is the office of
the tendons 1 What is their structure 1 What is the most common
texture or tissue of the body 1 Why is it called areolar or cellular /
How can you get the best idea of this texture ] Mention its different
uses!
39. In what portions of the body is this tissue most abundant 1 ? In
what ways does the free communication between the cells of this tissue
become manifest to us 1 How is its elasticity affected by dropsy in it 1
40. What are the uses of the fat deposited in the cells of this tissue' 1
* APPENDIX. 417
What fact is stated in regard to hybernating animals 1 How is the fat
kept from oozing through the pores of its cells'! What cavities does
the mucous tissue line 1 How is the secretion of mucus effected ? What
is its chief use ?
41. What parts of organs are lined by the serous tissue 1 In what
important respect do serous membranes differ from mucous ! What is
the appearance of the serous membranes 1 How is dropsy produced in
them ? Are the organs of the body composed of many tissues 1 Take
the stomach as an example, and describe its structure. Give a
summary of the nutritive functions as described in 69.
CHAPTER V.
42. Give a summary of the processes of digestion.
43. Of what substances is the body of a tooth composed, and how
are they arranged? What are the different shapes of teeth, and for
what different purposes are they fitted 1 How do the teeth of carnivor-
ous animals differ from those of the herbivorous? How does the
motion of the lower jaw differ in the two classes 1
44. What is the shape of the teeth in the insectivorous 1 What in
the frugivorous 1 What is the peculiar arrangement of the enamel in
the teeth of the herbivorous, and for what purpose? What can be
inferred about an animal from an examination of his teeth'! Why is
man said to be an omnivorous animal 1 Why are his tearing teeth less
in length and in power than those of carnivorous animals 1
45. What has the common whale in place of teeth 1 What is the
purpose of the arrangement 1 What supplies the place of teeth in
birds ? What is the use of the saliva 1 Describe the situation and
arrangement of the glands that supply this fluid.
46. How much saliva is secreted by the salivary glands during a
meal 1 Why is more saliva than usual needed when one is speaking 1
What effect does motion of the mouth have on the secretion? How
are these salivary glands affected by tobacco-chewing ?
47. Explain the influence of sympathy in the secretion of saliva.
What are the two kinds of fluid secreted by the salivary glands, and
what is the purpose of each kind ? Describe the various parts engaged
in the act of swallowing, as represented in figs. 10 and 11.
49. Describe the arrangement of muscular fibres in the oesophagus.
50. What is the character of the gastric juice? By what is it
formed ? Describe the appearance of the mucous membrane of the
stomach, as seen by Dr. Beaumont, in the case of Alexis St. Martin.
To what is the amount of gastric juice proportioned ? What is the
effect of stimulating the stomach to too large a secretion of it from day
to day ? What is the nature of its action on the food ? How is the
application of it to all portions of the food secured ?
51. Describe the arrangement of the muscular fibres of the stomach,
and the manner of their action. What is the chyme ? What is the
arrangement of the valve called the pylorus ?
52. When is the pylorus especially in action ? If there be difficulty
in digesting the food, what is the effect on the action of this valve?
53. What are the different theories in regard to the process of diges-
tion ? What is the true character of the process ? What is the conso
34
4 I < Q APPENDIX.
quence if fresh food be introduced into the stomach while the process is
going on 1 Why is the practice of eating between meals a bad one 1
Why does eating fast, do harm! What effect has great variety in
food ] How does exercise affect digestion 1 Relate the experiment
with the two dogs, and state what it proves.
54. What shows that hunger does not arise from emptiness ! What
that it does not arise from the irritation of the gastric juice! What is
the cause of hunger 1 What is the seat of the sensation ! Upon what
does the degree of hunger depend 1 What must be the state of the
stomach to have this sensation exist 1
55. How do mental impressions sometimes destroy the sensation of
hunger 1 How does food remove it so much before any nourishment is
diffused through the system 1 What is the cause of thirst 1 Where is
its seat 1
57. Describe the arrangement of the digestive organs as seen in fig.
16. What are the uses of the mesentery! Where are the bile and
the fluid secreted by the pancreas mingled with the chyme 1 What is
one of the offices which they execute !
58. What is the chyle ! What are the lacteals 1 What glands do
they enter ! After passing on from these glands, into what duct do they
empty the chyle ! What is the size of this duct, and where does it
pour its contents !
59. Describe the operation of the suction power at the mouth of
the thoracic duct. What becomes of the chyle thus forced into the
blood ! Why is the mucous coat of the intestine full of folds !
60. What is the general rule by which the variation in the digestive
apparatus in different animals is governed ! Exemplify by a compari-
son between herbivorous and carnivorous animals. What is the length
of the alimentary canal in the lion ! What in the sheep ! What in
man ! In what animals is the stomach most complicated ! Describe
the apparatus of digestion in the sheep, and its successive processes.
62. W T hich of the four cavities in the sheep's stomach is the real sto-
mach 1 Into which cavity does fluid matter always go ! What is the
arrangement when the animal is suckling! Describe the digestive
apparatus of birds as exemplified in the turkey.
63. What circumstances govern the variations of the digestive
organs in different animals ! What is true of the stomach in the lower
orders of animals ! What peculiarity is there in the Hydra in regard
to its stomach !
CHAPTER VI.
64. What are the different parts of the apparatus of the circulation 1
Describe the agency of each in circulating the blood.
65. What relation does the heart bear to the rest of the circulating
apparatus ! What is the difference between the arteries and the veins
in their structure ! What two reasons are there for this difference \
What is the pulse !
66. How do the arteries and veins differ in the mode of their divi-
sion ! How does the venous system differ from the arterial in capacity !
How in regard to rapidity of flow of the blood ! Describe the valves in
the veins.
APPENDIX. 419
67. Why are these valves needed 1 Why is it more dangerous to
wound an artery than a vein ] Give some examples, showing how on
this account the arteries are seated more deeply than the veins.
68. Where are the arteries superficially situated, and why 1 Describe
the common mode of bleeding from the arm. What is the proper way
to stop bleeding from an artery 1
69. What is an aneurism] When a ligature is tied around the
artery above an aneurism in a limb, how is the limb to be supplied with
blood 1 What is the chief agent in the circulation of the blood 1 How
can you illustrate the contraction and the dilatation of the heart 1
70. What phenomena show that the blood-vessels exert an active
agency in circulating the blood 1 How does the circulation through the
liver show that the capillaries are active agents in circulating the
blood 1
71. Why are the veins generally full of blood after death, while the
arteries arc nearly empty 1
72. What is the origin of the term artery 1 Why do we not in com-
mon language speak of the blood as running in the arteries as well as
in the veins 1 When did Harvey discover the circulation of the blood 1
What is the color of the blood in the arteries ! What color has it in
the veins 1 Where is it changed from red to purple 1 What other
changes besides that of color take place 1 What would be the conse-
quence if the dark venous blood should be sent to the brain 1
73. Where is the change in the blood from purple to red effected 1
How is the apparatus arranged so as to send the purple blood to the
lungs to be changed 1 Explain the diagram showing the plan of the
two circulations.
74. W T hat is the difference in the two circulations as to the color of
the blood in the veins and the arteries 1 What is the difference betweer.
the change of the blood in the capillaries of the lungs, and that which
takes place in the capillaries of the general system 1 Describe the parts
of the right half of the heart as represented in Fig. 26.
75. Describe the manner in which the auricle and ventricle, with the
valves, act. Give the illustration as represented in Fig. 27.
76. What is the difference in size and strength, between the auricle
and ventricle 1 What is the size of the heart 1 Describe the arrange-
ment of the valves of the aorta.
77. Describe the special provision to prevent leaking in these valves.
How are the walls of the heart supplied with blood 1
78. Describe the valves between the auricles and the ventricles.
"Why are they regulated by muscles ?
79. W T hy are there no valves where the blood pours into the auricle
from the vense cavse 1 Describe the parts of the heart as represented in
Fig. 31.
81. Describe the circulation as given in the map of the heart in
Fig. 32.
82. Describe the situation of the heart and its blood-vessels, as repre-
sented in Fig. 33.
83. How do the four parts of the heart act without disturbance 1 !
What is the difference between the two sounds of the heart 1 What is
the cause of the first sound 1 What of the second 1 How is the pulse
produced 1 Explain the impulse of the heart against the chest.
420 APPENDIX.
84. Explain the plan of the pericardium.
85. Has the heart any repose 1 Give some calculations as to the
amount of work it does in a lifetime.
CHAPTER VII.
86. What two objects are effected by the respiration 1 Of what are
the lungs composed 1 To what is their spongy lightness owing 1 How
minute are the air-cells or vesicles 1 In what way is the change pro-
duced by the air in them upon the blood ]
87. Describe the arrangement of the larynx, the trachea, the bronchi,
and the lungs, as exhibited in Fig. 36. How are the heart and the
lungs arranged in the chest 1
88. What is the pleura 1 Why are the lungs not fastened to the
walls of the chest 1 Describe the manner in which the air is made to
enter the chest in breathing. Describe the framework of the chest, as
represented in Fig. 37. How are both lightness and strength secured
in this structure 1
89. Why are the ribs joined to the breastbone by means of carti-
lages 1 What is the chief connecting material of this framework 1 !
What is the diaphragm, and how is it arranged 1
90. How does the diaphragm act 1 Describe inspiration and expira-
tion as illustrated by Figs. 38 and 39.
92. In what way do other muscles, besides the diaphragm, act in res-
piration 1 Describe their arrangement and action, as represented in
Fig. 40.
93. What is the arrangement of the muscular fibres between the ribs,
and their mode of action 1 In what directions are the ribs moved by the
muscles in the neck and between the ribs 1 Do these muscles act much,
if at all, in ordinary easy respiration 1 Under what circumstances do
they act strongly 1
94. If air were admitted to the outside of the lungs by openings in
the walls of the chest, what would be the result 1 How are the blood
and the air kept from mingling in the lungs, while they are brought so
near together that the air changes the blood ! What experiment shows
that blood can be acted upon by air through pores 1 How important is
the office of the air-cells ] What provisions are made for securing to
them sufficient room under all circumstances 1 Illustrate by reference
to the state of things in violent exercise.
95. If the expansion of the chest be restrained in any way, what in-
fluence is exerted upon the air-cells 1 In what two ways does violent
exercise injure the lungs when the chest cannot be well expanded !
What is said of the influence of compression of the chest in the pro-
duction of disease in the female sex 1
96. What is said of the extent to which compression of the chest is
often carried 1
97. What is said of the gradual moulding of the chest by continued
compression during its growth 1 How is death produced in drowning 1
How is water prevented from getting into the lungs in any quantity ]
If arterial blood could be supplied to all the organ* while the breathing
is stopped, what would be the result 1 What contrivance has the whale
for this purpose 1
APPENDIX. 421
98. What is the arrangement of the gills of a fash 1 By what expe-
riment can you prove that it is the air in the water that acts on the
blood in the gills, and thus keeps the fish alive 1 Why cannot the fish
use air that is not mingled with water 1 What provision in the land-crab
enables him to live in air as well as in water 1 Describe the arrange-
ment of the gills in the lob-worm, and the larva of the May-fly.
