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/ UNIVERSITY OF CALIFORNIA 
 
 DEPARTMENT OF EDUCATION 
 
 GIFT OF THE PUBLISHER 
 
 No. Received 
 
 

 
 
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PRIMARY LESSONS 
 
 IN 
 
 HUMAN PHYSIOLOGY 
 AND HEALTH 
 
 BY 
 
 OLIVER P. JENKINS, PH.D. 
 
 PROFESSOR OF PHYSIOLOGY AND HISTOIOGY IN LELAND 
 STANFORD JUNIOR UNIVERSITY 
 
 NEW YORK : CINCINNATI : CHICAGO 
 
 Q 
 
 AMERICAN BOOK COMPANY 
 
COPYRIGHT, 1906, BY 
 OLIVER P. JENKINS. 
 
606 
 
 A WORD TO THE TEACHER 
 
 THESE lessons have been prepared as a guide to an 
 elementary study of the body and the essentials for 
 maintaining its health. It is assumed by the author 
 that the book will be used as a guide only, and that it 
 is the body and its actions and not the book that is 
 to be studied. In these years of experience in teach- 
 ing nature study and science it has long been con- 
 ceded that the objects themselves present are necessary 
 for the formation of clear conceptions, and clear con- 
 ceptions must be obtained or the whole work will be a 
 failure. It will be readily seen that there are two 
 distinct subjects of these Lessons, Physiology and 
 Hygiene. Yet on account of the youth of the students 
 the subjects are intermingled in their treatment. 
 
 Perhaps it would not be out of place at this time 
 for the author to state his firm conviction as to the 
 relation of these two subjects. 
 
 The importance of hygiene will be admitted by all; 
 but clear conceptions of its aims and teachings cannot 
 exist without a foundation in the knowledge of the 
 structure and functions of the parts to be cared for. 
 This is true for children as well as adults. The inter- 
 est in pure air and the desire to obtain it will certainly 
 be much heightened in one who has at least a few- 
 clear ideas of what it is in the air that the body needs, 
 of where in the body the need exists, and what the 
 
 3 
 
4 A WORD TO THE TEACHER 
 
 apparatus is, and how it works, that brings the oxy- 
 gen to the place at which it is needed. A knowl- 
 edge of what the muscle is like, how it is attached to a 
 bone, and how it moves, adds greatly to the interest 
 in exercise of the muscle. So with the heart, the eye, 
 and any other organ, even an elementary view of its 
 beautiful structure and the way it performs its work 
 makes the whole subject of its care more interesting 
 and definite. 
 
 One of the causes of the failure of physiology and 
 hygiene to interest pupils is the indefiniteness of much 
 of the work and the haziness of the ideas gained from 
 it. This, the author believes, can be remedied by 
 making everything as clear as possible by illustration, 
 experiment, and observation. The subject then be- 
 comes real and the knowledge usable, and these quali- 
 ties always insure a lively interest. 
 
 The recent growing interest in nature study and 
 agriculture as school subjects makes greater demands 
 on the better teaching of physiology and hygiene. 
 The structure of the bodies of the domestic animals 
 and the functions of their organs are in general the 
 same as that of the human body. The laws of health 
 apply equally to them. Their needs of exercise, 
 good air, good food, and sunshine are the same. 
 Wounds, injuries, and disease are of the same nature 
 with them as with man. It is only certain modifica- 
 tions of the general knowledge and rules that are 
 necessary in each case. Physiology, then, even the 
 most elementary, has the responsibility of being an 
 introduction to a very large field and consequently 
 requires all the care and skill that can be given to it. 
 
A WORD TO THE TEACHER 5 
 
 A word about the anatomical and other terms 
 used in this little book. The author agrees with those 
 who oppose the introduction of terms which can 
 have no meaning to the pupils after fair attention is 
 given to the subject. But it is certainly a mistake 
 to avoid the use of words which are very convenient 
 terms for things that have been actually seen. It 
 is also a mistake to substitute terms not in common 
 use for those that are the real names of the parts, on 
 a supposition that it is easier for the children. The 
 fact is that such a custom makes the work harder for 
 the pupils. The terms used in this book, as the author 
 knows by actual experience with children, are as easily 
 learned as any terms when the thing named is seen 
 and its use is understood. They are certainly fewer in 
 number and as much within the powers of the pupils 
 as are those in the other subjects in the school, num- 
 ber, language, and history, for example. 
 
 A word also about how far we can go with young 
 children in explaining various functions and pro- 
 cesses of the body. This depends much on the method 
 of teaching, and teachers would differ greatly in their 
 judgment. The author believes that as far as the 
 teacher does go, what he gives should be definite and 
 mean something. To illustrate, some might main- 
 tain that with the heart it is enough with young pupils 
 to say that it is a pump to move the blood along, etc. 
 Now, to most of the pupils the word pump conveys no 
 definite notion. How it works is wholly unknown to 
 them. Then there are many kinds of pumps. No 
 one of them works like the heart. None of them 
 have valves like those of- the heart. To make the 
 
6 A WORD TO THE TEACHER 
 
 word pump clear a pump must be seen and its valves 
 examined. Would it not be easier and far better in 
 every way to examine a heart at the outset and see 
 what its valves are like and how they work. The 
 word heart gives a real and usable conception, while 
 the word pump without illustration and comparison 
 would be meaningless. Heart is as easy as pump. 
 Illustrations of such indefinite work in physiology 
 could easily be multiplied. 
 
 All of the anatomical and physiological parts of this 
 book can be illustrated by parts of the bodies of small 
 animals. If the part is prepared neatly, there can 
 be no objectionable feature about it. The leg of a 
 chicken or of a frog answers well to show how muscles 
 look and how they are attached to bones, how the 
 joints are formed, how the nerves appear, etc. These 
 animals will give much other material. A skeleton of 
 a cat or -a dog will illustrate well the human skeleton. 
 All these preparations can be made by the teacher or 
 by one of the older pupils. It hardly need be said that 
 no animal should be killed before the school or class, 
 or anything else done that would offend common 
 sense. It has been the observation of the author 
 that a personal knowledge on the part of pupils of the 
 beautiful structure of the bodies of animals has the 
 effect of increasing the admiration for animals and 
 begetting a sympathy for them in their bodily pains 
 or troubles. 
 
 The human body and the bodies of the lower animals 
 should be studied also in action, each in its own natural 
 surroundings, as organisms adapted to these surround- 
 ings. It is only by constantly seeing the organisms 
 
A WORD TO THE TEACHER 7 
 
 in their true relations to other things that even ele- 
 mentary conceptions of physiological facts can be 
 obtained. 
 
 The teacher need not feel discouraged because he 
 is not provided with charts or other apparatus; he can 
 make use of the living world around him to illustrate 
 the study of the most interesting of living organisms. 
 The work thus pursued will be of real value beyond 
 the interesting knowledge gained, and will bring the 
 reward of a satisfaction of having accomplished some- 
 thing of worth. 
 
 In the second book of this series the writer has intro- 
 duced directions for the practical demonstration of 
 many anatomical and physiological facts, which might 
 well be suggestive to the teacher of this book. For 
 these directions and for a fuller discussion of many of 
 the subjects treated here reference may be made to the 
 second book. There are now published many hand- 
 books for the dissection of many of the groups of the 
 lower animals, any one of which will be helpful in pre- 
 paring illustrations for the study of the human body. 
 
 But illustrations of the work, or subjects of study, 
 will be numerous enough and more vital if they 
 come from observation and experience with the objects 
 of study. 
 
 O. P. JENKINS. 
 
CONTENTS 
 
 CHAPTER PAGE 
 
 I. How MOTIONS OF THE BODY ARE PRODUCED. CARE 
 
 AND EXERCISE OF THE MUSCLES . . . .11 
 II. SKELETON OF THE UPPER EXTREMITIES ... 23 
 
 III. THE SKELETON. HYGIENE OF THE BONES AND 
 
 JOINTS o . 31 
 
 IV. PARTS OF THE CIRCULATORY ORGANS . . . - 44 
 V. PHYSIOLOGY OF THE CIRCULATORY ORGANS. THE 
 
 BLOOD. HYGIENE OF THE CIRCULATION . 52 
 VI. How THE BODY WORKS. ITS NEED FOR FOOD AND 
 
 OXYGEN 63 
 
 VII. FOODS .... 70 
 
 VIII. PARTS OF THE DIGESTIVE SYSTEM. CARE OF THE 
 
 TEETH 77 
 
 IX. DIGESTION. CARE OF THE DIGESTIVE ORGANS . 86 
 
 X. RESPIRATION 95 
 
 XI. PURE AIR, BREATHING, AND VENTILATION . . .105 
 
 XII. THE SKIN AND THE KIDNEYS 117 
 
 XIII. CARE OF THE SKIN 125 
 
 XIV. THE STRUCTURE OF THE NERVOUS SYSTEM . .130 
 XV. How THE NERVOUS SYSTEM is USED. CARE OF THE 
 
 NERVOUS SYSTEM 138 
 
 9 
 
10 CONTENTS 
 
 CHAPTER PAGE 
 
 XVI. SENSATIONS 147 
 
 XVII. SIGHT AND HEARING 153 
 
 XVIII. CARE OF THE EYE AND EAR 161 
 
 XIX. DISEASE, ITS CAUSES AND PREVENTION . . .168 
 
 XX. ALCOHOL, TEA, COFFEE, TOBACCO, OPIUM . . .181 
 
PRIMARY PHYSIOLOGY 
 
 CHAPTER I 
 
 HOW MOTIONS IN THE BODY ARE PRODUCED. CARE 
 AND EXERCISE OF THE MUSCLES 
 
 The Study of the Human Body. The human body is 
 made up of a great number of parts, which may be 
 called so many pieces of machinery. They work to- 
 gether so harmoniously that they all help one another. 
 When, for example, a boy climbs a tree, almost every 
 part of his body is aiding in this action. Many 
 parts of his arms, his legs, the muscles and bones of 
 the rest of the body, the eye, the touch organs, the 
 nerves, the lungs, the heart, and indeed almost all the 
 organs must act together to get the boy's body up 
 the tree. 
 
 To study how these actions are performed, and 
 how such a large number of separate parts come 
 to be so well controlled as to accomplish anything 
 the body can do, is well worth the trouble it takes. 
 To understand more clearly the parts of the wonder- 
 ful machine which is our constant servant, and to 
 learn how to keep it in the best order, is certainly 
 very important knowledge. 
 
12 HOW MOTIONS IN THE BODY ARE PRODUCED 
 
 Study of the Hand and Arm. One may well begin 
 the study of the human body by observing the com- 
 mon movements of his own arm and hand. Let him 
 pick up an object from the table and raise it toward 
 his mouth, and observe closely what takes place. 
 First, the arm is straightened that is, the part below 
 the elbow, or the forearm, is carried away from the 
 part above. The whole arm may also be moved away 
 from the body. The hand is carried toward the object, 
 and just as it reaches it, the fingers and thumb are 
 stretched out. The thumb and one or more fingers 
 close together over the object to hold it firmly, when 
 the forearm is carried toward the upper arm, and 
 the hand with the object is carried toward the mouth. 
 This is a very common action, and is repeated here 
 to observe just what happens. Let us look at the 
 actions separately, and attempt to see how they are 
 accomplished. 
 
 Let us first examine the fingers and the thumb, 
 and their actions. It is easy to determine that each 
 finger has running through its central portion a row 
 of three hard pieces, which are known well enough 
 to be bones. These bones form two joints in a finger, 
 and the one next to the hand forms a joint with 
 another bone at the knuckle. These joints allow 
 the fingers to fold toward the palm of the hand, and 
 to unfold again until straight, or even curved slightly 
 backward. It is plain that if it were not for the 
 rigid parts and the joints the fingers could not be 
 extended with much force. 
 
 Now let us examine what is the action by which 
 the bones of the finger are bent or straightened. If, 
 
WHAT THE MUSCLES ARE LIKE 13 
 
 while one is moving the forefinger rapidly by ex- 
 tending and bending it, he places the finger of the 
 other hand on the back of the hand just back of the 
 moving finger, he can detect a firm cord crossing 
 the knuckle and running toward the wrist. This be- 
 comes rigid every time the finger is extended. By 
 causing each of the other fingers to move in the same 
 manner, a similar cord for each one can be felt just 
 under the skin. These cords can be traced even 
 past the wrist into the forearm, where they are lost 
 to the touch. 
 
 The skin of the palm is thicker than that on the 
 back of the hand, so it is more difficult to detect 
 the cords running from the palm side of the fingers 
 at this place. But if we examine the region of the 
 palm side of the forearm just above the wrist while 
 the fingers are in motion, it is easy to see that there 
 is a number of cords here which are moved every time 
 the fingers are bent. 
 
 It is plain from this that the fingers are moved 
 backward and forward by these strings pulling, first 
 the one set, then the other. What pulls on the strings? 
 If, while the thumb and finger are closed and opened, as 
 before observed, the other hand be made to grasp 
 around the forearm just below the elbow, it will be 
 found that this part of the arm shows great activity 
 beneath the skin. This is due to the action of the 
 parts that pull on the cords. These parts are the 
 muscles. The cords are the tendons. 
 
 What the Muscles are Like. Not only are the 
 fingers extended and bent by muscles pulling on the 
 tendons which are tied to the finger bones, but when 
 
14 HOW MOTIONS IN THE BODY ARE PRODUCED 
 
 Fig. 1. 
 
 BICEPS MUSCLE ATTACHED TO THE RADIUS. 
 
 the arm is bent at 
 the elbow, the action 
 is accomplished by 
 a muscle in the up- 
 per arm pulling on 
 a tendon attached to 
 a long bone in the 
 forearm. 
 
 If with your left 
 hand you grasp the 
 right upper arm while 
 the arm is being bent, 
 
 the flesh on the front side of the arm will be 
 felt to swell up greatly. 
 
 If the firigers be held at the front side of 
 the elbow while the arm is being bent, a 
 very large cord, the tendon, can be felt. 
 The swelling flesh is a large muscle. Fig. i 
 shows the arm with all the parts removed 
 except the bones of the arm and this muscle 
 and its tendons which bend the arm. Fig. 2 
 shows the same muscle removed, so as to 
 better show its appearance. 
 
 Appearance of a Muscle. As seen in the 
 figure, this muscle, which is called the biceps, 
 has a thick body, tapering off at each end 
 to the tendons. The thick body is composed 
 of a reddish mass. The lean part of the 
 flesh of an animal, which is familiar to every 
 one, is muscle. 
 
 The muscle is surrounded by a tough F - 2 . 
 membrane, which holds all of its parts BICEPS. 
 
A REVIEW OF THESE POINTS 15 
 
 together, and runs off toward the ends of the muscle 
 and continues into the tendon. The tendon runs to 
 the bone, where it is continuous with a membranous 
 covering of the bone. Thus the muscle comes to be 
 firmly attached to the bone. 
 
 Action of the Muscle. It has already been seen 
 that when the hand clasps the arm over the biceps 
 muscle during the bending of the arm, it is felt to 
 swell up to a considerable thickness. If, when the 
 muscle is in action, it could be examined with the 
 covering of the arm removed, one could see it shorten 
 as well as thicken. It is this power of shortening 
 and thickening, or contracting, as it is called, which 
 enables the muscle to pull the bone and cause the 
 motion of the arm. 
 
 The cause of the motions of the fingers which we 
 observed is also the contraction of the muscles. In 
 the part of the arm just below the elbow is a num- 
 ber of muscles. Each one is smaller than the bi- 
 ceps, but it is shaped very much like it. Each one 
 ends in a tendon at each extremity, the one toward 
 the elbow being short and attached to some one of 
 the bones at points near the elbow joint. At *the 
 end toward the hand the tendons are long, some 
 passing to the* wrist, some to the hand, but most of 
 them passing on to the different joints of the fingers. 
 Some run along the back of the hand, as we ob- 
 served, and some on the palm side. 
 
 A Review of these Points. To bend a finger, we 
 contract a muscle in the forearm; to straighten it, 
 we contract another. To straighten more than one 
 finger, as in reaching for an object, we contract sev- 
 
1 6 HO W MOTIONS IN THE BODY ARE PRODUCED 
 
 eral muscles in the forearm; to bring them together 
 on the object, we contract several others in the same 
 position. To bend the arm at the elbow, we con- 
 tract the biceps. We may, by clasping the upper 
 arm, find that when we straighten the arm, muscles 
 on the opposite side from the biceps contract and 
 pull on tendons attached to the forearm, and bring 
 it back to its extended position. 
 
 Muscles that produce Other Motions of the Arm. - 
 If one place his hand at different positions around 
 his shoulder while he lifts his whole arm up, brings 
 it forward, backward, downward, or in any other 
 direction, he will find that the muscles of the breast, 
 of the top of the shoulder, or of the back, or just 
 below the shoulder, are acting. These muscles are 
 very large and make up most of the flesh in these 
 regions. Those parts which lie just beneath the skin 
 are shown in Fig. 3, but still others lie beneath these. 
 
 Other Muscles in the Body. Whenever any mo- 
 tion of a part of the body is made, it is by the 
 contraction of the muscles. To produce the very 
 many motions that the body performs, it is furnished 
 wUh about five hundred muscles. Figs. 3 and 4 
 show where many of these muscles are placed, but a 
 very large number lie deeper than these and many 
 are small, so that all can not be represented at once. 
 
 Number .of Motions. The five hundred muscles 
 can produce more than five hundred motions, for 
 each one can produce a motion acting alone, a still 
 different one when acting with another muscle, or 
 even with several other -muscles. For example, we 
 may carry the whole arm in many hundreds of dif- 
 
rig- 
 
 FRONT VIEV 
 
 BODY. 
 
BACK 
 PR.-I* 
 
 Fig. 4, 
 
 BODY. 
 
MUSCLES IN THE LOWER ANIMALS if 
 
 ferent positions with but a limited number of mus- 
 cles, by combining their contractions in different 
 ways. 
 
 Contractile Power of Muscles. The power oj 
 contractility which the living muscle has is the source 
 of the force which the body can exert. The con- 
 tractile muscular substance is to the machinery of 
 the human body what the steam is to the engine. 
 It is well known that hot steam presses against the 
 walls of the vessels containing it. It will lift the lid 
 of a kettle, or may push so hard as to burst the walls 
 of a steam boiler. Men take advantage of this great 
 power, and let the steam push against a piston, and 
 by its connections 'turn a crank which makes all the 
 motions in a great machine shop. 
 
 In the body, the muscular substance, instead of 
 pushing, as does steam, pulls on the ends of the ves- 
 sels which contain it, and thus, by means of strings 
 (tendons), pulls on the bones and makes the motions 
 of the body. 
 
 Muscles in the Lower Animals. The muscles 
 in the common animals, such as horses, dogs, cats, 
 rabbits, and the like, are of the same form, and are 
 attached to bones in the same way as those in man. 
 They have the same power of contracting and are in 
 every respect like those of the human body. 
 
 The motions of all animals, except certain forms, 
 chiefly microscopic, are produced by muscles. The 
 muscles of the higher animals are arranged in about 
 the same number and order on the limbs and the 
 remainder of the body as in man. The examination 
 of the muscles of the body of some small animal 
 
 IND. PR. PHYS. 2 
 
1 8 HOW MOTIONS IN THE BODY ARE PRODUCED 
 
 would teach very clearly how the muscles appeal 
 and how they are arranged in man, and how the ten* 
 dons attach them to the bones. 
 
 What causes the Muscles to Contract. We know 
 that we can cause the muscles to contract whenever 
 we wish to do so. The arm can be moved at the exact 
 moment and with just the force we desire. It is 
 said, for example, that the muscles of the arm are 
 under the control of the will. If the arm could be laid 
 open for examination, there could be seen some other 
 things besides muscles and tendons. 
 
 Among the latter would be seen some white cords, 
 which divide into many branches, one going to each 
 muscle. They penetrate the sheath of the muscle 
 and are lost in its substance. These cords, divid- 
 ing up into fine threads, are nerves. If they are traced 
 from the muscles, they are found to run up the arm, 
 through the shoulder, across to the backbone, and 
 into its center. Here they connect with a large nerve 
 cord, the spinal cord, which runs to the brain. These 
 we will study later, but mention them here to show 
 that the muscles are connected with the brain, through 
 which the will acts. 
 
 Now, if a nerve going to a muscle be cut in two, 
 then no power of the will can make it contract. It 
 is only when the nerve connects the muscle with the 
 brain that we can move the muscle when we wish to. 
 The brain can send some influence that the nerve is 
 able to conduct, which, when it reaches the muscle 
 substance, makes it contract. The exact nature of 
 this influence is unknown, nor is it known how it 
 makes the muscle contract. This influence is called 
 
VOLUNTARY AND INVOLUNTARY MUSCLES 1 9 
 
 a nervous Impulse. The nervous impulse in some way 
 stirs up the muscle, or excites it to contract. In 
 physiology this is called stimulation of the muscle. 
 The nervous impulse stimulates the muscle to con- 
 traction. 
 
 Voluntary and Involuntary Muscles. All those 
 muscles whose action may be controlled by the will 
 are called 'voluntary muscles. They are the great 
 majority of the muscles in the body. The muscles 
 of the heart and of the stomach, and of some of the 
 other organs, are stimulated to action from some 
 other source than the .will, and the will can not con- 
 trol them. Consequently, these are called involun- 
 tary muscles. 
 
 Some of the most important actions of the body, 
 such as those in the circulation of the blood, in breath- 
 ing, and in the digestion of food, are carried on by 
 involuntary muscles. The arrangement by which 
 certain muscles may act independently of our care 
 and attention allows important actions to go on 
 while we are asleep, and when the mind is so occu- 
 pied that they would be forgotten or neglected. 
 Such processes as circulation and respiration require 
 such careful regulation to get them just right for the 
 body in its different positions when it is active or rest- 
 ing that we never could of ourselves manage them 
 properly. The involuntary actions relieve us of the 
 care and trouble of these most necessary operations 
 and allow us to give our time, attention, and 
 strength to the other motions. We will refer to this 
 kind of action again when we study the nervous 
 system. 
 
2O CARE AND EXERCISE OF THE MUSCLES 
 
 CARE AND EXERCISE OF THE MUSCLES 
 
 We have just seen that the muscles make up the 
 greater part of the body. They do the work of the 
 body in walking, running, working in field or shop, or 
 showing activity in the playground. That the muscles 
 be kept in good condition is of the greatest importance. 
 First, because we wish to have the laboring part of 
 the body in good working order so that all that it has 
 to do may be done well. Second, because if so large a 
 part of the body is not in good condition, the general 
 health of the body is seriously affected. 
 
 The complete care of the muscles would demand 
 'good care of all the rest of the body because all the 
 rest of the body either directly or indirectly affects 
 the muscles. For example, the respiration furnishes 
 the muscles with oxygen and throws away their car- 
 bonic dioxide. The digestive system furnishes them 
 with food. The circulation sends through them the 
 blood which brings the food and oxygen and car- 
 ries away the carbonic dioxide. The nervous system 
 brings them the stimulus that makes them contract, 
 and it regulates their supply of blood. 
 
 Other parts of the body also help the muscles, and 
 the care of the muscles, as we have just said, includes 
 the care of these parts as well. But as we shall speak 
 of the care of these parts in other sections of this 
 book, we will consider here only the immediate care 
 of the muscles themselves. 
 
 First of all, the muscles must have exercise to keep 
 their health. If an arm were bound so that no part of 
 it could ever move, its muscles would wither away. 
 
EXERCISE FOR ADULTS 21 
 
 But if the muscles of the arm are well used, they grow 
 in size, becoming firm and strong. What is true of mus- 
 cles of the arm is true of all the other muscles of the 
 body. They must work to keep in good condition. 
 
 Thus the first law of health is that we must take 
 exercise. It is plain that the exercise must bring 
 into activity all the muscles of the body. If we re- 
 member these two facts, we need have no trouble in 
 deciding whether any form of exercise is good or 
 bad. 
 
 Since the working of the muscles demands an abun- 
 dance of pure air, it is best when possible that the exer- 
 cise be taken out of doors. If the weather or other 
 conditions require that it be taken within doors, the 
 rooms must be well ventilated, or much of the benefit 
 of the exercise will be lost. 
 
 Exercise of Children. The well-known out-of-door 
 games are all good forms of exercise, because they 
 require vigorous use of the muscles of all parts of the 
 body, arms, legs, and trunk. They also train the sight, 
 hearing, and touch to work well with the muscles, for 
 the motions must be guided well by these senses or 
 the player loses the game. 
 
 The helpful work on the farm and about the home 
 are all good forms of exercise. Those children who have 
 opportunity for such work are very fortunate, for not 
 only do they get necessary exercise, but they receive 
 training in doing useful things which gives them 
 advantages over those who do not get this training. 
 
 Exercise for Adults. Those people whose occupa- 
 tions require labor of the body, that is, constant exer- 
 cise of the muscles, of course do not need to plan for 
 
22 CARE AND EXERCISE OF THE MUSCLES 
 
 special exercise. They need mostly rest and recrea- 
 tion. But those whose -occupations do not require 
 much activity of the muscles need special provision 
 for exercise. This must be true also for those whose 
 employment requires some sort of work bringing into 
 activity only a limited group of muscles. An example 
 would be one working at a machine which requires 
 only a single hand or arm to be active. Another 
 would be an occupation which requires keeping the 
 body in a single position for long periods of time. 
 For such people there are two kinds of exercise. The 
 one includes out-of-door exercise in its various forms, 
 the other the different forms of exercise planned for 
 the gymnasium. 
 
 The outdoor sports will appeal to some, while oth- 
 ers will prefer the gymnasium. Since the exercise that 
 gives most pleasure is most beneficial, the most pleas- 
 ing form may be chosen. 
 
 Excessive exercise, or overwork of the muscles, is 
 injurious. Necessity may sometimes force one to 
 overwork, as to save a home from fire or flood, or to 
 meet some other unusual condition. One may become 
 exhausted from such excessive work and recover well 
 from it. But continuous overwork would be very 
 harmful. 
 
 To sum up. Exercise of all the muscles is necessary 
 for good health. The exercise should be taken in 
 good air. It should be sufficiently frequent, but not 
 excessive. 
 
CHAPTER II 
 SKELETON OF THE UPPER EXTREMITIES 
 
 General View. Since the bones of the arm and 
 hand are so easily traced, and their uses can be so 
 clearly made out, we will study them in some detail. 
 The bones of the arm illustrate many facts about 
 bones in general. They are generally grouped as 
 bones of the hand, the forearm, and the arm, and 
 are attached to the body by the shoulder girdle, the 
 whole group being sometimes referred to as the bones 
 of the upper extremities. 
 
 The Bones of the Hand. We have just seen that 
 the fingers have each three bones and the thumb 
 has two fourteen in all. They are called the pha- 
 langes, a single one a phalanx. The five bones which 
 we traced in the palm of the hand, and whose outer 
 ends are the knuckles, are called the metacarpals. 
 
 Notice that the metacarpal of the thumb is free to 
 move in many directions, while those of the fingers 
 are firmly bound together. This arrangement allows 
 the thumb to be brought opposite to any one of the 
 fingers or to most points on the palm. This power 
 of moving the thumb so freely increases very greatly 
 the usefulness of the hand. 
 
 To convince one's self of this, let him attempt to 
 use the hand without using the thumb in picking up 
 
 23 
 
24 SKELETON OF THE UPPER EXTREMITIES 
 
 objects, and in handling them, and then in contrast 
 
 repeat the operations with the help of the thumb. 
 
 While the fingers without the thumb may become 
 
 very expert, yet the thumb 
 wonderfully increases the 
 usefulness of the whole 
 hand. 
 
 If we attempt to trace 
 the metacarpals back to- 
 ward the arm by feeling 
 them under the skin, we 
 soon lose them in the flesh 
 that surrounds them. 
 
 Immediately under the 
 skin and flesh in the wrist 
 we can feel a solid portion. 
 This is a bunch of small 
 bones, eight in number, 
 arranged in two rows of 
 four in each row. They 
 
 are the bones of the wrist and are called the car pah. 
 
 Compare your own hand with the picture of the bones 
 
 of the hand shown in Fig. 5. 
 
 Bones of the Forearm. That part of the arm 
 
 between the wrist and the elbow joint is called the 
 
 forearm. Immediately back of the wrist joint the 
 
 ends of the two bones may be felt under the skin. 
 
 The end of one makes the little round knob which 
 
 shows under the skin on the little-finger side of the 
 
 arm. 
 This is the end of the ulna. The bone may be 
 
 traced for its whole length, and will be found to 
 
 F.g. 5. 
 
 BONES OF THE HAND. 
 
MOVEMENTS OF THE RADIUS 
 
 extend to the elbow joint. It makes the point of the 
 elbow where it is very close to the skin. 
 
 By the side of this bony knob of the ulna, near the 
 wrist, lies the end of the radius. The 
 broad 'end of this bone fills up the space 
 from the knob of the ulna to the edge of 
 the arm on the thumb side. 
 
 It is this broad end of the radius to 
 which the hand is joined to make up the 
 wrist joint. Thus the radius carries the 
 hand. The radius may also be traced 
 to the elbow joint. 
 
 Movements of the Radius. If the 
 hand be held out with the palm turned 
 upward, it will be found that the radius 
 and ulna lie side by side. Now, while 
 the arm is in this position, turn the 
 hand over, so as to bring the palm down, 
 and during this motion watch the motion 
 of the two bones of the forearm. It will 
 be seen that the radius turns over the 
 ulna until it comes to lie across it. 
 
 It ends at the elbow in a little shallow cup about 
 three fourths of an inch across, which fits on a knob 
 on the large bone of the arm. This cup-shaped end of 
 the radius allows it to turn on this knob as on a point. 
 
 A groove in the side of the wrist end of the bone 
 allows it to slide over the knob of the ulna. Now, 
 muscles are so arranged that they can quickly pull 
 the radius over the rigid ulna; and as the radius car- 
 ries the hand, of course the hand is turned over. 
 This arrangement is for turning the hand over. 
 
 Fig. 6. 
 
 BONES OF THE 
 FOREARM. 
 
26 SKELETON OF THE UPPER EXTREMITIES 
 
 The same bones in a dog's foreleg are bound firmly 
 together, and, consequently, it can not turn its fore- 
 paw over; but in the cat's foreleg the radius has a 
 little motion, and it may be seen that while the kitten 
 is playing with a ball, it will often turn its forepaw 
 slightly. 
 
 Now examine carefully the figures of the ulna and 
 radius given here, and determine which parts of them 
 you can trace in your own arm. It may 
 be remembered from the lesson on mus- 
 cles that it is to the radius that the biceps 
 muscle is attached. 
 
 The Humerus. In the part of the arm 
 between the elbow and the shoulder is a 
 very large bone called the humerus. A 
 picture of this bone is shown in Fig. 7. 
 
 The elbow end has grooves and a knob 
 for the ulna and radius to fit into. The 
 shoulder end is formed into one large, 
 smooth, round end to fit into a cup-shaped 
 part of a bone at the shoulder, called the 
 shoulder blade. 
 
 The sides of the broad end of the 
 humerus are very prominent at the elbow, 
 but the shoulder end, called the head of 
 the humerus, is so deeply buried in the 
 large muscles which move the arm that 
 it can not be so well examined. 
 Scapula and Clavicle. As was said, the round 
 head of the humerus is fitted to a part of the shoulder 
 blade, the scapula (seen in Fig. 8 ). One can not well 
 make out the whole outline of this bone in his own 
 
 Fig. 7. 
 
 THE HUMERUS. 
 
SCAPULA AND CLAVICLE 
 
 shoulder, but he may easily trace it in that of another 
 person. 
 
 The prominent hard part felt just at the top of the 
 shoulder is the upper end of the ridge which runs 
 across the bone. This ridge 
 lies near the skin, and can 
 be traced across the bone 
 to its posterior edge, where 
 it ends. The edges of the 
 scapula can also be made 
 out. It is a flat, triangular 
 bone fitted to the upper 
 part of the back. Besides 
 acting as a support to the 
 humerus, it serves also as a 
 place to which are fastened 
 many of the muscles that 
 move the arm. 
 
 The clavicle is the collar 
 bone. It is very near the 
 skin at the front part of the base of the neck, and 
 can be traced from the shoulder to a point at the top 
 of the front part of the chest. Its use is to hold the 
 shoulders and arms back from the chest. 
 
 The clavicle and scapula together make a firm brace 
 to support the arm and attach it to the body. 
 
 Often the arm is called upon to lift a heavy weight, 
 or push with great force against an object. These 
 actions would be impossible if the arm were not 
 thoroughly braced against the body. The scapula 
 and clavicle make this brace. 
 
 It will help us to understand the uses of the bones if 
 
 Fig. 8. 
 
 THE SCAPULA. 
 
28 SKELETON OF THE UPPER EXTREMITIES 
 
 we study how levers are used outside of the body. A 
 lever is a rigid rod or bar used in three ways. Thus, 
 
 one end of it may be 
 placed under a stone 
 to be lifted, the hand 
 exerting the fcvrce 
 downward may be 
 
 placed at the other 
 Fig. 9. 
 
 end, and the support 
 
 of the lever somewhere between the hand and the 
 
 stone (Fig. 9). 
 
 Another method is to place the weight to be lifted 
 
 somewhere between 
 
 the ends of the lever, 
 
 the hand exerting 
 
 the force upward at 
 
 one end, and the 
 
 support at the other 
 
 end of the lever 
 
 (Fig. ic). 
 
 A third way is to exert the force upward on the lever 
 
 at a point between the ends, while the weight is at 
 
 one end and the sup- 
 port at the other 
 (Fig. u). The point 
 
 Fig. 10. 
 
 of support is called 
 
 the julcrum. We can 
 arrange the levers in 
 the first two ways so 
 that a heavy weight 
 
 can be lifted slowly with small force acting quickly. 
 
 In the last way we can get a weight moved quickly by 
 
 Fig. 11. 
 
THE FORELIMBS OF THE LOWER ANIMALS 29 
 
 a large force acting slowly. Now if you compare the 
 levers with Fig. i, representing the arm, you will see 
 that the forearm is a lever used as in Fig. n, the 
 muscle acting as the force, the elbow as the support 
 to the lever, and the ball as the weight to be lifted. 
 With this kind of a lever, although the muscle moves 
 somewhat slowly but with great force, the hand can 
 move very quickly. Quickness of motion of the 
 hand is more important than mere strength of the 
 movement. Most of the levers of the body are of 
 this kind. 
 
 The Uses of the Bones of the Arm and Hand. - 
 Our study of the arm has shown that the uses of the 
 bones of the arm and hand are three: 
 
 1. To act as levers. 
 
 2. To serve as fulcrums to pry against. 
 
 3. To furnish places for the attachment of muscles. 
 Each of these uses is concerned with the move- 
 ments of the arm. 
 
 The Forelimbs of the Lower Animals. The bones 
 of the forelimbs of animals which have backbones 
 that is, mammals, birds, reptiles, frogs, and fishes 
 - correspond to those of our own arm and hand. 
 
 The bones in the foreleg of a cat are very much 
 like our own. The clavicle is very small, and there 
 are but seven carpals; with this exception the bones 
 are all present, and of nearly the same shape. 
 
 As different as the foreleg of a horse or of a cow 
 appears from our own arm and hand, a comparison 
 of the corresponding bones of each would show them 
 to be remarkably alike. 
 
 The wrist bones of these animals are at the joint 
 
30 SKELETON OF THE UPPER EXTREMITIES 
 
 usually known as the " knee." The hand is very 
 narrow, consisting of but one strong bone and two 
 slender rudiments of bones to represent the meta- 
 carpals, and with but one finger in the horse, and 
 four fingers in the cow two being fully developed, 
 and two only rudiments. 
 
