HUMAN 
 PHYSIOLOGY 
 
 RITCHIE 
 
V. 
 
 a 
 
 GIFT OF 
 John H. Mee 
 
NEW-WORLD SCIENCE SERIES 
 
 HUMANA 
 PHYSIOLOGY 
 
 AN ELEMENTARY TEXT-BOOK WITH SPECIAL 
 
 EMPHASIS ON HYGIENE AND 
 
 SANITATION 
 
 BY 
 
 JOHN W. RITCHIE 
 
 EDITOR OF NEW-WORLD SCIENCE SERIES ; JOINT AUTHOR OF 
 NEW-WORLD HEALTH SERIES 
 
 Illustrated by 
 MARY H. WELLMAN 
 
 1920 REVISION 
 
 YONKERS-ON-HUDSON, NEW YORK 
 
 WORLD BOOK COMPANY 
 
 1927 
 
^]~^P ~~- 
 
 WORLD BOOK COMPANY 
 
 THE HOUSE OF APPLIED KNOWLEDGE 
 Established, 1905, by Caspar W. Hodgson 
 
 J YONKERS-ON-HUDSON, NEW YORK 
 2126 PRAIRIE AVENUE, CHICAGO 
 
 j. \ ' 
 
 ~' 
 
 Know thyself! This precept of the an- 
 cients will hold good while the human race / ^? / 
 
 endures, and the first step in compliance / / ** 
 
 with it is to learn something about the bodies 3IOI.OGY 
 
 that we inhabit. The author of Human 
 Physiology believes that such knowledge " Q 
 
 ought to be given to the people by the 
 schools which have been founded for their 
 instruction; he is confident that modern 
 knowledge is able to free our people from 
 most of their illnesses. The purpose of 
 this book is to present to upper grammar 
 grade pupils the essentials of physiology, 
 hygiene, and sanitation that every American 
 citizen ought to know 
 
 SIFT OF 
 
 W 
 
 BlQtOGY 
 
 LIBRARY 
 
 G 
 
 Copyright, 1908, 1915, 1920, by World Book Company 
 
 Copyright in Great Britain 
 
 All rights reserved 
 
PREFACE 
 
 FROM a considerable experience with both very elementary 
 and more advanced classes, the author has been led to certain con- 
 clusions in regard to the teaching of elementary physiology and 
 hygiene. It is not proposed to enter here into a discussion of 
 the correctness of these conclusions, but a brief statement of a 
 few principles that seem fundamental may perhaps be allowable. 
 
 The chief object of teaching physiology in the public schools 
 is to train the pupils to keep their bodies in health. The mere 
 teaching of anatomy and physiology will not accomplish this, for 
 the pupil cannot master the structure and workings of the body 
 in a way that will enable him to frame the laws of health and 
 apply them. Neither can the desired end be reached by teach- 
 ing rules of health without an anatomical and physiological 
 basis ; for without such a basis, hygiene is an intangible and an 
 elusive subject. The author has therefore concluded that a 
 conservative middle course is wiser than either of the extremes 
 of method mentioned above. An elementary text in physiology 
 should be a balanced text, containing sufficient anatomy to make 
 clear the broader outlines of the structure of the human body, 
 enough physiology to make plain the great laws according to 
 which the body lives, and a full discussion of how a violation of 
 these laws may be avoided. 
 
 For the introduction of certain new matter, as, for example, 
 the cell idea, the work of enzymes, and matter relating to germ 
 diseases, there is little need for explanation. The groundwork 
 of physiology and pathology has in recent years so shifted and 
 extended itself, that the subject-matter of an elementary course 
 must to a considerable extent be altered if it is to furnish a 
 
 796431 
 
IV PREFACE 
 
 proper basis for hygiene. The importance of teaching the 
 known facts in regard to parasitic diseases and of training 
 American citizens to apply measures for the prevention of these 
 diseases, is now recognized, and the reason for the rather full 
 treatment of communicable diseases will be understood. 
 
 One other point in connection with the teaching of physiology 
 has constantly obtruded itself upon the writer. This is the age 
 of science, but instead of teaching elementary science in our 
 public schools, we are teaching unrelated fragments from differ- 
 ent parts of the field of science. Physiology more than any 
 other subject is the people's science, and it should be related to 
 the nature study and the agriculture of the public school course. 
 In a few places in this book an attempt has been made to lead 
 the pupil into some of the byways that connect his physiology 
 and nature study, and special emphasis has been given to cer- 
 tain facts that are necessary to an understanding not only of 
 physiology, but of other subjects in the public school curriculum. 
 
 For counsel and very great assistance during the preparation 
 of this text, the author must thank his friend, Dr. J. S. Caldwell 
 of the Bureau of Plant Industry, United States Department of 
 Agriculture. He is also under obligation to Mr. J. C. Freeman, 
 who made the calculations for the table on pages 351-352 ; and 
 for many suggestions and corrections he is indebted to the fol- 
 lowing persons : Dr. William H. Park, Dr. F. H. Pike, Dr. O. P. 
 Jenkins, Dr. C. M. Hazen, Dr. E. G. Williams, Dr. S. O. Mast, 
 Dr. J. A. C. Chandler, Professor C. W. Hetherington, Miss 
 Virginia Jones, Edward Hughes, and W. I. Chapman. 
 