99. Hov are the respiratory organs arranged in insects 1 What is
the effect of covering their stigmata with varnish 1
100. For what two purposes is the apparatus of respiration largely
developed .in birds 1 What special arrangement is there for securing
lightness 1
101. By what experiment can you show that carbonic acid is thrown
off from the lungs 1 What are the components of the air, and what is
their proportion ! Which of these is essential to life 1 Why would it
not be well to breathe pure oxygen alone 1 Where has it been sup-
posed till recently that the oxygen of the air unites with carbon to make
carbonic acid 1 Where does this union take place 1
102. What facts settle the last question 1 Does the change effected
by the air upon the blood in the lungs take place to some extent, when
blood drawn from a vein is exposed to air 1 What experiment illus-
trates the manner in which the air acts on the blood in the lungs 1
103. How much carbon is contained in the carbonic acid thrown off
from the lungs in twenty-four hours 1 What effect does this gas produce
upon the health if ventilation be imperfect 1
104. What becomes of the carbonic acid thrown off from the lungs
of animals 1 How is the air replenished with oxygen 1 How is the
equilibrium preserved in different climates 1 What effect has light upon
the discharge of oxygen from the leaves of plants 1 By what process
is the heat of the body maintained 1 Trace its analogy to ordinary com-
bustion.
105. What was formerly supposed in regard to the place of the pro-
duction of animal heat 1 What objection was made to this supposi-
tion 1 Where was it at length discovered that the heat is made ?
What are the three sources of fuel for keeping up the animal heat 1
Why is so large a quantity of oily food eaten in cold climates 1 How
do cold and tropical climates differ in the provisions of nature in this
respect 1
106. How is the use of fat in maintaining heat exemplified in hiber-
nating animals 1 Whence comes the heat produced by exercise 1 Why
is heat in different animals proportioned to their degree of activity 1
Contrast the warm and cold-blooded animals in this respect.
107. What is the ordinary temperature of the human body 1 What
is essential to comfort as to temperature in man 1 Detail experiments
which show how high a degree of temperature can be borne.
108. How are the evil effects of excessive heat in such cases chiefly
prevented 1 How much does the state of torpidity vary in different
animals 1 On what does the degree to which a deprivation of air can ba
borne depend 1
109. How are some strange recoveries from drowning to be explained 1
How far are the chemical changes described in this chapter dependent
on nervous action 1
36
422 APPENDIX.
CHAPTER VIII.
109. By what is the building and repairing of the body done
Have the vessels by which this is done, the power of selecting their m*
terial from the blood 1
110. Illustrate the variety of structures formed from the blood by
taking the eye as an example. Give examples of the co-operation of
the formative vessels in their work.
111. How is the concert of action in these vessels illustrated in the
definite but various shapes of the structures which they make 1 How
is the wonderfulness of this co-operation shown by comparison with
the formation of a crystal 1
112. Illustrate the agreement necessary between different neighbor-
ing sets of formative vessels in the process of growth. Illustrate the
wonderfulness of the concert of action in the formative vessels, when
there is a change of action. How is this exemplified in certain ani-
mals, as the frog and the silkworm 1
114. How is this change of action exemplified in the enlargement of
communicating arteries, after tying an artery in case of an aneurism 1
115. Describe the agreement of action seen in the successive changes
that take place in the formation, discharge, and healing of an abscess.
116. Notice the agreement of action between the formative vessels
and the absorbents in the cases mentioned. Are the secretions of
organs made from the same material that the organs themselves are 1
What exception is there 1
117. How many kinds of waste particles are there 1 By what ab-
sorbents are those particles taken up that can be used again ! What
organs probably fit them to be used again as a part of the building ma-
terial ! Where is the lymph, which they compose, mingled with the
blood ?
118. By what are the particles that are wholly useless absorbed 1 By
what organs are they excreted or thrown off from the body Do these
various organs excrete different parts of this waste 1 Do we know why
this waste matter is introduced into the blood, instead of being thrown
off in some more direct manner ? Give some examples in which other
functions besides excretion are performed by the same organ.
119. What are the various functions of the skin 1 Describe its struc-
ture to show how well it is fitted for these functions.
120. How extensive is the tubing of the sweat-glands 1 In what two
respects is the excretion from them important 1 What is the difference
between insensible and sensible perspiration 1 What are the sebaceous
glands'! What purpose do they serve] Where are they most abun-
dant 1
121. Upon what does the rapidity of the change constantly going on
in the body chiefly depend 1 W'hich has the most influence on this
change, mental or bodily labor 1 Illustrate the influence of activity on
this change by a comparison between the frog and the canary bird.
122. Illustrate the same influence by a comparison between different
parts of the body. Why does the change of the particles vary much in
rapidity at different times 1 W 7 hat is said of the mingling of life and
death in the changes of the particles 7
APPENDIX. 423
CHAPTER IX.
123. What has been the common idea about what are called forma
tive vessels '! By what are all the minute operations of the system per-
formed ! How do the cells differ from the cells in the cellular tissue 1
124. What do these cells contain ] What is to be said of their form
Describe them as seen in the blood. Of what are the solid parts of the
body composed !
125. How do the cells appear as seen in the Hydra"! Upon what
does the character of many of the textures of the body depend 1 What
is the chief difference between the various glands of the body 1 Upon
what do the colors of various parts depend ! How are the colors of
flowers varied in kind and in degree 1
126. Illustrate the selecting power of the cells. Can we account for
this power '? What is said of the idea that the selection is the result
of atfinity 1 What is said of the changes that take place in the con-
tents of the cells 1 In what two ways do cells produce other cells 1
127. How many kinds of cells are there in the blood 1 What gives
the red color to the blood 1 What are two of the offices of the colored
cells 1 How does their amount vary in different animals, and in differ-
ent individuals of the human race ]
128. DescriBl by the figure the manner in which absorption is per-
formed on the surface of the mucous membrane in the bowels.
129. Describe in like manner secretion by Fig. 63.
130. Of what is the cuticle or scarfskin composed 1 How many
fibrilla are there in a muscular fibre] What is each one of these
fibrillae 1 What takes place in them when the muscle contracts ?
What is the cause then of the swelling out of a muscle when it acts 1
How minute are the cells in muscles 1
131. What solid animal deposits are made by cells] Describe tho
arrangement in the enamel of the teeth. Of what are the nerves com-
posed !
132. What has been found in regard to combinations between the
tubuli of the nerves 1 How are these tubuli made from cells 1 In
what other parts of the nervous system besides the nerves, are they
found '? What is the office of the tubuli 1 What is the office of the
gray substance of the brain 1 Of what is this substance chiefly com-
posed 1 What is said of the form of its cells 1 Where does the micro-
scope show us is the beginning of life 1
133. What is the extent of the agency of the cells 1 In the forma-
tion of every animal what precedes the appearance of any diversity of
parts 1
134. Describe the arrangement of the contents of an egg.
135. Describe the succession of processes that take place in the yolk
preparatory to the formation of the bird. From what material are all
the parts of the bird made 1
136. What is the allantois, and what is its office 1 How can you
prevent it from performing its office, and thus arrest the development of
the animal ! When the bird is fully formed, how is he enabled to burst
the shell '! What is the grand distinction between organized and unor-
ganized substances I
424 APPENDIX.
137. What comparison is made between gravitation and cell-life?
Compare the exhibition of the Creator's power in the minute and in the
large operations of nature. What comparison can you make between
the beauty of nature as seen by the naked eye, and its inner beauty
revealed by the microscope 1
CHAPTER X.
139. How far are the functions of nutrition alike in animals and
plants 1 How has the microscope shown formation to be essentially the
same in both 1 Through what system are the uses for which the body
is constructed secured ?
140. Why are the functions that are performed through the nervous
system, called functions of animal life 1 Why are they also called func-
tions of relation 1 Through what intermediate instruments does this
system perform its functions 1 How does this system vary in compli
cation in different animals 1
141. How much is learned through the nerves and their subordinate
organs, the organs of the senses 1 Mention the subjects to be treated
of in this third part of the book. What are the three parts into which
the nervous system may be divided!
142. What three things are necessary to sensation V Illustrate the
necessity of each. What three things are necessary to voluntary mo-
tion 1 Describe the arrangement of the parts of the nervous system as
represented in Fig. 72.
144. Describe the arrangement and structure of the brain as repre-
sented in Fig. 73.
145. What part of the nervous system is most immediately essential
to the continuance of life 1 And why ? Illustrate by facts. What are
the convolutions of the brain 1 Describe the membranes of the brain
the pia mater the dura mater the arachnoid.
146. What is the consistence of the brain 1 What is the arrange-
ment of the gray and the white substance ?
147. Does the arrangement of the convolutions favor the idea of the
phrenologist 1 Of what is the white substance of the brain composed 1
What function is performed by it 1 What tubuli transmit impressions
from the brain 1 What transmit to it? What is said of the size of the
tubuli 1
148. What is the function of the gray substance 1 In proportion to
what does its amount vary in different animals 1 Is there gray matter
at the extremities of the nerves 1
149. With what are the cells in the gray substance mingled? What
is said of the necessity of a supply of arterial blood to this substance ?
How does the arrangement of the gray and the white substance differ
in the brain, in the spinal marrow, and in the ganglions ? What are
ganglions ? What are plexuses ?
150. Why is the gray matter so largely supplied with blood ? What
has the microscope shown in regard to the changes going on in this sub-
stance ? What is said of the manner in which the nerves terminate in
the organs of the body ?
151. Where are the Pacinian corpuscles mostly found? Describe
their structure. What do we know of their use ?
APPENDIX. 425
152. What is there that is wonderful in the healing of a divided
nerve 1 What do the observations of M. Sequard show! What fact
was proved by the experiments of Dr. Haighton 1 What does this fact
show '!
153. What nervous changes occur when a union takes place between
parts that do not belong together 1 Do the same nerves answer for sen-
sation and for motion ! In what part of the body are nerves of differ-
ent kinds kept separate 1 How is it in all other parts 1 What is the
arrangement of the nerves that branch out from the spinal marrow 1
What two purposes do the two roots of each nerve serve ! How is this
ascertained !
154. Are there different nerves for different kinds of sensation 11
How is it in the eye] How in the nose ! What is a nerve of common
sensation! What is a nerve of special sensation 1 Is each nerve fitted
for its own peculiar office 1 Illustrate by reference to the nerves of the
eye. Notice particularly the effects produced, if the nerve of common
sensation in the eye be paralyzed.
155. Why are different parts of the body endowed with different de-
grees of sensibility 1 What organ is more sensitive than any other 1
How much sensibility have the muscles ! How much have the bones 1
What fact is related to show the use of the sensibility of the skin in
preventing injury ! What change takes place in the sensibility of inter-
nal parts when they become inflamed! What benevolent purpose is
there in this 1 Does a nerve, as a matter of course, have sensibility !
156. What is true of the brain in relation to sensibility 1 What of
the heart 1 Relate the case given in illustration. Is the heart well en-
dowed with nerves 1 With what nerves is it endowed 1 What is said
of the nerves of motion in the face"? What are the appearances when
the nerve of expression in the face is paralyzed ! Why is this nerve
called the respiratory nerve of the face!
157. How are the motions of expression in the face connected with
the motions of respiration 1 Describe the results when this connection
is broken by a paralysis of the respiratory nerve of the face.
158. How many different nerves are devoted to the eye! What are
their different offices ! Of nerves going to the same part may one be
palsied while another is not ! Give some illustrations. Give the case
related by Sir C. Bell.
159. Are the nerves of different kinds all alike in their structure and
composition! Why cannot the impression producing sensation be
transmitted by the same nerve with the impression producing motion !
160. What has been till recently the most common theory in regard
to the action of the nerves ! Upon what circumstances is the opinion,
that nerve-force is identical with electricity, based ! Mention the facts
and experiments that disprove this.
161. In what direction is nervous action in sensation ? In what
direction is voluntary motion ! Does voluntary motion occur sometimes
in consequence of sensation, and sometimes not ! Illustrate this. Give
the resemblance of the nervous system to a telegraphic apparatus.