 Of course, we call these the feet of these animals, 
 but they correspond exactly to the last joint of our 
 fingers, the hoofs being the nails. 
 
 The forelimbs of animals differ greatly in order to 
 fit them to the different conditions of life in which 
 we find them. If you will examine why this is true 
 in the case of several animals, such as those just 
 mentioned, and also of others, such as a bird, a mole, 
 a squirrel, a rabbit, a sunfish, or a frog, the study 
 will make the knowledge of your own arm much 
 clearer. 
 
CHAPTER III 
 
 THE SKELETON. HYGIENE OF THE BONES AND 
 JOINTS 
 
 The Bones of the Leg. The bones of the leg 
 correspond very nearly to those of the arm. In the 
 toes the number is the same, and they are called by 
 the same name, the phalanges. There are five meta- 
 tarsals, in place of the metacarpals, and seven tarsals 
 in the instep, which corresponds with the wrist. 
 
 Fig. 12. 
 
 SECTION THROUGH THE BONES AND LIGAMENTS OF THE FOOT. THE PARTS OF 
 THE JOINTS ARE WELL SHOWN. 
 
 The tarsals are of larger size than the carpals, 
 while the phalanges of the foot are smaller than 
 those of the hand. In Fig. 12 the bones of the foot 
 are shown as sawed through. This shows the large 
 tarsal which makes the heel bone. 
 
 3 1 
 
THE BONES OF THE LEG 33 
 
 Just above this bone is the next largest tarsal, 
 which forms a joint with the bone of the lower part 
 of the leg. In this figure we may see also how the 
 tarsals with the metatarsals form an arch of bones on 
 which the weight of the body rests in standing. 
 
 The large bone of the lower leg resting on the tarsal 
 bone is the tibia. It extends from the instep to the 
 knee, where, with the bone above, it forms the knee 
 joint. By the side of the tibia lies the fibula, a long, 
 slender bone firmly attached to the tibia. 
 
 The bone in the thigh is the femur. It is the largest 
 bone in the body. The end at the knee is broad and 
 has a deep groove in it, while at the upper part there 
 
 is a turn in the bone which then ends in a smooth ball. 
 
 
 
 This ball of the femur fits closely into a cup-shaped 
 surface on the hip bone, to make the hip joint. The 
 hip bone, or os innominatum, as it is named, is a large, 
 irregularly shaped bone. It comes out from the 
 central line of the body, its posterior edge joining 
 firmly to the backbone, and the front edge being also 
 firmly joined to the corresponding edge of the hip 
 bone of the opposite side. Thus we see that the hip 
 bone acts as a strong brace, or arch, for the femur to 
 press against. 
 
 You will remember that the bones at the shoulder 
 form a brace for the arm to press against. The brace 
 at the hip is still stronger, as it must, during walking, 
 bear not only the whole weight of the body, but also 
 whatever heavy weights one may carry. If the leg 
 be straightened, there can be easily detected at the 
 knee a disk-shaped bone which is known as the patella, 
 or kneecap. 
 
 IND. PR. PHYS. 3 
 
34 
 
 THE SKELETON 
 
 This bone is embedded in a large tendon which 
 passes over the knee to join the tibia. The patella, 
 by fitting into a groove on the end of the femur, helps 
 the tendon work over the bend of the knee. 
 
 Uses of the Bones of the Leg. The bones of the 
 leg are, like the bones of the arm, mostly used as 
 levers. When the muscles of the front part of the 
 thigh contract, they pull upon the tibia 
 and extend the leg ; when those on the 
 opposite side contract, they bend the leg. 
 Muscles at the hip, by acting .on the 
 femur, may pull the leg in various direc- 
 tions. 
 
 A large muscle in the calf of the leg is 
 attached by a very large tendon to the 
 heel bone. This is shown in Fig. 14, and 
 can easily be felt under the skin at the 
 heel. 
 
 When this muscle contracts it acts on 
 the bones of the foot, which are bound 
 firmly together. It is a lever of the sec- 
 ond kind, to pry up the body resting 
 on it by the tibia. These muscles are 
 all used in the leg in standing, walking, 
 and running. The limbs should be 
 studied in these actions. 
 
 The Divisions of the Body. The evi- 
 dent parts of the body are the head, the 
 neck, the trunk, and the limbs. The 
 Fig. 14. limbs the arms and the legs are to 
 MUSCLES AND TEN- be thought of as mere appendages of the 
 body to serve its demands. The legs 
 
A VERTEBKA 
 
 35 
 
 carry the body about, and the arms carry to it what 
 it needs, defend it, and in a hundred ways attend to 
 its wants. 
 
 That the limbs may thus act, they must have a 
 firm support to push against. The 
 bony arches which carry them find 
 this support in the skeleton of the 
 rest of the body. 
 
 The Spinal Column. The spinal 
 column consists of twenty-six bones 
 very firmly bound together into one 
 firm beam. Its bones are twenty- 
 four Vertebrae, the sacrum, and the 
 coccyx. 
 
 The vertebrae are divided into 
 three groups: 'seven in the neck, the 
 cervical vertebrae; twelve to which 
 the ribs are attached, the dorsal 
 vertebrae; and five in the loins, 
 the lumbar vertebrae. The sacrum 
 is the base on which the column 
 of vertebrae stands, and serves as 
 the place for the pelvic arch to 
 brace against. 
 
 A Vertebra. Each vertebra (Figs. 
 16 and 17) has a central part from 
 which extend seven projections, 
 called processes. These serve for 
 the attachment of ligaments by 
 which the vertebrae are joined in 
 one mass. They serve also for the attachment of many 
 muscles which move the limbs and the head, and ac- 
 
 SPINAL COLUMN. 
 
36 THE SKELETON 
 
 complish other motions. Each vertebra has an open- 
 ing in its posterior part. When the vertebrae are 
 brought into line, these openings make a tube, called 
 the spinal canal, the upper part of which contains the v 
 spinal cord, and the lower part many nerves. 
 
 Bones of the Thorax. The walls of the chest are 
 supported by the twelve ribs on each side, the ster- 
 num or breastbone in front, and the dorsal vertebras 
 behind. The ribs end in cartilages in front. The 
 cartilages of the first seven are joined to the sternum; 
 
 Fig. 16. Fig. 17. 
 
 A DORSAL VERTEBRA. SIDE VIEW. VERTEBRA SEEN FROM ABOVE. 
 
 those of the next three are joined together and to the 
 seventh; the last two are free or "floating" in front. 
 
 The Skull. The skull, the skeleton of the head, 
 is placed on the upper vertebra. It consists of the 
 cranium and the bones of the face. The cranium is 
 the part that incloses the brain. As felt under the 
 scalp, it seems to be one spherical bone, but it is really 
 made of eight pieces which are so nicely joined together 
 that the joints can not be detected until the bones are 
 exposed. The whole eight make a box, with several 
 holes in the floor. 
 
 Bones of the Face. These are fourteen in num- 
 ber. The only one free to move is the lower jaw 
 
THE USES OF BONES 
 
 37 
 
 bone, called the lower maxillary. This bone bears 
 the lower teeth. It forms a joint with the skull. 
 It is drawn upward in closing the mouth by muscles 
 which can be felt in the cheeks, and is drawn down 
 by muscles in the neck. 
 
 The Uses of Bones. We have already seen that 
 the main uses of the bones of the arm and leg are 
 for levers, or for 
 the attachment 
 of muscles to 
 produce motions. 
 
 The shoulder 
 and hip bones are 
 for the attach- 
 ment of muscles, 
 and to serve as 
 braces for the 
 limbs to push 
 against. Many 
 of the bones of 
 the head serve 
 for the attach- 
 ment of muscles, 
 which make it possible to carry the head erect, and 
 to move it about. 
 
 Some of the bones of the head are the necessary 
 place of attachment of muscles to move the lower 
 jaw, the bone of the lower jaw being itself a lever 
 with motion as its chief purpose. 
 
 The spinal column is the main region for the attach- 
 ment of the great muscles of the body, and is at the 
 same time constantly acting as a lever. The ribs 
 
 Fig. 18. 
 
 BONES OF THE HEAD. 
 
THE SKELETON 
 
 make rigid walls to a part of the body to act as the 
 sides of a bellows in breathing. They act also as levers, 
 both in taking in the air and in expelling it from the 
 lungs. 
 
 The skeleton, then, has two chief functions: to fur- 
 nish levers, and surface for the attachment of muscles 
 to work these levers. 
 
 Secondary Uses of the Bones. Some of the bones 
 are incidentally used for protecting parts from outside 
 injuries, as in the case of the bones of the skull, guard- 
 ing the brain, and the bones of the chest, guarding 
 the heart, while they perform their more important 
 functions as well. 
 
 Different Kinds of Skeletons. All those animals 
 which have a spinal column are called vertebrates. 
 Dogs, cats, horses, cows, squir- 
 rels, birds, frogs, snakes, and 
 fishes all have spinal columns 
 and are examples of vertebrates. 
 But in animals like the craw- 
 fish, which performs vigorous 
 motions by means of muscles, 
 the same necessity exists for 
 hard' parts to act as levers, and 
 for the attachment of muscles. 
 In the crawfish, the skin, by 
 becoming a rigid crust, only 
 flexible at the joints, furnishes 
 the levers. The muscles inside 
 the limbs and the body 
 
 Fig. 19. 
 
 are 
 
 A CRAWFISH, AN ANIMAL WHOSE 
 SKELETON is THE OUTSIDE 
 
 SURFACE OF ITS BODY AND attached to this hard crust, and 
 SJStSJSJ" its divisions serve the same pur- 
 
STRUCTURE OF A BONE AND OF A JOINT 39 
 
 pose as the bones of man. Thus this animal wears its 
 skeleton on the outer surface of its body. 
 
 An examination of the crawfish or some large insect 
 will allow the arrangement of the muscles and of the 
 outside skeleton to be much better understood. 
 
 Animals without a Skeleton. There are animals 
 without a skeleton of any kind, but they are not able 
 to accomplish very powerful motions. Most of them 
 live in water, by which they are partly or wholly 
 held up, and they have only 
 slow motions. Most of these 
 animals are very small and 
 can be seen only by the 
 microscope. 
 
 Some, however, that live in 
 the sea are of considerable 
 size. Among these are the 
 jelly fishes. These beautiful 
 animals can swim about by Fig. 20. 
 
 Contracting their bell-Shaped A JELLYFISH, AN ANIMAL WITHOUT 
 i f mi i i* A FIRM SKELETON. IT LIVES IN 
 
 bodies. Their bodies are of 
 
 a jellylike-looking substance. 
 
 They get along well enough 
 
 as long as they are floating 
 
 in the water, but on land they can do nothing and soon 
 
 fall to pieces. 
 
 Structure of a Bone and of a Joint. The ex- 
 amination of a fresh joint of an animal, with the 
 bones that make it, would best teach how they 
 are formed. A joint from a leg of mutton would 
 answer well. The bone is made up of a hard, solid 
 portion covered over with a thin membrane. The 
 
 THE SEA AND SWIMS BY CONTRACT- 
 ING ITS UMBRELLA-SHAPED BQDY, 
 WHICH THROWS THE WATER OUT 
 OF THE HOLLOW PLACE ON THE 
 UNDER SIDE OF ITS BODY. 
 
40 
 
 THE SKELETON 
 
 Fl 9' 21 - 
 
 center of a leg bone is filled 
 with marrow. The ends of 
 bones which go to form the 
 joints are enlarged and have 
 roughened places on them 
 where the tendons and liga- 
 ments are attached. Before 
 cutting into the joint one can 
 see how it is covered by strings 
 and bands of membrane. 
 Some of these go from one 
 bone to another and hold 
 them together. Others tie the 
 muscles to the bone. Those 
 
 are called tendons, and those 
 
 fastening bones- to bones are named ligaments. It is 
 these which are 
 bruised or torn in 
 sprains and disloca- 
 tions of which we 
 shall soon speak. 
 
 Fig. 2 1 shows the 
 human shoulder 
 joint with some of 
 the ligaments fas- 
 tening the bones 
 together. Fig. 22 
 shows the human 
 hip joint with all 
 ligaments but one 
 
 , HIP JOINT, WITH LIGAMENTS REMOVED, EXCEPT THE 
 
 removed. ONE ON THE HEAD OF THE FEMUR. 
 
HYGIENE OF THE BONES AND JOINTS 41 
 
 The ends of the two bones fit together very nicely, 
 and are covered with cartilage, which is a very smooth 
 and a very elastic substance. Over the layers of 
 cartilage, fastened firmly to it, is a membrane which 
 secretes a liquid which keeps the surfaces of the joints 
 moist. 
 
 This arrangement allows motion with the least 
 friction. The elasticity of the cartilage lessens the 
 jarring effects of the motions of the body. 
 
 HYGIENE OF THE BONES AND JOINTS 
 
 The skeleton and its parts may suffer either in its 
 growth and development, or by injuries coming to it 
 by accident, as in broken bones, or sprained or dis- 
 located joints. 
 
 As the skeleton is the hardest material in the body, 
 its growth determines the outline of the form and size 
 of the body. Like all other parts of the body, its 
 growth and development from the time of childhood 
 to that of full growth are greatly influenced by the 
 food, the air, and the exercise it receives. Animals 
 which when growing have been poorly fed and ill 
 kept in general have smaller or less vigorous bodies 
 throughout life than they would otherwise have 
 possessed. 
 
 It is the same with man. Measurements taken of 
 large numbers of children living in conditions where 
 they have been ill fed and otherwise poorly cared for, 
 compared with those of children better fed, show the 
 growth of the better-fed children to be markedly 
 greater. 
 
42 HYGIENE OF THE BONES AND JOINTS 
 
 The skeleton is growing from birth to twenty or twenty- 
 five years. This is a slow growth. During the first half 
 of that time the bones are less rigid than they become 
 later on. During this time continuous pressure on any 
 of them, or unnatural positions long maintained, may 
 permanently distort or misform parts of the bony sys- 
 tem. For example, a habit of keeping a stooping posi- 
 tion in the growing period may result in a fixed stoop 
 that can not be changed. Or a practice of sitting in 
 a wrong position at a desk or in a chair in long periods 
 of reading, writing, or study may result in permanent 
 distortion of the body. Continuous pressure of cloth- 
 ing on the ribs may result in misforming the chest. 
 Pressure of badly shaped shoes may result in perma- 
 nently malformed feet. If it is desired that a child 
 should grow up with a well-formed body, with grace- 
 ful carriage and movements, the parts of the body 
 must be kept free from pressure, wrong positions for 
 long periods must be avoided, and habits of good 
 positions and graceful motions must be continu- 
 ously practiced; for as the skeleton is formed so it 
 remains. 
 
 We have seen that at the joints the bones are very 
 firmly bound by ligaments. Yet, a sudden twist 
 which may occur in violent action may bring a strain 
 on a joint, so that either the ends of the bones are 
 slipped past each other or the ligaments greatly 
 stretched or partly torn and bruised. The first is 
 called a dislocation of the joint, the second makes 
 what is known as a sprain. 
 
 Of course, for a dislocation a skilled physician will 
 be called to place the parts of the joint back in their 
 
HYGIENE OF THE BONES AND JOINTS 43 
 
 proper positions, and his directions for the care of 
 the injured joint should be strictly followed. Other- 
 wise a permanent distortion might result. For the 
 trouble of a little intelligent care one ought not to 
 risk having a lameness or disfigurement for the rest of 
 one's life, to say nothing of impairing the usefulness of 
 a part of the body. 
 
 In both a dislocation and a sprain the injuring of 
 the ligaments produces great pain, and the parts gen- 
 erally require considerable time in healing. In severe 
 cases of sprain a surgeon should be consulted as soon 
 as possible, as some serious injury may be present 
 which can best be attended to before much inflamma- 
 tion occurs. If the sprain is not very severe, it needs 
 only rest. If it is painful, bathing in warm water 
 may allay the pain. 
 
CHAPTER IV 
 
 PARTS OF THE CIRCULATORY ORGANS 
 
 The Use of Blood. We have long known that 
 we require food every day, and that water and air 
 are also absolute necessities. 
 
 The more active we are, the hungrier and thirstier 
 we become, and the more food we actually require. 
 We may not notice that we use more air, yet it is 
 a fact. 
 
 What is the cause of these demands? Just for 
 our present purpose we may say that in work the 
 body consumes the food, water, and air, and, in con- 
 sequence, there must be a further supply of these 
 substances. When we say that the body needs these, 
 we mean nothing more than that the parts of the 
 body need them that is, the muscles, the bones, the 
 nerves, and the like. Further* since work causes 
 an increased demand, it must be the parts that are 
 working most that are most in need of the food. 
 Those organs are the muscles, but, of course, many 
 other parts work with them. 
 
 Now, we know that the food we eat does not go 
 to the muscles in the form in which we see it. The 
 food of the muscles and of the other parts of the 
 body is the blood. 
 
 44 
 
HOW DOES THE BLOOD EXIST IN THE HAND? 45 
 
 They live upon the blood, which is formed from 
 the food, the water, and a part of the air, the gas 
 oxygen. The muscles, the nerves, and indeed every 
 tissue in the body gets its food, drink, and oxygen 
 from the blood. When, then, we take more food or 
 drink, or breathe faster, it is to add more food, water, 
 or air to the blood to take the place of what the tis- 
 sues of the body have used in the work. 
 
 How the blood receives the supply of food and 
 drink we take, and how its supply from the air is ob- 
 tained, we shall study later in the chapters on Diges- 
 tion and Respiration. At this place we shall study 
 the blood and its motion through the body. 
 
 The Blood in the Hand. The hand may answer 
 again as a beginning point for our study. Many 
 accidents have taught every one that the hand is full 
 of blood. If it is pierced at any point, even with a 
 very fine needle, the blood will flow from it, the only 
 exceptions being the very thin outer layer of the 
 skin, the epidermis, and the nails. 
 
 How does the Blood exist in the Hand? It might 
 be supposed from the experiments with the needle 
 that the blood is in the hand as water may be in 
 a sponge, but it can easily be shown that such is 
 not the case. If the hand is allowed to hang down 
 quietly for a short time, and the back is observed, a 
 network of ridges of a bluish color will appear under 
 the skin, and the whole hand will be of a deeper pink 
 color. Now, if the hand be held above the head, 
 it will be observed that this network will become 
 very much less prominent, if, indeed, it does not 
 entirely disappear. The network of ridges consists 
 
46 PARTS OF THE CIRCULATORY ORGANS 
 
 of tubes which are carrying the blood from the hand. 
 When the hand is held down, the blood in them has 
 to flow uphill, and consequently the tubes all be- 
 come well filled with the liquid. The pink color 
 shows that the rest of the hand has more blood in 
 it. 
 
 Now, when the hand is held up the blood runs out 
 of these tubes better, and they are left nearly empty. 
 There is less blood left in the rest of the hand also. 
 To show that the blood is flowing from* the hand 
 toward the shoulder, one can press the blood out of 
 the tubes of the back of the hand and watch them fill 
 again. They will always be seen to fill from the direc- 
 tion of the fingers. 
 
 How does the blood get into the hand? Find the 
 place above the wrist where you can feel the beating 
 of the pulse. It is just between the skin and the 
 end of the radius. This beating is in one of the tubes 
 which bring blood to the hand. That the blood 
 is coming from the shoulder to the hand can be proved 
 by pressing firmly on the tube until it is closed; and 
 then it will be found that the stroke of the beat is on 
 the shoulder side of the wrist. 
 
 The Names of the Tubes. The blood is running 
 along this and other tubes deeper in the arm, on 
 its way to the hand. These tubes are called arteries. 
 
 As the blood flows to the hand, the arteries divide 
 into many branches which become smaller as they 
 branch. These go to the muscles, bones, and skin, 
 which they penetrate, and in which they finally branch 
 off until they are so minute that they can not be seen 
 without a microscope. These very fine divisions of the 
 
THE BLOOD IN OTHER PARTS OF THE BODY 47 
 
 tubes are the capillaries. They are very numerous, 
 making an extremely fine network, which brings the 
 blood to even the minutest divisions of the muscles, 
 bones, etc. 
 
 This network of capillaries soon unites its vessels 
 into larger and larger ones, which leave the muscles, 
 bones, and other parts in the same way that the art- 
 eries enter them. 
 
 These returning tubes are the veins. The smaller 
 veins join into larger and larger ones, some of which 
 we have observed on the back 
 of the hand. Fig. 23 shows 
 how they appear in some tis- 
 sues. The picture represents 
 them with all the tissues re- 
 moved from the blood vessels. 
 The largest white vessel may 
 represent the smallest artery, 
 which is divided up to form 
 the network of capillaries, RELATIONS OF ARTER VEIN> AND 
 and the dark vessel the CAPILLARIES. 
 
 small vein with the returning blood. To sum up 
 what has just been learned of the hand, it may be said 
 that the blood comes into it by arteries which divide 
 until they finally become capillaries, which are in every 
 part except the nails and the outside layer of the skin, 
 and from the capillaries it returns by means of veins. 
 
 The Blood in Other Parts of the Body. What 
 has just been learned of the hand is true for every 
 other part of the body. To every part arteries are 
 distributed, ending in capillaries which join to form 
 veins. 
 
4 8 
 
 PARTS OF THE CIRCULATORY ORGANS 
 
 RA 
 
 When the hand hangs down, the blood in the veins 
 must be pushed uphill with great force the length of 
 the arm. When the hand is held above the head, the 
 same must be done in the arteries. If the arteries 
 and veins were exposed to view, we could see them 
 running up the arm, past the shoulder, across the 
 upper part of the chest, and finally ending in the 
 heart. The general view of the arteries is shown in 
 Fig. 26. 
 
 The Heart. The heart is a force pump which 
 night and day pumps the blood into the arteries 
 with enough force to send it on 
 through the capillaries and back 
 to itself through the veins. 
 
 The heart is in the lower 
 part of the cavity of the chest. 
 It is somewhat of the shape of 
 a cone, with the point turned 
 down and a little to the left, 
 with the broad end turned 
 toward the right shoulder. 
 The heart is about the size of 
 the person's fist. 
 
 The position of the point or 
 apex of the heart is easily de- 
 
 .11 11 
 
 termmed by the beats it makes 
 against the side of the chest, beween the fifth and 
 sixth ribs, a little to the left of the central line. 
 
 If the open hand be laid on the chest, so that the 
 tip of the middle finger is at the point where the 
 beats are felt, and the wrist is turned toward the right 
 shoulder, the hand will be over the heart. 
 
 LV 
 
 Fig. 24. 
 
 THE HEART. 
 RA , right auricle ; Rl', right 
 
 left ventricle. 
 
 , left auricle ; 
 
THE VESSELS CONNECTING WITH THE HEART 49 
 
 PA 
 
 PA 
 
 The Interior of the Heart. The heart is divided 
 into four rooms, two at the broad (upper ) end, the 
 auricles (Fig. 25 ), and two below these, in the nar- 
 rower end, the 'ventricles. There is a partition between 
 the auricles, and one 
 between the ventricles. 
 The auricles and ven- 
 tricles are distinguished 
 as right and lejt. 
 
 Between each auricle 
 and the ventricle below 
 it are flaps composed 
 of a strong membrane. 
 These flaps are arranged 
 as valves, which lie 
 against the ventricles 
 
 - LV 
 
 RV 
 
 when the blood passes 
 from the auricles to the 
 ventricles; but on an 
 
 Fig. 25. 
 
 DIAGRAM OF THE HEART. 
 
 'A, pulmonary a 
 >; FC/and VCS, 
 
 A, aorta; PA, pulmonary artery; P, 
 pulmonary veins; KC/and l/'CS, vena cava 
 
 . , , , , inferior and vena cava superior; 7 1 , tricuspid, 
 
 attempt OI the blOOd tO and M, mitral valve. The other letters same 
 . , as in preceding figure. 
 
 return to the auricles, 
 
 these valves are closed by the current. They are 
 shown closed in Fig. 25. The one on the right side, 
 the tricuspid valve, consists of three flaps, the one on 
 the left, the mitral valve, consists of two flaps. There 
 are also valves at the origin of each of the large 
 vessels leaving the heart, called semilunar valves. 
 
 The Vessels connecting with the Heart. From 
 the left ventricle there arises a large artery, the aorta, 
 whose branches are distributed to all parts of the 
 body. 
 
 From the right ventricle there arises an equally 
 
 IND. PR. PHYS. 4 
 
5O PARTS OF THE CIRCULATORY ORGANS 
 
 large vessel, the pulmonary artery. Its divisions go 
 to the lungs. 
 
 Opening into the right auricle are three large veins: 
 the superior vena cava, which receives blood from the 
 veins coming from the head, the neck, and the arms; 
 the inferior vena cava, which receives the blood com- 
 ing from the legs and most of the trunk; and the 
 vein from the heart itself, the coronary vein. 
 
 Opening into the left auricle are four pulmonary 
 veins, bringing blood from the lungs. 
 
 The Aorta and its Divisions. The aorta, as soon 
 as it leaves the heart, makes a turn called the arch of 
 the aorta, and passes down just in front of the spinal 
 column. It gives off branches at the very start from 
 the heart, and along its whole course. These branches 
 subdivide and go to each part of the body, where 
 they end in capillaries, as we have learned in the 
 study of the hand. Trace them in Fig. 26, represent- 
 ing the arteries. 
 
 The Veins. After the blood is gathered up by 
 the small veins it returns by a number of larger veins, 
 which correspond in their distribution generally in 
 each part of the body to the arteries. 
 
 Structure of the Heart. The walls of the heart 
 are made up of muscular tissue. The valves are of 
 connective tissue. There is a connective-tissue layer 
 covering the heart. A sac called the pericardium 
 surrounds the heart. Between it and the heart 
 is a liquid known as the pericardial liquid. This ar- 
 rangement allows the heart to beat with as little 
 friction as possible. The walls of the ventricles are 
 much thicker than those of the auricles, those of the 
 
Fig. 26. 
 
 DISTRIBUTION OF THE ARTERIES. 
 
THE DIVISIONS OF THE CIRCULATORY SYSTEM 51 
 
 left ventricle being thicker than those of the right. 
 The greater amount of work done by the left ventri- 
 cle requires this. 
 
 Structure of the Blood Vessels. The arteries 
 have strong walls of connective tissue, with some 
 muscular fibers, especially in the 
 small*arteries. The connective tis- 
 sue is largely of the elastic variety, 
 so that the walls of the arteries will 
 stretch like rubber. 
 
 The 'veins have much thinner 
 walls, which are mainly of inelastic 
 connective tissue, and consequently 
 they will not stretch. The small 
 veins have some muscular fibers in 
 their walls. Many of the veins have 
 valves in them, formed by pouches 
 of connective tissue, which allow 
 blood to pass toward the heart but prevent it from 
 going the other way. 
 
 The capillaries have extremely thin walls. 
 
 The Divisions of the Circulatory System. The 
 aorta, its branches and their subdivisions, the capilla- 
 ries into which they empty, and the returning veins 
 that empty into the right auricle, are known as the 
 vessels of the systemic circulation. The pulmonary 
 arteries, the capillaries of the lungs, with the pulmo- 
 nary veins, are the vessels of the pulmonary circula- 
 tion. 
 
 Fig. 27. 
 
 A VEIN LAID OPEN, 
 SHOWING ITS VALVES. 
 
CHAPTER V 
 
 THE PHYSIOLOGY OF THE CIRCULATORY ORGANS. 
 THE BLOOD. HYGIENE OF THE CIRCULATION 
 
 The Course of the Blood in Circulation. The 
 
 course of the blood in circulation is represented in 
 the diagram in Fig. 28. This shows how the heart 
 is a double pump, one portion being placed in each 
 of the systems of circulation, the pulmonary and 
 systemic. 
 
 As the valves are shown, the blood can flow but 
 one way, and before completing the circuit must pass 
 through the heart twice. It must also pass through 
 at least two sets of capillaries, those of the lungs 
 (pulmonary capillaries ), and those of some other part 
 of the body (systemic capillaries). 
 
 We may now consider the action of each part of 
 the circulatory system. 
 
 The Action of the Heart. The blood flows gently 
 from the large veins into the auricles, and these throw 
 the blood into the ventricles with enough force to 
 dash it up their sides, as water dashes up the sides of 
 a glass when poured into it. This action not only fills 
 the ventricles, but closes the valves between the auri- 
 cles and ventricles. 
 
 52 
 
THE BLOOD IN THE ARTERIES 
 
 53 
 
 Then the ventricles immediately contract and force 
 the blood past the semi- 
 lunar valves, the right 
 ventricle into the pul- 
 monary artery, and the 
 left ventricle into the 
 aorta. The heart is a 
 very active pump, mak- 
 ing about seventy- two 
 strokes a minute. 
 
 The Blood in the Ar- 
 teries. The pulse felt 
 near the wrist is caused 
 by the shock given to 
 the blood in the arteries 
 by the beat of the left 
 ventricle. 
 
 The capillaries are so 
 small and numerous 
 that their walls make a 
 very large surface for 
 the blood to flow over. 
 The friction from this 
 surface is great enough 
 to hold the blood back. 
 As the heart keeps up 
 the pumping, the ar- 
 teries become so full of 
 blood that their elastic 
 walls are stretched to 
 give it room. 
 
 Every time the heart 
 
 Fig. 28. 
 
 DIAGRAM OF THE COURSE OF THE BLOOD. 
 
 RA, right auricle; RV, right ventricle; LA 
 and LV, left auricle and left ventricle; VCf 
 and yCS, vena cava inferior and superior; 
 Ao, aorta; Lg t lungs; A I, alimentary canal; 
 Lr, liver; VP. portal vein; Ly, lymphatics; 
 Th D, thoracic duct; Let. lacteals; HA and 
 HV, hepatic artery and vein 
 
54 PHYSIOLOGY OF THE CIRCULATORY ORGANS 
 
 beats, the walls of the whole system of arteries spring 
 out. It is this that we feel in the pulse. 
 
 Pressure of the Blood in the Arteries. By being 
 held back at the capillaries and forced on at the 
 heart, the walls of the arteries stretching to receive 
 it, the blood becomes so crowded in the arteries that if 
 an artery is accidentally opened the blood spurts 
 from it with great force. This condition of the blood 
 in the arteries is like that of water in a reservoir; it 
 is under pressure. 
 
 The Blood in the Veins. In the veins the blood 
 flows by a steady stream, very slowly in the small- 
 est veins, and gradually quickening toward the heart. 
 If a vein be opened, the blood flows from it, but with 
 little force. It is not under very much pressure in 
 the veins. 
 
 The Use of the Blood Pressure in the Arteries. - 
 The advantages of the arrangement just discussed 
 are: 
 
 First. While the blood is thrown out from the 
 heart in jerks, it will flow into the capillaries in a 
 steady stream. The pulse gradually decreases in 
 force from the heart to the capillaries, where it dis- 
 appears. This is a very important advantage. The 
 walls of the capillaries must be thin to allow the 
 blood to soak through them to the tissues. Thin 
 walls could not endure a stream of strong jets with- 
 out breaking. 
 
 Second. As the blood is under pressure on the 
 arterial side, and under little or no pressure on the 
 venous side, the amount of blood going to any or- 
 gan may be regulated by widening or narrowing the 
 
ACTIONS OF THE CIRCULATORY ORGANS 55 
 
 arteries going to it. The muscular substance in the 
 walls of the small arteries does this by contracting or 
 relaxing. 
 
 This advantage is just as important as the first 
 given, for without it there would be no means of 
 regulating the supply of blood to each of the organs. 
 All parts would receive blood equally at all times, 
 whether they needed it or not. 
 
 The Action of the Capillaries. It may be re- 
 called that the blood supplies the tissues with food, 
 water, and oxygen from the air; but this is not all 
 that the blood does. It also takes away from the 
 tissues certain substances which they in their ac- 
 tivity are constantly making, and which, if they 
 remained in the tissues, would be very injurious to 
 them. 
 
 Now, the changes between the blood and the tis- 
 sues can take place only through the very thin walls 
 of the capillaries. The liquid part of the blood, and 
 whatever may be dissolved in it, can soak through 
 the thin walls of the capillaries, and the substances 
 dissolved in the liquid part of the tissues may soak 
 through in some way to the blood, which carries 
 them along in its current to be disposed of elsewhere 
 by processes to be described in other chapters. 
 
 Then it may be said that all the changes between 
 the blood and the tissues take place in the capillaries, 
 and that the object of the other parts of the circula- 
 tory system is to drive the blood continually through 
 the capillaries. 
 
 Regulation of the Actions of the Circulatory Organs. 
 The heart is composed of involuntary muscles and can 
 
56 PHYSIOLOGY OF THE CIRCULATORY ORGANS 
 
 not be influenced by the will, but its rate of beating 
 is often changed to suit the needs of the body. If one 
 counts his pulse before performing some vigorous 
 exercise, and again a short time after he has begun 
 it, he will find the pulse in the latter case more fre- 
 quent. The heart has been stimulated by its nerves 
 to greater action. 
 
 At the same time, in the parts of the body that 
 are in action the small arteries dilate a little by relax- 
 ing their muscular walls. This allows a greater amount 
 of blood to flow into them. When any part is not 
 in vigorous action, small arteries which furnish it 
 with blood contract their walls and lessen the supply. 
 
 These actions are regulated by nerves in a way to 
 be studied when we come to the nervous system. 
 
 Properties of the Blood. The blood is familiar 
 to every one as a bright red liquid. The shade of red 
 varies in the body from the bright red to a very dark 
 red. Seen through the thin walls of the veins, it 
 appears blue. 
 
 The microscope shows that the blood is com- 
 posed of a nearly transparent liquid, in which is 
 suspended a cloud of immense numbers of little 
 particles. 
 
 The liquid is plasma, and the particles are blood 
 corpuscles. 
 
 Blood Corpuscles. There are two kinds of blood 
 corpuscles the red and the white. 
 
 The red corpuscles, when very greatly magnified, 
 are seen to be thin round disks with slightly concave 
 sides. They are about 3^Vo ^ an ^ nc ^ * n diameter. 
 Although they are called red corpuscles, their color 
 
CO A G ULA TION 5 7 
 
 is but a faint yellow. It is only in great numbers 
 that they give the mass the appearance of red. 
 
 They differ somewhat in shape and size in different 
 animals. Fig. 29 shows the ap- 
 pearance of the red corpuscles 
 from the human blood, and Fig. 
 30 those from the blood of a frog. 
 The white corpuscles are few in 
 number compared with the red. 
 They are colorless and of irregu- 
 lar Shape. HUMAN RED BLOOD CORFUS- 
 
 The Use of the Red Corpuscles. CIES " HlGHLY MAGNIFIED - 
 The red corpuscles in the lungs take up oxygen, 
 one of the gases of which the air is composed, and 
 carry it to the tissues, which require oxygen constantly. 
 The Plasma. The liquid part of the blood is very 
 complex. It is receiving water and digested food 
 
 from the digestive 
 system all the time, 
 and various substances 
 which the tissues are 
 constantly producing. 
 It is very evident that 
 the blood must have 
 
 ^^ dissolved in it all the 
 Fig. 30. 
 