CONTENTS 
 
 PAGE 
 
 INTRODUCTORY i 
 
 I. THE HUMAN BODY A COLONY OF CELLS ... 3 
 
 II. THE PLAN OF THE HUMAN BODY 16 
 
 III. THE RULER OF THE BODY 23 
 
 IV. THE SKELETON ........ 31 
 
 V. THE SKELETON (continued} 45 
 
 VI. THE MUSCLES , 59 
 
 VII. FOODS AND ENERGY 78 
 
 VIII. THE DIGESTIVE ORGANS 88 
 
 IX. DIGESTION, ABSORPTION, AND OXIDATION OF FOODS . no 
 
 X. DIETETICS 120 
 
 XI. THE CIRCULATORY SYSTEM 135 
 
 XII. RESPIRATION 160 
 
 XIII. VENTILATION . 178 
 
 XIV. THE KIDNEYS AND THE BODY WASTES . . . .186 
 XV. THE SKIN AND THE BODY HEAT 191 
 
 XVI. THE NERVOUS SYSTEM . . . . . . .210 
 
 XVII. THE NERVOUS SYSTEM (continued') . . . ' . 225 
 
 XVIII. THE EFFECTS OF ALCOHOL ON THE HUMAN BODY . 238 
 
vi CONTENTS 
 
 CHAPTER PAGE 
 
 XIX- THE SPECIAL SENSES .... 245 
 
 XX. THE SPECIAL SENSES (continued) 259 
 
 XXI. ACCIDENTS 274 
 
 XXII. DISEASE GERMS . , 285 
 
 XXIII. DISEASES CAUSED BY PROTOZOA 292 
 
 XXIV. DISEASES CAUSED BY BACTERIA 303 
 
 XXV. PREVENTING THE SPREAD OF DISEASE GERMS . . 320 
 
 XXVI. TUBERCULOSIS 340 
 
 APPENDIX 347 
 
 A. FOODS 347 
 
 B. VENTILATION 358 
 
 C. ALCOHOL AND LENGTH OF LIFE 361 
 
 D. INTESTINAL DISEASES 362 
 
 GLOSSARY 365 
 
 INDEX 367 
 
INTRODUCTORY 
 
 DID you ever get up in the morning and find that all the 
 world seemed bright ? And did you ever get up on another 
 morning and find that all the world was dull ? Do you 
 remember how on the one morning you sang over your work 
 and ran on your way to school ? And how on the other 
 morning you blundered and fretted over your work and did 
 not care to play ? On the one day you were so happy that 
 every one was pleased to see you. On the other day you 
 were not a pleasant companion for any one. On the one 
 day the world seemed a beautiful place, and work was easy. 
 On the other day all the world was dull, and every task was 
 hard and disagreeable. 
 
 Why were you happy and joyous one morning and misera- 
 ble and unhappy the next ? Why did you cheerfully do your 
 work one day and hate the same work the next day ? Was 
 it money, clothes, or education that made you happy ? Was 
 it a lack of them that made you unhappy ? All these things 
 are important, but there is something else much more im- 
 portant than all of them, something that causes happiness to 
 bubble up within you no matter what the world is like ; some- 
 thing that keeps the heart beating strong with hope, and 
 makes you laugh at hard work Y something without which all 
 the wealth of the world cannot make you happy, and with 
 which any sound-minded person can lead a useful and a 
 
INTRODUCTORY 
 
 successful life. This something that can so change all the 
 world for you is the health of your own body. 
 
 It is not possible for every one to be always in perfect 
 health. Sickness is bound to come to some of us, for there 
 are many things about the human body that we still do not 
 understand and there are certain ailments that as yet we have 
 not learned to escape or cure. It is possible through the 
 knowledge that we now have, however, to be set free from 
 the greater part of the sickness that at present burdens us. 
 In this book we shall, therefore, study the human body and 
 how to keep it in health. 
 
CHAPTER I 
 
 THE HUMAN BODY A COLONY OF CELLS 
 
 WHEN you view a brick house from a distance you do not 
 see the bricks of which the house is built ; but if you look at 
 the house through a telescope or come close to it, you see 
 clearly the bricks in the walls of the house. The house which 
 from a distance appears to be one object is seen to be com- 
 
 FlG. i. Cells. A is a single cell as it appears under the microscope ; B is a cell 
 showing that it has length, breadth, and thickness; and Cis a group of cells. A cell 
 found alone usually has a somewhat spherical shape, as shown in A . When cells grow 
 in groups they press against each other and usually have an irregular shape, as shown 
 in C. 
 
 posed of a great number of smaller objects built together to 
 form one whole. 
 