What is true of motion caused by mental emotions!
162. Give some examples of muscles that are wholly involuntary, and
of muscles that are partially so. What is the difference between an
excitor and a motor nerve ! Illustrate by reference to the respiration
3o*
496 APPENDIX.
the contraction of the iris and the action of the muscular coat of the
stomach.
163. Why is the action of these two classes of nerves called a reflex
action 1 Do we know what is transmitted through the trunk of a nerve 1
Does reflex action ordinarily occur without positive sensation ? Under
what circumstances is sensation connected with it 1 Illustrate by refer
ence to the action of the respiratory muscles, and the muscular action
of the stomach. In relation to what class of muscles does the spinal
marrow act for the most part independently of the brain 1
164. What is the relation of the spinal marrow to the brain in regard
to the voluntary muscles 1 What is true therefore of injuries of the
spine 1 State now the two separate functions of the spinal marrow.
By what arrangement are they performed 1 Illustrate the modes of
ejecting sensation motion and reflex action.
165. How does the brain differ from the spinal marrow as to intervals
of rest ] Illustrate the continuous action of the spinal marrow, as seen
in the operations that go on in the system when the brain is asleep, or is
torpid with disease. Besides these operations, mention some of the mo-
tions that can be excited through the agency of the spinal marrow inde-
pendent of the brain. Explain the agency of the spinal marrow in con-
vulsions.
166. What is said of the fact, that in convulsions there is an invol-
untary action of muscles that are ordinarily under the control of the
will 1 Cite some facts to show that voluntary muscles act involuntarily
more often than is commonly supposed.
167. Explain the involuntary action of muscles in walking and other
like acts. How is it with one who is walking in a reverie 1 What was
formerly supposed in relation to the importance of the brain as a central
organ of the nervous system 1 How do we know that the brain is not
directly essential to the maintenance of life 1
168. What are the functions most essential to life 1 ? Upon what part
of the spinal marrow do these depend 1 Illustrate the extent to which
the different parts of the spinal marrow are independent of each other.
Is there any sensation independent of the brain 1
169. Why is the system of nerves, of which I have treated in this
chapter, called the cerebro-spinal system 1 What other system is there 1
What are its purposes 1 What are its arrangements 1 How does it
differ in its general arrangement from the cerebro-spinal system 1
CHAPTER XL
170. What two different purposes do the bones fulfil 1 What bene-
volent purpose is manifest in the predominance of the animal portion of
bone over the mineral in the child 1 In what two forms is bony sub-
stance deposited 1 How are these arranged in the flat bones 1 How in
the long 1
171. How are both lightness and strength secured in a long bone
first, in the body of the bone, and then, in its ends 1 Why are the eiids
not made like the shaft 1 What is the marrow of the bone 1
172. How is a bone nourished 1 What is the periosteum 1 Do arte-
ries enter the solid substance of the bone 1 Describe the manner in
which circulation is carried on in every point, as shown by the micro
scope.
APPENDIX. 427
173. What fluid circulates in the minute channels in bone, shown to
us by the microscope 1 What is said of the sensibility of bone ] Give
a general description of the skeleton, noticing the variety of shape in
the bones, and the purposes which they answer.
175. How many bones are there in the head 1 ? How many of these
belong to the face ? How many to the cranium 1 Describe the latter,
as represented in Fig. 87.
176. Why is the box (as the cranium may be called) holding the
brain, composed of so many bones ] Describe the structure of the prin-
cipal bones of the cranium. What is the difference between the join-
ings of the outer and those of the inner tables of these bones 1 What
is the reason of this difference 1
177. How are the principles seen in the construction of domes illus-
trated in the cranium ] Of what bones is the dome of the cranium
made up] Describe the different ways in which strength is secured
around the base of this dome. Describe especially the arrangement be-
tween the parietal and temporal bones.
178. When violence is inflicted upon the head, what is the direct cause
of the injurious effects felt by the brain 1 On what principle do the
guards of the brain defend against this cause of injury? Mention now
in their order the different textures through which the vibration of a
blow must pass before it reaches the brain, pointing out their agency in
lessening the vibration.
179. What arrangement is there of the lower part of the frontal bone
as a special guard against injury at that point 1 How is the side of the
head, so peculiarly exposed to violence, especially guarded 1 ? What other
organs, beside the brain, are protected by the cranium 1
180. Describe the arrangement of some of the bones of the face.
Describe the cavities of the nostrils, and the sinuses connected with
them. What is the object of the great extent of surface in these
cavities 1
181. Describe the lower jaw. How many distinct structures are
there in the teeth ] What is their arrangement]
182. How does a tooth differ from a bone 1 What is the reason for
this difference 1 ? What is the necessity for having a second set of
teeth ]
183. Describe the hyoid bone, its position, and its connections. Men-
tion other bones which, like this, are not directly connected with the
bones of the skeleton. Of .how many bones is the spinal column com-
posed] Acting as the great pillar of the body, what does it support?
What is the pedestal on which it stands, and in what manner is this
pedestal made firm] While this column is thus firm, it needs to be
flexible how is this accomplished] Notice its different degrees of
flexibility in different portions of it. W T hy is there so little motion in
that portion that supports the framework of the chest ]
184. Besides serving as a firm pillar and a flexible chain, what other
purpose does the spinal column fulfil ] Describe a vertebra. By what
are the vertebrae-bound together ]
185. Describe the canal in this column for the spinal marrow. What
is the arrangement for the nerves that pass from it ] How are the car-
tilages arranged ] What two purposes do they subserve 1
186. What is there in the shape of the spinal column that acts as a
428 APPENDIX.
safeguard against shocks to the brain 1 What are now the three objects
secured in the structure of the spine 1 Describe the contrivance at the
top of it, as represented in Figs. 95, 96 & 97. Compare this with the
mounting of a telescope. What is the difference in the two cases 1
188. By what arrangement is the freeness of motion in the neck of
birds made consistent with the security of the spinal marrow 1 What
is there peculiar in the spinal column of quadrupeds 1
189. What is the paxy-waxy 1 How are the vertebrae of fishes con-
structed and arranged 1 How is the great flexibility of the spine in
reptiles secured 1 How in the neck of the giraffe 1
190. Describe the arrangement of the breast-bone, the collar-bone,
and the shoulder-blades. What is the use of the collar-bone, and what
are its variations in different animals 1 How does the shoulder-blade
differ from all other bones in the body 1
192. Why is the socket of the shoulder-joint so shallow ? Describe
the arrangement of the radius and ulna, and the manner in which such
free and varied motion is given to the arm. Describe the three parts of
the hand.
193. Describe the ligaments that bind the bones of the hand together.
What is the principal object aimed at in the construction of the lower
extremity 1 What in the upper 1
194. Describe the thigh-bone. What is the patella 1 What pur-
poses does it answer 1 What part of the foot is formed by the tarsus 1
What part by the metatarsus 1
195. How many bones are there in the toes'! How many in the
whole foot 1 What object is secured by having so many bones in the
foot 1 Why is the foot arched 1 Describe its movement in walking.
With what are the ends of the bones tipped, and why 1 What is the
arrangement of the membrane that lines the ends of the bones 1
196. What contrivance is there in the knee-joint, and in the articula-
tion of the lower jaw 1
CHAPTER XII.
196. Give the summary in 294, in regard to the action of the mus-
cles, and their nervous connections.
197. What are the tendons 1 W T hat is said of the relation they bear
to the muscles their shape their mode of union with muscles and
with bones their strength and their size 1 How are the muscles and
tendons arranged in reference to convenience and beauty 1 Illustrate
by the arm and the hand.
198. Illustrate the application of the first kind of lever in the action
of muscles so also of the second kind.
199. And of the third kind. Which kind is most frequently used in
the body 1
200. What two different objects are aimed at in the application of
these two levers 1 Illustrate by examples of the second kind of lever.
201. Illustrate the same by examples of the third kind. What is the
difference between the motion of the forearm on the arm, and the mo-
tion of the lower jaw, in the application of the principles alluded to.
203. Show how quickness is secured at the sacrifice of power in the
case of the biceps muscle, as illustrated in Fig. 1 14. Under what me-
APPENDIX. 429
chanical disadvantage do most of the muscles act, as represented in
Fig. 1151
204. Show by this figure how quickness of movement is gained in
this case. Why is the muscle, the deltoid, whose action is represented
in this diagram, so large 1
205. How is the mechanical disadvantage, which thus results from
the oblique action of the muscles, in part obviated 1 Illustrate by Figs.
116 & 117. Describe the agency of the patella in this respect. To
what extent is the pulley used in the arrangement of muscles ?
206. Show the application of the pulley, as seen in the ankle.
207. Describe the pulley arrangement of the digastric muscle. What
is the necessity for such an arrangement 1 What other office does this
muscle perform, besides drawing down the lower jaw, and how does it
doit!
208. Describe the muscles that move the ball of the eye.
209. What is said of the actions of opponent muscles 1 What is
Paley's comparison 1 Is it strictly correct 1 Give some examples of the
tonic contraction of muscles. What is the cause of wry neck, and of
squinting I Illustrate the compound action of muscles by Fig. 1 13.
210. How does variation in the degree of the contraction of muscles
affect the variety of motion 1 What organ peculiarly exemplifies vari-
ety in muscular action 1 Give a general description of the muscles of
the body, as exhibited in Figs. 122 & 123.
214. What is said of the variety of size in muscles 1 What other
parts besides the bones are moved by muscles 1 How are the muscles
arranged in reference to convenience and symmetry 1
215. Describe a peculiar arrangement of tendons and muscles in the
sole of the foot. Describe the arrangement of tendons represented in
Fig. 124.
216. Describe the complicated action of the muscles in swallowing
and in speaking and singing. How are the epiglottis and the larynx
used in these acts 1 What is said of the ease and quickness of the
change from the one act to the other 1
217. Show how the variety and complication of muscular action are
illustrated in some of the general movements of the body : as walking,
pulling with the feet braced, and balancing. Describe the operation of
the toggle-joint.
218. Give examples of the application of this operation in the action
of muscles.
219. How many muscles are there in the hand and arm'? What is
said of the extent of the variety of their action ! Contrast the hand,
as doing light and heavy work. Give a summary of the endowments
of the hand.
220. Give a description of various muscular movements that may be
going on in the body at the same time. What is the muscular sense 1
221. Illustrate the operation of it in various ways. Is this sense a
source of enjoyment 1
CHAPTER XIII.
222. By what alone are thought and feeling expressed! What sub-
ordinate modes of expression are there 1 Illustrate the fact that these
430 APPENDIX.
require to be interpreted by muscular action. By what mode of muscu-
lar action are thought and feeling mostly communicated 1 What rela-
tion has writing to this mode of communication ! What other parts
beside the face are brought into action in the language of the muscles 1
223. Illustrate the extent of this language. How can we get the best
idea of its extent ? How do other animals differ from man in regard to
the parts used in the language of the muscles 1 What passion is almost
the only one that can be expressed by them in the countenance 1 What
distinction is sometimes made on this ground between man and other
animals 1
224. What are the principal muscles that give the face expression 1
How is a smile produced 1 How is sadness expressed 1 How do smil-
ing and laughing differ in the action of the muscles'!
225. How does weeping differ from mere sadness in muscular action 1 ?
What peculiarity is there in muscular action in weeping from pain 1
226. To what is to be attributed the apparent expression of the eye 1
How can it be proved that the eye has no active agency in expression 1
227. What is the common notion in regard to the eye as a means of
expression 1 How far is expression a result of combined muscular
action ?