 BLOOD CORPUSCLES OF A FROG. HIGHLY MAG- SUbstanC6S Which are 
 
 N1FIED - required for the growth 
 
 of the tissues, as they have no other source of supply. 
 Coagulation. Soon after the blood is taken from 
 the blood vessels it has the power to form into a 
 mass which has the appearance of jelly, called clot. 
 This process is called coagulation. This is accom- 
 
58 HYGIENE OF THE CIRCULATION 
 
 plished by some substances which are always in solu- 
 tion in healthy blood. But the moment that the 
 blood comes in contact with some other body than 
 the uninjured wall of the blood vessel, these sub- 
 stances form into very fine threads throughout the 
 whole mass of the blood, holding the corpuscles en- 
 tangled in their network. 
 
 HYGIENE OF THE CIRCULATION 
 
 In studying the hygiene of the circulation we have 
 to consider the blood on the one hand and the ma- 
 chinery for circulating it on the other hand. Since 
 we must rely on the blood to supply every part of the 
 body constantly with oxygen and food, and to carry 
 away its wastes, it is of the greatest importance that 
 the circulatory system be in the best condition possible. 
 
 Good Blood. Good blood, then, depends on good 
 food supplied to the digestive system, and on a good 
 condition of that system so that the food may be prop- 
 erly prepared and handed over to the blood. But it 
 depends also on pure air and the proper working of 
 the lungs ; and further on the working of the skin and 
 kidneys that get rid of certain wastes. The care of 
 the blood may, therefore, be studied in detail in con- 
 nection with the organs by which it is affected. 
 
 Germs of Disease. The blood is good food not 
 only for the cells of the body, but also for many germs 
 of disease, which are living microscopic animals or 
 plants that sometimes enter the blood. And since 
 the blood circulates to every part of the body, these 
 germs may be carried along and give rise to various 
 
USES OF COAGULATION 59 
 
 forms of disease. Some of these will* be spoken of 
 in another place at greater length. (See Chapter 
 XIX.) 
 
 Dangers of a Wound. Thus it happens that a 
 wound is dangerous not only because of the loss of 
 blood, but also because it gives entrance to the disease 
 germs in the air about us. 
 
 Uses of Coagulation. The blood has a successful 
 way of stopping its flow from a wound, if not too 
 large a vessel has been severed. It is by coagulation, a 
 process described in a former section, which by plug- 
 ging up the vessels prevents loss of blood. When, how- 
 ever, a moderately large artery is cut or broken, the 
 force of the current is so strong that before coagula- 
 tion can take place so much blood may be lost as to 
 produce death. In such a wound the blood vessels 
 must be compressed by force until coagulation can take 
 place. Of course, a physician should have charge of 
 such cases as soon as possible. But as death might 
 result before the physician could come, a knowledge of 
 what to do is of great importance. 
 
 If only capillaries or small vessels are cut, the bleed- 
 ing is slow, and chance for a clot to be formed is 
 good, so there is not much danger. It is when an 
 artery is cut that there is danger. By referring to Fig. 
 26, the positions of the main arteries may be seen. 
 Since the blood in the arteries flows from the heart 
 toward the ends of the extremities, it is plain that to 
 stop the flow of the blood we must press on the artery 
 on the side of the cut toward the heart. We can push 
 down hard on the artery with our fingers, or the pres- 
 sure can be made by tying a bandage tightly around 
 
60 HYGIENE OF THE CIRCULATION 
 
 the limb with a hard knot just over the artery. Hold- 
 ing the limb up above the heart will help much. If 
 the case is severe, the bandage may be made tighter 
 by twisting it up with a short stick. The knot may 
 be made harder by including in it a small, round stone 
 or other hard body to press down on the artery. 
 
 Care of the Heart. The center of the circulatory 
 system is the heart. Moment by moment our lives 
 depend on the correct and continuous action of this 
 pump that works night and day, it may be through a 
 long life. We have seen that its action is regulated 
 through the nervous system by the conditions of the 
 various parts of the body. It beats more quickly and 
 vigorously when exercise makes necessary a more rapid 
 circulation through the muscles, and more slowly dur- 
 ing sleep when the body is most quiet. During health 
 and good general condition of the body the heart does 
 its work without trouble or fault, adapting itself to 
 violent exercise or the most quiet rest. 
 
 Effects of Narcotics. It is very important then to 
 do nothing that will disturb the nicely regulated way 
 in which the circulatory system works. As has been 
 seen, the stimuli which come from the various parts of 
 the body by means of the nervous system make the 
 heart's action and the expanding and contracting of 
 the blood vessels just right for the needs of the different 
 parts of the body. If the heart or blood vessels re- 
 ceive stimuli from artificial sources, the natural regu- 
 lation of their action is disturbed, and the various parts 
 of the body must suffer in consequence. The most 
 common substances used by man causing this disturb- 
 ance of the circulation are: 
 
ALCOHOLIC DRINKS, ETC. 6 1 
 
 Alcoholic Drinks, Tobacco, Coffee, and Tea. Emi- 
 nent physiologists have come to the conclusion that 
 alcohol acts directly on the heart, weakening its action 
 and decreasing its power of doing work. While the 
 heart may beat faster through the presence of alcohol 
 in the blood, the beats are not so strong, and the whole 
 effect is to make the blood circulate less rapidly. Alco- 
 hol is thus regarded as having a paralyzing action on 
 the heart. 
 
 When alcohol is given to a patient suffering from 
 some disease or from an injury, the heart may be stimu- 
 lated to greater action. In such a case the result, it is 
 maintained, is not due to the direct action of the alcohol 
 on the heart. But this whole question would require 
 for its discussion much technical knowledge, and would 
 be out of place in this book. It is here brought to 
 notice simply to show that it is a more difficult subject 
 than it is considered by those who are ready to make 
 so many definite assertions regarding it. 
 
 Whatever may be the immediate cause, however, it 
 is well known that certain diseases of the heart are 
 likely to follow the long-continued use of alcoholic 
 drinks. The general vitality and tone of the heart are 
 impaired, and it is thus rendered more liable to attack 
 by disease. Its structure may become distinctly modi- 
 fied, fatty and connective tissue taking, to some ex- 
 tent, the place of muscular tissue, as seen in fatty 
 degeneration of the heart. The smaller blood vessels 
 in certain regions of the body may become in a 
 measure paralyzed, and thus permanently distended. 
 It is claimed also that alcohol has the power to take 
 a part of the oxygen out of the red Wood corpuscles, 
 
62 HYGIENE OF THE CIRCULATION 
 
 whose office, it will be remembered, is to carry 
 oxygen. 
 
 Tobacco used continuously in excess will affect the 
 heart injuriously, weakening it and making its action 
 irregular. It also weakens the blood vessels. Coffee 
 and tea also have an injurious effect when used in 
 excess. 
 
 Effect of Excessive Exercise. It has been pointed 
 out that when the muscles of the body are thrown into 
 exercise, the heart works harder to keep the circulation 
 in the right condition for the muscles. Continued vio- 
 lent action, such as running or climbing a mountain, 
 and the like, forces the heart to do much extra work. Of 
 course, like the other muscles, it can stand this without 
 injury if not carried to excess, but excessive exercise 
 affects the heart as well as the body muscles. Persons 
 with hearts that are naturally weak or that have been 
 weakened by sickness must be careful to avoid sudden 
 violent action of the body. Violent actions on the part 
 of young persons recovering from some weakening dis- 
 ease may lead to permanent weakness of the heart, or 
 in some cases may prove fatal. 
 
CHAPTER VI 
 
 HOW THE BODY WORKS. ITS NEED FOR FOOD AND 
 OXYGEN 
 
 WE take food so that we may be able to do work 
 and to grow, also to replace parts of the body that are 
 worn away. We know that if the body receives no 
 food it soon loses in weight, the person becomes faint 
 and weak, and after a time the body is unable to do 
 anything, the heart stops beating, and death results. 
 
 But how does food help us work ? This is a subject 
 difficult to study; but we may learn something of it if 
 we examine some of the machines invented by man 
 and see what conditions are necessary for them to keep 
 up their action. First, then, let us consider how the 
 body may be regarded as a machine. 
 
 The Body as a Machine. The study we have been 
 giving to the body shows it to be a very complex 
 machine. Many kinds of work are constantly being 
 performed by its different parts, such as pumping by 
 the heart, moving and changing the food by the 
 stomach and intestines, seeing by the eye, hearing by 
 the ear, and so on. 
 
 Organs and Systems. In physiology, a single part 
 that does one kind of work is called an organ. Thus 
 the eye is the organ of sight, the ear is the organ of 
 hearing, and the heart is one of the organs of circula- 
 tion. All the organs that together perform one of 
 
 63 
 
64 HOW THE BODY WORKS 
 
 the great actions of the body make up what we call 
 a system. The circulatory system includes the heart 
 together with the arteries, veins, and capillaries; that 
 is, all the organs which manage the blood and keep it 
 moving through the body. Besides, we have the nerv- 
 ous system, the muscular system, the bony system, and 
 the digestive system. In each case, the system includes 
 all the separate organs that do the parts of the work of 
 one big process. Now, as the body as a whole is com- 
 posed of these systems grouped together, it can be seen 
 what is meant by saying it is very complex. 
 
 What is meant by Organization. Its Advantage. 
 That all these parts work together so well proves that 
 all is well organized. What is meant by " organized "? 
 This can be illustrated by a school. The pupils in it 
 are put into various grades according to their age and 
 advancement in their studies, then in each grade are 
 arranged classes in the different subjects. The other 
 people about the school building the principal, the 
 teachers, and the janitor also have special things to 
 do. Then there are programmes of study, recitation, 
 and play. By planning the school in this way, a large 
 number of pupils study, recite, and do the other school 
 work without loss of time and energy. Without plans 
 of this kind, all would be confusion, and no work 
 could be accomplished. 
 
 A shop or store would further illustrate organiza- 
 tion, for in it each person employed does some part 
 of the whole work to be done. The one who manages 
 the business plans a great piece of work which no one 
 could do alone, but by dividing it up into parts which 
 separate people can do, the whole is easily done. When 
 
TISSUES 65 
 
 all that each does is brought together, the work of the 
 business is complete. It is only by organization that 
 great things can be accomplished. These are examples 
 of organization of people into systems. An example of 
 organization of non-living things would be that of a 
 steam engine. Here the parts are fitted together, so 
 that they accomplish their end, but in an unorganized 
 heap they could do nothing. In nature it is only in 
 animals and plants that we see organization of the 
 parts to accomplish the work. It is for this reason that 
 living things are called organisms. Man and the higher 
 animals are the most complex organisms. There are 
 forms of animals much more simple than man. They 
 do not have so many organs to do the work of living, 
 and, consequently, their lives are more simple. 
 
 Tissues. The word "tissue" is often used in physi- 
 ology, and as it is a convenient and important word we 
 should know its meaning. By it is meant one of the 
 materials of which the parts of the body are made. 
 Some examples of tissues are bony tissue, muscular 
 tissue, fatty tissue, connective tissue, nervous tissue. The 
 hard solid portion of a bone is made of bony tissue, the 
 part of a muscle which contracts and does the work is 
 the muscular tissue. The connective tissue includes the 
 tendons, ligaments, and bands that tie bones together 
 into joints, fasten muscles to bones, and hold parts of 
 organs together. Nervous tissue is the material of the 
 brain, the spinal cord, and the nerves. 
 
 The tissues are living, and it is they which must be 
 supplied with food and oxygen. The bony and con- 
 nective tissues are mostly used for support for other 
 tissues and organs, while the nervous and muscular 
 
 IND. PR. PHYS. 5 
 
66 . HOW THE BODY WORKS 
 
 tissues are the great workers of the body. Especially 
 is this true of the muscular tissue, as we have seen. 
 
 The Work of the Body. The main work of the body 
 is to produce motion, but there are other important 
 things its tissues must do. The body must make heat 
 to keep itself warm. Parts of it must make certain liq- 
 uids, such as saliva, gastric juice, and others, for diges- 
 tion and other purposes. Nervous impulses must be 
 formed to act on the muscles. These are some of the 
 things the body must do. How does the body perform 
 this work ? Heat and motion are produced by us out- 
 side of the body by certain contrivances for those pur- 
 poses, and we can best understand how the body can 
 produce heat and motion by comparison with our 
 invented machinery. 
 
 The Work of a Steam Engine. The steam engine is 
 a very common means of producing motion. The mo- 
 tion is made by burning coal in a furnace, which makes 
 great heat. This heats the water until it turns to 
 steam; the steam pushes on the piston and moves it. 
 The piston is connected with the rest of the machinery 
 and thus the work is done. In this we get both heat 
 and motion by burning coal. In burning the coal we 
 must have plenty of air. The air is a mixture of sev- 
 eral things. One of them is the gas oxygen. It is the 
 oxygen of the air that is used in burning the coal. Both 
 the coal and the oxygen are necessary to produce the 
 heat and motion. If either is lacking, the fire goes 
 out and the engine stops. 
 
 How the Body is like an Engine. To keep itself 
 warm and to perform its varied motions, the human 
 body, like the steam engine, requires oxygen, while 
 
WHAT HEAT DOES 6? 
 
 food takes the place of coal. Indeed, the food we eat 
 contains some of the same substances that are in coal, 
 and if we dry it, we can burn it in the furnace of an 
 engine and cause heat and motion. Now some other 
 things show the body to be acting like a steam engine* 
 If you catch all the substances which come out of the 
 chimney and examine them carefully, they are found 
 to be mainly carbonic dioxide and vapor of water, and 
 then if you examine the substances which the body 
 throws off at the lungs, skin, and kidneys, they also 
 are found to consist mainly of carbonic dioxide and 
 water. Coal and oxygen are burned to carbonic dioxide 
 and water in the engine, while food and oxygen are 
 burned to carbonic dioxide and water in the body, and 
 in both cases heat and motion are produced. 
 
 The " burning," as we have called it, seems different 
 in the body from that in the engine. In the engine it 
 takes place rapidly, causing great light and heat, while 
 in the body it takes place more slowly, causing much 
 less heat, less motion, and no light. But after all, the 
 union of the food with oxygen is the same as the union 
 of coal with oxygen. The chemical word for " burn- 
 ing," as used here, that is, for the union of oxygen with 
 other substances, is oxidation. The substance burned 
 is said to be oxidized. Just as the work of the engine 
 stops when coal and oxygen are no longer supplied, so 
 the work of the body stops when it is deprived of food 
 and oxygen. 
 
 What Heat Does. If we examine the work done in 
 the world, it can mostly be traced to the agency of 
 heat. 
 
 Heat gives rise to the currents of air or winds which 
 
68 HOW THE BODY WORKS 
 
 sail our ships or turn our windmills or form the waves 
 that beat against the shores, breaking them down and 
 grinding them up. 
 
 Heat evaporates the water from the ocean, which, 
 after being carried by the winds, falls on the land, to 
 run back again, in its course carving out mountains 
 and hills and building up new land, as well as carry- 
 ing loads for us, or running our machinery. 
 
 Heat from oxidations runs the many forms of en- 
 gines now employed to do a great amount of the work 
 that is accomplished by civilized nations. 
 
 Heat also does the work of our bodies by means of 
 oxidations of food and air. 
 
 Food needed for Growth and Repair. In one very 
 important way, however, the body is not like the 
 engine. An engine can not repair its own parts, and 
 the fuel supplied to it has nothing to do with building 
 up its own material. The body, however, not only 
 keeps warm and does work, but it grows and repairs 
 Us own parts, and the material needed for this repair, 
 as well as that burned up to produce heat, or motion, 
 or some other form of energy, must be supplied in the 
 food. 
 
 Composition of the Body. Every tissue of the body 
 contains compounds of carbon, hydrogen, oxygen, and 
 nitrogen. These compounds, with water, make up by 
 far the greatest part of the body. Besides these sub- 
 stances, there exist in many of the tissues some others 
 which serve particular purposes. The most conspicu- 
 ous example is that of osseous tissue, which contains, 
 as we have seen in the study of the bones, compounds 
 of lime. In the tissues small amounts of compounds 
 
WASTES 69 
 
 containing sulphur, phosphorus, iron, sodium, potas- 
 sium, chlorine, and some other substances may be 
 found. 
 
 All these substances must be in the food and drink, 
 the study of which will be taken up in the next chapter. 
 It may therefore be said that one other object of the 
 food is to supply materials for the growth and repair of 
 the tissues. 
 
 Wastes. This is a term which applies to the com- 
 pounds which result mainly from the oxidations of the 
 body during its work and growth. They are mainly 
 carbon dioxide, water, and a nitrogenous substance 
 (which is formed and excreted by the kidneys ) called 
 urea. They are called wastes because they can no 
 longer be of use to the body and must be thrown away 
 
CHAPTER VII 
 FOODS 
 
 The Forms of Food, as we see them brought to the 
 table, are mixtures of certain substances, some of which 
 occur in many different foods. For example, sugar is 
 naturally in the fruits, and is often added to other 
 foods in their preparation. Again, starch is present 
 in the bread, in the potatoes, in the pudding, and in the 
 pie. Fat or oil may occur in several foods, either natu- 
 rally, as in the meats, or by its use in cooking. 
 
 Kinds of Food Substances. For convenience in 
 study these foods are put into groups which may be 
 called the food groups. The food substances that is, 
 the substances which make up the foods that are placed 
 on the table are of two general classes, the organic 
 and the inorganic. 
 
 The organic food substances are those which are de- 
 rived from plants and animals, and make up most of 
 the food we take. Among these substances those most 
 alike in their composition are put together into groups. 
 
 The Starch and Sugar Group. Chemists have found 
 that the different kinds of starches and sugars are all 
 composed of the same elements, and are alike in many 
 other ways. Indeed, starch can be changed into sugar. 
 Gums, such as gum arabic, belong to the same group. 
 
 The starches are derived from plants, and are espe- 
 cially abundant in all grains and seeds used for food. 
 
 70 
 
THE GROUP OF PROTEIDS Jl 
 
 They occur also in the leaves, stems, and roots of plants, 
 as in cabbage, lettuce, potatoes, and sweet potatoes. 
 Sugars are usually obtained from plants, but one kind 
 is found in milk. They are found in ripe fruits, and, 
 indeed, may be in any part of the plant. 
 
 In the plant the starch is often changed to sugar, as 
 is seen in the change from a green to a ripe apple. Man 
 has learned how to accomplish this change, and every 
 year large quantities of starch are made into sugar for 
 the market. Gums form but an unimportant part of 
 the food. 
 
 The Group of Fats. This group includes the vari- 
 ous fats and oils found in milk, in the flesh of animals, 
 and in plants. The words "fats" and "oils" are simply 
 relative terms, fats being applied to those of the group 
 which are solid at an ordinary temperature, of which 
 tallow is an example, while oil is a liquid at the same 
 temperature, such as olive oil. 
 
 The Group of Proteids. A third group of organic 
 food substances consists of a number of substances 
 that are very common in the different forms of food, 
 but since they are not commonly separated from them, 
 as are starch, sugar, and fat, they are not familiar sub- 
 stances. The most familiar example of this group is 
 the white of an egg. This is mainly egg albumen, with 
 a large amount of water. 
 
 Most of the other members of the group of proteids, 
 if they could be separated from the substances which 
 contain them, would look and act very much like the 
 albumen of the white of an egg. For example, they 
 would coagulate when heated, and act in other ways 
 which lead chemists to recognize them as similar. 
 
72 FOODS 
 
 The lean of meats is rich in proteids. There is a 
 proteid in milk. 
 
 Cheese has a large amount of proteid in it. Peas 
 and beans are rich in proteids, and grains have a con- 
 siderable amount. Some vegetables, such as potatoes, 
 have small amounts. 
 
 The proteids contain nitrogen while the other groups 
 do not. From this fact the proteids are sometimes 
 called nitrogenous foods, and the fats, starches, and 
 sugars are called the non-nitrogenous foods. 
 
 Some plants can manufacture all the different kinds 
 of food substances from the soil, water, and air. 
 Animals can not do this, but must have the pro- 
 teids, fats, sugars, and starches already made for 
 them. Consequently, they must take for food either 
 such substances as a plant has produced, or the tis- 
 sues of some animal that has eaten plants or other 
 animals. 
 
 All animals live by the death of other organisms, 
 man being no exception. Many plants are like ani- 
 mals in this respect. Those which do not possess the 
 green color found in leaves, called chlorophyll, can not 
 live on inorganic foods. The mushrooms, molds, mil- 
 dews, and many forms of parasitic plants that is, 
 plants that live on the substance of other plants are 
 examples. All plants without chlorophyll must have 
 for their food some organic substance. 
 
 Food Substances ready to be Oxidized. The food 
 substances that we have just been studying can all be 
 burned; that is, they will unite with oxygen, either 
 within the body or outside the body. The fats, 
 starches, and sugars when oxidized produce water and 
 
THE USE OF INORGANIC FOODS 73 
 
 carbon dioxide as well as heat. The proteids, in addi- 
 tion, give off a substance containing nitrogen. 
 
 We could burn meat, bread, eggs, peas, beans, and 
 the various grains in the furnace of a boiler and get 
 sufficient heat to run the engine. We have already 
 seen that they are oxidized in the body with the same 
 results. 
 
 The Inorganic Foods. This division includes water 
 and various mineral substances, of which the great- 
 est amount used is common salt. The others are taken 
 in very small amounts mixed with the other foods. 
 The salts, or salines, are the same as those mentioned 
 as being in the tissues of the body. They are com- 
 pounds of lime, magnesium, sodium, and potassium. 
 They are absorbed by the plants from the soil, and 
 from this source we obtain them, either directly from 
 the plants or indirectly through the flesh of animals 
 which have fed on them. 
 
 The Use of Inorganic Foods. From the inorganic 
 group of foods the tissues obtain their supplies of the 
 mineral substances used in their structure, but none of 
 these can be oxidized, and hence can not be the source 
 of heat or motion. 
 
 Water, the principal one of the inorganic foods, 
 is also one of the most important. Its use is to 
 form solutions so that the liquid blood and lymph 
 may be possible, and that the tissues may make the 
 exchanges with the blood. All the processes of the 
 body depend on the presence of water. The tissues 
 might be said to live on substances dissolved in water. 
 A slight reduction of this water causes a severe thirst, 
 which drives us to make good the loss. 
 
74 FOODS 
 
 The Proportion of the Different Foods needed in the 
 Body. To accomplish the three main purposes of 
 foods viz. to keep the body warm, to furnish it 
 means to perform its work, and to furnish it with mate- 
 rial for growth it is evident that there might be a 
 combination of food substances that would have the 
 best proportions. 
 
 What these proportions are has been the subject of 
 much investigation. It has been shown that if too 
 much nitrogenous food be taken, the labor of the body 
 is greatly increased in getting rid of the extra amount. 
 If this is continued for a considerable length of time, 
 serious diseases are sure to follow. 
 
 The right proportion of the non-nitrogenous foods to 
 the nitrogenous is said to be about four parts of the 
 first to one of the second. These proportions are about 
 those in milk, or in wheat flour when in the form of 
 " Graham flour." 
 
 Meats, peas, and beans, when taken alone, have 
 more than the needed nitrogen, while rice and pota- 
 toes do not have enough. 
 
 Many experiments have been made to determine just 
 how much of each kind of food is sufficient for the body. 
 Such knowledge is of great practical value when food 
 must be provided for large numbers, such as armies, 
 navies, and large bodies of working men, to determine 
 how much of each kind to buy and how much to dis- 
 tribute to each man. If the same rules were applied 
 to the selection of food for family life, no doubt very 
 much could be saved that is now worse than wasted. 
 As the food is brought to the table of the ordinary 
 family, all the groups are pretty sure to be sufficiently 
 
THE USE AND ABUSE OF THE APPETITE 75 
 
 represented, so that each one is supplied with both sub- 
 stances that contain nitrogen and those that do not; 
 but people who are very poor are not always able to 
 procure food in enough variety to afford the proper 
 nourishment. 
 
 The Use and Abuse of the Appetite. It is important 
 to remember that the use of the appetite, or desire for 
 food, is to regulate the amount and kind of food neces- 
 sary for the body. Just as the body has a way of in- 
 creasing or diminishing the respiration according to its 
 needs, and a way of regulating the beating of the heart 
 for different conditions, so by means of hunger and 
 thirst it can regulate the amount of food and drink 
 necessary for its growth. As the needs of the body 
 vary much according to age, occupation, climate, and 
 the particular disposition of the individual, it would be 
 impossible to determine for each one on every day just 
 the amount and kind of food he needs. If the wisest 
 scientific men were wise enough to do this, it would 
 still be impossible for the great majority of people to 
 make use of this wisdom from hour to hour. Thus 
 we see the great importance of appetite and of having 
 it work naturally. If this one of nature's most impor- 
 tant gifts is disturbed or becomes unnatural, the body 
 may take in too much food or too little, or the food 
 may be of the wrong kind, lacking some of the elements, 
 and having too much of others, which in time is sure 
 to lead to very serious results. The appetite may be 
 disturbed or become unnatural either by sickness or by 
 forming habits of eating or drinking too much food or 
 food of the wrong kind. In case of sickness a physi- 
 cian should be consulted as to the proper diet. Where 
 
76 FOODS 
 
 poverty and want do not exist, the tendency seems to 
 be to get into habits of eating too much. Parents 
 often urge upon little children more food than they 
 need. Habits of eating are thus formed with an appe- 
 tite not quite natural. Craving for food then grows 
 beyond the needs of the activity of the body. When 
 more food is taken into the blood than is needed, the 
 body is overworked in trying to rid itself of the excess, 
 and this constant overwork is sure in time to bring on 
 severe troubles, like rheumatism, gout, kidney troubles, 
 etc., besides rendering the body less efficient for all its 
 work. A simple and moderate diet taken regularly is 
 of the greatest importance for maintaining health and 
 insuring a long life. 
 
CHAPTER VIII 
 
 PARTS OF THE DIGESTIVE SYSTEM. CARE OF THE 
 TEETH 
 
 As we learned in the last chapter, the tissues con- 
 stantly require food for their activity. But they can not 
 use this food until it is much changed. As has been 
 pointed out, the tissues are nourished by the blood, 
 which is carried to them by the blood vessels. The 
 blood gets its supply from the food we eat, but the 
 latter undergoes much change before it enters the blood. 
 
 Much of the food is solid material that will not dis- 
 solve in water, while the plasma of the blood, that is 
 all the blood except the corpuscles, is a liquid. It is 
 the plasma which gives food to the tissues. 
 
 Now it is the work of digestion to change the foods 
 so that they can pass through the lining membrane of 
 the alimentary canal and the walls of the capillary 
 blood vessels and into the plasma of the blood. All 
 this is possible only when the food is in a liquid form. 
 Whether the food be beans, meat, bread, or potatoes, 
 that part which is to be food for the tissues must be 
 dissolved. It is the object of digestion to reduce food 
 to a liquid form. 
 
 Foods that require Digestion. The sugar is readily 
 soluble in water and is usually already dissolved in the 
 food or drink that we take ; consequently, it needs no 
 further action that it may be absorbed into the body. 
 
 77 
 
78 PARTS OF THE DIGESTIVE SYSTEM 
 
 But of the starches or the proteids taken as foods some 
 can not dissolve sufficiently in water for this purpose, 
 others not at all. 
 
 The oils, it is true, are in a liquid form, and the fats 
 will be melted to a liquid form by the heat of the body, 
 but still they will not soak through the membranes 
 without special preparation. 
 
 The water remains unchanged, being absorbed as 
 water, passing to all parts of the body, and being 
 thrown out of the body as water. 
 
 The mineral substances taken in the food are in 
 minute quantities already dissolved, and, of course, 
 need no digestive action. 
 
 It may be said, then, that of the foods, the proteids, 
 the fats and oils, and the starches and the gums must 
 be digested. 
 
 How is Digestion Accomplished? The foods are 
 digested by being taken into the alimentary canal, 
 where at various parts they have mixed with them 
 certain liquids which will change the food substances 
 so that they become liquids; then the food substances 
 in liquid form are absorbed and brought into the blood. 
 
 The Alimentary Canal. The alimentary canal is a 
 tube about thirty feet in length, passing through the 
 body, into which the food is placed to be subjected to 
 the liquids which make these changes in the foods. 
 It is variously modified along its course into different 
 parts which perform different actions. 
 
 All these parts, together with the organs connected 
 with them which form the digestive liquids, are called 
 the digestive system. The digestive system consists of 
 the mouth and the salivary glands, the pharynx, the 
 
THE MOUTH 79 
 
 esophagus, the stomach, the small intestine, with the 
 liver and the pancreas, and the large intestine. 
 
 Glands. The essential part of digestion is accom- 
 plished by liquids poured upon the foods. These 
 liquids are formed by organs called glands. Glands 
 are used also in other parts of the body to form liquids, 
 as, for example, to form sweat and tears. 
 
 Very simple forms of glands are very minute tubes 
 or sacs, which are surrounded by a network of cap- 
 illaries. The lining of a gland forms the liquid pecul- 
 iar to it, which is called its secretion. This flows out 
 of the mouth of the tube. The gland tissue gets from 
 the blood near it the material from which it forms its 
 secretion. 
 
 In large glands, the tubes are divided into very 
 many branches, so that the gland is in the form of a 
 tree with its branches, except that the branches are 
 crowded and folded together in a somewhat solid 
 form. 
 
 The divisions of the parts of the tubes greatly in- 
 crease the secreting surface of the gland. In all the 
 branching a network of capillaries follows each minute 
 branch. 
 
 The Mouth. This part of the system can be so well 
 studied from a view of the object itself that the printed 
 description should be relied upon only for learning the 
 names of the parts. 
 
 The mouth forms a cavity, which, when closed, is 
 well filled by the tongue and the teeth projecting into 
 it. It has very movable walls at the front and sides in 
 the lips and cheeks, whose middle layers contain many 
 muscles, which produce their great number of motions. 
 
80 PARTS OF THE DIGESTIVE SYSTEM 
 
 The tongue, projecting from the floor of the mouth, 
 is extremely movable. The roof, the palate, is hard 
 in front and soft at the back, ending in a curtain 
 which hangs down to make the posterior wall of the 
 mouth. The two curved rows of teeth just strike each 
 other. 
 
 Besides the motions of the lips, cheeks, and tongue, 
 the whole lower part of the mouth can be moved up 
 and down, from side to side, and from front to back, 
 by the muscles that move the lower jaw. 
 
 Determine from your own mouth what these motions 
 are and where the muscles are placed that produce them. 
 
 Placed in the surface 
 of the tongue are the 
 little organs of taste. 
 In the walls of the 
 mouth everywhere are 
 little glands which se- 
 crete mucus, the liquid 
 which, mixed with the 
 secretion of the salivary 
 ig ' ' glands, is the one which 
 
 LOWER JAW BONE WITH THE TEETH. , , 
 
 we know as constantly 
 
 in the mouth. The salivary glands empty their secre- 
 tion into the mouth. 
 
 The Teeth. The position and characteristic forms 
 of the teeth can be plainly made out in one's own 
 mouth by the use of a mirror. Fig. 31 shows how 
 the teeth in the lower jaw are set into the bone. The 
 teeth appear in two sets. There are ten in each jaw 
 of the first set, which appears in childhood, and six- 
 teen in each jaw of the adult. The four front teeth 
 
MASTICA TION 
 
 81 
 
 in each jaw are called incisors ; the next one on each 
 side is a canine; the next two, the bicuspids or pre- 
 molars ; and the last three are the molars. The same 
 teeth occur in many animals and in the same order, 
 but not always of the same number. They are much 
 varied in form among the different animals to adapt 
 them to the many uses to be made of them. Many 
 animals use their teeth for other purposes besides that 
 of chewing. 
 
 Structure of a Tooth. Fig. 32 shows the inter- 
 nal view of a tooth cut through from the top or crown 
 to the tips of the roots. It 
 shows it to consist of three 
 substances: a layer of enamel 
 (i) over the crown; a layer of 
 cement, which is of the same 
 structure as bone, around the 
 roots; these lie on the main 
 substance of the tooth, the 
 dentine, or ivory (2). 
 
 These are very hard sub- 
 stances, the enamel being the 
 hardest. In the center of the 
 tooth the hollow space is filled 
 with blood vessels, nerves, and connective tissue. They 
 come in at the points of -the roots. These together 
 are called the pulp (3). 
 
 Mastication. The mouth has other uses besides its 
 action on the foods, the chief one of which is that of 
 speaking. Its work with the foods is to crush and 
 divide them, that they may be swallowed first, and 
 afterward may be moved along the remainder of the 
 
 IND. PR. PHYS. 6 
 
 Fig. 32. 
 
 STRUCTURE OF A TOOTH. 
 i, enamel; 2, dentine; 3, pulp cavity. 
 
82 PARTS OF THE DIGESTIVE SYSTEM 
 
 alimentary canal to be acted upon by the digestive 
 liquids. The process is known as mastication. 
 
 If one will take a portion of food into his mouth and 
 proceed to masticate it, and at the same time note the 
 action of the" tongue, lips, cheeks, lower jaw, and teeth, 
 he will learn how deftly the food is handled by them, 
 being first taken to one part of the mouth, then to an- 
 other. All the hard portions are brought between the 
 teeth, where they are crushed. In the meantime the 
 food is mixed with saliva until it is formed into a ball, 
 when it is, by a quick motion of the tongue against 
 the roof of the mouth, shot into the next division of 
 the alimentary canal, the pharynx. 
 
 The Saliva. The saliva has very important func- 
 tions. It allows dry food to be swallowed; it dis- 
 solves the food so that it may be tasted ; together with 
 the mucus it moistens the lining of the mouth and tjie 
 larynx, thus making possible the motions of speech. 
 
 It has also the power to digest the starch. It does 
 this by changing it into sugar. The food is in the 
 mouth so short a time that this action is only begun 
 there, but it is continued for a time in the stomach. 
 The starch is also digested in another place, as we 
 shall see. 
 
 The Salivary Glands. The salivary glands are ar- 
 ranged in three pairs, one pair in the sides of the face, 
 just in front of the ears, one pair by the angles of the 
 lower jaw, and one pair just under the tongue where 
 it is attached to the floor of the mouth. 
 
CARE OF THE TEETH 83 
 
 CARE OF THE TEETH 
 
 The second set of teeth, the permanent set, after it 
 is complete, must last us the rest of our lives. If one 
 is taken out, it is not replaced, or if a piece is broken off, 
 it does not grow again, as a piece of skin might do. 
 If a part of a tooth decays, leaving a hole in it, it never 
 heals, but on the contrary the hole gets larger and 
 larger until the whole tooth is destroyed. Since this 
 is true, it behooves us to take good care of these useful 
 tools which are to serve us daily, it may be for fifty or 
 sixty years or even a longer time in a long life. 
 
 Nature's method of protecting the human teeth is 
 by the enamel covering of the crown. This hard, im- 
 pervious covering not only gives a flinty surface for 
 cutting and grinding which stands the daily wear of 
 so many years, but it successfully keeps out the bac- 
 teria which cause decay of the dentine if they can 
 get at it. Thus we see the importance of prevent- 
 ing any break in the enamel, which is often chipped 
 off by cracking nuts or biting hard surfaces with the 
 teeth. Particles of food left on the teeth for long 
 periods will make places where colonies of bacteria 
 may form, resulting in the deposit of substances on 
 the teeth which may even cause the decay of the 
 enamel, and in course of time of the dentine as well. 
 
 This may especially occur near where the tooth 
 joins the gums, where the enamel is the thinnest and 
 where food particles find the easiest place to lodge. 
 It is plain that the best thing to be done is to keep 
 the surface of the enamel clean. This is done, of course, 
 by rinsing the mouth after eating, by cleaning with a 
 
84 CARE OF THE TEETH 
 
 cloth, toothbrush, toothpicks, and, for particles be- 
 tween the teeth, a thread. It is better that the brush 
 be soft, so as not to wound the gums, and that the tooth- 
 picks be of soft material, not metal, so as not to en- 
 danger the enamel. Although it is not easily scratched, 
 yet years of bad usage could affect it. The cleansing 
 should, when possible, occur after each meal, but 
 surely after the evening meal, since so long a time 
 intervenes between it and the next meal. 
 
