' '. &iMA >~^ . LIBRARY OF THE UNIVERSITY OF CALIFORNIA. IFT OF b,Q C BIOLOGY LIBRARY : Class THE VISCERA IN POSITION. TREATISE ON PHYSIOLOGY AND HYGIENE FOR EDUCATIONAL INSTITUTIONS AND GENERAL READERS. FULLY ILLUSTRATED. BY JOSEPH C. HUTCHISON, M. D., President of the New York Pathological Society, Vice-President of the New York Academy of Medicine, Surgeon to the Brooklyn City Hospital, late President of the Medical Society of the State of New York, etc. NEW YORK : CLARK & MAYNARD, PUBLISHERS, 5 BARCLAY STREET. 1880. BIOLOGY LIBRARY G Copyright, 1875, CLARK & MAYNARD. TO MY WIFE, WHOSE SYMPATHY HAS, FOR MORE THAN TWENTY YEARS, LIGHTENED THE CARES INCIDENT TO AN ACTIVE PROFESSIONAL LIFE, THIS HUMBLE VOLUME IS AFFECTIONATELY INSCRIBED 183669 PREFACE. THIS work is designed to present the leading facts and principles of human Physiology and Hygiene in cle^x and concise language, so that pupils in schools and colleges, and readers not familiar with the subjects, may readily comprehend them. Anatomy, or a de- scription of the structure of an organ, is of course necessary to the understanding of its Physiology, or its uses. Enough of the former study has, therefore, been introduced, to enable the pupil to enter intelligently upon the latter. Familiar language, as far as practicable, has been employed, rather than that of a technical character. With a view, however, to supply what might seem to some a deficiency in this regard, a Pronouncing Glossary has been added, which will enable the in- quirer to understand the meaning of many scientific terms not in common use. In the preparation of the work the writer has carefully examined all the best material at his command, and freely used it ; the special object being to have it abreast of the present knowledge on the sub- jects treated, as far as such is possible in a work so elementary as this. The discussion of disputed points has been avoided, it being manifestly inappropriate in a work of this kind. Instruction in the rudiments of Physiology in schools does not necessitate the general practice of dissections, or of experiments upon animals. The most important subjects may be illustrated by draw- 4 PREFACE. ings, such as are contained in this work. Models, especially those constructed by Auzoux of Paris, dried preparations of the human body, and the organs of the lower animals, may also be used with advantage. The writer desires to acknowledge his indebtedness to R. M WYCKOPF, M.D., for valuable aid in the preparation of the manu- script for the press; and to R. CRESSON STILES, M.D., a skilful microscopist and physician, for the chapter " On the Use of the Microscope in the Study of Physiology." Mr. AVON C. BURNHAM, the well-known teacher of gymnastics, furnished the drawing or tl-3 parlor g3^mnasium and the directions for its use. UNIVERSITY f CONTENTS. CHAPTER I. PAGE THE FRAMEWORK OF THE BODY , 15 The Bones Their form and composition The Properties of Bone The Skeleton The Joints The Spinal Column The Growth of Bone The Repair of Bone. CHAPTER II. THE MUSCLES 26 The Muscles Flexion and Extension The Tendons Contraction- Physical Strength Necessity for Exercise Its Effects Forms of Exercise Walking Riding Gymnastics Open-air Exercise Sleep Recreation. CHAPTER III. THE INTEGUMENT, OR SKIN 4" The Integument Its Structure The Nails and Hair The Complexion The Sebaceous Glands The Perspiratory Glands Perspiration and its uses Importance of Bathing Different kinds of Batlis Manner of Bathing The Benefits of the Sun Importance of Warm Clothing Poisonous Cosmetics. CHAPTER IV. THE CHEMISTRY OF FOOD 53 Tne Source of Food Inwganic Substances Water Salt Lime Iror Organic Substances Albumen, Fibrin, and Casein The Fats v Oils The Sugars, Sfa-?ch, and Gu,m Stimulating Substano* .T r efenty of a Regulated Diet. CONTENTS. CHAPTER V. PAGB FOOD AND DRINK 64 Necessity for Food Waste and Repair Hunger and Thirst Amount of Food Renovation of the Body Mixed Diet Milk Eggs Meat Cooking Vegetable Food Bread TJie Potato Fruits Purity of Water Action of Water upon Lead Coffee, Tea, and Chocolate Effects of Alcohol. CHAPTER VI. DIGESTION 80 The Principal Processes of Nutrition The General Plan of Digestion Mastication The Teeth Preservation of the Teeth Insalivation The Stomach and the Gastric Juice The Movements of the Stomach Gastric Digestion The Intestines The Bile and Pan- creatic Juice Intestinal Digestion Absolution by means of Blood- vessels and Lacteals The Lymphatic or Absorbent System The Lymph Conditions which affect Digestion The Quality, Quan- tity, and Temperature of the Food The Influence of Exercise and CHAPTER VII. THE CIRCULATION 101 The Blood Its Plasma and Corpuscles Coagulation of the Blood The Uses of the Blood Transfusion Change of Color The Organs of the Circulation The Heart, Arteries, and Veins The Cavities and Valves of the Heart Its Vital Energy Passage of the Blood through the Heart The Frequency and Activity of its Movements The Pulse The Spygmograph The Capillary Blood-vessels The Bate of the Circulation Assimilation Injuries to the Blood-vessels. CHAPTER VIII. RESPIRATION 123 The Objects of Respiration The Lungs The Air- Passages The Move- ments of Respiration Expiration and Inspiration The Frequency of Respiration Capacity of the Lungs The Air we Breathe Changes in the Air from Respiration Changes in the Blood In- terchange of Oases in the Lungs Comparison between Arterial and CONTENTS. 7 Venous Blood Respiratory Labor Impurities of the Air Dust Carbonic Acid Effects of Impure Air Nature's Provision for Purifying the Air Ventilation Animal Heat. CHAPTER IX. PAG* THE NERVOUS SYSTEM 1 48 Animal and Vegetative Functions Sensation, Motion, and Volition The Structure of the Nervous System The White and Gray Sub- stances The Brain Its Convolutions The Cerebellum The Spi- nal Cord and its System of Nerves The Anterior and Posterior Roots The Sympathetic System of Nerves The Properties of Nerv- ous Tissue Excitability of Nervous Tissues The Functions of the Spinal Nerves and Cord The Direction of the Fibres of the Cord Reflex Activity and its Uses The Functions of the Medulla Oblon- gata and the Cranial Ganglia The Reflex Action of the Brain. CHAPTER X. THE SPECIAL SENSES 177 The Production of Sensations Variety of Sensations General Sensi- bility Pain and its Function Special Sensation, Touch, Taste, Smell, Sight, and Hearing The Hand, the Organ of Touch The Sense of Touch Delicacy of Touch Sensation of Temperature and Weight The Tongue the Organ of Taste The Nerves of Taste The Sense of Taste, and its Relations with the other Senses The Influence of Education on the Taste The Nasal Cavities, or the Organs of Smell The Olfactory Nerve The Uses of the Sense of Smell The Sense of Sight Light The Optic Nerve The Eyeball and its Coverings The Function of the Iris The Sclerotic, Choroid, and Retina The Tears and their Func- tion The Movements of the Eyeball The Function of Ac- commodation The Sense of Hearing and Sound The Ear, or the Organ of Hearing The External, Middle, and Internal Ear. CHAPTER XI. THE VOICE 227 Voice and Speech The Larynx, or the Organ of the Voice The Vocal Vords The Laryngoscope The Production of the Voice The Use of me, Tongue The different Varieties of Voice The Change of Voice Its Compass - Purity of Tone Ventriloquy, 8 CONTENTS. CHAPTER XII. PAGE THE USE OP THE MICROSCOPE IX THE STUDY OF PHYSIOLOGY 236 The Law of Tissues Necessity of the Microscope Different kinds of Microscopes Additional Apparatus Preliminary Studies The Study of Human Tissues Tissues of the Inferior AnimaU Incen- tives to Study. APPENDIX. POISONS AND THEIR ANTIDOTES , . , . . . . * 247 GLOSSARY 252 LIST OF ILLUSTRATIONS FRONTISPIECE, VISCERA IN POSITION, > 1. Section of bone, . . . . . . 17 2. Structure of bone, magnified, . . . . 17 3. The skeleton, 18 4. Cells of cartilage, 20 5. Elbow-joint, 21 6. Spinal column, ........ 22 7. The muscles, 24 8. Muscular tissue, magnified, ..... 25 9. Biceps muscle of the arm, .... .26 10. View of knee-joint, 27 11. Appliance for strengthening the muscles, . . . 35 12. Appliance for strengthening the muscles, ... 35 13. Parlor gymnasium, ....... 36 14. Root and transverse section of hair, magnified, . . 43 15. Granules of potato starch, . . . . .61 1 6. Section of the trunk, 81 17. Section of a tooth, 82 1 8. Section of the jaws, ....... 82 19. Section of the jaws right side, 84 20. Structure of a salivary gland, 87 21. Head of a horse, showing salivary gland, etc. . . 87 22. Section of chest and abdomen, 90 23. Organs of digestion, 91 24. The lacteals, \ 97 25. Blood corpuscles, 102 26. Blood corpuscles of man and lower animals, . . " 103 27. Circulation of the blood, . . 108 10 LIST OF ILLUSTRATIONS. FIG. PAGE 28. Heart and large vessels, ...... 109 29. Section of the heart, 1 10 30. Form c. the pulse, 116 3 1 . Valves of the veins, 117 32. Web of frog's foot, magnified, 119 33. Circulation in a frog's foot, 119 34. Organs of the chest, 124 35. Larynx, trachea, and bronchial tubes, . . . . 125 36. Diagram of the structure of the air-cells, . . . 125 37. Section of the lungs, . . . . . . .126 38. Section of mouth and throat, . . . . . 127 39. Ciliated cells, 128 40. Cerebro-spinal system, . . . . . . 151 41. Upper surface of the cerebrum, . . . . . 153 42. Vertical section of the brain, 154 43. Base of the brain, . . . . . . . . 155 44. Brain and spinal cord, 156 45. Sense of touch, 185 46. Section of nasal cavity, . . . . . . 193 47. Front view of the eye, . 200 48. Vertical section of eye, 202 49. Diagram for blind point of eye, ..... 207 50. Retinal image, 210 51. Different shapes of the globe of the eye, . . .212 52. Function of accommodation, . . . . . 214 53. Diagram of the ear, 218 54. Section of the ear, 221 55. Section of larynx and trachea, 229 56. View of vocal cords by the laryngoscope, . . . 232 57. Different positions of vocal cords, 232 58. Simple microscope, . .... 238 59. Compound microscope, 239 60. Household microscope, 240 61. Popular microscope., 241 INTRODUCTION. THE Human Body is the abode of an immortal spirit, and is the most complete and perfect specimen of the Creator's handiwork. To examine its structure, to ascer- tain the uses and modes of action of its various parts, how to protect it from injury, and maintain it in a health/ condition, is the design of this work. The departments of knowledge which are concerned in these investigations, are the science of Human Physi- ology and the art of Hygiene. PHYSIOLOGY treats of the vital actions and uses of the various parts of living bodies, whether vegetable or ani- mal. Every living thing, therefore, has a Physiology. We have a Vegetable Physiology, which relates to plants; and an Animal Physiology, relating to the animal king- dom. The latter is also divided into Comparative Physiol- ogy, which treats of the inferior races of animals, and Human Physiology, which teaches the uses of the various parts of the human body. HYGIENE, or the art of preserving health, is the practi- cal use of Physiology. It teaches us how to cultivate our bodily and mental powers, so as to increase our strength and to fit us for a higher enjoyment of life. It also shows us how to prevent some of the accidents which may befall the body, and to avoid disease. It is proper that we should I'Z INTRODUCTION. understand the construction and powers of our bodies; but it is our duty, as rational beings, to know the laws by which health and strength may be maintained and disease warded off. There are various means by which we gain important information respecting the Physiology of man. Plants aid us in understanding the minute structure of the hu- man body, its circulation, and absorption. From inferior animals we learn much in respect to the workings of the different organs, as we call those parts of the system which have a particular duty to perform. In one of them, as in the foot of the frog, we can study the circulation of the blood; in another, we can study the action of the brain. By vivisection, or the laying bare of some organ of a living animal, we are able to investigate certain vital processes which are too deeply hidden in the human body to be studied directly. This is not necessarily a cruel procedure, as we can, by the use of anaesthetics, so blunt the sensibility of the animal under operation, that he need not suffer while the experiment is being performed. There are other means by which we gather our informa- tion. There are occasionally men, who, from some acci- dent, present certain parts, naturally out of view, in exposed positions. In these cases, our knowledge is of much greater value than when obtained from creatures lower in the scale of being than man. We are greatly aided, also, by the use of various instru- ments of modern invention. Chief among these is the microscope, which is, as we shall learn hereafter, an ar- rangement and combination of lenses in such a way as greatly to magnify the objects we wish to examine. INTRODUCTION. 13 We have much to say of Life, or vital activity, in the course of our study of Physiology; but the most that we know of it is seen in its results. What Life is, or where its precise position is, we are not able to determine. We dis- cover one thing, however, that all the parts of the body are united together with wonderful sympathy, so that one part cannot be injured and other parts not suifer damage. It is further evident that all organs are not equally im- portant in carrying on the work of Life; for some may temporarily suspend their action, without serious results to the system, while others must never cease from acting. Yet there is nothing superfluous or without aim in our frames, and no part or organ can suifer harm without actual loss to the general bodily health. On this point Science and Holy Writ strictlv PHYSIOLOGY, AND HYGIENE. CHAPTER I. THE FRAMEWORK OF THE BODY. The Bones Their Form and Composition The Properties of Bone-~ The Skeleton TJie Joints The Spinal Column The Growth of Bone The Repair of Bone. 1. The Bones. The framework which sustains the human body is composed of the Bones. The superstructure consists of the various organs on which the processes of life depend. These organs are soft and delicately formed, and, if unprotected, would, in most cases, rapidly be de- stroyed when subjected to violence, however slight. The bones, having great strength and power of resistance, afford the protection required. (Read Note i, end of Chapter) 2. The more delicate the organ, the more completely does Nature shield it. For example : the brain, which is soft in structure, is enclosed on all sides by a complete box of bone; the eye, though it must be near the surface of the body to command an extensive view, is sheltered from injury within a deep recess of bone; the lungs, requiring freedom of motion as well as protection, are surrounded by a large case of bone and muscle. The bones serve other useful purposes. They give permanence of form to the body, by 1 . The framework of the body ? The superstructure ? Softness and delicacy of tho organs ? How protected ? 2. The more delicate the organ ? Example in relation to the brain ? The eye ? The lungs ? The services performed by the bones ? 16 THE FRAMEWORK OF THE BODY. holding the softer parts in their proper places. They assist in movement, by affording points of attachment to those organs which have power of motion the muscles. 3. The Form and Composition of the Bones. Their shape and size vary greatly in different parts of the body, but generally they are arranged in pairs, one bone for each side of the body. They are composed of both mineral and animal substances, united in the proportion of two parts of the former to one of the latter; and we may sep- arate each of these substances from the other for examina- tion. First, if we expose a bone to the action of fire, the animal substance is driven off, or " burned out." We now find that, though the shape of the bone is perfectly retained, what is left is no longer tough, and does not sus- tain weight as before. Again, we may remove the mineral portion, which is a form of lime, by placing a bone into a dilute acid. The lime will be dissolved out, and the shape of the bone remain as before; but now its firmness has disappeared, and it may be bent without breaking. 4. If, for any reason, either of these ingredients is dis- proportionate in the bone during life, the body is in danger. The lime is useful in giving rigidity of form, while the animal substance insures toughness and elas- ticity. By their union, we are able to withstand greater shocks and heavier falls than would be possible with either alone. In. youth, the period of greatest activity, the animal constituent is in excess: a bone then does not break so readily, but, when broken, unites with great rapidity and strength. On the other hand, the bones of old persons are more easily broken, and in some cases fail to unite. The mineral matter being then in excess, indi- cates that the period of active exertion is drawing to a close. (Read Note 2, end of Chapter) 3. Their shape and size ? Of what composed? Possibility of being separated ? Effect of fire ? Of dilute acid ? 1 . Effect of deficiency of ingredient ? Usefulness of the lime ? Of the anima. Hiltr-iance? Effect of their union ? Condition, in youth ? THE FRAMEWORK OF THE BODY. 1? 5. The Structure of the Bones. If we examine one of the long bones, which has been sawn through length- wise, we observe that it is admirably fashioned for affording A.. Longitudinal B. Transverse section of bone. FIG. 1. SECTION OF BONE. lightness as well as strength (Fig. 1). Its exterior is hard and resisting, but it is porous at the broad extremities, while through the central portion there is a cavity or canal which con- tains an oily substance, called marrow. Let us now take a thin section of bone, and examine it under the mi- croscope; we discover that it is pierced by numerous fine tubes (Fig. 2), about which layers of bone-substance are arranged. Accordingly, though a bone be as hard as stone externally, it is by no means as heavy as stone, by reason of its light interior texture. Another element of power is found in the curved outline of the bones. The pis 2 curved line is said to be " the line of structure of bone en- beauty," as it certainly is the line of larged ' strength, and is uniformly employed in the bones whose position exposes them to accident. 5. In what respect admirably faehioned ? Its formation? Microscopic exam npon ? The inference? " Line of beauty ?" FIG. 3. THE SKELETON THE FRAMEWORK OF THE UODY. 19 6. The Skeleton. The number of bones in the human body exceeds two hundred. When these are joined together in the proper places, they form what is termed the Skeleton (Fig. 3). It embraces three important cavities. The first, surmounting the frame, is a box of bone, called the skull; below this, is a bony case, or " chest ;" anl lower down is a bony basin, called the pelvis. The two latter compose the trunk. The trunk and skull are maintained in their proper relations by the " spinal column." Branching from the trunk are two sets of limbs: the arms, which are attached to the chest by means of the " collar-bone" and " shoulder-blade ;" and the legs, directly joined to the lower part of the trunk. (Read Note 3, end of Chapter^ 7. The cavities of which we have spoken, are designed for the lodgment and protection of the more delicate and perishable parts of the system. Thus, the skull, together with the bones of the face, shelters the brain and the organs of four senses sight, hearing, smell, and taste. The chest contains the heart, lungs, and great blood-ves- sels, while the lower part of the trunk sustains the liver, stomach, and other organs I 8. The Joints. The point of union of two or more bones forms a joint or articulation, the connection being made in various ways according to the kind and amount of motion desired. The movable joints are compacted together by certain strong fibrous bands, called ligaments. These ligaments are of a shining, silvery whiteness, and very unyielding; so much so, that when sudden violence is brought to bear in the vicinity of a joint, the bone to which a ligament is attached may be broken, while the ligament itself remains uninjured. When this connect- ing material of the joints is strained or lacerated by an ac- 6. Number of bones ? Skeleton ? The skull ? Chest ? The trunk ? The trunk and skull, how maintained ? What of the arms ? Legs ? 7. Design of the cavities ? Give the examples. 8. Joint or articulation ? Movable joints, how compacted? The ligaments of the movable joint* ? What is a sprain ? Consequence of a serums eprain? THE FRAMEWORK OF THE BODY. cident, a "sprain" is the consequence, j An injury of this sort may be, and frequently is, quite as serious as the breaking of a bone. (Read Note 4, end of Chapter^ 9. The ligament, then, secures firmness to the joint; it must also have flexibility and smoothness of motion. This is accomplished by a beautiful mechanism the perfec- tion of which is only feebly imitated by the most ingenious contrivance of man. [T]ie ends of the bones are covered by a thin layer of cartilage/ which being smooth and elas- tic, renders all the movements of the joint very easy. In addition to this, there is an arrangement introduced for " lubricating" the joint, by means of a delicate sac con- taining fluid. This fluid is constantly supplied in small quantities, but only so fast as it is used up in exercise. In appearance, it is not unlike the white of an egg, and hence its name synovia, or egg-like. 10. Thus, we observe, that two very different substances enter into the composition of a joint. The ligament, very unyielding, affords strength, while the cartilage, elastic and moist, gives ease and smooth- ness of motion. The amount of motion provided for varies greatly in different joints. In some there is none at all, as in the skull, where one bone is dove-tailed into another by what are termed j^wres.; Others have a hinge-like motion, such as FIG. 4.-CELLS or CARTHAGE. thoge of the elbow? wns t, ankle, and knee ; the most complete of these being the elbow- joint (Fig. 5). Belonging to another class, the ball-and- 9. Office of the ligament ? What must it have ? How accomplished ? Describe it. Synovia ? 1 0. What do we observe as regards the composition of a joint ? The lie 1 roent and cartilage? What varies? Example of tho skull ? Other example* ? The bal]-and- c orkot i^lnt? THE FRAMEWORK OF THE BODY. socket joint, is that at the shoulder, possessing a freedom of motion greater than any other in the body. PIG 5. ELBOW JOINT. A, Bone of the arm ; B, C, Bones of the fore-arm. 11. The Spinal Column. The spinal column is often spoken of as the " back-bone," as if it were a single bone, while, in reality, it is composed of a chain of twenty-six small bones, called vertelrce. The spinal column is a wonderful piece of mechanism. It not only connects the important cavities of the body, as has already been shown, but, also, itself forms a canal, which contains the spinal cord. The joints of the vertebrae are remarkable for the thick layers of cartilage which separate the adjacent sur- faces of bone. The amount of motion between any two of these bones is not great; but these little movements, taken together, admit of very considerable flexibility, in several directions, without endangering the supporting power of the column. 1 1 . What is the spinal column ? What docs it connect and form ? Joints cf the vertebra ? Amount of motiou? Result? 22 THE FKAMEWOKK OF THE BODY. 12. The abundant supply of iiitervertebral cartilage has another important use, namely, it adds greatly to the elasticity of the frame. It is due, in part, to this elastic material, and in part to the frequent curves of the spine, that the brain and other delicate organs are protected from the shock of sudden falls or jars. During the day, the constant pressure upon these joints, while the body is erect, diminishes the thickness of the cartilages; so that a person is not so tall in the evening as in the morning. The effects of this compres- sion pass away when the body reclines in a horizontal position. (Read Note 5, end of Chapter) 13. The Growth of Bone. Bone, like all the other tissues of the body, is con- stantly undergoing change, old material being withdrawn, and new particles taking their place. This has been shown conclu- sively by experiments. If an animal be fed with madder a red coloring matter for a day or two, the bones soon become tinged ; then, if the madder be discontinued for a few days, the original color returns. If, how- ever, this material be alternately given and withheld, at short intervals, the bone will be marked by a succession of red and white rings. In very young animals, all the bones become colored in a single day; in older FIG. 6. THE ones, a longer time is required. The process SPINAL COLUMN. rt , *.* ^ of waste and repair, therefore, is constantly taking place in this hard substance, and with astonishing rapidity. 12. Elasticity of the frame ? Protection of the brain from shocks Tallness of persons? Effects of reclining ? 13. Change in hone? Example- animal and madder. Rapidity of change' in color? W*te and repair ! THE FRAMEWORK OF THE BODY. 23 J 14. The Repair of Bone. Nature's provision for ^uniting broken bones is very complete. At first, blood is \ poured out around the ends of the bone, as a result of the injury. This is gradually absorbed, and gives place to a watery fluid, which, thickening from day to day, ac- quires, at the end of two weeks, the consistency of jelly. This begins to harden, by a deposit of new bone-substance, until, at the expiration of five or six weeks, the broken bone may be said to be united. It is, however, still fragile, and must be used carefully a few weeks longer. The process of hardening continues, and months must pass hefore the union can be said to be complete. (Read Note 6.) QUESTIONS FOR TOPICAL REVIEW. PAGE 1. What useful purposes do the bone? serve *>. 15, 16 2. State what you can of tho composition of the bones 16 8. Of the usefulness of lime in the bones 16 1. Of the usefulness of animal substance in the bones 16 5. State what you can of the structure of the bones 17 6. Of the strength belonging to the bones 15. 16, 17 7. What is in eant by the human skeleton 1 19 8. Give-a description of .its construction , ; Tvr-rT-rj^^. 18 9. What is meant by a j oint in the human frame ? 19 K). State what you can of the movable joints 19, 20 11. What office is performed by the ligaments of the joints ? 19, 20 12. What by the cartilage at the joints ? 20 13. What movable joints are there ? 20, 21 14. Describe the construction of the spinal column. 21 15. What properties and powers does the spinal column possess ? 21, 22 16. When is a person taller than at other times ? 22 17. Give the reason for this 22 18. What can you state of the growth of bone? 22 19. Describe the process by which a broken bone is repaired S3 NOTES. 1. Self-knowledge (p. 15, ^ 1). "It has been said with truth that the human mind, which can survey the heavens and calculate the motion and density of the stars, finds itself confounded when, returning from these distant journey- ings, it enters its own dwelling-place the body. Man t? own organization is still among those mysteries of nature which he is least able to penetrate, in spite of his incessant efforts to lift the veil which hides it. In all ages he has sought to know himself. In all times he has studied the relations between his own existence and that of the world, and those universal influences which, though evident to him, are nearly all inexplicable in their action upon living beings. 11 ^ Pileuron the Human Body. 2. Some Properties of Bone (p. 16, 1 4). The power of bone to resist decay is remarkable. Fossil bones deposited in the ground long before the appear- ance of man upon the earth have been found by Cuvier exhibiting a considerable portion of cartilage. The jaw of the Cambridge mastodon contained over forty per cent, of animal matter enough to make a good glue and others about the same. From this we see that a nutritious soup might be made from the bones of animals that lived .before the creation of man. The teeth resemble bone in their structure, but resist decay longer ; they are brought up by deep-sea dredging, when all other parts of the animal have wasted away. The bones differ at differ- ent ages, and under different social conditions. In the disease called 'rickets,' quite common among the ill-fed children of the poor in Europe, but somewhat rare in America, there is an inadequate deposit of the mineral substance, render- ing the bones so flexible that they may be bent almost like wax. In females and weak men the bones are light and thin, while in a powerful frame they are dense and heavy. Exercise is as necessary to the strength of bone as to the strength of muscle ; if a limb be disused, from paralysis or long sickness, the bones lose in weight and strength as well as the soft parts. Bone is said to be twice as strong as oak, and, to crush a cubic inch of it, a pressure equal to 5,000 pounds is requi- site. Dunglison (in part)." 3. Two Forms of Skeleton among Animals (p. 19, 1 6). "The solid basis on which all the soft organs of the body rest is the skeleton. In the human body the skeleton is composed of a number of bones, each of which has a distinct name. In the animal kingdom there are two distinct forms of skeletons ; the one which is found chiefly in the lower animals is outside, and covers the soft parts, and is called an exo-skeleton. Examples of this kind of skeleton are seen in crabs, lobsters, insects, and the shells of mollusca, as oysters, mussels, and whelks. The shells of these animals are mostly composed of carbonate of lime. Fishes possess an internal skeleton ; and all the classes of animals above them, as reptiles, birds, and mammals, possess internal or endo-skeletons." Lankesler's Manual of Health. 4. How Joints may be Injured (p. 20, 1 8)." All the joints are liable to dislocation that is, bein - <% x-x -s .? i * -5 i a I i> S 10 1 l ft ii 1TKIJ8 3HX 'I CO O CQ oo ^^ CNJ ^ UJ fl 5 2 i 53 = Csauoa 8) HUMS *l I tf T c/5 CO ^A o II ? bfl i a s I fl 09 sawn naAioi *s fc o H H iJ W M 02 w K, Continue - ^H "Jj *72 " fl "jjn 1 03 1 C3 03 ^ 33 fl S g-gl ?^l ^ S ^ i'&& H^ PQ o O sain ani -aio/AH *8 ^ g'S ^ .2 7illll !! I V ^^ \ 2 ? -S 5 S 02 : s s S , ^= |Ja^.S(SH^ r^ S I S THE MUSCLES. FIG. 7. THE MUSCLES. THE MUSCLES. CHAPTER II. THE MUSCLES. The Muscles Flexion and Extension The Tendons Contraction ^ Physical Strength Necessity for Exercise Its Effects Forms of Exercise Walking Riding Gymnastics Open-air Exercise Sleep Recreation. 1. The Muscles. The great mass of the body exter- nal to the skeleton, is composed of the flesh, or Muscles, which largely determines its outline and weight. The muscles are the organs of motion. Their number is about four hundred, and to each of them is assigned a separate and distinct office. They have all been studied, one by one, and a name given to each, by the anatomist. Each is attached to bones which it is designed to move. A few are circular in form, and enclose cavities, the size of which they diminish by contraction. 2. If we examine a pl3ce of flesh, we observe that it is soft, and of a deep red color. Its structure appears to be composed of layers and bundles of small fibres. Let us fur- ther examine these fibres under the mi- croscope. We now discover that they are, in turn, made up of still finer fibres, or fibrillce : these are FIG. 8 MUSCULAB TISSUE. . , a, 5, Striped muscular fibres: c, The same more Seen in J^ Ig. O. Ine highly magnified. fibreg ^ Q beauti f ully J , What arc the muscles ? Their number ? The design of most of them F Of a few* 2. The structure of flesh? Its color, etc.? The composition of the fibres ': H<:w marked? THE MUSCLES. marked by parallel wavy lines, about ten thousand to an inch, which give the fibre its name of the striped muscular fibre. All of the voluntary muscles present this appearance. 3. Flexion and Extension. The muscles are, for the most part, so arranged in pairs, or corresponding sets, that when motion is produced in one direction by one set, there is, opposite to it, another muscle, or group of muscles, which brings the limb back to its place. When they act alternately, a to-and-fro move- ment results. When a joint is bent, the motion is called flexion ; and when it is made straight again, it is called exten- sion. When both sets act equally, and at the same moment, no motion is pro- duced, but the body or limb is main- tained in a fixed position: this occur? when we stand erect. The muscles which produce extension are more pow- erful than thoso opposite to them. 4. The muscles are also distinguished, on the other hand, as the voluntary and involuntary muscles, according as they are, or are not, under the control of the will. The heart is ^n example of the involuntary variety. We cannot change its action in the least by an FIG. 9. A, Biceps mus- .,, -,.. , cie of the arm: B, c, effort oi the will. When w^ sleep, and Its tendons. .,, ,11 , the will ceases to act, the heart contin- ues to beat without cessation. The voluntary muscles, on the other hand, are such as are used only when we wisn or will to use them as the muscles of the hand or arm ( Fig. 9 ) . (Read Note I , end of Chapter^ 3. Arrangement of the muscles ? Their action ? Flexion and extenson ? Ac- tion of the muscles when we stand erect ? 4. Kinds of muscles ? The voluntary ? Involuntary? The heart? G ; V > l c' example. The hand ? Arm - THE MUSCLES. 5. The Tendons. Tendons, or sinews, are the ex- tremities of muscles, and are compactly fastened upon bone. They are very strong, and of a silvery whiteness. They may be felt just beneath the skin, in certain parts of the body, when the muscles are being used, as at the bend of the elbow or knee. The largest tendon of the body is that which is inserted into the heel, called the tendon of Achilles, after the hero of the Grecian poet, the fable relating that it was at this point that he received his death- wound, no other part of his body being vulner- able. The muscles which extend into the leg unite to FIG. 10. VIEW OF KNEE-JOINT. A. Thigh bone: B, Knee-pan: C, D, Leg bones. form a single and very powerful tendon, and enclose a small bone called the knee-pan, which, acting like a pul- ley, greatly increases their power, and at the same time protects the front of the knee-joint (Fig. 10). 6. Muscular Contraction. The muscles, when acted upon by the appropriate stimulus, contract, or so change 5. What are the tendons or sinews ? Their strength ? Color ? Location ? Tendon of Achilles ? The fable ? Muscles of the leg ? 6. Contraction of the muscles ? Bending of the arm or finger ? Other agencies ? Automatic movements ? In cold-blooded animals ? 2$ THE MUSCLES. their shape, that their extremities are brought nearer to- gether. The bending of the arm, or of a finger, is eifected in this manner, by the will; but the will is not the only means of producing this effect. Electricity, a sharp blow over a muscle, and other stimuli, also cause it. Contrac- tion does not always cease with life. In man, after death from cholera, automatic movements of hands and feet have been observed, lasting not less than an hour. In certain cold-blooded animals, as the turtle, contraction has been known to take place for several days after the head has been cut off. 7. The property which, in muscle, enables these move- ments to take place is called contractility. If we grasp a muscle while in exercise (for example, the large muscle in the front of the arm), we notice the alternate swelling and decrease of the muscle, as we move the forearm to and fro. It was at one time supposed that the muscle actually in- creased in volume during contraction. This, however, is not the case; for the muscle, while gaining in thickness, loses in length in the same proportion; and thus, the volume remains the same in action and at rest. 8. Contraction is not the permanent, or normal, state of a muscle. It cannot long remain contracted, but after a shorter or longer time, it wearies and is obliged to relax. After a short rest, it can then again contract. It is for this reason that the heart can beat all through life, night and day, by having, as we shall hereafter see, a brief inter- val of rest between successive pulsations. For the same reason, it is more fatiguing to stand for any great length of time in one position, than to be walking the same period. 9. Relative Strength of Animals. The amount of muscular power which different animals can exert, has 7. Contractility? Give the illustration. What was supposed? What is the case? 8. What further in relation to contraction ? Weariness of a muscle ? Beating of the heart? Standing and walking? 9. Muscular power of animals ? How tested ? Man'* power? Horse's? The^ comparison ? THE MUSCLES. 29 been tested by experiment. By determining the number of pounds which an animal can drag upon a level surface, and afterward comparing that with its own weight, we can judge of its muscular force. It is found that man is able to drag a little less than his own weight. A draught-horse can exert a force equal to about two-thirds of his weight. The horse, therefore, though vastly heavier than man, is relatively not so powerful. 10. Insects are remarkable for their power of carrying objects larger and heavier than themselves. Many of them can drag ten, and even twenty times their weight. Some of the beetles have been known to move bodies more than forty times their own weight. So far, therefore, from it being a fact that animals have strength in proportion to their weight and bulk, the reverse of that statement seems to be the law. 11. Physical Strength. The difference in strength, as seen in different individuals, is not due to any original difference in their muscles. Nature gives essentially the same kind and amount of muscles to each person, and the power of one, or the weakness of another, arises, in great part, from the manner in which these organs are used or disused. 12. Many authors complain of the physical degeneracy of men at the present day, as compared with past genera- tions. There is room for doubt as to the correctness of this statement. Certain experiments have recently been made with the metallic armor worn seven hundred years ago, by which it is found that any man, of ordinary height and muscular development, can carry the armor and wield the weapons of an age supposed to be greatly our superior in strength. When we consider that in those days, only very strong men could endure the hardships of soldier-life, 10. Power of insects? Beetles? Give the conclusion. 1 1 . Difference in strength of individuals ? How caused ? 12. Complaint in relation to degeneracy? How true? HOW determined by armor ? The fair supposition ? 30 THE MUSCLES. it is fair to suppose that our age has not so greatly degen- erated in respect to physical strength. 13. Importance of Exercise. Action is the law of the living body. Every organ demands use to preserve it in full vigor, and to obtain from it its best services. The value of that training of the mind, which we call education, is everywhere recognized. The child is early put to school, and for many years continues to study, in order that his brain, which is the great centre of mental power, may act healthfully and with force. It is impor- tant that the body, also, should receive its education by exercise. This is especially true of persons belonging to certain classes of society, whose occupation confines them within doors, and requires chiefly brain-work. 14. Persons who are engaged in manual labor in the open air obtain all the exercise necessary for bodily health in their regular business : their need is more likely to be a discipline or exercise of the mind. A perfect business oi life, therefore, would be one which would combine both physical and mental labor in their proper proportions- If such a business were possible for all the human race, life would thereby be vastly prolonged. Such is, in fact, to a large extent, the occupation pertaining to one period of life childhood. A part of the time is spent by the child in improving his mind by study, and another part of the time he has physical exercise in his games and sports. 15. The Effects of Exercise. Exercise consists in a well-regulated use of the voluntary muscular system. The effects, however, are not limited to the parts used. Other organs, which are not under the control of the will, are indirectly influenced by it. For instance, the heart beats more rapidly, the skin acts more freely, and 13. Action ? Use of organs ? Training of the mind ? ' The child's brain ? Education of the body ? 14:. Work in the open air? A perfect business? Thejxmseciuence of universal perfect business ? Occupation of children ? 15. In what does exercise consist Effects of it ? THE MUSCLES. 31 becomes hotter, as well as the parts beneath it, and the ap- petite and power of digestion are increased. An increased exhalation from the lungs and skin purifies the current of the circulation, and the body as a whole thrives under its influence. (Read Note 2, end of Chapter^ 16. The immediate effect of exercise, however, is upon the muscles themselves; for by use they become firm and large, and increase in power. If we examine a muscle thus improved by exercise, we find that its fibres have become larger and more closely blended together, that its color is of a darker red, and that the supply of blood-vessels has increased. Without exercise the muscle appears thin, flabby, and pale. On the other hand, excessive exercise, without sufficient relaxation, produces in the muscle a condition not very different from that which follows dis- use. The muscle is worn out faster than nature builds it up, and it becomes flabby, pale, and weak. 17. Violent exercise is not beneficial; and spasmodic efforts to increase the muscular strength are not calculated to secure such a result. Strength is the result of a gradual growth, and is most surely acquired if the exercise be carried to a point short of fatigue, and after an adequate interval of rest. To gain the most beneficial results, the exercise should be at regular hours, and during a regular period. The activity of the exercise, and the time de- voted to it must vary, of course, with the strength of the individual, and should be carefully measured by it. (Note 3.) 18. Different Modes of Exercise. There are very few who have not the power to walk. There is required for it no expensive apparatus, nor does it demand a period of preliminary training. Walking may 1)6 called the uni* versal exercise. With certain foreign nations, the English 16. General effect upon the muscles? Special effect? Effects of junction? Of excessive exercise ? 17. Of violent and spasmodic efforts? Strength, how attained? Give the particulars. 18. What may walking be called ? What further IP PPI^ of walking? 32 THE MUSCLES. especially, it is a very popular exercise, and is practised habitually by almost every class of society ; by the wealthy as well as by those who have no carriages; by women as Well as by men. 19. Running, leaping, and certain other more rapid and violent movements, are the forms of exercise that are {nost enjoyed in childhood. For the child, they are not too severe, but they may be so prolonged as to become injurious. Instances have been recorded where sudden death has resulted after violent playing, from overtaxing the heart: for example, we have the case of a young girl who, while skipping the rope, and endeavoring to excel Jier playmates by jumping the greatest number of times, fell dead from rupture of the heart. 20. Carriage-riding, as a means of passive exercise, is par- ticularly well suited to invalids, and persons advanced in life. Horseback exercise brings into use a greater number of muscles than any other one exercise, and with it there :s an exhilaration of feeling which refreshes the mind at the same time. It is one of the manliest of exercises, but not less suitable for women than for men. To be skilful in riding, it is best to begin its practice in youth; but there are very few kinds of exercise of which the same is not equally true. 21. For those who live near streams or bodies of water, there are the delightful recreations of boating, swimming, and skating. Certain of these exercises have a practical importance aside from and above their use in increasing the physical vigor. This is especially true of boating and swimming, since they are often the means of saving life. Practice in these exercises also teaches self-reliance, courage, and presence of mind. Persons who have become proficient in these vigorous exercises are generally the ones, 1 9. What is said of running, and other hkc movements ? What, as related tc uhildhood ? What instances are alluded to ? Example '( 20. Carriage-riding? Horseback-riding? 21. Boating, swimming, and skating? THE MUSCLES. 33 who, in times of danger, are the quickest to act and the most certain to do so with judgment. 22. Physical Culture. That form of exercise which interests and excites the mind, will yield the best results ; but to some persons no kind of exertion whatever is, at first, agreeable. They should, nevertheless, make a trial of some exercise, in the expectation that, as they be- come proficient in it, it will become more pleasant. In exercise, as many sets of muscles should be employed as possible, open-air exercise being the best. Parlor gymnastics, and the discipline of the gymnasium are desirable, but they should not be the sole reliance for physical culture. No in-door exercise, however excellent in itself, can fill the place of hearty and vigorous activity jl the open air. (Read Notes 5 and 6.) r- 23. Gymnastic Exercises for Schools and Col- leges. In the system of education among the ancients, physical culture predominated. In ancient Greece, physi- cal exercises in schools were prescribed and regulated by law, and hence these schools were called gymnasia. At the present time, on the contrary, this culture is almost wholly unknown, as a part of the course of education, in our schools and colleges. In a few of our institutions of learning, however, physical exercises have been intro- duced, with manifest advantage to the students, and they form a part of the regular curriculum of exercises, as much so as the recitations in geography, grammar, or Greek. The good effect of the experiments, as shown in improved scholarship as well as increased bodily vigor, in the institutions where the plan has been tried, will, it is hoped, lead to its universal adoption. We should then hear less frequently of parents being obliged to withdraw their children from school, because they become exhausted 22. What kind of exercise yields the best results? What advice is given ? 23- Physical culture among the ancients ? In Greece ? In schoo at the present time ? Result to the body and mind ? 2* 34 THE MUSCLES. or, perchance, have lost their health from intense and pro tracted mental application. r~ 24. Were gymnastics more common in our educational institutions we should not so often witness the sad spectacle of young men and women leaving our colleges and semi- naries, with finished educations it may be, but with consti- tutions so impaired, that the life which should be devoted to the accomplishment of noble purposes must be spent in search of health. Spinal curvatures, which, according to the experience of physicians, are now extremely frequent, especially among ladies, would give place to the steady gait and erect carriage which God designed his human creatures should maintain. (Read Note 4, end of Chapter^ J5. All the exercises necessary for the proper develop- ment of the body may be obtained from the use of a few simple contrivances that every one can have at home, at little cost less by far than is spent for useless toys. Many of these may be made available in the parlor or chamber, though all exercises are far more useful in the open air. A small portion of the day thus spent will afford agreeable recreation as well as useful exercise. The Indian club, the wand, the ring, and the dumb-bells answer ordinary pur- poses very well. Illustrations are here introduced of a few simple contrivances that may be useful for general exer- cises, and are specially suitable for persons with weak spines, or with spines that are the subject of lateral curva- ture. 26. One of the simplest appliances for strengthening the muscles of the spine, designed chiefly to exercise the muscles on either side of the spine, consists of two wooden handles attached to india-rubber cords, one of which is attached to a hook made fast in the ceiling, or in the top of the door-case ; and the other to another hook fastened in the wall, door-post, or window-casing, about the height The result of gymnastics in our colleges and other institutions of learning THE MUSCLES. of the shoulder. When traction is made with the left hand, it exercises the muscles on the left side of the spine, while FIG. 11. those on the opposite side are left almost at rest, owing to the oblique direction given to the shoulders when the right hand grasps the horizontal cord. (This appliance will be understood by referring to Fig. 13.) 