228. Describe the muscles of the face, with the action of each, as ex-
hibited in Fig. 130.
229. Describe the muscles about the mouth, as shown in Fig. 131.
230. In what way is the expression of the face made the same in its
two halves 1 What nerve governs all the muscles of expression in the
face 1 What results when one of this pair of nerves is paralyzed 1
231. Is there commonly any one muscle devoted to the expression of
any one emotion or passion 1 Does the same muscle often take a part
in the expression of various emotions 1 Explain the agency of* various
muscles the frontal the corrugator supercilii the superbus. Illus-
trate the combination of muscular action in expression, as shown in Fig.
132, and also in Fig. 127 giving the differences in them. What is the
action of the muscles in quiet sorrow 1
233. What is their state in the expression of a calm pleasure"?
What in the expression of admiration 1 How does temperament affect
the state of the muscles in the two last-mentioned expressions 1 De-
scribe the action of the muscles in the expression of rage. By what
combination of the action of muscles are the canine teeth exposed '?
234. Describe the action of the muscles in fear. Show how it differs
from their action in rage.
235. Illustrate the agency of the muscles of the eyeball in expression.
What is said of the action of the oblique muscles 1
236. Why is the intoxicated man apt to squint and to see double "?
Why does he raise his eyebrows in the effort to keep his eyes open "?
What muscles of expression are found in the faces of animals 1 In re-
gard to what muscles is the horse specially endowed 1 What is said of
the muscles that distend the nostrils in the case of man 1
237. What muscles of expression are wholly peculiar to man 1 Re-
mark on each. What are almost the only passions that can be expressed
by the faces of animals 1 What special provisions are there in some for
the expression of rage about the mouth, and the eye 1 What peculiar
APPENDIX. 431
phenomenon in the reflection of light is seen in the eye of the cat tribcj
and what is the explanation of it 1
238. Give the substance of 348 in regard to the combinatior of
muscular action in the expression of the countenance. What is said in
349 of the action of the rest of the body in expression 1
239. What muscles of the body sympathize most with those of the
face in expression 1 Give examples in illustration. What effects are
produced by mental emotions on the circulation 1 What is the expla-
nation of blushing! What is said of the adaptation of the countenance
to the mind as an instrument of expression'! Draw the analogy be-
tween the hand and the face in this respect.
240. What is said of the importance of training the muscles of the
face 1 How far does beauty of countenance depend upon muscular ac-
tion ] W 7 hat difference is there in this respect between the living coun-
tenance, and the face of a statue 1 Give the remark of Addison.
241. What is said of skill in the use of the muscles of the face as
compared with those of the hand 1 In what cases may you see this
skill '! What is said of mistakes in interpreting the language of the
muscles 1 W T hat is said of the influence of moral and mental cultiva-
tion upon the countenance"?
242. Explain the expression of the countenance, as seen after death.
CHAPTER XIV.
243. What principles apply to the construction of the apparatus of
the voice 1 Illustrate its superiority to other instruments as a musical
instrument. What most particularly distinguishes it from them?
244. What is said of its power of fascination 1 What comparison is
made in this respect between the voice of conversation and that of song 1
What is said of the variety of voices in the brute creation 1
245. Into what two kinds are wind-instruments divided 1 Explain
the manner in which the variation of note is produced in those of the
first kind, by reference to the flute and the trombone.
246. Illustrate the same point in the operation of the flute-stop of the
organ. What influence does the width of the vibrating column of air
have upon the note? How is the note varied in those wind-instru-
ments in which the length of the column of air cannot be altered ?
How are the variations of note produced in whistling 1
247. What are some of the wind-instruments of the second class 1
How is the sound produced in these 1 How is the note varied 1 Illus-
trate by reference to the reed-stops of the organ. How are the various
notes produced in the clarionet 1 Trace the analogy, in the application
of the principles of musical sounds, between the vibrating column of
air, the reed, and the strings in such instruments as the piano and vio-
lin. Explain the relation of the tube of the reed-instrument to the reed,
as stated in 366.
248. What is the trachea, and of what is it composed 1 Why are its
rings of cartilage not perfect rings 1 What is the larynx ?
249. Describe the parts of the larynx as represented in Fig. 136.
Describe particularly the arrangement of the arytenoid cartilages and
the vocal ligaments, as represented in Figs. 137 & 138.
250 Describe, by means of Fig. 137, the manner in which the differ-
432 APPENDIX.
ent notes of the voice are produced. Describe the apparatus of the
voice, as represented in Fig. 139.
252. What is the arrangement of the two pairs of ligaments 1
253. How do we know that the lower ligaments are the true vocal
cnords 1 Apply now the principles regulating the variation of note in
common musical instruments to the vocal apparatus.
254. Give Magendie's experiment. What is said of the question as
to what kind of musical instrument the larynx most resembles 1 Give
the general conclusion as to the application of the great principle of
musical sounds. What is the tube of the vocal apparatus, which an-
swers to the tube of a reed-instrument 1 How many outlets has it 1
From which does the voice generally issue 1 How is it in humming 1
255. What influence do the cavities of the nose have on the voice 1
In what way is the reverberation in them regulated] In what two
ways is the size of the vibrating column of air in the tube of the vocal
instrument varied 1 What influence does this tube have on the charac-
ter of the voice 1 How would the voice sound if it should come directly
from the larynx, instead of passing through the tube attached to it 1
256. What is the cause of alterations in the voice, as hoarseness 1
Where is the difficulty when the voice is lost 1 In what two ways does
the epiglottis affect the voice 1
257. What is said of the variety and precision of the action of the
muscles in the modulation and articulation of the voice 1 How much
do the ligaments vary in length in producing all the variety of notes of
which the voice is capable 1 Give the calculation in regard to the mi-
nuteness of the muscular action in passing from one note to another.
How does the vocal instrument differ from others in the mode of pass-
ing from one note to another 1 With what instrument can the voice be
imitated in this respect 1 How does the voice of speech differ from thai
of song!
258. What is said of the training of the muscles of the vocal appara-
tus ! What is the analogy between the training of the muscles moving
the vocal ligaments, and the training of the lips in playing on a reed-
instrument 1 What is said of skill in managing the muscles of the
chest in speaking and singing 1 Give the illustration of the bag-pipe
259. What is one of the chief causes of "throat disease" in public
speakers 1 What circumstances tend to produce this disease 1 Where
is the voice formed in birds 1 How is the vocal tube in their case altered
in its length for the different notes 1
260. Describe the various parts of the vocal tube, that have an agency
in articulation. In the articulation of how many letters is the tongue
the chief agent 1 State some facts to show that the tongue is not so
essential to the power of speech as is commonly supposed.
261. What letters are chiefly formed by the teeth"? What is lisp-
ing 1 What letters are chiefly formed by the lips 1
262. Why do children use labials so early and so freely 1 Of what
are their terms of endearment composed in most languages 1 Give
other facts stated in this paragraph in relation to the use of labials.
Illustrate the agency of the nasal cavities in articulation. What consti-
tutes a distinguishing peculiarity of many consonants'!
263. Explain the difficulty called speaking through the nose. What
is said of articulation in whispering 1
APPENDIX. 433
264. How is the variation of note in whispering caused ] How can
you observe the mechanism of the parts necessary in producing any of
the alphabetic elements ! What is said of the common definition of
consonants ] Mention some of the attempts that have been made to
imitate the articulation of the voice by mechanism.
265. How many alphabetic elements are there, as reckoned by
Rushl By what is the adjustment of the articulating apparatus for
each one of them effected 1 What is said of the training of the mus-
cles of the voice 1 Describe the process of learning to talk in the child.
266. What is the chief instructor of the voice 1 What other organ
assists in this instruction 1 Illustrate the fact that it is difficult for any
but the young to acquire accurately the pronunciation of a language.
What is said of skill in the use of the vocal apparatus ] Compare this
with skill in the use of other muscles.
267. What is stammering] What facts are stated in regard to it 7
In deaf mutes what is the cause of the dumbness in almost every easel
What cases may be cited in proof] Give the case related by Magendie.
268. What other cases maybe cited that are more common'? Can
deaf mutes be taught to talk ! What objections are there to doing if?
269. Explain the difference between the voice of speech and that of
song. Illustrate the uses of the vanishing movement in speech.
270. What effect does the use of the vanish on the interval of a semi-
tone produce ] Illustrate this. What two reasons are given for the fact
that, while every one learns to talk, there are many that do not learn to
sing]
271. How is musical talent compared with other talents 1 What is
the explanation of ventriloquism 1
CHAPTER XV.
271. How is sound produced 1 ? When is sound musical, and when
discordant 1
272. What is said of the transmission of sound "? What of its re-
flection ] Illustrate the influence of the reflection of sound in accumu-
lating it.
273. How can you prove that sound, unlike light, cannot be trans-
mitted through a vacuum 1 What is true of the facility of the transmis-
sion of sound through solids and fluids as compared with air 1 Illus-
trate it by facts. How is the fact, that sonorous vibration does not rea-
dily pass from one medium to another, illustrated 1 Upon what does the
degree to which the vibration is lessened in passing from one substance
to another, depend]
274. In what cases is the intervention of a membrane of essential
service, and why 1 Give a general description of the process of hear-
ing. Describe the apparatus of hearing, as represented in Fig. 148.
275. What is the object of the external ear ] What is the use of
its ridges and prominences ]
276. What is said of the external ears of animals in comparison with
man ] Describe the tube of the ear. By what two means is it guarded
against intruders ] Describe the drum of the ear and the little bones.
277. What is the arrangement of these bones 1 What are their con-
nections, and how do their muscles act upon them ] How does the cav-
37
434 APPENDIX.
ity of the tympanum communicate with the mouth, and why 1 What
part of the ear is the essential part of the apparatus 1 How much of
the apparatus may be destroyed without entire loss of hearing ! Give
the case related by Sir Astley Cooper.
278. Describe the parts of the labyrinth. In what different ways
may deafness be produced by defects in this part of the apparatus 1
279. Why is it better that the vibrating substance in the labyrinth be
a fluid than a solid or a gaseous substance 1 ! What is the use of the
chain of bones 1 Describe the chalky concretions, and their use.
280. What is the use of the fencstra rotunda 1 Describe the arrange-
ment of the cochlea.
281. In what two directions is the vibration of the fluid in the laby-
rinth transmitted! What is the course of the vibration in the cochlea]
What is the arrangement of the membranes in the cavities of the laby-
rinth 1 What is the arrangement of the nerves in the semicircular canals 1
283. Describe the distribution of the nerve in the cochlea. In what
two ways does the nerve here receive impressions from the vibration of
the fluid 1
284. Describe now, step by step, the process of hearing. Is all our
hearing done in this way! Give examples of hearing through the bone
enclosing the labyrinth. How does the apparatus of hearing in fishes
differ from that of man 1 Why is it less complicated than in animals
that live in air 1
285. Mention some particulars in which the ear of birds differs from
that of man. What is the simplest form of the hearing apparatus
found in animals 1 What are some of the suppositions in regard to the
offices of particular parts of the labyrinth 1 What is true of them 1
What part of the process of hearing can we trace and understand!
How much do we know about the transmission of the impression from
the fluid through the nerve to the mind !
286. Is it true that the eye is a more wonderful organ than the ear!
What is said of the mingling of the spiritual and the simply mechani
cal in the process of hearing ! What are to be considered the two ends
of the apparatus of hearing !
CHAPTER XVI.