 The teeth of some people are much more ready to 
 decay than those of others, and consequently more 
 care must be taken by tjiem to avoid trouble. But 
 with the greatest care decayed places will appear 
 sometimes. These begin as very small places and may 
 remain unnoticed unless a special search is made for 
 them. They may even grow to considerable size in 
 the mouth of a careless person. Now the dentist 
 knows how to stop the decay of a tooth. He fills it 
 with hard material which preserves it and makes it still 
 a useful tooth. But the sooner the dentist discovers 
 the defect, the better it can be treated, the more of the 
 tooth saved, to say nothing of the pain, trouble, and ex- 
 pense escaped. It would be best then for a dentist to 
 examine the teeth occasionally to see if any trouble has 
 begun. Once a year is not too often, and if the teeth 
 show a disposition to have coats of tartar form on them 
 the dentist should be employed to clean them. 
 
 Sometimes the permanent set comes in before the 
 jaw bones have grown large enough to receive them 
 in even rows and the teeth become crowded, and in 
 some people these bones never are large enough to 
 hold the teeth properly. In such a case, if it is thought 
 
CARE OF THE TEETH 85 
 
 desirable to apply any remedy, a dentist should be 
 consulted early, and he may help in the matter and 
 the rows of teeth may be kept straight and even. 
 
 The teeth, like other parts of the body, may suffer 
 from general ill health or from disease of the body. 
 In such a case the remedy must go further than simple 
 care of the teeth. A physician is our help in such a 
 case, as the bad teeth are only a sign of other troubles 
 in the body. 
 
CHAPTER IX 
 
 DIGESTION. CARE OF THE DIGESTIVE ORGANS 
 
 The Pharynx. Just beyond 
 tary tube becomes the pharynx. 
 
 LI - 
 
 Fig. 33. 
 
 GENERAL VIEW OF THE ALIMENTARY CANAL. 
 
 O, esophagus; S, stomach; SI, small intes- 
 tine; LI, large intestine; Sp, spleen; Z., liver 
 (raised up); G, gall bladder; Pa, pancreas. 
 
 86 
 
 the mouth the alimen- 
 There are several open- 
 ings into this portion, 
 one from the mouth, 
 one from each nostril, 
 one from each middle 
 ear, one into the lar- 
 ynx, the organ where 
 the voice is produced, 
 and the opening into 
 the next division of 
 the alimentary canal, 
 the esophagus. 
 
 The Esophagus. - 
 This is the portion 
 of the alimentary 
 canal which extends 
 from the pharynx to 
 the stomach. It is 
 eight or nine inches 
 in length. It and the 
 pharynx are lined 
 internally with a 
 mucous membrane. 
 Outside of this are 
 the muscular walls. 
 
THE STOMACH 
 
 Swallowing. The food is sent forcibly from the 
 mouth into the pharynx. The pharynx acts some- 
 thing like a funnel over the top of the esophagus. 
 When the food is in the pharynx, its muscular walls 
 close around it and quickly push it into the esophagus, 
 where portions of the circular bands of muscles relax 
 before the food, and others contract behind it to push 
 it on into the stomach. Water is served exactly in the 
 same way, and both water and food can be swallowed 
 when the head is down as well as when it is erect. 
 
 The Stomach. This organ is a part of the ali- 
 mentary canal more dilated than the other portions, 
 and so arranged 
 
 as to retain the ^|^ Esophagus 
 
 food in it a cer- 
 tain length of 
 time. (Fig. 34.) 
 
 It is in the 
 upper part of 
 the abdominal 
 cavity some- 
 what to the left 
 side. The open- 
 ing at the point 
 where the esoph- 
 agus joins it is 
 called the car- 
 diac opening; the one at the opposite end, where the 
 small intestine joins it, is called the pylorus. 
 
 In this latter place the muscular walls form a ring, 
 which remains contracted some time after a meal is 
 taken, opening and closing from time to time to allow 
 
 Fig. 34. 
 
 SECTION OF THE STOMACH. 
 
88 DIGESTION 
 
 liquids to pass, thus retaining the more solid portions 
 for the digestion which takes place in the stomach. 
 It finally relaxes and allows all the contents to pass 
 on to the small intestine. 
 
 Digestion in the Stomach. The mucous coat of the 
 stomach is filled with small glands which secrete a 
 liquid known as gastric juice. During the presence of 
 food in the stomach this liquid is poured out on it in 
 considerable quantities. 
 
 Gastric juice affects only one of the food groups, the 
 proteids. When these food substances are kept with 
 gastric juice a certain length of time, they are changed 
 into soluble forms of proteids called peptones. This 
 change takes place slowly. To cause the gastric juice 
 to become thoroughly mixed with the food, the muscu- 
 lar walls of the stomach, by contracting in many differ- 
 ent directions, push it around, backward and forward, 
 many times. 
 
 Absorption from the Stomach. A very great num- 
 ber of capillary blood vessels forms a close network 
 in the mucous coat immediately next to its surface. 
 This arrangement brings the blood so near the liquid 
 in the stomach that nothing but a very thin wall of 
 membrane lies between them. This allows the liquid 
 contents of the stomach and what may be dissolved 
 in it to soak through to the blood. 
 
 Besides these blood vessels, there are also the lym- 
 phatics, arranged in the same position, so that they 
 may also receive liquids from the stomach. 
 
 The process by which a liquid may pass into either 
 of these vessels is called absorption. The rapidity with 
 which it occurs is shown by the quick effect which some 
 
THE SMALL INTESTINE 
 
 8 9 
 
 medicines have on the body when taken into the 
 stomach. 
 
 The Small Intestine. The small intestine is a much 
 narrower tube than the stomach. It is about twenty 
 feet in length. It is suspended from the margin of a 
 membrane called the mesentery, the inner edge of which 
 
 Fig. 35. 
 
 DIAGRAMMATIC. 
 
 SECTION OF THE Mucous COAT OF THE SMALL INTESTINE. 
 GREATLY MAGNIFIED. 
 
 Some of the villi have their covering layer removed to show the structure. The 
 tubes are intestinal glands. 
 
 is gathered together in one place and fastened to the 
 back of the abdominal cavity. 
 
 The coats of the small intestine are exactly the 
 same in name and arrangement as those of the stom- 
 ach. But the mucous coat differs from the same coat 
 of the stomach in being densely covered with minute 
 projections. 
 
90 DIGESTION 
 
 These are shown very much enlarged in Fig. 35. 
 They are the mill. They are special arrangements 
 for absorption. Each one has in it, as shown in the 
 figure, a network of capillary blood vessels, and an- 
 other kind of small vessels called the lacteals. They 
 empty into the thoracic duct. Over each villus is a 
 very thin layer of tissue, which allows digested food 
 substances to pass through either to the blood vessels 
 or the lacteals, from which it soon enters the general 
 circulation. 
 
 Secretions coming into the Small Intestine. The 
 mucous coat has in it besides the villi a very great 
 number of glands which secrete the intestinal juice. 
 
 The pancreas is a large gland lying just behind the 
 stomach. It forms the pancreatic juice , and pours it 
 into the small intestine by its duct, which empties 
 into the small intestine a short distance below the 
 pylorus. 
 
 The Liver. The liver is a very large gland, placed 
 just under the diaphragm, mainly on the right side. 
 It empties its secretion, the bile, into the small intes- 
 tine at a point very near the opening of the pancreatic 
 duct. The pancreatic juice and bile are immediately 
 mixed with each other and with the food. 
 
 Digestion in the Small Intestine. The digestion 
 which goes on in the small intestine may be considered 
 as the most important of all, since the pancreatic juice 
 acts with energy on proteids to change them into the 
 soluble peptones, on the starches to change them into 
 sugar, and on the fats to change them into a state in 
 which their particles are extremely minute, small 
 enough to find their way through the thin layer over 
 
THE BILE 
 
 the villi. Some of the fats are also changed into sub- 
 stances which will dissolve. 
 
 The Bile. This liquid comes in very large amounts 
 into the intestine during digestion. 
 
 It has been shown to have very slight direct diges- 
 tive action on any of the foods, but it is known to aid 
 the process of digestion 
 in various ways. Among 
 them it may be men- 
 tioned that the bile makes 
 the contents of the intes- 
 tine alkaline, which is 
 necessary to the action 
 of the pancreatic juice, 
 and that it in some way 
 aids in the absorption of 
 the fats. 
 
 It has probably many 
 other uses, as it is a very 
 complex liquid. Our or- 
 dinary foods contain a 
 considerable amount of 
 substances which are not 
 acted on by any of these 
 fluids, termed indigest- 
 ible parts. 
 
 These are, by the constant motions of the small in- 
 testine, sent along to accumulate in the large intestine. 
 They move more and more slowly as they pass along, 
 that the last amount of digested food may be ab- 
 sorbed before these substances are removed from the 
 body. 
 
 Fig. 36. 
 
 LACTEALS. 
 
 Showing the connection of the small intes- 
 tine to the thoracic duct by the lacteals lying 
 in the mesentery. Th, thoracic duct. 
 
Q2 DIGESTION 
 
 Absorption. As already mentioned, absorption 
 may take place from the stomach and from the small 
 and large intestines. It is mainly from the small in- 
 testine. The food, after being absorbed, may reach 
 the heart, and from it the general circulation, by two 
 different courses: 
 
 i st. That which is taken up by the blood vessels goes 
 by the portal vein to the liver, through the capil- 
 laries of the liver to the hepatic vein in the liver, 
 into the inferior vena cava, and thence to the 
 heart. 
 
 2d. That which is taken up by the lacteals passes on 
 to the thoracic duct, Fig. 36, from which it empties 
 into the left subclavian vein, and from this it soon 
 reaches the superior vena cava. 
 These two courses will be made clear by consulting 
 the diagram of the circulation of the blood, given in 
 the chapter on Circulation. 
 
 Conclusion. In a former section it was said that 
 the food of the tissues is the blood. We have now 
 seen one source from which the food is constantly added 
 to the blood. It is placed in parts of a vessel, the ali- 
 mentary canal, and at different places the liquids 
 change different members of the food groups into 
 solutions. These are given in the following table: 
 
 1. Saliva acts on the Starches. 
 
 2. Gastric Juice acts on the Proteids. 
 
 ( Starches. 
 
 3. Pancreatic Juice acts on the \ Fats. 
 
 [ Proteids. 
 
 These made soluble and the sugar already dissolved 
 bring all the principal foods into liquid form. 
 
CARE OF THE DIGESTIVE ORGANS 93 
 
 THE CARE OF THE DIGESTIVE ORGANS 
 
 The processes of digestion are all reflex, involuntary 
 acts, and in good health generally take care of them- 
 selves. It has been found that the various foods take 
 quite different lengths of time for digestion. It does 
 not seem that a food is better for being quick to digest. 
 For those who live on a vegetable diet do not suffer 
 inconvenience from the fact and are certainly as 
 healthy as a rule as those who eat largely of meats, 
 although meats are the more easily digested. The 
 human digestive system seems to be adapted to the 
 digestion of foods that take a long time to digest as 
 well as to those taking a short time. The secretion of 
 the digestive juices and the movements of the stomach 
 and intestines are accomplished by nervous impulses 
 which under good conditions of the body are just 
 sufficient to get the best results by reflex action. But 
 the normal working of the nerves controlling these 
 acts may be disturbed and thus disturb the proper 
 action of the digestive system. Through this means 
 the digestive system may be affected by nervous states 
 of the body. 
 
 A fit of indigestion may be due to excitement or mental 
 distress. Dyspepsia may be induced and fostered by 
 constantly thinking of the effect that this or that kind of 
 food has upon one. Of course if some one with delicate 
 digestive organs learns by experience that a certain 
 food disagrees with him, he ought to avoid it. But, 
 to say nothing of bad taste, it is a bad habit from a 
 hygienic standpoint constantly to question any kind 
 of food presented and to discuss its effects. 
 
94 CARE OF THE ^DIGESTIVE ORGANS 
 
 We have already spoken of the importance of a 
 healthy appetite in the selection of food. It may be 
 added that when food is palatable, that is, " tastes 
 good," digestion generally proceeds better. Thus there 
 is good physiological reason for the proper prepara- 
 tion of the food. And this is the principal purpose 
 of cooking. Cooking, however, serves other important 
 purposes. It makes many foods more digestible, for 
 example, potatoes, and destroys the germs of many 
 diseases which may possibly be present. The alimen- 
 tary canal is a great gateway through which disease 
 may enter the body. This subject, however, will be 
 more fully explained under Disease. 
 
CHAPTER X 
 RESPIRATION 
 
 IT has already been shown how very necessary 
 oxygen is to all the tissues of the body. The mus- 
 cles and the brain especially use large amounts of 
 oxygen and they must have a supply every moment. 
 The oxygen, as was explained in the chapter on Cir- 
 culation, is mainly carried by the red blood corpuscles 
 to the tissues. But the blood gets its oxygen from the 
 lungs, and the lungs get their supply from the air 
 breathed into them. 
 
 Breathing has another use besides bringing oxygen 
 to the blood. It carries carbonic acid away from the 
 blood. It will be remembered that when the food of 
 the tissues unites with the oxygen, one of the things 
 made is carbonic dioxide. This is sometimes known 
 as a " waste " substance. It must be removed. The 
 blood carries it away from the tissues to the lungs, 
 and every time the air is breathed out from the lungs 
 some of this carbonic dioxide is thrown from the body. 
 Thus we see that breathing has two very important 
 uses : one, the bringing of oxygen into the body, and the 
 other, the taking of carbonic dioxide out of the body. 
 
 Respiration is the term for breathing. We shall 
 now study the apparatus for respiration: what its 
 parts are and how they work to draw the air in and 
 throw it out again. 
 
 95 
 
9 6 
 
 RESPIRA TION 
 
 The Respiratory Organs. The part of the appa- 
 ratus which accomplishes the constant removal of 
 the air consists of the thorax and the lungs, which 
 hang as two sacs in its cavity, and the tubes in the 
 lungs, and the large one which connects them with 
 the outer air. 
 
 If we name the air passages in order from without, 
 they are the nostrils and the mouth, the pharynx, the 
 larynx, the trachea, its two large 
 branches, the bronchi and their 
 numerous branches, the bronchial 
 tubes, which become so small in 
 their subdivisions as to require the 
 microscope to see them. These end 
 in groups of minute air sacs, men- 
 tioned above. They are micro- 
 scopic. 
 
 A group of these air sacs, or vesi- 
 cles, is shown in Fig. 37. Among 
 these are close networks of pul- 
 monary capillaries. 
 Structure of Air Tubes. The trachea, bronchi, and 
 bronchial tubes have a framework of cartilaginous 
 rings, which hold them open on all sides. The rings 
 have connective tissue between them and around 
 them. The lining of the passage is mucous membrane, 
 in which is a large number of mucous glands, whose 
 secretion is constantly forming. 
 
 The mucus is made to flow toward the throat by 
 means of very minute projections, seen only with 
 higher powers of the microscope, which are on the 
 surface of the mucous membrane. These are the cilia. 
 
 i 
 Fig. 37. 
 
 AIR VESICLES. 
 
 
THE RESPIRATORY APPARATUS 
 
 97 
 
 They keep up a constant waving motion, which car- 
 ries the mucus along, together with dust which settles 
 on it from the air. 
 
 The Thorax. The lungs are suspended in the cavity 
 of the thorax. The bony support of the thorax is 
 shown in Fig. 38, and 
 consists of the dorsal 
 vertebrae, the ribs, and 
 the sternum. In this 
 framework, while the 
 ribs are attached at 
 their extremities, their 
 middle portion can be 
 moved up and down 
 by muscles between 
 them and those attached 
 to them from above and 
 below. The muscular 
 partition between the 
 abdomen and the tho- 
 rax, the diaphragm, forms the bottom of the thorax. 
 
 The Respiratory Apparatus. The essential part 
 of the breathing apparatus is a thin membrane, so 
 arranged that the oxygen can come on one side and 
 the blood on the other. In such a case the oxygen 
 can pass into the blood and the carbon dioxide out. 
 
 In the lower animals, the breathing apparatus is 
 found in many different forms. The gills of a fish 
 are familiar to all. But all these forms, different as 
 they may be in other regards, have the essential 
 arrangement spoken of above. The oxygen is always 
 either in the air, mixed with the other gases before 
 
 IND. PR. PHYS. 7 
 
 Fig. 38. 
 
 BONY WALLS OF THE THORAX. 
 
9 8 
 
 RESPIRA TION 
 
 mentioned, or it is dissolved in the water which has 
 obtained it from the air. 
 
 In the gills of the fish the delicate fringes are so 
 many projections of very thin skin, through the core of 
 which the blood circulates, but on the outside of which 
 
 Larynx. 
 
 Fig. 39. 
 
 THE HEART AND LUNGS. 
 
 the water with the dissolved oxygen is made to pass. 
 In the lungs of a man there are little thin-walled sacs, 
 into the centers of which the air comes, and around the 
 surface of which the blood circulates. The rest of the 
 apparatus is to pump the air in and out of the passages 
 
INSPIRA TION 
 
 99 
 
 which are connected with these little air sacs, so. that 
 there may be a constant change of the air. 
 
 The Respiratory Acts. Respiration consists of 
 two acts: inspiration, by which an amount of air is 
 brought into the lungs ; and expiration, by which 
 about the same amount is expelled. The lungs hang 
 in the thorax as elastic sacs in air-tight cavities. As 
 there is nothing but a little liquid between the outer 
 walls of the lungs and the walls of the thorax, the 
 
 Fig. 40. 
 
 THORAX IN EXPIRATION. 
 
 Fig. 41. 
 
 THORAX IN INSPIRATION. 
 
 pressure of the air, which is fifteen pounds to the 
 square inch, swells the lungs out against these walls. 
 
 If now the walls of the thorax are pulled away a 
 little more, the pressure of the air on the inside of 
 the lungs makes them follow the retreating walls of 
 the thorax. On the other hand, when the walls of the 
 thorax press upon the lungs they are emptied to the 
 same extent. 
 
 Inspiration. In inspiration the cavity is enlarged. 
 
1 00 RESPIRA TION 
 
 This is accomplished in two ways: First, the dia- 
 phragm being curved upward pulls itself down by 
 contraction. Second, by the contraction of one set 
 of the muscles between the ribs (the external inter- 
 costals ) the ribs are raised, which motion, from the 
 way they are attached (see Figs. 40 and 41 ), throws 
 them out. 
 
 Expiration. This act consists in making the cav- 
 ity of the thorax smaller. This is done in two ways: 
 First, by the muscles of the walls of the abdomen 
 contracting and pressing upon the contents of the 
 abdomen, and thus forcing the diaphragm up again. 
 Second, by the other set of intercostals (the internal ) 
 contracting to pull the ribs down. In both acts many 
 other muscles may take part. 
 
 Nervous Control. These motions are regulated 
 by nerves, so that one follows the other in the proper 
 succession, frequency, and strength, each of which 
 varies much with the varying activity of the body. 
 For, the more work done, the greater must be the 
 supply of oxygen, and the greater the amount of 
 carbon dioxide to be got rid of. 
 
 Although these actions are involuntary, yet the will 
 may modify them, as it does in the act of speaking. 
 Ordinary respirations average about seventeen a minute. 
 
 It will be profitable to study in oneself or another 
 how this rate will vary in various kinds and degrees of 
 exercise, as well as the character of the act. Sighing, 
 crying, laughing, coughing, sneezing all are modifi- 
 cations of the respiratory actions, the character of each 
 of which the pupil should study from the actions 
 themselves. 
 
HO W OXYGEN IS BROUGHT TO THE AIR CELLS IOI 
 
 Changes in the Respiration. When air comes from 
 the lungs it has in it an increased amount of water and 
 carbon dioxide. It also has less oxygen and is warmer. 
 Besides these changes, air from the lungs contains cer- 
 tain organic substances, which are very small in amount 
 and can not be obtained in sufficient quantity to be 
 weighed. They are easily detected by the sense of 
 smell when one passes from the open air into a poorly 
 ventilated room in which a number of people are 
 gathered. 
 
 From these causes, air once breathed is not fit to 
 breathe again. There is not enough oxygen in it, and 
 the organic substances it contains seem to be real 
 poisons. 
 
 Amount of Air Breathed. The lungs of an adult 
 contain about one gallon of air. In an ordinary ex- 
 piration only about one pint of air is thrown , out. 
 This can be shown by breathing through a tube pass- 
 ing under the mouth of a bottle filled with water, and 
 inverted over water in such a way as to catch the air 
 breathed out. 
 
 The amount of air breathed into the lungs is about 
 the same. It can easily be seen that a pint of air 
 would only fill the trachea and the upper air pas- 
 sages. 
 
 How the Oxygen is brought to the Air Cells. - 
 Gases have the power to pass freely into each other. 
 This property is called diffusion. If a pint of each of 
 a dozen gases were put in different parts of a closed 
 room, in a short time they would be equally distributed 
 throughout the room. 
 
 By this property the oxygen that is in the upper 
 
IO2 
 
 RESPIRA TION 
 
 part of the lungs diffuses through the rest of the air 
 to the air vesicles, and the carbon dioxide diffuses 
 out to the upper part, where the acts of breathing 
 remove the old air and bring in the new. 
 
 Changes in the Blood. Once in the air vesicles, 
 the oxygen passes through the very thin membrane 
 
 Fig. 42. 
 
 LARYNX, SIDE VIEW. 
 
 T, thyroid cartilage; C, cri- 
 coid cartilage; TV, trachea; 
 H, hyoid bone; E, epiglottis; 
 /, joint of thyroid cartilage. 
 
 Fig. 43. 
 
 LARYNX, BACK VIEW. 
 
 Ar, arytenoid cartilages. The 
 other letters the same as in the pre- 
 ceding figure. 
 
 of their walls and the walls of the capillaries into the 
 plasma, where it is taken up by the red corpuscles. 
 These, by the current of the blood, are carried to the 
 tissues, to which the corpuscles give up the oxygen. 
 
 The carbon dioxide, on the other hand, passes from 
 the tissues to the blood, which sweeps it around to 
 the lungs, where it escapes. The water is also con- 
 tinually escaping at the lungs. 
 
THE LARYNX 
 
 103 
 
 Thus the organs of respiration and of circulation 
 are made the mediums of exchange between the out- 
 side air and the tissues far removed from them. 
 
 The Voice. Vocal sounds are produced in the 
 larynx by the air passing between the parallel edges 
 of two folds of the lining membrane of that organ. 
 These folds are the vocal cords, and are tightly stretched 
 and close together at the time of the sound, but are 
 relaxed and fall apart at other times. 
 
 The Larynx. The larynx, Fig. 42, placed on the 
 top of the trachea, consists of a box formed of a frame 
 of cartilaginous plates, some 4 
 
 of which can be moved on 
 the others by a number of 
 muscles. 
 
 The largest of these car- 
 tilages, the thyroid (see the 
 figure), forms the projec- 
 tion in the neck known as 
 11 Adam's Apple." It rests 
 on a ringlike base, the cricoid 
 cartilage. 
 
 The vocal cords are at- 
 tached to small cartilages at f/ g 44 
 
 the back Called the arytenoid, LIGAMENTS OF THE VOCAL CORDS. 
 
 and tO the thyroid in front. (' and 2), the ligaments; 3, aryte- 
 
 noid cartilages; 4, thyroid cartilage. 
 
 By the movements of these 
 
 cartilages the membranes of the vocal cords are 
 
 stretched and brought together, or separated. 
 
 The sound is produced by the air passing these in 
 a stretched condition and with their edges close to- 
 gether. Fig. 44 shows the ligaments and the cords 
 
1 04 RESPIRA TION 
 
 with the covering membrane removed. The sounds 
 of the letters are made to differ from each other by 
 giving different shapes to the mouth, pharynx, and 
 larynx. 
 
 The epiglottis is a lid which is made to close over 
 the larynx during swallowing, for the evident pur- 
 pose of keeping food out of the larynx. It will also 
 close promptly on breathing some poisonous gases. 
 The larynx, trachea, and lungs of some animal should 
 be studied. Also the movements and forms of the 
 mouth in forming the letters. 
 
 No other muscles in the body can be moved with 
 the rapidity and precision of those used in speaking. 
 They are greatly under the control of the will, and 
 can be trained to wonderful feats of singing and speak- 
 ing, and ought to be trained in every one for reading 
 and talking well. 
 
CHAPTER XI 
 
 PURE AIR, BREATHING, AND VENTILATION 
 
 GOOD health can not be kept unless the body is 
 supplied at all times with an abundance of pure air. 
 The reason for this has been repeatedly stated, and the 
 importance of the fact can not be too strongly empha- 
 sized. At this place we are to consider: (i) what pure 
 air is; (2) how much each one needs; and (3) how it 
 can be supplied. 
 
 Pure Air. What we call pure air is such as we find 
 out of doors in most places. It is about the same the 
 world over, because the winds which blow first in one 
 direction and then in another keep it well mixed up 
 and about the same in its make-up. When man and 
 animals can be supplied with this kind of air for breath- 
 ing they thrive well on it. Such air is a mixture of 
 certain gases. It consists of about one fifth oxygen 
 and nearly four fifths nitrogen, with small amounts of 
 carbonic dioxide and vapor of water and very small 
 amounts of other substances. Now if much more than 
 the usual amount of any of these gases is present 
 or if other gases are added, the air is said to be impure. 
 It is especially harmful for man or animals if the oxygen 
 is diminished or the carbonic dioxide is increased. 
 
 We have just seen that in inspiration about a pint 
 of air is taken into the lungs and air passages, and 
 
 I0 5 
 
106 PURE AIR, BREATHING, AND VENTILATION 
 
 during the expiration that follows a pint of air is 
 thrown out. The air that is thrown out has lost 
 considerable of its oxygen and has gained much car- 
 bonic dioxide, and besides it has gained other impuri- 
 ties coming from the body. It is now quite impure, 
 and should not be breathed again. Indeed, it has so 
 much of impurity in it that it will spoil for breathing 
 four pints of good air. If one is out of doors when he 
 breathes out this impure pint of air, the winds or cur- 
 rents of air, which are always in motion, carry it away 
 and bring for the next breath a fresh pint of pure air, 
 and thus one is constantly supplied with an abundance 
 of the right kind of air. But if the body is confined 
 in a closed room, the breathed-out air remains in the 
 room. If the room is large, the small amount of air 
 thrown out for a short time, mixed with the large 
 amount in the room, does not make much change. But 
 if the room is small, or if a large room is occupied for a 
 long time without change of air, the many pints of im- 
 pure air breathed out will make the whole roomful 
 impure. That is, the air in it will be lacking in oxygen 
 and have far too much carbonic dioxide. It would be 
 only a question of time, if all openings were closed so 
 that the air in the room could not either get out nor 
 fresh air get in, before death would result. This would 
 occur in a short time, if the room were quite small. 
 
 Ventilation. Thus rooms in which people live must 
 be so arranged that the air can be changed in them. 
 The changing of the air in a room is called 'ventilation. 
 Out of doors the movements of air, winds, and currents 
 provide a perfect ventilation. To get good ventila- 
 tion in a room or house it is important to know how 
 
VENTILA TION I O/ 
 
 much air should be supplied to each person. We will 
 now see how currents of air may be made so that the 
 air will flow in and out of the room and give the needed 
 supply. 
 
 Those who have studied this question by taking the 
 amount of air made impure by a single breath and 
 noting that there are seventeen or eighteen breaths in 
 a minute tell us that there ought to be supplied to 
 each grown person from 3000 to 3500 cubic feet of air 
 each hour, and to each child not less than 2000 cubic 
 feet of air per hour. Since the body when actively 
 at work uses more oxygen and throws off more car- 
 bonic dioxide than when at rest, it will need a greater 
 supply of air than the resting body. To illustrate 
 what these figures mean, an example might be used. 
 Three thousand cubic feet would be represented by a 
 room 10 feet high with a floor 20 feet long and 15 feet 
 wide. Now if one person were working in this room, 
 the ventilation should be good enough to change all 
 the air in it once every hour. If two were working in 
 the room, the ventilation should be good enough to 
 change the whole of the air in it every half hour. Or if 
 four persons were working in the room, the air should 
 be changed every fifteen minutes, and so on. You can 
 calculate the number of cubic feet in your schoolroom; 
 and then, taking into account the number of pupils 
 in the room, you can see how often the whole air in the 
 room should be changed. You can thus see whether 
 the ventilation is good enough for the number in the 
 room. 
 
 Many schools, workshops, and rooms where people 
 gather for various purposes are very badly ventilated. 
 
108 PURE AIR, BREATHING, AND VENTILATION 
 
 Either not enough space is given to each person or not 
 enough air is supplied to keep the air good. Sleeping 
 rooms are often too close, as well as the living rooms of 
 the home. Great care should be taken to have the 
 ventilation in all these right. There is no harm in 
 " night air " as some seem to think. Out-of-door air 
 is pure even at night, while indoor air at night in a 
 poorly ventilated room may become very bad. 
 
 How to secure Ventilation. One way of removing 
 the air and bringing in new air is by pumps or fans 
 run by machinery. These are sometimes used in 
 mines or in large buildings, but are, of course, out of 
 the question in most buildings 
 and ordinary homes. We have 
 to make use of the currents 
 formed in the air, by which 
 streams of air can be made to 
 flow into and out of the rooms. 
 Now how are currents in air 
 made? If you examine the air 
 
 Fig. 46. about a stove, or a lamp, when it 
 
 DIAGRAM OF THE CURRENTS OF J s heated, yOU will find that there 
 
 AlR IN A ROOM HEATED BY . . . 
 
 A STOVE, s. ALL OPENINGS is a current of air rapidly rising 
 over the stove, and that other cur- 
 rents near the floor are moving toward the stove. It is 
 the same with the lamp. The cause of these currents 
 is this: when air is heated it expands. If a certain 
 amount of air is expanded, it will be lighter than the rest 
 of the air about it, and the lighter will rise in the heavier 
 like a cork in water. Hot-air balloons rise because 
 the heated air in them is lighter than the air around 
 them. All the large currents of air out of doors which 
 
HOW TO SECURE VENTILATION 
 
 we call winds or breezes are made in the same way. 
 The sun warms some part of the earth and makes 
 the air next to it warm. This expands it, makes it 
 lighter, and the cooler, heavier air moves underneath 
 it and forces it up. When currents are started in 
 one place, these cause others to form in other places. 
 As the sun shines on most of the earth every day, these 
 changes are all the time going on out of doors, and 
 thus currents of air are all the time moving all over the 
 face of the earth, making a perfect ventilation. If we 
 always remember that warm air is lighter than cool 
 air and will rise in it, we can 
 always tell just how the currents 
 of air will be moving in a room. 
 As just seen, air will always 
 rise from a heated stove or radi- 
 ator, and cooler air will move 
 toward it. If the air in a 
 room is warmer than the air out- 
 side, a window open at the top 
 and at the bottom will allow the F '9' 4G - 
 
 , ,i CURRENTS OF AIR IN A ROOM 
 
 warm air to go out at the top as HEATED BY A STOVE> St WlN . 
 the cool air comes in at the lower DOW OPEN AT Top AND BOT - 
 
 TOM. 
 
 opening. If it is only open at the 
 
 top, the warm air will go out at that opening and cold air 
 will come in at the cracks about the door, windows, or 
 floor that are lower than the opening. In other words, 
 in a warm room warm air is all the time leaving by all 
 openings in the upper part of the room, and cool air 
 is coming in by all openings in the lower part of the 
 room. If the air in the room is colder than the out- 
 side air, just the opposite takes place; the cold air 
 
1 10 PURE AIR, BREATHING, AND VENTILATION 
 
 leaves by the lower openings and warmer air comes in 
 by the upper openings. If the air in the room is just 
 as warm as the outside air, no currents will take place 
 by natural means. Ventilation can then only be secured 
 by fanning or pumping the air in. Now these facts 
 show that it is easiest to ventilate a room when it is 
 warmer than the outside air. On a cold day in winter 
 small openings will serve as well to change the air in a 
 room as wide open windows would on a warm day in 
 summer. We can see, too, how it is difficult to keep 
 the room warm and at the same time well ventilated 
 in winter, or cool and at the same time well ventilated 
 in summer. In winter the warm air is escaping and 
 cold air is coming in, in summer the cooler air is escap- 
 ing and the warm air is coming in. 
 
 Some houses are arranged so that the air from the 
 oustide is brought in just under the stove or radia- 
 tor, and by this means it is heated as it comes into the 
 room. Hot-air furnaces bring warm air into the room 
 from without. This air is pure if the outside supply 
 to the furnace is good. When a room is heated by a 
 furnace, then the upper openings in the room should 
 be kept closed, and the lower ones opened. The warm 
 air comes in and pushes the cooler air, which is also 
 less pure, out of the lower openings. Thus ventilation 
 is secured without loss of so much of the warm air. 
 Openings in the upper part of a room heated by a 
 furnace allow both the warm air and the pure air to 
 escape. In whatever house one lives, in whatever room 
 he works or spends much of his time, and especially in 
 his sleeping room, he should examine the means of 
 heating and ventilation, and then study how to arrange 
 
HO W TO SECURE VENTILATION 
 
 III 
 
 Fig. 47. 
 
 CURRENTS IN A ROOM HEATED 
 BY A HOT-AIR FURNACE. WIN- 
 DOW OPEN AT BOTTOM. AIR 
 ENTERS FROM FURNACE AT F. 
 
 everything to have an abundant supply of air passing 
 through the room. This should not be less than 3000 to 
 3500 cubic jeet per hour jor a _ 
 grown person or 2000 jor a child. 
 As every room used will be some- 
 what different, each one must be 
 examined and arranged for. 
 
 In schoolhouses, factories, and 
 other buildings where numbers 
 of people are brought together 
 those skilled in the knowledge of 
 ventilation should be employed 
 to plan the buildings. It often 
 happens that a schoolroom must 
 have in it a large number of 
 pupils, with not enough space 
 for each and no way of ventilating except by windows 
 and doors. 
 
 On a cold day the opening of windows or doors will 
 cause a cold draft on some of the pupils, which is 
 of course very dangerous for them. Keeping all open- 
 ings closed is also harmful. This is a very bad arrange- 
 ment, as the room should be dangerous to no one. 
 Those in power should seek to remedy the difficulty as 
 soon as possible ; but until this is done the teacher and 
 pupils will have to manage the ventilation as best they can. 
 
 By experiment it should be determined which win- 
 dows and doors can be opened to give ventilation and 
 the least draft. Then every hour or so the pupils can 
 take a rest, and all windows should be opened for a 
 short time to clear out all the air. The drafts are not 
 so dangerous if the pupils are moving about. Then 
 
112 PURE AIR, BREATHING, AND VENTILATION 
 
 at recess all can leave the room, and the windows and 
 doors should be opened until the air is thoroughly 
 purified. 
 
 Other Impurities in Air. Thus far we have spoken 
 only of air made bad by breathing it. There are 
 other sources of impurities in the air. . When a candle, 
 lamp, or gas flame is burning in a room it uses up oxy- 
 gen quickly and throws into the air much carbon dioxide 
 and sometimes other gases more or less poisonous. 
 This is especially true of gas flames. When, then, 
 these are burning in rooms, the ventilation must be 
 increased. 
 