 The human body is composed of many small parts called 
 cells. When we look at the body we cannot see the cells; 
 but when a small portion of flesh or skin or other part of the 
 body is examined under the microscope, the little parts which 
 
 3 
 
4 HUMAN PHYSIOLOGY 
 
 make up the body can be distinctly seen. As the walls of the 
 house are built of bricks, so the human body is built of cells. 
 
 The Cell. A cell is a small portion of a transparent, 
 jelly-like material called protoplasm}- Usually a cell has a 
 thin wall about it, so that it is like a little sac filled with a 
 clear, half -liquid substance. In each cell is a nucleus, which 
 is a denser portion of the protoplasm. Both the nucleus 
 and the less dense material 2 around it take in food and 
 grow ; both of them are alive. Taken together they are the 
 protoplasm, the living substance of the cell. 
 
 Living Things composed of Cells. As a heap of sand is 
 composed of small grains, so are living things composed of 
 very tiny cells. 3 Every blade of grass, every weed, every 
 flower, and every tree is made of cells. Every animal, 
 whether it be large or small, whether it live in the water, on 
 the land, or in the air, is composed of cells. Dead materials, 
 like earth, stones, water, and air, are not made of cells, but 
 there is nothing living that is not composed of cells. 
 
 How Cells are formed. The ancient Egyptians thought 
 that crocodiles and frogs came from the mud of the river 
 Nile, and a great Grecian philosopher believed that insects 
 sprang from the dew. A wise old scholar once told the 
 people how mice could be created from wheat and stagnant 
 water. Two hundred years ago, it was commonly believed 
 that maggots came from meat and cheese, and that worms, 
 insects, snails, and eels came out of decaying matter and 
 
 1 In the back of the book the pupil will find a glossary that gives the pronun- 
 ciations and meanings of many of the more difficult words. 
 
 2 The lighter portion of the protoplasm is called cytoplasm. 
 
 3 A few cells, for example, a frog's egg, are large enough to be seen with the 
 naked eye. In general, however, cells are very small; so small that it would 
 require twenty-five hundred cells from the human body to make a row an inch 
 long. 
 
THE HUMAN BODY A COLONY OF CELLS 
 
 5 
 
 mud. Fifty years ago, many physicians and other scientific 
 men believed that disease germs ^and other little microbes 
 were formed from unclean and decaying matter, and many 
 persons still think that this is true. 
 
 We know now that all these ideas are incorrect. All living 
 things, from the smallest germ to the greatest whale, are 
 made of cells, and a cell can come, not from dead matter, 
 but only from another living cell. 
 
 FIG. 2. Cell division. The nucleus of the cell divides and part goes to each end 
 of the cell. A wall is formed across the cell, dividing it into two parts, each of which 
 is a cell. All new cells are formed in this way. 
 
 The nucleus of a cell divides, and part of it goes to each 
 end of the . cell. Then a wall forms across the cell, and 
 divides it into two parts. Each part is a new cell with its 
 own nucleus, and each part grows as large as the parent 
 cell. All new cells are formed in this way. "Every cell 
 comes from a cell." 
 
 One-Celled and Many-Celled Animals. In a drop of stag- 
 nant water many hundreds of little animals may sometimes 
 be found, animals so small that you can see them only 
 with a microscope. One of these little animals has only one 
 cell in its body. The animal is a single cell that swims 
 about alone and lives by itself. When this cell divides, the 
 two new cells separate, and each one forms a new animal. 
 
6 HUMAN PHYSIOLOGY 
 
 The bodies of all the larger animals (for example, the 
 body of the chick in an egg) begin with a single cell, but 
 when this cell divides, the new cells do not separate, like 
 those of the one-celled animals. The cells remain together 
 and keep on dividing and dividing until, in the body of a 
 large animal, like a man, there are millions and millions of 
 cells, more than you could count in many years. The 
 
 FlG. 3. A one-celled animal dividing. This cell swims about in the water by 
 means of small hair-like cilia which beat the water. When it divides, the new cells 
 separate instead of remaining together as they do in the many-celled animals. 
 
 difference between the little one-celled animals and the larger 
 many-celled animals is therefore this : in one-celled animals, 
 the cells separate after they divide and each cell lives alone. 
 In the many-celled animals, the cells remain together after 
 division, and live in a great colony. 
 
 Your body, therefore, is a great colony of cells, and each 
 cell in it corresponds to an entire one-celled animal. You 
 might almost think of yourself as made up of a great com- 
 munity of little animals, yet this idea would not be wholly 
 correct. The cells of our bodies have learned to live to- 
 gether. They would die if separated, and it takes them all 
 to make one complete animal. 
 