36 THE MUSCLES. 27. Fig. 11 shows an appliance consisting of two strong elastic cords, with handles, secured to a hook in the floor, so arranged that the patient has to stoop forward to reach them. On raising the body the spinal muscles are power- fully exercised. Fig. 12 shows other modes of using the ^astic cords for strengthening the spine and chest. FIG. 13. 28. These various appliances have been combined so as to form a system of gymnastics suitable for parlor use; other appliances have been added by which the muscles of THE MUSCLES. 3? the legs may be called into action as well as those of the spine and upper part of the body (Fig. 13). Combinations of cords suitable for particular cases may also be made, and by using one or several cords on the same hook, their power may be adapted to the strength of the most robust as well as to that of the invalid, or of the most delicate child. The entire apparatus is quite simple in its construction and inexpensive, requiring but little space, and at the same time affording a great variety of exercises. EXERCISES THAT MAY BE PRACTISED ox THIS APPA- RATUS. EXERCISE I. (Fig. 18). Stand erect under the cords and place the heels together. Grasp the handles firmly, keeping the knees and elbows stiff, and pull downward and forward until the fingers nearly touch the toes. Return slowly to the erect position. Repeat. EXERCISE II. (Fig. 13). Stand erect, and having grasped the handles overhead firmly, separate them and bring them down slowly until they touch the sides : then return them slowly to the original position. Repeat. EXERCISE III. (Fig. 13). Stand erect, heels together, grasp the handles overhead, and charge forward with the right foot. Return to first position, and then charge with the left. Repeat, using the right and left foot alternately. EXERCISE IV. (Fig. 13). Stand erect, heels together. Grasp the handle overhead, and charge forward with the right foot, knee bent. Remain in this position and bring the arms down to the sides so that the arm and fore-arm may form a right angle. Still holding the handles, thrust forward, first the right hand and then the left, until the arm is straight. Repeat. Return to first position, then charge forward with the left foot, performing the same movements as before. EXERCISE V. (Fig. 13). In this exercise we change to the pulleys leading from the side posts, which can be used in several different ways. 1st. Stand erect, heels together, facing one of the posts, grasp the handle with the right hand, the arm being extended, then flex the fore-arm on the arm. Repeat. Perform the same move- ments with the left hand. 3d. Stand with back to the post ; grasp the pulley behind with the right hand, then gradually bring the hand forward until it is extended in a straight line in front. Repeat Perform the same exercise with the left hand. 38 THE MUSCLES. EXERCISE VI. (Fig. 13). This exercise is especially adapted to the legs. Stirrups are so arranged that they can be attached to the pulleys overhead, and can hang down to within three or four feet of the floor. Place the foot in the stirrup, and then press down until it touches the floor. Repeat. Exercise the left foot in the same way. EXERCISE VII. (Fig. 13). This exercise requires a little attention in the adjustment of the apparatus. Under the pulleys in the floor are passed ropes which can be attached to the snap-hooks that hold the handles overhead. Stoop forward with the knees stiff, and take uold of the handles, and then raise the body to the erect position. Repeat EXERCISE VIII. (Fig. 13). Sit on the floor or on a seat three or four inches high ; bend forward, take hold of the handles, and per- form the same movements that you would in rowing a boat. EXERCISE IX. (Fig. 13). The trapeze can now be let down ; take hold of it with both hands, sustaining the weight of the body with the arms, then rotate the body first from right to left, then from left to right alternately. This exercise is especially suitable for females. EXERCISE X. (Fig. 13). Grasp the trapeze as before, bearing all the weight with the arms : then draw the body up slowly until you can place the chin over the bars. This requires strength of muscle, and might strain if done too violently ; if slowly performed there is no danger. These are but a few of the exercises that can be practised with this apparatus. As these become familiar they can easily be modi- fied, and new ones can be arranged to meet the requirements of particular cases. Most of the exercises described can be practised with one hand so as to strengthen the muscles on one side. 29. Rest. We cannot always be active: repose must succeed labor. We obtain this rest partly by suspending all exertion, as in sleep, and partly by a change of employ- ment. It is said that Alfred the Great recommended that each day should be divided in the following manner : "Eight hours for work, eight hours for recreation, and eight hours for sleep." This division of time is as good as any that could now be made, if it be borne in mind that, when the work is physical, the time of recreation should 29. Need of repose? How do we obtain rest ? Alfred the Groat ? The eight hour division of time ? THE MUSCLES. 39 6e devoted to the improvement of the mind; and when mental, we should then recreate by means of physical exercise. 30. During sleep, all voluntary activity ceases, the rapid- ity of the circulation and breathing diminishes, and the temperature of the body falls one or two degrees. In con- sequence, the body needs warmer coverings than during the hours of wakefulness. During sleep, the body seems wholly at rest, and the mind is also inactive, if we except those involuntary mental wanderings which we call dreams. .Nevertheless a very active and important physical process is going on. Nutrition, or the nourishing of the tissues, now takes place. While the body is in action, the process of pulling down predominates, but in sleep, that of build- ing up takes place more actively. In this way we are re- freshed each night, and prepared for the work and pleasures of another day. If sleep is insufficient, the effects are seen in the lassitude and weakness which follow. Wakefulness is very frequently the forerunner of insanity, especially among those who perform excessive mental labor. 31. All persons do not require the same amount of sleep, but the average of men need from seven to nine hours. There are well-authenticated cases where individuals have remained without sleep for many days without apparent injury. Frederick the Great required only five hours of sleep daily. Bonaparte could pass days with only a few hours of rest. But this long continued absence of sleep is attended with danger. After loss of sleep for along period, in some instances, stupor has come on so profoundly, that there has been no awaking. 32. There are instances related of sailors falling asleep 30. Cessation, of voluntary activity ? Temperature of the body ? Consequence ? Body and mind during sleep ? Nutrition ? Describe it. Consequence of insuffi- cient sleep ? 31. Amount of sleep in different persons? Cases? Frederick the Great? Bonaparte ? Instances of long deprivation of sleep ? 32. Instances of sailors ? French soldiers ? During torture ? 40 THE MUSCLES. on the gun-deck of their ships while in action. On the retreat from Moscow, the French soldiers would fall asleep on the march, and could only be aroused by the cry, "The Cossacks are coming !" Tortured persons are said to have slept upon the rack in the intervals of their torture. In early life, while engaged in a laborious country practice, the writer not unfrequently slept soundly on horseback. These instances, and others, show the imperative demand which nature makes for rest in sleep. QUESTIONS FOR TOPICAL REVIEW. PAGE 1. What can you state of the number and division of the muscles ? 25, 26 2. Describe the structure of the muscles 25, 26 3. Their arrangement in pairs and consequent action 26 4. What is the difference between the motion called flexion and that called extension ? 26 5. Describe their action, and state which are the more powerful 26 6. What is the difference between voluntary and involuntary muscles ? 26 7. Illustrate the difference between the two 26 8. State all you can of the tendons or sinews 27 9. What is meant by contraction of the muscles ? 27, 28 10. In how many and what ways may contraction be effected ? 28 11. What is stated of after-death contraction? 28 12. Why cannot a muscle in life continue contracted a long time ? 28 13. How then can the constant beating of the heart be explained ? 28 14. How does the strength of a man compare with that of a horse ? 29 15. What can you state in relation to the relative strength of animals ? 28, 20 16. What, in rc-lation to physical strength ? 29 17. What, in relation to physical degeneracy ? . 29. 30 18. What, in relation to the importance of exercise ? 30 19. What is the effect of exercise upon the heart, skin, and appetite ? 30, 31 20. How does exercise affect the current of the body's circulation ? 31 21. How does judicious exercise affect the muscles ? 31 22. What is stated of violent and spasmodic exercise ? 31 23. Of the exercise of walking ? 31, 32, as 24. Of running, leaping, and other modes of exercise"? 3 J 25. Of physical culture, in connection with out-door exercises ? 3. 26. Of the importance of gymnastics in our schools and colleges f 33, 34 27. Of the importance of rest from labor or exercise ? 38, 39 28. What processes take place during sleep ? *| 29. What effects follow insufficient sleep ? ]STOTES. 1. The Perfection of the Human Hand (p. 26, 1 4). "Grrdy counts thirty-four distinct movements of the hand, and if we include the combi- nations of these different movements, we shall reach a much higher number. Prop- erly speaking, the hand belongs to man alone, and its form does not permit us to consider it an organ of locomotion, as is the case with certain animals most closely resembling man. Nothing gives a more complete idea of the perfection of the mechanism of the hand than the execution of instrumental music. Examine ;m artist while he plays the violin. His fingers rest upon the strings so as to leave them exactly of the length necessary for the tones they are to give. The half of a millimetre, more or less, greatly changes the accuracy of the note; and a chord a millimetre out of place produces a note which even the unpractised ear can recog- nize as false. But the fingers fall upon the strings at precisely the point required. They run over them, succeeding each other with giddy rapidity, following every imaginable combination, and yet the hand gliding over the instrument incessantly changes its position. Sometimes a single finger produces an isolated note ; some- times two or three act simultaneously to produce a concord ; while a fourth, strik- ing a string with increasing rapidity, produces a trill which rivals the nightingale. Add to all these the modifications necessary to swell the sound or let it die away all, in a word, that constitutes musical expression, and it will be admitted that this mechanism is allied to the wonderful, and that it surpasses the most per- fect productions of human art." A further idea of the rapidity of the hand's movements is given in the playing of a skilful pianist, whose hands, oftenest oc- cupied together, pro 'uce on an average six to eight notes at a time, or about 640 notes in a minute in medium time, and 960 notes in extremely quick time. The Wonders of the Human Body. 2. Health in Athletic Exercise (p. 81, 1 15). " Health is perpetual youth that is, a state of positive health. Merely negative health, the mere keep- ing out of the hospital for a number of years, is not health. Health is to feel the body a luxury, as every vigorous child does; as the bird does when it shoots and quivers through the air, not flying for the sake of the goal, but for the sake of flight ; as the dog does when he scours madly across the meadows, or plunges into the muddy blissfulness of the stream ; but neither bird, nor dog, nor child en- joys his cup of physical happiness let the dull or the worldly say what they will with a felicity so cordial as the educated palate of conscious manhood. To ' feel one's life in every limb,' this is the secret bliss of which all forms of ath- letic exercise are merely varying disguises ; and it is absurd to say that we cannot possess this when character is mature, but only when it is half developed. As the flower is better than the bud, so should the fruit be better than the flower." 3. The Ill-effects of Over-exertion (p. 31, 1 17). "It should be recollected that the action of the muscles has limits, as well as that of every other organ of the body. The muscles and the heart may be taxed too severely, and permanent derangements may be produced by overtaxing the human body. The ancient gymnasts among the Greeks are said to have become prematurely old, and the clowns (or acrobat?) and athletes of our own days suffer from the severe strain put upon their muscular systems. 1 " The effects of boat-racing in England have been thus described by Mr. Skey, an eminent surgeon: " The men look utter- ly exhausted. Their white and sunken features and pallid lips show serious con- gestion of the heart and lungs, and the air of weakness and lassitude makes it a marvel how such great exertion should have been so nobly undergone. We bave repeatedly seen the after ill-effects spitting of blood, congested lungs, and weak- ness of the heart from over-distension." "Persons should neither walk, run, NOTES. leap, or play at any game, to the extent of producing permanent or painful exhaus- tion. All exercise should be attended with pleasurable feelings ; and when pain is produced by proper exercise, those who suffer should rather seek medical advice than persevere in exercise. 1 ' Lanktster's Manual of Health. 4. Health and Strength are not always Identical (p. 34, 124). " Health and strength are not. synonymous terms. A person may have great strength in his limbs, or in certain muscles about the body, but really not have good health. It is altogether a mistaken idea to suppose that physical exercises have for their sole object the attainment of strength. There are other tissues and organs in the human system besides the muscular ; and the healthy action of the lungs and the stomach is far more important than great strength in the arms, legs, or the back. It is here, in this general exercise of all the muscles and parts of the body, that a well-regulated system of gymnastics has Its great excellence. It aims to produce just that development of the human system upon which good health is permanently based, described by a distinguished writer as follows : 'Health is the uniform and regular performance of all the functions of the body, arising from the harmonious action of all its parts,' a physical condition imply- ing that all are sound, well-fitting and well-matched. Some minds do not look far enough into life to see this distinction, or to value it if seen; they fix their eyes longingly upon strength upon strength now, and seemingly care not for the power to work long, to work well, to work successfully hereafter, which is health.' 1 '' Dr. Nathan Allen on Physical Culture. 5. Exercise should be Pleasurable (p. 33, t 22). "The world seldom attaches much value to things which are plain and easily understood. The der- vish in the Eastern allegory, well aware of this weakness, knew that it would be in vain to recommend the sultan, for the cure of his disease, simply to take exer- cise. He knew that, mankind in general required to be cheated, gulled, cajoled, even into doing that which is to benefit themselves. He did not, therefore, tell the eultan, who consulted him, to take exercise, but he said to him : 4 Here is a ball, which I have stuffed with certain rare, costly, and precious medicinal herbs. And here is a bat, the handle of which I have also stuffed with similar herbs. Your highness must take this bat, and with it beat about this ball until you perspire very freely. You must do this every day.' His highness did so, and in a short time the exercise of playing at bat and ball with the dervish cured his malady." First Help. 6. On Recreation. "Our whole method of amusements, especially for the young, should be reformed. Gas-light should yield to daylight, night vapors in heated and close rooms should irive way to fresh air under the open heavens, and our young people should be brought up to work and play under the ministry of that great solar force which is the most benign and god-like agent known to men. Ardent spirits and tobacco should be given up, and in their stead genial exercise of riding, gymnastics, and the dance, with music and all beautiful arts, should be employed to stir the Mn-ruid powers and soothe the troubled affections. The old Greeks taught music and gymnastics as parts of education, and Plato, in urging the importance of these, still maintains that the soul is superior to the body, and religion is the crown of all true culture. Why may not Christian peo- ple take as broad a position on higher ground, and with a generous and genial cul- ture- associate a faith that is no dreamy sentiment or ideal abstraction, but the best power of man and the supreme grace of God? "7?^. T)r. Ozgood on "The Skeleton in Modern r r ci--t ! /." > TABLE OF THE PRINCIPAL MUSCLES. $EE PLATE 7, PAGE 24.) THE HEAD. Oc-cipi-to ft'on-tti'lis 9 moves the scalp and eyebrows. Or-bic-u-laris paipe-brae^ closes the c; * Le-va'tor pal'pe-brae 9 opens the eye. The Recti muscles, (4 in number) move the eye-ball. Tempo-rat,) raige ^ Jower IHas-seter, ) THE NECK. o Mastoid, Scale'ni muscles move the neck from side to side. THE TRUNK. moves the arm forwards. Li-tis'si-inirs dor ni^ moves the arm backwards. Tra-pe'zi-ns, \ Ser-ra'tns magnu*, ( move shoulder-blade. Rhotn-boi deun, ; In ter-costals, mo^e the ribs in respiration. External Obliaue. ) ' [ move the trunk forwards Internal E rector spi'nae* move the trunk THE UPPER LIMB. Deltoid, raises the arm Te'res major, lowers tlie arm. Sub-scap-u-la'ris, ) rota t e tlie arm. Spi-nattis, Jfi'ceps, bends forearm. Triceps, straightens forearm. Pro na tor, ) rotate forearm . Sa-pinator, } Flex' or car'pi ra-dia'lis, 1 " *>., 'j. m ove the hand. Exten'sor car'pi ra-di-a lis* ul-na'ris, J More than 30 muscles take part in moving tne lingers. THE LOWER LIMB. ll-i'a-cus, I Psoas magnus, I moye ^ ^ h forwards Fec-tin-e'us, Adduc'tor, J Glu-te'us, } move the thigh backwards. Pyr-iform'is, ) Sar-to'ri-us, (from Sartor, a tailor) crosses one thigh over the other. Rec'tus, ) moye tte leg f orwar ds. Vas'tus, ) Biceps, I moye the leg backwards. rac'i-lis ) Grac'i-lis, Tibia'lis, Gas ti'oc-ne' mi-us, \ So-le'us, J 20 muscles take part in moving the toes. THE INTEGUMENT, OR SKIN. 41 CHAPTER III. THE INTEGUMENT, OR SKIN. The Integument Its Structure The Nails and Hair The Complexion The Sebaceous Glands The Perspiratory Glands Perspiration and its Uses Importance of Bathing Different kinds of Baths Manner of Bathing The Benefits of the Sun Importance of Warm Clothing Poisonous Cosmetics. I I. The Integument. The skin is the outer covering / of the body. The parts directly beneath it are very sensi- tive, and require protection. This is shown whenever by accident the skin is broken, pierced, or torn off, the bared surface being very tender, and painful to the touch. Nature has provided the body with a garment that is soft, pliable, close-fitting, and very thin, and yet sufficiently strong to enable us to come in contact with the objects that sur- round us, without inconvenience or suffering. ' 2. The Structure of the Skin. When examined with the aid of the microscope, the skin is found to be made up of two layers the outer and the inner. The inner one is called the cutis, or true skin ; the outer one is the epider- mis, or scarf-skin. The latter is also known as the cuticle. These two layers are closely united, but they may be sepa- rated from each other. This separation takes place when- ever, from a burn, or other cause, a blister is formed; a watery fluid is poured out between the two layers, and lifts the epidermis from the true skin. Of the two layers, the cuticle is the thinner in most parts of the body, and has the appearance of a whitish mem- brane. It is tough and elastic, is without feeling, and does 1 . What is the skin ? Parts directly beneath ? What is shown ? 2. Microscopic examination ? What is the cutis ? The cuticle ? Their union ? How separated ? What further is said of the cuticle ? ^?x 42 THE INTEGUMENT, OR SKIN. not bleed,when cut. Examine it more closely, and we observe that it is composed of minute flat cells, closely compacted, and arranged layer upon layer. A 3. The outer layer is constantly being worn out, and /falls from the body in the form of very fine scales. It is, also, continually forming anew on the surface of the inner layer. Its thickness varies in different parts of the body. Where exposed to use, it is thick, hard, and horn-like, as may be seen on the soles of the feet, or on the palms of the hands, especially of those who are accustomed to perform much manual labor. This is an admirable provision for the increased protection of the sensitive parts below the skin against all extraordinary exposure. Even the liabil- ities of these parts to injury, are thus kindly provided for by "the Hand that made us." (Read Note 10, end of Chapter.) 4. The cutis, or true skin, lies beneath the epidermis, and is its origin and support. It is firm, dense, elastic, very sensitive, and is freely supplied with blood-vessels. It is closely connected with the tissues below it, but may be separated by means of a sharp instrument. The surface of the cutis is not smooth, but is covered here and there with minute elevations, called papillm. These are arranged in rows, along fine lines, or ridges, such as those which mark the palm and fingers ; their number is about 80 to the square line (a line being one-twelfth of an inch). These papillm contain the blood-vessels which carry the supply of blood needed by the ever-wasting skin. They contain nerves also, and are largely concerned in the sense of touch; hence they are particularly abundant where the touch is most delicate, as at the ends of the ^ fingers. 5. The Nails and Hair, These are appendages of the 3. Wearing out of the cuticle ? What then ? Variety in thickness of cuticle r How accounted for? 4. Location and office of the cutis? What further is said of it? Papillae? Touch ? 5. What are the nails and hair ? The growth of the nail ? The rapidity of its growth ? Accident to the nail ? THE INTEGUMENT, OR SKIN. 43 skin, and although very unlike the cuticle as it appears on the surface of the body, they are, in reality, modified forms of that layer of the skin. The nail grows from a fold of the cuticle at the root, and from the under surface. As fast as it is formed, it is constantly being pushed outward. The rapidity of its growth can be ascer- tained by filing a slight groove on its surface, and noticing how the space be- tween it and the root of the nail increases, in the course of a few weeks. When the nail is removed by any accident, it will be replaced by a new one, if the root be not injured. * /* 6. The hairs are pro- x duced in a similar manner; Fig. 14. a, b. THE ROOT OF A HAIR. the Skin forming depres- j, 2 , 3. The skin forming the hair sac. 4. Se. Sions, Or hair SaCS, * baceous glands. The hair sac. c. TRANSVERSE SECTION OF A HAIR. hair sacs, from the bottom of which they grow and are nourished (Fig. 14). They are found, ot greater or less length, on almost all parts of the surface, except the palms of the hands and soles of the feet. On certain parts of the body, they grow to great length ; on other parts they are so short, that they do not rise beyond the hair sac in which they originate. 7. The bulb, or root, from which the hair arises, is lodged in a small pouch, or depression in the skin. The shaft is the part which grows out beyond the level of the skin. Its growth is altogether in one direction, in length alone. The outer part of the hair is quite firm, while its 6. How are the hairs produced ? Difference in their length ? 7. Root of the hair Shaft ? Firmness and softness of the hair? (* Read Note n, end of Chapter.) 44 THE INTEGUMENT, OR SKIN. interior is softer, and probably conveys the fluids by which it is nourished. The hair is more glossy in health than at other times. A 8. The nail serves as a protection to the end of the f finger, and also enables us to grasp more firmly, and to pick up small objects. The hair, too, is a protection to the parts it covers. On the head, it shields the brain from extremes of heat and cold, and moderates the force of blows upon the scalp. On the body, it is useful in affording a more extensive surface for carrying off the perspiration. 9. Complexion. In the deeper cells of the cuticle lies a pigment, or coloring matter, consisting of minute colored grains. On this pigment complexion depends; and, according as it is present in less or greater amount, occa- sions the difference of hue, that exists between the light and dark races of men, and between the blonde and bru- nette of the white races. Freckles are due to an irregular increase of coloring matter. A 10. The sun has a powerful influence over the develop- / ment of this pigment, as is shown by the swarthy hue of those of the white race who have colonized in tropical climates. It is also well illustrated by the fact, that among the Jews who have settled in northern Europe, there are many who are fair complexioned, while those residing in India, are as dark as the Hindoos around them. f* 11. An Albino is a person who may be said to have no complexion; that is, there is an entire absence of coloring matter from the skin, hair, and iris of the eye. This con- dition more frequently occurs among the dark races, and in hot climates, although it has been observed in almost every race and clime. 12. Sebaceous Glands. There are in the skin certain 8. Office of the nail? Of the hair? Give the illustrations. 9. On what does the complexion depend? Light and dark races ? Freckles? 10. Influence of the sun ? How illustrated? Jews? 11. What is an Albino ? Where are Albinos found ? 12. What are sebaceous glands ? How do they act ? Sebaceous glands of the * How do they act ? THE INTEGUMENT, OR SKIN. 45 small glands, which produce an oily substance, called se- baceous matter. These glands are little rounded sacs, usually connected with the hair-bulbs; and upon these bulbs, they empty their product of oil, which acts as a natural and adequate dressing for the hair (4, Fig. 13). A portion of the sebaceous matter passes out upon the sur- face, and prevents the cuticle from becoming dry and hard. The glands situated upon the face and forehead, open directly upon the skin. In these, the sebaceous matter is liable to collect, and become too hard to flow off naturally. 13. These glands on the face and forehead frequently appear, on the faces of the young, as small black points, which are incorrectly called "worms." It is true, that oc- casionally living animalcules are found in this thickened sebaceous matter, but they can only be detected by the aid of the microscope. This sebaceous matter acts not only to keep the skin flexible, and furnish for the hair an oily dressing, but it especially serves to protect the skin and hair, from the acridity arising from the perspiration. i 14. The Perspiratory Glands. The chief product of the skin's action is the perspiration. For the forma- tion of this, there are furnished countless numbers of little sweat-glands in the true skin. They consist of fine tubes, with globe-like coils at their deeper extremity. Their mouths or openings may be seen with an ordinary magnifying glass, upon the fine ridges which mark the fingers. These tubes, if uncoiled, measure about one-tenth of an inch in length. In diameter, they are about one three-hundredth of an inch, and upon certain parts of the body there are not far from three thousand of these glands to the square inch. Their whole number in the body is, therefore, very great; and, in fact, it is computed if they were all united, end to end. their combined measurement would exceed three miles. 1 3 , Black points, called worms ? Animalcules ? Service performed by seba- ceous matter? 14. Perspiration? Sweat glands? Of what do they consist ? Dimension of the tubes? 46 THE INTEGUMENT, OR SKIN, /* 15. The Sensible and Insensible Perspiration. The pores of the skin are constantly exhaling a watery fluid; but, under ordinary circumstances, there is no moisture apparent upon the surface, for it evaporates as rapidly as it is formed. This is called insensible perspira- tion. Under the influence of heat or exercise, however, this fluid is excreted more abundantly, and appears on the surface in the form of minute, colorless drops. It is then termed sensible perspiration. , 16. Water is the chief component of this fluid, there being about ninety-eight parts of water to two parts of solid matter. The quantity escaping from the body varies greatly, according to the temperature of the air, the occupation of the individual, and other circumstances. The average daily amount of this excretion, in the adult, is not far from thirty ounces, nearly two pints, or more tfian nine grains each minute. N 17. The Uses of the Perspiration. Besides liber- ating from the blood this large amount of water, with the effete matter it contains, the perspiration serves to regulate the temperature of the body. That is to say, as evapora- tion always diminishes temperature, so the perspiration, as it passes off in the form of fine vapor, cools the surface. Accordingly, in hot weather this function is much more active, and the cooling influence increases in proportion. When the air is already charged with moisture, and does not readily receive this vapor of the body, the heat of the atmosphere apparently increases, and the discomfort therefrom is relatively greater. N 18. The importance of this excretion is shown by the effects that often follow its temporary interruption, namely, headache, fever, and the other symptoms that accompany 1 5. What is sensible perspiration ? Insensible perspiration ? 16. Components of perspiration? Upon what does perspiration depend? Amount of perspiration daily ? 1 7. What does perspiration set free from the blood ? What other service doe;s perspiration perform? Explain the process. 18. Effect of interruption of excretion ? What experiments are mentioned. ? THE INTEGUMENT, OR SKIN. 47 " taking cold."' When the perspiration is completely checked, the consequences are very serious. Experiments have been performed upon certain smaller animals, as rab- bits, to ascertain the results of closing the perspiratory tubes. When they are covered by a coating of varnish impervious to water and gases, death ensues in from six to twelve hours ; the attendant symptoms resembling those Of Suffocation. (Read Note I, end of Chapter) A 19. It is related that, at the coronation of one of the Popes about three hundred years ago, a little boy was chosen to act the part of an angel : and in order that his appearance might be as gorgeous as possible, he was cov- ered from head to foot with a coating of gold foil. He was soon taken sick, and although every known means were employed for his recovery, except the removal of his fatal golden covering, he died in a few hours. 20. The Importance of Bathing. From these con- siderations, it is evident that health must greatly depend upon the free action of the skin. " He who keeps the skin ruddy and soft, shuts many gates against disease." When the watery portion of the perspiration evaporates, the solid matter is left behind on the surface. There, also, remain the scales of the worn-out cuticle, and the excess of seba- ceous matter. In order to secure the natural action of the skin, these impurities require to be removed by the frequent application of Water. (Read Note 8, end of Chapter.} 21. Iii warm climates, and during hot weather, ablution ' should be more frequently practised. For a person in good health, a daily cold bath is advisable. To this should be added occasionally a tepid bath, with soap, water alone not being sufficient to remove impurities of a greasy nature. Soap facilitates this, by forming with such substances a chemical mixture, which is readily soluble in water, and is by it removed from the body. (Read Note 7, end of Chapter.} 19. Give the story in relation to the boy covered with gold foil. 2O Give the quotation. Perspiration ? 2 1 . Ablution in warm climate's ? What advice is grivea ? 48 THE INTEGUMENT, OR SKIN. / A 22. There is a maxim by the chemist Liebig, to the effect^ ' that the civilization of a nation is high, in proportion to the amount of soap that it consumes ; and that it is low, in proportion to its use of perfumes. In some degree, we may apply the same test to the refinement of an individual. The soap removes impurity; the perfume covers, while retaining it. (Read Notes 6 and 12, end of Chapter^ . The different kinds of Baths. All persons are not alike able to use the cold bath. When the health is vigorous, and the system does not feel a shock after such a bath, a prompt reaction and glow upon the surface will show that it is beneficial. \Yhere this pleasurable feeling is not experienced, but rather a chill and sense of depres- sion ensues, we are warned that the system will not, with impunity, endure cold bathing. 24. It should also be borne in mind, that the warm or hot bath cannot be continued so long, or repeated so frequently as the cold, on account of the enervating effect of unusual heat so applied to the body. For persons who are not in robust health, one warm bath each week is sufficient ; this class should be careful to avoid every extreme in reference to bathing, clothing, and whatever greatly affects the actiou of the skin. 25. Sea-bathing is even more invigorating than fresh - water bathing. Those who cannot endure the fresh water, are often benefited by the salt-water baths. This may be accounted for, in part, by the stimulant action upon the surface, of the saline particles of the sea-water; but the exciting scenes and circumstances of sea-bathing also exert an important influence. The open-air exercise, the rolling surf, the genial weather, and usually the cheerful company, add to its intrinsic benefits. (Read Note 2.) 22. LiebigV maxim ? What, further it* added ? 23. What is said about cold bathing ? 24. What is said about warm bathing ? 25. What is said about sea-bathing? . / THE INTEGUMENT, OR SKIN. 49 26. Time and Manner of Bathing. A person in sound health may take a bath at almost any time, except directly after a full meal. The most appropriate time is about three hours after a meal, the noon-hour being proba- bly the best. For the cold bath, taken rapidly, no time is better than immediately after rising. Those beginning the use of cold baths should first try them at 70 Fahr., and gradually use those of a lower temperature. From five to twenty minutes may be considered the proper limit of time to remain in a bath ; but a sensation of chilliness is a signal to withdraw instantly, whether at home, or at the sea-side Two sea-baths may be taken daily ; one of any other kind is sufficient. 27. The body should be warm, rather than cold, when stepping into the bath; and after it, the skin should be thoroughly dried with a coarse towel. It is best to continue friction until there is a sensation of warmth or "glow" throughout the entire surface. This reaction is the test of the good effects of the bath. If reaction is still incom- plete, a short walk may be taken, especially in the sunshine. It is very congenial, however, both to health and comfort, to rest for a short time directly after bathing, or to take some light refreshment. This is better than severe exer- cise or a full meal. A 28. Bathing among the Ancients. The Romans and other nations of antiquity made great use of the vapor-bath as a means of preserving the health, but more particularly as a luxury. Their method was not unlike that employed in northern Europe, at the present day. The public baths of Rome and other cities are among the grandest and most interesting monuments of ancient luxury and splendor; and from their ruins have been re- covered some of the most beautiful works of art. 26. What is said as to the time and manner of bathing ? 27. Condition of the body when bathing? Direction, after bathing? 28. Bathing among the ancients? Baths of Rome? 60 THE INTEGUMENT, OR SKIN. K 29. The Thermae, as the baths of Eome were called; * were of great extent, built very substantially, and orna^ mented at vast expense. They were practically free to all, the cost of a bath having been less than a cent, It is related that some persons bathed seven times a day. After the bath their bodies were anointed with perfumed oil. If the weather was fine, they passed directly from the Thermae into the gymnasium, and engaged in some gentle exercise previous to taking the midday meal. Between two r"d three in the afternoon was the favorite hour for this ancient luxury. Swimming was a favorite exercise, and a knowl- edge of it was regarded as necessary to every educated man. Their common expression, when speaking of an ignorant person, was, " He can neither read nor swim." X 30. The Sun-Bath. Some also were accustomed daily to anoint themselves, and lie or walk in apartments ar- ranged for the purpose, with naked bodies exposed to the direct rays of the sun. There is an interesting allusion to this practice, in a letter of the younger Pliny to the his- torian Tacitus, describing the destruction of Pompeii by an eruption of Vesuvius. " My uncle," (Pliny the elder,) "was at that time in command of the fleet at Misenum. On the 24th of August, about one in the afternoon, my mother desired him to notice a cloud which seemed of un- usual shape and dimensions. He had just returned from talcing the benefit of the sun, and after a cold bath, and a slight repast, had retired to his study." Then follows a description of the destruction of Pompeii, and the death of the elder Pliny. A 31. We may judge somewhat of " the benefits of the sun," by observing the unnatural and undeveloped condi- tion of plants and animals which are deprived of light. Plants become blanched and tender ; the fish of subterra- 29. After tvi bath ? Swimming among the ancients ? 30. The Sun-bath ? The story of Pliny ? 3 1 . Benefit of the sun ? Effect upon plants ? Skin f THE INTEGUMENT, OR SKIN. 51 r, nean lakes, where no light enters, are undersized, and have no eyes; tadpoles kept in the dark do not develop into frogs; men growing up in mines are sallow, pale, and deformed. Besides the well-known effect of solar light in tanning the skin, it also makes it thicker and better able to resist exposure; though the complexion may be thereby injured, the health gains more than compensates for the loss of beauty. " To make good the loss of the lily, where the sun has cast his ray, he seldom fails to plant the rose." * 32. Clothing. In reference to clothing, we are far more apt, in our changeful climate, to use too little than too much. An aphorism of Boerhaave, worth remember- ing, if not of adopting, is, "We should put off our winter clothing 011 midsummer's day, and put it on again the day after." He also says, " Only fools and beggars suffer from the cold ; the latter not being able to get sufficient clothes, the others not having the sense to wear them." The prac- tice of exposing the limbs and necks of young children, for the alleged purpose of "hardening" them, is quite hazardous. It is not to be denied that some seem to be made tough by the process ; but it is so only with the rugged children, the delicate ones will invariably suffer under this fanciful treatment. As has been stated before, the skin is constantly acting, by night as well as by day. It is there- fore conducive both to cleanliness and comfort to change entirely the clothing on retiring for the night. The day- clothing should be aired during the night, and the bedding should be aired in the morning, for the same reason, f 33. Poisonous Cosmetics. The extensive use of wsmetics for the complexion is a fertile source of disease. The majority of these preparations contain certain poison- ous mineral substances, chiefly lead. Now, the skin rapidly absorbs the fine particles of lead, and the system 32. Direction about clothing? Exposing limbs of children? Clothing, night and day ? 33. Cosmetics ? Painters' colic ? C* Read Notes 3 and 4, end of Chapter.} (t Read ffotes 5 and 9, end of CJiapter.} 52 THE INTEGUMENT, OR SKIN. experiences the same evil effects that are observed among the operatives in lead works and painters, namely, "paint- ers' colic," and paralysis of the hands, called "wrist-drop." r34. Certain hair-dyes also contain lead, together with other noxious and filthy ing 7 edients. These do not work as great harm as the cosn? ;tics, since they are purposely kept away from the skir, but they rob the hair of its vitality. Eye-washes, too, are made from solutions of lead, and many an eye has been ruined by their use. They de- posit a white metallic scale on the surface of the eye, which becomes a permanent obstruction to the vision. QUESTIONS FO.^ TOPICAL REVIEW. PAGE 1. What are the characteristics of the skin, and what office does it perform ? 41 2. What can you state of the structure of the skin ? 41 3. Describe the cuticle and tell its use 41,42 4. Describe the cutis or true skin and tell its use 42 5. What can you state of the nature and growth of the nail ? . . 42, 43 6. Of the nature and growth of the hair ? 42, 43, 44 7. Of the offices performed by the nails and hair ? 44 8. How is the difference in complexion in different persons accounted for ?. 44 9. How is the presence of freckles accounted for ? 44 10. How does Nature provide a dressing for the hair ? 44, 45 11. What other service do the sebaceous glands perform ? 45 12. State what you can of the perspiratory glands 45 18. What is the difference between sensible and insensible perspiration?.. . 46 14. State, the uses and importance of perspiration 46, 47 15. WhaMmpurities gather naturally on the skin ? 47 16. Repeat what is said of the importance of bathing 47, 48 17. When should we indulge in cold, warm, and sea bathing ? 48, 49 18. What is the effect in each case ? 48 19. What directions are given as to the time and manner for bathing ? 49 20. What is related of bathing among the ancients ? 49, 50 21. What, is related to show the antiquity of sun-bathing ? 50 22. What are the effects of sun bathing? 50,51 23. What directions arc given in relation to clothing the body ? 51 24. What can you state of poisonous cosmetics ? 51, 52 25. Of hair-dyes and eye-washes? 52 NOTES. 1. On taking Cold (p. 47, 1 18). "Of all the things to which humanity Is liable, there is none which recurs more frequently, and whose consequences are more troublesome and often dangerous, than ' taking cold.'' Some persons have quite a faculty for taking cold, while others do so but rarely. And yet the one does not argue delicacy of constitutition, or the other strength. The body of man has a constant and agreeable temperature in health, the variation being slight. In fact any great variation is incompatible with health, and constitutes disease. Clothes, by preventing the radiation away of heat from the surface, retain it, and so the feel- ing of cold is not so great, that is, the surface does not become so cold. Clothes are non-conductors of heat when dry, but let them be saturated with water, and un- less the loss of heat be met by increased production, there is a lowering of the body temperature ' taking cold.' Thus, if exertion be continued, and more heat is pro- duced to meet the loss until a change of dry clothing is procurable, no injury results. But let the wet clothes be worn without a corresponding heat production, as when, children sit down in school in their wet clothes, or the shop-bay stands in his moist garments ; then there is a rapid loss of heat, a lowering of body temperature, and a cold is ' caught.' So is a cold caught by wet feet, when the heat is radiated away from the feet ; if exercise be continued the cold is not experienced. A damp bed gives cold because the moist beclclother conduct away the heat, and the body temperature is lowered.'" Fotherglli on the Maintenance of Health. 2. The Proper Use of Sea-bathing (p. 48, 1 25)." The length of time during which a person should remain in the water necessarily varies accord- ing to the age, sex, and constitutional strength of the bather. Due regard should also be had to the state of the weather and season of the year. " In the case of children, five, gradually extended to ten minutes; of women, ten to fifteen minutes; and of men, a quarter of an hour or more, is a fair average period. There are some prople, doubtless, to whom these periods will appear insuf- ficient, and who insist on remaining so long in the water that their skin becomes cold and blue, their teeth begin to chatter, and a condition of general exhaustion comes on ; people, in short, who have the ' most ' for their money, like the country- man who grumbled at having been conveyed thirty mile? in about half-an-hour by an express train, on the score that the length of time occupied in the journey wat not proportionate to the fare that he had paid. On entering the water, the bather should immerse the whole of the body two or three times, so as to get the action of the shock from the cold water distributed over its entire surface. There should bo no hesitancy, no dabbling about with the feet, but a good plunge at once into the next wave that washes in. Upon coming out of the water the bather should dry the body with good rough towels, dress quickly and take a brisk walk for a short distance. If there be any feeling of exhaustion or nervous depression, a little food or drink should be taken." Abbotts Smith or. Sea-bathing. 3. Light Influences Growth and Health (p. 51, ^ 31).- "I have several times taken two potatoes which were as nearly as possible alike, and placed one under a bell-glass through which the light could pass, and the other under a similar cover rendered opaque by several coats of black paint. Sprouting went on unchecked under the translucent glass, while it was always notably retarded and sometimes prevented in the potato under the dark glass. Milne Edwards, a distinguished Frejich physiologist, performed a series of experiments which showed that tadpoles when deprived of light did not develop into the frog. I have several times repeated his experiments, and always with confirmatory results. On NOTES. one occasion I prevented for one hundred and twenty-five days the development of a tadpole, by confining it in a vessel to which the ray? of light had no access. On placing it in a receptacle open to the light, the process of transformation was at once begun, and was completed in fifteen days. The practical application of these and similar observations is this, that care should be taken both in health and disease to ensure a sufficient amount of sunlight to the inmates of houses, and that it is impossible to rear well-formed, strong, and robust children unless at- tention is paid to this requirement." Hammond on the Influence of Light. 4. Light ill tlie Sick-room (p. 51, t 31). "It is the unqualified result of all my experience with the sick, that second only to their need of fresh air is their need of light; that, after a close room, what hurts them most is a dark room, and that it is not only light, but direct sunlight they want. You had better carry your patient about after the sun, according to the aspect of the rooms, if circumstances permit, than let him linger in a room when the fun is off. People think that the effect is upon the spirits only. This is by no means the case. Who has not observed the purifying effect of light, and especially of direct sunlight, upon the air of a room 1 Here is an observation within everybody's experience. Go into a room where the shutters are always shut (in a sick-room or a bedroom there should never be shutters shut), and though the room be uninhabited, though the air has never been polluted by the breathing of human beings, you will observe a close, musty smell of corrupt air of air, unpurified by the effect of the Fun's rays. The mustiness of dark rooms and corners, indeed, is proverbial. The cheerfulness of a room, the usefulness of light in treating disease, is all-important. It is a curious thing to observe how almost all patients lie with their faces turned to the light, exactly as plants always make their way towards the light." Florence Nightingale* s Notes on Nursing. 