 Gases that come from sewers, cesspools, or decaying 
 materials may contain poisonous substances or germs 
 of disease. Care should be taken that no such places 
 with bad gases escaping from them are near dwellings- 
 Spaces underneath dwelling houses should be well 
 ventilated; otherwise the air there may become foul 
 and the ventilation of the house is sure to carry it up 
 into the house rooms. 
 
 All the air near the earth about dwelling houses, 
 along streets and roads, has more or less dust in it. 
 Much of this dust is harmless, and when it is breathed 
 into the lungs settles on the walls of the air passages, 
 where a slow current of mucus, which is made to flow 
 up and out along the lining of the walls, will carry this 
 dust out (see Respiration). But the dust may contain 
 germs of disease, which may thus get into the body 
 through the lungs. All this only shows still stronger 
 reasons for keeping all the ground under and about 
 the house clean and free from all these sources of foul 
 air and dust. 
 
METHOD OF BREATHING 113 
 
 Where houses are gathered together into towns 
 and cities, the public officers look after keeping the 
 streets and alleys clean. Every one should insist 
 that this be done, and help in doing it. 
 
 Effects of Impure Air. It has been pointed out 
 that death would soon follow if a person were confined 
 in a small and perfectly closed room without any ven- 
 tilation. Living in rooms poorly ventilated would not 
 produce death immediately, but would lead first to the 
 contraction of diseases, more or less dangerous as the 
 rooms were more or less poorly ventilated. One of 
 the surest cures for many diseases is life in the open 
 air, which insures perfect ventilation. If pure air can 
 be a cure for these diseases, surely pure air at the start 
 would have prevented them. 
 
 Method of Breathing. Even with plenty of good 
 air, habits of breathing may be such as not to make 
 the best use of the air. The lungs are best filled 
 when the body is erect, with the shoulders thrown 
 well backward, and as little pressure of clothing as 
 possible on the chest or abdomen. Air is a very 
 light substance, and a little pressure will easily prevent 
 the full amount from coming into the lungs. How 
 foolish to interfere at all with so important a thing as 
 breathing! In bed we should take such a position 
 that breathing will be not at all interfered with, and 
 the bed clothing should not rest too heavily on the 
 body. 
 
 It is good to form a habit of occasionally taking 
 a deep breath while walking or exercising in the 
 open air. By this means all parts of the lungs are 
 well expanded and rendered active. A habit of stoop- 
 
 IND. PR. PHYS. 8 
 
114 PURE AIR, BREATHING, AND VENTILATION 
 
 ing and of never expanding the lungs deeply may favor 
 parts becoming feeble or diseased from little use. It 
 is certainly most important to cultivate good habits 
 of breathing. No part of Hygiene is more essential 
 than that concerning pure air, good ventilation, and 
 good breathing. 
 
 Tobacco and the Lungs. The most usual way of 
 using tobacco is by smoking, which is done by drawing 
 the smoke into the air passages. By this means 
 vapors of the burning tobacco pass into the blood 
 vessels. Nicotine is among these vapors, and to it the 
 particular effects of tobacco are due. There are other 
 substances among the vapors which have an injurious 
 effect either on the blood or on the tissues. The most 
 noticeable effect of tobacco is on the heart and on the 
 nervous system rather than on the lungs themselves. 
 
 Asphyxia is the term applied to the apparent death 
 which may occur in suffocation from immersion in 
 water or any other cause. The movements of respira- 
 tion have been suspended, and death may soon follow. 
 The course to be taken is to produce artificial respira- 
 tion until natural respiration returns. The following 
 are the celebrated directions known as: 
 
 Marshall Hall's Ready Method in Asphyxia. - 
 i st. 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. 
 
MARSHALL HALVS METHOD IN ASPHYXIA 115 
 
 3d. To excite respiration, turn the patient slightly 
 on his side, and apply some irritating or 
 stimulating agent to the nostrils, as vera- 
 trine, dilute ammonia, etc. 
 
 4th. Make the face warm by brisk friction; then 
 dash cold water upon it. 
 
 5th. If not successful, lose no time; but, to imitate 
 respiration, place the patient on his face, and 
 turn the body gently, but completely, on the 
 side, and a little beyond; then again on the 
 face, and so on, alternately. Repeat these 
 movements deliberately and perseveringly, 
 fifteen times only in a minute. (When the 
 patient lies on the thorax, this cavity is 
 compressed by the weight of the body, and 
 expiration takes place. When he is turned 
 on the side, this pressure is removed, and 
 inspiration occurs.) 
 
 6th. When the prone position is resumed, make a 
 uniform and efficient pressure along the spine, 
 removing the pressure immediately before 
 rotation on the side. (The pressure aug- 
 ments the expiration; the rotation com- 
 mences inspiration.) Continue these meas- 
 ures. 
 
 yth. Rub the limbs upward, with firm pressure and 
 with energy (the object being to aid the 
 return of venous blood to the heart). 
 
 8th. If possible, substitute for the patient's wet 
 clothing such other covering as can be in- 
 stantly procured, each bystander supplying 
 a coat or a cloak, etc. Meantime, and from 
 
Il6 PURE AIR, BREATHING, AND VENTILATION 
 
 time to time, to excite inspiration, let the 
 
 surface of the body be slapped briskly with 
 
 the hand. 
 Qth. Rub the body briskly till it is dry and warm; 
 
 then dash cold water upon it and repeat the 
 
 rubbing. 
 
 Avoid the immediate removal of the patient, as it 
 involves a dangerous loss of time; also, the use of 
 bellows, or any forcing instrument; also, the warm 
 bath and all rough treatment. 
 
CHAPTER XII 
 
 THE SKIN AND THE KIDNEYS 
 
 The covering of the body is one of the most im- 
 portant, and at the same time one of the most inter- 
 esting, organs to study. It has, as we shall see pres- 
 ently, several important uses. The one which is most 
 evident is that of protecting the parts below it from 
 mechanical injuries. In this way it acts as a strong 
 suit of clothing flexible and yielding, yet not easily 
 broken or torn. 
 
 General View. The skin is of a very complex 
 structure. It consists of two layers, which are so 
 arranged as to support very many different organs. 
 Fig. 48 is a considerably magnified representation of a 
 section made vertically through the skin. The whole 
 skin is about one tenth of an inch thick, or less in 
 many parts. It is thickest on the palms of the hands 
 and soles of the feet; and is thinnest at the joints 
 and wherever rapid motions are required, as over the 
 eyelids. 
 
 Structure of the Skin. The skin is composed of 
 two layers, as shown in the figure. The outer layer 
 is called the epidermis. It forms a thjn covering over 
 the dermis. The epidermis has no blood vessels in it, 
 and as to nerves, it has only the smallest nerve fibrils 
 in its lowest parts. It forms a layer that will not let 
 
 117 
 
THE SKIN AND THE KIDNEYS 
 
 water pass through it either into or out from the body. 
 It prevents poisonous substances from passing into the 
 body, and furnishes proper covering for the ends of 
 
 the nerves of touch and of 
 temperature. 
 
 Growth of the Epidermis. 
 The epidermis grows in its 
 lower layer of cells, which 
 crowd on those that lie above 
 and push them out. The 
 outer layers are constantly 
 wearing away. Thus one's 
 skin is always a comparatively 
 fresh one. 
 
 The Dennis. The lower 
 layer of the skin is the der- 
 mis. It is composed of a 
 closely woven sheet of connec- 
 tive tissue. In it are placed 
 great numbers of blood ves- 
 sels, a network of nerves, a 
 network of lymphatic vessels, 
 Fig, 48. immense numbers of sweat 
 
 SECTION OF THE SKIN. MAGNIFIED, glands, the sheaths of the 
 
 roots of hairs, and the oil 
 glands. 
 
 When the skin of an animal is made into leather 
 it is mainly the connective tissue of the dermis that 
 is tanned. 
 
 The dermis is tied fast to the rest of the body by 
 a layer of connective tissue. It is so fastened that it 
 may be loose enough to be pushed about a little over 
 
 H, hair; E, epidermis; D, der- 
 mis; P, papillae; S, mouth of 
 sweat gland; O, oil gland. 
 
FAT IN THE SKIN II 9 
 
 each point, and at the same time be pretty firmly 
 held in place over the whole body. The skin is really 
 stronger and tougher than one might suppose from its 
 appearance. 
 
 Papillae. The upper surface of the dermis is raised 
 into an immense number of small projections called 
 papilla. Fig. 49 shows some 
 from the palm of the hand from 
 which the epidermis has been re- 
 moved. These are found every- 
 where in the skin, but are most 
 numerous on the palms of the F '9- 49- 
 
 hands and the soles of the feet. 
 
 The epidermis fits Closely Over AMOVED. MAGNIFIED. 
 
 these and so nearly levels up the space between them 
 that their existence would not be known if viewed from 
 the surface of the skin. 
 
 But on the palms of the hands and soles of the 
 feet the epidermis can be seen to be in fine parallel 
 ridges. These ridges are over rows of papillae, just 
 beneath in the dermis. The papillae are shown both 
 in Fig. 48 and Fig. 49. In each papilla is a capillary 
 blood vessel and a network of nerves, and in very many 
 a minute, curiously formed body in which a nerve 
 ends, which may be a nerve of touch or one of 
 temperature. 
 
 Fat in the Skin. In the lower layer of the dermis, 
 in the meshes of the connective tissue, are many little 
 globules of fat. Sometimes the fat may increase to 
 such an extent as to make a thick layer between the 
 skin and the muscles and other parts beneath. When 
 this is the case the body is more rounded in outline. 
 
I2O THE SKIN AND THE KIDNEYS 
 
 This layer of fat serves to lessen the effects of blows 
 on the body and helps to keep it warm. 
 
 In some of the lower animals, such as seals and 
 whales, this layer is enormously developed. In the 
 whale it is known as the blubber. This arrangement 
 allows these animals to live in extremely cold climates, 
 and in the case of seals and walruses, to bear the 
 rough contact with rocks and ice which the manner 
 of life of a seal or walrus requires. The large amount 
 of fat found in these animals causes them to be hunted 
 for their oil. 
 
 The Sweat Glands. A sweat gland, Fig. 48, is 
 formed of a knot of a coiled tube placed in the lower 
 layer of the dermis. It is connected with the outer 
 surface of the skin by a continuation of its tube through 
 the two layers of the skin. 
 
 The coiled part secretes the sweat or perspiration, 
 which, carried to the surface, is poured out, to evapo- 
 rate completely if it comes out slowly, or to gather 
 into drops if it flows out rapidly. 
 
 The secretion of the sweat is regulated by nerve 
 fibers which come to the coiled part. The material 
 of the perspiration, which is mostly water, is fur- 
 nished by the blood flowing through a network of 
 capillaries inclosing the coiled tube. 
 
 Perspiration and the Temperature of the Body. - 
 Each one knows well that rapid running or exercise 
 of any kind, or even very little exercise on a very hot 
 day, will cause the sweat to form in large quantities 
 over the surface of the body. 
 
 Now, as this always occurs under the same cir- 
 cumstances, it might be supposed that there is some 
 
REGULA TION OF THE TEMPERA TURE OF BODY 121 
 
 reason for the connection of the two occurrences. 
 And such is the case. 
 
 Source of Heat in the Body. Let it be recalled 
 that the increase of motion of the body can occur only 
 by increase of the oxidations. This increase we found 
 always to be accompanied by the production of heat. 
 Increase of activity of any tissue increases the amount 
 of heat in the body. When the digestion is most active, 
 it is found that the blood coming away from the diges- 
 tive organs is warmer than that going to them. Besides 
 the heat produced in connection with the usual activi- 
 ties of the tissues, the body has the power to produce 
 oxidations in some of the tissues for the sole purpose 
 of increasing the heat. 
 
 The body is so constructed that it works best at a 
 temperature of 98 Fahr. If the temperature rises 
 above that limit only one or two degrees, there is 
 something wrong, and if it mounts two. or three degrees 
 still higher, life is in danger. If it fall much below 
 98, it is also in danger. 
 
 Regulation of the Temperature of the Body. 
 Now, special activity in the muscles in vigorous exer- 
 cise produces heat which would raise the temperature 
 higher than 98 if there were not a way to reduce it 
 by some pooling process. This process is by evapo- 
 ration of the water of the sweat. 
 
 Evaporation is a very effective means of cooling. 
 It requires a large amount of heat to evaporate a 
 small amount of water. 
 
 This is shown by placing a moist cloth on the bulb 
 of a thermometer. As the cloth dries, the mercury 
 shows, by falling several degrees, that it is cooled. If 
 
122 THE SKIN AND THE KIDNEYS 
 
 some substance like gasolene or ether, which evapo- 
 rates more quickly, is used, a very low temperature 
 can be produced, even though the experiment is car- 
 ried on in a warm atmosphere. 
 
 The sweat glands are all the time sending out water, 
 which generally evaporates as soon as it reaches the 
 surface. When an increase of heat in the body that 
 might bring the temperature of the body above 98 
 Fahr. occurs, the nerves stimulate the glands to work, 
 and thus to pour out a greater amount of sweat. The 
 amount sent out will be according to what may be 
 needed at that particular time to cool the body suf- 
 ficiently to overcome the increase in the heat. 
 
 This arrangement must act very promptly and very 
 perfectly, so that the body may keep the same degree 
 of temperature on going from a cold room to a warm 
 room, or from a cold day to a warm day, or from one 
 season to another. 
 
 We may say, then, that one of the most important 
 uses of the sweat glands is to regulate the temperature 
 of the body. 
 
 Perspiration as a Secretion. The sweat is mostly 
 water, but as it passes out it carries a very small amount 
 of salines and a small amount of organic substances. 
 These are regarded as excretions to be cast ^ut of the 
 body. 
 
 The Skin as an Organ of Touch and Temperature. - 
 In the skin, as was mentioned, the nerves of sensation 
 end in special organs, which are affected, the one by 
 pressure, the other by change in temperature. 
 
 By means of these bodies, the skin becomes an 
 organ with the important duty of giving the knowledge 
 
USES OF THE SKIN 12$ 
 
 obtained from these senses. It thus becomes a con- 
 stant guard, both to warn us of all danger, and to give 
 us the information needed at every moment of our 
 existence. 
 
 The Hair. The hairs are really epidermis grown 
 out into long threads. Each one forms on the top of 
 a special papilla. This papilla is very much like any 
 other papilla, except that it is at the bottom of a little 
 pit. See Fig. 48. 
 
 The cap of epidermis (which is formed over it ) re- 
 mains, new portions being formed beneath it, and so 
 on until it becomes a very slender, but, in some cases, 
 an enormously elongated rod of epidermis. 
 
 Minute hairs are scattered all over the body. A 
 little experiment with some of them, say those on the 
 back of the hand, will show that they greatly aid in 
 touch. Each one has a nerve at the bottom of its 
 papilla. 
 
 The Nails. The nails are thick plates of epidermis 
 growing out from a number of papillae. They grow 
 continually, and thus provide for a comparatively 
 new nail all the time. One may determine the rate 
 of growth by making a line on one and observing 
 the number of days it takes to move a certain dis- 
 tance. The use of the nails is made very plain in 
 attempting to take hold of very small objects. 
 
 Uses of the Skin. We may sum up the most im- 
 portant uses of the skin as follows: 
 
 i st. It makes a strong suit of clothing to protect the 
 body against mechanical injuries. 
 
 2d. It prevents the absorption of injurious sub- 
 stances from without. 
 
124 THE SKIN AND THE KIDNEYS 
 
 3d. It prevents evaporation, except under control. 
 
 4th. It helps regulate the temperature of the body. 
 
 5th. It gives us, through the organs of sense in it, 
 very important and really necessary knowledge. 
 
 The Kidneys. It may be repeated here that from 
 the changes that take place in the body, the three 
 principal wastes are: 
 
 i st. Carbon dioxide, which is got rid of mainly at 
 the lungs ; 
 
 2d. Water, which is principally thrown off at the 
 skin ; and 
 
 3d. The waste containing nitrogen, a substance 
 something like ammonia, called urea, which 
 is thrown off by the kidneys. 
 
 The kidneys are placed one on each side of the 
 spinal column in the abdominal cavity, near the last 
 dorsal and the two or three upper lumbar vertebras. 
 They are large glands, through which a great amount 
 of blood passes. They separate from the blood that 
 goes through them certain substances dissolved in 
 water. The principal one is urea. 
 
 These substances are removed from the body. 
 Thus the blood in its circuit passes the lungs, where 
 it loses carbon dioxide ; the kidneys, where it loses 
 urea; and the skin, where it loses water. If any one 
 of these excretions be stopped, the result will be fatal. 
 
CHAPTER XIII 
 
 CARE OF THE SKIN 
 
 THE uses of the skin just learned show us how im- 
 portant an organ it is and guide us in the kind of care 
 to give it. 
 
 First of all it should be kept clean. The dirt that 
 gathers on the skin is of two classes : that which comes 
 from the body itself in perspiration, and that which 
 gathers on it from outside sources. The gathering of 
 the latter may in time interfere with the secretion of 
 the perspiration. This would be harmful because it 
 would hinder the best regulation of the temperature. 
 It would also be injurious to the body to stop any 
 part of the excretion of the poisonous wastes that are 
 thrown out with the sweat. The dirt which gathers 
 from outside sources is dangerous to the body, be- 
 cause it may contain harmful bacteria, which a break 
 in the skin by a scratch or wound may permit to get 
 into the body and produce some kind of disease (see 
 Chapter XIX on Disease). For these reasons the im- 
 portance of keeping the skin clean is very plain. A 
 body with a clean skin is much safer from disease 
 than one which is not clean. 
 
 Bathing. Thus we see there are very important 
 physiological reasons for bathing besides the equally 
 
 I2 5 
 
126 CARE OF THE SKIN 
 
 important one that good breeding requires cleanliness 
 of the body. No definite rules for bathing suitable for 
 everybody can be laid down, because occupations of 
 people differ so greatly. The hands and face, being the 
 most exposed, naturally must be bathed frequently. The 
 whole body, except the scalp, should be washed daily 
 and a bath should be taken at least once a week, and 
 as much oftener as possible. To remove thoroughly 
 the substances accumulating on the skin, warm water 
 and a little soap are necessary. The soap ought to 
 be pure and of a good quality, for there are soaps 
 with substances in them that injure the skin rather 
 than help it. The bath is, of course, made use of 
 for other purposes besides that of keeping the body 
 clean. Bathing in summer in streams, ponds, and at 
 the seashore is for pleasure, and it is a very healthful 
 form of sport and exercise. There are many forms 
 of baths used for special purposes. The experience 
 of very large numbers of people show that a very health- 
 ful habit to form is that of taking a bath in cool water 
 every day. It should be done very quickly and the 
 skin should be thoroughly rubbed. This quickens 
 the circulation in the skin and improves its condition, 
 and through it benefits the whole body. Every dwell- 
 ing house, no matter how small, ought to have a bath 
 room, so that bathing will not be neglected for lack of 
 convenience. 
 
 Hair and Nails. The most important thing in the 
 care of the hair is that the scalp should be thoroughly 
 washed and afterward rubbed dry, " shampooed " as 
 it is called, at least twice a month. Oftener would be 
 better. This is the best thing to be done to keep the 
 
CLOTHING 127 
 
 scalp and hair in a healthy condition. The dirt accumu- 
 lating under the nails is dangerous, for it may contain 
 disease germs which a splinter might push into the 
 finger. 
 
 Clothing. By the use of clothing man can make 
 himself comfortable in all kinds of climate, which is 
 impossible for the lower animals. Thus, man can be 
 active and carry on his work in every part of the world 
 and in all seasons. There are many uses of clothing. 
 Clothing covering the body helps to keep the heat from 
 being lost from it. Consequently in cold air clothing 
 allows a great saving of energy and of food. But 
 when one is exposed to the scorching rays of the 
 sun, the clothing protects the body from the heat. 
 
 Clothing also protects the body from injury from 
 external things. It saves the body many a bruise and 
 scratch. For example, scrambling through a thicket 
 of brush would be a painful exercise without clothing. 
 Even in ordinary life about the shop, farm, or house, 
 clothing helps us much in this way. The hunter and the 
 football player often have special kinds of clothing 
 to protect their bodies. 
 
 Clothing is, of course, used also from custom and for 
 ornament. Wrong use of clothing may become the 
 source of ill health. For example, if a boy on the 
 school ground by playing hard becomes warm, and 
 then takes off his coat and sits in a cool place to cool 
 off, he is in great danger of taking cold. It would be 
 better to take off the coat to play, and put it on when 
 stopping, and thus cool off more gradually. 
 
 Sometimes one who is accustomed to a warm, com- 
 fortable dress will on some special occasion change 
 
128 CARE OF THE SKIN 
 
 it for a very thin one, and thus run great risk of a cold 
 or of even more severe illness, as, for example, pneu- 
 monia. 
 
 Long experience has taught people what kinds of 
 clothing are comfortable at different seasons and in 
 different climates. It is easy to learn what to use in 
 each case. It is bad to get into a habit of wearing too 
 much clothing for the season. Nor is it wise to go 
 with too little clothing during cold weather. In other 
 places in this book it has been insisted that the cloth- 
 ing should not press on any part of the body so as 
 to interfere with circulation or respiration. All that 
 has been said regarding the necessity of keeping the 
 body clean applies to the clothing, especially that which 
 comes in contact with the skin. 
 
 Clothing for the Feet. As the feet must constantly 
 strike the hard, rough ground and go through water, 
 mud, ice, and snow, we have long ago learned to 
 give them especial care in clothing. But often wrong 
 things are done with the foot coverings. For ex- 
 ample, thin shoes and stockings, which in winter 
 could only be suitable for the warm house, are some- 
 times worn on cold, wet, or snowy streets. Even with 
 good shoes the feet may become wet, and if one remains 
 for a long time in a cold, damp place with the feet in 
 that condition, the health becomes endangered. The 
 feet should be kept dry, warm, and clean as much 
 of the time as possible. 
 
 As for shoes, common sense would teach that they 
 should be adapted to conditions in which we must use 
 them. They should always fit snugly and comfortably, 
 and never compress the feet, if we wish well- formed 
 
CLOTHING FOR THE FEET I2Q 
 
 feet instead of deformed feet, with painful corns and 
 bunions. The habit of wearing rubber overshoes in 
 winter in the wet and snow is a very good one, but 
 they should be kept on only when needed, since they 
 keep in the moisture arising from the foot and do not 
 allow the air to circulate. 
 
 IND. PR. PHYS. 9 
 
CHAPTER XIV 
 
 THE STRUCTURE OF THE NERVOUS SYSTEM 
 
 All Parts of the Body work together through the 
 Nervous System. In our first lesson it was noted 
 that in any movement of the body the parts worked 
 together in some sort of harmony. The boy in climb- 
 ing a tree sees a limb and reaches out his hand for it. 
 In this action the eye and the arm must have some 
 connection. In the whole action the feet, legs, hands, 
 arms, eye, ear, the heart, the lungs, and very many 
 other parts of the body work with each other, and not 
 against each other, in accomplishing this act. 
 
 Now, when the muscles of the legs are in greater 
 activity, the heart must beat more vigorously. This 
 could not occur if there were not some means of com- 
 munication between them. So it is with the hun- 
 dreds of other examples that might be given. The 
 means of communication in all these cases is the 
 Nervous System. We shall try to see as clearly as 
 possible how this is the case. 
 
 Nerves in the Arm. In studying the motions of 
 the fingers it was observed that nerves pass to each 
 muscle, and that every muscle is made to contract 
 by a nervous stimulus sent into it. What this stimu- 
 lus is like it would be hard to say. 
 
 130 
 
NERVOUS IMPULSES 
 
 If the nerves of the arm could be exposed as shown 
 in the figure, and a single nerve be cut, then the will 
 would lose all power to cause the muscles with which 
 the nerve is connected to con- 
 tract, and at the same time a 
 touch on the hand could not 
 be felt. Now, if the end of 
 the part of the nerve con- 
 nected with the muscle should 
 be pinched, the muscle would 
 contract promptly. If the end 
 connected with the brain were 
 pinched, pain would be felt. 
 
 Nervous Impulses. This 
 shows that the nerves conduct 
 some kind of energy which, 
 coming into the muscle, makes 
 it contract, but coming into 
 the brain causes a feeling of 
 pain, touch, or other sensation. 
 
 What these nervous impulses 
 are like we can not answer. 
 In electricity we have an ex- 
 ample of an impulse, which 
 metal wires will conduct a long 
 distance. By its means an in- 
 strument in one city may be 
 set in motion by a movement 
 in a distant city. 
 
 Nervous impulses act something like the electrical 
 impulses, but still it is not thought that they are the 
 same. What we can see well enough is that they do 
 
 Fig. 50. 
 
 NERVES OF THE FOREARM. 
 
 The white cords are the nerves. 
 The shaded tubes are arteries. 
 
132 THE STRUCTURE OF THE NERVOUS SYSTEM 
 
 for the body what the electrical currents do by means 
 of the wires for a city. 
 
 Nerves. The larger nerves look like white cords. 
 They branch into smaller and smaller white threads, 
 which go to the various parts of the body. The small- 
 est branches are so minute that they can not be seen 
 without a microscope. Fig. 50 shows some of the 
 larger nerves in the forearm as they would appear 
 if the skin and some of the muscles were removed. 
 The white cords in the picture are nerves and the 
 shaded ones are arteries. 
 
 A Nerve Fiber. The smallest division of a nerve 
 is a nerve fiber. A nerve is like the cable sometimes 
 used in a telephone system. The cable is made up 
 of a bundle of wires, all kept separate so that they can 
 not touch one another, but bound up into one cable 
 with a covering to protect it and allow it to be fastened 
 to its support. It finally divides up into separate wires, 
 which run to the separate telephones in the house. So 
 the nerve is a bundle of fibers, which finally divides 
 into the separate fibers, which run to separate muscle 
 fibers, or to separate cells in a sense organ; that is, 
 eye, ear, touch, taste, or smell organ. If a single 
 little fiber be traced from a muscle or eye or touch 
 organ in the skin inward toward the central part of 
 the body, it would be found to run to the spinal cord. 
 Some of the fibers end here and some go on to the 
 brain. In the" spinal cord and in the brain the fibers 
 are connected with little bodies called nerve cells. 
 
 There are many thousands of nerve cells in the brain 
 and spinal cord. To understand better how these 
 parts are arranged, let us imagine that we could pick 
 
THE NERVOUS SYSTEM 
 
 133 
 
 up one of the tiny nerve cells in the brain and spinal 
 cord, and that we could lift it out without breaking 
 the minute fiber to which it is attached, and then 
 unravel the fiber farther through the 
 nerve right down to the organ to which 
 it goes, which in this case we may sup- 
 pose is a muscle. We would find it 
 attached to a microscopic bit of muscle, 
 a muscle fiber. If this little bit of mus- 
 cle were taken out also, and magnified, we 
 should have the arrangement shown in 
 Fig. 51. This shows how the cells in 
 the spinal cord are connected with 
 muscle fibers in the muscle. Now cells 
 in the retina of the eye, certain cells in 
 the ear, in the tongue, in certain parts 
 of the nasal passages, and in the skjg> 
 are connected in the same way with 
 fibers which run along in the nerves 
 until they come to the spinal cord and 
 the brain. In this way, then, the fibers DlAGRA 'f ' T0 ' SHOW 
 connect the brain and spinal cord with How A NERVE 
 the muscle fibers and can make them 
 move, and the sense organs are con- 
 nected with the spinal cord and brain, and by the fibers 
 can make the brain feel. 
 
 The Nervous System. The brain, spinal cord, and 
 all the nerves in all parts of the body taken together 
 are called the nervous system. Fig. 52 gives a general 
 view of how the parts are arranged. The brain is in 
 the skull, the spinal cord is in the spinal column. The 
 nerves are connected with the brain and spinal cord 
 
 CELL is JOINED TO 
 A MUSCLE CELL 
 BY A NERVE FIBER. 
 
134 THE STRUCTURE OF THE NERVOUS SYSTEM 
 
 in pairs. Altogether there are twelve pairs of nerves 
 
 connected with the brain and thirty-one pairs with the 
 
 spinal cord. 
 The Nerve Cells. The nerve cells are arranged as 
 
 a thin layer on the outer surface of the brain, and in 
 
 groups in the lower 
 parts of the brain. 
 They also form the 
 central part of the 
 spinal cord. There 
 are many hundreds 
 of thousands of 
 these tiny nerve 
 cells. Because they 
 have a slight shade 
 of color, the parts 
 they are in are 
 called the " gray 
 matter." The nerve 
 fibers are white, and 
 parts of the brain 
 Fig. 53. and spinal cord in 
 
 BRAIN, SEEN FROM ABOVE, CEREBRUM ONLY which they He are 
 
 SHOWING. 11 1 j.1 ' T_'i 
 
 called the white 
 
 i, longitudinal fissure separating the hemispheres ; 
 2, frontal lobes of the cerebrum; 3, posterior lobes. rn^ttCT." 
 
 The Spinal Cord. The spinal cord in man is about 
 as large around as the little finger, and eighteen inches 
 in length. It continues from the medulla (Fig. 55), at 
 the opening in the occipital bone, to about the second 
 lumbar vertebra. Its central portion is occupied by 
 gray matter ; that is, the nerve cells. Outside of these 
 are nerve fibers, making up its white matter. The 
 
THE BRAIN 
 
 135 
 
 -6 
 
 roots of the spinal nerves are nerve fibers, most of which 
 are connected with the cells in the spinal cord. Many 
 fibers run on up to the brain just outside of the 
 core of nerve cells. The spinal cord is like a large 
 nerve, except that it has gray matter in its central 
 portion. 
 
 The Brain. The brain is the large portion of the 
 nervous system inclosed in the cranium. The weight 
 is about three 
 and one fourth 
 pounds. Fig. 
 53 shows it, 
 seen from 
 above; and 
 Fig. 54, from 
 below. Fig. 
 55 shows a 
 side view with 
 certain parts 
 cut through 
 vertically. 
 
 Of the parts 
 shown in these 
 views the cer- 
 ebrum is the 
 largest and is Fig. 54. 
 
 also the UP- BRAIN, SEEN FROM BELOW. 
 
 i. TJ. i, longitudinal fissure; 2 and 3, front and posterior lobes of 
 
 '^*- L the cerebrum; 4, cerebellum; 5, optic nerve; 6, olfactory 
 
 is divided into 1( 
 
 the right and left hemispheres by a deep ditch, called 
 the longitudinal fissure. Its surface is broken up into 
 many curving ridges, which are called the convolu- 
 
136 THE STRUCTURE OF THE NERVOUS SYSTEM 
 
 tions. They are shown in Figs. 53, 54, and 55. The 
 part which is like a stem to the cerebrum is the me- 
 dulla oblongata, MD in Fig. 55 and 7 in Fig. 54. 
 
 The medulla continues down into the spinal column 
 as the spinal cord. In Fig. 55 that portion marked 
 Sp N, to which the roots of two nerves are attached, 
 is a part of the spinal cord. 
 
 Attached to the back part of the medulla, close up 
 
 c 
 
 Fig. 55. 
 
 BRAIN AND CRANIAL NERVES, SEEN PARTLY IN SECTION AND PARTLY IN SIDE VIEW. 
 
 C, convolutions of the cerebrum; Cbl, cerebellum in section; MD, medulla oblon- 
 gata; Sp N, spinal nerves. The numbers indicate the twelve pairs of cranial nerves 
 in their order. 
 
 to the cerebrum, is the cerebellum. This is shown as 
 cut through in Fig. 55, Cbl, and at 4 in Fig. 54. 
 
 At the base of the cerebrum, near where the medulla 
 joins it, are several parts not shown in the figures, 
 which are sometimes referred to as the ganglia at the 
 base of the brain. 
 
THE SYMPATHETIC SYSTEM 
 
 137 
 
 In Fig. 55 are shown the twelve pairs of cranial 
 nerves, which are often known by the terms 
 first cranial nerve, second, third, etc. The 
 most important of these are the following: 
 The first pair are the nerves of smell, the 
 second pair the nerves of sight, the third 
 pair the movers of the eyeballs, the seventh 
 pair go to the muscles of the face and scalp, 
 the eighth pair are the nerves of hearing, 
 the ninth pair go chiefly to the tongue and 
 pharynx, and the twelfth pair to the muscles 
 of the tongue. 
 
 The Spinal Nerves. From the spinal 
 cord thirty-one pairs of nerves pass out to 
 be distributed to the organs of the body. 
 Each of these nerves starts from two roots, 
 an anterior and a posterior root, which soon 
 join together to make one nerve; but the 
 nerve soon separates into a great number 
 of smaller and still smaller branches, until, 
 as was seen in a former section, they reach 
 all the smallest parts of each organ. 
 
 The Sympathetic System. This term is 
 applied to that part of the general nervous 
 system which consists of a row of ganglia on 
 each side of the spinal column, and the net- 
 work of nerves with which it is connected, 
 that run all through the body. The ganglia 
 are connected with each other, and, through 
 the spinal and cranial nerves, with the spinal 
 cord and the brain. It is really not a sep- 
 arate system, but a part of the general nervous system. 
 
 ATTA?HED. ES 
 
CHAPTER XV 
 
 HOW THE NERVOUS SYSTEM IS USED. CARE OF THE 
 NERVOUS SYSTEM 
 
 How the People of a Large City work together quickly. 
 If one examines a large city he will see immense num- 
 bers of wires running in every direction. Large groups 
 of wires are carried by poles along different streets. 
 Sometimes they are bound up into bundles which we 
 call cables. These may be carried on poles or they 
 may be placed under the ground. Now if the groups 
 of telephone wires be followed in one direction, they 
 will be found to be coming together in certain places, 
 which we call the central telephone exchanges. If we 
 follow the wires in the opposite direction, we find them 
 ending at the telephones in the rooms of the various 
 houses. Messages are continually arriving at the cen- 
 tral stations and are continually going out from them 
 again. By this means an immense amount of busi- 
 ness is carried on. At a certain house groceries are 
 needed. A message is sent in, the grocer gets it 
 through the central office, and brings the food to 
 the house. A fire occurs. A message through the 
 central office brings the fire engine. Movements 
 of railroad trains are managed so that they will 
 not run into one another. Meetings are arranged at 
 a special time and place for thousands of people en- 
 
 138 
 
ACTION OF THE NERVOUS SYSTEM 139 
 
 gaged in thousands of transactions which require the 
 most perfect working together of these people. The 
 telephone and telegraph systems manage this for us in 
 a special way. The postal system does the same thing 
 in a much slower way. It would not be available for 
 fires or for preventing collision of trains, but it is a good 
 means of communication where rapidity is not so nec- 
 essary. In the body the nervous system is more like 
 the telephone and telegraph systems. The body is the 
 city, with work at different parts going on. The nerves 
 are the wires. The brain and spinal cord are the 
 central offices. They are sometimes called the central 
 nervous system. 
 
 Action of the Nervous System. It has already been 
 shown that the nervous system is an arrangement for 
 allowing the different parts of the body to work to- 
 gether. We have just seen that there are thousands 
 upon thousands of nerve fibers coming into the spinal 
 cord and brain from all the sense organs, and that there 
 are as many thousands of fibers going out from the spinal 
 cord and brain to the muscles. When light comes to the 
 eye, it starts a nervous impulse in the retina; this goes 
 over the nerve fibers to the brain. We see the object.. 
 The nervous impulses go from the brain down to the 
 spinal cord and out to the nerves until they reach the 
 muscles of the arm or leg, where they cause motions, 
 such as picking up an object or walking away from it. 
 Thus the eye is able to guide the motions of the body 
 through the nervous system. This is what is meant 
 by the eye and hand working together. 
 