THE HUMAN BODY A COLONY OF CELLS 7 
 
 Different Kinds of Cells do Different Kinds of Work. The 
 
 single cell of a one-celled animal must do many different 
 kinds of work to live. It has no hands to get food for it, 
 no teeth to chew the food, and no stomach to digest it. It 
 has no lungs to breathe in oxygen, and no kidneys to throw 
 off its poisonous wastes. It lives all alone, with no other 
 cells to help it, and it must do everything for itself. Each 
 cell in the human body has the same needs as the little 
 animal cell which lives alone. Each must have food, must 
 get oxygen from the air, and must get rid of its poison- 
 ous wastes. Many of our cells are shut up in the center 
 of the body, where they can get neither food nor oxygen for 
 themselves, and their waste matter would poison both them- 
 selves and their neighbors if there were not some way of 
 getting it entirely out of the body. Each cell cannot 
 take care of itself, as does the little animal in the drop of 
 water. 
 
 You can easily see how much it would be to the advantage 
 of all the cells in the body for each one to give up trying 
 to do everything for itself, and for all of them to unite and 
 work for the good of the whole community. This they have 
 done. They have divided the work, and 
 each cell has taken for its own some special 
 task. The cells of the stomach digest the 
 food ; the bone cells build up a strong frame- 
 work to support the body ; the muscle cells 
 
 .. , , ^ . ., 11 ,.!_ FIG. 4. Cells from 
 
 move the body; the kidney cells throw out aglandof the St0 m 
 wastes ; the lung cells take in oxygen from ach. The function 
 the air and the cells of the blood (red blood 5 work) . of these <*"* 
 
 is to digest the food 
 
 corpuscles) carry oxygen through all the 
 
 body to the cells. Each cell is a skilled workman doing 
 
 some particular work for the body as a whole, and not 
 
A muscle cell from the stomach. The 
 muscle cells have the work of moving the 
 body. 
 
 Connective tissue. In its first stage 
 connective tissue is a group of cells 
 which build around themselves a mass 
 of jelly-like material, as shown in A. 
 This material hardens into the fibers 
 that are seen between the cells in B. 
 All through the body a framework of 
 connective tissue runs, holding the 
 cells, organs, and tissues in place. 
 
 Bone cells. These much-branched cells 
 deposit around themselves bone material 
 (b), thus building bones to support the body. 
 The bone cells build a network of fibers like 
 dense connective tissue and then fill the 
 spaces between the fibers with hard mineral 
 matter, a is a cavity from which the bone 
 cell has been removed. 
 
 One of the Cells of the outer 
 
 nerve cells layer of the skin, 
 from the These cells form a 
 brain. These protective covering 
 cells are asso- for the body. The 
 ciated with outer cells die and 
 thought. dry up until they are 
 
 mere scales. 
 
 FIG. 5. Cells from the human body 
 
 Fat cells. Food for the body is stored in 
 these cells. Large quantities of fat collect 
 in the cell, and crowd the protoplasm (a 
 and b) to one side. A fat cell is little more 
 than a bag of oil. 
 
 Each kind of cell in the body has a 
 particular work to do for the body as a whole. 
 8 
 
THE HUMAN BOD* A COLONY O* CELLS 
 
 an unskilled laborer trying to do all the many different kinds 
 of work necessary to provide for hys own wants. 
 
 The Cells Dependent on Each Other. You will now under- 
 stand that the cells in the body must depend on each other for 
 many things. If the stomach fails to digest the food, there 
 will be a lack of food in all the cells. If the kidneys do not 
 throw off the wastes, all the cells will be poisoned. If the 
 lungs stop taking in oxygen, all the cells must die for lack 
 of oxygen. If part of the cells fail in their work, all the 
 cells must suffer, and death usually comes to the body because 
 part of the cells have ceased to work. 
 
 The Body compared to a Community. The resemblance 
 between the body and a community of people must now 
 be very clear to you. In both the body and the com 
 munity we have individuals, each leading his own life and 
 yet making a part of a greater whole. In 
 the community we have individuals of dif- 
 ferent occupations, doctors, teachers, car- 
 penters, blacksmiths, grocers, and milkmen. 
 In the body we have, as we have seen, cells 
 of different kinds, muscle cells, bone cells, 
 digestive cells, and many others. In both 
 the body and the community the individual 
 does not provide everything that he uses, 
 but depends on others for many things. 
 The carpenter builds houses for the milk- 
 man and the grocer, and these persons 
 bring the carpenter his food. The stom- 
 ach cells digest food for the cells of the 
 lungs, and the lung cells take in oxygen 
 for the stomach cells. 
 
 Communities are prosperous and the body is healthy only 
 
 FIG. 6. Cells from 
 the lining of the tra- 
 chea, a is a cell that 
 manufactures sticky 
 mucus (V) in which dust 
 and germs from the air 
 are caught. The cilia 
 (c) on the other cells 
 beat upward and sweep 
 the mucus, dust, and 
 germs up out of the 
 air passages and lungs. 
 