5. Under-clotliiiig and Bedding (p. 51, ^ 32). All clothing worn during the day should be removed at night. A practice prevails in tropical countries of shaking thoroughly every article of apparel just before it is placed on the body. The motive which prompts this comes from the fear lest a centipede or other lively and virulent specimen of natural history has hid itself somewhere within the folds of the garment. Even without the danger of wearing one's shirt in con- junction with such an intruder, it is an excellent practice to shake it and every other article of clothing thoroughly before putting them on. The garments worn next to the skin should be changed before they become saturated with the secretions of the sebaceous glands. This can be accomplished by renewing them twice a week, though the majority of people only change them once in that period. Combe recommends to wear two sets of flannels, each being worn and aired by turns, on alternate days ; he likewise praises a practice common in Italy; namely, instead of beds being made up in the morning the moment they are vacated, and whilo still saturated with the nocturnal exhalations, the bed-clothes are thrown over the backs of chairs, the mattresses shaken up, and the window thrown open for the greater part of the day. This practice, so consonant with reason, imparts a freshness which is peculiarly grateful and conducive to sleep. Florence Nightingale, who never fails to speak plainly, says: " Feverishness is generally sup- P'>ppd to be a symptom of fever; in nine capes out of ten it is a symptom oJ bedding. A real patient should have two beds?, remaining only twelve houj in each; on no account to carry his sheets with him." Draper (in part}. NOTES. 6. Care of the Skin and Nails (p. 48, 1 22). Much ignorance prevails amongst the public as to the use of soap and water. Those who have very sensi- tive skins should use soft water, for the face at all events, and the best water, if it can be had, is rain-water with the cold taken off it. Nor is it every kind of soap which is tolerated by such persons ; probably the safest soaps are, not those which are said to contain, but those which really do contain, a large portion of glycerine. The culture of the nails, which when perfect constitute so great a beauty, is of much importance ; but the tendency is to injure them by too much attention. The scissors should never be used, except to pare the free edges when they have become ragged or too long, and the folds of scarf skin which overlap the roots should not, as a rule, be touched. The upper surfaces of the nails should on no account be touched with the knife, as it is so often done, the nail brush being amply sufficient to keep them clean, without imparing their smooth and polished surfaces. People's Magazine. 7- An Imaginary Conversation on Baths and Bathing (p. 47,! 21). " I have often amused myself, by fancying one question which an old Roman emperor would ask, were he to rise from his grave and visit the sights of London under the guidance of some minister of state. The august shade would, doubt- less, admire our railroads and bridges, our cathedrals and our public parks, and much more of which we need not be ashamed. But after a while, I think, he would look round, whether in London or in most of our great cities, inquiringly and in vain, for one class of buildings, which in his empire were wont to be most conspicuous and splendid. 'And where,' he would ask, ' are your public baths? ' And if the minister of state who was his guide shonld answer' O great Caesar, I really do not know. I believe there are some somewhere in some out-of-the-way place ; and I think there have been some meetings lately, and an amateur concert, for restoring, by private subscriptions, some baths and wash-houses which had fallen to decay. And there may be two or three more about the metropolis ; for parishes have power to establish such places, if they think fit, and choose to pay for them out of the rates : 'Then, I think, the august shade might well make answer ' We used to call you, in old Rome, northern barbarians. It seems that you have not lost all your barbarian habits. Are you aware that, in every city in the Roman empire, there were, as a matter of course, public baths open, not only to the poorest freeman, but to the slave, usually for the payment of the smallest current coin, and often gratuitously? Are you aware that in Rome itself, millionaire after million- aire, emperor after emperor, built baths, and yet more baths ; and connected with them gymnasia for exercise, libraries, and porticos, wherein the people might have shade and shelter, and rest ? Are you aware that these baths were of the most magnificent architecture, decorated with marbles, paintings, sculptures, fountains, what not? And yet I had heard, in Hades down below, that you prided your- selves here on the study of the learned languages.' " Rev. Charles Kingsley on the A ir-mothers. ^ 8. Bathing (p. 47, T 20). "When the civilization of Egypt, Greece, and Rome faded, the world passed through dark ages of mental and physical bar- barism. For a thousand years there was not a man or woman in Europe that ever took a bath, if the historian of those times, Michelet, is to be believed. No wonder that there came the wondrous epidemics of the middle ages, which cut off one-fourth of the population of Europe the spotted plague, the black death, sweating sickness, and the terrible mental epidemics which followed in their train the dancing mania, the mewing mania, and the biting mania. Not only their persons, but their houses were uncleanly, even in the classes that were well- to-do. Filth, instead of being abhorred, was almost sanctified." Lyon Play fair. 9. Rules as to Clothing (p. 51, 1 32). -Protection against Cold.Yor equal thicknesses, wool is much superior to either cotton or linen, and should be NOTES. worn for all under clothing. In case of extreme cold, besides wool, leather or water-proof clothing is useful. Cotton and linen are nearly equal. Protection against Heat. Texture has nothing to do with protection from the direct solar rays ; this depends entirely on color. White is the best color; then gray, yellow, pink, blue, black. In hot countries therefore, white or light-gray clothing should be chosen. In the shade the effect of color is not marked. The thickness and the conducting power of the material are the conditions (especially the former) which influence heat. The body should not only be so protected by its covering as to be kept from rain and damp ; but the clothing must be so ventilated that the emanations from the skin shall not accumulate. The wearing of the unventilated beaver hat, or fur cap, is a ready method of suppressing the natural growth of the hair, and of caus- ing the retention of that effete eplLl-elial scale commonly called scurf, or dandruff. The wearing of tightly-fitting water -proof coats cannot be habitually practiced without danger to the wearer ; the very painful and troublesome ailment, rheuma- tism, has in many persons been produced by this manner of locking in the excre- tions of the surface. Dr. B. \V. Richardson. 1 0. The Renewal of the Cuticle (p. 42, f 3). The skin is not a permanent sheath, but is, as it were, always wearing out and rubbing off, and new skin is always rising up from underneath. A snake leaves off his whole skin at once, as we leave off a suit of clothes or a dress, and sometimes we may find his whole cast-off covering turned inside out, just as he crept out of it. In man, generally we do not notice the dead particles of the skin as it wears off, but where the cuticle is pretty thick, as on the soles of the feet, we can see it peel off in little rolls whenever we wash the feet in hot water. After scarlet fever, too, sometimes the dead skin comes off in great flakes, and from the hands almost like the fingers of a glove. Berners. 11. The Life of the Cells of the Body (p. 43, t 5). "The life of the body is long under fortunate circumstances ; that of our cells is short. We all know that the surface of the body is covered by layers of cells. The superficial layers are in loose connection ; they are cells in old age. The friction of our clothing daily removes an immense number of them. A cleanly person who uses sponge and towel energetically every day rubs off a still greater quantity. " This takes place very actively in one month. We swallow ; our tongue acts in speaking; drink and food pass this way. Now, the mucous membrane of the mouth is covered with layers of cells. Here, also, many thousand senile cells are rubbed off daily. And so on through the entire digestive tract. An immense number of cells, these living corner-stones of the body, is thus lost daily. " To show the duration of life in one kind of cell, let us turn to the human nail. The latter, growing from a furrow of the skin, is made up of skin-cells. In the depth of the furrow, youth prevails ; at the upper margin which we trim old age. Berthold proved that a nail-cell lives four months in ^frnmer and five in winter. A person dying in his Both year, has changed his nail 200 times, at least and the nail appeared such an inanimate, unvarying thing ! No other cells, AVC believe, have a life nearly so long as that of the nail." Compendium of Histology by Heinrich Frey. 12. On Scents (p. 48, [ 22)." They are the only resource of rude and dirty times against offensive emanations from decaying animal and vegetable sub- stances, from undrained and untidy dwellings, from unclean clothes, from ill- washed skins, and from ill-used stomachs. The scented handkerchief, in these circumstances, takes the place of the spoc ge and the bath ; the pastile hides the want of ventilation ; the otto of roses seems to render the scavenger unnecessary ; and a sprinkling of musk sets all other smells and stinks at defiance." Johnston. THE CHEMISTRY OF FOOD. 53 CHAPTER IV. THE CHEMISTRY OF FOOD. The Source of Food Inorganic Substances Water Salt Lime Iron Organic Substances Albumen, Fibrin, and Casein The Fats or Oils The Sugars, Starch, and Gum Stimulating Substances Necessity of a Regulated Diet. /* 1. The Source of Food. The term food includes all I those substances, whether liquid or solid, which are neces- ~ary for the nourishment of the body. The original source of all food is the earth, which the poet has fitly styled the " Mother of all living." In her bosom, and in the atmos- phere about her, are contained all the elements on which life depends. But man is unable to obtain nourishment directly from such crude chemical forms as he finds in the inorganic world. They must, with a few exceptions, be prepared for his use, by being transformed into new and higher combinations, more closely resembling the tissues of his own body. r2. This transformation is effected, first, by the vegetable world. But all plants are not alike useful to man ; while some are absolutely hurtful. Accordingly, he must learn to discriminate between that which is poisonous and that which is lirttupporting. Again, all parts of the same plant or tree are not alike beneficial: in some, the fruit, in others, the leaves, and in others, the seeds only are sufficiently refined for his use. These he must learn to select ; he must also learn the proper modes of prepar' ing each kind for his table, whether by cooking or othef processes. (Read Note 6, end of Chapter) 1 . The term food ? Source of food ? Need of preparing food ? 2. Usefulness and hurtfulawM of plants ? Wht then must man do 1 Part* ot the same plant or tree ? 54 THE CHEMISTRY OF FOOD. 3. Again, certain forms of the vegetable creation which are unfit, in their crude state, for man's food, and which he rejects, are chosen as food by some of the lower animals, and are, by them, made ready for his use. Thus the bee takes the clover, that man cannot eat, and from it collects honey. The cattle eat the husks of corn and the dried grass, that are by far too coarse for man, and in their own flesh convert them into tissues closely resembling his mus- cular tissue. In this way, by the aid of the transforming processes of the vegetable and animal creations, the simple chemical elements of the mineral kingdom are elaborated into Our choice articles of food. (Read Note 13, end of Chapter^ r4. Inorganic Substances. The substances we use as food are classified as organic and inorganic. By organic substances are meant those derived from living forms, such as vegetables and animals. Inorganic substances are those simpler inanimate forms which belong to the mineral kingdom. The former alone are commonly spoken of as food, but the latter enter very largely into the constitution of the body, and must therefore be present in our food. With the exception of two articles, water and common salt, these substances only enter the system when blended with organic substances. r 5. Water. Water, from a physiological point of view, is the most important of all the articles of food. It is every- where found in the body, even in the bones and the teeth- It has been computed that as large a proportion as two" thirds of the body is water. The teeth, thedensest of the solids in the human system, contain ten per cent, of water. The muscles, tendons, and ligaments are more than half water; for it is found that they lose more than half their 3. Certain forms of vegetable creation? Example of the bee? Cattle? The inference ? 4. What classification ? Define organic substances. Inorganic. Organic, how spoken of? The inorganic ? Water and salt ? 5. Water in physiology ? Where found ? Computation? Water in the teeth* Muscles, tendons, and ligaments ? ITmv ascertained ? Water in the fluids of th-* body ? What is the advantage ~; THE CHEMISTRY OF FOOD. 55 weight when dried with moderate heat. But it is in the -fluids of tho body that water is found most abundantly. It gives to them the power of holding a great variety of substances in solution, and is the great highway by which new supplies are conveyed to the point where they are required, and by which old particles of matter, that have served their uses, are brought to the outlets of the body to be thus removed from the system. (Read Notes i and 7.) 6. Man can remain a longer time without solid food than without water. He may be deprived of the former for ten to twelve hours without great suffering, but depri- vation of water for the same length of time will produce both severe pain and great weakness. The food should contain not less than two parts of water to one of solid nutriment. Water constitutes the great bulk of all our drinks, and is also a large constituent of the meats, vegetables, and fruits which come upon the table. Fruits, especially, contain it in great abundance, and, in their proper season, furnish most agreeable and refreshing supplies of the needed fluid. 7. Common Salt. Salt, or sodium chloride, as an article of food, is obtained chiefly from the mineral king- dom: although plants contain it in small quantities, and it is also found in the tissues of nearly all animals used as food. In the human body, it is an ingredient of all the solids and fluids. The importance of salt to animal life in general, is shown by the great appetite for it mani- fested by domestic animals, and also by the habitual resort of herds of -Cold beasts to the " salt-licks" or springs. In those parts of the world where salt is obtained with diffi- culty, man places a very high price upon it. F 8. Experiments upon domestic animals show that the withdrawal of salt from their food, not only makes their 6. Length of time man can do without food or water ? Give the comparison? Rulk of drinks ? Constituent of meats, etc. ? Fruite ? 7. Salt, how obtained ? Where found? In the human body? Importance ol a t ''. What else can you et.atp of the value of talt ? 8. Experiments npon animals? 53 THE CHEMISTRY OF FOOD. r. r hides rough and causes the hair to fall out, but also inter- feres with the proper digestion of food. If it be withheld persistently, they become entirely unable to appropriate nourishment, and die of starvation. (Read Note 2.) 9. Salt is usually taken into the -system in sufficient quantities in our food. Even the water we drink often has traces of it. The habitual use of much salt in cook- ing, or as a seasoning at the table, is not wise; and while it may not lead to consumption, as some writers declare, it is a bad habit in itself, and leads to the desire for other and more injurious condiments. 10. Lime. This is the mineral substance which we have spoken of before as entering very largely into the com- position of the bones. It is the important element which gives solidity and permanence to the framework upon which the body is built. Calcium tri-phosphate, or "bone- earth," is the chief ingredient of the bones and teeth, but is found in the cartilages and other parts of the body in smaller quantities. (Read Note 5.) 11. How does this substance find its way into the body? Meat, milk, and other articles obtained from the animal kingdom contain it, and it is abundantly stored away also in the grains from which our bread is made, in wheat, rye, and Indian corn. In early life, while the body is growing, the supplies of this substance should be carefully provided. The evil effects of the deprivation of it are too often and painfully evident in the softening of the bones, and in the predisposition to curvature of the spine delQmities which are most deplorable and which continue through life. 12. Iron. This substance is probably the most abun- dant and widely diffused of the metals. It is found in 9. Salt, hovr taken into the system? Its use in cooking ? Consumption? 10. Lime in the bones ? What does it impart ? Chief ingredient of the bones and teeth ? Where else found ? 11. How does lime find its way into the body? Early life? Effect of it* deprivation ? 1 2. Iron, its abundance and diffusion ? Where found ? What part of the blood is it T How supplied to the system ? In case of loss of blood or wasting disease ? THE CHEMISTRY OF FOOD. 57 most of the vegetables, and is a very important component of animal tissues. It enters into the composition of hu- man blood in about one part per thousand. Ordinarily, the food conveys to the system enough iron for its use, but it must sometimes be introduced separately as a remedy, especially after great loss of blood, or after some wasting disease. Under its influence the blood seems to be rapidly restored, and a natural color of the lips and skin replaces the pallor caused by disease. 13. Other Inorganic Substances. In addition to the substances mentioned, the mineral kingdom supplies, compounds of soda, potash, and magnesia, which are es- sential for the use of the body. They occur in small quantities in the body, and enter it in combination with the various articles of diet. 14. Organic Substances. These substances are derived from the vegetable and animal creations. They comprise all those articles which are commonly spoken of as " food," and which are essential to sustain the body in life and strength. They are divided into three groups, namely: the Albuminoid substances, the Fats, and Sugars. 15. The Albuminoids. This class includes three im - portant nutritive substances (I) Albumen, which gives it its name; (2) Fibrin, including gluten; and (3) Casein. These compounds constitute a large part of the human body, and the food contains them in proportionally large quantities. Their importance is so great, and the system so promptly suffers from their absence, that they have been styled the "nutritious substances." The properties which they hold in common are, that they do not crystallize, and have a jelly-like form, except when heat is applied to them, when they harden, or coagulate. 1 3. Soda, potash, and magnesia ? How do they occur ? 14. Organic substances, whence derived ? What do they comprise ? Groups ? 15. The Albuminoid class, includes what? These compounds constitute irhat) The food? Thir importance ? Their properties t 58 THE CHEMISTRY OF FOOD. ; I 16. They likewise decompose, or putrefy, under the influ- ence of warmth and moisture. Hence the decay of all dead animal tissues. Cold arrests this process. It is well known that milk, eggs, and the like, " keep" much longer in winter than at other seasons. The bodies of elephants, caught in the ice many hundred years ago, are occasion- ally borne by the icebergs to the coast of Siberia, com- pletely frozen, but preserved almost perfectly in form and limb. 17. Albumen exists in milk, meat, the grains, and the juices of many plants; but the purest form is obtained from the white of egg. When we consider that an egg is composed chiefly of albumen and water namely, six parts in seven; and when we also consider the numerous, diverse, and complex tissues the muscles, bones, internal organs, bill, claws, and feathers with which the chick is equipped on leaving his shell, we are impressed with the importance of these apparently simple constituents of the food and body. (Read Note 9, end of Chapter) 18. Fibrin is derived from meats, and exists in the blood both of man and the lower animals. Gluten, 01 vegetable fibrin, resembles closely true fibrin, and is abun- dantly furnished in wheat and other grains from which flour is commonly made. Animal fibrin coagulates spon- taneously when it is removed from the body, and thus causes the " clotting" of the blood. 19. Casein is the curdy ingredient of milk, and a highly important food-substance. Its coagulation in milk takes place not from heat, but by the addition of an acid, and also when milk becomes sour from exposure to the air. It is commonly effected, however, by introducing a piece of rennet, a preparation made from a calf s stomach. The curds, or casein, may then be separated from the whey, 16. Decomposition? Effect of cold ? Illustrations? Elephants? 1 7. In what substances does albumen exist ? What further is said of the egg 18. Fibrin, gluten, clotting of the blood ? 19. Casein? Its coagulation ? Eft'ect of rennet ? Making of cheese* THE CHEMISTRY OF FOOD. 59 and made into cheese, by pressing it sufficiently to drive off the water. 20. The Fats or Oils. This is the second group of organic foods. Those which are more solid are called fats: the more fluid ones are the oils. Oleaginous substances are supplied in both animal and vegetable food ; but, from whatever source derived, they are chemically much alike. They are insoluble in water, and yet they unite readily with the watery fluids of the body, and are by them con- veyed to its various parts for their nourishment. This is due to their property of "emulsifying;" that is, they are held in suspension, in a finely divided state, in water. Or- dinary milk is an example of an emulsion. We know that it contains fat; for butter is obtained from it, and, under the microscope, the minute oil-globules may be distinctly seen. 21. In our country and climate, and also in colder climates, fatty articles of food are principally derived from the animal creation, such as meat or flesh, milk and butter. But most of the bread-stuffs contain more or less fat or oil; Indian meal as much as nine parts in a hundred. 22. Among persons living in cold climates, the appetite for oleaginous food is especially eager ; and they require large quantities of it to enable them to resist the depress- ing influences of cold. Since vegetation is scanty and innutritions, and the waters of the frozen regions abound in animal life, they must rely wholly upon a diet derived from the latter source. The Esquimaux consumes daily from ten to fifteen pounds of meat or blubber, a large proportion of which is fat. The Laplander will drink train-oil, and regards tallow-candles as a great delicacy. In hot climates, on the contrary, where flourish the olive 20. What are the fats ? The oils ? How supplied ? How alike ? Emulsifying 7 Example ? How do we know it? 21. Whence are fatty articles of food derived? 22. Appetite of persons in cold climates? What do they require ? Upon wiia roust thty jely T Why? Thw Esquimaux ? Laplander' Ollv<* and paluu r 60 THE CHEMISTRY OF FOOD. and the palm, this kind of food may be obtained from vegetable sources in abundant quantities. (Read Notes 4 a3 instance, sugar changes to fat in the body ; and hence, as is well known, the " hands" on a sugar plantation grow fat during the sugar season, by partaking freely of the ripened juices of the Cane. (Read Note 10, end of Chapter.} 31. That is the best diet therefore which contains some of each of these principles, in due proportion; and that is the worst which excludes the most of them. The cravings and experience of man had unerringly guided him to a correct regulation of his diet, long before the chemistry of food was understood ; so that his ordinary meals long ago combined these various principles, the necessity and value of which are now explained. (Read Notes n and 12, end of Chapter.") QUESTIONS FOR TOPICAL REVIEW. PAGE 1. What is understood by the term food ? 53 2. What can you state in relation to the source of food ? 53 3. What discriminations and selections are necessary ? 53, 54 4. How can you tell the organic from the inorganic :-ubstances * 54 5. What relative position does water hold as an article of food ? 54 6. In what parts of the body is water found ? 54, 55 7. In what articles that we eat is it found ? 55 8. If you were required to go without water or solid food for a number of days, which would you prefer to have, and why ? 55 9. What can you state of the importance of salt as an article of food ? 55, 56 10. How abundant is salt, and how does it find its way into the human sys- tem ? 55, 56 11. What can you state of the importance of lime in the body ? 56 12. What, of the importance of iron ? 56, 57 13. What further is stater! of other inorganic substances ? 57 14. What in relation to organic substances ? *? 15. What can you state in relation to the albuminoids ? 57, 58 16. What, in relation to albumen ? ^ 17. What, in relation to casein ? 58, 59 18. In relation to the fats or oils, and how generally consumed ? 59, 60 19. What do we understand by the sugars or saccharine substances ? 20. Sta'e what you can of sn JJULNK. 42. What is the physiological action of alcohol ? Its first and most evident action is stimulation : this effect is tran- sient, and is followed by a variable degree of depression At first it sharpens the appetite and quickens digestion, but its habitual use impairs both. This stimulation is efficient in giving the system an artificial strength during some temporary derangement, and in enabling the endur, ance of unusual fatigue or exposure. The experience oi Dr. Hayes, and other explorers of the polar regions, is that alcohol does not enable the body to resist the influence of cold, but, on the contrary, is always injurious. 43. Another property it has in common with tea and coffee. It supports the powers of life, economizes food, and retards the waste of tissues; in other words, it " banks the fires," and prevents their burning wastefully. On this principle we explain the restorative influence of wines or liquors during exhausting diseases, in convalescence, and after excessive labors of mind or body. 44. Pure alcohol, or an excessive quantity of ardent spirits, is an undoubted poison, and has been frequently known to produce fatal results. Stimulants in moderate quantities have been thought to increase strength, and in this view they have been called "alcoholic foods." This is not now conceded by scientific men. The prevailing opin- ion is, that they serve no useful purpose as an article of diet, and that their beneficial influence is limited to cases where the system is enfeebled, where some unnatural de- mand is made upon the vital powers, or where the supply of food is insufficient. Hence, while alcohol has not the power to build up, it may obstruct the process of pulling down. 42. Describe the action of alcohol upon the human system ? Experience of Dr. Hayes and others ? 43. Another property of alcohol ? How do we explain the restorative influence of wines and liquors ? 44. Alcohol, a poison ? Moderate stimulants? Prevailing opinion ? Hence? HEVIEW QUESTIONS. 79 QUESTIONb 7OR TOPICAL REVIEW. PAGB 1. How is the necessity for food shown ? 04 2. To what process of waste and repair is> the body constantly subjected ? 64 3. How do you account for the sensations ot hanger and thirst ? G5 4. What further can you state having relation to the subject ? 05 5. What can you state in regard to the quantity of food required for the support of life ? 65, G6 6. What circumstances change the needs of persons, old a:id young, as re- gards food and drink ? 65 i 57 7. What becomes of all the food and drink we consume ? 66 8. What further can you state iu relation to the process of renovation through which the body passes ? 66 9. What can you state of the habits of nations in respect to diet ? 66, 67, 69 10. What in relation to the selection of articles for food ? 67 11. What as respects the necessity for changing or varying the diet ? 67 12. What has been proved as regards animal food ? 67 13. Of what importance is milk as an article of food ? 67, 68 14. What are the constituents of milk ? . . 68 15. What can you state of eggs as an article of food? 68 16. Of the meats, so called, as an article of food ? 68, 69 17. What effect does cold have upon meats ? 69 18. In what ot her way may beef and pork be preserved ? 69 19. What can you state of salted meat as food, and of its continued use ? 09 20. What change doe? meat undergo in the cooking ? 70, 71 21. What directions are given for boiling meat ? 70 22. What for roasting, and with what results? 70, 71 83. What is said about the frying of meats? 7i 24. Give the statement in relation to trichina 7' 25. State what is said in relation to fish 71 26. What is stated of the usefulness and other properties of the products of the vegetable kingdom ? 71, 72 27. What further is said of vegetable food ? 71, 72 28. Why is bread made of wheat flour so important as an article of food ? 72 29. State whatever else you can in relation to bread 72, 73 30. Give the statement respec' ing the potato - 73 31. What is stated of fruits, the use of them, their nutritious qualities, etc.? 73, 74 32. How general is the existence of perfectly pare water ? 74 33. What is stated in relation to drinking water ? 74, 75 34. How does the action of water upon lead affect lead ? 75 35. What further can you state on the subject? 75 3(i. What properties has coffee as an article of diet ? 75. 7G 37. In what circumstances has coffee been found peculiarly beneficial ? 76 38. What comparison is made between coffee, tea, and chocolate ? 76 39. How are the wines, and malt and other alcoholic beverages produced ? 77 40. What articles are employed in their production ? TT 41. Describe the physiological action of alcohol. T8 42. What comparison is made between tea, coffee, and alcohol ? 78 43. What can yon state of alcohol, as a poison, a stimulant, and article of diet ? 73 44. What, then, can be said of alcohol as a recommendation ? 78 NOTES. 1. Hunger and Thirst (p. 65, 1 4). " We none of n object to a pharp-set appetite ; that is by no means unpleasant, especially when there is food at hand; but if this is not the case it soon becomes a craving passion, a strong impelling power. The cravings of hunger have done much for this world ; ' look where we may, we see it as the motive power which sets the vast array of human machinery in action.' Hunger is also the incentive which directs our attention to the system's need for food, and if it be sharp enough the most loathsome substances are greedily devoured. By it has man, and civilized man, too, been driven to feed upon the putrid corpse of his comrade. Hunger is one of the great forces in action, in the preservation of the life of the individual ; and the fear of it is one of the s-trongest incentives to action. But the pangs of hunger are tolerable in compari- son with the tortures of raging thirst. In fact, so terrible are the latter that they form one of the crudest tortures which man can inflict on man; so cruel a tor- ture, indeed, that it has rarely been used, except in cases of bitter personal ani- mosity, by others than brutal Eastern tyrants, or bigots under the influence of religious fanaticism. 1 ' Fothergill on the Maintenance of Health. 2. The Renewal of the Body (p. 66, 17). "To meet these constant chemical changes, material is taken in, in the form of food and drink, which is being constantly assimilated, and so nutrition and repair are conducted. The rapidity with which these changes are carried on is much greater than is usually supposed. Paley, in his 'Natural Theology,' states that seven years are requisite for the per- fect renewal of the body ; and this statement, owing partly to the mysticism associa- ted with t he number 7, is generally accepted and believed. The time really is rather months than years ; but it is absurd to fix a time which must necessarily vary iu different individuals, being much less in the infant than in the aged, in the active than the indolent ; widely different, too, in various tissues, from the epithelium lin- ing of the glands of the stomach, renewed several times in each act of digestion, to the enamel of the tooth, which is probably never renewed during a lifetime. 1 " 3. A Lifetime Allowance of Food (p. 66,1 6). ' M.Soyer, in his 'Mod- ern Housewife,' makes a calculation as to how much food an epicure of 70 years of age has consumed. This imaginary epicure, who is supposed to be a wealthy per- sonage, is placed by him on Primrose Hill at ten years old and told to look around him at the vast assemblage of animals and other objects he will in the course of a lifetime send down his throat the sight of which is, of course, described as appalling. Among the other things, he is to devour 30 oxen, 200 sheep, 100 calves, 200 lambs, 50 pigs, 1,200 fowls, 300 turkeys, 263 pigeons, 120 turbot, 140 salmon, 30,000 oysters, 5.745 Ibs. of vegetables, 243% Ibs. of butter, 24,000 eggs, and 4^ tons of bread, besides fruits, sweetmeats, etc., and 49 hogsheads of wine, 548 gals, of spirits, and about 3,000 gals, of tea and coffee. This is a mere outline of what we are told is destined to be consumed. To show there is no exaggeration, Soyer assures us that he has from experience made up a scale of food for the day for a period of 60 years, and it amounts to 33% tons of meat, farinaceous food, and vegetable?, etc." Journal of Chemistry. 4. A Mixed Diet afford* the best Results (p. 67, 1 10). "The mixed diet to which the inclination of man in temperate climates seems unusually to lead him, when circumstances allow that inclination to develop itself freely, appears to be fully conformable to the construction of his dental and digestive apparatus, as well as to his instinctive cravings. And whilst on the one hand it maybe freely conceded to the advocates of 'vegetarianism,' that a well-selected vegetable diet is capable of producing, in the greatest number of individuals, the highest physical development of which they are capable, it may, on the other hand, be affirmed with equal certainty, that the substitution of a moderate proportion NOTES. of animal Ae*h is in no way injurious; but, so far as our evidence at present extends, this seems rather to favor the highest mental development. And we can scarcely avoid the conclusion that the Creator, by conferring on man a remarka- ble range of choice, intended to qualify him for subsisting on those articles of diet, whether animal or vegetable, which he finds most suitable to his tastes and wants." W. B. Carpenter on the Principles of Physiology. 5, Bread (p. 72, 124). "The health and power of a nation, as of an army, depend greatly on its food. The quality of bread in any nation, community, or family is a pretty good measure of its civilization. No one can entirely dispense with it. Good or bad, in some form it must be had. So it is, and has been from the earliest records of the race, and so it will doubtless continue. Leavened or fermented bread is as old as the time of Moses, and its value has been fully tested. Whatever be the precise action of the leaven, it transforms the grain by partial decomposition of its original elements, and leaves as its resultant what all men in all ages have approved. Is the art of making good, honest, leavened, Bible bread lost in Massachusetts, as some of our friends declare ? Baker's bread is almost uni- versally adulterated. Bread hastily made in families is mixed in a varietyof ways, with a variety of chemicals, and is generally imperfectly cooked. Very often the elements of wheat and fat which the body demands (a wise and witty clergyman of the last generation used to say, 'bread is the staff of life, but bread and butter is a gold-headed cane') are furnished in underdone pastry, made from flour and hog's lard. Any family can have good bread who will take the pains. It involves not more than ordinary skill and judgment. It ' is to be found on the continent of Europe on all the great lines of travel, and is as common among the people in France and Germany as it is rare with us.' The materials for an honest, wholesome loaf are simple and not expensive. The value of time and labor required for kneading the dough are the only difficulties, and these we would not undervalue; they are in many families very serious, and not easily overcome." Derby on the Food of Massachusetts. 6. Impure Water Spreads Disease (p. 75, t 32). "In the year 1867, three millions of pilgrims, of whom a handful had come from a cholera district, assembled at Hurdwar, a few miles from the spot where the Ganges escapes from the Himalayas. On the 12th of April the three millions resolved to bathe and drink. 'The bathing-place of the pilgrims was a space 650 feet long by 30 feet wide, shut off from the rest of the Ganges by rails. Into this long and narrow in- closure pilgrims from all parts of the encampment crowded as closely as possible from early morn to sunset ; the water within this space, during the whole time, was thick and dirty partly from the ashes of the dead, brought by surviving rela- tives to be deposited in the water of their river god, and partly from the washing of the clothes and bodies of the bathers. Now, pilgrims at the bathing ghaut, after entering the stream, dip themselves under the water three times or more, and then drink of the holy water, whilst saying their prayer. The drinking of the water is never omitted ; and when twoormore members of a family bathe together, each from his own hand gives to the other water to drink. On the evening of the next day, the 13th of April, eight cases of cholera were admitted into one of the hospitals at Hurdwar. By the 15th, the whole of this vast concourse of pilgrims had dispersed,' carrying the cholera in every direction over India; it attacked the British troops along the various routes, it passed the northern frontier, got into Persia, and so on into Europe, where it will work its wicked will for some time to come. That is a sample of the mischief water can do in the way of spreading disease." London Medical Press. NOTES. 7. The Waste of the Body (p. 64,! 2.}. " In the physical life of man there is scarcely such a thing as rest the numberless organs and tissues which compose his frame are undergoing perpetual change, and in the exercise of the function of each some part of it is destroyed. Thus, we cannot think, feel or move without wasting some proportion, great or small, according to the energy of the act, of the apparatuses concerned such as brain, nerve or muscles. Now this waste-product cannot remain in its original situation, where it would not only be useless dross, but also obstructive and injurious. Such old material is being daily removed from our bodies to the average amount of three or more pounds ; and that an equal quantity of new shall take its place is the first piinciple of alimenta- tion. To express it in commercial language, the income must be equal to the expenditure ; and in each of us the amount of this exchange must in a lifetime reach many tons. This tissue-change is so complete, that not a particle of our present body will be ours a short time hence ; and we will be, as I have lately seen it prased, like the knife which, after having had several new blades, and at least one new handle, was still the same old knife to its owner. We are, in fact, constantly ' moulting.' " Mapother's Lectures on Public Health. 8. A Daily Ration for an Adult Man (p. 66, ^6). " We may arrive at something like an average daily diet by taking the case of the man in good health, weighing 154 Ibs., and measuring 5 feet 8 inches in height. Simply to maintain his body, without loss or gain in weight, his ration of food should not contain less, during 24 hours, than the following proportions and quantities of the main ingredients : THE AVERAGE DAILY DIET FOR AN ADULT. FOOD SUBSTANCES. PER CENTUM. WEIGHT. Water 81 < Ibs. oz. grs. r g 020 Albuminoids or flesh formers. .. 3-9 4 no ii 178 Fat Phosphates, potash, salts, etc 3 170 100. 6 13 128 " Water, it will be remembered, enters into the composition of every article of food as well as in the liquids we drink. In reality, the weight of the dry food we take will exceed that given above ; chiefly for the reason that they do not come to us pure and unmixed with fibrous material and gelatine, whose use in nourishing the body is limited and uncertain." Kensington Museum Hand-book on Food. 9. Different Effects of Animal and Vegetable Food (p. 67. \ 8). u Raw meat gives fierceness to animals, and would do the same to man. This is so true that the English, who eat their meat underdone, seem to partake of this fierceness more or Isss, as shown in pride, hatred and contempt of other nations." De La Mettrie. " The carnivora are in general stronger, bolder and more pugnacious than the herbivora on which they prey ; in like manner, those nations who live on vege- table food differ in disposition from such as live on flesh." Liebig. NOTES. A bear at Giessen was very gentle when fed on bread, but a day or two on meat made him savage and dangerous. " The hunted deer will outrun the leopard in a fair open chase, because the force supplied to its muscles by vegetable food is given out continuously for a long time ; but in a sudden rush at a near distance, the leopard will infallibly overtake the deer, decause its flesh food stores up in the blood a reserve of force capable of being given out instantaneously in exceedingly rapid muscular action." Haughtorfs A nimal Mechanics. 10. A Summary Concerning Diet (p. 68,1 ). " The food on which the man who would be healthy should live, should be selected so as to ensure variety without excess. Animal food should not be taken ottener than twice daily. The amount of animal and vegetable food combined should not exceed 30 ounces in the 24 hours ; and for the majority of persons an average of 24 ounces of mixed solid food, a third only of which should be animal, is sufficient. All animal foods should be eaten while they are fresh, and after they have been well cooked. The habit of eating underdone flesh is an almost certain cause of parasitic disease. The amount of fluid taken, in any form, should not exceed the average of 24 ounces daily. Water is the only natural beverage." Dr. B. W. Richardson, The Diseases of Modern Life. 1 1 . Cooking Paves the Way for Easy Digestion (p. 70, 1 19). The objects to be obtained by cooking meat are : i. To coagulate the albumen and blood of the tissues, so as to render the meat agreeable to the sight 2. To develop flavors, and to make the tissue crisp, as well as tender, and therefore more easy of mastication and digestion. 3. To secure a certain temperature, and thus to be a means of conveying warmth to the system. 4. To kill parasites hi the tissues of the meat The action of heat should not be continued after these objects are accomplished, as the meat will thereby be rendered indigestible. If a piece of meat be placed in water which is briskly boiling, a crust, so to speak, is formed by the rapid coagu- lation of the albumen upon and near the surface ; so that the juice of the meat can not escape, nor the water penetrate its interior. If, on the other hand, the meat be put in cold water and slowly heated, the albumen is gradually dissolved, and exudes into the water, making good soup, but leaving the meat poor and tasteless. Even in roasting meat the heat must be strongest at first, and it may then be much reduced. The juice which, as in boiling, flows out, evaporates, in careful roasting, from the surface of the meat, and gives to it the dark brown color, the lustre, and the strong aromatic taste of roast meat. All baked and roasted fatty foods are apt to disagree with delicate stomachs ; and it is often remarked that, although bread and butter, boiled puddings, boiled fish, or boiled poultry can be eaten freely without discomfort, yet toast and butter, or meat pies and pastry, or fried fish, or roasted fowl will disagree with the stomach. Letheby on Food. 12. L.ead in Drinking- Water (p. 75, t 33). The danger of using lea. for pipes or cisterns is now well known ; the case of the late royal family o France at Claremont having made the matter notorious. In this case there wai one-tenth of a grain in the gallon, and one-third of the persons who drank thi water were affected. But even one-hundredth of a grain per gallon has produce palsy in those who drank this impurity habitually. It is remarkable that tU Thames water will at one time dissolve lead, and not at another. Health Lectures. 80 DIGESTION. CHAPTER VI. DIGESTION". The Principal Processes of Nutrition The General Plan of Digestion Mastication The Teeth Preservation of the Teeth Insalivation The Stomach and the Gastric Juice The Movements of the Stomach Gastric Digestion The Intestines TJie Bile and Pan- creatic Juice Intestinal Digestion Absorption by means of Blood- vessels and Lactcals The Lymphatic or Absorbent System The Lymph Conditions which affect Digestion The Quality, Quan- tity, and Temperature of the Food The Influence of Exercise and f. ' 1. Nutrition. The great design of food is to give nutriment or nourishment to the body. But this is not accomplished directly, as the food must first pass through certain preparatory changes, as follows : (1), Digestion, by which the food is reduced to a soluble condition; (2), Ab- sorption, by which, when digested, it is imbibed into the blood; (3), Circulation, which carries the enriched blood to the various parts of the system; and (4), Assimilation, by which each tissue derives from the blood the materials necessary for its support. 2. By these means the sustaining power of food is grad- ually developed and employed, and the vital machinery kept in working order, somewhat after the manner of the steam-engine. To operate the latter, the force imprisoned within the coal and water is set free and converted into motion by the combustion of the fuel and the vaporization of the water. It will be seen, however, when we come to study these operations in the human body, that they are conducted silently and harmoniously, with marvellous deli- cacy and completeness, and without that friction, and con- 1 . Design pf food ? How accomplished ? 2. Sustaining power of food ? Simile of the engine ? Operation in tho human body ? DIGESTION. 81 loss of power, which attend the working of the most perfect machinery of mini's invention. ./ 3. General Plan of Digestion. The great change which food undergoes in digestion is essentially a reform- ing process, reducing articles of diet, which are at first more or less solid, crude, and coarse, to a liquid and finely comminuted condition, suitable for absorption into the blood. The entire pro- cess of digestion takes place in what is called the alimentary canal, a narrow, tortuous tube, about thirty feet in its entire length. This canal begins in the mouth, extends thence down- ward through the gullet to the stomach (a receptacle in which the principal work of digestion is performed), and thence omvard through the small and large in- testines. 4. The stomach and intestines are situated in the cavity of the abdomen (Fig. 16, 0, and Fig. 2?), FlG 16> _ 8ECTIoy OF TFIE - TRUNK and OCCUpV about two-thirds of SHOWING THE CAVITIES OP THE ,. mi ,' T -i ,1 CHEST AND ABDOMEN. its space. I he action to wh icli the Ai cavity of chest ; food is subjected in these organs g' Sme? m is of two kinds mechanical and D < E ' s P inal ' lumn - chemical. By the former it is crushed, agitated, and car- ried onward from one point to another; by the latter it is changed in form through the solvent power of the various digestive juices. 3. Change of food in digestion? Process of digestion? Describ-* '*a: Mmen- tary canal. 4. Situation of th ptomach and intestines ? Action cf the food ? M jhanic&l action ? Chemical ? 82" DIGESTION. 