 In the same way sounds may guide our motions. 
 Taste, touch, and smell may tell us what to do. 
 
I4O HOW THE NERVOUS SYSTEM IS USED 
 
 When studying the circulation and respiration it was 
 seen that the heart beats faster and breathing is quicker 
 when the body is thrown into vigorous motions. In these 
 cases, nervous impulses come into some part of the cen- 
 tral nervous system and these cause impulses to go out 
 to the heart and muscles for breathing. Thus the heart 
 and lungs are made to work just to suit the working 
 of the muscles. In this way perspiration is increased 
 when the body becomes too warm, saliva is secreted 
 when food is placed in the mouth, gastric juice flows 
 more freely when food is in the stomach, and other 
 secretions occur at the proper time. Thus from the 
 different parts of the body impulses are pouring in all 
 the time into the central nervous system and pouring 
 out again to the very places where motions and secre- 
 tions are required for the action of the body at that 
 moment. In this way we see that the complex busi- 
 ness of the body is carried on in a harmonious way. 
 The parts act together for the good of the whole body. 
 
 Voluntary Actions. When the muscles were studied 
 it was said that certain muscles, those attached to the 
 skeleton, are voluntary muscles. That is, these mus- 
 cles can be controlled by the will. For example, 
 we can control the motions of the arm or leg. It 
 seems that the impulses which cause voluntary mo- 
 tions go from the cerebrum of the brain. They go 
 from the " gray matter "; that is, the nerve cells in the 
 surface of the convolutions of the cerebrum. Also 
 when we see an object, hear a sound, smell, touch, or 
 taste anything, or feel pain, impulses come from the 
 sense organs to some part of the gray matter of the 
 cerebrum. It is also believed that when we remember 
 
INVOLUNTARY ACTIONS 141 
 
 anything, know anything, or feel love, hope, fear, 
 anger, or the like, it is some part of the cerebrum that 
 is affected. We may say then the cerebrum has to do 
 with sensations, feelings, all mental work, and all 
 voluntary acts. 
 
 Involuntary Actions. Every one knows that a 
 chicken for a few minutes after its head is taken of! 
 will jump about and flap its wings violently. With- 
 out its head, of course, it has no brain. The part of 
 the central nervous system that is left is the spinal 
 cord. There is no longer any will or feeling in the 
 animal, yet the spinal cord is able to make the mus- 
 cles contract in jumping and flopping. But in this 
 case it has been proved that the spinal cord will not 
 send out impulses unless impulses come to it ; that is, 
 unless the body of the animal touches against something. 
 The nerves carry an impulse to the cord and it sends 
 out the impulses to the muscles. This is an action 
 without use of the will. It is called reflex action. 
 There are many such actions. A few examples in 
 the human body will illustrate them. If an object is 
 suddenly thrust in front of the eye, it will cause wink- 
 ing. The sight of the object makes a nervous impulse 
 that goes to the central nervous system; this sends one 
 out to muscles that move the eyelids. This will all 
 happen before we have time to think or will. If a 
 finger is touched with a hot wire, it will be jerked away 
 by the spinal cord even before the pain is felt. Food 
 in the mouth will cause saliva to flow. Food in the 
 stomach will cause secretion of gastric juice. A crumb 
 of bread in the larynx will produce violent coughing. 
 Particles of dust in the nose will cause sneezing. These 
 
142 CARE OF THE NERVOUS SYSTEM 
 
 actions, as we know, are not caused by the will, but are 
 reflex actions. 
 
 Uses of Reflex Actions. It is easy to understand 
 the importance of having parts of the nervous system 
 which will act in this way. This was discussed in con- 
 nection with the study of muscles. The eye is better 
 protected if it has machinery to make it work quickly, 
 even before we take the time to think and act. So 
 for many acts. Perhaps we never could learn just 
 how much of the different secretions ought to be made 
 and when they should begin. We surely could not 
 regulate the heart beat and the breathing motions just 
 as they should be at every moment, nor could we keep 
 them going every minute of our lives. Thus a very 
 great part of the necessary actions of the body go on 
 perfectly by reflex action, in little children as well as in 
 adults, without their having to give even a thought to 
 them. 
 
 CARE OF THE NERVOUS SYSTEM 
 
 We have seen that the nervous system is the most 
 important of all the organs or systems of the body. 
 Its duty is the most complex. It manages the action 
 of every organ so that each works when it should and 
 ceases at the right time. Through it all our acts are 
 guided. On its working just right depends our proper 
 conduct at every moment, and the proper action of 
 each part of the body. With these facts before us, 
 it is plain why the care of the nervous system is of the 
 utmost importance. 
 
 The nervous system, even more than other parts of 
 
CARE OF THE NERVOUS SYSTEM 143 
 
 the body, is quickly affected by the character of the air 
 breathed, and by the quality and quantity of jood. It 
 is affected also by the poisons which may be retained 
 in the body by failure to have them discharged by the 
 excretory organs. Consequently all of these matters 
 must be attended to well to secure a healthy working 
 of the nervous system. 
 
 Sleep has for its special function restoration of the 
 nervous system when it is fatigued. Of course, the 
 muscles also gain a needed rest during sleep, but sleep 
 seems to be especially necessary for the brain and 
 spinal cord. It is generally thought that about eight 
 hours of the twenty-four should be spent by adults 
 in sleep. Children as a rule should have more, and 
 very young children much more. Adults vary a 
 good deal in the amount of sleep required, accord- 
 ing to the individual disposition and employment. 
 People may accustom themselves to do without the 
 proper amount of sleep for a while, but lack of sleep 
 is a dangerous state and is sure to bring bad re- 
 sults. A clear mind and a healthy body demand 
 regular hours of sleep and enough of them. People 
 should take greater care to keep their sleeping time 
 correct than to preserve their property, as it is of the 
 greater value. Overwork, worry, with lack of sleep, are 
 great enemies to the nervous system. Therefore we 
 repeat that plenty of good jood, pure air, out-oj-door 
 exercise, and sufficient sleep are necessary to keep the 
 nervous system in good working order. These will 
 prevent nervous troubles, and will in many cases be 
 sufficient to restore health where nervous troubles 
 exist. Whatever else may be necessary to effect a 
 
144 CARE OF THE NERVOUS SYSTEM 
 
 cure in more serious cases, these conditions are es- 
 sential. 
 
 The Nervous System and Education. A habit is a 
 way of doing a thing or a way of thinking which has 
 been repeated so often that it has become the easiest 
 way. The forming of a habit is accomplished by 
 drilling the nervous system in a particular way of 
 doing. The daily life of an adult is largely the carry- 
 ing out of habits which have been formed. When 
 we consider that a well-fixed habit means a certain 
 growth of the nervous system, we can understand how 
 it is that a habit is so hard to change. We speak of 
 good habits and bad habits. They are ways of doing 
 and thinking which are to our advantage or disad- 
 vantage, or which make us pleasant or unpleasant 
 companions. Our education consists very largely of 
 forming habits. 
 
 The fact that to form a habit requires frequent re- 
 petition of the same act teaches us the necessity of doing 
 carefully and frequently that which we wish to be part 
 of our conduct, and to refrain from repeating those 
 acts which we do not wish to be a part of our lives. 
 To do away with a bad habit which has been acquired, 
 it is necessary to watch carefully not to use it at all, 
 so that the nervous system may lose the power to per- 
 form the habit easily. This is very hard to do some- 
 times, so it is of great importance that the habit should 
 not be formed. Habits are most easily formed and 
 changed in youth, while the nervous system is growing. 
 In adult life, when the nervous system is more fixed 
 in structure and form, habits are more difficult to 
 form or change. These facts have long been known. 
 
EFFECT OF ALCOHOL UPON NERVOUS SYSTEM 145 
 
 Such old sayings as, " As the twig is bent the tree is 
 inclined," " You can't teach an old dog new tricks," 
 express this feeling. The subject is mentioned here 
 to emphasize the fact that habits are really connected 
 with certain changes in the body itself, and should, 
 therefore, be seriously considered in their formation. 
 
 The Effect of Alcohol on the Nervous System. (For 
 a fuller discussion of effects of alcohol, see Chapter 
 XX.) There is no part of the body on which alcohol has 
 so marked an effect as on the nervous system. When 
 taken into the stomach it is soon absorbed and circu- 
 lated through the body, and its effect on the central 
 nervous system (brain and spinal cord) is immediate. 
 Even a small amount of alcohol disturbs the action 
 of the brain. This is seen in the false judgments 
 directly following its use. The person may feel warmer 
 when it can be shown that he really is no warmer. 
 He says the drink has produced an exhilarating effect 
 on him. This simply shows that the alcohol has so 
 affected his brain that he cannot judge correctly even 
 about his own bodily state. 
 
 In the next stage he gets very happy or angry about 
 almost nothing, or he becomes silly where, in his 
 normal state, he would be much in earnest. All 
 these feelings are the result of a disordered condition 
 of his nervous system. He is deceived, and he can not 
 adapt himself to his conditions. If he should be in 
 such a state for a considerable time, he could not escape 
 making great mistakes in his conduct. A man thus 
 deliberately makes himself a less intelligent being. 
 He disturbs those functions which we regard as the 
 highest, and which we are accustomed to look upon 
 
 IND. PR. PHYS. IO 
 
146 CARE OF THE NERVOUS SYSTEM 
 
 with pride as the chief characteristics by which we 
 are distinguished from the lower animals. 
 
 If greater amounts of alcohol are used, all these 
 symptoms are intensified until there may be a com- 
 plete overthrow of the reason and a loss of voluntary 
 control over the body. The sense impressions may 
 be wholly misinterpreted. Such excessive use of 
 alcohol, if long continued, will so profoundly disturb 
 the action of the brain, that the patient may be at- 
 tacked with such diseases as delirium tremens or 
 insanity, whose final outcome, after much misery, is 
 death. 
 
 The moderate but long-continued use of alcohol 
 has not the same effect on all people. In some it 
 may cause little apparent injury, while in others it 
 will in time produce changes in the structure of the 
 brain. These changes are similar in character to 
 those which occur in the kidneys, the liver, and the 
 heart; that is, there is a greater development of the 
 connective tissues at the expense of the nervous ele- 
 ments of the brain. The effect, however, is more 
 injurious on the body, as a whole, when the central 
 nervous system becomes deranged, for through it all 
 the other organs are more seriously affected. 
 
CHAPTER XVI 
 SENSATIONS 
 
 Definition. By the term " sensations" is meant the 
 impressions or feelings which are made upon our 
 minds by the things outside of our bodies, or by 
 changes within our bodies. For example, a bright 
 light gives us one kind of an impression, a vibrating 
 tuning-fork another, an odor still another. Or, we 
 may have sensations from changes within the body, 
 as a feeling of thirst or of fatigue. 
 
 It is through parts of the body which give us these 
 impressions or feelings that we gain our knowledge of 
 things outside of us, or of the state of our own bodies. 
 
 Special and General Sensations. If one con- 
 siders the various sensations he has, and will com- 
 pare them, he will see that they differ very much in 
 the definiteness with which they can be located in 
 the body. When one feels tired, it is hard to say 
 just where the feeling is located. Even after one has 
 become tired from continued action of the arms, the 
 feeling of fatigue can not be located in any particular 
 part of the arms, nor does it seem to be confined to 
 the arms alone. 
 
 It is very different when we receive a sensation from 
 an object touching the finger. In this case it can be 
 
148 SENSATIONS 
 
 determined just where the point is that is touched, and 
 the idea gained by the sensation is more definite and 
 distinct. 
 
 Sensations like the latter are called special sensa- 
 tions, while those like fatigue are known as general 
 sensations. 
 
 Sense Organs. The special sensations are those 
 of sight, hearing, smell, taste, touch, and temperature. 
 Each of these has a special kind of apparatus with 
 which the sensation is produced. In each case it 
 consists of, first, an outer part which is . so formed 
 that it can be affected by some peculiar kind of energy, 
 the perception of which energy, as something differ- 
 ent from any thing else, leads us to call the organ 
 a special- sense organ ; second, the sensory nerve ; and 
 third, the nerve center in the brain. 
 
 General Sensations. In the production of gen- 
 eral sensations there are also the inner parts, the 
 nerve centers, and the sensory nerves, and there may 
 be special outer nerve endings. But how they ap- 
 pear and where they are located is not known. The 
 general sensations are numerous, and many of them 
 hard even to describe. Among them are pain, hunger, 
 thirst, nausea, and fatigue. 
 
 Pain. Any one of the sensory nerves, whether of 
 the special or general sensations, seems to be able to 
 give rise to the sensation of pain if stimulated with 
 too great energy. Thus, light, sound, things that 
 touch the skin, or that affect the nerves connected with 
 any part of the body, in fact, which either give rise 
 to a pleasurable sensation or to no feeling at all, and 
 thus are known .only by the reflex actions which they 
 
THE SENSE OF TOUCH 149 
 
 produce, may cause intense pain if the stimulus is 
 increased beyond a certain degree. 
 
 The Use of Pain. A means of producing pain is 
 of the greatest importance to the body. It is simply 
 the way in which the nervous system calls attention 
 in the most emphatic manner to the fact that some- 
 thing is wrong. 
 
 Pain even does more than call attention to the 
 wrong. It drives us to right the wrong, to get rid of 
 the pain. We are sometimes rather slow to do what 
 is right, even when our attention is called to it. We 
 must have a stronger stimulus to action. Pain fur- 
 nishes us that stimulus. Pain is graded all the way 
 from simply being an unpleasant feeling up to the 
 most intense suffering. To avoid the latter it is cer- 
 tainly well to pay attention to the former. 
 
 Hunger and thirst are forms of sensations which 
 arise from a diminished supply of food and water to 
 the tissues. They are produced through parts of the 
 nervous system not definitely known. These, to- 
 gether with the feeling of having had enough when 
 sufficient food and drink have been taken, are of the 
 utmost importance in regulating the supply of both. 
 
 Above all, we should attempt to preserve the healthy 
 action of these sensations, since, when they are not 
 abused or abnormally developed, they furnish us 
 with the very best guides in the extremely important 
 process of taking food and drink. With these dis- 
 turbed, the preservation of the general health is almost 
 impossible. 
 
 The Sense of Touch. This sensation is produced 
 by pressure on the epidermis,, also on the mucous 
 
I 50 SENS A TIONS 
 
 lining of the mouth and in the beginning of the nasal 
 passages. The special organs of touch are micro- 
 scopic bodies of a peculiar form placed in the papillae, 
 or just underneath the epidermis. The nerves of 
 touch end in these bodies, and when pressure is brought 
 to bear on the epidermis it starts impulses in the nerves, 
 which, coming to the brain, give the sensation of 
 touch. 
 
 These organs are unequally distributed in different 
 parts of the skin, being much greater in number in 
 the palms of the hands, the lips and tongue, and in 
 the soles of the feet, than in other parts of the body. 
 The little hairs scattered over the body, which have at 
 their roots branches of sensory nerves, greatly aid in 
 determining the pressure of anything against the skin. 
 
 Different parts of the skin differ very much in the 
 accuracy with which they report about the things 
 touched. It is only by the palms of the hands, bot- 
 toms of- the feet and toes, tip's of the fingers, and by 
 the lips and tongue that the shapes of things can be 
 made out when touch alone is used. 
 
 Other parts of the body, such as the skin on the 
 forehead, can determine the presence of a lesser pres- 
 sure than can the fingers and the palms of the hands. 
 It would be profitable for the pupil to experiment 
 in these particulars with different parts of the sur- 
 face of the body. 
 
 The Sense of Temperature. This is the sense 
 by which we determine the differences of the tem- 
 perature of objects. Its outer organs are in the skin, 
 in the lining of the mouth, pharynx, and esophagus. 
 These outer parts of the sense organ of temperature 
 
THE SENSE OF TASTE 151 
 
 are mingled in many places with those of touch, but 
 the two have been clearly proved to be distinct sen- 
 sations and must have different nerves. 
 
 One may, by employing a warm or a cold rod, ex- 
 plore the surface of the skin and determine what parts 
 are most and what parts least sensitive to heat and cold. 
 
 The uses of the senses of touch and temperature 
 are very obvious. We may say for them that they 
 are not the least important of the senses. The sense 
 of touch seems to be possessed to a greater or less 
 degree of definiteness by all animals. 
 
 The Sense of Taste. The nerves of taste end 
 in little bodies in the mucous covering of the tongue 
 and in the soft palate. This sense determines cer- 
 tain properties of liquids. The forms of the sensa- 
 tion of taste have been stated to be included in the 
 four following: bitter, sweet, saline, and sour. 
 
 The little bodies in which the nerves of taste end 
 are placed in some of the papillae in the parts named, 
 and are only affected when the substances are dis- 
 solved. In this the saliva is of great aid. 
 
 We are accustomed to think that we taste many 
 things which we know only by the sense of smell. 
 This is the case with flavors, like that of vanilla, of 
 onion, of garlic, and with the flavors of different kinds 
 of meats. 
 
 Our opinion in this regard is only an example of 
 how we often make use of things a long time with- 
 out stopping to determine accurately anything about 
 them. By carefully keeping the odors of such sub- 
 stances that have flavors out of the nostrils their so- 
 called flavors can not be tasted. 
 
152 SENSATIONS 
 
 The Sense of Smell. The fibers of the nerve of 
 smell end in little cells embedded in the mucous mem- 
 brane of the higher parts of the nasal passages. These 
 cells come to the very surface, where their extremities 
 are kept moist by mucus. They are affected by 
 vapors and gases. 
 
 A very great number of odors can be distinguished 
 by the organ of smell. Its sensitiveness is remark- 
 able when it is considered what small quantities of 
 substances can fill a large room with odors which 
 can be detected by the sense of smell, although but 
 a very small part of the air containing the odor can 
 reach the olfactory surface of the nose. 
 
 The Uses of Taste and Smell. The chief uses 
 of these senses are plainly to examine both the food 
 taken and the air breathed, and both organs are lo- 
 cated admirably for these purposes. 
 
CHAPTER XVII 
 
 SIGHT AND HEARING 
 
 External Parts of the Eye. We may begin our 
 study of the eye by observing what is exposed to view 
 in our own or in our companion's eye. First we 
 have the curtain, the eyelids, fringed by the eyelashes. 
 Just back of the eyelids is the front part of the ball 
 of the eye. 
 
 This looks like glass. Its shining appearance is 
 due to its being very smooth and continually washed 
 over by the secretion of tears. This secretion is rubbed 
 over the eye by the act of winking, which is kept up 
 incessantly. 
 
 As the tears pass over the eye they flow away and 
 are gathered up by two tiny openings in the inner 
 corner of the eye. These openings lead to the tear 
 ducts (lachrymal ducts). The ducts, after passing 
 through the lachrymal bones, empty upon the inner 
 surface of the nostrils. 
 
 The very front of the eyeball is transparent, and 
 when viewed from one side is seen to protrude slightly 
 from the rest of the surface. This is the cornea. 
 Beyond the edges of the cornea comes the white of 
 the eye. 
 
 Looking through the cornea, we see the colored 
 '53 
 
154 SIGHT AND HEARING 
 
 part, called the iris. It has a round black spot in the 
 center known as the pupil. 
 
 The pupil is only a round hole in the iris. It is 
 black, as is a hole in any closed box, because there 
 is very little light inside to come out. 
 
 Fitting closely over the visible front part of the 
 eyeball is a very thin layer of skin called conjunc- 
 tiva. It runs from the eyeball to the under side of 
 the lids, at whose edges it becomes continuous with 
 the skin of the outer surface .of the lid. 
 
 The conjunctiva is well supplied with nerves, which 
 
 give a sensation of great pain on the presence of any 
 
 foreign body on the surface of the eye or under the lid. 
 
 The Eyeball. The ball of the eye is a globe about 
 
 one inch in diameter. It rests in a bony socket, 
 
 in which it can be 
 turned in every direc- 
 tion by its muscles. 
 Between the eyeball 
 and the walls of the 
 socket is a padding, 
 principally of fat and 
 connective tissue. The 
 
 THE EYEBALL WITH ITS MUSCLES. . , , , , 
 
 eye is held in place 
 
 very firmly, as one will find when he attempts to re- 
 move the eyeball from the head of some animal for 
 study. 
 
 Fig. 57 shows the eyeball with its muscles attached. 
 The upper muscle not attached to the ball belongs to 
 the upper eyelid. The muscle in front is cut away 
 to show the optic nerve at 2 just back of it. The 
 ball and optic nerve are also shown in Fig. 58. 
 
THE WALLS OF THE EYE 
 
 155 
 
 The Walls of the Eye. The eye may be con- 
 sidered as a globular box. The outer walls consist 
 of three layers or coats. Fig. 58 is a section of an 
 eye which well shows these parts. The front part 
 consists of the transparent cornea, continuing as the 
 
 Cm, 
 
 Fig. 58. 
 
 SECTION OF THE EYEBALL. 
 
 COM, conjunctiva; C, cornea; A, aqueous humor; /, iris; L, crystalline lens; 
 V, vitreous humor; Sc, sclerotic coat; Ch, choroid coat; R, retina; O, optic nerve; 
 Cut, ciliary muscle; Sh, sheath of optic nerve. 
 
 white of the eye, which is called the sclerotic coat (Sc). 
 This at the back extends over the optic nerve as its 
 sheath. 
 
 This covering is of very tough connective tissue, 
 and is the main part of the wall of the box, support- 
 ing the other parts and furnishing places for the at- 
 tachment of muscles, as seen in Fig. 57. 
 
156 SIGHT AND HEARING 
 
 Just inside of this coat lies the choroid coat (Ch 
 in Fig. 58). It is dark in color and closely filled 
 with blood vessels. Toward the front part of the 
 eye it contains the muscular fibers (Cm) of the ciliary 
 muscle. Farther forward it is continued into the 
 iris, marked (/). Just inside the choroid is the very 
 thin transparent retina (R). It is continuous with 
 the optic nerve (O). 
 
 The walls are held out firmly in their spherical 
 shape by the contents of the globe, which are the 
 vitreous humor (V), the crystalline lens (L), and the 
 aqueous humor (A). The vitreous humor looks like 
 a very transparent jelly; the lens is firmer, and when 
 fresh has the appearance of a clear convex lens of 
 glass; while the aqueous humor consists of but a few 
 drops of a liquid that is mostly water. The lens is held 
 in place by a sheath of a kind of connective tissue. 
 
 Seeing. As was stated above, it is a part of the 
 retina that is affected by light. It is that part which 
 lies against the choroid coat. The retina, although 
 exceedingly thin, is a very complex structure. While 
 the description of its microscopic parts may be omitted, 
 it may be stated that the fibers of the optic nerve pass 
 to the front of the retina, where they spread over the 
 whole retina. The end of each fiber, however, turns 
 toward the choroid coat, and, through different parts 
 of the retina, becomes connected with each one of the 
 vast numbers of minute bodies in the retina known 
 as the rods and -cones, whose ends point toward the 
 choroid coat. 
 
 The light affects these rods and cones, and they 
 start the stimulus, which, traveling along the optic 
 
ACCOMMODATION OF THE EYE TO DISTANCES 157 
 
 nerve to the nerve center in the brain, produces the 
 sensation. 
 
 Distinct Vision. Perception of the exact out- 
 lines of an object can only occur when a definite image 
 of the object is formed on the rod and cone layer 
 of the retina. Every one knows that an image of a 
 lamp flame or of the window can be formed on a 
 sheet of white paper by the use of a convex lens. 
 
 The photographer uses a convex lens also to form 
 an image in the camera. In the eye, the cornea and 
 the crystalline lens are the convex lenses which form 
 the image on the rods and cones. 
 
 The iris, by narrowing and enlarging the pupil, which 
 actions are accomplished by muscular fibers in its 
 substance, regulates the amount of light, and thus 
 helps to make the image more distinct. 
 
 Accommodation of the Eye to Different Distances. - 
 If, while you keep your eyes fixed on the words of this 
 page, you give attention to some object beyond the 
 book, the farther object wi-11 be found to be indistinct. 
 If now you look at the object beyond, the words of 
 the book are indistinct. The reason for this is that 
 a lens can not make on a screen definite images of 
 objects at different distances at the same time. If 
 the lenses and the retina of the eye were to remain 
 just exactly the same in shape and distance from each 
 other, we could never see anything in definite outline 
 except at one certain definite distance. 
 
 The eye is enabled to accommodate itself to ob- 
 jects at different distances by changing the amount 
 of curvature of the crystalline lens. This is done by 
 the action of the ciliary muscle (Cm) in conjunction 
 
158 SIGHT AND HEARING 
 
 with other parts. The lens becomes more curved for 
 a near object and less so for distant objects; that 
 is, objects more than twenty feet away. 
 
 Shortsightedness. A normal eye can accom- 
 modate itself, as has just been shown, to both near 
 and distant objects. In a nearsighted e.ye, generally 
 on account of the too great length of the eyeball, 
 the lens can not make the image of distant objects 
 fall on the rods and cones, and even near objects 
 must be brought close to the eye to be seen clearly. 
 Concave glasses will correct this defect. 
 
 In Longsightedness the eyeball is commonly too 
 short, and thus prevents images of near objects from 
 being formed at the proper place. Convex glasses 
 are used to correct this defect. 
 
 There are many other defects which eyes may pos- 
 sess which can not be explained here. As most of 
 them are such in nature that they grow worse in time 
 and may prove serious, it is always best, when any 
 are suspected, to have the eye examined by an 
 oculist. 
 
 Sensation of Hearing. An object producing a 
 sound, such as a violin string, does so by vibrating 
 very rapidly; that is, it swings backward and for- 
 ward with great rapidity. These vibrations give 
 their motions to the wood of the body of the violin, 
 and this in turn sets the air to vibrating. Every 
 little particle of air is swinging to and fro with the 
 same rate as the vibrating body. 
 
 The sensations of hearing are produced by these 
 vibrations being transmitted by parts of the hear- 
 ing apparatus to the little bodies in the innermost 
 
THE AUDITORY APPARATUS 
 
 159 
 
 part of the ear, in which the auditory nerve fibers 
 end. 
 
 The Auditory Apparatus is very complicated, and 
 our description will include but a brief outline. The 
 apparatus is generally con- 
 sidered in three divisions: 
 the external ear, the middle 
 ear, and the internal ear. 
 
 The external ear includes 
 the visible projections called 
 the pinna, and the tube that 
 leads from it, known as 
 the external auditory canal, 
 which, at its inner end, is 
 closed by a membrane 
 called the membrana tym- 
 
 sc 
 
 Fig. 59. 
 
 THE AUDITORY APPARATUS WITH THE 
 SURROUNDING BONE REMOVED. 
 
 ^/.external auditory canal; SC, semi- 
 circular canals; C, cochlea. 
 
 pani, which separates it 
 from the middle ear. 
 
 The middle ear is a small 
 cavity in the temporal 
 bone, lined by a thin mucous membrane. It opens 
 into the pharynx by the Eustachian tube. It is sepa- 
 rated from the external canal by the membrana tym- 
 pani. Three small bones, the malleus, the incus, and 
 the stapes, fastened together and attached to the sides 
 of the cavity, connect the membrana tympani with a 
 membrane between the middle and the internal ear. 
 The middle ear contains air, which comes into it through 
 the Eustachian tube. 
 
 The internal ear consists of very small tubes of mem- 
 brane, which lie in corresponding tubes of bony chan- 
 nels in the temporal bone. Both inside and outside 
 
i6o 
 
 SIGHT AND HEARING 
 
 sc 
 
 of these tubes of membrane is a liquid which is mainly 
 water. The three divisions of the internal ear are the 
 semicircular canals, the vestibule, and the cochlea. 
 
 The auditory nerve 
 fibers end in cells 
 on certain parts of 
 the internal lining 
 of these membra- 
 nous tubes. 
 
 The functions of 
 some of these parts 
 are not definitely 
 F '9- 60 - known, but it is 
 
 A DIAGRAM OF A SECTION OF THE AUDITORY believed that the 
 
 E, external canal; M, in the middle ear, where is Sensation of SOUnd 
 the chain. of bones; I', vestibule; SC, semicircular i i i ,1 
 
 canals; N, auditory nerve; C, cochlea; ET, Eusta- IS produced by the 
 
 stimuli to the nerve 
 
 endings in the internal parts of the cochlea. The 
 cochlea consists of three tubes wound around in the 
 shape of a snail shell. The nerve fibers end in the 
 walls of the middle tube. 
 
 General View of the Action of the Auditory Appa- 
 ratus. The motions of the vibrating body set the 
 air into vibrations; the vibrating air causes the mem- 
 brana tympani to swing to and fro with the same 
 rate; these swings are communicated by the series 
 of bones to the membrane to which the stapes is at- 
 tached. The motions of this membrane set the liquid 
 of the internal ear in motion, and this acts on parts 
 that set in motion the bodies in which the auditory 
 fibers end. The motions start this stimulus, which 
 causes the sensation of hearing. 
 
CHAPTER XVIII 
 
 CARE OF THE EYE AND EAR 
 
 CARE OF THE EYE 
 
 THE eyes are such extremely useful organs, and at 
 the same .time so delicate, that they call for special 
 care to shield them from harm. It is especially neces- 
 sary to guard against injuries from the outside, wrong 
 use of the eyes, and contagious diseases of the eyes. 
 
 We have seen that the eyes are naturally well pro- 
 tected by being placed in bony sockets with slightly 
 projecting rims, so that blows or sources of injury, 
 except from directly in front, do not have much chance 
 of injuring them, and the eyelids offer quite a protec- 
 tion for those coming from that direction. The large 
 objects which might make severe wounds we are usu- 
 ally careful to look out for. Children, however, may 
 sometimes carelessly play with such toys as bow and 
 arrows or pea shooters and endanger their playmates' 
 eyes. Small things which we can not so well control, 
 such as flying insects, cinders, or other particles carried 
 by the wind, or minute pieces of steel thrown off in 
 working with machinery, may be the cause of much pain 
 or even of permanent injury. Of course these should 
 be removed without delay. The pain usually drives 
 us to get them out as soon as possible. Fortunately, 
 most of these things can be easily removed, if they 
 
 IND. PR.' PHYS. II l6l 
 
1 62 CARE OF THE EYE AND EAR 
 
 have not become embedded in the eye. By drawing 
 out the eyelids and having the eyeball turned in dif- 
 ferent directions a good part of its surface and the 
 inner surface of the lids can be examined. It will 
 be remembered that the conjunctiva, that is, the mem- 
 brane which covers the inside surface of the lids, and 
 the part of the eyeball covered by them, will not per- 
 mit objects to get behind the eyeball without piercing 
 that membrane. Thus by examining carefully all its 
 surface these small objects may usually be found and 
 removed. 
 
 The inner surface of the upper lid is more difficult 
 to examine, as it can not be so easily turned back as 
 the lower. There is in it a plate of cartilage which 
 makes it more firm. With a little skill, however, it 
 can be turned inside out. Take hold of the eyelashes 
 with one hand and draw out the edge of the lid. At 
 the same time, with some smooth, slender object, like a 
 lead pencil, press on the middle of the outside surface 
 of the lid while the edge of the lid is drawn upward. If 
 properly managed, the firm cartilage in the lid is turned 
 upside down and brings the inner surface of the lid out- 
 side so that it can be examined. The offending body can 
 then be removed by a clean silk or linen handkerchief 
 folded to a point over a lead pencil or toothpick. If 
 the foreign body has been embedded in the eyeball, 
 great care should be taken in removing it. Such an 
 operation ought to be intrusted only to a skilled phy- 
 sician or to an oculist. 
 
 If any chemical substance should chance to be thrown 
 into the eye, it should be washed out immediately with 
 abundant clean water; if the substance is alkaline, like 
 
CARE OF THE EYE 163 
 
 lye or lime, a little vinegar could be added to the water; if 
 it is an acid substance, a soap solution could be used, but 
 all must be finally removed with clean water. The most 
 common of such substances to get into people's eyes is 
 lime, since it is used in making whitewash and mortar 
 and plaster. A bit of one of these substances in the 
 eye is very painful and dangerous, and should be washed 
 out immediately. Any one engaged in an occupation 
 which exposes the eyes to flying particles, such as grind- 
 ing or polishing metals or glass, should wear some- 
 thing over the eyes to protect them. 
 
 Quite different kinds of injuries come from the 
 wrong use of the eyes. If the eyes are good, that is, 
 if they see distinctly, are not nearsighted or farsighted, 
 they may be injured by habits of using them on fine 
 work or in a poor light. If the light is poor, we are 
 likely to strain the eyes unconsciously, by trying to focus 
 them so as to bring out more clearly the objects we 
 are looking at. The straining at focusing will do no 
 good if the light is not there, and the continued strain- 
 ing of the eyes is sure to change them permanently so 
 that they are no longer normal. They become weak 
 or nearsighted or astigmatic. Besides injuring the 
 eyes, the " eye strain " may become through its peculiar 
 reflex connections the cause of very many other severe 
 troubles not apparently connected with seeing. Some 
 of these are headaches, dizziness, fainting, dyspepsia, 
 and other intestinal troubles. Often people have suf- 
 fered with quite severe bodily troubles and have been 
 treated for these without relief, when finally proper 
 treatment of the eyes, so as to do away with eye strain, 
 has completely 'cured them of the trouble. 
 
164 CARE OF THE EYE AND EAR 
 
 The book or work should be in a good light and 
 near enough to be seen with perfect comfort. It is 
 best that the light come in from the left. When the 
 light comes from the back or right, shadows of the 
 head or hands fall across the work and annoy one, 
 and when from the front, it pours directly into the 
 eyes as well as on the work, and tires the eyes very 
 much. These uncomfortable positions or a poor 
 light may be endured by good eyes for a short time, 
 but continuous exposure^ to them will surely affect 
 the eyes injuriously Jn time. 
 
 If the eyes are not normal, that is, if they are weak, 
 astigmatic, nearsighted or f arsighted, then they are con- 
 stantly being put to a strain in any reading or fine work, 
 and any of the many troubles which go with eye strain 
 may result, while the eyes themselves grow constantly 
 worse. When any trouble of this kind is present, the 
 eyes should be examined by a competent oculist, who 
 will with his instruments determine the trouble and 
 prescribe the glasses necessary to be worn. His advice 
 should be carefully followed. Sometimes the muscles 
 of the eyes do not work properly, so that both eyes are 
 not accurately turned on the object examined at the 
 same time, that is, one eye may be turned in too much, 
 " cross-eye," or turned out too much, " wall eye," or 
 too much in some other direction. For these troubles 
 only those trained in the treatment of the eye should be 
 employed. 
 
 There is a great number of diseases which may affect 
 the eyes, and when any of them appears, the advice of a 
 physician or oculist should be sought as to the remedies 
 to be applied. Avoid using any kind of " eye wash," 
 
CARE OF THE EYE 165 
 
 lotion, or other remedy advised by any other person. 
 The edges of the lids, as also the lids themselves and the 
 rest of the face, should be kept clean by washing with 
 water or soap and water. The surface of the healthy 
 eye does not need any other cleansing than the means na- 
 ture has provided, that is, the tears and winking. Even 
 clean water continuously applied would cause injury. 
 