10 HUMAN PHYSIOLOGY 
 
 when the individuals do their work faithfully and well ; foi 
 
 no person in a community lives to 
 himself, and no cell in the body lives 
 to itself, but each has a share in the 
 life of all. New individuals from time 
 to time are born into the community 
 
 FIG. 7. Cells from the blood. and other individuals die . New cells 
 A is a white corpuscle whose 
 
 function is to kill disease germs; are constantly being formed in the 
 B is an edge view and ds a side body, and every day millions of cells 
 
 view of the red corpuscles that , , -, -, i ^ 
 
 carry oxygen through the body. m the b d y are . destroyed. Com- 
 
 munities increase in size when the 
 
 number of births in them exceeds the number of deaths, and 
 the body grows when the number of new cells formed in it is 
 greater than is the number of the cells that die. Thus in 
 many ways the body resembles a community of people where 
 each individual is doing something for the good of all. 
 
 Tissues. If you have now in mind what has been said 
 about cells and their work, you will have no difficulty in 
 understanding what is meant by tissues. In a factory we 
 usually find the workmen who do the same kind of work all 
 collected in one part of the factory. So in the body we 
 usually find grouped together the cells which do the same 
 kind of work. The great group of nerve cells is in the brain. 
 The muscle cells are collected in the muscles, and the kidney 
 cells in the kidneys. Where cells of one kind are grouped, 
 a tissue is formed, so we may say that a tissue is a group of 
 cells whick do the same kind of work. Muscle tissue is 
 made of muscle cells, fatty tissue of fat cells, and nerve 
 tissue of nerve cells. Each tissue is a group of cells which 
 do some particular work for the body as a whole, and in 
 return have many things done for them by the cells of othei 
 tissues, 
 
THE HUMAN BODY A COLONY OF CELLS n 
 
 Organs. An organ is a part of the body that does a special 
 work. The kidney is an organ for throwing out wastes, the 
 lungs are organs for taking in oxygen, the eye is an organ 
 for seeing, and the stomach is an organ for storing and digest- 
 ing food. Some organs, like the liver, the kidneys, and the 
 heart, are chiefly of one kind of tissue. Other organs have 
 in them many kinds of tissues. The hand is an example 
 of an organ of this kind, bone, connective tissue, muscle, and 
 skin all being united in it to form an organ for grasping. 
 
 Why you should understand the Cell. It is very impor- 
 tant for you to understand the cell, because a clear idea of 
 the cell will give you a new way of thinking about all 
 living things. Having an understanding of it, you will 
 not only think of an animal as a living thing, but you will 
 also think of the millions of cells in its body, each filled 
 with living protoplasm. When you see a plant cut down, 
 or an insect, or a frog, or a bird killed, you will not only 
 think of how the plant or animal dies, but you will think 
 of how all the little cells in its body also die; and from 
 thinking of the living objects about you in this new way, 
 you will become interested in many things which you do not 
 now notice, and will understand much that now seems strange 
 to you. When you see a rose living for several days after it 
 has been cut from the bush and placed in water, or when 
 you see a branch of a plant living and growing when placed 
 in the soil, you will know that when a part of a plant is cut 
 off from the body of the plant, its cells need not always 
 die. If you read that when a starfish, or certain kinds of 
 worms, are cut into pieces, each piece grows into a complete 
 animal, you will see that in these animals, as in plants, 
 the cells are more independent than in the human body, 
 and that a group of them is able to live without the rest of 
 
12 HUMAN PHYSIOLOGY 
 
 the body. Also, when you learn to think of animals as groups 
 of cells, you will not wonder that a frog's legs should twitch 
 and jerk in the skillet; or that after the head has been cut 
 off, a snake's tail can live and move, and a turtle can walk 
 about. For you will understand that in these animals, as 
 in the rose, part of the cells can live for a time without the 
 others, and that the muscle cells are living and moving after 
 the brain cells are dead. All these things and many others 
 you can clear up for yourself, if you will think about the 
 cell instead of about the body as a whole. 
 
 A second very important reason why you should under- 
 stand the cell is that you may intelligently care for your own 
 bodies. Each of the great multitude- of cells in your body is 
 following out its own little life, and each is industriously work- 
 ing for the good of the community in which it lives. We 
 hope that you will, understand that your cells must have 
 proper food, oxygen, exercise, and rest, and that they must 
 get rid of their waste matter. You should realize that any 
 medicine you take can act on the body only by being carried 
 by the blood through the body and entering the living proto- 
 plasm of the cells. If it helps the cells, it is beneficial to the 
 body, and if it injures the cells, it injures the body. You 
 should understand how reckless it is to take in among all these 
 delicate cells patent medicines, headache remedies, alcohol, or 
 tobacco, unless you are perfectly certain that these things will 
 not harm the cells. For the cells of your body are the most 
 important things in all the world to you. If they become 
 diseased, you will fall sick ; and if they fail in their work, your 
 life must cease. When the bricks crumble, the house falls ; 
 and when the cells are dead, the body is dead, for the life is 
 in the cell. 
 