5. Mastication. As soon as solid food is taken into the mouth, it undergoes mastication, or chewing. It is caught between the opposite surfaces of the teeth, and by them is cut and crushed into very small fragments. In the movements of chewing, the lower jaw plays the chief part; the upper jaw, having almost no motion, acts sim- ply as a point of resistance, to meet the action of the former. These movements of the lower jaw are of three sorts: a vertical or cutting, a lateral or grinding, and a to-and-fro or gnawing mo- tion. 6. The teeth are composed of a bone-like material, and are held in place by roots running deeply into the jaw. The exposed portion, or "crown," is protected by a thin layer of enamel (Fig. 17, ), the hardest substance in the body, and, like flint, is capable of striking fire with steel. In the interior of each tooth is a cavity, containing blood-vessels and a nerve, which enter it through a minute opening at the point of the root (Fig. 19). tv 7. There are two sets of teeth ; first, those belonging to the earlier years of childhood, called the milk teeth, which are twenty in number and small. At six or eight years of age, when the jaw expands, and when the growing body requires a more powerful and numerous set, the roots of FIQ. 17. SECTION op A TOOTH. a, Enamel; , Cavity; cc, Roots; d, Body of the Tooth. 5. Describe the process of mastication ? How many and what movements ? 6. Composition of the teeth? Enamel of the teeth? Interior of teeth? 1. The milk teeth ? The permanent troth 1 DIGESTION. 83 the milk teeth are absorbed, and the latter are "shed," or fall out, one after another (Fig. 15), to make room for the permanent sut. FIG. 18. SECTION or THE JAWS. 1' 2' 3' 4 5', The Milk Teeth ; 1" to 8", The Germs of the Permanent Set. 8. There are thirty- two teeth in the permanent set, many being in one jaw as the other. Each half-jaw has eight teeth, similarly shaped and arranged in the same order : thus, two incisors, one canine, two bicuspids, and three molars. The front teeth are small, sharp, and chisel- edged, and are well adapted for cutting purposes; hence their name incisors. The canines stand next, one on each side of the jaw; these receive their name from their resem- blance to the long, pointed tusks of the dog (Fig. 19). 8, 9. Nurnbev of tueth ? How distributed ? 84 DIGESTIOK. A 9. The bicuspids, next in order, are larger and have a / broader crown than the former ; while behind them are the molars, the largest and most powerful of the entire set. These large back teeth, or "grinders," present a broad, rough surface, suitable for holding and crushing the food. FIG. 19. SECTION OF THE JAWS RIGHT SIDE. V, A, N, Veins, Arteries, and Nerves of the Teeth. The root of one tooth in each jaw is cut vertically to show the cavity and the blood-vessel*, etc., within it. 1 to 8, Permanent Teeth. The third molar, or " wisdom tooth," is the last to be cut, and does not appear until about the twenty-first year. DIGESTION. 85 The order of arrangement of the teeth is indicated by the following dental formula: M *^- M B- ' 10. It is interesting, at this point, to notice the different forms of teeth in different animals, and observe how ad- mirably their teeth are suited to the respective kinds of food upon which they subsist. In the carnivora, or flesh- feeders, the teeth are sharp and pointed, enabling them both to seize their prey, and tear it in pieces ; while the herbivora, or vegetable- feeders, have broad, blunt teeth, with rough crowns, suitable for grinding the tongh grasses and grains upon which they feed. Human teeth partake of both forms ; some of them are sharp, and others are blunt; they are therefore well adapted for the, mastication of both flesh and vegetables. Hence we argue that, although man 'may live exclusively upon either vegetable or animal food, he should, when possible, choose a diet made up of both varieties. 11. Preservation of the Teeth. In order that the teeth shall remain in a sound and serviceable condition, some care is of course requisite. In the first place, they require frequent cleansing ; for every time we take food, some particles of it remain in the mouth ; and these, on account of the heat and moisture present, soon begin to putrefy. This not only renders the breath very offensive, but promotes decay of the teeth. 10. Different forms of teeth ? Human teeth ? The inference ? 1 1 . Cleaning of teeth ? Effects of not cleaning ? 80 DIGESTION". ' ' The saliva, or moisture of the mouth, undergoes a putrefactive change, and becomes the fertile soil in which a certain minute fungus has its growth. This fluid, too., if allowed to dry. in the mouth, collects upon the teeth in the form of an unsightly, yellow concretion, called tartar. To prevent this formation, and to remove other offensive substances, the teeth should be frequently cleaned with water, applied by means of a soft tooth-brush. The de- struction of the tartar fungus is best effected by the use of a weak solution of carbolic acid. 13. Again, it should be borne in mind that the enamel, Nature's protection for the teeth, when once destroyed, is not formed anew; and the body of the tooth thus exposed, is liable to rapid decay. On this account, certain articles are to be guarded against; such as sharply acid substances that corrode the enamel, and hard substances that break or scratch it as gritty tooth powders, metal tooth picks, and the shells of hard nuts. Sudden alternations from heat to cold", when eating or drinking, also tend to crack the enamel. ^ 14. Insalivation. When the morsel of food i& cut and 'ground by the teeth, it is at the same time also intimately mixed with the saliva, or fluids of the mouth. This con- stitutes the second step of digestion, and is called insaliva- tion. The saliva, the first of the digestive solvents, is a colorless, watery, and frothy fluid. It is secreted (i. e. separated from the blood) partly by the mucous mem- brane which lines the mouth ; but chiefly by the salivary glands, of which there are three pairs situated near the mouth. 15. These glands consist of clusters of very small 12. Effects upon the saliva? Formation of tartar? How prevented? How destroyed ? 13. Destruction of the enamel!' How guarded against? 14. Mixing of food with the saliva ? What is the. saliva ? How secreted ? The salivary glands ? 15. The flow of saliva ? The thought of food. ? Anxiety and gr'ef ? Animals fed upon dry and, course food ? DIGESTION. pouches, around which a delicate network of blood-vessels is arranged: they empty into the mouth by means of little tubes, or ducts. The flow from these glands is at all times suf- ficient to maintain a soft and moist condition of the tongue and mouth; but when they are excited by the pres- ence and taste of food, forth they the pour saliva PIG. 20. STRUCTURE OP A SALIVARY GLAND. more freely. Even the mere thought of food will at times cause the saliva to flow, as when the appetite is stimulated by the sight or smell of some savory article ; so that the common expres- sion is correct that " the mouth waters" for the fa- vorite articles of food. Anxiety and grief prevent its flow, and cause "the tongue to cleave to the roof of the mouth." In the horse and other ani- mals, that feed upon dry and coarse fodder, and re- -, -i FIG. 21. THE HEAD OF A HOKSE, showing the quire an abundant SUp- large salivary gland (a), its duct (6), the i r* v n 3 i muscles of mastication (c. d. e,f, and a). ply of saliva, we find large salivary glands, as well as powerful muscles of mastication. A 16. The mingling of the saliva with the food seems a simple process, but it is one that plays an important part 1 6, Importance of the process ? The first place ? The second ? The third ? 88 DIGESTION. a ', in digestion. In the first place, it facilitates the motions of mastication, by moistening the food and lubricating the various organs of the mouth. Secondly, it prepares the way for other digestive acts : by the action of the teeth, the saliva is forced into the solid food, softens the harder substances, and assists in converting the whole morsel into a semi-solid, pulpy mass, that can be easily swallowed, and readily permeated by other digestive fluids. The saliva also, by dissolving certain substances, as sugar and salt, develops the peculiar taste of each ; whereas, if the tongue be dry and coated, they are tasteless. Hence, if substances are insoluble, they are devoid of taste. 17. Finally, the saliva has the property of acting chemi- ' cally upon the food. As we have before stated (Chap. IV.), Starch, as starch, cannot enter the tissues of the body ; but, in order to become nutriment, must first be changed to grape sugar. This change is, in part, effected by the saliva, and takes place almost instantly, whenever it comes in con- tact with cooked starch. This important function is due to an organic ingredient of the saliva called ptyalin. This substance has been extracted from the saliva by the chemist, and has been found, by experiment, to convert into sugar two thousand times its own weight of Starch. (Read Note I, end of Chapter) 18. Importance of Mastication and Insaliva- tion. Each of these processes complements the other, and makes the entire work available; for, by their joint action, they prepare the food in the best possible mannei for further digestive changes. The knowledge of these preliminary functions will appear the more important, when we reflect that they are the only ones which we can regulate by the will. For, as soon as the act of swallowing begins, the food not only passes out of sight, but beyond 17. Its final importance? Starch? How effected ? PtyaUn . 18. Each of the processes? Why is a knowledge of the f the soft and yielding texture of the stomach ? DIGESTION. 91 and, under ordinary circumstances, permits only such matters to pass it as have first been properly acted upon in the stomach. Coins, buttons, and the like are, however, readily allowed to pass, because they can be of no use if retained. The soft and yielding texture of this organ the stomach indicates that it is not designed to crush and comminute solid articles of food. 24. The Gastric Juice. We have seen how the presence of food in the mouth excites the salivary glands, causing the saliva quickly to flow. In the same man- ner, when food reaches - the stomach, its inner -- lining, the mucous mem- brane, is at once excited to activity. At first its surface, which while the stomach is empty pre- sents a pale pink hue, turns to a bright red color, for the minute blood-vessels which course through it, are filled with blood. Presently a clear, colorless, and acid fluid exudes, drop by drop, from its nu- merous minute glands or "tubules," until finally the surface is moistened in every part, and the fluid begins to mingle with the food. This fluid is termed the gastric juice. FIG. 23. THE ORGANS OP DIGESTION. O, (Esophagus. I, Small Intestines. S, Stomach. C, Large Intestines. L, Liver. P, Pancreas. M, Pylorus. N, Spleen. G, Gall-bladder. What ie meant by the gastric juice ? 92 DIGESTION. 25. The gastric juice is the proper solvent of certain articles of food, especially those belonging to the albu- minoid class. This solvent power is due to its peculiar in- gredient, pepsin; in digestion, this substance acts like a ferment; that is, it induces changes in the food simply by its presence, but does not itself undergo change. The acid- ity of the gastric juice, which is due to lactic acid, is not accidental; for we find that the pepsin cannot act in an alkaline solution that is, one which is not acid or neutral The quantity of gastric juice secreted daily is very large probably not less than three or four pints at each meal Though this fluid is at once used in the reduction of the food, it is not lost; since it is soon re-absorbed by the stomach, together with those parts of the food which it has digested and holds in solution. ^. 26. Movements of the Stomach. The inner coat- ing of the stomach is the mucous membrane, which, as we have seen, furnishes the gastric juice. (Next to this coating lies another, called the muscular coat, composed of invol- untary muscular fibres, some of which run circularly, and others in a longitudinal direction. These expand to ac- commodate the food as it is introduced, and contract as it passes out. In addition, these fibres are in continual mo- tion while food remains in the stomach, and they act in such manner that the contents are gently turned round from side to side, or from one end of it to the other. 27. By these incessant movements of the stomach, called the peristaltic movements, thes, gastric juice comes in contact with all parts of the fbod:^ We are, however, not conscious that these movements take place, nor have we the power to control them. When such portions of the food as are sufficiently digested approach the pylorus, it 25. What is the office of the gastric juice? Acidity of the gastric juice! Quantity of gastric juice used ? What becomes of it ? 26. Muscular coat of the stomach? Expansion and contraction of its fibres? Action of the fibres? 27. Peristaltic movements? What if said of our consciousness of and power over these movements ? Describe thu movements of the pylorus. DIGESTION. 93 expands to allow them to pass out, and it closes again to confine the residue for further preparation. 28. The knowledge of these and other interesting and instructive facts has been obtained by actual observation ; the workings of the stomach of a living human being have been laid open to view and examined the result of a re- markable accident. Alexis St. Martin, a Canadian voyageur> received a gun-shot wound which laid open his stomach, and which, in healing, left a permanent orifice nearly an inch in diameter. Through this opening the observer could watch the progress of digestion, and experiment with different articles of food. Since that occurrence, artificial openings into the stomach of the inferior animals have been repeatedly made, so that the facts of stomach-digestion are very well ascertained and verified. (Read Note 2.) 29. Gastric Digestion. What portions of the food are digested in the .stomach ? It was formerly thought that all the great changes of digestion were wrought here, but later investigation has taught us better. We now know that the first change in digestion takes place in the mouth, in the partial conversion of starch into sugar. We also know that, of the three organic food principles (considered in Chapter IV.) two the fats and the sugars are but slightly affected by the stomach ; but that its action is confined to that third and very important class, from which the tissues are renewed, the albuminoids. A few articles need no preparation before entering the system, as water, salt, and grape-sugar. These are rapidly taken up by the blood- vessels of the stomach, which everywhere underlie ifo mucous membrane in an intricate and most delicate net- work. In this way the function of absorption begins. 30. The albuminoid substances are speedily attacked and 28. How has the knowledge and the workings of the stomach been ascertained ? St. Martin ? How else ? 29. What was formerly thought ? What do we now know ? What elae do we now know? Water, salt, and sugar? Absorption? 30. Albuniinose ? The process ? Cayme ? DIGESTION. digested by the gastric juice. From whatever source they are derived, vegetable or animal, they are all transformed into the same digestive product, called albuminose. This is very soluble in water, and is in part absorbed by the blood- vessels of the stomach. After a longer or shorter time, varying from one to five hours, according to the individual and the quantity and quality of his food, the stomach will be found empty. Not only the unabsorbed digested food, but also those substances which the stomach could not digest, have passed little by little through the pylorus, to undergo further action in the intestines. At the time of its exit the digested food is of a pulpy consistence, and dark color, and is then known as the chyme. (Read Note 6.) ^ 31. The Intestines. The intestines, or "bowels," are continuous with, the stomach, and consist of a fleshy tube, or canal, twenty-five feet in length. The small intestine, whose diameter is about one inch and a half, is twenty feet long and very tortuous. The large intestine is much wider than the former, and five feet long (Fig. 23). The general structure of these organs resembles that of the stomach. Like it, they are provided with a mucous mem- brane, or inner lining, whence flow their digestive juices; and, just outside of this, a muscular coat, which propels the food onward from one point to another. 32. Moreover, both the intestines and stomach are envel- in the folds of the same outer tunic or membrane, called the peritoneum. This is so smooth and so well lubricated, that the intestines have the utmost freedom of motion. In the small intestines, the work of digestion is completed, the large intestine receiving from them the indigestible residue of the food, and in time expelling it from the body. 33. Intestinal Digestion. As soon as the food f passes the pylorus and begins to accumulate in the upper N x oped 31. What are the intestines? The small intestines? The larr rpnrlprprl nn fVii incrlp -nm'nr The five email ones at the ence rendered on tnis single point, uppei . part of the flirliref rep . the detecting of the human from other blood. 7. The character of the blood of dead, extinct, and even fossil animals, such as the mastodon, has been ascertained by obtaining and examining traces of it which had been shut up, perhaps for ages, in the circulatory canals of bone. A means of detecting blood in minute quantities is found 6. The size and shape of the corpuscles? Why is the fact important ? 7. Tin character of the blood of dead animals f Meana of detecting such blood r 104 THE CIRCULATION. in the spectroscope, the same instrument by \vnich the constitution of the heavenly bodies has been studied. If a solution containing not more than one-thousandth part of a grain of the coloring matter of the corpuscle, be ex- amined, this instrument will detect it. 8. The corpuscles, just described, are known as the red blood corpuscles. Besides these, and floating along in the same plasma, are the white corpuscles. These are fewer in number, but larger and globular in form. They are colorless, and their motion is less rapid than that of the other variety. The total number of both varieties of these little bodies in the blood is enormous. It is calculated that in a cubic inch of that fluid there are eighty-three mil- lions, and at least five hundred times that number in f he whole body. (Read Note i.) 9. Coagulation. The blood, in its natural condit. n Nin the body, remains perfectly fluid; but, within a fe r minutes after its removal from its proper vessels, whether by accident or design, a change takes place. It begins to coagulate, or assume a semi-solid consistence. If allowed to stand, after several hours it separates into two distinct parts, one of them being a dark red jelly, the coagulum, or clot, which is heavy and sinks: and the other, a clear, straw-colored liquid, called serum, which covers the clot. This change is dependent upon the presence in the blood of fibrin, which possesses the property of solidifying under certain circumstances; one of these circumstances being when the blood is separated from living tissues. The color of the clot is due to the entanglement of the corpuscles with the fibrin. 10. In this law of the coagulation of the blood is our r safeguard against death by haemorrhage, or against undue loss of blood. If coagulation were impossible, the slight- 8, White corpuscles ? Total number of corpuscle? in the body ">. 9. The blood in its natural condition in the body ": Describe the process by which the coagulation of blood takes place; ? 10. If coagulation were impossible ? How is it iu fact ? THE CIRCULATION. 105 est injury in drawing blood would prove fatal. Whereas now, in vastly the larger proportion of cases, bleeding ceases spontaneously, because the blood, as it coagulates, stops the mouths of the injured blood-vessels. In another class of cases, where larger vessels are cut or torn, it is simply necessary to close them by a temporary pressure ; for in a few minutes the clot will form and seal them up. In still more serious cases, where the blood-vessel is of large size, the surgeon is obliged to tie a " ligature" about it, and thus prevent the force of the blood-current from washing away the clots, which, forming within and around the vessel, would close it effectually. K 11. It is worthy of remark that this peculiarity is early implanted in the blood, even before birth, and in advance of any existing necessity for it; thus anticipating and guarding against danger. But this is not all. Of most of the inferior animals, which, as compared with man, are quite helpless, the blood coagulates more rapidly, and in the case of the birds, almost instantly. The relative composition of fluid and coagulated blood may be thus ^resented: Fluid Blood. Coagulated Blood. Plasma,... Serum Serum --Fibrin---.... Corpuscles Corpuscles l':::-:-Clot. , 12. The Uses of the Blood. The blood is the great /provider and purifier of the body. It both carries new materials to all the tissues, and removes the worn out par- ticles of matter. This is effected by the plasma. It both conveys oxygen and removes carbonic acid. This is done through the corpuscles. Some singular experiments have 11. What is worthy of remark ? Coagulation of the blood of inferior animals f Of the blood of bird^ ? 12. The blood, as a provider and purifier? What uses does the blood sub- serve ? Experiments ? Transfusion ? 106 THE CIRCULATION. been tried to illustrate the life-giving power of the blood. An animal that has bled so freely as to be at the point of dying, is promptly brought back to life by an operation called transfusion, by which fresh blood from a living animal is injected into the blood-vessels of his body. ~ 13. It is related that a dog, deaf and feeble from age, f had hearing and activity restored to him by the introduc- tion into his veins of blood taken from a young dog ; and, that a horse, twenty-six years old, having received the blood of four lambs acquired new vigor. And further, that a dog, just dead from an acute disease, was so far revived by trans- fusion, as to be able to stand and make a few movements. 14. Transfusion has been practised upon man. At one T time, shortly after Harvey's discovery of the " Circulation of the Blood," it became quite a fashionable remedy, it being thought possible by it to cure all forms of disease, and even to make the old young again. But these claims were soon found extravagant, and many unhappy accidents occurred in its practice ; so that being forbidden by govern- ment and interdicted by the Pope, it rapidly fell into disuse. At the present time, however, it is sometimes re- sorted to in extreme cases, when there has been a great and rapid loss of blood ; and there are upon record several instances where, other means having failed, life has been restored or prolonged by the operation of transfusion. 15. This reviving power of the blood seems to reside in the corpuscles; for transfusion, when attempted to be per- formed with the serum alone, has, in every case, proved fruit- less. Now, though so much depends upon the blood and its corpuscles, it is a mistake to suppose that in them alone is the seat of life, or that they are, in an exclusive manner, alive. All the organs and parts of the body are mutually dependent one upon the other; and the complete usefulness 13. The case of the deaf and fei-bli 1 dog? Horse? Dead dog ? 14. Transfusion, as a fashionable remedy ? What further of transfusion ? 15. The seat of the reviving power of the blood ? What further is related ? THE CIRCULATION. !(/? of the blood, or of any other part, flows out of the har- monious action of all the parts. r 16. Change of Color. The blood undergoes a variety of changes in its journey through the system. As it visits the different organs it both gives out and takes up mate- rials. In one place it is enriched, in another it is impover- ished. By reason of these alterations in its composition, the blood also changes its color. In one part of the body it is bright red, or arterial ; in another it is dark blue, or venous. In the former case it is pure and fit for the sup- port of the tissues ; in the latter, it is impure and charged with effete materials. (The details of the change from dark to bright will be given in the chapter on Respira- tion.) (Read Note 2.) r 17. Circulation. The blood is in constant motion during life. From the heart, as a centre, a current is always setting toward the different organs; and from these organs a current is constantly returning to the heart. In this way a ceaseless circular movement is kept up, which is called the Circulation of the Blood. This stream of the vital fluid is confined to certain fixed channels, the blood- vessels. Those branching from the heart are the arteries; those converging to it are the veins. The true course of the blood was unknown before the beginning of the seven' teenth century. In 1619 it was discovered by the illustri- ous William Harvey. Like many other great discoverers, he suffered persecution and loss, but unlike some of them, he was fortunate enough to conquer and survive opposi- tion. He lived long enough to see his discovery universally accepted, and himself honored as a benefactor of mankind. 18. The Heart. The heart is the central engine of the circulation. In this wonderful little organ, hardly ' 16. Changes in the blood ? What further is slater! ? 17. Motion of the blood? What is meant by the circulation of the blood? How confined ? Discovery made by Harvey ? 18. Office of the heart ? Location of the heart ? Its beat? Its shape? Pro- tection to the heart ? What else is said in relation to the heart ? 108 THE CIRCULATION. . 27. THE ORGANS op CIRCULATION. THE CIRCULATION". 109 larger than a man's fist, resides that sleepless force by which, during the whole of life, the current of the blood is kept in motion. It is placed in the middle and front part of the chest, inclining to the left side. The heart- beat may be felt and heard between the fifth and sixth ribs, near the breast-bone. Theshapeofthehenrt is conical, with the apex or point down- ward and . in front. The base, which is upward, is attached so as to hold it se- curely in its place, while the apex is freely moveable. In order that loss of power from friction may be obviated, the heart is enclosed between two layers of serous membrane, which forms a kind of sac. This membrane is as smooth as satin, and itself secretes a fluid in sufficient quantities to keep it at all times well lubricated. The lining mem- brane of the heart, likewise, is extremely delicate and Smooth. (Read Note 3.) ' 19. The Cavities of the Heart. The heart is hol- low, and so partitioned as to contain four chambers or cavities; two at the base, known as the auricles, from a FIG. 28. THE HEART AND LARGE VESSELS. A, Right Ventricle. D, Left Auricle. B, Left C, Right Auricle. E, Aorta. F, Pulmonary Artery. 19. Formation of the heart ? Right and left heart ? TI1E CIRCULATION. 110 /fancied resemblance to the ear of a dog, and two at the apex or point, called ventricles. An auricle and a ventricle on the same side, communicate with each other, but there is no opening from side to side. It is customary to regard the heart as a double organ, and to speak of its division into the right and left heart. For while both halves act to- gether in point of time, each half sus- tains an entirely dis- tinct portion of the labor of the circu- lation. Thus, the right heart always carries the dark or venous blood, and the left always circulates the bright or arterial blood. 20. If we examine the heart, we at once notice that I though its various chambers have about the same capacity, the walls of the ventricles are thicker and stronger than those of the auricles. This is a wise provision, for it is by the powerful action of the former that the blood is forced to the most remote regions of the body. The auricles, on the contrary, need much less power, for they simply dis- charge their contents into the cavities of the heart near at hand and below them into the ventricles. FIG. 29. SECTION OP THE HEART. A, Right Ventricle. B, Left C, Right Auricle. D, Left Auricle. E, F, Inlets to the Ventricles. G, Pulmonary Artery. H, Aorta. 20. Capacity of the chambers of the heart? What wise provision is men- tioned ? The auricles ? THE CIRCULATION". Ill * 21. Action of the Heart. The substance of the heart is of a deep red color, and its fibres resemble those of the voluntary muscles by which we move our bodies. But the heart's movements are entirely involuntary. The advantage of this is evident; for if it depended upon us to will each movement, our entire attention would be thus engaged, and we would find no time for study, pleas- ure, or even sleep. The action of the heart consists in alternate contractions and dilatations. During contrac- tion the walls come forcibly together, and thus drive out the blood. In dilatation, they expand and receive a renewed supply. These movements are called systole and diastole. The latter may be called the heart's period of repose; and although it lasts only during two-fifths of a heart-beat, or about a third of a second, yet during the day it amounts to more than nine hours of total rest. ' 22. A remarkable property of tne tissue of the heart is its intense vitality. For while it is more constantly active than any other organ of the body, it is the last to part with its vital energy. This is especially interesting in view of the fact that after life is apparently extinguished, as from drowning, or poisoning by chloroform, there yet lingers a spark of vitality in the heart, which, by contin- ued effort, may be fanned into a flame so as to revivify the whole body. In cold-blooded animals this irritability of the heart is especially remarkable. The heart of a turtle will pulsate, and the blood circulate for a week after its head lias been cut off; and the heart will throb regularly many hours after being cut out from the creature's chest. The heart of a frog or serpent, separated entirely from the body, will contract at the end of ten or twelve hours: that of an alligator has been known to beat twenty-eight hours after the death of the animal. 21. Substance of the heart,? Its fibres? Its movements? The advantage of such movements? Action of the heart? It* period of ivpose ? 22. Remarkable property of the tissue of the heart ? How shown ? How in- teresting ? In cold-blooded animals ? Heart of a turtle ? Of a frog ? Alligator? 112 THE CIRCULATION. 23. Passage of the Blood through the Heart. Let us now trace the course of the blood through the several cavities of the heart. In the first place, the venous blood, rendered dark and impure by contact with the changing tissues of the body, returns to the right heart by the veins. It enters and fills the right auricle during its dilatation : the auricle then contracts and fills the right ventricle. Almost instantly, the ventricle contracts forcibly and hurries the blood along the great artery of the lungs, to be purified in those organs. Secondly, having completed the circuit of the lungs, the pure and bright arterial blood enters the left auricle. This now contracts and fills the left ventricle, which cavity, in its turn, contracts and sends the blood forth on its journey again through the system. This general direction from right to left is the uniform and un- deviating course of heart-currents. r 24. The mechanism which enforces and regulates it, is vis simple as it is beautiful. Each ventricle has two open- ings, an inlet and an outlet, each of which is guarded by strong curtains, or valves. These valves open freely to admit the blood entering from the right, but close inflex- ibly against its return. Thus, when the auricle contracts, the inlet valve opens ; but as soon as the ventricle begins to contract, it closes promptly. The contents are then, so to speak, cornered, and have but one avenue of escape, that through the outlet valve into the arteries beyond. As soon as the ventricle begins to dilate again, this valve shuts tightly and obstructs the passage. The closing of these valves occasions the two heart-sounds, which we hear at the front of the chest. f 25. Frequency of the Heart's Action. The alter- nation of contraction and dilation constitutes the heart- 23. Course of the blood through the heart ? Course of heart-currents ? 24. Openings of the ventricles ? How guarded ? How do the valves operate ? The consequence ? Heart-sounds ? 25. Heart-beats? The heart as a susceptible organ? Heat, exercise, etc,,? Posture f THE CIRCULATION. 113 beats. These follow each other not only with great regularity, but with great rapidity. The average number in an adult man is about seventy-two in a minute. But the heart is a susceptible organ, and many circumstances affect its rate of action. Heat, exercise, and food will increase its action, as cold, fasting, and sleep will decrease it. Posture, too, has a curious influence; for if while sit- ting, the beats of the heart number seventy-one; standing erect will increase them to eighty-one, and lying down will lower them to sixty-six. 26. The modifying influence of mental emotions is very powerful. Sudden excitement of feeling will cause the heart to palpitate, or throb violently. Depressing emotions sometimes temporarily interrupt its movements, and the person faints in consequence. Excessive joy, grief, or fear, lias occasionally suspended the heart's action entirely, and thus caused death. The rate of the heart-beat may be naturally above or below seventy-two. Thus it is stated that the pulse of the savage is always slower than that of the civilized man. Bonaparte and Wellington were very much alike in their heart's pulsations, which were less than fifty in the case of each. /S 27. Activity of the Heart. The average number of heart-beats during a lifetime may be considered as at the rate of seventy-two per minute, although this estimate is probably low ; for during several years of early life the rate is above one hundred a minute. In one hour, then, the heart pulsates four thousand times ; in a day, one hundred thousand times; and in a year, nearly thirty-eight million times. If we compute the number during a lifetime, thirty- nine years being the present average longevity of civilized mankind, we obtain as the vast aggregate, fourteen hun- dred millions of pulsations. (Read Note 5.) 26. Mental emotion?? . Sudden excitement? Excessive joy ? The heart-beat rate ? Bonaparte and Wellington ? 2*?. Average number of heart-bea:s? In one hour ? Year? Lifetime? 114 THE CIRCULATION. 28. Again, if we estimate the amount of blood expelled by each contraction of the ventricles, at four ounces, tnen the weight of the blood moved during one minute will amount to eighteen pounds. In a day it will be about twelve tons; in a year, four thousand tons; and in the course of a lifetime, over one hundred and fifty thousand tons. These large figures indicate, in some measure, the immense labor necessary to carry on the interior and vital operations of our bodies. In this connection, we call to mind the fanciful theories of the ancients in reference to the uses of the heart. They regarded it as the abode of the soul, and the source of the nobler emotions bravery, generosity, mercy, and love. The words courage and cordiality are derived from a Latin word signifying heart. Many other words and phrases, as hearty, heart-felt, to learn by heart, and large-hearted, show how tenaciously these ex- ploded opinions have fastened themselves upon our language. 29. At the present time the tendency is to ascribe purely mechanical functions to the heart. This view, like the older one, is inadequate; for it expresses only a small part of our knowledge of this organ. The heart is unlike a simple machine, because its motive power is not applied from without, but resides in its own substance. Moreover, it repairs its own waste, it lubricates its own action, and it modifies its movements according to the varying needs of the system. It is more than a mere force-pump, just as the stomach is something more than a crucible, and the eye something more than an optical instrument. * 30. The Arteries. The tube-like canals which carry the blood away from the heart are the arteries. Their walls are made of tough, fibrous materials, so that they sustain the mighty impulse of the heart, and are not rup- tured. In common with the heart, the arteries huve a del- 2S. Amount of blood expelled ? Theories of the ancient* ? 29. The tendency at, the present tim ; ? Whv is this view inadequate ? 3 What are the arteries? Their walU ? Their membrane ? THE CIRCULATION. 115 icately smooth lining membrane. They are also elastic, and thus re-enforce the action of the heart: they always remain open when cut across, and after death are usually found empty. /^ 31. The early anatomists observed this phenomenon, and supposing that the same condition existed during life, came to the conclusion that these tubes were designed to act as air-vessels, hence the name artery, from a Greek word which signifies containing air. This circumstance affords us an illustration of the confused notions of the ancients in reference to the internal operations of the body. Cicero speaks of the arteries as "conveying the breath to all parts of the body," 32. The arterial system springs from the heart by a single trunk, like a minute and hollow tree, with number- less branches. As these branches leave the heart they divide and subdivide, continually growing smaller and smaller, until they can no longer be traced with the naked eye. If, then, we continue the examination by the aid of a microscope, we see these small branches sending off still smaller ones, until all the organs of the body are penetrated by arteries. f 33. The Pulse. With each contraction of the left heart, the impulse causes a wave-like motion to traverse the entire arterial system. If the arteries were exposed to view, we might see successive undulations speeding from the heart to the smallest of the branches, in about one- sixth part of a second. The general course of the arteries is as far as possible from the surface. This arrangement is certainly wise, as it renders them less liable to injury, the wounding of an artery being especially dangerous. It also protects the arteries from external and unequal pres- sure, by which the force of the heart would be counter- 3 1 . Early anatomists ? The service of the illustration ? 32. The arterial system ? The branches and Rib-branches of the arteries ? 33. Successive undulations from the heart ? (' on n-e of the arteries? Protec tion of the arteri'.-s * General locution of !,h" ai-tciics 5* THE CIRCULATION. acted and wasted. Accordingly, we generally find these vessels hugging close to the bones, or hiding behind the muscles and within the cavities of the body. 34. In a few situations, however, the arteries lie near the surface ; and if we apply the finger to any of these parts, we will distinctly feel the movement described, taking place in harmony with the heart-beat. This is part of the wave- motion just mentioned, and is known as the pulse. All are more familiar with the pulse at the wrist, in the radial artery ; but the pulse is not peculiar to that position, for it may be felt in the carotid of the neck, in the temporal at the temple, and elsewhere, especially near the joints. 35. Since the heart-beat makes the pulse, whatevei aifects the former aifects the latter also. Accordingly, the pulse is a good index of the state of the health, so far aej the health depends upon the action of the heart. It in- forms the physician of the condition of the circulation in four particulars: its rate, regularity, force, and fullness; and nearly every disease modifies in some respect the con- dition of the pulse. A very ingenious instrument, known as the sphygmograph, or pulse-writer, has recently been invented, by the aid of which the pulse is made to write upon paper its own signature, or rather to sketch its own nrofile. This instrument shows with great accuracy the 30. THE FORM OF THE PULSE. difference between the pulses of health and those of disease. In Fig. 30 is traced the form of the pulse in health, which should be read from left to right. That part of the trace 3 1. Where do the arteries lie ? If we apply the finger ? Pulse ? Where felt ? 35. The: pulse as an index V Of what does it inform the physician ? Instrument tor recording pulsation ' THE CIRCULATION. 117 which is nearly perpendicular coincides with the contrac- tion of the ventricles; while the wavy portion marks their dilatation. A 36. The Veins. The vessels which convey the blood ' on its return to the heart are the veins. They begin in the several organs of the body, and at first are extremely small; but uniting together as they advance, they con- stantly increase in size, reminding us of the way in which the fine rootlets of the plant join together to form the large roots, or of the rills and rivulets that flow together to form the large streams and rivers. In structure, the veins resemble the arteries, but their walls are compara- tively inelastic. They are more numerous, and commu- nicate with each other freely in their course, by means of interlacing branches. ^ 37. But the chief point of distinction is in the presence of the valves in the veins. These are little folds of mem- brane, disposed in such a way, that they only open to receive blood flowing toward the heart, and close against a current in the opposite direction. Their position in the veins on the back of the hand may be readily observed, if we first ob- pra> 31 _ THE VALVBS op THE struct the return of blood by a cord VEINS. tied around the forearm or wrist. In a few minutes the veins will appear swollen, and upon them will be seen certain prominences, about an inch apart. These latter indicate the location of the valves, or, rather, they show that the vessels in front of the valves are distended by the blood, which cannot force a passage back through them. 38. This simple experiment proves that the true direction of the venous blood is toward the heart. That the color 36. What are the veinf ? How do they form ? What do they resemble ? 37. Valves in the veins? What are they? Their position ? Experiment with the cord ? 38. What will be proved by the experiment ? What inference is drawn ? 118 THE CIRCULATION. F of the blood is dark, will be evident, if we compare tLe hand thus bound by a cord with the hand not so bound It also proves that the veins lie superficially, while the arteries are beneath the muscles, well protected from pres- sure ; and that free communication exists from one vein to another. If now we test the temperature of the constricted member by means of a thermometer, we will find that it is colder than natural, although the amount of blood is* larger than usual. From this fact we infer, that whatever impedes the venous circulation tends to diminish vitality ; and hence, articles of clothing or constrained postures, that confine the body or limbs, and hinder the circulation of the blood, are to be avoided as injurious to the health. V 39. The Capillaries. A third set of vessels completes the list of the organs of the circulation, namely, the capil- lary vessels, so called (from the Latin word capillaris, hair-like), because of their extreme fineness. They are, however, smaller than any hair, having a diameter of about yjsVtf f an inch, and can only be observed by the use of the microscope. These vessels may be regarded as the connect- ing link between the last of the arteries and the first of the veins. The existence of these vessels was unknown to Harvey, and was the one step wanting to complete his great work. The capillaries were not discovered until 1661, a short time after the invention of the microscope. 40. The circulation of the blood, as seen under the microscope, in the transparent web of a frog's foot, is a spectacle of rare beauty, possessing more than ordinary interest, when we consider that something very similar is taking place in our own bodies, on a most magnificent scale. It is like opening a secret page in the history of our own frames. We there see distinctly the three classes of vessels with their moving contents ; first, the artery, 39. Capillaries? How regarded ? Harvey? 40. The circulation of the blood in the web of a frogV foot? Descrioe it How irc-neral 1^ tin- existence of the tissues ? THE CIRCULATION-. 119 with its torrent of blood rushing down from the heart, secondly, the vein, with its slow, steady stream flowing in the opposite direction; and between them lies the network of capillaries, so fine that the corpuscles can only pass through "in single file." The current has h^re an uncer- tain or swaying motion, hurrying first in one direction, then hesitating, and then turning back in the opposite direction, FIG. 32. WEB op A FROG'S FOOT, slightly magnified. FIG 33. MARGIN OF FROG'S W magnified 30 diameters. and sometimes the capillaries contract so as to be entirely empty. Certain of the tissues are destitute of capillaries ; such are cartilage, hair, and a few others on the exterior of the body. In all other structures, networks of these vessels are spread out in countless numbers : so abundant is the supply, that it is almost impossible to puncture any part with the point of a needle without lacerating tens, or even hundreds of these vessels. (Read Note 5.) 41. The capillaries are elastic, and may so expand as to produce an effect visible to the naked eye. If a grain of sand, or some other foreign particle, lodge in the eye, it will become irritated, and in a short time the white of the eye will be "blood-shot." This appearance is due to an in- 41.- Elasticity of the capillaries? Grain of sand in the eye! cases ? Blush ? Other THE CIRCULATION. crease in the size of these vessels. A blush is another exam- ple of this, but the excitement comes through the nervous system, and the cause is some transient emotion, either of pleasure or pain. Another example is sometimes seen in purplish faces of men addicted to drinking brandy ; in them the condition is a congestion of the capillary circula- tion, and is permanent, the vessels having lost their power of elastic contraction. 42. Rapidity of the Circulation. That the blood moves with great rapidity is evident from the almost instant effects of certain poisons, as prussic acid, which act through the blood. Experiments upon the horse, dog, and other inferior animals, have been made to measure its velocity. If a substance, which is capable of a distinct chemical reaction (as potassium ferrocyanide, or barium nitrate), be introduced into a vein of a horse on one side, and blood be taken from a distant vein on the other side, its presence may be detected at the end of twenty or thirty- two seconds. In man, the blood moves with greater speed, and the circuit is completed in twenty-four seconds. 43. What length of time is required for all the blood of the body to make a complete round of the circulation ? This question cannot be answered with absolute accuracy, since the amount of the blood is subject to continual variations. But, if we assume this to be one-eighth of the weight of the body, about eighteen pounds, it will be suf- ficiently correct for our purpose. Now to complete the circuit, this blood must pass once through the left ventricle, the capacity of which is two ounces. Accordingly, we find that, under ordinary circumstances, all the blood makes one complete rotation every two minutes; passing successively through the heart, the capillaries of the lungs, the arteries, the capillaries of the extremities, and through the veins. 42. Show what time is required for a given portion of blood to travel ouce ii'ounc] the body. 43* Time required for all the blood to circulate completely around? THE CIRCULATION. 121 44. Assimilation. The crowning act of the circula- tion, the furnishing of supplies to the different parts of the body, is effected by means of the capillaries. The or- gans have been wasted by use ; the blood has been enriched by the products of digestion. Here, within the meshes of the capillary network, the needy tissues and the needed nutriment are brought together. By some mysterious chemistry, each tissue selects and withdraws from the blood the materials it requires, and converts them into a substance like itself. This conversion of lifeless food into living tissue is called assimilation. The process probably takes place at all times, but the period especially favorable for it is during sleep. Then the circulation is slower, and more regular, and most of the functions are at rest. The body is then like some trusty ship, which after a long voy- age is " hauled up for repairs." 