 There are some diseases of the eyes which are very 
 contagious. As there is special danger of communica- 
 tion by means of a common towel, the one with the 
 " sore eyes " should have a towel and basin to himself, 
 and care should be taken that he use no other. The 
 term " sore eyes " is applied to several different diseases 
 of the eyes, some of which are and others are not 
 contagious or very dangerous. The physician should 
 be consulted in every case, and if the disease is conta- 
 gious or dangerous, his directions for the treatment, and 
 for the protection of others from the contagion, should 
 be strictly followed. Carelessness in this regard has 
 sometimes allowed one person to be the cause of injury 
 and even blindness in many others. 
 
 To sum up: Be careful to have a good light on read- 
 ing or work, preferably from the left or from above. 
 Have the work in a convenient position so that there 
 will be no strain of eyes or other parts of body to see 
 it distinctly. If working where there are flying parti- 
 cles, wear a protective covering for the eyes. If there 
 is any indication of nearsightedness, farsightedness, 
 or any question of weakness of the eyes, have them 
 examined for the proper glasses; if any disease of the 
 eyes appears, have them examined promptly, and be 
 faithful in following the treatment prescribed. 
 
1 66 CARE OF THE EAR 
 
 CARE OF THE EAR 
 
 Foreign bodies may get into the external canal of 
 the ear. The greatest care should be taken in attempt- 
 ing to remove them. For, as we have just seen, the 
 canal is only about one inch long, and at its end is the 
 delicate membrane of the drum of the ear, which would 
 be injured very readily by the instrument used. It is 
 best to attempt first to remove the object by washing 
 it out with a stream of warm water sent gently into 
 the ear by means of a syringe. The small nozzle of 
 the syringe should be so directed that the stream 
 will go past the object and behind it so that the 
 stream will turn back against the object and carry 
 it back out of the ear. If an insect should get into 
 the ear, it must be killed as quickly as possible, which 
 can be done by a few drops of olive or sweet oil run 
 into the ear. The oil is harmless to the ear, but kills 
 the insect by getting into its breathing apparatus. 
 The insect can then be washed out with warm water 
 as described. If it becomes necessary to use an in- 
 strument in removing the insect, it would be safer 
 to go to a physician or surgeon. The wax of the 
 canal usually works out of the ear about as fast as it 
 is formed. When this is the case, no attempt should 
 be made to clean out the canal with either water or 
 instruments. It is sufficient to keep clean the external 
 ear as far as the opening of the canal. Sometimes 
 the wax does not come out as it should, but may 
 accumulate and gather into a hard mass, which may 
 affect the hearing and become the source of serious 
 
CARE OF THE EAR 1 6? 
 
 trouble. In such cases the wax should be removed by 
 a physician. 
 
 A blow on the side of the head may affect the hear- 
 ing. It has been known to rupture the membrane of 
 the drum by compressing the air and driving it inward. 
 
 Inflammation of the mucous membrane of the throat, 
 as in colds or catarrh, may extend along the Eustachian 
 tube to the middle ear, where, if long continued,* it may 
 produce serious trouble which can not be cured. Early 
 attention should be given such troubles. The parts of 
 the ear are so deep in the head that they are very 
 difficult to get at, consequently only those skilled in 
 such matters ought to attempt to cure any trouble. 
 
 It is best not to try without the advice of a physician 
 any advertised remedy for troubles with the ear or 
 hearing, and especially not to put any such medicines or 
 other objects into the ear. In case of earache or pain 
 in the region of the ear, the simple remedy of apply- 
 ing a hot-water bag or heated dry cloths may be used 
 to relieve the pain until the proper treatment can be 
 given. 
 
CHAPTER XIX 
 
 DISEASE, ITS CAUSES AND PREVENTION 
 
 THE word " disease" is used as a general term for any 
 form of wrong action of one or more parts of the body. 
 Only a single part may be diseased, as the heart or eye, 
 or the whole body may be affected. Even when but 
 a single part is diseased, the rest of the body may feel 
 some of the effects. 
 
 Perhaps no one can always be safe from every form 
 of disease. Yet if the cause of a disease is known, 
 we can surely be better defended against it. In study- 
 ing the various organs and how to take care of them, 
 the way to avoid certain diseases of these organs was 
 shown. At this place we will point out some general 
 facts to help us avoid other forms of disease. It can 
 not be said too strongly or too often that impure air, 
 bad food, lack of exercise, and lack of sleep are among 
 the most frequent causes of diseases. As long as one 
 of these causes remains, perfect health is impossible. 
 When any of these things is the cause of disease, no 
 medicine will effect a cure. The thing to do is to 
 remove the cause. 
 
 The Power of the Body against Disease. The 
 body has a certain amount of power in itself to con- 
 tend against disease. The more vigorous and healthy 
 the body is, the greater its power to keep out disease 
 
 1 68 
 
INFECTIOUS DISEASES 169 
 
 or to cure it if it gets a start. We all know that wounds, 
 bruises, and sprains get well from what the body 
 itself does to cure them. All that can be done outside 
 the body is to help a little by keeping the parts clean 
 and comfortable, and by guiding the repair, so that, for 
 example, a joint may not become crooked in healing. 
 So with more serious diseases the cure depends on 
 the powers of the body to contend with the disease 
 and right itself again. We can only help the body 
 in its fight with the disease; we can not supply any 
 new power for healing that the body itself does not 
 possess. 
 
 It is plain, then, that the most important protection 
 against disease is to keep the body at all times best 
 prepared to fight it. This is done by keeping it in the 
 best condition of health. Good health prevents many 
 forms of disease, and gives the body the best chance 
 of getting through safely those it can not prevent. 
 
 Infectious Diseases. In recent years great dis- 
 coveries have been made concerning the causes of 
 many of the most dreaded diseases. It has been 
 found out that they are caused by very minute living 
 organisms, some being plants and others animals, 
 which get into the body and live and grow in the 
 blood or other liquids in the body. The word " infec- 
 tion" means getting some of these organisms started 
 to grow in the body. The diseases caused in this way 
 are called infectious diseases. The little organisms, 
 which will grow in the blood and cause disease, are 
 sometimes called disease germs. It is very important 
 to know something about the way these minute organ- 
 isms live, so as to be able to avoid them or destroy them. 
 
I/O DISEASE, ITS CAUSES AND PREVENTION 
 
 Bacteria. There are many kinds of disease germs. 
 One group of them belongs to the most minute of all 
 kinds of plants called bacteria. Most kinds of bac- 
 teria are so very small that they can be seen only 
 with a good microscope. Millions of them might exist 
 in a small drop of liquid. Very many kinds of bac- 
 teria are harmless, but some of them are very harmful, 
 causing the death every year of great numbers of 
 people. A knowledge of how some of the harmless 
 bacteria grow outside of the body will teach us how 
 the disease-making bacteria grow inside of the body, 
 and how the body gets injections diseases. 
 
 If a cup of soup, or of any kind of liquid contain- 
 ing juices of plants or animals, be set aside in a warm 
 place, in a day or more it " spoils," as we say. That 
 is, it gets a bad taste, or a bad smell, and is no longer 
 fit to eat. Now if a drop of the liquid is examined 
 properly with a good microscope, millions of minute 
 bacteria will be found in the liquid. These little plants 
 in growing have fed upon the soup and changed much 
 of it to the bad-smelling and bad-tasting substances. 
 It has been proved that there are so many of these 
 kinds of bacteria mingled with dust in the air that some 
 are sure to fall into everything left open to them. 
 When they fall into liquids which contain substances 
 good for their food, they grow, and use up that food. 
 Meat juices are food for such bacteria. If a cup of 
 soup boiled so as to kill the bacteria be placed where 
 it is impossible for bacteria to fall into it, it will " keep." 
 That is the way we " can " foods. They are heated to 
 kill the bacteria and sealed up so that no more can get 
 to them and spoil them. If we take some soup which 
 
BACTERIA 171 
 
 has no bacteria in it, and which is kept carefully away 
 from bacteria that may fall into it from the air, and 
 put in it a drop of soup having bacteria, it, too, will 
 soon be rilled with bacteria and will be spoiled. This 
 would happen if we took the minutest quantity of soup 
 containing bacteria on the fine point of a needle and 
 touched the good soup with it. This is because the 
 bacteria are plants. Putting a few bacteria in a cup 
 of good soup is really planting them there, and like 
 all plants they grow and produce more plants like 
 themselves. This they do very rapidly. If the seeds 
 of some weed are planted in a field, that weed may 
 become so abundant that it will cover the field in the 
 course of a few years. Bacteria grow so rapidly that 
 they can fill their field in a day or so. 
 
 The disease bacteria live and grow in the same way 
 as do those which spoil the soup, but they grow in the 
 blood of man by using it or other juices in the body 
 as food and leaving in it poisonous substances. Thus 
 they cause disease. Now, the most important thing to 
 know about the disease-making bacteria is that they 
 can not appear in the body unless they are planted 
 there ; that is, they must be brought from some place 
 oustide of the body. If then we keep all disease- 
 making bacteria from entering the body, the body will 
 always be free from the bacteria diseases. In this 
 way the blood of the body is like the cup of soup 
 spoken of above. But if ever so small a quantity of 
 substance from a body that has the disease-making bac- 
 teria in it, comes in contact with the blood of the 
 healthy body, the disease bacteria may grow and in- 
 crease in it until the body becomes diseased. We have 
 
1/2 DISEASE, ITS CAUSES AND PREVENTION 
 
 spoken only of bacteria producing disease, but there 
 are also some very minute animals which produce dis- 
 ease in much the same way as do the disease bacteria. 
 For just the same reasons we can say that diseases 
 made by them will not occur if we keep these little 
 living animals away from the body. 
 
 Prevention of Infectious Diseases. Since the dis- 
 covery that some of the most severe diseases are caused 
 by minute plants or animals, very much study has been 
 given to finding out just the kind of disease germ that 
 is the cause of each kind of disease, and just how 
 that particular kind gets from one body to another. 
 When this is known then we can keep diseases from 
 spreading. If every one knew these facts and all 
 would help, we could stamp out completely many of 
 these diseases. This shows us how important it is to 
 know of these things. There is much yet to be learned, 
 but much has already been found out which has 
 helped very greatly to save lives. In civilized coun- 
 tries now there are public officers whose duty it is to 
 try to prevent the spread of diseases. In this country 
 they are the boards of health and other health officers. 
 When any one gets sick with an infectious disease, the 
 physicians and the health officers plan according to 
 the particular kind of disease to keep the germs from 
 getting to any one else. Everybody should help them 
 in every way and keep all their rules; for if any one 
 breaks their rules he may not only become sick him- 
 self, but he may be the means of much sickness and 
 suffering to others as well. 
 
 Examples of Infectious Diseases. It is not a proper 
 place in this book to describe the details of diseases 
 
DIPHTHERIA 1 73 
 
 and explain methods of curing them. But it may 
 make matters clearer if some examples of these diseases 
 are mentioned, and some of the general facts about 
 them given. 
 
 Diphtheria. This is one of the most dreaded dis- 
 eases caused by bacteria. The linings of the throat, 
 nose, and air passages become inflamed and false 
 growths take place in them. The parts affected are 
 crowded with the bacteria of diphtheria. Any minute 
 particles from these parts have bacteria of diphtheria 
 in them, which will start the same growth in another 
 person's throat. These little particles in coughing may 
 get upon the things in the room about the patient. 
 They may get on the vessels he drinks out of or eats 
 from. By these means, or by common house flies, 
 they may be carried away to other houses. For these 
 reasons it can be understood why the person sick with 
 diphtheria must be kept away from all except those 
 who care for him. All the clothing and things used 
 by him, or by his nurses, and the whole room must 
 be thoroughly cleaned and all the bacteria on them 
 killed. If it is known soon enough that one has this 
 disease, and all this care is taken, until the proper time 
 after the patient is well, no other case will start from 
 this one; but if proper care is neglected in this case, 
 the disease may spread rapidly and many deaths may 
 occur from it. In such cases every one should always 
 remember how much harm may come from his care- 
 lessness. 
 
 Scarlet Fever, Measles, Erysipelas, and Smallpox are 
 also examples of diseases that are spread by particles 
 from the body of the sick person which contain the 
 
1/4 DISEASE, ITS CAUSES AND PREVENTION 
 
 germs of the disease. These are carried by touch, 
 clothing, or other things used by the sick one. The 
 same rules should be followed with these diseases as 
 with diphtheria. 
 
 Vaccination. Many years ago Dr. Jenner made a 
 great discovery in regard to smallpox. It was known 
 that a person who had once had smallpox did not 
 easily take it the second time, for some years at least. 
 He found a way of giving a very slight attack of small- 
 pox by vaccination. This made the person not liable 
 to take smallpox for several years, and if he did take 
 it he had it very lightly. The practice of vaccination 
 is universal in civilized countries. It has saved great 
 numbers of lives and an immense amount of suffering. 
 Before this discovery great epidemics of smallpox 
 frequently occurred. Now in countries where vac- 
 cination is used only a few cases occasionally are known. 
 Vaccination not only helps the person vaccinated by 
 keeping him from taking smallpox, but helps the whole 
 community, for if there are some in the community 
 not vaccinated there is always a chance for smallpox 
 to get a start there. Much study is being made to 
 find means of doing for other diseases what vaccina- 
 tion does for smallpox. 
 
 Consumption, Tuberculosis of the Lungs. This 
 disease is caused by a certain kind of bacteria which 
 gets into the lungs by breathing. The disease is spread 
 by bacteria from the lungs of the sick person. They 
 pass from the lungs to the miicus which is coughed 
 up and spit out. Particles of dried sputa may get 
 into the air with the dust and thus may be breathed 
 into the lungs. If all the substance thrown off from 
 
TYPHOID FEVER 1/5 
 
 the throat and lungs of the patient were caught in 
 cloths or vessels and destroyed, there would be little 
 danger of communication of the disease. If the direc- 
 tions of physicians in regard to this disease were 
 carried out carefully, it would soon cease to be so 
 widespread as it is now. This disease is an example 
 of one that can usually be prevented by keeping the 
 general health good and especially by taking good care 
 to have plenty of pure air. Outdoor life is considered 
 the best medicine for consumptives. Therefore out- 
 door life must be a good preventive of the disease. 
 
 Typhoid Fever. This disease is caused by a kind 
 of bacteria. They grow in the intestines. A person 
 takes typhoid fever by swallowing some of the typhoid 
 fever bacteria with his food or drink. How the bac- 
 teria get in the food or drink has sometimes been a 
 great puzzle. But in many cases where people in a 
 town have been taken sick with typhoid fever the 
 puzzle has been solved. In some cases it was found 
 that they had all drunk water that had typhoid bac- 
 teria in it, and that these bacteria had come from 
 letting discharges from the bowels of typhoid fever 
 patients get into the source of the water supply. In 
 other cases the fever came from drinking milk from 
 an unclean dairy. The dairy people had washed their 
 cans with water that was contaminated with the dis- 
 charge of typhoid fever patients. In other cases the 
 bacteria have been carried from the discharges of sick 
 people to the food of other people by the common 
 house fly. By such examples and others it has been 
 proved that typhoid fever bacteria in some such ways 
 always came from typhoid fever patients. This shows 
 
1/6 DISEASE, ITS CAUSES AND PREVENTION 
 
 the danger in sewers, and the importance of destroying 
 all discharges of typhoid fever patients. During an 
 epidemic of typhoid fever one may be safe if he is 
 careful to eat no food that has not been cooked at 
 home and drink no water or milk that has not been 
 boiled. Heat kills the bacteria. 
 
 Cholera. This disease also is caused by a kind of 
 bacteria growing in the intestines. The cholera bac- 
 teria, like the typhoid fever bacteria, can be carried by 
 food, by flies, by drinking water, or by milk. The, 
 most usual means is by the water used for drinking. 
 
 Water Supply for Drinking. There are other kinds 
 of germs that can be carried by water, which cause 
 intestinal troubles. Since this is the case, the water 
 supply for drinking should be most carefully guarded. 
 If it is from springs or wells it should be seen to that 
 there is no possible chance for the drainage of any 
 filthy places getting to them. Sometimes the soil is 
 such that it will allow water from these sources to soak 
 through it a long distance. In this way the well may 
 become polluted when there does not seem to be any- 
 thing wrong with it. When cities get their water from 
 lakes or streams, disease germs may get to the supply. 
 We have to depend on the health officers to take care 
 of us in such cases by the means that they have for 
 the remedy. If at any time there may be danger from 
 the water, it should be boiled before being used for 
 drinking or for washing dishes or anything which may 
 get to our mouths. 
 
 Malaria. Malaria is also known as " fever and 
 ague," " chills and fever," and it has other names as 
 well. There are different forms of malaria. Within 
 
YELLOW FEVER 1/7 
 
 the past few years it has been found that certain kinds 
 of mosquitoes are the means of carrying malaria about. 
 The minute germs of malaria live part of their life in 
 this mosquito and part of their life in the blood of man. 
 When a man is sick with malaria, the little organisms 
 are abundant in his blood. If now a mosquito of this 
 kind bites him, it draws through its bill with the 
 blood of the man many of the malaria organisms. 
 Later if this mosquito bites another man, the disease 
 germs may be injected into his blood and he may get 
 malaria. It is plain then that if we could in any re- 
 gion destroy all of the malaria-carrying mosquitoes, 
 malaria would die out. We can see, too, how a man 
 with malaria can supply mosquitoes with germs to 
 carry to other people. 
 
 Yellow Fever. This disease is such a fearful one 
 that its appearance frightens all in the community. 
 It has been recently discovered that, like malaria, it 
 is caused by germs carried by a certain kind of mos- 
 quito. If these mosquitoes are kept away or killed, 
 there is no danger of yellow fever, even if one is in the 
 same room with the patient. The well person should 
 be protected from the mosquitoes, so that he can not 
 be bitten and get the disease. The patient must be 
 guarded from mosquitoes, so that the germs can not 
 be carried from him to others. 
 
 The way one person may start a yellow fever epi- 
 demic in a large region is as follows : If there has been 
 no yellow fever in a region for some time, none of the 
 mosquitoes have the germs of the disease in them. 
 Now some one from a yellow fever region, who has 
 been bitten by mosquitoes with yellow fever germs, 
 
 IND. PR. PHYS. 12 
 
1/8 DISEASE, ITS CAUSES AND PREVENTION 
 
 may come to visit this region before the disease de- 
 velops in him. Soon he is taken sick. Through neg- 
 lect of care, or ignorance of the danger, some yellow 
 fever mosquitoes may get to him and bite him. Then 
 they bite others and inject the yellow fever germs into 
 them, other mosquitoes bite the new patients, and so 
 the cases of yellow fever increase with alarming rapidity. 
 Fighting Mosquitoes. Not all kinds of mosquitoes 
 carry malaria or yellow fever, so we need not feel afraid 
 every time we see a mosquito. But if malaria or yellow 
 fever is in a community, it is time to look after the mos- 
 quitoes. Screens and netting can keep them out of the 
 houses by using much care. To make a good fight 
 against them people now try to do away with their 
 breeding places or kill them in these places. As 
 they breed in water, ditches, ponds, water barrels, old 
 tin cans with water in them, all furnish good places 
 for them to breed in. Mosquitoes lay eggs in these 
 places, the eggs hatch into " wrigglers " or " wiggle- 
 tails," as they are called. These are the larva. From 
 the " wiggle-tails " the mosquitoes come. If the breed- 
 ing places are cleaned up or drained so that they become 
 dry, of course no mosquitoes can breed in them. If 
 the places can not be drained it has been found that 
 the larvae, or " wiggle- tails," can be quickly killed by 
 pouring kerosene on the water. A very little of the 
 oil will spread out in a very thin layer over a large 
 surface of water. Now the larvae must come to the 
 surface to breathe. When they do so the oil kills 
 them instantly. Thus it seems as if we have a way 
 to get rid of these very dangerous mosquitoes. Frosts 
 and cold weather in winter help us part of the year. 
 
WOUNDS 179 
 
 New cases of yellow fever or malaria do not appear 
 after a few heavy frosts. 
 
 Fighting House Flies. Since typhoid fever and 
 cholera may be brought into a house by flies, these 
 should be shut out of the house by screens, but it is 
 also easy to destroy most of them before' they are fully 
 developed. The eggs of the most common species of 
 house flies are laid in the refuse of the horse stable. 
 This refuse should be frequently removed and piled in 
 a mass. By this means the eggs are buried and the 
 pupae are destroyed. 
 
 Wounds. When studying the skin, it was shown 
 that one use of the epidermis is to keep out bacteria. 
 There seem to be several kinds of bacteria which will 
 cause inflammation of a wound 'and blood poisoning. 
 These bacteria may be present in various kinds of 
 dirt and filth. They may be in decaying substances. 
 When they get on our skin the epidermis keeps them 
 out until they are washed off. If, however, there is 
 a break in the epidermis they get in and cause trouble. 
 It is best, as has been shown, to bathe the skin fre- 
 quently. The hands should, of course, be cleaned im- 
 mediately after anything with dangerous dirt of any 
 kind on it has been handled. Cleanliness makes 
 the body at all times safer in case of an accidental 
 wound. But even if the body is clean, the object 
 making the wound may have some of the dangerous 
 kinds of bacteria on it and a very slight wound may 
 in this way become very serious. Every wound should 
 as soon as possible be carefully cleaned and kept so. 
 The wound should be washed also with some liquid 
 that has been prepared for such a purpose, called an 
 
180 DISEASE, ITS CAUSES AND PREVENTION 
 
 antiseptic. An antiseptic is something that kills bac- 
 teria. Various substances are used as antiseptics. 
 Most of them are poisons, and should be used only 
 when they are prepared by some one who understands 
 about them, with careful following of the directions 
 given. When the wound is cleaned of bacteria, the 
 next thing is to keep any more bacteria from getting 
 into it. This is done by covering it with cotton 
 that has been made very clean for this purpose. It 
 is called absorbent cotton. If the wound is kept care- 
 fully covered with this, all bacteria that would fall on 
 the wound are caught by it. If one receives a severe 
 wound, of course the physician should be asked to treat 
 it. Still it is well to know about these matters so that 
 we can give immediate aid to the injured, and can follow 
 the physician's directions with intelligence. 
 
 When a surgeon is compelled to make a wound in 
 performing an operation, he is careful that the instru- 
 ments he uses, his clothing, and his hands are as free 
 as possible from bacteria. The room is also made clean. 
 When all this is done properly and the wound guarded 
 against bacteria afterward, it will heal without trouble. 
 If this is not done, the most severe troubles may arise 
 from even a slight wound. 
 
CHAPTER XX 
 
 ALCOHOL, TEA, COFFEE, TOBACCO, OPIUM 
 
 IN certain chapters throughout this book we have 
 called attention to the effects of alcohol on the spe- 
 cial organs there described. It seems desirable now 
 to speak of the effects, on the body as a whole, of 
 alcohol, as well as of tea, coffee, tobacco, and opium. 
 It is on the body as a whole that the most injurious 
 work of these agents is to be seen. These substances 
 are so widely used, and the consequences of their 
 excessive use are so serious, that a special chapter 
 may well be devoted to a discussion of their effects 
 in the hope that many may be deterred from the for- 
 mation of dangerous habits in their use. 
 
 Description of Alcohol. Alcohol in a pure state 
 is a transparent liquid. It is somewhat lighter than 
 water. It is so nearly a true liquid that it forms no 
 lasting bubbles when shaken up in a bottle. It burns 
 with a pale blue flame, without smoke, thus produc- 
 ing a great amount of heat. Pure alcohol is known 
 as " absolute alcohol." Alcohol mixes readily with 
 water in all proportions. The alcohol usually sold, 
 known as " commercial alcohol," generally contains 
 five per cent or more of water. 
 
 Source of Alcohol. Alcohol is formed by the 
 growth of the yeast plant in solutions containing 
 
 181 
 
1 82 ALCOHOL, TEA, COFFEE, TOBACCO, OPIUM 
 
 sugar. When yeast is placed in a solution contain- 
 ing sugar of the right proportions, and it is kept in 
 a warm place, the yeast grows rapidly, and in its 
 growth converts the sugar into alcohol and carbonic 
 acid. The carbonic acid, being a gas, generally 
 bubbles up through the solution and escapes; but the 
 alcohol being a liquid remains dissolved in the 
 solution." 
 
 In making bread, however, the carbonic acid re- 
 sulting from the growing yeast is held by the sticky 
 dough, which it lifts up and makes " light." In the 
 process of baking, both the carbonic acid and the 
 alcohol are driven off. 
 
 The juices of ripe fruits contain sugar. If these 
 juices are left exposed so that the minute yeast plants 
 in the air can get into them, they undergo a process 
 called " fermentation." This process of fermenta- 
 tion is the growth of the yeast plants, and, as just 
 explained, it produces carbonic acid, which mainly 
 escapes from the juice and leaves the alcohol remain- 
 ing in the liquid. Thus the juice of grapes is changed 
 into wine, the juice of apples into cider. If the juices, 
 after the formation of alcohol in them, are allowed 
 to stand exposed to the air, other minute organisms 
 grow in them, which will change the alcohol to acetic 
 acid. Wine and cider are thus changed to vinegar. 
 Many other solutions of sugar are used to allow the 
 formation of alcohol, and thus many forms of alco- 
 holic drinks are produced. 
 
 Beer, ale, and porter belong to the group of malt 
 liquors. In making these, barley is kept moist and 
 warm till it begins to sprout. In the act of sprout- 
 
PHYSIOLOGICAL ACTION OF ALCOHOL 183 
 
 ing, the starch of the grain is changed to sugar. The 
 sprouted grain is dried and ground up, and water 
 is added, which dissolves the sugar and other sub- 
 stances of the grain. To this solution yeast is then 
 added, which converts the sugar into alcohol and 
 carbonic acid. The resulting clear liquid containing 
 the alcohol separated from the undissolved parts 
 constitutes beer, ale, or porter, the distinctions being 
 due to certain differences of treatment in the manu- 
 facture of the liquids. 
 
 Another class of alcoholic drinks is produced by 
 first allowing alcoholic fermentation by yeast to take 
 place, and then separating the liquor by distillation 
 from the other matters in the mixture. Examples 
 of such drinks are whisky, brandy, rum, and gin. 
 These contain a far greater amount of alcohol than 
 the wines or beer. 
 
 The quantity of alcohol in the different drinks 
 varies greatly. In some kinds of beer the amount 
 is as low as two per cent, while in some forms of 
 brandy it reaches 'fifty-five per cent. In all alcoholic 
 drinks, however much they differ in flavor, the alco- 
 hol is of the same nature, and has the same origin. 
 The different flavors by which the various alcoholic 
 drinks are distinguished are due mainly to substances 
 extracted from the materials used in their manu- 
 facture. The most characteristic effects resulting 
 from the use of alcoholic drinks are due to the alco- 
 hol contained in them. 
 
 Physiological Action of Alcohol. In considering 
 the physiological effects of alcohol, there are certain 
 facts which must be kept in mind. 
 
1 84 ALCOHOL, TEA, COFFEE, TOBACCO, OPIUM 
 
 First, there is the great difficulty of determining 
 the exact effect, on any special organ, of any sub- 
 stance taken as food, medicine, or poison. We can 
 usually say that a certain food is good or bad be- 
 cause, when it is used constantly, the general health- 
 of the body is improved or impaired. But it would, 
 in most cases, be impossible to tell the special effect 
 of that food on the various tissues. Of course, in all 
 such cases, there are people ready to advance theo- 
 ries to explain the exact action of the various foods 
 on each of the tissues. But explanations which 
 have not been experimentally proved are of no value. 
 There are many medicines whose general tendencies 
 are pretty clearly known, but whose special effects on 
 the cells of any tissue are wholly unknown. Quinine 
 is a good example. It is well known that if given in 
 a proper way it will, in a grqat number of cases, cure 
 certain diseases; but it is impossible to say definitely 
 how the cure is effected, and it certainly is not pos- 
 sible to show with microscopic sections any changes 
 in the tissues produced by such small quantities of 
 quinine. 
 
 Some of the most active poisons, while they show, 
 by causing death, their sure and speedy effect on the 
 body as a whole, give no indication, under the most 
 careful examination, of their special action on the 
 various tissues of the body. 
 
 There is no doubt that when any substance, as a 
 food, a medicine, or a poison, produces an effect on 
 the body, it does so by causing certain changes in the 
 cells of some or all of the tissues. But what these 
 changes are, it is usually impossible to determine. 
 
PHYSIOLOGICAL ACTION OF ALCOHOL 185 
 
 A second fact that should be kept in mind in con- 
 sidering this subject is that individuals vary greatly 
 in the way they are affected by different kinds of 
 foods and drugs. Often it is found that a food that 
 seems beneficial or harmless to most people may pro- 
 duce in certain individuals unpleasant or distressing 
 symptoms. A drug that may powerfully affect a ma- 
 jority of people may be used by a few without marked 
 injurious results. Even the effects that generally follow 
 the use of any drug vary greatly in character and de- 
 gree in different persons. Hence we must not draw 
 any definite conclusions from a single experience or 
 from a few observations on a few individuals. 
 
 A third fact important to remember is this: The 
 effects of substances may vary under different condi- 
 tions ; as, in various degrees of health, in connection 
 with different kinds of diet, in activity or rest of the 
 body, in different climates, and in different ages. 
 In view of these facts, the following statements of 
 the physiological effects of alcohol must of necessity 
 be of a general character, and they can not be made 
 applicable to each individual case. 
 
 If a small amount of alcohol is taken, it may pro- 
 duce no perceptible effect except a slight increase of 
 the pulse rate. -^ 
 
 The effects of large amounts of alcohol are well 
 summed up by Dr. Emerson, as follows: 
 
 " If large doses be given a healthy person, the 
 usual course is, first, a flushing of the face, with a 
 greater flow of words and ideas, and tendency of 
 muscular activity; then imperfect articulation, loss 
 of judgment, unsteady gait, dulled moral sense, irregu- 
 
1 86 ALCOHOL, TEA, COFFEE, TOBACCO, OPIUM 
 
 lar eyesight, loss of sensation, then of consciousness, 
 and, finally, even impaired (vegetative functions) 
 breathing and circulation all of these phenomena 
 being successive paralyses of nervous centers of the 
 brain, medulla, and spinal cord. 
 
 " If large doses be often repeated, the alcohol car- 
 ried through the various organs modifies their nutri- 
 tion and the growth of the mere connecting tissues 
 (framework) at the expense of their more important 
 special tissues. Thus the stomach and liver, kidneys, 
 and, finally, even the voluntary muscles, and the 
 all-important involuntary muscle called the heart, 
 degenerate. These processes are slow and only result 
 from the decided abuse of alcohol, especially spirits." 
 
 The student is referred to the chapters on circula- 
 tion (p. 52), foods (p. 70), and the nervous system 
 (p. 130), for a description of the special effects on 
 these organs of the use of alcohol. But to under- 
 stand the full action of alcohol on the body as a whole, 
 we must remember that the results described for these 
 various organs occur all together. These organs, as 
 we have learned, have very important functions. 
 When the action of one is interfered with, its effect 
 is felt on the whole body, and thus the direct injury 
 occasioned by alcohoHs heightened. If the functions 
 of these important organs are being interfered with, 
 the general health of the body is sure to be under- 
 mined. The capability of the body for accomplish- 
 ing physical or 'mental work is greatly lessened. Its 
 power of resisting the attacks of disease is decreased. 
 Its power of recovery when disease has invaded the 
 system becomes much weakened. This condition of 
 
ALCOHOL AS A MEDICINE 1 87 
 
 the body is sometimes described as " an undermined 
 constitution " or " a lowered vitality." While it is 
 hard to describe accurately what has occurred to the 
 body, the condition is none the less real. It can be 
 easily recognized, and is indeed a serious matter. 
 
 If the body sustains accidental injury, or if for some 
 cause a surgical operation is to be performed, the 
 surgeon realizes that recovery is likely to be less speedy, 
 or less sure, if the patient has been accustomed to the 
 use of alcoholic drinks. 
 
 Under training for any athletic contest, experi- 
 ence has shown that the greatest success can not be 
 secured when alcoholic drinks are indulged in; con- 
 sequently their use is forbidden. In cases where 
 long-continued, severe bodily exertion is necessary, 
 or an unusual amount of exposure to fatigue, cold, 
 or heat, experience has also shown that the drinking 
 of alcohol is detrimental. In these cases the objec- 
 tion to the use of alcohol is clear. Still the effects 
 are the same whether we are engaged in a severe 
 contest or not. We are all the time in some sort 
 of contest, and certainly each one wishes to be at 
 his best. Experience shows clearly that we are not 
 at our best after using alcohol. The same may be 
 said of the use of tea, coffee, and opium, and its com- 
 pounds. 
 
 Alcohol as a Medicine. The discussion of the 
 question as to whether alcohol may be beneficial 
 in the treatment of disease is out of place here. 
 When we are sick we should be put under the care 
 of a well-trained physician. Then we must trust to 
 his learning and skill, and follow his directions. The 
 
1 88 ALCOHOL, TEA, COFFEE, TOBACCO, OPIUM 
 
 forms, conditions, degrees, and courses of diseases are 
 so varied, and so obscure, that it would generally be 
 dangerous to trust ourselves to any one not trained 
 or skilled in the practice of medicine. There are 
 many poisons and other injurious substances that 
 may be used with great benefit in certain conditions 
 or phases of disease. Physicians differ in opinion as 
 to whether alcohol is one of them. But, in any case, 
 the problem must be solved by the physicians, and, 
 however settled, it will not affect the question of the 
 effect of alcohol on the healthy body. 
 
 Other Substances in Alcoholic Drinks. Thus far 
 we have spoken only of the alcohol in alcoholic drinks, 
 but they contain a number of other substances. Some 
 of these occur naturally, and others are added either to 
 change the flavor or as adulterations. Some of these 
 are known to be injurious and others to be harmless. 
 The number of these substances is so great that a special 
 treatment of each is impossible here. 
 
 Intoxication. Thus far we have dwelt mainly on 
 the effects of long-continued use of alcohol on the 
 general health of the ' body. There is, however, one 
 result which is so evident that neither physiologist 
 nor physician is needed to detect it or to point out 
 its evils; that is, the intoxicating effect of alcohol 
 taken in large doses. This is known in common lan- 
 guage as getting drunk. The evils of drunkenness 
 are so great and so well known that we need not dwell 
 on them here. Fortunately, a large number of those 
 who use alcoholic drinks do not become habitual 
 drunkards. However, it is of the greatest importance 
 that the fact be emphasized that the moderate use 
 
EFFECTS OF ALCOHOLIC DRINKING 189 
 
 is in danger of becoming immoderate. It is only from 
 the ranks of the moderate users that the great army of 
 drunkards is recruited. It is impossible for a man to 
 foretell, when forming the habit of drinking, whether 
 or not he will be able to control himself from running 
 into excess.- Hence when ajnan cultivates this habit 
 he runs this risk. 
 
 It would seem as if no person who has contem- 
 plated the terrible things which have been done under 
 intoxication would voluntarily assume a habit which 
 involved even the bare possibility of such an end. 
 Indeed, all such arguments against the use of alcohol 
 as those contained in the facts of its effect on the 
 heart, the kidneys, or the liver, or on the general 
 health, pale before .the undisputed evidence that 
 by means of alcohol an intelligent man may act with- 
 out reason; that a kind-hearted man may become 
 brutal to his most loved friends; that an honorable 
 man may become dishonorable; that a man with a 
 noble nature may acquire the most depraved tastes; 
 that its use has over and over again been the cause 
 of bitter disappointments, of intense sufferings, and 
 of crime. 
 