 There is a third reason why you should understand the 
 
THE HUMAN BODY A COLONY OF CELLS 13 
 
 cell, and that is because in physiology we constantly study tht 
 work of the different kinds of cell's. If you did not under- 
 stand the figures i, 2, 3, and 4, you would get very little 
 pleasure or profit from trying to solve problems in arith- 
 metic; and if you do not understand what a cell is and 
 how the body is made up of cells, you will think that physi- 
 ology is a dull subject indeed, and it will never mean much to 
 you. But understanding the cell, you can study the differ- 
 ent parts of the body intelligently, and in all the world you 
 will find nothing more wonderful or interesting than your 
 own body. 
 
 Anatomy, Physiology, and Hygiene. Anatomy is the study 
 of the structtire of the body, the study of the way all its 
 organs are composed of tissues and its tissues made of cells, 
 and of how all the organs and tissues are joined together to 
 make one body. Physiology is the study of the function of 
 the different cells, tissues, and organs, the study of the work 
 which all the different parts of the body do. Hygiene is the 
 study of how to keep the body in health. These three subjects 
 we must study in this book. * 
 
 Summary The human body, like all other living things, 
 is composed of cells. Each cell is a little piece of protoplasm 
 that takes in food and grows and is alive. Cells are formed 
 only by the division of other cells, and living things can come 
 only from other living things of the same kind. They can- 
 not come from dead matter, although this has often been 
 believed. 
 
 When a one-celled animal divides, the new cells separate. 
 In many-celled animals t*he cells remain together after divi- 
 sion, and the bodies of the larger animals are great colonies 
 of cells. Each cell of the human body corresponds to an 
 entire one-celled animal. Each cell in the body, like a one- 
 
14 HUMAN PHYSIOLOGY 
 
 celled animal, must have food and oxygen and must get rid 
 of its wastes. 
 
 It would not be possible for a cell in the body to supply 
 all of its own wants, so each cell spends all its time in one 
 kind of work, and depends on other cells for many things 
 that are necessary to its life. It follows, therefore, that when 
 part of the cells in the body fail in their work the whole body 
 must die. The division of labor among the cells causes the 
 body in a striking way to resemble a community where the 
 people have different occupations 'and each one has many of 
 his wants supplied by others. 
 
 As the workmen who do the same kind of work in a fac- 
 tory are often found together, so the cells that do the same 
 kind of work in the body are found in groups. Such a group 
 of cells cells that do the same kind of work is called a 
 tissue. An organ is a part of the body that, like the hand or 
 the eye, is fitted for some special work. It may be composed 
 chiefly of one or of many kinds of tissues. 
 
 A clear idea of the cell is a very great help in understand- 
 ing all living things, in caring for our own bodies, and in the 
 study of physiology. Anatomy is the study of the structure 
 of the body, Physiology is the study of the function of the 
 different organs of the body, and Hygiene is the study of how 
 to keep the body in health. 
 
 QUESTIONS 
 
 Of what is the human body composed ? Describe or draw a cell. 
 What kind of objects are composed of cells? How are new cells 
 formed? Where do living things come from? Give some of the 
 beliefs that have been held by different people in regard to the ori- 
 gin of animals and plants. Describe the process of cell division. 
 
THE HUMAN BODY A COLONY OF CELLS 15 
 
 In a one-celled animal what do the cells do after division ? What 
 do the cells do after division in a many-celled animal ? What in the 
 human body corresponds to an entire one-celled animal ? What are 
 some of the needs of a cell ? 
 
 Explain why a cell in the body could not provide for all its own 
 wants. Name some of the different kinds of cells in the body and 
 explain the function (work) of each. What happens to the body if 
 part of the cells fail in their work? Give examples of cells that 
 must do their work to keep the body alive. Mention some ways in 
 which the body corresponds to a community of people. 
 
 What is a tissue ? Name some of the body tissues. What is an 
 organ ? Name some organs of the body and give their functions. 
 
 Give three reasons why it is important to understand the cell. 
 
 What is Anatomy ? Physiology ? Hygiene ? 
 
 If a cell and a peach were compared, what part of the cell would 
 correspond to the seed of the peach ? to the flesh of the peach ? to 
 the skin of the peach ? 
 
 In an egg there is one living cell lying on the side of the yolk. 
 What is necessary to make this cell grow and divide ? Of what use 
 are the yolk and white of the egg to the cell within the egg ? Into 
 what have the yolk and the white been changed by the time the egg 
 hatches ? 
 
 Does the cell in a duck's egg grow into a duck and the cell in a 
 hen's egg into a chick because the food supply in the eggs is different, 
 or because the living cells in the eggs are different ? Are the cells of 
 your body always composed of the same materials, no matter what 
 kind of food you eat ? 
 
 Can a branch be transferred from one tree to another and still 
 live ? Can a piece of tissue be transferred from one person to an- 
 other ? Ask a physician if cells from the body of an animal can be 
 transplanted to the human body. 
 
 What happens in a wound when it heals ? Ask a physician how 
 the cells in a scar differ from the cells in other parts of the skin. 
 
CHAPTER II 
 
 THORACIC CAVITY 
 
 VENTRAL CAVITY. 
 