45. Injuries to the Blood-vessels. It is important to be able to discriminate between an artery and a vein, in the case of a wound, and if we remember the physiology of the circulation we may readily do so. For, as we have already seen, haemorrhage from an artery is much more dangerous than that from a vein. The latter tends to cease spontaneously after a short time. The arterial blood flows away from the heart with considerable force, in jets; its color being bright scarlet. The venous blood flows toward the heart from that side of the wound furthest from the heart; its stream being continuous and sluggish; its color dark. In an injury to an artery, pressure should be made between the heart and the wound; and in the case of a vein that persistently bleeds, it should be made upon the vessel beyond its point of injury. (Read Note 6.) 44. What is meant by assimilation ? What can you say of its use, etc. ? Tim-j * 45. What is stated of the injuries to the blood-vessels ? 122 REVIEW QUESTIONS. QUESTIONS FOR TOPICAL REVIEW. TAOB 1. In what organisms is the so-called circulatory fluid found ? 101 2. How is it designated in the different organisms ? 101 3. What can you state of the importance of blood to the body ? 101, 105 4. Of its great abundance, color, and composition ? 101, 102, 107 5. Describe the corpuscles of the human blood 102, 103, 104 6. What is said of them in comparison with those of the lower animals ? 103 7. Of the importance of sometimes detecting human from other blood ? 103 8. What means have we of detecting blood in spots or stains ? 103, 101 9. What is meant by coagulation of the blood ? 104 10. What wisdom is there in the law of the blood's coagulation ? 104 JOS 11. How is this wisdom made manifest ? 105 12. In what cases is the aid of the surgeon required ? 105 13. What are the two great uses of the blood ? 105 14. Through what mediums is the blood provided with new material and re- lieved of the old material ? 105 15. What do you understand by the operation called transfusion ?. . 106 16. What cases of transfusion are reported of the lower animals ? 106 17. What can you state of transfusion as practised upon man ? 106 18. What further can you say on the subject ? 106, 107 19. What change? take place in the color of the blood in its journey through the system ? 107 20. State all you can in relation to the circulation of the blood 107 21. All, in relation to the size, shape, and location of the heart 107, 109 22. How is the loss of power in the heart movements obviated ? 109 23. Give a description of the formation of the heart 109, 110, 111 24. What can you state of the ventricles and auricles of the heart ? 110 25. Describe the action of the heart Ill 26. What special vitality does the tissue of the heart possess ? Ill 27. State all you can on the subject Ill 28. Describe the course of the blood through the cavities of the heart 112 29. Describe the mechanism that regulates the heart-currents 112 30. How do you account for the two heart-sounds at the front of the chest ?. . . 112 31. State what you can of the frequency of the heart's action 112, 113 32. Of the activity of the heart 113,114 33. What do you understand by the arteries ? 114, 115 34. State what you can of the arteries and the arterial system 114, 115 35. What do you understand by the pulse ? 115, 116 36. In what part of the body may the pulse be felt ? 116 37. What further can you state of the pulse ? 1x6, 117 8S. What are the veins ? , 117 89. Where do they exist, and how are they formed ? 117 40. Describe the valves of the veins and their uses 117 41. Now give a full description of the construction of the veins 117 42. What further can you siate of the veins ? 117, 118 43. What do you understand by the capillaries ? 118, 119 M. What service do the capillaries perform ? 118, 119, 121 45. Describe the circulation of the blood in the region of the heart 118, 119 46. What can you state of the rapidity of the blood's circulation ? 1 :0 47. Of the process known as assimilation ? 121 48. Of injuries to the blood-vessels ? 121 NOTES. 1. The Blood (p. 104, 18). "You feel quite sure that blood is red, do yon not ? Well, it is no more red than the water of a stream would be if you were to fill it with little red fishes. Suppose the fishes to be very, very small, as small as a grain of sand, and closely crowded together through the whole depth of the stream, the water would look red, would it not ? And this is the way in which the blood looks red : only observe one thing; a grain of sand is a mountain in comparison with the little red bodies that float in the blood, which we have likened to little fishes. If I were to tell you they measured about the 3200th part of an inch in diameter, you would not be much the wiser; but if I tell you that m a single drop of blood, such as might haug on the point of a needle, there are a million of these bodies, you will perceive that they are both very minute and very numerous. Not that any one has ever counted them, as you may suppose, but this is as close an estimate as can be made in view of what is known of their minute size." M ace's History of a Mouthful of Bread. 2. By Means of the Blood Exercise Benefits the Whole Body (p. 107, ^ 16). "The employment of the muscles in exercise not only benefits their especial structure, but it acts on the whole system. When the muscles are put in action, the capillary blood-vessels with which they are sup- plied become more rapidly charged with blood, and active changes take place, not only in the muscles, but iu all the surrounding tissues. The heart is thus required to supply more blood, and accordingly beats more rapidly in order to supply the demand. A large quantity of blood is sent through the lungs, and larger supplies of oxygen are taken in and carried to the various tissues of the body." The oxygen engenders a large amount of heat, which produces an action on the skin whereby the increase of heat may be got rid of. By this means the skin is exorcised, the perspirati m is poured forth, the surf ice is caused to glow and is kept in health. " Not only are these organs benefited by the increased circulation of the blood, produced by exercise, but wherever the blood is sent, changes of a healthful character occur. The brain and the rest of the nervous system are invigorated ; the stomach has its powers of digestion improved ; and the liver, pancreas, and other organs perform their functions with more vigor." Lankester's Manual of Health. 3. A Poet's Summary of the Circulation (p. 109, f 18). " The smooth, soft air with pulse-like waves Flows murmuring through its hidden caves, Whose ptreams of brightning purple rush, Fired with a new and livelier blush ; While all their burden of decay The ebbing current steals away, And, red with Nature's flame, they start From the warm fountains of the heart. No rest that throbbing slave may ask, Forever quivering o'er his task, While far and wide a crimson jet Leaps forth to fill the woven net, Which, in unnumbered crossing tides, The flood of burning life divides : Then, kindling each decaying part, Creeps back to find the throbbing heart." Dr. 0. W. Holmes. 4. The Heart a Vital machine (p. 113, If 27). "The heart is a machine. It is an organ constructed of muscular chambers and communicating passages, and supplied with mechanical contrivances, adapted to guide the stream of blood NOTES. puling through it, and to prevent a reflux in ihe backward duvci.oii. i^uos not this take away wonderfully from the character of fanciful mystery with which poets and sentimentalists have invested it? The heart that we have always heard of as the centre of the affections, the home of sensibility, the dwelling-place of courage, of faith, of hope, and all the rest of the virtues, is, after all, nothing but an organ to serve for the impulsion of the blood ; a mere force-pump, a machine. Does not this bring down our ideas, and show that no poetical mys- tery can escape the searching investigation of the anatomist ? Not at ail. ' For this machine that we carry about with us in our breasts is alive. There, at its post, at the central point of the circulation, with the soft lobes of the lungs folded round it like a curtain, it contracts and relaxes and relaxes and contracts, with a steady and unremitting industry that by itself is something worthy of our admiration. No other muscle in the body can do this. By some incomprehensible vitality of its own, it keeps up its rhythmical contractions without the aid of our will and even without our knowledge. While you are asleep and while you are awake, from the first moment of your birth, even from before your birth, up to the present time, it has never for one moment stopped or flagged in its movements, ibr if it were to do so death would be the result." Dr. J. C. Dalton. 5. Course of the Blood in the Capillaries (p. 119, 1 40). The phenomena of the capillary circulation are only observable with the aid of the micro- scope. It was not granted to the discoverer of the circulation to see the blood moving through the capillaries, and he never knew the exact mode of communi- cation between the arteries and veins. After it was pretty generally acknowl- edged that the blood did pass from the arteries to the veins, it was disputed whether it passed in an intermediate system of vessels, or became diffused in the substance of the tissues, like a river flowing between numberless little islands, to be collected by the venous radicles and conveyed to the heart. Accurate micro- Bcopic investigations have now demonstrated the existence, and given us a clear idea of the anatomy of the intermediate vessels. In 1661 the celebrated anato- mist Malpighi first saw the movement of the blood in the capillaries, in the lungs of a frog. This spectacle has ever since been the delight of the physiolo- gist. We see the great arterial rivers, in which the blood flows with wonderful rapidity, branching and subdividing, until the blood is brought to the superb net- work of fine capillaries, where the corpuscles dart along one by one, the fluid then being collected by the veins, and carried in great currents to the heart." Flint. 6. The Varieties and Management of Haemorrhage (p. 121, T 45)." Uxmorrhage is the loss of blood either from an artery or a vein. When an artery is cut, the blood flows in jets corresponding to the beats of the heart and to the pulse. The jets mark that it is an artery that is wounded ; and indicate that the pressure must be applied above the haemorrhage, that is, betwixt it and the heart. On the other hand, the blood returns to the heart by the veins in a steady, continuous flow. When then the haemorrhage is steady and not in jets, it indi- cates that the bleeding is from a vein. Here the pressure must be applied to the limb away from the trunk, or the peripheral end of the limb, or below the bleed- ing. In addition to this, arerial blood is bright scarlet, while venous biood is dark and crimson. But these are matters of comparison, and the presence or absence of jets is the great point of distinction. " When then a person is wounded, a handkerchief must be bound as tightly as may be about the limb ; if the haemorrhage is arterial above the point of issue, if venous below it. Under any circumstances it is best to lay the person down quietly, especially if the bleeding is from the lower limbs. If they faint, let them alone in the horizontal posture." FoLkeryill on the Maintenance of Health. TABLE OF THE PRINCIPAL ARTERIES. (SEE FIG. OPPOSITE PAGE 101.) THE HEAD. Internal Ca-rot'id,) g ^ braln Verte-bral 9 > Oph-thal'mic, supplies tlie eye. 1Lin'gual 9 supplies the tongue. Fa'ci-al 9 " " lower part of face Tem'po-ral, " " upper part oi head and face. THE TRUNK. The A-or'ta^ arising from the heart, is the main arterial trunk Cor' o-na-ry 9 supplies the walls of the heart. Brorichi-al* " " lungs. In-ter-cos'tals 9 supply the walls of the chest. Gas'tric, supplies the stomach. He-pat' id " " liver. Spleriic, " " spleen. Re'nal, " " kidney. Mes-en-ter'ics 9 supply the bowels. Spi'nal 9 " " spinal cord. THE UPPER LIMB. Branches of the Ax-ilJa'ry, supply the shoulder. " Bra'c7ii-fil 9 " " arm. Ma'di-al, ) tt forearm and fi ngers " " Ulnar 9 ) THE LOWER LIMB. Branches of the Fem'o-ra1 9 supply the hip and thigh, " " Popliteal 9 \ " " " Tib'i-al 9 ! supply the leg and foot " Per-oneal ) RESPIRATION. 123 CHAPTER VIII. RESPIRATION. The Objects of Respiration The Lungs The Air-Passages The Move- ments of Respiration Expiration and Inspiration TJie Frequency of Respiration Capacity of the Lungs The Air we breathe Changes in the Air from Respiration Changes in the Blood In- terchange of Oases in the Lungs Comparison between Arterial and Venous Blood Respiratory Labor Impurities of the Air Dust Carbonic Acid Effects of Impure Air Nature's Provision for Purifying the Air Ventilation Animal Heat Spontaneous Com- bustion. 1. The Object of Respiration. In one set of capil- laries, or hair-like vessels, the blood is impoverished for the support of the different members and organs of the body. In another capillary system the blood is refreshed and again made fit to sustain life. The former belongs to the greater or systemic circulation ; the latter to the lesser or pulmo- nary, so called from pulmo, the lungs, in which organs it is situated. The blood, as sent from the right side of the heart to the lungs, is venous, dark, impure, and of a nature unfit to circulate again through the tissues. But, when the blood returns from the lungs to the left side of the heart, it has become arterial, bright, pure, and no longer hurtful to the tissues. This marvellous purifying change is effected by means of the very familiar act of respiration, or breathing. ^ 2. The Lungs. The lungs are the special organs of respiration. There are two of them, one on each side of the chest, which cavity they, with the heart, almost wholly occupy. The lung-substance is soft, elastic, and sponge- like. Under pressure of_the finger, it crepitates, or crackles, and floats when thrown into water ; these properties being 1 . Difference between the two sets of capillaries ? Change effected by respira- tion or breathing? 2. What are the lung?? How many lunge are there? Lung-substance? Its properties ? The pleura ? RESPIRATION". due to the presence of air in the minute air-cells of the lungs. To facilitate the movements necessary to these organs, each of them is provided with a double covering of an exceedingly smooth and delicate membrane, called the D FIG. 34. OKGAAS OF THE CHEST. A, Lungs. B, Heart. D, Pulmonary Artery. E, Trachea. pleura. One layer of the pleura is attached to the walls of the chest, and the other to the lungs; and they glide, one upon the other, with utmost freedom. Like the mem- brane which envelops the heart, the pleura secretes its own lubricating fluid, in quantities sufficient to keep it always moist. 3. The Air-Passages. The lungs communicate with the external air by means of certain air-tubes, the longest of 3. Communication of the lungs with the external air? Bronchial Uibes 9 RESPIRATION. 1*5 which, the trachea, or windpipe, runs along the front of the neck (Fig. 34, E, and 35) .With- ' in the chest this tube divides into two branches, one entering each lung; these in turn give rise to numerous branches, or bronchial tubes, as they are called, which gradually dimin- ish in size until they are about one- twenty-fifth of an inch. in diameter. Each of these ter- minates in a cluster of little pouches, or "air-cells," having very thin walls, and covered with a capillary network, the most intricate in the body (Fig. 36). 4. These tubes are some- what flexible, sufficiently so to bend when the parts move in which they are situated ; but they are greatly strengthened by bands or rings of cartilage which keep the passages always open; otherwise there would be a constantly-recurring ten- dency to collapse after every breath. The lung-substance essentially consists of these bronchial tubes and terminal air-cells, with the blood-ves- sels ramifying about them (Fig. 37). At the top of the trachea is the larynx, a sort of FIG. 35. LARYNX, TRACHEA, AND BRONCHIAL TUBES. FTS. 36. DIAGRAM AND SECTION OF THE AIR-CELLS. 4. Office of the bronchial tubes ? What further can you state of them ? 126 RESPIRATION". box of cartilage, across which are stretched the vocal cords. Here the voice is produced chiefly by the passage of the respired air over these cords, causing them to vibrate. FIG. 37. SECTION OP THE LUNGS. 5. Over the opening of the larynx is found the epiglottis, which fits like the lid of a box at the entrance to the lungs, and closes during the act of swallowing, so that food and drink shall pass backward to the oesophagus, or gullet (Fig. 38). Occasionally it does not close in time, and some substance intrudes within the larynx, when we at once discover, by a choking sensation, that "something has gone the wrong way," and, by coughing, we attempt to ex- pel the unwelcome intruder. The epiglottis is one of the many safeguards furnished by nature for our security and 5. The epiglottis ? When it does not clo^c in time, wh$t is the consequence? RESPIRATION. 12? comfort, and is planned and put in place long before these organs are brought into actual use in breathing and ? ventilation; and during those years the statistics showed that consumption was the cause of a very large proportion of deaths, j^t last the government began to improve the condition of the buildings, giving larger space and air- supply; and as a consequence, the mortality from con- sumption has diminished more than one-third. 37. The lower animals confined in the impure atmos- phere of menageries, contract the same diseases as man. Those brought from a tropical climate, and requiring arti- ficial warmth, generally die of consumption. In the Zoo- logical gardens of Paris, this disease affected nearly all monkeys, until care was taken to introduce fresh air by ventilation; and then it almost wholly disappeared. The tendency of certain occupations to shorten life is well known; disease being occasioned by the fumes and dust which arise from the material employed, in addition to the unhealthful condition of the workshop or factory where many hours are passed daily. (Read Note 4.) 38. The following table shows the comparative amount of carbonic acid in the air under different conditions and the effects sometimes produced: PROPOKTION OF CARBONIC ACID. in 1000 parts of Air. A.ir of country 4 " " city 5 In hospital, well ventilated 6 In school, church, etc., fairly ventilated 1.2 to 2.5 In court-house, factory, etc., without ventilation.. .. 4. to 40. In bedroom, before being aired 4.5 In bedroom, after being aired 1.5 Constantly breathed, causing ill health 2. Occasionally breathed, causing discomfort 3. Occasionally breathed, causing distress 10. Expired air 40. Air no longer yielding oxygen 100. 3 7. How, in the case of the lower animals ? Tendency of certain occupations ? 38. Give the fact as set forth in the table. RESPIKAT10N. 141 39. Nature's Provision for Purifying the Air. We have seen that carbonic acid is heavier than air, and is poisonous. Why, then, does it not sink upon and over- whelm mankind with a silent, invisible wave of death ? Among the gases there is a more potent force than gravity, which forever precludes such a tragedy. It is known as the diffusive power of gases. It acts according to a defi- nite law, and with a resistless energy compelling these gases, when in contact, to mingle until they are thor- oughly diffused. The added influence of the winds is useful, by insuring more rapid changes in the air; air in motion being perfectly wholesome. The rains also wash the air. 40. We have seen that the whole animal creation is con- stantly abstracting oxygen from the atmosphere, and as constantly adding to it vast volumes of a gas injurious alike to all, even in small quantities. How, then, does the air re- tain, unchanged, its life-giving properties ? The constant purity of the air is secured by means of the vegetable cre- ation. Carbonic acid is the food of the plants, and oxygen is its waste product. The leaves are its lungs, and under the stimulus of sunlight a vegetable respiration is set in motion, the effects of which are just the reverse of the function we have been considering. Thus nature purifies the air, and at the same time builds up beautiful and use- ful forms of life from elements of decay. (Read Note 5.) 41. In the sea, as in the air, the same circle of changes is observed. Marine animals consume oxygen and give off carbonic acid; while marine plants consume carbonic acid and liberate oxygen. Taking advantage of this fact, we may so arrange aquaria with fishes and sea-plants, in their proper combinations, so that each supplies the needs of the other, and the water requires seldom to be renewed. This 39. What can you state of the diffusive power of gases ? The added influence of the winds? 40. How is the constant purity of the air secured ? Explain the process ? 4 1 . What process occurs in the sea '( How is the fact illustrated 1 142 RESPIRATION. affords us, on a small scale, an illustration of the mutual dependence of the two great kingdoms of nature; as well as of those compensating changes which are taking place on such a grand scale in the world about us. / 42. Ventilation. Since the external atmosphere, as provided by nature, is always pure, and since the air in our dwellings and other buildings is almost always impure, it becomes imperative that there should be a free communica- tion from the one to the other. This we aim to accomplish by ventilation. As our houses are ordinarily constructed, the theory of ventilation, "to make the internal as pure as the external air," is seldom carried out. Doors, windows, and flues, the natural means of replenishing the air, are too often closed, almost hermetically, against the precious element. Special means, or special attention, must there- fore be used to secure even a fair supply of fresh air. This is still more true of those places of public resort, where many persons are crowded together. '\ 43. If there are two openings in a room, one as a vent for foul air, and the other an inlet for atmospheric air, and if the openings be large, in proportion to the number of air consumers, the principal object will be attained. Thus, a door and window, each opening into the outer air, will ordinarily ventilate a small apartment ; or a window alone will answer, if it be open both above and below, and the open space at each end be not less than one inch for each occupant of the room, when the window is about a yard wide. The direction of the current is generally from below upward, since the foul, heated air tends to rise; but this is not essential. Its rate need not be rapid ; a "draught," or perceptible current, is never necessary to good ventilation. The temperature of the air admitted may be warm or cold. It is thought by many that if the 42. Character of the external air? Of the air in onr dwellings ? What becomes imperative ? Imperfect ventilation of our dwellings? 43. What hints are given for the ventilation of our dwellings ? RESPIRATION. 143 air is cold, it is pure ; but this is an error, since cold air will receive and retain the same impurities as warm air. 44. Shall we open our bedrooms to the night air ? Flor- ence Nightingale says, in effect, that night air is the only air that we can then breathe. " The choice is between pure air without and impure air within. Most people prefer the latter, an unaccountable choice. An open window, most nights in the year, can hurt no one. In great cities, night air is the best and purest to be had in twenty-four hours. I could better understand, in towns, shutting the windows during the day than during the night." (Read Notes 6 and 7.) 45. Animal Heat. Intimately connected with respi- ration is the production of animal heat, or the power of maintaining the temperature of the body above that of the medium in which the creature moves; thus, the bird is warmer than the air, and the fish than the water. This elevation of temperature is a result of the various chemi- cal changes which are constantly taking place in the system. Although common to all animals, in a greater or less degree, heat is not peculiar to them ; since plants also gen- erate it, especially at the time of sprouting and flowering. If a thermometer be placed in a cluster of geranium flow- ers, it will indicate a temperature several degrees above that of the surrounding air. 46. Among animals great differences are noticed in this respect, but the degree of heat produced is always propor- tional to the activity of respiration and the amount of oxygen consumed. Accordingly, the birds, whose habits are extremely active, and whose breathing capacity is the greatest, have uniformly the highest temperature. Slug- gish animals, on the contrary, as frogs, lizards, and snakes, have little need for oxygen, and have incompletely de- 44. State what Florence Nightingale says about inhaling night air? 45. Warmth of the bird as compared with that of the air? Of the fish and the water ? Heat in animals and plants ? How illustrated with the thermometer ? 46. Amount of heat in animals, how apportioned ? As regards the birds? Frogs, and other sluggish animals ? Arrangement made by zoohgsts ? 144 RESPIRATION. veloped lungs ; these animals are cold to the touch, that is, they have relatively a lower temperature than man, and their positive temperature is but little above that of the external air. Accordingly, zoologists have so arranged the animal kingdom that warm-blooded animals, including man, the birds, and the quadrupeds, are classified together; while the cold-blooded animals, such as the fish, tortoise, frog, and all tnat have no vertebral column, are classed by themselves. 47. The temperature of the human body is about 100 Fahrenheit, and remains about the same through winter and summer, in the tropics as well as in the frozen regions of the north. It may change temporarily within the range of about twelve degrees; but any considerable, or long-con- tinued elevation or diminution of the bodily heat is certain to result disastrously. 48. Man is able to adapt himself to all extremes of climate; and, in fact, by means of clothing, shelter, and food, is able to create for himself an artificial climate where- ever he choses to reside. The power to resist cold consists chiefly in preventing the heat which is generated by the vital processes of the body from being lost by radiation. Warm clothing, such as we wear in winter, has, in reality, the same temperature as that which is worn in summer; but, by reason of being thick and porous, it is a bad con- ductor of heat, and thus prevents the escape of that produced by the body. If woollen fabrics were intrinsically warm, no one would wrap a piece of flannel, or blanket, around a block of ice to prevent its melting in summer. 49. The faculty of generating heat explains how it is that we are enabled to resist the effects of cold; but how does the body withstand a temperature higher than its 47. State what is said respecting the temperature of the human body. 48 - Ability of man to adapt himself to different climate;* ? In what does the power to resist cold consist ? What is said about warm clothing? 49. Men in an atmosphere above the boiling-point ? In foundries and glass. works ? RESPIRATION. 145 own ? Men have been known to remain several minutes in an atmosphere heated above the boiling-point of water, and yet the temperature of their own bodies was not greatly ele- vated. Those who labor in foundries and glass-works are habitually subjected to very high degrees of temperature, but they do not suffer in health more than those engaged in many other occupations. 50. The regulation of the temperature of the body is effected by means of perspiration, and by its evaporation. So long as the skin acts freely and the air freely absorbs the moisture, the heat of the body does not increase, for whenever evaporation takes place, it is attended by the abstraction of heat that is, the part becomes relatively colder. This may be tested by moistening some part of the surface with cologne, ether, or other volatile liquid, and then causing it to evaporate rapidly by fanning. The principle that evaporation produces cold has been in- geniously and practically employed, in the manufacture of ice, by means of freezing machines. (Read Note 8.) 51. Spontaneous Combustion. Is it possible that the temperature of the living body can be so increased, that its tissues will burn spontaneously ? From time to time, cases have been reported in which, by some mysteri- ous means, considerable portions of the human body have been consumed, apparently by fire, the victim being found dead, or inqapable of explaining the occurrence. Hence, the theory has been current that, under certain condi- tions, the tissues of the body might become self-ignited ; and the fact that this so-called spontaneous combustion has ordinarily taken place in those who had been addicted to the use of alcoholic drinks, has given a color of proba- bility to the opinion. It has been supposed that the flesh of these unfortunate persons becoming saturated with the inflammable properties of the alcohol thus taken into the 50. The regulation of the temperature of the body. Give the explanation. 51, 52. State what is said of spontaneous combustion. 146 RESPIRATION. system, took fire upon being exposed to a flame, as of & lighted candle, or, indeed, without any external cause. But, whether this be possible or not, one thing is certain, this strange kind of combustion has never been actually wit- nessed by any one competent to give a satisfactory account of it. 52. The results that have been observed may be satis- factorily explained by the accidental ignition of the clothes, or other articles near the body, and by the supposition that the individual was at the time too much stupefied by intoxication, to notice the source of danger, and provide for his safety. The highest temperature that has been observed in the body, about 112 Fahrenheit, is too low to ignite the vapor of alcohol; much less will it cause the burning of animal tissues. It is undoubtedly true that when the tissues are filled with alcohol, combus- tion will more easily take place than when the body is in a normal state ; but, under any condition, the combustion of the body requires a higher degree of heat than can be generated by the body itself, or the mere proximity of a lighted candle, or any cause of a similar character. HEVIEW QUESTIONS. 147 QUESTIONS FOR TOPICAL REVIEW. PAGE 1. What is the object of respiration? 123 2. What are the special organs of respiration ? 123 3. In what organs do :s a change in the blood take place ? 123 4. What is the nature of the change ? 123, 133 5. Where are the lungs situated, and what is the character of the sub- stance of which they are composed ? 123, 125 6. Describe the facilities provided for the lung movements 124 7. Describe the trachea, or windpipe 124, 125, 127, 128 8. Describe the bronchial tubes, and their uses 125, 126 9. What can you state in relation to the epiglottis 9 126, 127 10. What are the cilia and what use do they probably serve? 128 11. How may the lungs be affected by not being properly protected ? 128 12. Describe the movements necessary to the act of perfect respiration. . . 128, 123 13. What is the diaphragm, and what is its office? 128, 129 14. How may the organs of respiration be so improved as to increase their capacity and power ? 129, 37 15. What is stated in relation to the frequency of respiration ? 129, 130 16. To what extent may the act of respiration be subjected to our wills ? 130 17. What may be said to be the capacity of the lungs ? 130, 131 18. How long does it take every particle of air in the lungs to be expelled and new air to take its place ? 130 19. What would be the consequences, if the entire capacity of the lungs were constantly used ? 130, 131 20. What would be the consequences to a fish put into water from which the air had been completely exhausted ? Why ? 13J 21. What is the air, and what are its parts ? 131, 136, 138 22. What is the character of the air that has been just breathed ? 132 23. Why is it that such air is not fit for respiration ? 132, 139 24. What are the effects, as recorded in notable cases, of confinement in places the air of which has been breathed kt over and over ?" 133 25. What can you state of changes in the blood from respiration ? 133 26. What of the air, as an article of food ? 133, 134 27. What, on the subject of interchange of gases in the lungs ? 134 28. Explain the difference between arterial and venous blood 134, 135 29. Explain, if you can, the cause of the difference 135 30. State what you can in relation to blue blood 135 31. In relation to the amount of labor exerted in respiration 135, 156 32. In relation to the deleterious properties of different gases 136, 137 33. In relation to the dust that floats in the air 137, 138 34. What are the properties of carbonic acid gas ? 132, 138, 141 35. In what places is carbonic acid gas commonly found ? 132, 138, 139 36. Describe the effects of carbonic acid gas 132, 128, 139, 141 37. What are the general effects of breathing any impure atmosphere ? 139, 140 38. What are Nature's provisions for purifying the air ? 141, 142 39. What hints and directions are given on the subject of ventilation ?. . . . 142, 143 40. How does the temperature of the body compare with the medium in which it lives ? 143 41. How is temperature of the body regulated and sustained ? 148, 144, 145 4-7. State what you can on the subject of spontaneous combu.-Uoa 145. 146 NOTES. 1. The Atmosphere (p. 131, 1 13). "It surrounds us on all sides, yet wo see it iiot ; it presses on us with a load of fifteen pounds to every square inch of surface of our bodies, or from seventy to one hundred tons on us in all, yet we do not so much as feel its weight. Softer than the softest down more impalpable than the finest gossamer it leaves the cobweb undisturbed, and scarcely stirs the lightest flower that feeds on the dew it supplies ; yet it bear? the fleets of nations on its wings around the world, and crushes the most refractory substances beneath its weight. When in motion, its force is sufficient to level the most stately forests with the earth ; to raise the waters of the ocean into ridges like mountains, and dash the strongest ships to pieces like toys. It bends the rays of the sun from their path, to give us the twilight of evening and of dawn ; it disperses and refracts their various tints, to beautify the approach and retreat of the orb of day. But for the atmosphere, sunshine would burst on us and fail us at once, and at once remove us from midnight darkness to the blaze of noon. We should have no twilight to soften and beautify the landscape, no clouds to shade us from the scorching heat ; but the bald earth, as it revolved on its axis, would turn its tanned and weakened front to the full and unmitigated rays of the lord of day." Buith. 2. The Two Breaths (p. 132, 1 17)." Every time you breathe, you breathe two different breaths : you take in one, you give out another. The composition of those two breaths is different. Their effects are different. The breath which has been breathed out must not be breathed in again. To te'l you why it must not would load me into anatomical details, not quite in place here as yet ; but this I may say : those who habitually take in fresh breath will probably grow up large strong, ruddy, cheerful, active, clear-headed, fit for their work. Those who habitu- ally take in the breath which has been breathed out by themselves, or any other living creature, will certainly grow up, if they grow up at all, small, weak, pale, nervous, depressed, unfit for work, and tempted continually to resort to stimu- lants, and become drunkards. "If you want to see how different the breath breathed out is from the breath taken in, you have only to try a somewhat cruel experiment, but one which, peo- ple too often try upon themselves, their children, and their work-people. If you take any small animal with lungs like your own a mouse for instance and force it to breathe no air but what you have breathed already ; if you put it in a closo box, and, while you take in breath from the outer air, send out your breath through a tube into that box, the animal will soon faint; if you go on long with this process, he will die. * * * * What becomes of this breath which passes from your lips ^ Is it merely harmful, merely waste ? God forbid I God has forbidden that anything should be merely harmful or merely waste in this so wise and well- made world. The carbonic acid which passes from your lips at every breath is a precious boon to thousands of things of which you have daily need. For though you must riot breath your breath atrain, you may at least eat your breath, if you will allow the sun to transmute it for you into vegetables ; or you may enjoy its fragrance and its color in the shape of a lily or a rose. When you walk in a sunlit garden, every word you speafc, every breath you breathe, is feeding the plants and flowers around." Rev. Charles Kinqsley on the Two Breaths. 3. The Ground- Atmosphere audits Relations to Dwellings (p. 139, 1 35). "The soil, which naturally contains wholesome air, and gives facility to its every movement, is not less permeable by poisonous gases, which are often found to pervade and issue from it. It is easy to find illustrations of the fact that people are poisoned through the ground, since it is almost a daily NOTES. occurrence. Here is one, related by an eminent authority, von Pettenkofer: ' In a residence at Augsburg, apparently endued with every qualification for health and comfort, several priests lived together. On a certain morning one of these, not the least zealous and prompt in the performance of his duties, was missed from his usual post at thematiu service. His colleagues hurried back to their common dwelling in search of the missing priest, and found him lying prostrate and insensible upon the floor of his bed-chamber. A doctor was immediately culled in, and at the first sight of his patient, declared him to be suffering from an attack of typhus fever. The Sisters of Charity, upon whom devolved the duty of nursing him, and those clerical associates who were active in their sympathy and prompt to visit him and give assistance, were, a few hours after, attacked in the same way. The doctor did not hesitate in his diagnosis, and pronounced the additional cases also typhus fever. A general alarm prevailed in the city, and many called at the house of the priest, wiio was greatly beloved. Among others, was an old woman, who discovered a strong smell of gas, and believing this to bo the cause of the sickness, obtained permission to remove the priest to her own house. The priest had no sooner breathed the fresh air than he began to revive, and during the very first evening of his removal to the new abode he became so much beiter as to make an importunate demand for food. He soon got entirely well. The old woman, thus confirmed in her gas theory, and eager to save the remain- ing patients, who had continued to increase in number in the priests' house, now had an interview with the manasrer of the gas-works which supplied the town, aud prevailed upon him to investigate the condition of the gas-pipes in the vicinity of the priest's residence. This wns done, and a leak from which the gas was escaping into the ground was found and stopped. The air of the house was perceived at once to improve, and with it the health of the patients that were not removed ; these finally completely recovered from what the doctor even was com- pelled to admit was not typhus fever, but poisoning by gas. 111 The Book of Health. 4. Consumption Is Lung Starvation (p. 140, T 37). "The practiceof allowing the lungs only improper food, in the form of vitiated air, is one of the most prevalent habits of civilized life, and diseases of the lungs are its greatest bane and greatest dread. More persons die by consumption than by any other single disease. If there be added to those the large number that, perish every year by inflammation of the lungs and bronchial tubes, disease and premature death may be well said to have in these organs their chief citadel. The leading cause of all this is, undoubtedly, the poor quality of the food on which the lungs are nurtured. The very best physicians, when their attention is directed to the subject, admit the full force of this conclusion, and that it has not received the attention it deserves. Professor Hartshorne remarks on this point, that 'the influence of impure air in promoting consumption has probably heretofore been underrated.' 'The vitiated air of the European barrack system for soldiers,' s-iys Professor Parkes, ' is the only way in which the great prevalence of con- sumption in European armies can be accounted for.' This is the conclusion to which the Sanitary Commissioners for the army came, in their celebrated report : ' A great amount of phthi-is (consumption) has prevailed in the most varied stations ot the army and in the most beautiful climates in Gibraltar, Malta, Ionia. Jamaica, Trinidad, Bermuda, etc. in all of which places the only common condition was the vitiated atmosphere which our barrack system everywhere pro- duced. And, as if to clinch the argument, there has been of late years a most decided decline in phthisis in these stations, while the only circumstance which NOTES. has notably changed in the time has been the condition of the air.' A very. emi- nent authority, the late Dr. Marshall Hall, of England, said, in reference to pure air in the treatment of consumption, ' If I were seriously ill of consumption, I would live out doors day and night, except in rainy weather, or midwinter ; then I would sleep in an unplastered log house. Physic has no nutriment, gaspings for air cannot, cure you, monkey capers in a gymnasium cannot cure you, and stimu- lants cannot cure you. What consumptives want is pure air, not physic pure air, not medicated air plenty of meat and bread.' Let it be remembered, in this connection, that every hygienic or health-promoting measure which tends to cure a disease is much more efficacious in preventing it." Black's Ten Laws of Health. 5. Plants and the Air (p. 141, 1 40). "Though the air is dependent for the renewal of its oxygen on the action of the green leaves of plants, it must not be forgotten that it is only in the presence and under the stimulus of light that these organisms decompo-e carbonic acid. All plants, irrespective of their kind or nature, absorb oxygen and exhale carbonic acid in the dark. The quantity of noxious gas thus eleminated is, however, exceedingly small when compared with the oxygen thrown out during the day. Aside from the highly deleterious action that plants may exert on the atmosphere of a sleeping room, by increasinsr the proportion of carbonic acid during the night, there is another and more important objection to be urged against their presence i"a such apartments. Like animals, they exhale peculiar volatile organic principles, which in many instances render the air unfit for the purposes of respiration. Even in the days of Andronicus this fact was recognized, for he says, in epeaking of Arabia Felix, that ' by reason of myrrh, frankincense, and hot spices there growing, the air was so obnoxious to thjir brains, that the very inhabitants at some times cannot avoid its influence. 1 What the influence on the brains of the inhabitants may have been does not at present interest us : we have only quoted the statement to show that long ago the emanations from plant? were regarded as having an influence on the condition of the air ; and, in view of our present ignorance, it would be wise to banish them from our sleeping apartments, at least until we are better informed regarding their true properties." draper on Poisoned Air. 6. Pure Air in our Homes during Cold Weather (p. 143, 1 44). " Fresh air is the great natural disinfectant, antiseptic, and purifier, and not to be compared for a moment with any of artificial contrivance. There is plenty of it in the world ; yet, disguise the fact as we may, there is no getting over the unwelcome truth, that to provide in abundance in our climate is expensive, since during seven months in the year it must be artificially Maimed, in cider that our homes may be comfortable. To take in air at the average winter tem- perature of 28, raise it to 68, and discharge it again from our houses even once in an hour, is a process which cannot be accomplished without paying roundly; yet on no other condition can we reasonably expect health and long life. The best way is to freely admit that it is expensive, but worth the money it costs. If Benjamin Franklin thought that ' a penny saved is a penny earned,' he is equally sure that 'health is wealth.' "George Derby on the Prevention of Disease. 7. Pure Air and Good Morals (p. 139, If 35) " Cleanliness and self- respect go together, and it is no paradox to affirm that you tend to purify men's thoughts and feelings when you purify the air they breathe. * * * * With a low average of popular health you will have a low average of national morality, and probably also of national intellect. Drunkenness and vice of other kinds will flourish in such a soil, and you cannot get healthy brains to grow on unhealthy bodies.' 1 - Lord Derby.. NOTES. 8. Animal Heat (p. 145, ^ 50). " Infants produce much less heat during their early days than during any later period of their life ; their temperature falls very easily, therefore, and the influence of cold is especially hurtful to them. For this reason, and because those who have care of them do not know the facts, young children die from exposure in much larger numbers during the winter than any other season of the year. * * * * But how is it that warm-blooded animals can preserve their own proper heat when they are placed in an air that is hotter than their bodies ? A man, for example, can remain for a certain time in an oven where the air is raised to a temperature nearly equal to that of boiling water, without a marked increase of the heat of the body; it rises a few degrees only." Exposures of this kind cannot be long continued, on account, as it is supposed, of an expansion of the blood. A case is on record of a person remaining ten minutes in a dry hot-air bath, at 284, or seventy-two degrees above the boiling point of water; and Chabert, the so-called "Fire-King," went into ovens heated from 400 to 000 degrees, but, of course, for a much shorter period. Sun heat is often fatal, even in the temperate zone, but still more frequently in the tropics, amongst troops on the march and amongst coolies working on plantations or on public works. In Pekin during about ten days in July, 1743, the thermometer stood at the extreme height of 104 in the shade, and, in that period, 11,400 people died. Habit accustoms the Chinese, negroes, and others to bear a greater heat than the natives of temperate climates can support. " The faculty of resisting heat depends upon the evaporation of water which takes place continually from the skin and lungs, and which constitutes the 'cutaneous and pulmonary transpiration;' for water, as it changes into vapor, carries off the caloric of whatever surrounds it, and thus the body is cooled in proportion as the external heat warms it. It is on thisprinciple that water placed in certain porous vessels called 'alcarazas,' becomes cool so promptly, even in midsummer. These vases permit the water contained in them to leak out through numerous pores, so that their surface is constantly moist; by a rapid evaporation of this moisture, the liquid within is made cool." Milne- Edwards on " Zoologie." 9. Cleanliness the Sum Total of Hygiene (p. 137, t 29). Disinfect- ants have the power of destroying tlie cause and of arresting the spr< ad of most epi- demics and contagious diseases, but cleanliness is the best preventive of disease. Whenever practicable, the abundant use of water is better than disinfection. "Let no one ever depend upon disinfectants, fumigations, and the like, for puri- fying the air. The offensive thing, not its smell, must be removed. Florence Nightingale, Notes on Nursing (in pent.) 10. The True Prevention of Epidemics (p. 137, 1 29).-" It was in England that solution of the great problem of hygiene was first attempted : 'Preventive Medicine,' it is there called. Palmerston told a deputation which waited on him in order to ask him to order a fast on the approach of the second epidemic of cholera, to cleanse their sewers and diligently visit the dwellings of the poor. And he did not confine himself to good advice, but, with his usual energy, he laid his hand on sanitary legislation, and purified the air of London, and the large manufacturing towns. The result of the sanitary measures carried out was a reduction of ihe mortality of London from 26 to 23 per 1,000, and in some of the towns to 17 per 1,000 a low death-rate previously only equalled in the Isle of Wight. More than four thousand lives have been preserved yearly in London ; and, assuming that the mortality among the sick is 1 in 20, this number represents a diminution in yearly sickness to the extent of eighty thousand. '*- Dr. Joseph Seegen in the Vienna Medical Weekly. 