287. Into what two parts may the process of seeing be divided 1
What principles govern the construction of the mechanical part of the
apparatus ! What is the object of its arrangements ! How is the sec-
ond part of the process executed! How does the transmission of light
resemble that of sound! What is the refraction of light! Illustrate
by Fig. 156.
288. How are the rays bent in relation to a perpendicular when they
pass from a denser into a rarer medium ! How, when they pass from
a rarer into a denser! How are the rays refracted when they pass
through a medium that presents a convex surface!
289. How are the rays refracted when they pass through a medium
which has a concave surface !
290. How many coats has the eye ! Describe the arrangement of
the parts of the eye, as represented in Fig. 159. What is the use of
the sclerotic coat ! How is the cornea fitted into it ! What is the colo>
APPENDIX. 435
of the choroid coat, and to what is it owing ? Of what is the retina
chiefly composed 1 What are the three .humors of the eye 1 Describe
the chamber in which the aqueous humor is. What is the consistence
of the crystalline immor or lens ? Describe the vitreous humor. Why
is it called vitreous ?
291. Describe the various parts as they are more minutely delineated
in Fig. 160. How is the aqueous humor formed 1 How is it continu-
ally changed 1 Describe the membrane called the conjunctiva. W r hat
are the ciliary processes 1 Describe their arrangement.
292. What is their use 1 How are images of objects formed upon the
retina 1 How can the fact, that such images are formed, be proved 7
293. Why are these images inverted 1 What is the plan of a camera
obscura 1 Compare the eye in its arrangements to an instrument of
this kind.
294. What qualities are needed in the cornea? How is its transpa-
rency secured 1 Why is it more convex than the sclerotic coat 1 On
what does the color of the iris depend 1 What is the principal office of
the iris 1 By what arrangement of its muscular fibres are its motions
effected? How does the pupil differ in carnivorous and herbivorous
animals 1
295. What is the office of the crystalline lens 1 What is its shape 1
Its structure 1 What disease has its seat here 1 What are the three
modes of remedying the difficulty 1 What two purposes does the cho-
roid coat serve 1 Why is its color dark 1
296. What is the state of the choroid coat in the albino 1 What
gives the bright red or pinky hue to the iris in his case 1 How does the
color of the choroid coat vary in different animals 1 What is the cha-
racter of the retina, and its office 1 Trace the analogy between the
optic nerve and the other nerves of sense 1 What resemblance is there
to the nerve of touch in its termination ? What is the defect in the opera-
tion of optical instruments, called spherical aberration, and how is it
obviated in the eye 1
297. What is the difficulty in the operation of a common lens, called
chromatic aberration 1 How is this obviated in the lens 1 How in the
eye?
298. Contrast the eye with the telescope in regard to the facility with
which the eye accommodates itself to objects at different distances. In
what two ways is this accommodation effected ?
299. By what defects in the structure of the eye in the near-sighted
is this power of adjustment counteracted ? How is this difficulty obvi-
ated ? In what way is near-sightedness often produced ? What is the
difficulty in the far-sighted ? How is it obviated ? At what different
periods of life are these two defects apt to appear, and why ? How is
the fact, that objects appear in their right position, although their images
are inverted on the retina, sometimes accounted for ?
300. What objection is there to this explanation ? Upon what erro-
neous idea are such explanations based ? Do we really know how the
mind gets the right idea of the relative position of objects ?
301. What is necessary to single vision in regard to the two images
formed in the two eyes ? Why do you see double when you press one
of the eyes a little out of its place ? What is necessary to single vision
In the action of the muscles ? Why does the intoxicated man often see
436 APPENDIX.
confusedly, or even sometimes double 1 Relate and explain the case
given to show how disease may produce double vision. Why is there
not double vision ordinarily in squinting 1
302. When are the two images in the eyes alike 1 In what cases are
they unlike 1 Relate the experiment given in explanation. How is it
that in such a case, while there are two images, and therefore two im-
pressions sent along the two optic nerves, yet the impression on the
mind is single 1 How does a person who has but one eye, acquire the
idea of solidity 1
303. Explain Professor Wheatstone's stereoscope on the principles
developed in 454.
304. Mention the particulars in which the harmony of action in the
two eyes is wonderful.
305. Notice the correspondence between the two eyes in that part of
the process which belongs to the optic nerves. What peculiarity is there
in the arrangement of these nerves 1 Do we instinctively perceive the
size, distance and figure of objects, or is it an acquired power 1 Relate
in illustration the case given by Cheselden.
306. How does the experience thus related compare with the experi-
ence of the child in learning to see? Give the analogy between learn-
ing to see and learning to walk or talk. In learning to appreciate the
sizes, shapes and distances of objects, what sense acts as the educator
of vision ! What is said of the frequency of mistakes in vision 1 What
of okill in seeing 1 What is the visual angle 1
307. Can we get a correct idea of magnitude by the visual angle
alone 1 Illustrate by the Figure. What circumstance must be known
in regard to an object, in order to have our estimate by the visual angle
correct 1 Mention another means that we use in connection with the
visual angle. Give examples of mistakes that we are apt to make in
the use of this means.
308. Illustrate the manner in which we get ideas of the magnitude of
objects by comparison. Show how we sometimes are made aware of
our dependence on this source of evidence. Why does the moon ap-
pear so large when rising 1 Explain the use of the muscular sense in
acquiring an idea of the size and distance of objects. What use is
made of it in looking at very near objects 1 What is said of our consci-
ousness of the effort in doing this 1
309. Why can you not judge accurately of the locality of very near
and minute objects when you use but one eye 1 What do we observe
in regard to the use of the convergence of the eyes, when we look at
the eyes of others ? How far is seeing a mental process 1 What is
said of the common notion, that it is a simple and easy process 1 What
is said of the training required for its performance 1
310. Do all the images formed on the retina transmit impressions to
the mindl Illustrate by reference to squinting. Also illustrate in
reference to ordinary vision by an experiment. Explain this by
Fig. 175.
311. Show now how it is that, notwithstanding the facts stated in
464, we are not conscious of seeing double. Show too how we can
by an effort of the will have this consciousness.
312. What is the paint of distinct vision, as it is called ? Show hov?
the mental attention makes use of this how in looking at an object
APPENDIX. 437
in reading in looking at a prospect 1 Why do we seem to see tho
whole of a page or of a prospect at once with equal distinctness 1
How far do we see the whole of a page or a prospect at once 1 "What
is said of the minuteness and correctness of the pictures formed on the
retina 1
313. How do we in part estimate the motion of objects 1 What is
said of the delicacy of the process by which this is done 1 Illustrate 1
the frequent erroneousness of our impressions in regard to motion.
Why is it that when we are moving rapidly, near objects seem to fly
back, and distant objects seem to go along with us 1 Illustrate by the
Figure.
314. What is said of the rapidity with which impressions received
from the images on the retina succeed each other 1 Show how this
may be measured by experiment. To what is the difference in time
required for distinct transmission in different individuals owing ] Trace
the analogy between this difference ad that which we see in different
individuals in regard to the use of the muscles.
315. Explain the Thaumatrope. How is the eye situated so as to
protect against injury 1 How does the cushion of fat on which it rests
serve to protect it? In what two ways does the muscle that closes the
eyelids serve as a protection to the eye 1
316. How is it protected by the eyelashes ? How by the eyebrows 1
How are the eyelids constructed in reference to the protection of the
eye 1 How do the tears serve as a protection i Why do fishes have no
tear-apparatus 1
317. Describe the arrangement of the tear apparatus. Why do the
tears overflow the edges of the eyelids when they are abundant 1 What
arrangement of glands is there on the eyelids ] What two purposes
does the oily substance formed by them serve 1 How are the tears con-
ducted into the mouths of the ducts when the eyelids are closed 1 De-
scribe the nictitating membrane in the eyes of birds.
CHAPTER XVII.
,318. Give the recapitulation presented in 476.
319. What is said of the brain as the organ of the mind 1 What
facts show that motion and sensation are dependent on the brain 1
How does it appear that the mind thinks only by means of the brain 1
How is life continued when sensation, motion, and thought are stopped
by compression of the brain 1 How does the variation of the degree of
compression vary the effect on the mental functions 1 How is the de-
pendence of the mind on the brain shown in disease 1
320. Of what is insanity always the result ? How do moral causes
produce it 1 If the mind were separate from the body, could insanity
be produced in it] Can the disease in the organization in insanity,
be always discovered in an examination after death 1 Describe the situ-
ation of the brain and its' immediate connections.
321. What is said of the face 1 Illustrate the rapidity of the commu-
nication between the mind and the different parts of the body. In exe-
cuting muscular motion skilfully, is any assistance derived from a know-
ledge of the particular muscles 1 By what arrangement is the mind
enabled to excite so accurately the motion of the muscular fibres *
87'
438 APPENDIX.
322. Upon what besides combined action in the muscles doer; the end-
less variety in motion depend ! Mention some cases in which we best
realize the variety and accuracy of the messages sent from the brain to
the muscles. What is said of the training of the organs of sense and
of motion ] What of the amount of knowledge acquired by the child
in the first years of his life 1
323. Describe the training of the muscles in the child. What is true
of what is called native grace 1 What is said of the training of tho
muscles of the face !
324. What is said of skill in the use of the muscles 1 What is said
of the training of the senses 1 How do other animals differ from man
at the first in the use of the muscles and the senses ] How do they dif-
fer from him in the amount of skill that training gives 1
325. Illustrate the fact, that the senses and muscles are mutual teach-
ers in their training. How does the dependence of the muscles on the
senses differ from that of the sgpses on the muscles 1 What fact illus-
trates the absolute dependenceof the muscles on the senses ; In the
education of the muscles and the senses, what is, strictly speaking,
educated or trained ! Illustrate by reference to the idiot and the deaf
mute.
326. What is said of the muscles of the face in the idiot 1 Why
does not the education of the muscles extend to those that are involun-
tary 1
327. What difference is there in the different stages of the training
of the muscles in the degree of cognizance which the mind takes of
their action 1 Illustrate by reference to learning to walk, to read and to
sing. What has been the general belief in regard to the means of
communication between different minds {
328. What is claimed by some on this point in regard to what is
called animal magnetism 1 What has always been found to be true of
this when its pretensions are properly tested ] Illustrate the manner in
which this was done in one case.
329. What is s^id of the illustrations afforded by animal magnetism
of the influence that can be exerted upon the body through the mind t
To what diseased states is the condition produced in the subject analo-
gous 1 Does the explanation of the phenomena show that there is any
true magnetic influence in the case 1
330. What is said of the mingling of moral and physical perversion
in the subjects of animal magnetism] What is said of suggestive
influences !
331. What is said of the exaltation of the powers of the senses in
the subjects of animal magnetism ? What is true of clairvoyance, so
called ! What is said in the note of test evidence I Give the fact
stated in illustration.
332. What part of the brain has an especial connection with the
mind 1 What is the chief office of the cerebellum 1 Give the evidence
from comparative anatomy on which this poiut is settled. What expe-
riments lead to the same conclusion 1 What two reasons are given why
the evidence on this point from disease is defective] What fact haa
been observed in cases of disease of the cerebellum'! What negative
testimony is sometimes afforded by disease in regard to the office of the
cerebellum i
APPENDIX. 439
333. Give the summary of results arrived at by studying the compar-
ative physiology of the nervous system, as stated in 502. What is
said of the comparative amounts of the white and the gray substance in
the biain ! What are the two sources of evidence in regard to the func-
tion of the gray substance 1
334. What evidence is there in regard to phrenology from the arrange-
ment of the gray substance ! What is the conclusion from all the facts
collected in relation to the external examination of the head 1 What
evidence is the real test of the pretensions of phrenology '!