 THE PLAN OF THE HUMAN BODY 
 
 THE human body is com 
 posed of a head, a trunk, and 
 two pairs of limbs. It is sup- 
 ported by a skeleton, the most 
 n important part of which is the 
 spinal column, or backbone. 
 In the head are eyes, ears, a 
 nose, and a mouth. The body 
 has in it two cavities, a dorsal 
 or back cavity, and a ventral 
 or front cavity. In these two 
 cavities are found most of the 
 organs of the body. 
 
 The Dorsal Cavity. In the 
 head is a great cavity, and 
 opening out of this cavity at 
 the base is a long passage- 
 way that runs through the 
 spinal column from top to 
 bottom. The cavity in the 
 FIG. 8. The cavities of the body. The head and the canal in the 
 
 dorsal cavity is in the head and the spinal backbone taken together, are 
 
 column. The ventral cavity is in the front 
 
 of the trunk and is divided by the diaphragm the dorsal * Cavity. In this 
 
 into an upper and a lower part. cavity lie the great centers of 
 
 the nervous system, the brain and the spinal cord. 
 
 1 The name dorsal comes from dor' sum, the Latin word for back. In the lower 
 animals it is easy to see that the cavity in the head and the canal in the spinal 
 
 16 
 
 ABDOMINAL CAVITY. 
 
THE PLAN OF THE HUMAN BODY 
 
 The Ventral Cavity. The ven- 
 tral cavity is a great hollow in 
 the front part of the trunk. 
 Stretched across it is a thin 
 sheet of muscle, called the dia- 
 phragm, which divides it into an 
 upper and a lower part. The TRACHEA 
 upper part is the chest or thoracic ESOPHAGUS 
 cavity. It contains the heart 
 and lungs and many of the great 
 blood vessels. The lower part 
 is the abdominal cavity. In the 
 left side of this cavity, its outer 
 end close up under the dia- 
 phragm, lies the stomach. On 
 the right side of the body and 
 partly covering the stomach 
 is the liver. The intestine is 
 very long and is coiled again 
 and again in the abdominal cav- 
 ity, filling most of it. Attached 
 to the back walls of the cavity 
 are the two kidneys, which FIG. 9. Section of the body show. 
 
 take waste matter OUt Of the in & the Positions of the organs in the 
 
 body. At the left end of the cavities< 
 
 stomach is a dark red organ called the spleen. Along the 
 lower back part of the stomach is the pancreas, a very im- 
 portant digestive organ, whose work we must take up in 
 another chapter. 
 Man's Place in the Animal Kingdom Man has a spinal 
 
 column are all part of one long cavity that runs along the back of the body and 
 widens out at the head end to make room for the brain. 
 
r8 
 
 HUMAN PHYSIOLOGY 
 
 column, and therefore 
 belongs among the ver- 
 tebrates^- or backboned 
 animals. He has hair, 
 and when young lives 
 on milk, and therefore 
 he belongs among the 
 mammals, the highest 
 class of the vertebrates. 
 The five classes of ver- 
 tebrates are the fishes, 
 amphibians, reptiles, 
 birds, and mammals. 
 By examining a book 
 on animals, you can 
 learn which ones belong 
 in each of these classes 
 and which ones most 
 nearly resemble man. 
 
 The Bodies of Verte- 
 brates Similar. A fish, a frog, a lizard, a bird, and a cat do 
 
 * The vertebrates differ from worms, insects, and other lower animals in having 
 backbones. The five classes of vertebrates have the following distinguishing 
 characteristics : 
 
 Fishes live in the water and breathe by means of gills. 
 
 Amphibians have sticky skins, and both lungs and gills. Some salamanders 
 have lungs and gills at the same time and can breathe either in the water or in 
 the air. Other salamanders have gills at one time and lungs at another. Frogs 
 and toads have gills in their early life and Lungs in their later life. 
 
 Reptiles have scaly skins and breathe by means of lungs. Like the fishes and 
 amphibians, reptiles are cold blooded. 
 
 Birds have wings and a body covering of feathers. 
 
 Mammals have the body partly or entirely covered with hair and feed their 
 young with milk. The mammals and birds are warm blooded. 
 
 FIG. 10. 
 
 The organs in the ventral cavity, seen 
 from the front. 
 
American Museum of Natural History 
 
 FIG. ii. Skeleton of a man and of a horse. The bodies of vertebrates are all built 
 on the same general plan. 
 
 19 
 
20 HUMAN PHYSIOLOGY 
 
 not seem much alike ; and because man walks upright, the 
 human body seems very different from the bodies of all these 
 animals. Yet man and all other vertebrate animals are built 
 on the same general plan. 
 