148 THE NERVOUS SYSTEM. CHAPTER IX. THE NERVOUS SYSTEM. Animal and Vegetative Functions Sensation, Motion, and Volition The Structure of the Nervous System The White and Gray Sub- stances The Brain Its Convolutions The Cerebellum The Spi- nal Cord and its System of Nerves The Anterior and Posterior Roots Tlie Sympathetic System of Nerves The Properties of Nerv- ous Tissue Excitability of Nervous Tissues TJie Functions of the Spinal Nerves and Cord The Direction of the Fibres of the Cord Reflex Activity, and its Uses The Functions of the Medulla Oblon- gata and the Cranial Ganglia The Reflex Action of tlie Brain. 1. Animal Functions. The vital processes which we have been considering, in the three previous chapters, of digestion, circulation, and respiration belong to the class of functions known as vegetative functions. That is, they are common to vegetables as well as animals; for the plant, like the animal, can originate nothing, not even the smallest particle of matter; and yet it grows, blossoms, and bears fruit, by reason of obtaining and digesting the nutriment which the air and soil provide. The plant has its circulatory fluid and channels, by which the nutriment is distributed to all its parts. It has, also, a curious ap- paratus in its foliage, by which it abstracts from the air those gaseous elements so necessary to its support; and thus it accomplishes vegetable respiration. These vege- tative functions have their beginning and end within the organism of the plant; and their object is the preservation of the plant itself, as well as of the entire species. 2. The animal, in addition to these vegetative functions, has another set of powers, by the use of which he becomes conscious of a world external to himself, and brings him- 1. What processes are known as the vegetative functions? Why so called? What properties and functions does the plant possess ? Their object ? 2. What second set of powers has the animal ? What functions are mentioned ? The advantage they give ? : THE NERVOUS SYSTEM. 149 St- If into active relations with it. By means of the vege- tative processes, his life and species are maintained; while, by means of certain animal functions, he feels, acts, and thinks. These functions, among which are sensation, motion, and volition, not only distinguish the animal from the plant, but, in proportion to their development, elevate oiitf creature above another; and it is' by virtue of his pre- eminent endowment, in these respects, that man holds his position at the head of the animal creation. 3. Among animals whose structure is very simple, the hydra, or fresh-water polyp, being an example, no special organs are empowered to perform separate functions ; but every part is endowed alike, so that if the animal be cut into pieces, each portion has all the properties of the entire original; and, if the circumstances be favorable, each of the pieces will soon become a complete hydra. As we ap- proach man, in the scale of beings, we find that the organs multiply, and the functions become more complete. The function of motion, the instruments of which the muscles and bones have been considered in former chapters, and all the other animal functions of man, depend upon the set of organs known as the nervous system. 4. The Nervous System. The intimate structure of this system differs from any tissue which we have be- fore examined. It is composed of a soft, pulpy substance, which, early in life, is almost fluid, but which gradually hardens with the growth of the body. When examined under the microscope, it is found to be composed of two distinct elements : (1) the white substance, composing the larger proportion of the nervous organs of the body, which is formed of delicate cylindrical filaments, about 6o * 00 of an inch in diameter, termed the nerve-fibres ; and (2) the gray substance, composed of grayish-red, or ashen- 3. Animals whose structure is simple? As we approach man? Dependence of the animal functions of man ? 4. The nervous tissues, of what composed ? When examined by the aid of the microscope ? The white substance ? The gray substance ? - 150 THE NERVOUS SYSTEM, colored cells, of various sizes, generally possessing one or more off-shoots, which are continuous with the nerve- fibres just mentioned. 5. The gray, cellular substance constitutes the larger portion of those important masses, which bear the name of nervous centres and ganglia (from ganglion, a knot), and in which all the nerve-fibres unite. These white nerve- fibres are found combined together in long and dense cords, called nerves (from neuron, a cord), which serve to connect the nervous centres with each other, and to place them in communication with all the other parts of the body which have sensibility or power of motion. That part of the nervous system which is concerned in the ani- mal functions, comprises the brain, the spinal cord, and the nerves which are derived therefrom; these are, together, called the cerebro- spinal system (Fig. 40) ; while that other set of organs, which presides over, and regulates the vege- tative functions, is called the sympathetic system of nerves. 6. The Brain. The brain is the great volume of nerv- ous tissue that is lodged within the skull. It is the largest and most complex of the nervous centres, its weight, in the adult, being about fifty ounces, or one-fortieth of that of the whole body. The shape of the brain is oval, or egg- shaped, with one extremity larger than the other, which is placed posteriorly in the skull, to the concavity of which it very closely conforms. The brain consists chiefly of two parts; the cerebrum, or brain proper, and the cerebellum, or "little brain." In addition to these, there are several smaller organs at the base, among which is the commence- ment or expansion of the spinal cord, termed the medulla oblongata, or oblong marrow. 7. The tissue of the brain is soft and easily altered in 5. Nervous centres and ganglia? Nerves? What do they serve? Cerebro- epinal system ? 6. Location of the brain ? Its weight? Its shape ? Of what, it consists ? What organs at the base ? 7. The tissue of the brain ? What, therefore, is required ? Blows on the head ? Hcmbranes of the brain ? Blood sent to the brain ? THE NERVOUS SYSTEM. 151 FIQ. 40. THE CEREBKO-SPINAL SYSTEM. 152 THE NEBYOUS SYSTEM. shape by pressure; it therefore requires to be placed in a well-protected position, such as is afforded by the skull, or cranium, which is strong without being cumbrous. In the course of an ordinary lifetime, this bony box sustains many blows, with little inconvenience; while, if they fell directly upon the brain, they would at once, and com- pletely, disorganize that structure. < Within the skull, the brain is enveloped by certain memlSranes, which at once protect it from friction, and furnish it with a supply of nutrient vessels; they are called the arachnoid, or "spider's web," the dura mater and the pia mater, or the "tough" and "delicate coverings." The supply of blood sent to the brain is very liberal, amounting to one-fifth of all that the entire body possesses. The' brain of man is heavier than that of any other animal, except the ele- phant and whale. 8. The Cerebrum. The brain proper, or cerebrum, is J the largest of the intracranial organs, and occupies the en- tire upper and front portion of the skull. It is almost com- pletely bisected, by a fissure, or cleft, running through it lengthwise, into two equal parts called hemispheres. The exterior of these hemispheres is gray in color, consisting chiefly of nerve-cells, arranged so as to form a layer of gray matter one-fifth of an inch in thickness, and is abundantly supplied with blood-vessels. The interior of the brain, however, is composed almost wholly of white substance, or nerve-fibres. 9. The surface of the cerebrum is divided by a consid- erable number of tortuous and irregular furrows, about an inch deep/ into "convolutions," as shown in Fig. 41. Into these furrows the gray matter of the surface is ex- tended, and, in this manner, its quantity is vastly in- creased. The extent of the entire surface of the brain, 8. Size of the brain proper? How divided? The exterior of the hemispheres ? The interior ? 9. The surface of the cerebrum, how marked ? The gray matter of the surface ? Extent of the entire brain surface ? Source of nervous power ? What further ? THE NERVOUS SYSTEM. 153 with the convolutions unfolded, is computed to be equal to four square feet ; and yet it is easily enclosed within the narrow limits of the skull. When it is stated that the gray matter is the true source of nervous power, it becomes evident that this arrangement has an important bearing on the mental ca- pacity of the indi- vidual. And it is noticed that in children, before the mind is brought into vigorous use, these markings or furrows on the sur- face are compara- tively shallow and indistinct; the same fact is true of the brain in the less civilized races of mankind and in the lower animals. It is also noticeable, that among animals, those are the most capable of being educated which have the best develop- ment of the cerebrum. (Read Note i.) 10. The Cerebellum. The "little brain" is placed beneath the posterior part of the cerebrum, and, like the latter, is divided into hemispheres. Like it, also, the sur- face of the cerebellum is composed of gray matter, and its interior is chiefly white matter. It has, however, no con- volutions, but is subdivided by many crescentic, parallel ridges, which, sending down gray matter deeply into the FIG. 41. UPPER SURFACE OP THE CEREBRUM. A, Longitudinal Fissure. B, The Hemispheres. 10. Location of tho "little brain ?" How divided ? Its surface and interior 1 Jts subdivisions ? Its size ? 154 THE NERVOUS SYSTEM. white, central portion, gives the latter a somewhat branched appearance. This peculiar appearance has been called FIG. 42. VERTICAL SECTION OF THE BUAIN. A, Left Hemisphere of Cerebrvfta. D, The Pone Varolii. B, Corpus Callosum. E, Upper extremity of the Spinal Cord. C, Optic Thalamus. F, The Arbor Vitae. the arbor vitce, or the "tree of life," from the fact that when a section of the organ is made, it bears some resem- blance to the trunk and branches of a tree (Fig. 42, F). In size, this cerebellum, or "little brain," is less than one- eighth of the cerebrum. /\ 11. From the under surface of the cerebrum, and from the front margin of the cerebellum, fibres collect together fo form the medulla oHongaia (Fig. 43, MA), which, on is- suing from the skull, enters the spinal column, and then becomes known as the spinal cord. From the base of the brain, and from the sides of the medulla originate, also, the cranial nerves, of which there are twelve pairs. These nerves are round cords of glistening white appearance, and, 11. Medulla oblcngata Crauid- uervee? Tiieir sioaoe and oition f THE NERVOUS SYSTEM. 155 like the arteries, generally lie remote from the surface of the body, and are well protected from injury. FIG. 43. THE BASE OF THE BRAIN. 12. The Spinal Cord. The 'spinal cord, or " marrow," is a cylindrical mass of soft nervous tissue, which occupies a chamber, or tunnel, fashioned for it in the spinal column (Fig. 44). It is composed of the same substances as the brain ; but the arrangement is exactly reversed, the white matter encompassing or surrounding the gray matter in- stead of being encompassed by it. The amount of the white substance is also greatly in excess of the other ma- terial. A vertical fissure partly separates the cord into two lateral halves, and each half is composed of two sep- arate bundles of fibres, which are named the anterior and posterior columns. 13. These columns have entirely different uses, and each 1 2. The spinal cord ? Of what composed ? How divided ? Each half? 13. Uses of these columns? Importance of this part of the nervous system? How protected ? 156 THE NERVOUS SYSTEM. PIG. 44. A, Cerebrum. B, Cerebellum. D, D, Spinal Cord. of them unites with a different portion of the nerves which have their origin in the spinal cord. The importance of this part of the nervous system is apparent from the extreme care taken to protect it from external injury. For, while a very slight disturb- ance of its structure suffices to disarm it of its power, yet so staunch is its bony enclosure, that only by very severe injuries is it put in peril. The three membranes that cover the brain are continued downward so as to envelope and still further shield this delicate organism. 14. The Spinal Nerves. The spinal nerves, thirty -one pairs in number, spring from each side of the cord by two roofs, an anterior and a poste- rior root, which have the same functions as the columns bear- ing similar names. The poste- rior root is distinguished by pos- sessing a ganglion of gray mat- ter, and by a somewhat larger size. The successive points of departure, or the off-shooting of these nerves, occur at short and nearly regular intervals along the course of the spinal cord. Soon after leaving these points, 14. The spinal nerves ? The posterior root? The nerves, uuw arranged? Their office ? THE NERVOUS SYSTEM. 157 the anterior and posterior roots unite to form the trunk of a nerve, whioh is distributed, by means of branches, to the various organs of that part of the body which this nerve is designed to serve. The spinal nerves supply chiefly the muscles of the trunk and limbs and the ex- ternal surface of the body. 15. The tissue composing the nerves is entirely of the white variety, or, in other words, the nerve-fibres; the same as we have observed forming a part of the brain. But the nerves, instead of being soft and pulpy, as in the case of the brain, are dense in structure, being hardened and strengthened by means of a fibrous tissue which sur- rounds each of these delicate fibres, and binds them to- gether in glistening, silvery bundles. Delicate and mi- nutely fine as are these nerve-fibres, it is probable that each of them pursues an unbroken, isolated course, from its origin, in the brain or elsewhere, to that particular point which it is intended to serve. For, although their extrem- ities are often only a hair's breadth distant from each other, the impression which any one of them communicates is perfectly distinct, and is referred to the exact point whence it came. 16. This may be illustrated in a simple manner, thus: if two fingers be pressed closely together, and the point of a pin be carried lightly across from one to the other, the eyes may be closed, and yet we can easily note the precise instant when the pin passes from one finger to the other. If the nerve-fibres were less independent, and if it were necessary that they should blend with and support each other, all accuracy of perception would be lost, and all information thus afforded would be pointless and confused. These sil- very threads must, therefore, be spun out with an infinite degree of nicety. Imagine, for instance, the fibre which 1 5. The nerve tissue ? Its character? Course of each nerve fibre ? 16. How may we illustrate the fact? The fibre connecting the brain with a point in the foot ? 158 THE NERVOUS SYSTEM. connects the brain with some point on the foot, its length cannot be less than one hundred thousand times greatox than its diameter ; and yet it performs its work with as much precision as fibres that are comparatively much Stronger and less exposed. (Read Note 7, end of Chapter.} A IT. The Sympathetic System. The sympathetic 'system of nerves remains to be described. It consists of a double chain of ganglia, situated on each side of the spinal column, and extending through the cavities of the trunk, and along the neck into the head. These ganglia are made up for the most part of small collections of gray nerve-cells, and are the nerve-centres of this system. From these, numerous small nerves are derived, which connect the ganglia together, send out branches to the cranial and spinal nerves, and form networks in the vicin- ity of the stomach and other large organs. A considerable portion of them also follows the distribution of the large and small blood-vessels, in which the muscular tunic ap- pears. Branches also ascend into the head, and supply the muscles of the eye and ear, and other organs of sense. 18. In this manner, the various regions of the body are associated with each other by a nervous apparatus, which is only indirectly connected with the brain and spinal cord; and thus it is arranged that the most widely sep- arated organs of the body are brought into close and active sympathy with each other, so that, "if one member suffers, all the other members suffer with it." From this fact, the name sympathetic system, or the great sympathetic verve, has been given to the complicated apparatus we have "briefly described. Blushing and pallor are caused by men- tal emotions, as modesty and fear, which produce opposite conditions of the capillaries of the face by means of these Sympathetic nerves. (Read Note 8, end of Chapter.} \ 7. The sympathetic system of nerves ? Of what does it consist ? 18. Association of the various regions of the body ? If one member suffers ? Rlnshinsr ? THE NERVOUS SYSTEM. 159 19. The Properties of Nervous Tissue. We have seen that in all parts of this system, there are only two forms of nervous tissue ; namely, the gray substance and the white substance, so called from their difference of color as seen by the naked eye; or the nerve-cell, and the nerve- fibre, so called from their microscopic appearance. Now these two tissues are not commonly mingled together, but either form separate organs, or distinct parts of the same organs. This leads us to the conclusion that their respec- tive uses are distinct. And this proves to be the simple fact ; wherever we find the gray su bstance, we must look upon it as performing an active part in the system, that is, it originates nervous impulses ; the white matter, on the contrary, is a passive agent, and serves merely as a con- ductor of nervous influences. Accordingly, the nervous centres, composed so largely of the gray cells, are the great centres of power, and the white fibres are simply the in- struments by which the former communicate with the near and distant regions of the body under their control. 20. We may compare the brain, then, to the capital, or seat of government, while the various ganglia, including the gray matter of the cord, like so many subordinate official posts, are invested with authority over the outly- ing provinces ; and the nerves, with the white matter of the cord, are the highways over which messages go and return between these provinces and the local or central governments. But both forms of nervous tissue possess the same vital property, called excitability ; by which term is meant, that when a nerve-cell or fibre is stimulated by some external agent, it is capable of receiving an impres- sion and of being by it excited into activity. A ray of light, for example, falling upon one extremity of a fibre in the eye, excites it throughout its whole length ; and its 1 9. Properties of nervous tissue ? Office of the gray substance ? Of the white ? the nervous centres ? White fibres ? 20. What comparison is made between the brain and the nation's capitol ? The vital property, excitability ? What example is given? 160 THE NERVOUS SYSTEM. other extremity, within the brain, communicating with a nerve-cell, the latter, in its turn, is excited, and the sensa- tion of sight is produced. (Read Note 2.) 21. What sort of change takes place in the nervous tissue when its excitability is aroused, is not known ; certainly none is visible. On this account, it has been thought by some, that the nerve-fibre acts after the man- ner of a telegraph wire : that is, it transmits its messages without undergoing any material change of form. But, though the comparison is a convenient one, it is far from being strictly applicable ; and the notion that nerve-force is identical with electricity has been fully proved to be incorrect. * 22. The Functions of the Nerves. The nerves are the instruments of the two grand functions of the nervous system, Sensation and Motion. They are not the true centres of either function, but they are the conductors of influences which occasion both. If the nerve in a limb of a living animal be laid bare, and irritated by pinching, galvanizing, or the like, two results follow, namely: the animal experiences a sensation, that of pain, in the part to which the nerve is distributed, and the limb is thrown into convulsive action. When a nerve in a human body is cut by accident, or destroyed by disease, the part in which it ramifies loses both sensation and power of motion ; or, in other words, it is paralyzed. We accordingly say that the nerves have a twofold use, a sensory and motor function. 23. If a nerve that has been exposed be divided, and the inner end, or that still in connection with the nerve-cen- tres, be irritated, sensation is produced, but no movement takes place. But if the outer end, or that still connected with the limb, be irritated, then no pain is felt, but mus- 21 . Change in the nervous tissues V Nerve force and electricity ? 22. Function* of the nerves ? In the case of the nerve of a living animal ? Of the human body ? 23. If an exposed nerve be divided ? What is proved? The course of the sensory fti-t of fibres ? Of the motor s a? To what are they likened 't THE NERVOUS SYSTEM. 1G1 cular contractions are produced. Thus we prove that there are two distinct sets of fibres in the nerves ; one of which, the sensory fibres, conduct toward the brain, and another, the motor fibres, conduct to the muscles. The former may be said to begin in the skin and other organs, and end in the brain ; while the latter begin in the nervous centres and end in the muscles. They are like a double line of telegraph wires, one for inquiries, the other for responses. 24. We have already spoken 01 the two roots of the spinal nerves, called from their points of origin in the spinal cord, the anterior and posterior roots. These have been separately cut and irritated in the living animal, and it has been found that the posterior root contains only sensory fibres, and the anterior root has only motor fibres. So that the nerves of a limb may be injured in such a way that it will retain power of motion and yet lose sensation ; or the reverse condition, feeling without motion, may exist. Be- tween these two sorts of fibres, no difference of structure can be found; and where they have joined to form a nerve it is impossible to distinguish one sort from the other. 25. Occasionally a nerve is so compressed as to be tem- porarily unable to perform its functions: a transient par- alysis then takes place. This is the case when the leg or arm "gets asleep," as it is expressed. When such is the condition with the leg, and the person suddenly attempts to walk, he is liable to fall, inasmuch as the motor fibres cannot convey orders to the muscles of the limb. Another fact is observed : there is no sensation in this nerve at the point of its compression ; but the whole limb is numb, and tingling sensations are felt in the foot, the point from which the sensory fibres arise. 26. This illustrates the manner in which the brain in- 24. The two roots of the spinal nerves ? What ha? been found ? Difference of the two sorts of fibres ? Result of their union * 25. Transient paralysis? When such is the case with the leg? What other fact is observed ? 26. What does this illustrate ? Sensation ? The feeling after a limb has been amputated ? Striking of the " funny bone ?" 162 THE NERVOUS SYSTEM. terprets all injuries of the trunk of a nerve. Sensation or pain is not felt at the point of injury, but is referred to the outer extremities of the nerve, where impressions are habit- ually received. This is the reason why, after a limb has been amputated by the surgeon, the patient appears to suffer pain in the member that has been severed from the body; while some form of irritation at the end of the nerve in the wound, or stump, is the real source of his distress. Again, when the "funny-bone" that is, the ulnar nerve at the elbow, is accidentally struck, the tingling sensa- tions thus produced are referred to the outer side of the hand and the little finger, the parts to which that nerve is distributed. 27. All the spinal nerves, and two from the brain, are concerned in both sensation and motion. Of the remainder of the cranial nerves, some are exclusively motor, others exclusively sensory; and still others convey, not ordinary sensations, but special impressions, such as sight, hearing, and smell, which we have yet to consider. However much the functions of the nerves seem to vary, there is but little difference discoverable in the nerves themselves, when ex- amined under the microscope. Whatever difference exists must be accounted for in consequence of the nerves com- municating with different portions of the gray matter of the brain. The rate of motion of a message, to or from the brain along a nerve, has been measured by experi- ment upon the lower animals, and estimated in the case of man at about two hundred feet per second. As compared with that of electricity, this is a very slow rate, but, in respect to the size of the human body, it is practically in- stantaneous. (Read Note 3.) 28. The Functions of the Spinal Cord. As the 27. The spinal nerves, and two from the brain ? Of the remainder? Difference in the nerves ? How accounted for ? The rate of conduction along a nerve ? As compared with electricity? 28. Functions of the'anterior and posterior columns of the cord ? If the cord be divided? THE NERVOUS SYSTEM. 163 anterior and posterior roots of the spinal nerves have sepa- rate functions, so the anterior and posterior columns of the cord are distinct in function. The former are con- cerned in the production of motion, the latter in sensation. If the cord be divided, as before in the case of the nerve, it is found that the parts below the point of injury are de- prived of sensation and of the power of voluntary motion on both sides of the body, a form of paralysis which is called paraplegia. 29. This form of disease, paraplegia, is sometimes seen among men, generally as the result of a fall, or some other severe accident, by which the bones of the spine are broken, and the cord is crushed, or pierced by fragments of bone. The parts which are supplied by nerves from the cord above the point of injury are as sensitive and mobile as before. The results are similar, whether the division hap- pens at a higher or lower portion of the spinal cord ; but the danger to life increases proportionally as the injury approaches the brain. When it occurs in the neck, the muscles of inspiration are paralyzed, .since they are sup- plied by nerves issuing from that region ; and as a result of this paralysis, the lungs are unable to act, and life is speedily brought to a close. 30. When the spinal cord of an animal has been cut, in experiment, it may be irritated in a manner similar to that alluded to when considering the nerves. If, then, the upper cut surface be excited, it is found that pain, refer- able to the parts below the cut, is produced ; but when the lower cut surface is irritated, no feeling is manifested. So we conclude that in respect to sensation, the spinal cord is not its true centre, but that it is merely a conductor, and is therefore the great sensory nerve of the body. When the lower surface of the cut is irritated, the muscles of the 20. Paraplegia? Result and danger to life? When the injury occurs in the neck ? 3O. Experiment of cutting the spinal cord ot an animal ? What inference is dra ,vn ? 164 THE NERVOUS SYSTEM. parts below the section are violently contracted. Hence, we conclude that, in respect to the movements ordered by the will, the spinal cord is not their source ; but that it acts only as a conductor, and is, accordingly, the great motor nerve of the body. 31. Direction of the Fibres of the Cord. If one lateral half of the spinal cord be cut, or injured, a very sin- gular iact is observed. All voluntary power over the mus- cles of the corresponding half of the body is lost, but the sensibility of that side remains undiminished. This result seems to show that the motor fibres of the cord pursue a direct course, while its sensory fibres are bent from their course. And this has been proved to be the fact; for im- mediately after the posterior roots the conductors of sen- sory impressions join the posterior columns, they enter the gray matter of the cord, and passing over, ascend to the brain on the opposite side. Accordingly, the sensory fibres from the right and left sides interlace each other in the gray matter; this arrangement has been termed the decus- sation, or crossing of these fibres. This condition serves to explain how a disease or injury of the cord may cause a paralysis of motion in one leg, and a loss of sensation in the other. 32. The direction of the anterior, or motor columns of the cord, is downward from the brain. In the cord itself, the course of the motor fibres is for the most part, a direct one; but in the medulla oblongata, or upper extremity of the cord, and therefore early in their career, these fibres decussate, or cross from side to side in a mass; and riot separately, as in the case of the posterior fibres just men- tioned. This arrangement is termed the decussation of the anterior columns of the medulla. 33. From this double interlacing of fibres results a 3 1 . What singular fact is noticed ? What does the result show ? 32. Direction of the anterior or motor columns? In the cord itself? In the medulla oblongata ? The decussation ? 33. Result of the double interlacing of fibres? Where is the seat of paiu THE NERVOUS SYSTEM. crossed action between the original and terminal extremity of all nerve-fibres which pass through the medulla ; namely, those of all the spinal nerves. Consequently, if the right hand be hurt, the left side of the brain feels the pain ; and if the left foot move, it is the right hemisphere which dictates its movement. For the same reason, when a loss of sensation and power of motion affecting the right side of the body alone is observed, the physiologist under- stands that the brain has been invaded by disease upon its left side. This affection is termed Jiemiplegia y or the " half- stroke." The full-stroke, which often follows the rupture of a blood-vessel in the brain, is commonly called paralysis. 34. The Reflex Action of the Cord. We have already considered the cord as the great motor and sensory nerve of the body, but it has another and extremely impor- tant use. By virtue of the gray matter, which occupies its central portion, it plays the part of an independent nerve centre. The spinal cord not only conducts some impressions to the brain, but it also arrests others; and, as it is expressed, " reflects" them into movements by its own power. This mode of nervous activity is denominated the Reflex Action of the cord. 35. A familiar example of this power of the cord is found in the violent movements which agitate a fowl after its head has been cut off. The cold-blooded animals also exhibit reflex movements in an astonishing degree. A decapitated centipede will run rapidly forward, and will seemingly strive to overturn, or else climb over obstacles placed in its way. A frog similarly mutilated will sustain its headless body upon its feet, in the standing posture, just as it might do if it were still alive. If pushed over, it will regain its feet; and if the feet are irritated, it will when the right hand is hurt ? The moving of the foot ? Loss of sensation it, one side of the body ? 34. What other important use has the cord? What is the activity denomi aated ? 3 5 . Example of the fowl ? Centipede ? Prog ? What dc they prove ? ICG THE NERVOUS SYSTEM. jump forward. There can be no doubt that, in the lower animals, movements may take place which are completely divorced from the will, sensation, and consciousness; for in those animals, as well as in man, these faculties have their principal seat within the brain. 36. An irritation is necessary, in most instances, to awaken reflex movements. In the case of the decapitated fowl, its muscles are excited to convulsive action by reason of its being thrown upon the hard ground and roughly handled. Let it be treated differently, and the convulsions will not take place : let it be laid gently upon soft cotton, and the body will remain comparatively quiet. It may comfort some people to know that the convulsions which follow decapitation are not attended with pain ; nor are they a necessary part of the " act of death," as some suppose. 37. In the human body, likewise, actions are excited that are entirely distinct from the ordinary voluntary efforts. It is not permissible, desirable, nor even necessary to decapitate a man that the body may be disconnected from his brain, in order to test the effect of irritation upon the spinal cord; although the bodies of beheaded crimi- nals have been experimented upon, and caused to move by powerful galvanic batteries. The resort to such means of experiment is rendered unnecessary by the occurrence of certain deplorable cases of disease and injury, which effect- ually sever all communication between the brain and a large part ot the body. 38. Thus, the cord may be so far injured, as the result of accident, as to terminate all sensation and voluntary motion in the lower half of the body, the patient seem- ingly becoming lifeless and powerless from the waist down- ward. And yet, by tickling or pinching either foot, the leg 36. What is necessary in most cases to awaken reflex movements? In the Case of the fowl ? Convulsion!* which follow decapitation ? 37. Actions in the human body distinct from voluntary effort* ? 38. Reflex action after injury of the cord? Why not due to the muscles t THE KEKVOUS SYSTEM. 167 of the same side may be made to jerk, or even to kick with considerable force; but, unless the patient is observing his limbs, he is wholly unconscious of these movements, which are, therefore, performed independently of the brain. And they are in nowise due to the muscles of the limb; for, if the cord itself becomes diseased below the point of in- jury, the muscles cease to contract. 39. For the production of this form of nervous action* three things are requisite (1) a nerve to conduct messa- ges from the surface of the body, one of that variety for- merly described as sensory, but which are now incapable of awakening sensation ; (2) a portion of uninjured spinal cord which shall reflect or convert impressions into im- pulses; and (3) a motor nerve to conduct impulses outward to the muscles. The power of the cord to enforce reflex acts resides in the gray matter, into which the reflex nerves enter and from which they depart, by means of their pos- terior and anterior roots respectively. 40. The Uses of the Reflex Action. The reflex activity of the cord is exhibited in the healthy body in many ways, but since it is never accompanied with sensa- tion, we do not readily recognize it in our own bodies. Eeflex movements are best studied in the cases of other persons, when the conditions enable us to distinguish between acts that are consciously, and those that are un- consciously performed. For example, if the foot of a per- son soundly asleep be tickled or pinched, it will be quickly withdrawn from the irritation. 41. Similar movements may be observed in cases where the consciousness and sensation are temporarily obliter- ated by disease, or by means of narcotic poisons. If the arm of a person who has been rendered insensible by 39. What arc the requisites for the production of this form of nervous action? 40. Whv do we not readily recotjnize the reflex activity of the cord in our own bodies ? How best studied in others ? Example ? 4 1 . Similar movements ? Arm of a oerson ? Melted wax or heated coin on the hand? 168 THE NERVOUS SYSTEM. chloroform, be raised, and then allowed to fall, it will be noticed that the limb does not drop instantly, like a life- less member, but a certain amount of rigidity remains in its muscles, which resists or breaks the force of its descent. Again, when a substance like melted sealing-wax, or a heated coin, falls upon the hand, the limb is snatched away at once, even before the feeling of pain has been recognized by the brain. When jolted in a rapidly moving car, we involuntarily step forward or backward, so as to preserve the centre of gravity of the body. 42. These and similar acts are executed by the same mechanism as that previously described in the case of paralysis from an injury of the spinal cord. The muscles thus called into play, are those which are ordinarily under the sway of the will, but which in these cases act through this reflex action of the cord, altogether independently of the will. A healthful reflex activity produces an elasticity, or " tone," of the voluntary muscular system, which, in a great measure, explains the existence in the young and vigorous of a feeling of buoyancy and reserve power. Its possessor is restlessly active, and it may appropriately be said of him, " he rejoiceth as a strong man to run a race." But this reflex energy may be deficient. This is true when the blood is poor and wanting in its solid ingredients, or the circulation is feeble ; the muscles, then, are flabby and weak, and the person himself is said to be " nerveless," or indisposed to exertion. Shivering from cold, and trem- bling from fear, may, in part, be referred to a temporary loss of tone, resulting from a powerful impression upon the brain, (Read Note 9, end of Chapter) 43. An excess of this activity may also be observed in disease. In this condition, the excitability of the cord is unnaturally aroused, and frequent and violent movements 41. Result of healthful reflex activity ? When may the reflex energy he defi- cient ? 43. Excess of this activity 'n disease ? Hydrophobia, etc, ? The difference IE severity of the convulsions " THE NERVOUS SYSTEM. 169 of the limbs and body, called convulsions, are the result. The convulsions of young children, and the nervous agita- tion of chorea, or St. Vitus's dance, are reilex in character ; as are also the symptoms attending poisoning by strychnine, and those terrible diseases, tetanus, or " locked jaw," and hydrophobia. The severity of the convulsions is not the same in all cases of these disorders ; but, in those last men- tioned the most violent spasmodic movements are provoked by the slightest form of irritation such as the sound of pouring water, the sight of any glittering object, the glanc- ing of a mirror, the contact of cool air, or even the touch of the bedclothes. 44. Another variety of reflex motions takes place in cer- tain involuntary muscles, and over these the cord exercises supreme control. They are principally those movements which aid the performance of digestion and nutrition, the valve-action of the pylorus, and other movements of the stomach and intestines. In these movements the mind shares no part. And it is well that this is so ; for since the mind is largely occupied with affairs external to the body, it acts irregularly, becomes fatigued, and needs fre- quent rest. The spinal cord, on the contrary, is well fitted for the form of work on which depends the growth and support of the body, as it acts uniformly, and with a ma- chine-like regularity. 45. These operations are not accompanied by conscious- ness; for, as a general rule, the attention is only called to them when they become disordered. Many a person does not know where his stomach is situated, until he discovers 'its position by reason of a feeling of distress within it, produced by giving that organ improper work to perform. In this manner the higher and nobler faculties of the mind are liberated from the simply routine duties of the 44. Another variety of reflex motions ? What are they? What is stated of the mind in connection with these movement? ? 45. Consciousness in these operations? Physical wants ? 170 THE NERVOUS SYSTEM. body; and we are thus left to direct the attention, the rea- son, and the will to the accomplishment of the great ends of our existence. If it were otherwise, we could only find time to attend to our ordinary physical wants. 46. The objects of the reflex activity of the cord are threefold. In the first place, it acts as the protector of man, in his unconscious moments. It is his unseen guardian, always ready to act, never growing weary, and never re- quiring sleep. Nor does its faithful action wholly cease with the cessation of life in other parts. In the second place, it is the regulator of numerous involuntary motions that are necessary to the nutrition of the body. Here its actions are entirely independent of the brain, and are per- formed in a secret and automatic manner. And. thirdly, it acts as a substitute, and regulates involuntary movements in the muscles usually under the influence of the will. It thus takes the place of the higher faculties in performing habitual acts, and permits them to extend their operations more and more beyond the body and its material wants. A 47. The Functions of the Medulla Oblongata. The prolongation of the spinal cord, within the skull, has been previously spoken of as the medulla oblongata. It resembles the cord, in being composed of both white and gray matter, and in conducting sensory and motor in- fluences. It likewise gives rise to certain nerves, which are here called cranial nerves (from cranium, the skull). All except two of these important nerves spring from the me- dulla, or the parts immediately adjoining it ; the exceptions are the two nerves taking part in the special senses of sight and smell, which nerves have their origin at the base of the cerebrum. 48. The decussation, or crossing of the motor columns, has been previously described, when treating of the direc- 46. How many objects may the reflex activity be said to have ? State the first The second. The third. 47. How does the medulla oblongata resemble the cord ? 48. What final fact ia observed in the crowing of the motor columns ? THE NERVOUS SYSTEM. 171 tion of the nerve-fibres of the cord; and the singular fact has been alluded to, that when one side of the brain is injured, its effects are limited to the opposite side of the body. One more fact remains to be observed in this con- nection, namely, this crossed action does not usually take place in the cranial nerves. Accordingly, when apoplexy, or the rupture of a blood-vessel, occurs in the right hemi- sphere of the cerebrum, the left side of the body is paralyzed, but the right side of the face is affected ; this is because that part of the body is supplied by the cranial nerves. 49. A portion of the medulla presides over the impor- tant function of respiration, and from it arises the pneu- mogastric nerve, so called because its branches serve both the lungs and stomach. The feelings of hunger, thirst, and the desire for air are aroused by means of this nerve. The wounding of the gray matter of the medulla, even of a small portion of it, near the origin of the pneumogastric nerve, at once stops the action of the lungs and causes death. In consequence of the importance of this part, it has been termed the "vital knot." We find, also, that its location within the skull is exceedingly well protected, it being quite beyond the reach of any ordinary form of harm from without. 50. The Functions of the Cranial Ganglia. The uses of the smaller gray masses lying at the basv. of the brain are not well ascertained ; and, on account of their position, so remote from the surface, it would, at first, seem well-nigh impossible to study them. But, from the results following diseases in these parts, and from experiments upon inferior animals, they are becoming gradually better understood; and there is reason to believe that eventually the physiological office of each part will be clearly ascer- tained and defined. It is believed, however, but not abso- 49. The pneumogastric nerve ? The feelings aroused by it ? The '" vital knot?" 50. The uses of the smaller gray masses at the base of the brain ? 172 THE NERVOUS SYSTEM. iutely proven, that the anterior masses, like the anterior roots of the spinal nerves and the anterior columns of the cord, are concerned in the production of motion; in fact, that they are the central organs of that function. The posterior gray masses are, on the contrary, supposed to be the seat of sensation. 51. The Function of the Cerebellum. The func- tion of the cerebellum, or " little brain,' 7 is the direction of the movements of the voluntary muscles. When this organ is the seat of disease or injury, it is usually observed that the person is unable to execute orderly and regular acts, but moves in a confused manner as if in a state of intoxication. Like the larger brain, or cerebrum, it appears to be devoid of feeling; but it takes no part in the operations of the mind. i 52. The Function of the Cerebrum. The cere- brum, or brain proper, is the seat of the mind; or, speak- ing more exactly, it is the material instrument by which the mind acts; and, as it occupies the highest position in the body, so it fulfils the loftiest uses. All the other organs are subordinate to it: the senses are its messengers, which bring it information from the outer world, and the organs of motion are its servants, which execute its com- mands. Here, as in the nervous apparatus of lower grade already considered, the gray matter is the element of power; and, in proportion as this substance increases in extent, and in proportion to the number of convolutions in the hemispheres, do the mental faculties expand. * 53. There have been a few, but only a few, men of dis- tinguished ability whose brains have been comparatively small in size ; the rule being that great men possess large brains. The relative weight of the brain of man, as com- 5 1 . Function of the cerebellum ? When it is diseased ? 52. Where i? the seat of the mind? The subordination of the other orgcins . The gray matter ? 53. What is stated of men in connection with the size of their brain ? With the brains of other animals ? (* RwdNqte 10, end of Ch THE KEBYOUS SYSTEM. 173 pared with the weight of the body, does not, in all instan~ ces, exceed that of the inferior animals ; the canary and other singing-birds have a greater relative amount of nerv- ous matter than man ; but man surpasses all other crea- tures in the size of the hemispheres of the cerebrum, and in the amount of gray substance which they contain. * 54. It is a singular fact that this cerebral substance is insensitive, and may be cut without causing pain. The removal of a considerable quantity of the brain has taken place, as the result of accident, without causing death, and without even affecting seriously the intellect. A remark- able case of injury of the brain is recorded, in which, from the accidental explosion of gunpowder used in blast- ing a rock, the " tamping-iron" was driven directly through the skull of a man. This iron rod, three feet and seven inches long, an inch and a quarter in diameter, and weigh- ing more than thirteen pounds, entered the head below the ear and passed out at the top of the skull, carrying with it portions of the brain and fragments of bone. The man sustained the loss of sight on one side, but otherwise recovered his health and the use of his faculties. More- over, disease has occurred, compromising a large portion of the brain, without impairing the faculties of the mind, when the disease was limited to one side only. 55. Impressions conveyed to the hemispheres from the external world arouse the mental operations called thought, emotion, and the will. These are the god- like attributes which enable man to subjugate a world, and afterward cause him to " sigh for other worlds to con- quer;" which enable him to acquaint himself with the properties of planets millions of miles distant from him, and which give him that creative power by which he builds and peoples the new worlds of poetry and art. 54. Sensitiveness of the brain substance? The removal of a portion of the Irain ? State the remarkable case mentione i ? 55, Thought, emotion, and will ? What power do they give us? (* Read Not? n, end of Chapter.) 174 THE NERVOUS SYSTEM. 