335. What is true of the pretended locality of organs in the region
of the frontal sinus 1 What of the organs said to be in that part of the
head where the cerebellum is 1 What is the only fact that seems to give
countenance to phrenology 1 Why does this fact fail to prove that the
special seat of the intellectual faculties is in the upper and front part of
the head ! What evidence have we on this point from the phenomena
furnished by disease and injuries 1
336. What is the facial angle ? What is the difference in regard to
this between the skull of the European and that of the African t
What between the skull of animals and that of man! What is the
common measure of this angle in ancient statues of deities and heroes]
W'hat is said of the rule, that the amount of intelligence, both in man
and in animals, is proportioned to the amount of the cerebrum]
337. What facts show that size is far from being the only measure of
power in case of the brain 1 In studying the comparative physiology of
the brain, what significant fact do we find when we come to pass from
the higher animals to man 1 Of what character is the mental difference
between them and man 1 What is said of the definiteness of the dis-
tinction between man and animals 1
338. What note ought to be made of this distinction by the compara-
tive physiologist] What is said of the intimacy of the union between
the mind and the body 1 What might we infer from the closeness of
this union in regard to death, if we had no Revelation 1
339. What is said of the supposed independence of the mind on the
body 1 Is there proof that mind is of itself indestructible ] What are
the three sources of our knowledge in relation to the connection of the
mind and the body 1 What is the consequence if we rely upon any one
of these alone 1 What is the alternative to which one is driven, if he
confine himself to the evidence which physiology furnishes ] What
course is commonly pursued by those who take this narrow view of the
subject]
340. What is said of the distinction between organized and unorgan-
ized matter '! What are the common suppositions in regard to the en-
dowment of organized or living matter ] What is said of those endow-
ments of living matter that are connected with the nervous system!
What question now arises in relation to intelligence in its connection
with matter '{
341. What does physiology show us in regard to this connection!
Point out the deficiencies of its teaching in relation to the nature of this
connection. What is the tendency of its presumptive evidence 1 Look-
ing at the subject solely in the light of physiology, what would be the
conclusion in regard to the dependence of mind on organization, when
we observe the origin and growth of a thinking animal] What bear-
440 APPENDIX.
ing on this point has the fact, that the intellect grows with the brain, and
appears at last to perish with it 1
342. What is said of the evidence that may be drawn by the physi-
ologist from the design obvious in the efforts of the mind ! Trace the
analogy, in this respect, between mental phenomena and those that we
see in the common operations of life, both animal and vegetable. Show
how the analogy holds good in the accommodation to varying circum-
stances in the cases cited. What is the extent of the analogy seen in
the phenomena alluded to 1 To what idea has the contemplation of this
analogy sometimes, led 1
343. Give examples of phenomena in vegetable life, that are often
called instinctive. What fact in comparative physiology is strongly ad-
verse to materialism 1 In which direction, however, on the whole, does
the evidence from physiology, taken alone, preponderate I
344. State the ground of the great need which the physiologist has
of the evidence from other sources beside his physiology. What is the
testimony of consciousness in relation to the independence of the soul
in its action 1 What in regard to its responsibility for its acts 1 How
far is this testimony acted upon by all, when physiological speculations
are left out of view 1
345. What does the evidence from consciousness show us in relation
to the connection of the mind with the material organization 1 To what
alternative does it drive us '! How is this testimony of consciousness
treated by the Bible 1 Illustrate our dependence on the Bible for the
proof of the soul's immortality.
346. How may the discrepancies in the evidence from physiology in
regard to the connection of the mind and the body be cleared up 1
347. What is said of the character of the evidence drawn from con-
sciousness and Revelation 1 What is said of the presumptive evidence
from physiology in comparison with it 1 W ; hat is said of the present
moral tendencies of physiological investigations 1
CHAPTER XVIII.
347. What was Lord Monboddo's idea of the development of man 1
348. What recent theory has an analogy to this 1 What is true of
man and animals in relation to instinct and reason 1 Do we know what
the nature of instinct is ] Which can be understood best, the actions
of instinct or those of reason 1 Illustrate this point.
349. What seems to produce the actions of instinct 1 W r hat influ-
ence does the intelligence of the animal exert upon them 1 What is
said of the invariableness of the actions of instinct 1
350. Describe the nests of the Baya and the Tailor Bird.
351. What is said of the perfection of the actions of instinct 1 Why
are the cells of the honevcomb made hexagonal 1 Describe the arrange-
ment of the ends of these cells. Give the fact stated in regard to the
angle made by the surfaces at their ends.
' 352. How is the perfection of the actions of instinct seen in animals
that live in communities'! Describe the structure of a wasp's nest.
Give, the description of the habits of the beaver.
354. In what respect may instinct be said to be blind 1 Illustrate bj
APPENDIX. 441
reference to animals that provide for a progeny which they are never to
see.
355. Why is it often difficult to distinguish between the results of
reason and those of instinct 1 What would be true of instinct if it
were at all rational? Under what circumstances is there perfection in
the actions of instinct 1 Under what circumstances does it fail '{ Con-
trast instinct and reason in this respect. Give some illustrations of the
characteristics of instinct alluded to.
356. Give Mr. Broderip's account of the beaver. If the beaver in this
case had been guided by reason, what would lie have done ? How far
is the care that animals take of their progeny governed by a blind
instinct ? What is said of the temporary character of parental affection
in their case 1 In what case is there no affection at all ?
357. What degree of intelligence is shown in the power of imitation
in animals 1 How do animals show that they reason '! How far did the
beaver, whose story is given in $ 541, reason 1 How does the character
of the inferences made by animals differ from that of those made by
man 1 Illustrate by reference to Newton and his dog. Of what are the
inferences made by animals the results?
358. When the processes of thought in animals are extended and
complicated, what is true of them ? Illustrate by examples the extent
to which mental association may be carried in the animal.
359. How do animals learn the relation of cause and effect 1 Illus-
trate by examples. How does this knowledge of cause and effect differ
in man and in animals 1 Is the mental difference between man and
animals one of degree only?
360. What attribute constitutes the great superiority of the human
mind? Show how this attribute is the origin of language in man.
What is the character of the language of animals ? Why cannot they
have a language of arbitrary signs 1 What is the source of man's be-
lief in a Creator 1 Illustrate this point. Is this belief implanted in the
mind 1 What two suppositions have been offered in relation to con-
science 1
361. What is said of the doubts which some entertain as to the exist-
ence of conscience I What is true of those cases in which animals
seem to some to have a moral sense 1 Illustrate the fact that in common
language we recognize the difference between man and animals as to
the possession of a conscience. Give a summary of the mental differ-
ences between man and animals.
362. Give the gradations which we find in the nervous system as wo
trace the animal kingdom upward. Why does instinct collect no expe-
rience 1 What is the difference between the two kinds of reasoning,
before spoken of, in collecting experience 1 What is said of the amount
of improvement of which some animals are capable by means of the
lower order of reasoning 1
363. What is the basis of improvement in man ? What ordinarily
constitutes the intellectual superiority of one man to another 1 In what
consists the merit of an inventor or discoverer? Illustrate by reference
to Jenner. What is the difference between the capabilities of instinct
and those of reason in the rapidity of their development ? Which form
of reasoning is developed first ?
364. Is the higher reasoning to some extent developed quite early 1
442 APPENDIX.
What is said of its deficiency in those cases in which the organization
is defective 1 What is said of the achievements of this reasoning power 1
What of the separation it makes between man and animals 1 What is
said of the slowness of development of man's physical structure 1 .
What is the general law as to the development of capabilities, both men-
tal and physical?
365. What is said of the prominence generally given to the difference
between man and animals in regard to physical endowments \ Illustrate
by reference to the hand. In all animals, to what are bodily endow-
ments suited 1 Mentjpn some bodily endowments in which some animals
excel man, and state the reason. In what respect is man most signally
superior to animals in physical endowment ] Illustrate this by refer-
ence to the hand and the vocal organs.
366. Illustrate the same point by the general motions of the body.
What is said of the human form in repose 1 How do we get the most
perfect idea of the superiority of the human organization 1
CHAPTER XIX.
367. Mention some of the contrasts which we find on looking over
the human race. How many varieties of the race are commonly reck-
oned ] What are the characteristics of the Caucasian variety 1
368. What are the characteristics of the Ethiopian varieties the
Mongolian the American the Malay 1 What is said of the extent
to which the race may be divided into varieties 1
369. What is said of the way in which national differences are pro-
duced 1 What is the opinion of most naturalists in regard to the pro-
duction of the races 1 What is the doctrine of Professor Agassis and
others 1 State the grounds on which he bases his doctrine.
370. What is his opinion in regard to climatic and other influences ?
What is his opinion of the history given in Genesis I Are the different
branches of the race iu his view different species, or mere varieties *
What is the distinction between a species and a variety 1
371. Mention the influences included in the expression, climatic and
other influences. What is said of the influence of climate 1 What is
the circumstance which has most influence in producing varieties in man
and in animals 1 What is included in the term domestication / What is
the precise question in regard to climatic and other influences 1
372. Mention some facts that show that climate has a great influence
on the color of the race. What influence do intellectual and moral
causes exert upon the shape of the head 1
373. What is said of certain changes in form produced by causes, the
operation of which we do not understand? What are the three differ-
ent types of form in the head stated by Dr. Pritchard, and by what
causes are they produced 1 State in regard to each : the prognathous
the pyramidal the oval. Give some facts showing that these types
are convertible into each other.
374. What is said of the insensible gradations by which the varieties
of the race pass into each other ? What two objections are brought
against the alleged competency of climatic and other influences to pro-
duce the varieties of the race ? What great fact is a sufficient reply to
these objections ! State and illustrate this.
APPENDIX. 443
375. Apply this fact in explanation of the production of the varieties
of the human race. What is said of the analogy thus drawn between
man and animals, in comparison with that which Professor Agassis has
tried to establish ! What consideration weakens his analogy 1
376. If the climatic and other influences appear to any one incompe
tent to produce the varieties of the race, is he driven necessarily to ad
mit its multiple origin ! What is said oif the occasional introduction oi
new causes by the Creator] Upon what do our calculations upon the
regularity of nature depend 1 What is said of the change in the age
of man effected at the time of the flood ! W r hat is said of the occa-
sional appearance of new diseases 1
377. What is said of the convulsions which have evidently taken
place in the earth 1 Does it make any difference to the argument,
whether the results came directly from causes, or from a chain of causes 1
Apply the argument to the production of the varieties of the race.
What is said of the objection to the argument, that it is supposing a
miraculous interposition !
378. Is the supposition thus made needed! What is said of it in
comparison with the supposition of Agassis 1 On what principles is the
testimony of the Bible as to the origin of the race to be interpreted I
What are the main facts which it gives in relation to it 1 How is the
truth of its testimony confirmed 1
379. Of what force is analogical and presumptive evidence in oppo-
sition to it! Is any fear to be entertained in regard to bringing the
Bible to the test of ascertained facts 1 If the account in Genesis be
true, to what alternative are the advocates of the multiple origin of the
race dftven ! How does it appear that the truth of the Bible and the
unity of the race must stand or fall together 1 Does the argument hold
good, even if the Mosaic account be considered a myth 1
380. What is the general conclusion in view of the whole subject 1
What moral bearing has the doctrine of the unity of the race ! What
is said of the pretended resemblance between the Ethiopian variety and
the monkey tribe of animals 1
CHAPTER XX.