 Effects of Alcoholic Drinking on the Community. - 
 It has been shown beyond doubt, by repeated study 
 of statistics gathered from prisons, insane asylums, 
 and almshouses, that the use of alcoholic drinks 
 is the most frequent cause of crime, insanity, and 
 poverty. These facts are so well known, and have 
 been before us so long, that they do not impress the 
 general community in proportion to their enormity. 
 If some new form of drug or food, or some new politi- 
 
IQO ALCOHOL, TEA, COFFEE, TOBACCO, OPIUM 
 
 cal or social movement, were introduced which, in a 
 year after its introduction, would bring about in the 
 civilized world physical and moral results as harmful 
 as those produced by alcohol, the fact would stir every 
 class up to arms. There would be a universal, ener- 
 getic, and immediate movement toward its suppres- 
 sion. 
 
 Most other poisons so affect their victims that they 
 alone suffer the consequences of their use. But 
 alcohol renders its slaves active agents in bringing suf- 
 fering and degradation on others in the community. 
 Other vices are the usual associates of drunkenness. 
 
 The evil influences of most drinking places and of 
 many drinking customs are well known and undis- 
 puted. Thus alcohol comes to affect not individuals 
 alone, but the moral tone of the community as a whole. 
 In these facts, again, we are forcibly shown that argu- 
 ments against the use of alcohol based on moral grounds 
 far outweigh all those drawn from physiological con- 
 siderations. 
 
 Tea and Coffee. Tea consists of the dried leaves 
 of a plant extensively cultivated in China, Japan, 
 Ceylon, and India. The leaves contain a number 
 of vegetable substances common to all leaves, but in 
 addition they contain an alkaloid known as theine, 
 which is characteristic of tea leaves. There is also a 
 large amount of tannin. 
 
 Coffee consists of the seeds or so-called " berries " 
 of a plant which is cultivated for drinking purposes. 
 The berries are roasted, and by this means an aro- 
 matic substance is developed which gives coffee its 
 peculiar flavor. Besides this aromatic substance there 
 
TEA AND COFFEE IQI 
 
 are, of course, many other ingredients in the berries, 
 prominent among which are tannin, certain vegetable 
 acids, and caffeine. 
 
 Theine and Caffeine. It is to these substances 
 that the characteristic physiological effects of tea 
 and coffee are due. Theine and caffeine are exactly 
 alike in their chemical composition, and the same 
 physiological effects have been assigned to both. In 
 tea there is a greater amount of tannin. This has an 
 injurious action on the digestive processes. 
 
 After speaking of the beneficial effects of a mod- 
 erate use of tea for some persons, Dr. Yeo says: 
 
 " On the other hand, it is quite certain that tea 
 taken in excess, and in some constitutions, may be- 
 come very injurious. It will not infrequently excite 
 and maintain most troublesome gastric catarrh, the 
 only remedy for which is an entire abstinence from 
 tea for a considerable period. It is often also the 
 cause of troublesome cardiac palpitations, together 
 with muscular tremors and general nervous agita- 
 tion. We have noticed that tea will often commence 
 somewhat suddenly to disagree with a person, and 
 excite dyspeptic symptoms, coincidently with the 
 occurrence of nervous worry, and that after the cause 
 of the nervous worry has passed away tea may again 
 be taken, in moderation, with impunity. In irritable 
 states of the stomach, tea is also apt to disagree, espe- 
 cially if the coarser teas containing much tannin are 
 taken; these, when taken in large quantities during, 
 or too soon after, a meal, will disturb and often seriously 
 hinder the digestive processes." 
 
 The beneficial effects which are thought to belong 
 
IQ2 ALCOHOL, TEA, COFFEE, TOBACCO, OPIUM 
 
 to the moderate use of tea and coffee are no doubt 
 often more apparent than real; they produce an 
 agreeable feeling, which makes the user believe that 
 he is benefited when perhaps only a harmful change 
 has taken place. 
 
 If no other harm came from the use of these sub- 
 stances than the constant deception as to the true 
 state of the body, even that would be considerable 
 damage. For, if the proper appetite is interfered 
 with, it is quite certain that at times too much or 
 too little food will be taken. Tea and coffee have 
 also the power of relieving the sense of fatigue, and 
 while they may thus be valuable aids as a temporary 
 relief from suffering, they become very harmful if 
 they lead us to overlook and disregard the cause of 
 the weariness. Fatigue itself has its uses, and we 
 would sooner or later suffer if deprived of its warn- 
 ing voice. In other words, the delicate balance of 
 coordination between the processes of nutrition and 
 necessities of the various organs would be lost. Such 
 a state continued could not result* otherwise than inju- 
 riously, the extent of injury depending on the degree 
 to which the organism was affected. The claim that 
 tea or coffee will enable the body to do more work 
 on a smaller amount of food is absurd. Energy can 
 not come from nothing. As the source of energy 
 in the body is oxidation of oxidizable substances 
 (foods), it is impossible for a substance to cause work 
 to be done by doing away with its source of energy. 
 
 Whatever makes us " feel better " when we really 
 are not better, forces our nervous system to tell lies 
 to us. This " feeling better " is followed by " feel- 
 
TOBACCO 193 
 
 ing worse," which is also a lie. These waves of 
 feeling caused by stimulants destroy the unity and 
 effectiveness of life. The greater the wave of exalta- 
 tion, the lower is the depression which follows. This 
 depression finds its extreme in discouragement, pes- 
 simism, and delirium tremens. The user of stimulants 
 leads in a sense a double life, and no form of " double 
 life " can be an effective one. 
 
 It is unwise to use even in so-called moderation 
 these stimuli which thus distort the natural action of 
 the nervous mechanisms regulating the nutritive pro- 
 cesses. But it is worse than folly to indulge in them 
 to an excess which brings on one the most serious 
 results. Between moderation and excess the grada- 
 tion is very gradual. Moderation in the great major- 
 ity of cases becomes a greater or less degree of excess. 
 It is certainly the part of wisdom to forego the passing 
 pleasure that these beverages may give, and avoid 
 the risk of the more lasting suffering or disability 
 which their use may entail. 
 
 Tobacco. Tobacco, as is well known, consists of 
 the leaves of a plant which is raised in many warm 
 countries. It is used in the form of snuff, or is chewed, 
 or smoked as cigars, cigarettes, or in a pipe. It was 
 introduced into Europe at the time of Queen Eliza- 
 beth by Sir Walter Raleigh, who learned its qualities 
 from the Indians of North America. From this time 
 its use gradually spread throughout the civilized 
 world. 
 
 Among the many substances in the leaves of the 
 tobacco plant the most characteristic is nicotine. 
 This is oily and aromatic. It is distilled from the 
 
 IND, PR. PHYS. 13 
 
194 ALCOHOL, TEA, COFFEE, TOBACCO, OPIUM 
 
 leaves by the heat of the burning tobacco. The 
 vapor of this oil is partly condensed in the cigar or 
 cigarette, or in the bottom of the bowl or along the 
 stem of a pipe; but part of it passes on to the throat 
 and lungs of the smoker. 
 
 From these regions it gets into the body. Nicotine 
 is an active poison, even in small quantities. The 
 amount that usually gets into the body by the user 
 of tobacco is very small, otherwise the results would 
 be fatal. As it is, many persons use tobacco for 
 many years, apparently without bad effects. The 
 body, which at first is greatly shocked at the intro- 
 duction of the poison, seems later to adapt itself to 
 its presence. Still to a great number of persons it is 
 always a poison, more or less undermining the health, 
 or even breaking it down entirely ; used in excess 
 and there is constantly this danger the results are 
 most serious. The physiological effects of tobacco 
 are as follows: 
 
 It affects the heart, and excessive use may produce 
 palpitation and weakening of that organ; it inter- 
 feres with the digestion and causes a loss of appetite. 
 A long series of carefully conducted experiments 
 show that immediately after smoking there is a 
 marked loss of the power of doing work with the 
 voluntary muscles. Tobacco is also said to interfere 
 with the development of the red blood coipuscles, 
 whose great importance has been shown in another 
 place. 
 
 Of the other substances besides the nicotine which 
 are vaporized by the heat of the burning tobacco, 
 and pass with the smoke into the mouth, throat, and 
 
OPIUM 195 
 
 lungs, some produce irritation of the mucous lining 
 and may bring about a diseased state of those organs, 
 such as chronic sore throat and other affections. 
 It is thought that many cases of cancer of the mouth 
 can be traced to the habit of smoking. It is agreed 
 on all sides that the use of tobacco is very injurious 
 to the young, and should be avoided by them in every 
 form. There have been many cases recorded of death 
 of young boys through nicotine poisoning from excess 
 in smoking. 
 
 The evil effects of tobacco come on in such an in- 
 sidious way, that very often the sufferer has no hint 
 of the true cause of his troubles; this renders it all 
 the more a dangerous enemy. 
 
 The tobacco habit grows on a person till it becomes, 
 in the great majority of cases, a somewhat tyrannical 
 master, demanding great sacrifices of time, health, 
 and money to satisfy its desires. This itself is a form 
 of disease. There is another point of view we should 
 consider. How will it affect our associates? Both 
 smoking and chewing are offensive to most people 
 who do not use tobacco. We should indeed hesitate 
 before forming a habit which will render our close 
 presence disagreeable to many, if not to most of our 
 friends. 
 
 Opium. The use of opium or some of its com- 
 pounds may become a habit impossible to control. 
 When this is the case the result is usually a most 
 disastrous one. Opium occurs in various forms. 
 Morphine is a substance made from it. Some com- 
 pound of opium is found in many medicines, such 
 as paregoric and laudanum. Many of the so-called 
 
196 ALCOHOL, TEA, COFFEE, TOBACCO, OPIUM 
 
 11 cough mixtures " and " soothing sirups " contain 
 some form of it. It is a very dangerous drug. A 
 small amount of it will produce death. In the hands 
 of the doctor it becomes, in disease, one of the most 
 important medicines; but, on account of the danger 
 in its use, it should be given only under direction of 
 a physician. The frequent use of medicines contain- 
 ing opium or its compounds may lead to the formation 
 of the opium habit. 
 
 General Considerations in Regard to Stimulants. 
 The body, as we have seen, is a combination of deli- 
 cately balanced mechanisms. Through the nervous 
 system many of them are self-regulating. These 
 work most correctly when the stimuli which direct 
 their action come from the actual condition of the 
 body. Thus the movements of respiration are con- 
 trolled by the amount of carbonic acid in the blood. 
 The beat of the heart is regulated by nervous im- 
 pulses arising from actual conditions of various parts 
 of the body. We have shown that the actions of the 
 glands, and of other organs, are regulated in a similar 
 manner. Now, if any artificial stimulus acts on these 
 mechanisms, they no longer work in just the manner 
 they should, to be in harmony with the remainder of 
 the system. The body is then not in its best con- 
 dition. 
 
 By means of the nervous system we have sensa- 
 tions which tell us of the outside world through the 
 special senses, and of the state of our own body, 
 as in hunger, thirst, fatigue, pain, etc. Furthermore, 
 we have the power of coming to conclusions in regard 
 to our actions on receiving impressions through these 
 
CONSIDERATIONS IN REGARD TO STIMULANTS 197 
 
 sensations. The whole is a very complex means by 
 which we adapt our actions to conditions in which 
 we are placed. 
 
 For the greatest success, for the clearest seeing, 
 for the most efficient action, it is of the utmost im- 
 portance that correct reports come in for the judg- 
 ment to act upon. In other words, we wish to know 
 the world as it really is, and we wish to know the 
 actual conditions of the body. This is impossible 
 when the sensations are modified by stimulants. 
 They make us fe'el warm, cool, hungry, thirsty, well, 
 or ill, when we are not really in such condition. We 
 have reporters about us which make false reports; hence 
 when we act on those reports our conduct can not be 
 right. 
 
 In the close competition we are sure to meet with 
 in any pursuit in life, the degree of success will depend 
 upon our equipment. How great, then, is the im- 
 portance of keeping in good condition the delicate 
 mechanisms upon the true working of which depend 
 our chances of success and our capability for happi- 
 ness! How unwise is the person who voluntarily 
 does anything that may prove a hindrance to the best 
 action of his mind or body! 
 
INDEX 
 
 Abdomen, 87, 100. 
 Absolute alcohol, 181. 
 Absorption, from small intestine, 
 92. 
 
 from stomach, 88, 89. 
 Accommodation of eye, 157, 158. 
 Adam's apple, 103. 
 Air, impure, 106, 112, 113, 168. 
 
 pressure of, 98. 
 
 pure, 105. 
 
 Air sacs or vesicles, 96. 
 Air tubes, structure of, 96. 
 Albumen, 71. 
 Alcohol, as medicine, 187, 188. 
 
 description of, 181. 
 
 distillation of, 183. 
 
 effect on community, 189, 
 190. 
 
 effect on heart, 61, 62. 
 
 effect on nervous system, 145, 
 146. 
 
 physiological action of, 183- 
 187. 
 
 source of, 181, 182. 
 Alimentary canal, 78, 79. 
 Alkaline contents of small in- 
 testine, 91. 
 Antiseptics, 180. 
 Aorta, 49, 50. 
 
 arch of, 50. 
 
 Appetite, use and abuse of, 75, 
 76. 
 
 Aqueous humor, 156. 
 
 Arm and hand, bones of, 23-29. 
 
 study of, 12, 13. 
 Arms, function of, 34, 35. 
 Arteries, aorta, 49, 50. 
 
 blood pressure in, 53, 54. 
 
 description of, 46, 47. 
 
 pulmonary artery, 50. 
 
 structure of, 51. 
 Arytenoid cartilages, 103. 
 Asphyxia, 114-116. 
 Astigmatic eyes, 163, 164. 
 Auditory apparatus, 159, 160. 
 Auditory nerve, 159, 160. 
 Auricles, 49. 
 
 Bacteria, 170-180. 
 Bathing, 125, 126. 
 Beans, as food, 72, 74. 
 Biceps muscle, 14, 26. 
 Bicuspid teeth, 81. 
 Bile, 90, 91. 
 Blood, care of, 58. 
 
 coagulation of, 57-60. 
 
 composition of, 56. 
 
 corpuscles of, 56, 57. 
 
 course of, in circulation, 52. 
 
 flow of, in arteries and veins, 
 
 53, 54- 
 
 in hand, 45, 46. 
 plasma, 57. 
 pressure of, 53, 54. 
 
 199 
 
20O 
 
 INDEX 
 
 Blood (continued} 
 
 regulation of supply of, 55, 
 56. 
 
 use of, 44, 45. 
 
 Blood vessels, structure of, 51. 
 Blubber of whale, 1 20. 
 Body, compared to an engine, 
 67, 68. 
 
 composition of, 69. 
 
 divisions of, 34. 
 
 plan of, 63, 64. 
 
 proportion of foods needed, 
 
 74, 75- 
 
 regulation of temperature of, 
 121, 122. 
 
 wastes of, 69. 
 
 work of, 66, 67. 
 
 Bones, as levers, 29, 34, 37, 
 38. 
 
 hygiene of, 41-43. 
 
 of arm and hand, 23-29. 
 
 of ear, 159. 
 
 of face, 36, 37. 
 
 of leg, 31-34- 
 
 of thorax, 36. 
 
 structure of, 39, 40. 
 
 uses of, 37. 
 Bony tissue, 65, 66. 
 Brain, bones of skull protect, 
 38. 
 
 nerve cells, 132, 133. 
 
 part of nervous system, 133, 
 
 134- 
 
 structure of, 135, 136. 
 
 weight of, 135. 
 Breastbone, 36. 
 Breathing, correct, 113, 114. 
 Bronchi, 96. 
 Bronchial tubes, 96. 
 Bruises, 169. 
 
 Cabbage, starch in, 71. 
 Caffeine, 191. 
 Canine teeth, 81. 
 Canned foods, 170, 171. 
 Capillaries, absorption by, 55, 88, 
 92. 
 
 action of, 55. 
 
 description of, 46, 47, 51. 
 Carbon, 69. 
 Carbon dioxide, in air, 105, 106. 
 
 in circulation, 20. 
 
 in oxidation, 67, 69, 72, 73. 
 
 in respiration, 20, 95, 105, 106, 
 
 124. 
 
 Cardiac opening of stomach, 87. 
 Carpals, 24. 
 Cartilage, defined, 41. 
 
 of ribs, 36. 
 Cement of tooth. 81. 
 Central nervous system, 139. 
 Cerebellum, 136. 
 Cerebrum, 135, 140, 141. 
 Cervical vertebrae, 35. 
 Cheese, as food, 72. 
 Chest, 36. 
 Chlorine, 69. 
 Chlorophyll, 72. 
 Cholera, 176. 
 Choroid coat of eye, 156. 
 Cilia, 96, 97. 
 
 Ciliary muscle of eye, 156, 157. 
 Circulatory system, blood, 44-48. 
 
 blood vessels, 46-50. 
 
 divisions of, 51. 
 
 heart, 48. 
 
 hygiene of, 58-62. 
 
 physiology of, 52-58. 
 
 regulation of actions of, 55, 56. 
 Clavicle, 27. 
 
INDEX 
 
 201 
 
 Cleanliness, 125, 126, 179. 
 Clot, 57. 
 
 Clothing, 127-129. 
 Coagulation, 57, 58. 
 Coats of eye, 155, 156. 
 Coccyx bone, 35. 
 Cochlea, 160. 
 
 Coffee, effects of, 62, 190-192. 
 Collar bone, 27. 
 Commercial alcohol, 181. 
 Concave glasses, 158. 
 Conjunctiva of eye, 154, 162. 
 Connective tissue, 50, 65, 66. 
 Consumption, 174, 175. 
 Contractile power of muscles, 
 
 15, 17, 18. 
 
 Convex glasses, 158. 
 Convolutions of cerebrum, 135. 
 Cooking, value of, 94. 
 Cords, vocal, 103. 
 Cornea of eye, 153, 157. 
 Coronary vein, 50. 
 Corpuscles, of blood, 56, 57. 
 Course of blood in circulation, 5 2 . 
 Cranial nerves, 137. 
 Cranium, 36. 
 Crawfish, 38. 
 Cricoid cartilage, 103. 
 Cross-eye, 164. 
 
 Crystalline lens of eye, 156, 157. 
 Currents, air, 108, 109. 
 
 Delirium tremens, 146. 
 Dentine of teeth, 81, 83. 
 Dermis, 118, 119. 
 Diaphragm, 97. 
 Diffusion, 101. 
 
 Digestive system, absorption, 92. 
 alimentary canal, 78, 79. 
 
 Digestive system (continued} 
 
 bile, 90, 91. 
 
 care of, 93, 94. 
 
 esophagus, 86, 87. 
 
 foods requiring digestion, 77, 
 78. 
 
 glands, 79. 
 
 liver, 90. 
 
 mastication, 81. 
 
 mouth, 79-82. 
 
 pancreas, 90. 
 
 parts of, 79. 
 
 pharynx, 86, 87. 
 
 processes in digestion, 78. 
 
 saliva, 82. 
 
 salivary glands, 82. 
 
 small intestine, 89, 90. 
 
 stomach, 87-89. 
 Diphtheria, 173. 
 Diseases, causes of, 168. 
 
 infectious, 169-180. 
 
 of ear, 167. 
 
 of eye, 1 65 . 
 
 power of body against, 168, 
 
 169. 
 
 Dislocation of joint, 42, 43. 
 Distilled liquors, 183. 
 Dorsal vertebras, 35, 36, 97. 
 Dyspepsia, 93. 
 
 Ear, care of, 166, 167. 
 
 parts of, 159, 1 60. 
 Enamel of tooth, 81, 83. 
 Epidermis, 45, 117, 118. 
 Epiglottis, 104. 
 Erysipelas, 173, 174. 
 Esophagus, 86, 87. 
 Eustachian tube, 159. 
 Evaporation, 121, 122. 
 
202 
 
 INDEX 
 
 Excretions, 122, 124. 
 Exercise, 21, 22. 
 
 excessive, 22, 62. 
 
 lack of, 1 68. 
 Expiration, 99, 100. 
 External auditory canal, 159. 
 External ear, 159. 
 Eye, accommodation to different 
 distances, 157, 158. 
 
 care of, 161-165. 
 
 coats of, 155, 156. 
 
 external parts of, 153, 154. 
 
 eyeball, 154. 
 
 longsightedness, 158. 
 
 seeing, 156, 157. 
 
 shortsightedness, 158. 
 Eyeball, 154. 
 Eyelashes, 153. 
 Eyelids, 153. 
 Eye strain, 163, 164. 
 
 Face, bones of, 36, 37. 
 Fats, action of pancreatic juice 
 on, 90, 91. 
 
 defined, 71. 
 
 digestion of, 78. 
 
 in skin, 119, 120. 
 Fatty tissue, 65. 
 Femur bone, 33. 
 Fermentation, 182. 
 Fibula bone, 33. 
 Fingers, actions of, 12, 13, 15. 
 
 bones of, 23, 24. 
 Flavors, 151. 
 Flies, diseases carried by, 173, 
 
 175, 176, 179. 
 Floating ribs, 36. 
 Flour, as food, 74. 
 Food groups, 70. 
 
 Foods, canned, 170, 171. 
 fats, 71. 
 forms of, 70. 
 inorganic, 70, 73. 
 need for, 63, 67-69. 
 organic, 70, 71. 
 oxidation of, 72. 
 properties needed in body, 
 
 74, 75- 
 
 proteids, 71. 
 
 use and abuse of, 75, 76. 
 
 See also Digestive system. 
 Forearm, bones of, 24-26. 
 Forelimbs of lower animals. 
 29, 30. 
 
 G 
 
 Ganglia, 136, 137. 
 Gastric juice, 88. 
 General sensations, 147, 148. 
 Germs, disease, 169-172. 
 Gills offish, 97,98. 
 Glands, 79, 120-122. 124. 
 Graham flour, as food, 74. 
 G/ains, as food, 72. 
 Gray matter, 134. 
 Growth and repair, 68. 
 Gums. 70, 78. 
 
 H 
 
 Habits, 144, 145. 
 Hair, 118, 123, 126. 
 Hand and arm, blood in, 45, 46. 
 
 bones of, 23-29. 
 
 movements of, 12, 13. 
 Hearing, 148, 158-160. 
 Heart, action of, 52, 53. 
 
 bones of chest protect, 38. 
 
 care of, 60. 
 
 description of, 48. 
 
 effect of alcohol on, 61, 62. 
 
 function and position of, 48. 
 
INDEX 
 
 203 
 
 Heart (continued} 
 
 interior of, 49. 
 
 structure of, 50, 51. 
 
 valves of, 49. 
 Heat, production of, 67, 68. 
 
 source of, 121. 
 Hemispheres of brain, 135. 
 Hepatic vein, 92. 
 Hip bone, 33. 
 Hip joint, 33, 40. 
 Humerus, 26. 
 Hunger, 149. 
 Hydrogen, 69. 
 Hygiene, of bones and joints, 
 
 41-43- 
 
 of circulation, 58-62. 
 of digestive organs, 93, 94. 
 of ear, 166, 167. 
 of eye, 161-165. 
 of muscles, 20-22. 
 of nervous system, 142-146. 
 of respiration, 105-115 
 of skin, 125-129. 
 of teeth, 83-85. 
 
 Incisor teeth, 81. 
 Incus bone, 159. 
 Indigestion, 93. 
 Infectious diseases, 169-180. 
 Inferior vena cava, 50, 92. 
 Inorganic foods, 70*, 73. 
 Insanity, 146. 
 Inspiration, 99, 100. 
 Instep, 31. 
 
 Intercostal ribs, 100. 
 Internal ear, 159, 160. 
 Intestinal juice, 90. 
 Intestine, large, 91, 92. 
 small, 89, 90. 
 
 Intoxication, 188, 189. 
 Involuntary actions, 141, 142. 
 Involuntary muscles, 19. 
 Iris, 154, 156, 157. 
 Iron, 69. 
 
 Jawbone, 36, 37. 
 
 Jellyfish, 39. 
 
 Joints, dislocation of, 42, 43 
 
 hygiene of, 41-43. 
 
 structure of, 39, 40. 
 
 K 
 
 Kidneys, 124. 
 Kneecap, 33, 34. 
 Knee joint, 33. 
 Knuckles, 23. 
 
 L 
 
 Lachrymal ducts, 153. 
 Lacteals, 90. 
 Larynx, 96, 103. 
 Leg, bones of, 31-34. 
 
 function of, 34, 35. 
 Lettuce, starch in, 71. 
 Levers of body, 29. 
 Ligaments, defined, 40. 
 
 injury to, 42, 43. 
 Lime, 69. 
 Liver, 90, 92. 
 Longitudinal fissure, 135. 
 Longsightedness, 158. 
 Lower maxillary bone, 36. 37 
 Lumbar vertebrae, 35. 
 Lungs, description of, 96-99. 
 
 effect of tobacco on, 1 14, 
 Lymphatics, 88. 
 
 M 
 
 Malaria, 176, 177. 
 Malleus bone, 159. 
 Marrow of bone, 40. 
 
204 
 
 INDEX 
 
 Mastication, 82. 
 
 Maxillary bones, 36, 37. 
 
 Measles, 173, 174. 
 
 Meat, 72, 74. 
 
 Medulla oblongata, 135, 136. 
 
 Membrana tympani, 159, 160. 
 
 Membrane, 41. 
 
 Mesentery, 89. 
 
 Metacarpals, 23, 24. 
 
 Metatarsals, 31, 33. 
 
 Middle ear, 159. 
 
 Mildews, 72. 
 
 Milk, 71, 72. 
 
 Mitral valve, 49. 
 
 Molar teeth, 81. 
 
 Molds, 72. 
 
 Mosquitoes, carriers of disease 
 
 germs, 177-179. 
 Motions, number of, 16, 17. 
 
 production of, 16, 17. 
 Mouth, 79, 80, 96. 
 Mucous coat of small intestine, 
 
 89, 90. 
 
 Mucous coat of stomach, 88. 
 Mucous membrane of air tubes, 
 
 96. 
 
 Mucus, 80, 96, 97. 
 Muscle fiber, 133. 
 Muscles, care of, 20-22. 
 
 contractile power of, 15, 17, 1 8. 
 
 description of, 13-15. 
 
 in lower animals, 17. 
 
 involuntary, 19. 
 
 number of, 16. 
 
 voluntary, 19. 
 Muscular tissue, 50, 65, 66. 
 Mushrooms, 72. 
 
 N 
 
 Nails, 123, 127. 
 
 Narcotics, 60-62. 
 Nearsightedness, 163, 164. 
 Nerve cells, 132, 133. 
 Nerve center, 148. 
 Nerve fiber, 132, 134. 
 Nerves, cranial, 137. 
 
 description of, 18, 132. 
 
 in arm, 18, 130, 131. 
 
 part of nervous system, 133, 
 
 134- 
 
 sensory, 148. 
 
 spinal, 137. 
 Nervous control of respiration, 
 
 100. 
 Nervous impulses, 18, 19, 131, 
 
 139, 140. 
 Nervous system, action of, 139. 
 
 brain, 135-137. 
 
 care of, 142-144. 
 
 effects of alcohol on, 145, 
 146. 
 
 habits, 144, 145. 
 
 involuntary actions, 14.1, 142. 
 
 nerve cells, 134. 
 
 nerve fibers, 132, 133. 
 
 nerves, 132. 
 
 nervous impulses, 18, 19, 131, 
 139, 140. 
 
 parts of, 133, 134. 
 
 spinal cord, 134, 135, 137. 
 
 sympathetic system, 137. 
 
 voluntary'actions, 140, 141, 
 Nervous tissue, 65. 66. 
 Nicotine, 114, 193-195. 
 Nitrogen in air, 105. 
 
 in proteids, 72, 73. 
 
 in tissues, 69. 
 Nitrogenous foods, 72, 74. 
 Non-nitrogenous foods, 72, 74. 
 Nostrils, 96. 
 
INDEX 
 
 205 
 
 Occipital bone, 134. 
 Odors, 152. 
 Oil glands, 118. 
 Oils, 71, 78. 
 Opium, 195, 196. 
 Optic nerve, 155, 156, 
 Organ, denned, 63. 
 Organic foods, 70, 71. 
 Organisms, 65. 
 Organization in body, 64, 65. 
 Os innominatum, 33. 
 Osseous tissue, 69. 
 Oxidation, 67-69, 72, 73. 
 Oxygen, in air, 105, 106. 
 
 in circulation, 20, 57. 
 
 in oxidation, 67-69. 
 
 in respiration, 95, 97, 101, 
 102. 
 
 P 
 
 Pain, 148, 149. 
 Palate, 80. 
 soft, 151. 
 Pancreas, 90. 
 Pancreatic juice, 90. 
 Papillae of skin, 119. 
 Patella bone, 33, 34. 
 Peas, as food, 72, 74. 
 Pelvic arch, 35. 
 Peptones, 88, 90. 
 Pericardial liquid, 50. 
 Pericardium, 50. 
 Perspiration, 79, 120-122. 
 Phalanges, 23, 31. 
 Pharynx, 86, 87, 96. 
 Phosphorus, 69. 
 Pinna, 159. 
 Plasma, 56, 57. 
 Poisons, 184. 
 Portal vein, 92. 
 
 Potassium, 69. 
 
 Potatoes, food substances in, 71, 
 
 72, 74- 
 
 Premolar teeth, 81. 
 Pressure of blood, 53, 54. 
 Processes, 35. . 
 
 Proteids, action of gastric juice 
 on, 88. 
 
 action of pancreatic juice on, 
 90. 
 
 digestion of, 78. 
 
 foods containing, 71, 72, 
 
 oxidation of, 73. 
 Pulmonary artery and veins, 49, 
 
 50. 
 
 Pulmonary circulation., 51. 
 Pulp of tooth, 81. 
 Pulse, 46, 53, 54. 
 Pupil of eye, 154. 
 Pylorus, 87. 
 
 R 
 
 Radius bone, 25, 26. 
 Reflex actions, 141, 142. 
 Repair and growth, 68. 
 Respiration, amount of air 
 breathed, 101. 
 
 artificial, 114-116. 
 
 in lower animals, 97, 98. 
 
 nervous control^ 100. 
 
 respiratory acts, 99, 100. 
 
 respiratory organs, 96, 97, 
 Retina, 156. 
 Ribs, 36-38, 97. 
 Rice, 74. 
 Rods and cones of eye, 156, I57 
 
 Sacrum bone, 35. 
 Salines, 73. 
 Saliva, 82. 
 
206 
 
 INDEX 
 
 Salivary glands, 80, 82. 
 Scapula bone, 26, 27. 
 Scarlet fever, 173, 174. 
 Sclerotic coat of eye, 155. 
 Secretion of glands, 79, 120-122, 
 
 124. 
 
 Seeing, 156, 157. 
 Semicircular canals, 160. ^ 
 Semilunar valves, 49. 
 Sensations, defined, 147. 
 
 general and special, 147, 148. 
 Sense organs, 133, 148. 
 Sensory nerves, 148. 
 Shortsightedness, 158. 
 Shoulder blade, 26. 
 Shoulder girdle, 23. 
 Shoulder joint, 40. 
 Sight, 148, 153-158- 
 Skeleton, animals without, 39. 
 
 bones of arm and hand, 23-30. 
 
 bones of face, 36, 37. 
 
 bones of leg, 31-34. 
 
 bones of thorax, 36. 
 
 different kinds of, 38. 
 
 divisions of body, 34, 35. 
 
 skull, 36. 
 
 spinal column, 35. 
 Skin, as organ of temperature, 
 
 122, 123. 
 
 care of, 125-129. 
 
 structure of, 117, 118. 
 
 sweat glands in, 120, 122. 
 
 touch organs in, 122, 150, 151. 
 
 uses of, 123, 124. 
 Skull, 36. 
 Sleep, function of, 143. 
 
 lack of, 1 68. 
 Smallpox, 173, 174. 
 Smell, 148, 152. 
 Sodium, 69. 
 
 Sore eyes, 165. 
 
 Sound, sensation of, 158, 160. 
 
 Special sensation, 148. 
 
 Special-sense organ, 148. 
 
 Spinal canal, 36. 
 
 Spinal column, 35, 37. 
 
 Spinal cord, nerve cells in, 132, 
 
 133- 
 part of nervous system, 132- 
 
 134- 
 
 position of, 36. 
 
 structure of, 134, 135. 
 Spinal nerves, 137. 
 Sprain, 42, 43, 169. 
 Stapes bone, 159, 160. 
 Starches, action of pancreatic 
 juice on, 90. 
 
 digestion of, 78, 82. 
 
 foods containing, 70-72. 
 Sternum, 36, 97. 
 Stimulants, 181-197. 
 Stimulation of muscles, 19. 
 Stimulus, nervous, 19, 130. 
 Stomach, 87-89. 
 Subclavian vein, left, 92. 
 Sugar, digestion of, 77, 78. 
 
 foods containing, 70-72. 
 Sulphur, 69. 
 
 Superior vena cava, 50, 92. 
 Swallowing, 87. 
 Sweat, 79, 120-122. 
 Sweat glands, 79, 120, 122. 
 Sweet potatoes, starch in, 71. 
 Sympathetic nervous system, 
 
 137- 
 
 Systemic circulation, 51. 
 Systems, 64. 
 
 T 
 
 Tannin, 190, 191. 
 Tarsals, 31, 33. 
 
INDEX 
 
 207 
 
 Taste, organs of, 80, 148. 
 
 sense of, 151, 152. 
 Tea, 62, 190-192. 
 Tear ducts, 153. 
 Tears, 79, 153. 
 Teeth, care of, 83-85. 
 
 description of, 80, 81 . 
 
 structure of, 81. 
 
 Temperature, of body, 121, 
 122. 
 
 sense of, 148. 150, 151. 
 Tendons, 13-15, 40. 
 Theine, 190, 191. 
 Thirst, 149. 
 Thorax, bones of, 36. 
 
 in respiration, 96, 97. 
 Thumb, 23, 24. 
 Thyroid cartilage, 103. 
 Tibia bone, 33. 
 Tissues, 65, 66. 
 Tobacco, physiological effects 
 
 of, 62, 114, 193-195. 
 Tongue, 80, 151. 
 Tooth, see Teeth. 
 Touch, 122, 148-151. 
 Trachea, 96. 
 Tricuspid valve, 49. 
 Tuberculosis of lungs, 174, 
 
 *75- 
 
 Typhoid fever, 175, 176. 
 
 U 
 
 Ulna bone, 24-26. 
 Urea, 69, 124. 
 
 Vaccination, 174. 
 Valves of heart, 49, 5 it- 
 
 Veins, described, 47. 
 
 flow of blood in, 54. 
 
 function of, 50. 
 
 structure of, 51. 
 Ventilation, 106-112. 
 Ventricles, 49. 
 Vertebrae, 35, 36, 97. 
 Vertebrates, 38. 
 Vestibule of ear, 160. 
 Vibrations, 158, 159. 
 Villi of small intestine, 90. 
 Vision, distinct, 157. 
 Vitreous humor, 156. 
 Vocal cords, 103. 
 Voice, 103. 
 
 Voluntary actions, 140, 141. 
 Voluntary muscles, 19. 
 
 W 
 
 Wall-eye, 164. 
 Wastes of body, 69, 124. 
 Water, as inorganic food, 73, 
 
 74- 
 
 excretion of, 122, 124. 
 
 germs carried by, 176. 
 
 in air, 105. 
 
 in digestion, 78. 
 
 in oxidation, 67, 72. 
 
 in tissues, 69. 
 White matter, 134. 
 Will, muscles controlled by, 
 
 18, 19. 
 
 Wounds, 59, 169, 179, 180. 
 Wrist, 24. 
 
 Yeast, 181-183. 
 Yellow fever, 177, 178. 
 
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