56. All these mental acts, and many others, are devel- oped through the action of the brain ; not that the brain and the mind are the same, or that the brain secrete memory, imagination, or the ideas of truth and justice, as the stomach secretes the gastric juice. But rather, as the nerve of the eye, stimulated by the subtile waves of light, occasions the notion of color, so the brain, called into action by the mysterious influences of the immaterial soul, gives rise to all the intellectual, emotional, and voluntary activities of mankind. (Read Note 5) 57. The cerebrum, according to our present knowledge of it, must be regarded as a single organ, which producer different results, according as it is acted upon by the im- material mind in different ways. Recent investigations, however, seem to prove that the faculty of language is de- pendent upon a small part of the left hemisphere of the cerebrum, near the temple. At least, in almost every instance where this part is diseased, the patient can no longer express himself in speech and writing. 58. The Reflex Action of the Brain. The reflex function of the organs within the skull is very active and important. Like that of the cord, it protects the body by involuntary movements, it regulates the so-called vegeta- tive acts, and it takes the place of the will in controlling the voluntary muscles, when the attention is turned in other directions. The reflex power of the medulla governs the acts of respiration, which are absolutely and continu- ously essential to life. Eespiration is, as we have seen, partly under the influence of the will; but this is due in part to the fact that respiration is indirectly concerned in one of the animal functions, that of speech. 59. Reflex action also occasions coughing and sneezing, 56. Are the brain and the mina identical ? 57. What do we know of the cerebrum and its powers ? 58. The reflex function of the organs within the skull? The reflex power of the medulla ? Respiration ? 59. What else does reflex action occasion ? Winking? Other examples ? THE NERVOUS SYSTEM. 175 whenever improper substances enter the air-passages. Winking is an act of the same sort, and serves both to shield the eyes from too great glare of light, and to pre- serve them by keeping the cornea moist. Looking at the sun or other strong light, causes sneezing by reflex action. Laughing, whether caused by tickling the feet or by some happy thought, and also sobbing, are reflex acts, taking place by means of the respiratory muscles. 60. Certain of the protective reflex movements call into play a large number of muscles, as in the balancing of the body when walking along a narrow ledge, or on a slippery pavement. The dodging motion of the recruit, when the first cannon ball passes over his head, is reflex and invol- untary. The fact that these involuntary, reflex acts are performed with great precision, will explain why it is that accidents seldom befall the somnambulist, or sleep-walker, although he often ventures in most perilous places. 61. Walking, sitting, and other acts of daily life, be- come automatic, or reflex, from habit : the mind is seldom directed to them, but delegates their control to the medulla and spinal cord. Thus a person in walking, may traverse several miles while absorbed in thought, or in argument with a companion, and yet be conscious of scarcely one in a thousand of the acts that have been necessary to carry his body from one point to another. By this admirable and beautiful provision, the mind is released from the charge of the ordinary mechanical acts of life, and may devote itself to the exercise of its nobler faculties. And if is worthy of notice, that the greater the use of these facul- ties, the more work does the reflex function assume and perform ; and thus the employment of the one insures the improvement of the other. (Read Note 6.) 60. Musclep called Into play by certain reflex movements ? The somnambulist ? 61. What is said of walking and other acts in connection with the office per formed by the medulla and spinal cord ? 176 REVIEW QUESTIONS. QUESTIONS FOR TOPICAL REVIEW. PAGE 1. State fully what is meant by the term vegetable function 148 2. To what is man indebted for his position as the head of the animal crea- tion ? 148, 149 3. What can you state on the subject of special organs for separate functions ? 149 4. Describe, as fully as you can, the structure of the nervous system 149, 150 5. Describe the brain, its location, size, shape, and structure 150, 152 6. Describe the brain proper, or cerebrum 152, 153, 174 7. What connection is noticed between the cerebrum and mental power? 153, 172,174 8. Describe the little brain, or cerebellum 153, 154, 172 9. Describe the spinal cord 154, 155,156 10. What are the spinal nerves, and how are they arranged ? 156, 157 11. What is the character and substance of their tissues ? 157 12. State how the nerve-fibres perform their office, and give the illustra- tion 157,158 13. Describe the sympathetic system of nerves 158 14. State what is meant by the properties of nervous tissue, and give the illustration 159, 160 15. Explain what is meant by the functions of the nerves, and give the illustration 160,161,162 16. What is meant by a transient paralysis of a nerve ? Give the illustra- tion 161,163 17. What can you state of the rate of message-motion along a nerve ? 162 18. What are the functions of the spinal cord ? 162, 163, 164, 165 19. State what you can of the form of paralysis known as paraplegia 162 20. What experiments, with results, upon the spinal cord are noted ? 163, 164 21. Explain how injury of the cord may produce paralysis of motion in one leg, and at the same time a loss of sensation in the other 104 22. Explain how, if the right hand be hurt, the left side of the brain is made to feel the pain 165 23. Now, explain as fully as you can the direction of the fibres of the cord. 164, 165 24. What is understood by the reflex action of the cord ? 165 25. What experiments are mentioned to prove this power of the cord ? . . . . 165, 16(5 26. What are the uses of the reflex action of the cord ? 167-170 27. What illustrations are mentioned to show such uses ? 167-170 28. What is the medulla oblongata ? 154, 170 29. What are the functions of the medulla oblongata ? 170, 171 30. What can you state of the functions of the cranial ganglia ? 171, 172 31. What are the functions of the cerebellum ? 172 32. What is the function of the cerebrum ? 172, 174 33. lu what way does the size of tne brain generally indicate the character of the man? 172,173 34. What facts show that the gray substance of the brain is insensitive '( 173 35. Upon what does the faculty of language seem to depend ? 174 36. What has been observed in support of this statement ? 174 37. Of what importance is the reflex action of the brain ? 174, 175 ?8. In what ways is this importance made manifest ? 174, 175 NOTES. 1. The Brain (p. 153, T9). "Our brains are seventy-year clocks. The Angel of Life winds them up once for all, then closes the case, and gives the key to the Angel of the Resurrection. Tic-tac ! tic-tac ! go the wheels of thought ; our will cannot stop them; they cannot stop themselves ; sleep caunot stop them ; madness only makes them go faster ; death alone can break into the case, and, seizing the ever-swinging pendulum, which we call the heart, silence at last the clicking of the terrible escapement we have carried so long beneath our wrinkled foreheads. * * * Now, when a gentleman's brain is ill- regulated or empty % it is, to a great extent, his own fault, and so it is simple retribution that, while he lies slothfully sleeping or aimlessly dreaming, the fatal habit settles on him like a vampire and sucks his blood, fanning him all the while with its hot wings into deeper slumber or idler dreams." Holmes' The Autocrat of the Breakfast- Table. 2. The Relations of the Brain and Sympathetic Nerve (p. 160, T 20). ''Buried in the hidden recesses of the body, between the spinal column and the great organs of nutrition, there is a double row of small knots of nervous substance, bound together by a series of nerves running from one to another, in succession, from the neck to the base of the column. The whole appears like a long, fine cord, with knots at various distances a collection of little brains, if I may use a rather crude expression. It is, as the Swiss would say, the 'great council' of this federative republic, which counterpoises that cerebral royalty within us. It has been well named the great sympathetic nerve, and this it is which makes the laws by which our interior life is governed. The nutritive apparatus of a country, its commerce, its industry, the incessant labor of its citizens by which the public wealth is built up and let us also add, the throbs of a national heart all this the sympathetic system full plainly shows us requires to be left to itself. It would be a fine affair if the brain had to watch over the service of the stomach, or if, at its conven- ience, it regulated the movements of the master who disposes of its life. Besides, what would become of the poor body, if the least drowsiness attacked the uni- versal centre ? Happy is it for us and let us not be slow to own it that nature has armed herself against these encroachments of power." MacPs The Little Kingdom 3. The Speed of Sensation and Thought (p. 162, 127). "The rate of nervous and mental action is not the same in all individuals. In com- paring the records made by astronomers, it has been found that an appreciable difference exists in the rapidity with which the same occurrence may be noted by different observers. This is known as the 'personal equation, 1 and is allowed for With the greatest nicety in the making up of astronomical reports. With very delicate apparatus for marking time, the various nervous impulses have been observed; from forty to a hundred feet in a second are the estimates of different experiments as to the speed of sensation; or, as it has been expressed, it would take a full grown whale a second to feel the stroke of a harpoon in his tail." 4. The emotion* Influence the Bodily Health (p. 173, t 5'). "The exciting emotions which are pleasurable, such as joy and hope, are of a kind that seldom tend to a dangerous excess, and may be regarded as exercising gener- ally an eminently healthful influence upon the body. Hilarity i.s a great refresher and strengthener of life. Laughter is a wholesome exercise, which, beginning at the lungs, diaphragm, and connected muscles, is continued to the whole body, ' shaking the sides,' and causing that jelly-like vibration of the frame of which, we are so agreeably conscious when under its influence. The heart beats more briskly, but with a safe regularity of action, and send* the blood to the smallest and most distant vessel. The face glows with warmth and color, the eye bright- ens, and the temperature of the whole body is moderately raised. With the Universal pleasurable sensation there comes a disposition of every organ to NOTES. healthy action. When hilarity and its ordinary expression of laughter become habitual, the insensible perspiration of the skin is increased, the breathing quick- ened, the lungs and chest expanded, the appetite and digestion strengthened, and nutrition contequently increased. The old proverb, ' Laugh and grow fat,' states a scientific truth. The influence of laughter upon the body is recognized by Shakspere, in his description of the 'spare Cassius'' Seldom he smiles.' 'To be free-minded and cheerfully disposed at hours of meat, and sleep and exercise, is one of the best precepts of long-lasting.' Such is the testimony of Lord Bacon to the favorable influence of the pleasurable emotions upon the body. The depressing emotions, such as fear, anxiety, and grief, are always fatal to health, and frequent causes of death. There is an Eastern apologue which describes a stranger on the road meeting the Plague coming out of Bagdad. * You have been committing great havoc there,' said the traveller, pointing to the city. 'Not so great! ' replied the Plague. 'I only killed one-third of those who died ; the other two-thirds killed themselves with fright.' "The, Book of Health. 5. Mental Exercise necessary to Perfect Health (p. 174, t 56). "The improvement of the memory is a familiar instance of an increase of mental power produced by exercise ; and the beating sense of fulness and quick- ened circulation in the head induced by intense study or thought, shows that an organic process goes on when the brain is in activity, similar to that which takes place in the muscular system under exercise. On the contrary, when the org^n is little used, little expenditure of its power and substance takes place, little blood and little nervous energy are required for its support, and, therefore, little is sent: nutrition in consequence soon becomes languid, and strength im- paired. To all these laws the brain is subject equally as the rest of the body. Frequent and regular exercise gives it increased susceptibility of action, with power to sustain it, the nervous energy acquiring strength as well as the vascular. Disuse of its functions, or, in other words, inactivity of intellect and of feeling, impairs its structure, and weakens the several powers which it serves to manifest. The brain, therefore, in order to maintain its healthy state, requires to be duly exercised." Barlow on Physical Education. 6. Automatic Action of the Brain (p. 175, 1"61). "A large part of our mental activity consists of this unconscious work of the brain. There are many cases in which the mind has obviously worked more clearly and more suc- cessfully in this automatic condition, when left entirely to itself, than when we have been cudgeling our brains, so to speak, to get the solution. An instance, well authenticated, is related of a college student ; he had been attending a class in mathematics, and the professor said to his students one day: 'A question of great difficulty has been referred to me by a banker a very com- plicated question of accounts, which they have not themselves been able to bring to a satisfactory issue, and they have asked my assistance. T have been trying, and I cannot resolve it. I have covered whole sheets of paper with calcu- lations, and have not been able to make it out. Will you try ? ' He gave it to them as a sort of problem, and said he would be extremely obliged to any one who would bring him the solution by a certain day. This gentleman tried it over and over again ; he covered many slates with figures, but did not succeed. He was ' put on his mettle,' and determined to achieve the result. But he went to bed on the night before the solution was to be given in, without having succeeded. In the morning, when he went to his desk, he found the whole problem worked out and in his own hand. He had risen in the night and unconsciously worked it out correctly, as the result proved ; and what is more curious still, the process was very much shorter than any of his previous trials." W. B. Carpenter on Unconscious Action. 7. How Bodily Sensations are Located (p. 158, T 16.) "A nervous fibre which ends in the skin forms, as far as its union with the brain or cord is concerned, one long, fine, unbroken thread. The fibres, thus ending in the skin, very soon join to form small branches and finally in thick nerve-trunks, but in no case do two nerve fibres coalesce so as to lose their identity. Every part of the skin has its own separate connections with the centre of the nervous system, which unite there just as telegraph wires unite at a terminus. The brain is the terminus of these lines of nerves, and, as it were, receives and explains the messages sent to it. It distinguishes very clearly by what particular fibre such a message h;;s come, and just as the clerk in a telegraph office, where a great many wires meet from all sides, knows by experience from what direction each wire brings its mes- sage, so the brain aiso knows by experience what part of the skin is involved when a sensation reaches it along a certain nerve-fibre. It is probable that the brain, by its imaginative faculty, has formed a complete picture of the surface of the body ; a kind of chart slowly made and always being more highly perfected, by means of which, with each impression from without, there arises in the brain a picture of the spot upon the skin where the irritation has taken place. Now, if an irritation were to pass from one nerve fibre to another, it is very plain, the brain could not tell the place from which it came, and could not localize impres- sions received from the world about MS " Bernstein 1 s Five Senses of Man. S. The Wonderful Operations of the Sympathetic System. Blushing or " Shame-redness " (p. 158, ^ 18). "A blow upon the head will knock a man senseless, but he still lives and survives ; a blow of like vio- lence upon the pit of the stomach is followed by instant death, because the great centre of the organic nerves lies there, and the vital actions are suspended by the blow, so that the system never lives to recover, but abolition of function and of life at once follows. Other actions also belong to this organic nervous system. It controls the calibre of the blood-vessels, for which end filaments run along each of them. The body temperature is maintained by the production and dispersion of heat thus regulated, a continuous oscillation going on betwixt the internal ves- sels and those of the skin. It is connected with the emotions ; and so the heart beats perceptibly with excitement, and the maiden's cheek blushes before words that should never be spoken or thoughts that should never arise. The momentary dilatation of the vessels of the skin constitutes the blush, in the German, 'shame- redness,' which is not confined to the face, though of course it is only seen there, the body being hid by the clothes." Fotkergill on the Maintenance of Health. There is an old tradition that when the executioner of Charlotte Corday lifted her severed head high in air, and smote the face with his hand, the cheeks were seen to resent the insult with a blush. This reddening is not impossible, for a decapitated head certainly may exhibit, for a time, certain reflex movements. But whether sensibility is retained cannot be known. 9. On Nervous, Health, or Tone (p. 168, t 42). " That state of general vigor, which we call 'tone,' depends upon the healthy action of the nervous centres. It consists in the habitual moderate contraction of the muscles, due to a constant stimulus exerted on them by the cord, and is valuable less for itself, than as a sign of a sound nervous balance. Tone is maintained partly by healthful im- pressions radiated upon the spinal cord through the nerves from all parts of the body, and partly by the simulus poured down upon it from the brain. So it is dis- turbed by whatever conveys irritating or depressing influences in either direction. A single injudicious meal, a single sleepless night, a single passion or piece of bad news, will destroy it. On the other hand, a vivid hope, a cheerful resolve, an absorbing interest will restore it as if by magic. For in man, these lower officers in the nervous hierarchy draw their very breath according to the bidding of the NOTES. higher powers. But the dependence of the higher on the lower is no less direct. The mutual action takes place in each line. A chief condition of keeping the brain healthy is to keep these unconscious nervous functions in full vigor, and in natural alternations of activity and repose. We see evidence of this law in the delightful effect of a cheerful walk after a depressed or irritated state of mind. Every part of the nervous system makes its influence felt by all the rest. A sort of constitutional monarchy exists within us ; no power in this small state is abso- lute, or can escape the checks and limitations which the other powers impose. Doubtless the Brain is King, but Lords and Commons have their seats below and guard their privilege with jealous zeal. If the k constitution ' of your personal realm is to be preserved intact, it must be by the efforts of each part, lawfully directed to a common end." Hinton on Health and its Conditions. 10. The Alliance of Mind and Body (p. 172, 1 52.) "The regular routine of our daily life is the counterpart of the mental routine. A healthy man wakens in the morning with a flush of spirits and energy ; his first meal confirms and re-inforces the state. The mental powers and susceptibilities are then at a maximum ; as the nutrition is used up in the system they gradually fade, but may be renewed once and again by refreshment and brief remission of toil. Towards the end of the day lassitude sets in, and fades into the deep unconsciousness of healthy sleep. * * * The influences that affect the body extend not only to the grosser modes of feeling, and to such familiar exhibitions as after-dinner oratory, but also to the highest emotions love, anger, aesthetic feeling, and moral sensi- bility. ' Health keeps an Atheist in the dark.' Bodilj- affliction is often the cause of a total change in the moral nature." Bain's Mind and Body. 11. Large Brains (p. 173, ^ 53.) "As a rule the size of the brain is pro- portional to the mental development in human beings. The rule is not strictly maintained in every instance ; occasionally a stupid man has a larger brain than a clever man. But these are only individual exceptions to a prevailing arrange- ment. The following are the brain weights of several distinguished men : Cuvier 64.5 oz. Abercrombie .... 63 " Daniel Webster . . 53.5 u Lord Campbell . . . 53.5 oz. Agassiz 53.4 " De Morgan 52.7 u "The average male brain in Europeans is 49.5 oz. ; the female, 44 oz. Among idiots the weights have run from 27 to 8.5 oz. The brains of the insane are below the average of the sane. Tall men, as a rule, have larger brains than small men." Bain's Mind and Body. 12. The Mind Should be Intelligently Cultivated " The cultiva- tion of the mind should be carried on with judgment, and in due submission to the requirements of the body. If study be the duty of the youth, let him pursue it diligently, but with such intervals of rest and bodily exertion as may maintain good appetite and health. "The proportion of hours of study and bodily exercise may vary with the degree of mental work, the healthfulness of the room and surrounding air, the natural strength of the body and the degree of health ; but as a general rule it may be doubted whether any young person can sit at close study for more than two hours at a time without requiring bodily exertion to sustain vital action, and rest to recruit the mind. Two hours' mental work, and a quarter to half an hour's bodily exercise, will be quite compatible with the greatest progress in study. " Moreover, it may be doubted whether such a student can work with advantage for more than eight hours a day, in addition to the intervals of rest, for the issue will not turn on the number of hours devoted to work, but the intensity of the attention given." Ed-ward Smith on Health. THE SPECIAL SENSES. 177 CHAPTER X. THE SPECIAL SEKSES. The -Production of Sensations Variety of Sensations General Sensi- bility Pain and its Function Special Sensation, Touch, Taste, Smell, Sight, and Hearing The Hand, the Organ of Touch The Sense of Touch Delicacy of Touch Sensation of Temperature and Weight The Tongue the Organ of Taste TJie Nerves of Taste The Se-nse of Taste and its Relations with tlie oilier Senses The Influence of Education on the Taste The Nasal Cavities, or the organs of SmeUTlw Olfactory Nerve The Uses of the Sense oj Smell The Sense of Sight Light The Optic Nerve The Eyeball and its Coverings The Function of the Iris The Sclerotic, Choroid, and Retina The Tears and their Func- tion The Movements of the Eyeball The Function of Ac- commodation The Sense of Hearing and Sound The Ear, or the organ of Heoring The External, Middle, and Internal Ear 1. Production of Sensations. We have already seen that the true centre of sensation is some organ within the skull, probably among the gray masses at the base of the brain ; but the mind never perceives impressions at that point ; but, on the contrary, always refers them to the external organs of sensation. Hence, it is convenient to say, that those outer pp.rts possess the property of sensibil- ity. For instance, we say that we hear with the ear, taste with the tongue, and feel with the fingers. That this is not the exact truth is proven by the fact, that whenever the nerve connecting one of these organs with the brain is severed, it at once loses its capacity for sensation. 2. Consciousness, another faculty of the brain, is neces- sary to complete a sensation. During sleep, and in other unconscious states, the usual impressions are presented to 1 . True centre of sensation ? Place of the mind's impressions ? What is convenient to say ? What further is stated ? 2. Consciousness ? During sleep ? In profound insensibility ? 178 THE SPECIAL SENSES. the ear, the nose, and the skin, but they fail to excite sen- sations, because the nerve-centres are inactive. In pro- found insensibility, from chloroform or ether, a limb may be removed without occasioning the least feeling. 3. Variety of Sensations. All animals have some legree of sensibility. It is of course feeble and indistinct :n the lower forms of life, but increases in power and vari- ety as we ascend the scale. In the earth-worm, the nerv- ous system is very simple, the sensibility being moderate and alike in all parts : hence, if its body be cut into two pieces, each piece will have the same degree of feeling as before. As we approach man, however, the sensations multiply and become more acute; the organs are more complex, and special parts are endowed with special gifts. These special organs cannot be separated from the rest of the body without the loss of the functions they are de- signed to exercise. 4. The lowest form of sensation, that of simple contact, is possessed by the lowest of the animal creation. The highest forms are those by which we are enabled to know the properties of external objects, such as shape, size, sound, and color. A variety of means of communicating with the outer world is the necessary possession of a high intelligence. Sensations are modified by use. They be- some more acute and powerful oy moderate exercise ; or, they are dulled by undue excitement. The former is shown by the acute hearing of the Indian, by the sharp sight of the sailor, and by the delicate touch of the blind. The latter is exemplified by the impaired hearing of the boiler-maker, and the depraved taste of him who uses pungent condiments with his food. Again, impressions habitually presented may not be consciously felt; as is the case with the rumbling of carriages in a neighboring 3. Sensibility in animals ? In the earth-worm ? In man ? 4. The lowest form of sensation ? The highest? Sensations, how modified? What further can you state as to habitual impressions? THE SPECIAL SENSES. 179 street, or the regular ticking of a clock. All sensations become less vivid with the advance of age, especially hear- ing and vision. 5. General Sensibility .There is a property pos- sessed by nearly all parts of the human body which we call general sensibility. We have recently seen that the brain is wholly insensitive, and may be cut or pinched without pain. The same is true of the nails, hair, the scarf-skin or external covering of the body, and a few other structures. In these parts no nerves are found. On the other hand, the sensibility of the true skin, and of mucous membranes, as of the eye and nose, is exquisite, these or- gans having a large supply of senso*/ nerve-fibres. The bones and tendons have less of these fibres, and are only moderately sensitive. 6. The sensibility of any part of the body, then, de- pends upon the number of nerves present; and, as a rule, the nervous supply is proportional to the importance of the part, and to its liability to injury. When, therefore, a surgical operation is performed, the most painful part of it is the incision through the skin ; the muscles, cartilage, and bone being comparatively without sensation. Hence, if we could benumb the surface, certain of the lesser oper- ations might be undergone without great inconvenience. This is, in fact, very successfully accomplished by means of the cold produced by throwing a spray of ether, or of some other rapidly evaporating liquid, upon the part to be cut. 7. Tickling is a modification of general sensibility. At first, it excites a pleasurable sensation, but this soon passes into pain. It is only present in those parts where the sense of touch is feeble. But all impressions are not received from without: there are, also, certain internal 5. General sensibility? What have we seen as regards the brain? Of what other structures is the same true? 6. The cause of sensibility ? Painful part in a surgical operation ? Benumb- ing the surface ? How done by ether ? 7 Tickling? Internal sensations? The nerves of general sensibility ? 180 THE SPECIAL SENSES. sensations, as they are called, which depend upon the con- dition of the internal organs, such as appetite, hunger, thirst, the sense of satisfaction after taking food, dizziness when looking down from some lofty position, lassitude, drowsiness, fatigue, and other feelings of comfort or dis- comfort. General sensibility, whether of the internal or external organs of the body, chiefly depends upon the sensory fibres of the spinal nerve. The face, however, is supplied by the sensory cranial nerves. The sympathetic system has a low grade of feeling in health ; but disease in the parts served by it arouses an intense degree of pain. 8. The Sensation of Pain. What then is pain ? Is it identical with ordinary sensibility ? There seems to be some necessary connection between the two feelings, for they take place through the same channels, and they are alike intense in the same situations. But sensibility habitually contributes to our sources of pleasure, the very opposite of pain ; hence, these feelings cannot be identical. 9. Pain must, therefore, be a modification of the general sensibility, which follows an excessive degree of excitement of the nerves ; there being a natural limit to the amount of stimulation which they will sustain. So long as this limit is observed, the part excited may be said to be simply sen- sitive; but when it is exceeded, the impression becomes painful. This difference between sensibility and pain is well shown by the effects of sunlight upon the eye. The indirect illumination of the sun arouses only the former feeling, and is indispensable to our comfort and existence ; while the direct ray received into the eye occasions great pain. 10. The Uses of Pain. The dread of pain is a valu- able monitor to the body. It puts us on our guard in the presence of danger; teaches moderation in the use of our 8. Connection between pain and sensibility? 9. Explain the difference between pain and sensibility. 1O- Dread of pain ? How may its value be appreciated ? Example THE SPECIAL SENSES. 181 powers; indicates the approach of disease; and calls at- tention to it when present. The word disease, in fact, according to its original use, had reference simply to the pain, or want of ease, which commonly attends disordered health. When we observe the serious mishaps which occur when sensibility and pain are absent, we cannot fail to appreciate its value. For example, a paralytic in taking a foot-bath, forgets to test its temperature, and putting his limbs into water while it is too hot, is severely scalded without knowing it. 11. A traveller, overcome by cold and fatigue, lies down and falls asleep near a large fire, and when he is aroused in the morning, it is discovered that one of his feet has been insensibly destroyed. A grain of sand, lodging in an insen- sitive eye, may cause inflammation and even the loss of sight. If intense light were not painful to the eye, many a child would innocently gaze upon the glories of the sun to the ruin of his sight. 12. Pain is, indeed, a present evil, but its relations with the future prove its mission merciful. Painful impressions 'cannot be recollected from past experience ; and they can- not be called into existence by the fancy. Considered in the light of results, pain has a use above that of pleasure ; for while the immoderate pursuit of the latter leads to harm, the tendency of pain is to restrict the hurtful courses of life, and in this manner to protect the body. 13. The relations of pain to pleasure are thus described by the eminent physiologist, Magendie: "By these sensa- tions Nature induces us to concur in 'the order which she has established among organized beings. Though it may appear like sophistry to say that pain is the shadow of pleasure, yet it is certain that those who have exhausted the ordinary sources of pleasure have recourse to th 1 1 . The case of the traveller ? Grain of sand ? The snn and child ? 12. Mission of pain ? Painful impressions compared with those of pleasure 7 1 3. What doea Magendie eay of the relation of pain to pleasure? 182 THE SPECIAL ' causes of pain, and gratify themselves by their effects. Do we not see in all large cities, that men who are debauched and depraved find agreeable sensations, where others ex- perience only intolerable pain ?" (Read Note i.) 14. As to painful sensation among the inferior animals, the plan of Nature seems to be, that the higher the intel- ligence of the creature, and the more complete its power of defence, the more acute is its sensibility. We infer, therefore, that animals low in the scale of existence, and helpless, are not very liable to suffer pain. 15. Special Sensation. The sensations of simple contact and pain are felt by nearly all parts of the system, whether external or internal, and are the necessary con- sequence of the general sensibility ; but, so far as the ob- jects which surround us are concerned, these impressions are vague and passive in character, and inform the mind of none of the properties or powers of these objects. Be- sides these feelings, therefore, man is endowed with certain special sensations, which are positive and distinct in char- acter,, and which he can call into exercise at will, and em- ploy in the pursuit of knowledge. For reasons relating to the original constitution of the body, these sensations are to be regarded as modifications of the general sensibility already alluded to, constructed with special reference to the different forces of Nature, of which we have any ^knowledge, such as heat, motion, gravity, sunlight, and the like. (Read Note 6, end of Chapter.) 16. These distinct and active faculties are termed the special senses, and are five in number, viz., Touch, Taste, Smell, Sight, and Hearing. For the exercise of these senses, special organs are furnished, such as the hand, the tongue, the nose, the eye, and the ear. The manner in which the nerves of special sense terminate, varies in the 14. The law of Nature as regards painful sensations amon? animals ? 15. The sensation of conuict and pain? Special sensations of man? How teparded ? 6. What are the special senses ? Special organs for them ? THE SPECIAL SENSES. 183 case of each organ, so that each is adapted to one set of sensations alone, and is incapable of perceiving any other. Thus the nerve of hearing is excited by the undulations of sound, and not by those of light, while the reverse is true of the nerve of sight; and the nerve of smell can appreciate neither of them, being capable only of taking cognizance f the odorous properties of bodies. (Note 7, end of Chapter.} 17. By some writers six senses are accorded to man ; the additional one being either the sense of temperature, for as we shall presently see this is not the same as touch ; or according to others, the muscular sense by which we are enabled to estimate the weights of bodies. The latter also differs in some respects from the sense of touch. fl 18. Organs of Touch. The sense of touch is pos- sessed by nearly all portions of the general surface of the body, but it finds its highest development in the hands. The human hand is properly regarded as the model organ of touch. The minute structure of the skin fits it admi- rably for this form of sensation : the cuticle, or scarf-skin, is fine and flexible, while the cutis, or true skin, contains multitudes of nerve-filaments, arranged in rows of papilla-. or cone-like projections, about one-hundredth of an inch in length. It is estimated that there are 20,000 of these papillae in a square inch of the palmar surface of the hand. Now, although the nerves of the cutis are the instruments by which impressions are received and transmitted to the brain, yet the cuticle is essential to the sensation of touch. This is shown by the fact that whenever the true skin is laid bare, as by a burn or blister, the only feeling that it experiences from contact is one of pain, not that of touch. 19. The office of the cuticle is thus made evident: it is to shield the nerve filaments from direct contact with ex- 1 7. What, is paid in relation to one more than the five senses ? 18. The sense of touch, how prevalent ? What is said of the hand ? 19. Office of the cuticle ? Tips oi the fingers ? The fingers with thumb ? 184 THE SPECIAL SENSES. fcernal objects. At the tips of the fingers, where touch is most delicate, the skin rests upon a cushion of elastic material, and receives firmness and permanence of shape by means of the nail placed upon the less sensitive side. Besides these favorable conditions, the form of the arm is such, and its motions are so easy and varied, that we are able to apply the test of touch in a great number of direc- tions. The slender, tapering fingers, with their pliant joints, together with the strong opposable thumb, enable the hand to mold itself upon and grasp a great variety of objects; so that great as are the delicacy and grace of the hand, it is not wanting in the elements of power. 20. Its beauty and adaptation to the wants of man have made the hand an attractive theme for philosophers. They do not, however, always agree in their conclusions. One has the opinion that man has acquired his intelligence and achieved his place as " lord of creation," because he has this organ. Buflfon, in effect, declares that with fingers twice as numerous and twice as long, we would become proportionally wiser; but Galen long ago took a more reasonable view, when he taught that "man is the wisest of animals, not because he possesses the hand ; but because he is the wisest and understands its use, the hand has been given to him; for his mind, not his hand has taught him the arts." Another has well said, that " no one can study carefully the human hand and fail to be convinced of the existence of the Deity." 21. The Sense of Touch. Touch is the simplest of the senses. It is that which the child first calls into ex- ercise in solving the early problems of existence; and it is that which is in the most constant use throughout life. We are brought by the touch into the most intimate rela- tions with external objects, and by it we learn th* greater number, if not the most important, of the properties of tO. What special importance is attributed to the hand? 1 . The simplicity of touch ? What docs it tyach us ? THE SPECIAL SENSES. 185 these objects; such as size, figure, solidity, motion, and smoothness or roughness of surface. 22. The sense of touch assists the other senses, especially that of sight, giving foundation and reality to their per- ceptions. Without it, the impressions received by the eye would be as vague and unreal as the figures that float through our dreams. A boy who had been blind from birth, at the age of twelve years received sight by means of a surgical operation : at first, he was unable to distinguish between a globe and a circular card, of the same color, be- fore he had touched them. After that, he at once recog- nized the difference in their form. He knew the peculiari- ties of a dog and a cat by feeling, but not by sight, until one day, happening to take up the cat, he recognized the connection of the two sorts of impressions, those of touch and sight; and then, putting the cat, down, he said: "So, puss, I shall know you next time." 23. Touch is considered the least liable to error of all the senses ; yet, if that part of the skin by which the sense is exercised is removed from its customary position, a false FIG. 45. impression may be created in the mind. This is well il- lustrated by an experiment, which dates from the time of Aristotle. If we cross the middle finger behind the fore- 22. Importance of the sense of touch to the development of the other senses ? 23. Liability of touch to err? Describe the illustration. 186 THE SPECIAL SENSES. finger, and then roll a marble, or some small object, upon the tips of the fingers (see Fig. 45), the impression will be that two marbles are felt. If the fingers, thus transposed, be applied to the end of the tongue, two tongues will be felt. When the nose is accidentally destroyed, the surgeon sometimes performs an operation for the purpose of form- ing a new one, by transplanting a partially removed piece of the skin of the forehead upon the injured part : then, if the new nose be touched or pinched, the feeling is referred to the forehead. This fact illustrates one important truth, that the nerves will re-unite after they have been cut, and feeling will be restored : if it were otherwise, a succession of slight cuts upon the fingers would seriously impair their tactile sensibility. 24. The Delicacy of Touch. Although the hand is the proper organ . of this sense, yet it is exercised by various parts of the body, their degree of sensibility being proportional to the number of papillae they contain. The varying degrees of tactile delicacy of the diiferent part? of the surface have been measured, in an ingenious manner, by means of a pair of compasses, tipped with small pieces of cork. The two points of the compasses are touched at the same moment to the skin, the eyes being closed, and it is found that, in sensitive parts, the distance between the points may be quite slight, and yet each be plainly felt ; while, in less sensitive parts, the points of the compasses are felt as a single point, although they are separated one or two inches. 25. At the tips of the fingers, the distance between the points being one-twentieth of an inch, a double impression is felt. The distance must be twice as great, for the palm; four times as great, for the lips ; and, on the forehead, it must be twenty times greater. At the middle of the back, where the touch is least acute, the points must be sepa- 24. The delicacy of touch 1 Experiments with a pair of compasses 7 25. Further experiments and results ? THE SPECIAL SEKSES. 187 rated more than two inches before they can be .separately felt. Therefore, the sense of touch in the fingers is said to be fifty times more delicate than upon the posterior sur- face of the body. 26. Exquisite delicacy of touch is attained by practice. This is shown in many of the lighter and more graceful employments of daily life. Without it, the skill of the painter, sculptor, and musician would be rude indeed. By training, also, the physician acquires the tactus eruditus, or discriminating touch ; but among the blind, delicacy of touch is most remarkable, and it here finds its highest value; for its possession, in a measure, compensates the loss of sight by enabling them to read, by means of* raised letters, to work with certain tools, and even to play upon musical instruments. A person born without sight, and without hearing or voice, may, by the education of the touch, be rescued from apparent imbecility, and be taught not only to read and write, but even to perform household and other useful labors. 27. Sensations of Temperature and Weight. Each of these sensations has been described by the physi- ologists as a special sense, and they are rival candidates, so to speak, for the position and title of the sixth sense. In the sensation of temperature, or the thermal sense, touch bears a part, but the two feelings appear to be distinct. In proof of this, we observe, firstly, that they are not alike intense in the same situations; as, fo r example, the skin of the face and elbow, where the sense of touch is feeble, is very sensi- tive to impressions of heat and cold. Secondly, the ability to recognize temperature may be lost by paralysis, while the ^ sensibility of touch remains unaffected. When the skin comes in contact with a very hot substance, the sen- sation felt is that of pain, not of touch. In like manner, a 26. Exquisite delicacy of touch ? The same among the blind ? 27. Rival candidates for the sixth sense? Give the two reasons on the sub- ject. r 188 THE SPECIAL SENSES. very cold substance causes pain, not the feeling of cold. So that a red-hot iron, and solid carbonic acid (the tem- perature of which is 108 below zero), feel alike ; and each, if pressed slightly, will produce a blister. (Read Note 8.) 28. The muscular sense, by some considered distinct from touch, gives rise to the sensations of weight, and other forms of external resistance. That this feeling exists, is shown by the following simple experiment. If the hand be placed flat upon a table, and a somewhat heavy weight be put into it, touch alone is exercised and a feeling of pressure results; but if the hand be raised, a certain amount of muscular effort must be put forth, and thus the sensation of weight is recognized. Through the muscular sense, precision of effort is rendered possible ; for by it we learn to adjust the force exerted to the weight of the object to be lifted, moved, or carried. Without it, all our movements would necessarily become ill-regulated and spasmodic. In cases of disease, where the sensibility of the lower limbs is lost, while power of motion remains, the patient is able to stand erect so long as he can see his limbs; but just as soon as his eyes are closed, he begins to waver, and will fall unless supported. 29. The Organ of Taste. The tongue is the special organ of the sense of taste ; but the back part of the mouth also possesses this faculty. The tongue is a muscular organ, the muscles composing it being so numerous and interwoven as to give it the freedom and variety of motion which it possesses. It can curve itself upward or down- ward; it can extend or contract itself; and, with its point, can sweep the cavity of the mouth, in all directions, in the search for scattered particles of food. 30. The upper surface of the tongue is peculiar, being marked by the presence of innumerable papillce, some of 28. The muscular sense ? State what IP said to illustrate the subject. 29. The oriran of taste ? The lonjnie ? Its powers of motion? 30. Peculiarities of the tongue ? Uses of the papillae ? THE SPECIAL SENSES. 189 which are of microscopic size, resembling those thai abound in the fingers, and in other parts of the body that have the sense of touch. Others are much larger, and give to the tongue its roughness of feeling and ap- pearance. Through the medium of these papillae, the tongue receives impressions of touch and temperature, as well as taste : indeed, its extremity is fully as delicate, in respect to tactile sensations, as the tips of the fingers them- selves. It can recognize the two points of the compasses when separated not more than one-twenty-fourth of an inch ; the back of it is much less sensitive to touch, while at the same time it is more highly sensitive to impressions of taste. 31. Each lateral half of the tongue resembles the other in structure, and each receives the same number of nerves three. One of these regulates motion, the other two are nerves of special sense. One of the latter supplies the front half of the tongue, and is called the gustatory nerve. This is a branch of the great cranial nerve, called the "fifth pair," which ramifies in all parts of the face. The back of the tongue is endowed with the power of taste through a nerve known as the glosso-pliaryngeal, because it is distributed both to the tongue and throat. This dif- ference in the nervous supply of the tongue becomes signif- icant, when we learn, as we shall presently, that each part of it perceives a different class of flavors. 32. The Sense of Taste. Taste is the special sense by means of which we discover the savors, or flavoring properties of the substances, which come in contact with the tongue. Mere contact with the surface of the tongue, however, is not sufficient, but contact with the extremities of the nerves of taste within the papillae is required. In order that the substance to be tasted may penetrate the 31. Resemblance tn the parts of the tongue? Powers and functions of thf pa/tp ? J2. Taste ? What are the requisites? to taste ? 190 THE SPECIAL SENSES. cells covering the nerves, it must either be liquid in form, or readily soluble in the watery secretion of the mouth, the saliva. The tongue must be moist also. If the sub- stance be insoluble, as glass or sand, or the tongue dry, the sense of taste is not awakened. In sickness, when the tongue is heavily coated, the taste is very defective, or, as is frequently expressed, " nothing tastes aright." 