381. What is said of the diversity in the manifestations of life!
How is life always the same in relation to its origin ! Remark on the
wonderful variety of results worked out by the vital force beginning in
a simple cell. How is life always essentially the same in its processes
as well as in its origin 1
382. Do we know what life is ! How does the vital force differ from
such forces as light, heat, and electricity, in regard to its power of diffu-
sion ! How in regard to self-generation ! How in regard to the variety
of its effects !
383. Do we know whether life is one thing! What is said of the
supposition, that the principle of life resides chiefly in the blood ! What
are the relations that exist in living bodies between the laws of chemis-
try and mechanics and those of life! Illustrate this point. W T hat is
said of the materials of which the human body is composed, and of the
degree of heat in which they are kept!
384. Show the difference in the operation of heat on dead and on liv
444: APPENDIX.
ing matter, as seen in the egg. How is the power of the vital force ex-
hibited in the uniformity of the heat of the body 1 What is said of the
changes going on by the operation of the vital force 1 Remark on the
dormant condition of this force in the case of seeds.
385. Remark on the analogy between the hibernation of animals and
Jie state of most of the vegetable world in winter. What portions of
the human system are some of the time dormant, and why ] What is
the most mysterious circumstance in regard to the vital force 1 Show
how the soul and the vital force are two distinct, and, in some measure,
opposing forces. In what different senses are they both present every-
where in the system 1
386. What is said of the development of the soul in the body 1 ?
What of the mystery of this connection 1 What is said of the limit of
the vital force 1 W'hat facts show that the endowments of life are not
commonly all destroyed at the moment of death 1
387. What is the distinction between systemic and molecular death 1
What three great systems of the body are each essential to the continu-
ance of life ! How may death begin in the circulating system 1 Give
the three classes of causes by which death may begin in the respiratory
system.
388. Give examples of death beginning in the nervous system. Illus-
trate the fact, that death is commonly a complex event. What is said
of the signs of death 1
389. What is said of the clearness of the evidence in all ordinary
cases in regard to the fact of death 1 In the very few cases in which
there is any doubt, what course should be pursued 1 What light can
physiology give us in relation to what is beyond this life 1 What is
said of the conjectures on this subject which its investigations may
prompt ?
CHAPTER XXL
390. From what two sources are the rules of hygiene to be learn-
ed 1 How far is a knowledge of physiology necessary to a proper
understanding of these rules 1
391. What division of topics should be made in the subject of
hygiene 1 What points in the hygiene of digestion have been before
noticed 1 What is said in regard to the amount of food needed by the
body 1 How can we know what this amount is 1
392. What errors are committed in regard to quantity of food 1 From
what causes is too little food sometimes taken 1 What is said of the
intervals between our meals 1
393. What is said of eating regularly 1 What of the different kinds
of food? What of fruits] What influence has the mind on digestion 1 ?
394. What is the general statement in $ 625 in regard to the hygiene
of respiration 1 In what two ways is the free access of the air to the
lungs interfered with 1 What general rule is given as to dress in re-
gard to the chest 1 In what ways does compression of the chest occa-
sion disease 1
395. Why ordinarily is the influence of defective aeration (or airing)
of the blood not appreciated 1
396. What influence has muscular exercise on the development of
APPENDIX. 445
the organs of the body ? How is it a preservative against disease 1
What is said of violent exercise 1 What is the change going on con-
tinually in all parts of the body ? What two conditions are necessary
to the proper performance of this change ?
397. What is said of the discharge of waste matter from the system 1
What organs effect this discharge 1 How much matter is discharged
from the skin 1
398. How is the animal heat produced 1 How does exercise increase
it? What influence has the quality of the blood upon it? What is
essential to a comfortable temperature of the body 1 When one is too
much heated how is the extra heat disposed of? What is the object in
covering the body with clothing and in surrounding it with heated air !
What is said of cold as a cause of disease ?
399. What are our means of guarding against cold? How should
we regulate the amount of clothing ? What is said of guarding against
cold when the body is in a state of rest ?
400. What is said of warming houses ? Why is the influence of
cold in producing disease commonly so little appreciated ? Under what
circumstances does cold act as a stimulant ?
401. What rules should be observed in the use of cold bathing?
What are the best times for using it? What occasions the wear and
tear of the system ?
402. When is most of the repairing of the system done ? What is
said of the relation of exercise to health? What effect has it on the
muscles themselves ? What on the other textures? How does if. pre-
vent deformity ?
403. What, are the two causes of the common deformity of the spine?
Explain their action. Why is this deformity found so much more
often in females than in males ? How much influence has posture in
producing it 1
404. What especially debilitates the muscles of the back in the
female ? Illustrate the necessity of having exercise varied also of
having it general. What is said of gymnastics and calisthenics ?
405. What is said of having the exercise habitual ? How does too
much exercise do harm ? What is said of having the exercise agree-
able ? What is said of the hygiene of the senses ?
406. What is said of the necessity of seasons of rest for the brain ]
What significant fact in regard to insanity shows this ? What is said
of the conditions under which the mind can perform much, labor without
harm? What is said of overworking the brain during its growth?
What of the manner in which the child's mind is ordinarily exercised ?
407. What two mental causes acting together injure the health and
sometimes produce insanity ? What influence has the regulation of the
passions on the health ? On what portions of the system do alcohol
and tobacco chiefly act ? What is said of alcoholic stimulants ?
408. Show how tobacco may act indirectly as a stimulant. What
are its effects on the system ? To what class of persons is it especially
injurious ? What is the evidence in regard to the influence of tea and
coffee ?
409. What is said of emanations from filth as producing disease ?
Give a summary of the chief causes of disease. Is disease commonly
38
446 APPENDIX.
produced by any one of these causes alone ? What is said of our con-
trol over these causes ?
410. What other causes of disease are there? To what extent do
they act compared with those mentioned in $ 674 1 How may we often
escape their influence ? What is said of the comparative value of pre-
ventive and curative measures 1 Illustrate the prevalent error on this
point by reference to consumption. From what does the common
neglect of preventive measures arise, and how can this be obviated!
INDEX.
(The numbers refer to the pages.)
Aberration, spherical 296
chromatic 297
avoided in the eye 297
Absorption 3
by lacteals 58
by lymphatics 117
by veins 118
by cells 128
Abscess, concert of action in. .115
Aeration of the Blood, how
done 86, 102
how interfered with 394
Agassis, his doctrine of the
multiple origin of the hu-
man race 369
Air, composition of and changes
in it by respiration 101
agency of plants in keeping
it pure 104
necessity of a good supply of
it to health 394
Air-cells of the lungs 86
importance of their function. 94
harm done in compressing
them 95
Air-sacs in birds 100
Alcoholic Stimulants, their in-
fluence on health 407
Alimentary Canal, meaning of
the term 15
of different lengths in differ-
ent animals 60
Allantois 136
Aneurism. 65, 69
Animals, distinctions between
them and plants 21
intelligence of 357
their associations of ideas.. .358
their mode of learning rela-
tion of cause and effect. . .359
Animal Magnetism 327
Aorta 65
valves of. 76
Arm, bones of. 192
Arteries, why so called 72
why made strong 65
situation of 67
how to stop their bleeding. . . 69
Articulation of the voice 259
Arytenoid Cartilages 249
Assimilation 15
Balancing, action of muscles in. 217
Bathing, how it should be
practised 401
Baya's nest 350
Beaver, habits of 350
Beauty, regard to in the ar-
rangement of the muscles. 197,
207, 214
Birds, respiration of 100
spinal column of 188
vocal apparatus of. 259
Blood, its changes 72
its course 73
variety of textures made
from it 110
cells in it 125, 127
life in 383
Bones, composition of 37
uses of. 170
insensibility of. 1 73
very sensible when inflamed. 155
marrow in 171
various shapes of. 173
of the head 175
of the nose 180
of the leg 194
of the foot 195
Bony socket of the eye 170
448
INDEX.
Brain 144-146
how guarded from violence. . 178
organ of the mind 319
its situation and connections 320
size of as measure of the
intellect .....336
its development influenced
by mental activity 372
hygiene of 406
Breast Bone 88
Buccinator Muscle 229
Calisthenics 404
Capillaries 65
their agency in keeping up
the circulation 70
Carnivorous Animals 43, 60
Carbonic Acid Gas, thrown off
from the lungs 101
where formed 102
quantity of it discharged
from the lungs 103
absorbed by plants 104
Cartilage 37
Cartilages joining the ribs to
the breast bone 88
between the vertebrae 185
Camera Obscura 293
Carpus 192
Cataract 295
Causes, evidence that new ones
have been introduced since
the original creation 376
Cells, the true formative ves-
sels 123
their shape 124
seen both in fluids and solids . 124
their contents 125
their selecting power 125
their operation incomprehen-
sible 126, 137
some make other cells 126
two kinds in the blood 127
cells perform absorption 128
and secretion 129
fibres of muscles made up of
cells 130
cells make teeth, nails, &c. .131
how they make nerves 132
cells in the gray substance
of the brain. . ..132
all living things built by
cells 132, 136
operation of cells in the egg
during incubation 133
Cellular tissue, structure of. 38
Cementum 181
Cerebellum, functions of. 332
Change, constant in the system. 121
Chemical laws controlled by
vital 383
Chest, framework of 88
compression of 95, 394
Chin, possessed only by man. . 30
Choroid coat of the eye 295
Chyle 58
Chyme 51
Ciliary processes 292
Circulation, its apparatus 64
double 73
affected by emotions of the
mind 239
hygiene of 395
Climate, influence of in causing
the varieties of the race. . .371
Cochlea 281
Coffee, influence of on health. .408
Cold, depressing influence of. .398
sometimes a stimulant 400
Cold-blooded animals 106
Collar bone 88, 190
Concert of action in formative
and other vessels 110-116
Conscience, not possessed by
animals 27, 360
Consciousness, its evidence
against materialism 344
Consonants, incorrectness of
the common definition. . . .264
nasal reverberation the pecu-
liarity of some of them. . .262
Convolutions of the brain 145
Convulsions 165
Coracoid process 190
Coronary arteries 80
Corrugator supercilii .228
Cranium, bones of. 175
Creator, belief in and knowl-
edge of result of the power
of abstract reasoning 360
Cricoid Cartilage 249
Crystalline lens 295
INDEX.
449
Cuticle 119
made up of cells 130
Daisy 18
Deaf and Dumb. . ..223
on the heat of the body 398
Experience, no transmission of
it in animals as in man. . . . 362
Expiration, mode of perform-
in g 90
why they are dumb 267: Expression, nerve of in the
teaching them to talk 268 | face paralyzed 157
Expression effected by muscles. 222
its principal muscles in man. 224
in animals 236
Eye, optical instrument. 287
nerves of 158
muscles of 208
in itself inexpressive 226
its parts 290-292
how it accommodates itself
to objects at different dis-
Death 387
Deformity, how produced 402
Deglutition 47
Dentals 261
Dentine 181
Diaphragm 89
Digastric muscle 206
Digestion 42
hygiene of. 53, 391
Disease, summary of its causes . 409
prevention of 410 |
Distinct vision, point of 312
Dog, his muscles of expression. 237
sagacity of 358
Dome, principles of seen in the
cranium 177
Domestication, influence of. . . .371
Drowning expla'ned 97
explanation of some cases of
restoration... ..109
tatices 298
its defences 315
Eye-brow, its agency in expres-
sion 225, 228
Face, muscles of. 202, 228
its capabilities in expression. 239
training of its muscles 240
state of its muscles after
death 242
Facial angle 336
Ear, its shape 275 I Far-sightedness 299
its bones 276
its winding passages 277
Egg, section of 1 34
how cells develop the bird. . . 135
Electricity not nerve force 160
Elementary substances in ani-
mals and vegetables 20
Elbow joint 194
Emphasis some of the princi-
ples of 269
Enamel, structure of. . . . .131, 182
Epiglottis 48, 216, 256
Erect posture of man 30
Ethiopian variety of the race ;
evidence of its existence
in early ages 374
Excretion, by what organs per-
formed 118
Exercise, influence of on diges-
tion 54
on the circulation 395
on the development of the
body 396
Fat, uses of.
Fear, action of muscles of face
in.
40
.235
Fibrillse muscular 130, 196
Fingers, arrangement of ten-
dons in 215
Fishes, respiration of 98
spinal column in 189
Food, quantity needed 391
regularity in taking 393
Foot, bones of 195
Fordyce, his experiments on
heat 107
Formation and repair, by what
done 109
hygiene of 396,401
Formative vessels, selecting
power of HO
their concert of action illus-
trated iu various ways. 1 10116
are really cells 123
Frog, changes from the tadpole
state ..112
38'
450
INDEX.
cells seen in the circulation
in web of the foot 124
Frontal sinus 179
different sizes of 335
Functions, distinctions be-
tween nutritive and animal. 36
Ganglions 149
Gastric juice 50
Gills, truly lungs 98
Gizzard, in birds 62
Grace, in the action of the
muscles 242, 366
Gradations, doctrine of. 32
Grasshopper, respiration in. ... 99
Gray substance of brain.. . 132, 147
amount of compared with
the white substance 3:?3
dependence of mind on 334
Gymnastics 404
Hand, really possessed only by
man 29
variety of its motions 218
Harvey, discoverer of the cir-
culation 72
Head, bones of 175
Hearing, apparatus of 274
nerves of 282
organ of in fishes 284
in birds , 285
Heart, a forcing and suction
pump 65
its action illustrated 69
double 73
valves in 74
its auricles and ventricles . .74-79
front view of. 80
map of 81
situation of 82
sounds of 83
its sac 84
its number of beats 85
insensibility of to touch 156
Heat of the body, how main-
tained 104, 397
where made.. . . .105
its uniformity in man. . . 107, 398
Herbivorous animals 43, 60
Hibernation 108
Hoarseness, cause of. 256
Honeycomb, the perfection of
it as a structure 351
Human race, varieties of 367
Humerus 190
Hunger, cause of and seat. ... 54
Hydra 23, 26
cells in 125
Hygiene, how its principles are"
learned 390
Hyoid bone 183, 248
Ilium 175
Images on retina, inverted. . . .293
why the mind sees them erect.299
rapidity of their succession. .314
minuteness of. 312
Immortality of man 28
known only from Revelation . 345
Insanity, result of disease in
the organization 320
some of its causes noticed. ..407
influence of sleeplessness in
producing it 406
Inspiration, mode of performing. 90
Instinct, more mysterious than
reason 348
uniformity of its action 349
its perfection 351
exhibited in communities of
animals 352
blindness of it 354-356
Involuntary muscles 162
not trained like voluntary. . . .326
Iris 294
Iron, in the blood 20
carried in cells 127
Jaw, lower 181
its digastric muscle 207
Joints, lining of 195
Knowledge, communicated only
by muscles 222
sources of the fuel for it 105
on what its amount depends. 106 Labials 261
effect of exercise on it 106 Lacteals 58
degrees of heat in the air | Language, result of the power
which the body will bear. . 107 j of abstract reasoning 360
INDEX.
451
Larynx 248-252
Laughter, by what muscles
done 224
Leaves, discharge oxygen and
absorb carbonic acid gas. .104
Lever, the three kinds of exem-
plified in the muscles 198
Ligaments, of the hand 193
of the wrist and ankle 206
vocal ..250
Life, its origin and processes.. .381
its nature unknown 382
differs from other forces 382
controls chemical forces 383
sometimes dormant 384
its connection with the soul. 385
Light, refraction of. 287-289
Lips, their agency in speech. . .261
Lime, in animals and vegeta-
bles 20
Lobworm, respiration of. 98
Locomotion, distinguishing ani-
mals from plants 21
Lungs, structure of 86
Lymphatic absorbents 59
what they absorb 117
Man, distinctions between him
and animals. .27-31, 347, 365
their definiteness 337
Mastication 43
Materialism, tendency to in
some physiologists, and
why ". 339
Meals, intervals between 393
Mechanical disadvantage under
which muscles act 203
Mesentery, plan of 57
Metacarpus 192
Metatarsus 194
Mind, dependence of on the
brain 319
rapidity of its communica-
tion with all parts of the
body 321
training of in the use of the
senses and muscles ...... 322
its supposed indestructibility. 339
sources of evidence as to the
nature of its union with
the body 339-347
intimacy of its union with
the body 338
influence of mind on diges-
tion 393
Miracle, supposition of in caus-
ing the varieties of the
race 377
Monboddo's notion 347
Motion, spontaneous 22, 142
automatic 24
involuntary 162
Mouth, agency of in expression. 224
Mucous membranes 40
Muscles 38
their structure 130
mode of action 196
of arm 199
of face and neck 202
of the eye 208
of larynx 251
various shapes of 210
combined motions of.210, 216, 220
variety of size of 214
constant change in action of. 21 7
all knowledge communica-
ted by muscles 222
skill in their use 324
their associated action 327
Muscular sense 220, 308
Nails, made by cells 131
Nasal sounds 262
National differences 369
Nature, its inner beauty great-
er than its outer 137
Near sightedness 299
Nerves made from cells 131
terminations of 150
healing of 152
different sets of for different
purposes 1 53
for different sensations 154
for different motions 156
nerves of the eye 158
of the ear '. 281
Nervous system, distinguishing
animals from vegetables.. 23
its different parts 141, 143
Nerve-force, not identical with
electricity 160
Nitrogen, how far peculiar to
animals 27
452
INDEX.
Nictitating membrane 317
Nose, bones of. ISO
nerves of 154
Note, variations of, how pro-
duced in wind instruments. 246
in reed 247
in the vocal instrument 257
Oesophagus described 49
Objects, how they are pictured
on the retina 292
how the eye is adjusted to
their different distances. . .298
how we estimate their motion. 3 13
Optic nerves, crossing of 305
Organ, flute stop of 245
Organic life, distinguished from
animal life 24, 139
Organized and unorganized
substances 13
difference between in per-
manency 15
in regularity 17
in size 19
in structure 20
organized built by cells 136
Ostrich, respiratory apparatus of. 1 00
Oval form of head 373
Oxygen, absorbed by the lungs. 101
exhaled by plants 104
Pacinian corpuscles 151
Pain, a warning of danger. . . .154
expression of the courten-
ance in 225
Papillae of the skin 120, 150
Patella 183, 194
action of the muscles on. . . .205
Pelvis 173
Perspiration, influence of in
enabling the body to bear
very hot air 108, 398
Petrous (rock-like) bone. . . 180, 275
Pharynx 47
Phrenology 334
Plants, distinctions between
them and animals. ....... 21
Pleura 88
Plexuses of nerves 149
Prognathous type of head 373
Pulse, cause of . . 65
Pylorus 51
Pyramidal type of head 373
Quickness of action the chief
object in most muscles 200
Radius 192
Rage, action of muscles of
face in 234
Reaction against cold, how pro-
duced 400
Reason, not confined to man.. .348
of a lower order in animals. .362
Reasoning abstract, peculiar to
man 27, 359
source of language 360
of a belief in a creator 360
of knowledge of right and
wrong 360
Reed instruments 247
Reflex action explained 162
Respiration, its apparatus 86
mechanism of 88
hygiene of 394
Respiratory apparatus of fishes. 98
of insects 99
of birds 100
Retina, structure of 296
images formed on 292
Revelation, its evidence against
materialism 345
testimony of in regard to
unity of origin of the race. 378
Reverie, involuntary action of
muscles in 167, 327
Ribs, arrangement of. 88
movement of in respiration.. 92
Ringentes (muscles) 237
Robinet, his doctrines 31
Sacrum 173
Salivary glands 45
Scapula 190
Scintillantes (muscles) 237
Secretions, formed from the
blood 116
by cells 129
Sebaceous glands 120
Seeing, a process that is learn-
ed 305
Semicircular canals 278, 282
Sensation, distinguishes ani
mals from plants 22
INDEX.
453
a compound act 141
what is necessary to it 142
special and common 154
Sensibility, various in different
parts 155
Serous membranes 41
Silex in plants 20
Silkworm, its changes illus-
trating concert of action
in the formative vessels.. ..113
Skeleton, description of 173
Skin, structure and functions of. 1 19
hygiene of . , 397
great sensibility of 155
Somnambulism 330
Song, how it differs from speech. 268
why more difficult 270
Soul, its connection with the
vital force 385
Sound, how produced and trans-
mitted 272
difference in transmission
through solids, liquids and
gases .273
Sound musical, how it differs
from noise 271
how its note is varied in wind
instruments 246
how in reed 247
how in the vocal instrument. 253
Speech, instruments for imita-
ting it 264
Species, how it differs from
variety 371
Spinal column... 88, 173, 183-187
of birds 188
of fishes and reptiles 189
deformity of, how caused. . . .403
Spinal cord or marrow 153
its functions 164,167
Squinting 209, 30 1
Stammering 267
Stereoscope 302
Stomach, used in two senses. . . 15
distinguishing animals from
plants 21
its three coats 41
its muscular coat 51
difference of this organ in
different animals 60
Stigmata 99
Superbus muscle 230
Sutures of the skull 177
Sweat glands.. .. . . 120
Sympathetic system of nerves . . 169
Talking, how learned 265
Tarsus 194
Tailor-bird's nest 350
Tea, influence of on health 408
Tear apparatus 316
Teeth, different kinds 43
structure of. 131, 181
nerves in 151
why second set needed 182
Tendons 38, 197
Temporal bone 177
Thaumatrope 315
Thigh bone 194
Thirst, cause of and seat 55
Thoracic duct 59
Throat disease 259
Thyroid cartilage 248
Tobacco, its influence onhealth.408
Togg'e-joint, exemplified in the
joints of the body 217
Tongue, its variety of motion.,210
its agency in speech 260
Training of the muscles and
the senses 325
Tubuli of the nerves 147, 152
Ulna
..192
Valves of the heart 74, 78
of the aorta 77
of the veins 67
Vanishing movement in the
voice 269
Veins, structure and situation
of. 65
why the blood accumulates
in them at death 71
what they absorb 118
Ventilation, effects of, defective. 103
Ventriloquism 271
Vertebrae described 184
Violin, imitation of the voice
with 257
Vision, apparatus of 287
why commonly single 300
sometimes double 301
vision mostly a mental pro-
cess .. ..309-311
454
INDEX.
how the figure, size and dis-
tances of objects are
known 305-308
mistakes in, how rectified. . .308
Visual angle 305
Vitreous table of the bones of
the skull 176
Vocal ligaments 250
Vocal muscles, education of. . .258
trained by the ear 258, 266
Voice, chief means of com-
municating knowledge 222
its apparatus a musical in-
strument 243 !
articulation of. 259
Waste of the system, by what
organs thrown off.. . . 118, 397
influence of its retention. . . .397
Wasp's nest 352
Water-scorpion, respiration of. 99
Weeping, action of the mus-
cles in 225
Whale, arrangement for catch-
ing its food 45
its reservoirs for containing
arterial blood 97
Whispering, how done 263
White substance of the brain. .147
office of 334
Wind instruments 245
Zoological provinces 370
Agassis's analogy in this re-
spect fails in regard to
man 375
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