33. All portions of the tongue are not alike endowed with the sense of taste, that function being limited to the posterior third, and to the margin and tip of this organ. The soft palate, also, possesses the sense of taste ; hence, an article that has an agreeable flavor may very properly be spoken of as palatable, as is often done. All parts of the tongue do not perceive equally well the same flavors. Thus, the front extremity and margin, which is the por- jion supplied by the "fifth pair" of nerves, perceives more acutely sweet and sour tastes; but the base of the tongue, supplied by the glosso-pliaryngeal nerve, is especially sen- sitive to salt and bitter substances. The nerve of the front part of the tongue, as before stated, is in active sympathy with those of the face, while the relations of the other nerve are chiefly with the throat and stomach ; so that when an intensely sour taste is perceived, the countenance is involuntarily distorted, and is said to wear an acid ex- pression. On the other hand, a very bitter taste affects certain internal organs, and occasions & sensation of nau- sea, or sickness of the stomach. (Read Note 2.) 34. Relations of Taste with other Senses. Taste is not a simple sense. Certain other sensations, as those of touch, temperature, smell, and pain, are blended and confused with it; and certain so-called tastes are really sensations of another kind. Thus an astringent taste, like that of alum, is more properly an astringent feeling, and 33. Portions of the tongue endowed with taste? Where else does the sense !odr ? What is stated in respect to sweet and hitter flavors ? Reflex effects men- tioned ? 34 1 What is stated of the relations of tasty with other sense.s ? THE SPECIAL SENSES. 191 results from an impression made upon the nerves of touch, that ramify in the tongue. In like manner, the qualities known as smooth, oily, watery, and mealy tastes, are depend- ent upon these same nerves of touch. A burning or pungent taste is a sensation of pain, having its seat in the tongue and throat. A cooling taste, like that of mint, pertains to that modification of touch called the sense of temperature. 35. Taste is largely dependent upon the sense of smell. A considerable number of substances, like vanilla, coffee, and garlic, which appear to possess a strong and distinct flavor, have in reality a powerful odor, but only a feeble taste. When the sense of smell is interfered with by hold- ing the nose, it becomes difficult to distinguish between sub- stances of this class. The same effect is frequently observed when smell is blunted during an ordinary cold in the head. Sight also contributes to taste. With the eyes closed, food appears comparatively insipid; and a person smoking tobacco in the dark is unable to determine by the taste whether his cigar is lighted or not. Accordingly, it is not a bad plan to close the nose and shut the eyes when about to swallow some disagreeable medicine. 36. Influence of Education on the Taste. The chief use of the sense of taste appears to be to act as a guide in the selection of proper food. Hence its organs are properly placed at the entrance of the digestive canal. As a general rule, those articles which gratify the taste are wholesome ; while the opposite is true of those which im- press it disagreeably. This statement is more exact in reference to the early years of life than to later years, when, by reason of mischievous habits, the sense of taste has become dulled or perverted. The desires of a child are simple ; he is fully satisfied with plain and wholesome articles of diet, and must usually "learn to like" those 35. Its dependence on smell? on sight ? 36. The chief use of the sense of taste? The position of its organs ? The rule as regards wholesome and unwholesome food ? Remarks respecting the rule? 1.92 THE SPECIAL SENSES. which, have a strongly marked flavor. Accordingly, it is far easier at this age to encourage the preference for plain food, and thus establish healthful habits, than later in life to uproot habits of indulgence in stimulating substances, after their ill effects begin to manifest themselves. 37. The tastes of men present the most singular diversi- ties, partly the result of necessity and partly of habit or education. The Esquimaux like the rank smell of whale oil, which is a kind of food admirably suited to the require- ments of their icy climate ; and travellers who go from oui climate to theirs are not slow to develop a liking for the same articles that the natives themselves enjoy. The sense of taste is rendered very acute by education, as is shown in an especial manner by those who become professional " tasters" of tea and wine. 38. The Sense of Smell the Nasal Cavities. The sense of smell is located in the delicate mucous membrane which lines the interior of the nose. That prominent feature of the face, the nose, which is merely the front boundary of the true nasal organ, is composed partly of bone and partly of cartilage. The upper part of it is united with the skull by means of a few small bones ; to which circumstance is due its permanence of shape. The lower portion, or tip of the nose, contains several thin pieces of cartilage, which render it flexible and better able to resist the effects of blows and pressure. Behind the nose we find quite a spacious chamber, separated from the mouth by the hard palate, forming the "roof of the mouth," and by the soft palate (see Fig. 46) ; and divided into two cavities by a central partition running from be- fore backward. 39. These nasal cavities, constituting the true beginning of the air-passages, extend from the nose backward to the- 37. Diversity in tastes of men ? How shown ? The education of the sense ol taste? 38. Location of the sense of smell? The nose? " Roof of the mouth?" 39 1 Cavities of the nose '( Obstruction of the passage of air through them ? THE SPECIAL SENSES. 193 upper opening of the throat, and rise as high as the junc- tion of the nose with the forehead. The inner wall of each cavity is straight and smooth ; but from the outer wall there jut into each cavity three small scroll-like bones. The structure of these bones is very light, and hence they have been called the " spongy" bones of the nose. In this manner, while the extent of surface is greatly in- creased by the formation of these winding passages, the cavities are rendered extremely narrow ; so much so, in fact, that a moderate swelling of the mucous membrane which lines them, as from a cold, is sufficient to obstruct the pass- age of air through them. 40. The Nerve of Smell. The internal surface of the nasal passages is covered by a delicate and sensitive mucous membrane. Its surface is quite extensive, follow- ing as it does, all the inequalities produced by the curved spongy bones of the nose. The upper portion of it alone is the seat of smell, since that part alone receives branches from the "first pair" of cranial nerves, or the olfactory nerve, which is the special nerve of smell (see Fig. 43). v In Fig. 46 is shown the distri- bution of this nerve, in the form of an intricate network upon the two upper spongy bones. The nerve itself (1) does not issue from the skull, but rests upon a thin bone which separates it from the cavity of the nose; and the branches which proceed from it pass through this bone by means of numerous small openings. The en- FIG. 46. SECTION OF THE RIGHT NASAL CAVITY. 40. The special nerve of smell ? Its location ? r 194: THE SPECIAL SENSES. graving represents the outer surface of the right nasal cavity; the three wave-like inequalities, upon which the nervous network is spread out, are due to the spongy bones. ^The left cavity is supplied in the same manner. 41. The nerves which ramify over the lower part of the membrane, and which endow it with sensibility to touch and pain, are branches of the " fifth pair" of nerves. An irritation applied to the parts where this nerve is distrib- uted occasions sneezing, that is, a spasmodic contraction of the diaphragm ; the object of which is the expulsion of the irritating cause. The manner in which the olfactory nerve-fibres terminate is peculiar. Unlike the extremities of other nerves, which are covered in by a greater or less thickness of tissue, these come directly to the surface of the mucous membrane, and thus come into very close con- tact with the odorous particles that are carried along by the respired air. The surface is at all times kept in a moist condition by an abundant flow of nasal mucus ; otherwise it would become dry, hard, and insensitive from the con- tinual passage of air to and fro in breathing. Birds, which respire more actively than men, have a special gland, for secreting a lubricating fluid, located in the air- passages of the head. 42. The Uses of the Sense of Smell, Smell is the special sense which enables us to appreciate odors. Touch, as we have seen, is largely concerned with solid bodies; and taste, with fluids, or with solids in solution. Smell, on the other hand, is designed to afford us informa- tion in reference to substances in a volatile or gaseous form. Invisible and subtile particles emanate from odor- ous bodies, and are brought by the respired air in contact with the terminal filaments of the olfactory nerve, upon which an agreeable or disagreeable impression is. produced. 4 1 . Branches of the " fifth pair 11 of nerves ? Nasal mucus ? Birds ? 42. Smell? Touch? Taste? Design of smell ? Invisible and #a>eous parti cles ? The extreme fineness of the particles 1 Musk ? Ju gther cases ? THE SPECIAL SENSES. 195 The fineness of the particles that constitute odors is often so extreme, that they elude all attempts to measure or weigh them. A piece of musk, for instance, may be kept for sev- eral years, constantly emitting perfume, without any ap- preciable loss of weight. In other cases, a loss of substance is perceptible, such as the essential oils, which enter into the composition of the ordinary perfumes. 43. Smell, like taste, aids us in the choice of proper food, leading us to reject such articles as have a rank or putrid odor, and which are, as a rule, unfit to be eaten. The highest usefulness of this sense, however, consists in the protection it affords to the organs of respiration. Sta- tioned at the gateways of the air-passages, it examines the current of air as it enters, and warns us of the presence of noxious gases, and of other and generally invisible ene- mies to health. Not all dangerous vapors are offensive, but almost all offensive vapors are unfit to be breathed. A number of small stiff hairs grow from the margin of the nostrils to prevent the entrance of dust and other at- mospheric impurities, which would be alike injurious to the olfactory mucous membrane and to the lungs. The benev- olent design of the Maker of our bodies may be observed in all parts of their mechanism ; but, probably, in none is it more clearly displayed than in connection with the sense of Smell. (Read Note ^ 44. The sense of smell is developed in a remarkable de- gree in certain of the inferior animals, and is especially acute in reference to the peculiar emanations that appear to characterize the different animals. The lion and other carnivorous beasts scent their prey from a great distance; and the fox-hound is able to track the fox through thickets and over open country for many miles ; while the timid, helpless herbivora, such as the deer and sheep, find in the 43. Aid given by nmell? The highest nse of the sense? Explain the manner. 44. Sense of smell in the inferior animals? How, and iu what cases, toted* 196 THE SPECIAL SENSES. sense of smell a means of protection against their natural enemies, of whose approach they are in this manner warned. By training this sense in the dog, and making it subservi- ent to his use, man is able to hunt with success certain shy and very fleet animals, which otherwise he could but sel- dom approach. Among men, individuals differ greatly in respect to the development of this sense; and especially in certain savage tribes it is found to be extremely deli- cate. Humboldt states that the natives of Peru can, by this sense, distinguish in the dark between persons of dif- ( ferent races. (Read Note 4.) p 45. The Sense of Sight. Sight, or Vision, is the / special sense by means of which we appreciate the color, form, size, distance, and other physical properties of the objects of external nature. Primarily, this sense furnishes us with information concerning the different shades of color and the different degrees of brightness: these are the simple sensations of sight, such as the yellowness and glitter of a gold coin. In addition to these, there are com- posite visual sensations, produced by the joint action of the other senses and by the use of the memory and judg- ment; such as, in the case of the coin, its roundness, solidity, size, its distance and direction from us. So that many jof our sensations, commonly considered as due to sight, are in reality the results of intellectual processes which take place instantaneously and unconsciously. 46. This faculty not only has value in the practical every-day affairs of life, but it contributes so largely to the culture of the intellect and to our higher forms of pleasure, that some writers are disposed to rate it as the first and most valuable of the senses. Others, however, maintain that the sense of hearing does not yield in importance to that of sight; and they cite in support of their position 45. What is sight ? What information docs it furnish ? Composite visual sen- 46. Comparison between sight and hearing? Relative capacity of deaf and THE SPECIAL SENSES. 197 the fact that the blind are commonly cheerful and gay, while the deaf are inclined to be morose and melancholy. In respect to the relative capacity for receiving education in the deaf and blind, it is found that the former learn more quickly, but their attainments are not profound; while the blind acquire more slowly, but are able to study more thoroughly. 47. Light. The Optic Nerve. Unlike the senses previously considered touch, taste, and smell sight does not bring us into immediate contact with the bodies that are examined; but, by it, we perceive the existence and qualities of objects that are at a greater or less distance from us. In the case of the stars, the distance is incalcu- lable, while the book we read is removed but a few inches Light is the agent which gives to this sense its wide range. The nature of this mysterious force is not known, and it is not here to be discussed; since its study belongs more properly to the province of natural philosophy. 48. It is sufficient, in this connection, to state that the theory of light now generally accepted, and which best explains the facts of optics, is that known as the undula- tory theory. This theory supposes that there exists an intangible, elastic medium, which fills all space, and pene- trates all transparent substances, and which is thrown into exceedingly rapid undulations or waves, by the sun and every other luminous body ; the undulations being propa- gated with extreme rapidity, and moving not less than 186,000 miles in a second. 49. These waves are thought to produce in the eye the sensation of light, in the same manner as the sonorous vibrations of the air produce in the ear the sensation of sound. That part of the eye which is sensitive to these waves is the expansion of the optic nerve. It is sensitive 47. Sight, unlike the oth^r pauses? In the case of the stars ? 48. The umlulatory theory ol'liuct is shown by the dotted /ine. The * marks the orifice iu the lower lid. 54. The Eyelids. The eyelids are two movable cur- tains, or folds, which, when shut, cover the front part of the orbit, and hide the eye from view. The up- per lid is the larger, has a curved margin, and moves freel} 7 , while the lower lid is comparatively short and straight, and has but a slight degree of motion (Fig. 47). Skin covers the exterior of the lids, while a fine mucous membrane lines their in- ner surface, and is like- The central black spot is the pupil; sur- -WICA crvrpo/l nnf nvpr flip rounding it is the iris; and the triangular W1S6 s P reatl out ^ er tne SiS^ paces are the visible portion Ol the entire front of the eye- ball. This membrane, which is called the Conjunctiva, is highly sensitive, and thus plays an important part in protecting the eye against the lodgment of sand, ashes, chaff, and other foreign parti- cles that are blown about in the air. This sensitive mem- brane will not endure the presence of these particles. If any find access, it causes a constant winking, a flow of tears, and other signs of irritation, until it is removed. 55. The long, silky eyelashes, which garnish the edges of the lids, act like a sieve to prevent the entry of dust and the like; and together with the lids, they regulate the amount of light which is permitted to enter the eye, so that it is shielded from a sudden flood or glare of light. The little points seen in the figure just within the line of the lashes, especially on the lower lid, represent the mouths of numer- ous little sebaceous glands (Fig. 48, D,D), such as are always 54, What are the eyelids? The upper lid? The lower one? The mucous membrane of the eye ? 55. The eyelashes ? The little points within the line of the lashes ? Of wha: use are these glands ? THE SPECIAL SENSES. 201 found in the neighborhood of hairs. These glands supply a thick, oily material which greases the edges of the lids and prevents their adhering together, and likewise prevents the overflow of the tears upon the cheek. 56. The Lachrymal Fluid, or the Tears. Just within the outer part of the bony arch cf the brow, where the bone may be felt to be sharper than in other positions, is lodged a little organ called the lachrymal gland, the sit- uation of which is indicated in Fig. 4t, 1. This is the gland whence flows the watery secretion, commonly called the tears, which is designed to perform an exceedingly im- portant duty in lubricating the lids, and in keeping the exposed surface of the eyeball moist and transparent. For, without this or some similar liquid, the front of the eye would speedily become dry and lustreless, like that of a Ssh which has been removed from the water : the simple exposure of the eye to the air would then suffice to destroy vision. 57. This secretion of the tears takes place at all times, during the night as well as the day; but it is seldom noticed, except when under the influence of some strong mental emotion, whether of sorrow or happiness, it is poured forth in excess, so as to overflow the lids. Strong light or a rapid breeze will, among many other causes, ex- cite the flow of the tears. That portion of this secretion which is not used in moistening the eye is carried off into the nose by a canal situated near the inner angle of the eye, called the nasal duct. This duct is shown in Fig. 47, 2, and is connected with each lid by delicate tubes, which are indicated by dotted lines in the figure ; the as- terisk marks the little opening in the lower lid, by which the tears enter the nasal duct. By gently turning the inner part of that lid downward, and looking in a mirror, 5 6. The location of the lachrymal gland ? The use of the gland ? 57. When does the secretion of the tears occur? The secretion not used for the eye? Location o*' the nasal duct? It* uso? The overflow of tears in old people 2 202 THE SPECIAL SENSES. this small "lachrymal point" may be seen in your own eye. In old people, these points become everted, and do not conduct the tears to the nasal cavity, so that they are inconvenienced by an overflow of tears upon the face. 58. Thus we observe that the gland which forms the tears is placed g.t the outer part of the eye, while their means of exit is at the inner angle of the eye ; which fact renders it necessary that this watery fluid shall pass over the surface of the eyeball before it can escape. This ar- FIG. 48. VERTICAL SECTION OF THE EYE. (Enlarged.) C, The Cornea. A, The Aqueous Humor. I, The Iris. P, The Pupil. L, The Crystalline Lens. H, The Ligament of the Lens. B, The Ciliary Process. V, The Cavity containing the Vit- reous Humor. S, The Sclerotic. Ch, The Choroid. R, The Retina. N. The Optic Nerve- DD, The Eyelids. X, The Levator Muscle of the Upper Lid. Y, The Upper Straight Muscle of the Eye. Z, The Lower Straight Muscle. rangement cannot be accidental, but evinces design, for it thus secures the perfect lubrication of the surface of the eve, and cleanses it from the smaller particles of dust 58. The watery fluid passing over the eyeball ? Design of the arrangement > Winking ? THE SPECIAL SENSES. 203 which may enter it, in spite of the vigilance of the lids and lashes. The act of winking, which is generally un- consciously performed, and which takes place six or more times in a minute, assists this passage of the tears across the eye, and is especially frequent when the secretion is most abundant. 59. The Eyeball. The remarkable optical instru- ment called the eyeball, or the globe of the eye, upon which sight depends, is, as the name indicates, spherical in shape. It is not a perfect sphere, since the front part pro- jects somewhat beyond the rest, and at the posterior part the optic nerve (Fig. 48, N") is united to it, resembling the junction of the stem with a fruit. In its long diameter, that is, the horizontal or from side to side, it measures a little more than an inch ; in other directions it is rather less than an inch. In structure, the ball of the eye is firm, and its tense round contour may in part be felt by pressing the fingers over the closed lids. /* 60. The eyeball is composed chiefly of three internal, transparent media, called humors; and three investing coats, or tunics. The former are the aqueous humor, Fig. 48, A, the crystalline lens L, and the vitreous humor v. Of these the lens alone is solid. The three coats of the eyeball are called the sclerotic s, the choroid CH, and the retina R. This arrangement exists in respect to five-sixths of the globe of the eye, but in the anterior one-sixth, these coats are replaced by the cornea c, which is thin and trans- parent, so that the rays of light pass freely through it, as through a clear window-pane. A 61. In shape, the cornea is circular and prominent, ' resembling a miniature watch-glass, about % of an inch thick. In structure, it resembles horn (as the name signi- fies), or the nail of the finger, and is destitute of blood- 59. Depcrilv 1 the shape of th" ovob.ill. It? structure. 60. Of what if the eyeball composed!' State how. 61. The shape of the cornea 'i Its structure '* The " white of the eye r 204 THE SPECIAL SENSES. vessels. The Sclerotic (from scleros, hard) is composed of dense, white fibrous tissue, and gives to the eyeball its firmness of figure and its white color; in front, it consti' tutes the part commonly called "the white of the eye." It is one of the strongest tissues in the body; it possesses very few vessels, and is not very sensitive. It affords pro- tection to the extremely delicate interior parts of the eye ; and the little muscles which effect its movements are in- serted into the sclerotic a short distance behind the cornea (see Fig. 48, Y, z). It is perforated posteriorly to admit the optic nerve. k 62. The Choroid is the second or middle coat of the eye- ball, and lies closely attached to the inner surface of the sclerotic. Unlike the latter tunic, its structure is soft and tender, it is dark in color, and possesses a great abundance of blood-vessels. Its dark color is due to a layer of dark brown or chocolate-colored cells spread out over its inner surface. This dark layer serves to absorb the rays of light after they have traversed the transparent structures in front of it ; if the rays were reflected from side to side within the eye, instead of being thus absorbed, confused vision would result from the multitude of images which would be impressed upon the optic nerve. 63. This mechanism has been unconsciously imitated by the opticians, who, when they make a microscope or tele- scope, take care that the interior of its tube shall be coated with a thick layer of black paint or lamp-black; for with- out it, a clear delineation of the object to be viewed is im- possible. The albinos, in whom these dark cells of the choroid are wanting, have imperfect vision, especially in the daytime and in strong lights. The dark cells are also wanting in white rabbits, and other animals that have red or pink eyes ; their vision appears to be imperfect in the presence of a bright light. 62. The second or middle coat of the eyeball ? Its dark color? 63. Similar mechanism in microscopes ? The albinos ? THE SPECIAL SENSES. 205 64. The Iris. Continuous with the choroid, in the front part of the globe of the eye, is a thin, circular curtain, which occasions the brown, blue, or gray color of the eye in different individuals. On account of the varieties of its color, this membrane has received the name Iris, which is the Greek word for " rainbow" (see Fig. 48, i). A front view of it is shown in Fig. 47. The iris is pierced in its centre by a round opening, called tine pupil (P), which is constantly varying in size. In olden times it was spoken of as the " apple of the eye." The hinder surface of the iris, except in albinos, has a layer of dark coloring matter resembling that of the choroid. The iris is a muscular organ, and contains two distinct sets of fibres; one of which is circular, while the other radiates outward from the pupil. The action of these sets of fibres regulates the size of the pupil ; for when the circular set acts, the pupil contracts, and when the other set acts, the opening expands. Their action is involuntary, and depends on the reflex system of nerves, which causes the contraction of the pupil when a strong light falls upon the eye, and its expansion when the illumination is feeble. 65. The iris, accordingly, serves a very useful purpose in regulating the admission of light to the eye. It, how- ever, does not act instantaneously; and hence, when we pass quickly from a dark room into the bright sunlight, the vision is at first confused by the glare of light, but as soon as the pupil contracts, the ability to see becomes per- fect. On the other hand, when we enter a dark apart- ment, such as a cellar, for a short time we can see nothing clearly ; but as soon as the pupil expands and admits more light, we are enabled to distinguish the surrounding ob- jects. Animals of the cat species, and others which prowl around after nightfall, are enabled to see in the dark by 64. What is the iris ? Its construction ? How is the size of the pupil regu- lated ? 65. The admission of light to the eye ? The action of the iris under different circumstances ? The lustre of the eye, Iiow'affected in youth and old age ? 206 THE SPECIAL SENSES. having the iris very dilatable. The size of the pupil affects the lustre of the eye. When it is large, as it usually is dur- ing youth, the eye appears clear and brilliant ; while in old age the pupil is small and the eye is dull. The brilliancy of the eye is in part, at least, dependent upon the reflec- tion of light from the front surface of the crystalline lens. 66. Certain poisonous vegetables have the property of causing the pupil to dilate, and have been used in small doses to increase the beauty of the eye. One of these drugs has been so largely used by the ladies for this pur- pose, that it has received the name belladonna, from the Italian words meaning " beautiful lady." This hazardous practice has resulted more than once in the death of the person desiring thus to increase her personal attraction. The common English name for belladonna is "deadly nightshade." (In the diagram on page 214 the shape and relations of the iris are more accurately shown than in the figure referred to above.) 67. The Retina constitutes the third and inner coat of the globe of the eye. This, the important part of the eye that is sensitive to light, is a kind of nervous membrane, formed by the expansion of the ultimate filaments of the optic nerve. Its texture is soft, smooth, and very thin; it is translucent and of an opaline, or grayish-white color. It is sensitive to light alone ; and if any form of mechanical irritation be applied to it, the sensations of touch and pain are not experienced, but flashes of fire, sparks, and other luminous appearances are perceived. Thus an electric shock given to the eye-ball occasions a flash of light; and a sudden fall, or a blow upon the eye, is often apparently accompanied by the vision of "stars." 68. These phenomena are due to what is termed the 66. Means used to increase the beauty of the eye? The injurious conse qiumces * 67. What part does the retina constitute ? How formed ? Its texture ? Color ? Sensitiveness ? 68. Specific energy of the optic nerve ? Trial in Germany ? THE SPECIAL SENSES. 207 " specific energy" of the optic nerve, which nerve, in com- mon with the other nerves of special sense, obeys a general law of nature, which requires that, whenever one of these nerves is stimulated, it shall respond with the sensation peculiar to itself. These flashes of retinal light have no power to illuminate external objects, although the opposite of this statement has been maintained. On the occasion 'of a remarkable trial in Germany, it was claimed by a per- son who had been severely assaulted on a very dark night, that the flashes of light caused by repeated blows upon the head enabled him to see with sufficient distinctness to recognize his assailant. But the evidence of scientific men entirely refuted this claim, by pronouncing that the eye, under the circumstances named, was incapacitated for vision. Too intense light occasions a feeling of pain, but it is of a peculiar kind, and is termed "dazzling." 69. All parts of the retina are not equally sensitive, and singularly enough, the point of entry of the nerve of sight, in the back part of the eyeball, is entirely insensible to light, and is called the " blind spot." The existence of this point may be proven by a simple experiment. Hold the accom- FIG. 49. panying figure, on page 207, directly in front of and paral- lel with the eyes. Close the left eye, and fix the sight steadily on the left-hand circle ; then, by gradually varying the distance of the figure from the eye, at a certain dis- tance (about six inches), the right-hand circle will disappear, 69. Sensitiveness of all parts of the retina? Experiment to prove the existr ence of the "blind spot." 208 THE SPECIAL SENSES. but nearer or further than that, it will be plainly seen. The other eye may be also tried, with a similar result : if the gaze be directed to the right-hand circle, the left one will seem to disappear. The experiment may be repeated by using two black buttons on the marble top of a .bureau, or on some other white surface. The blind spot does not practically interfere with vision, since the eye is seldom fixed immovably on an object, and the insensitive parts of the two eyes can never be directed upon the same object at the same time. 70. Impressions made upon the retina are not at once lost, but persist a measurable length of time, and then gradually fade away. Thus, a bright light or color, gazed at intently, cannot be immediately dismissed from sight by closing or turning away the eyes. A stick lighted at one end, if whirled around rapidly in the dark, presents the appearance of an unbroken luminous ring; and the spokes of a rapidly revolving carriage-wheel seem to be merged into a plane surface. If an object move too rapidly to pro- duce this sort of lasting impression, it is invisible, as in the case of a cannon-ball passing through the air in front of us. 71. If a card, painted with two primary colors as red and yellow be made to rotate swiftly, the eye perceives neither of them distinctly ; but the card appears painted with their secondary color orange. The average duration of retinal images is estimated at one-eighth of a second ; and it is because they thus endure, that the act of winking, which takes place so frequently, but so quickly, is not noticed and does not interrupt the vision. The retina is easily fatigued or deprived of its sensibility. After looking steadfastly at a bright light, or at a white object on a black ground, a dark spot, corresponding in shape to the bright object, 70. Duration of impressions npon the retina ? How illustrated ? 71. What further illustration? Winking, why it is not noticed. Ease wit' which the retina is fatigued or deprived of sensibility ? How shown ? THE SPECIAL SENSES. 209 presents itself in whatever direction we look. This spot passes away as the retina resumes its activity. 72. If a bright color be gazed at intently, and the eyes then be turned to a white surface, a spot will appear ; but its color will be the complement of that of the object. Fix the eye upon a red wafer upon a white ground, and on re- moving the wafer a greenish spot of the same shape takes its place. This result happens because a certain portion of the retina has exhausted its power to perceive the red ray, and perceives only its complementary ray, which is green. The color thus substituted by the exhausted retina is called a physiological or accidental color. In some persons the retina is incapable of distinguishing different colors, when they are said to be affected with " color-blindness." Thus, red and green may appear alike, and then a cherry-tree, full of ripe fruit, will seem of the same color in every part. Railroad accidents nave occurred because the engineer of the train, who was color -blind, has mistaken the color of a signal. (Read Note 9, end of Chapter?) A 73. The Crystalline Lens. Across the front of the eve, just behind the iris, is situated the Crystalline lens, enclosed within its own capsule. It is supported in its place partly by a delicate circular ligament, and partly by the pressure of adjacent structures. It is colorless and per- fectly transparent, and has a firm but elastic texture. In shape it is doubly convex, and may be rudely compared to a small lemon-drop. The front face of the lens is flatter than the other, and is in contact with the iris near its pupillary margin, as is represented in the diagram on page 214. It is only one-fourth of an inch thick. A 74. When this little body becomes opaque, and no longer affords free passage to the rays of light, as often happens 72. How further shown? How is the result accounted for? "Color-blind- ness?" 73. The location of the crystalline lens? How supported? Its color and texture ? Shape ? Size ? 74. Cataract? Aqueous humor ? Vitreous humor ? 210 THE SPECIAL with the advance of age, an affection termed " cataract" is produced. Between the crystalline lens and the cornea is a small space which contains the aqueous humor (see Fig. 48, A). This humor consists of five or six drops of a clear, colorless liquid very much like water, as its name implies. That part of the globe of the eye lying behind the lens is occupied by the vitreous humor, so called from its fancied resemblance to melted glass (Fig. 48, v). This humor is a transparent, jelly-like mass, enclosed within an exceed- ingly thin membrane. It lies very closely applied to the retina, or nervous membrane of the eye, and constitutes fully two-thirds of the bulk of the eyeball. ^ 75. The Uses of the Crystalline Lens. A con- vex lens has the property of converging the rays of light which pass through it; and the point at which it causes PIG. 50. THE RETINAL IMAGE. them to meet is termed its focus. If a lens of this descrip- tion, such as a magnifying or burning-glass, be held in front of an open window, in such a position as to allow its focus to fall upon a piece of paper, it will be found to depict upon the paper a miniature image of the scene out- side of the window. It will be further noticed that the image is inverted, or upside down, and that the paper 75. What is a lens and its focufl ? i'he miniature image, how produced? THE SPECIAL SENSES. at the place upon which the image is thrown is much brighter than any other part. 76. Now all the transparent structures of the eye, but especially the crystalline lens, operate upon its posterior part, or retina, as the convex lens acts upon the paper; that is, they paint upon the retina a bright inverted miniature of the objects that appear in front of the eye (Fig. 50). That this actually takes place may be proved by experi- ment. If the eyeball of a white rabbit, the walls of which are transparent, be examined while a lighted candle is held before the cornea, an image of the candle-flame may be seen upon the retina. 77. The form and structure of the crystalline lens endow it with a remarkable degree of refractive power, and en- able it to converge all the rays of light that enter it through the pupil, to a focus exactly at the surface of the retina. When this lens is removed from the eye, as is frequently done for the cure of cataract, it is found that the rays of light then have their focus three-eighths of an inch behind the retina; that the image is four times larger than in the healthy eye, that it is less brilliant, and that its outline is very indistinct. From this we learn that one of the uses of the crystalline lens is to make the retinal image bright and sharply-defined, at the same time that it reduces its size. Indeed, the small size of the image is a great advantage, as it enables the limited surface of the retina to receive, at a glance, impressions from a consider- able field of vision. 78. As the image upon the retina is inverted, how does the mind perceive the object in its true, erect position ? Many explanations have been advanced, but the simplest and most satisfactory appears to be found in the fact that 76. How are figures painted upon the retina ? How proved ? 77. What can be said in respect to the form and structure of the crystalline lens? 78. How is the inverted image upon the retina presented in its true position to the mind ? 212 THE SPECIAL SENSES. the retina observes no difference, so to speak, between the right and left or the upper and lower positions of objects. In fact, the mind is never conscious of the formation of a retinal image, and until instructed, has no knowledge that it exists. Consequently, our knowledge of the relative location of external objects must be obtained from some other source than the retina. The probable source of this knowledge is the habitual comparison of those objects with the position of our own bodies: thus, to see an elevated object, we know we must raise the head and eyes ; and to see one at our right hand, we must turn the head and eyes to the right. 79. Long-sight or Hyperopia, and Short-sight or Myopia. The eye is not in ali cases perfectly formed. For example, persons may from birth have ths comea too prominent or too flat, or the lens may be too th ick or too thin. In either of these conditions sight will FIG. SI. THE DIFFERENT SHAPES OF THE GLOBE OF THE EYB. N, The Natural Eye. M, The Short-sighted Eye. H, The Long-sighted Eye. S, Parallel Rays from the Sun. be more or less defective from the first, and the defect will not tend to disappear as life advances. The most common imperfection, however, is in the shape of the globe ; which may be short (Fig. 5j., H), as compared with the natural eye, K, or it may be too long, M. 80. When the globe is short, objects can only be clearly 79. The uniform perfection of the eye? Examples? The most common im- perfection? 80. How is " Ions-sight 11 explained ? " Short-sight ?" THE SPECIAL SENSES. 213 seen that are at a distance, and the condition of the vision is known as "long-sight," or hyperopia. It will be ob- served, by reference to Fig. 51, that the focus of the rays of light would fall behind the retina of this eye. When the globe is too long, objects can only be clearly seen that are very near to the eye; and the condition resulting from this defect is termed "short-sight," or myopia. The focus of the rays of light is, in this case, formed in the interior of the eye in front of the retina. 81. Long-sight, or hyperopia, is common among school- children, nearly as much so as short-sight, and must not be confounded with the defect known as the "far sight" of old people; although in both affections the sight is im- proved by the use of convex glasses. Children not infre- quently discover that they see much better when they chance to put on the spectacles of old persons. For the relief of short-sight, concave glasses should be employed; as they so scatter the rays of light as to bring the focus to the retina, and thus cause the vision of remote objects to become at once distinct. That form of "squint," in which the eyes are turned inward, is generally dependent upon long-sight, while that rarer form, when they turn outward, is due to short-sight. (Read Note 5.) 82. The Function of Accommodation. If, after looking through an opera-glass at a very distant object, it is desired to view another nearer at hand, it will be found impossible to obtain a clear vision of the second object un- less the adjustment of the instrument is altered; which is effected by means of the screw. If an object, like the end of a pencil, be held near the eye, in a line with another object at the other side of the room, or out of the window, and the eye be fixed first apon one and then upon the other, it will be found that when the pencil is clearly seen, the fur- 8 1 . Lon round mustard mixed with warm water, or some other active ernet V 250 APPENDIX. and after its operation an active purgative should be given. Aftei evacuating as much of the poison as possible, strong coffee or vinegar and water may be given with advantage. Poisonous Fish. Conger eel, mussels, crabs, etc. ANTIDOTE. Evacuate, as soon as possible, the contents of the stom- ach and bowels by emetics (ground mustard mixed with warm water or powdered alum), and castor oil, drinking freely at the same time of vinegar and water. Ether, with a few drops of laudanum mixer, with sugar and water, may afterward be taken freely. Poisonous Serpents. ANTIDOTE. A ligature or handkerchief should be applied moderately tight above the bite, and a cupping-glass over the wound. The patient should drink freely of alcoholic stim ulants containing a small quantity of ammonia. The physician may inject ammonia into the veins. Poisonous Insects. Stings of scorpion, hornet, wasp, bee, etc. ANTIDOTE. A piece of rag moistened with a solution of carbolic acid may be kept on the affected part until the pain is relieved ; and a few drops of carbolic acid may be given frequently in a little water. The sting may be removed by making strong pressure around it with the barrt. ^f a small watch-key. DROWNING. MARSHALL HALL'S " READY METHOD" of treatment in asphyxia from drowning, chloroform, coal gas, etc. 1st. Treat the patient instantly on the spot, in the open air, freely exposing the face, neck, and chest to the breeze, except in severe weather. 2d. In order to clear the throat, place the patient gently on the face, with one wrist under the forehead, that all fluid, and the tongue itself, may fall forward, and leave the entrance into the windpipe free. 3d. To excite respiration, turn the patient slightly on his side, and apply some irritating or stimulating agent to the nostrils, as ver sphaim, a sphere). Halt a sphere, the lateral halves of the cerebrum, or brain proper. HE- PAT' ic (Gr. rfTtap, Jiepar y the liver). Pertaining to the liver. HER-BIV'O-ROUS (L. her'ba, an herb, and r><> ' ro to devour). Applied to animals that subsist upon vegetable food. HU'MOR (L.). Moisture: the humors are transparent contents of the eyeball. HY-DRO-PHO'BI-A (Gr. vdop, hudor, water, and , ap.% the eye). A defect of vision dependent upon a too short eyeball ; so called because the rays of light are brought to a focus at a point behind the retina ; the true " far sight." LN-CI'SOR (L. ind'do, to cut). Applied to the four front teeth of both jaws, which have sharp cutting edges. LN'CUS (L). An anvil ; the name of one of the bones of the middle ear. LN-SAL-I-VA'TION (L. in, and salfva, the fluid of the mouth). The mingling of the saliva with the food during the act of chewing. IN-SPI-RA'TION (L. in, and spi'ro, spira'tum, to breathe). The act of drawing in the breath. IN-TEG'U-MENT (L. in, and te'go, to cover). The skin, or outer covering of the body. IN-TES'TINE (L. m'tus, within). The part of the alimentary canal which is continuous with the lower end of the stomach ; also called the intestines, or the bowels. I'RIS (L. fris, the rainbow). The thin muscular ring which lies be 2-58 GLOSSARY. tween the cornea and crystalline lens, and which gives the eye its brown, blue, or other color. JD'GU-LAR (Tj.ju'gulum, the throat). The name of the large veins which run along the front of the neck. LAB'Y-RINTH (Gr. kafidpivSoS, laburirithos, a building with many grinding passages). The very tortuous cavity of the inner ear, comprising the vestibule, semicircular canals, and the cochlea. LACH'RY-MAL APPARATUS (L. lach'ryma, a tear). The organs for forming and conveying away the tears. LAC'TE-ALS (L. lac, lac'tis, milk). The absorbent vessels of the small intestines ; during digestion they are filled with chyle, which has a milky appearance. LA-RYN'GO-SCOPE (Gr. Xdpvyt,, larunx, the larynx, and tixoTteca, akopeo, to look at). The instrument by which the larynx may be examined in the living subject. LAR'YNX (Gr.). The cartilaginous tube situated at the top of the windpipe, or trachea ; the organ of the voice. LENS (L.). Literally, a lentil ; a piece of transparent glass or other sub- stance so shaped as either to converge or disperse the rays of light. Lie A-MENT (L. li'go, to bind). A strong, fibrous material binding bones or other solid parts together; it is especially necessary to give strength to joints. LIG'A-TURE. A thread of silk or other material used untying around an artery. LYMPH (L. lym'pTia, spring- water). The colorless, watery fluid con- veyed by the lymphatic vessels. LYM-PHAT'IC VESSELS. A system of absorbent vessels. MAL'LE-US (L.). Literally, the mallet ; one of the small bones of the middle ear. MAR' ROW. The soft; fatty substance contained in the central cavities of the bones : the spinal marrow, however, is composed of nervous tissue. MAS-TI-CA'TION (L. mas'tico, to chew). The act of cutting and grind ing the food to pieces by means of the teeth. ME-DUL'LA OB-LON-GA'TA. The " oblong marrow," or nervous cord, which is continuous with the spinal cord within the skull. MEM-BRA'NA TYM'PAN-I (L.). Literally, the membrane of the drum ; a delicate partition separating the outer from the middle ear ; it is sometimes incorrectly called the drum of the ear. MEM'BRANE. A thin layer of tissue serving to cover some pan ol the body. MT'CRO-SCOPJC (Gr. ntKpot, mikm*^ small, and tSwirsoo, skopeo, to GLOSSARY. 259 look at). An optical instrument which assists hi the examinatioD of minute objects. MO'LAR (L. mo'la, a mill). The name applied to the three back teeti of each side of the jaw ; the grinders, or mill-like teeth. MO'TOR (L. mo'veo, mo' turn, to move). Causing motion ; the namf of those nerves which conduct to the muscles the stimulus which causes them to contract Mu'cous MEM'BRANE. The thin layer of tissue which covers those in- ternal cavities or passages which communicate with the external air. Mu'cus. The glairy fluid which is secreted by mucous membranes, and which serves to keep them in a moist condition. MY-O'PI-A (Gr. X/I'GJ, muo, to contract, and o>^, ops, the eye). A de- fect of vision dependent upon an eyeball that is too long, rendering distant objects indistinct ; near-sight. NA'SAL (L. na'sus, the nose). Pertaining to the nose ; the 7iasa> cavities contain the distribution of the special nerve of smell. NERVE (Gr. vEvpov, neuron, a cord or string). A glistening, white cord of cylindrical shape, connecting the brain or spinai cord with some other organ of the body. NERVE CELL. A minute, round and ashen-gray eel 1 found in the brain and other nervous centres. NERVE FI'BRE. An exceedingly slender thread of nervous tissue found in the various nervous organs, but especially hi the nerves ; it is of a white color. NU-TRI'TION (L. nu'trio, to nourish). The processes by which the nourishment of the body is accomplished. CE-SOPH'A-GUS (Gr.). Literally, that which carries food. The tube leading from the throat to the stomach ; the gullet. O-LE-AG'I-NOUS (L. o'leum, oil). Of the nature of oil : applied to an important group of food-principles the fats. OL-FAC'TO-RY (L. olfa'cio, to smell). Pertaining to the sense of smell OPH-THAL'MO-SCOPE (Gr. o, peritrino, to stretch around). In. investing membrane of the stomach, Intestines, and oth-r ahdom- nal organs. :R-SPI-RA'TION (L. perujn'ro, to breathe through). The sweat, or watery exhalation of the skin; when vi called perspiration, when invisible, it is called intenribU pvrs S'TROUB (Gr. ne r pa t petra, a rcxik). The name of the hard portion of the temporal bone, in which is situa'.ol UK drum of the ear and labyrinth. LAR'YNX (Gr.