 Like man, all the vertebrate animals have a head and trunk, 
 with eyes, ears, and a mouth in the head. All of them have 
 a dorsal and a ventral cavity in the body, with in general the 
 same organs in these cavities as are found in man. All have 
 skeletons resembling the human skeleton, not only in the 
 spinal column, but also in many other parts, as we shall see 
 later. All of them have two pairs of limbs corresponding to 
 the arms and the legs of man. In a fish, the limbs are the 
 two pairs of fins found on the sides of the body. In the seal 
 and the whale, they are paddles for swimming. In most 
 other animals, they are the fore and hind legs, but in bats 
 and birds the fore limbs are wings, and in man they are arms. 
 Most snakes have lost their limbs, but in some of the great 
 snakes the remains of little legs can be found, and in other 
 reptiles the limbs are well developed. 
 
 How Man differs from Other Vertebrates. The brain of 
 man is better developed than is the brain of any other animal, 
 and in many ways the human body differs to a certain extent 
 from the bodies of other vertebrates. But the great difference 
 between man's body and the bodies of other animals is that 
 man is built to walk erect. Instead of carrying the head 
 in front of the body and walking on all four limbs in the 
 position that a fish is in when it swims or a cat is in when it 
 walks, the human body stands on the hind limbs, with the body 
 erect and the head above the body. When the body stands 
 upright the fore limbs do not touch the ground. Therefore, in 
 man the fore limbs are not fitted for walking, but are arms 
 and have hands for grasping. 
 
THE PLAN" OF THE HUMAN BODY 21 
 
 Summary. The human body is composed of a head, a 
 trunk, and two pairs of limbs. It has in it a dorsal and a ven- 
 tral cavity. The dorsal cavity contains the brain and the 
 spinal cord ; the ventral cavity is divided by the diaphragm 
 into the thoracic cavity and the abdominal cavity. The tho- 
 racic cavity contains the heart, the lungs, and many great 
 blood vessels. The abdominal cavity contains the stomach, 
 intestine, liver, spleen, pancreas, and kidneys. 
 
 Animals with backbones are called vertebrates. Vertebrates 
 are divided into five classes, fishes, amphibians, reptiles, 
 birds, and mammals. Man has a backbone, and is a verte- 
 brate. He has hair, and when young lives on milk; he is 
 therefore a mammal. 
 
 The bodies of other vertebrates are built on the same plan 
 as the human body. Every vertebrate has a head, trunk, 
 eyes, ears, and a mouth. In the body are a dorsal cavity and 
 a ventral cavity. It has a skeleton with a backbone, and has 
 two pairs of limbs corresponding to our arms and legs. 
 
 Man's body differs from other vertebrate bodies chiefly in 
 that it stands erect. The fore limbs do not touch the ground 
 in walking, and are arms with hands 
 
 QUESTIONS 
 
 Name the principal divisions of the human body. How is the 
 body supported ? What two cavities are in the body ? 
 
 Where is the dorsal cavity ? What does it contain ? Into what 
 two parts is the ventral cavity divided ? What is the partition be- 
 tween these parts called ? Name the organs in the thoracic cavity ; 
 in the abdominal cavity. Locate the stomach. Locate the liver. 
 
 Name the five classes of vertebrates. To which class does man 
 belong ? How does this class differ from other vertebrates ? 
 
22 HUMAN PHYSIOLOGY 
 
 Give four ways in which the bodies of all vertebrates are similar. 
 Mention some different kinds of vertebrate limbs. How does man 
 differ from other vertebrate animals ? 
 
 What animals do you know that are not vertebrates? Can you 
 name an animal that has no head ? one with no mouth ? one with no 
 eyes? one with no ears? Name some animals that differ from verte- 
 brates in the number of their limbs. 
 
 How does a fish differ from other vertebrates? What is the dif- 
 ference between a shark and a true fish ? How does an amphibian 
 differ from other vertebrates? a reptile? What are the four reptile 
 groups? What do you know about the reptiles that lived in forme* 
 ages of the world ? 
 
CHAPTER III 
 
 THE RULER OF THE BODY 
 
 ALL parts of the body must be controlled and made to 
 work together. Over them all a ruler must be set. Not 
 only must the different organs be kept at work, but each 
 must be made to do the proper amount of work, and to do 
 it at the right time. If the digestive organs should begin 
 to work when nothing had been eaten, their work would 
 be useless. If the sweat glands should begin to pour out 
 sweat on the skin when the body was not hot, their work 
 would be not only useless, but even harmful. If all the 
 muscles should begin to puil and jerk without any order 
 or system (as they do in convulsions), they would succeed 
 only in throwing the body to the ground. 
 
 The ruler of the body is the nervous system. When we 
 walk, it is the nervous system that causes the right muscles 
 to move. When we eat, the nervous system sets the diges- 
 tive organs to work. It keeps the heart and lungs going, 
 and governs all the body. The function of the nervous sys- 
 tem is to govern all the organs of the body, and to cause them 
 all to work together for the common good. 
 
 The Divisions of the Nervous System. The nervous sys- 
 tem has two great divisions, the central nervous system 
 and the sympathetic nervous system. The great centers of 
 the central nervous system are the brain and the spinal 
 cord. The central nervous system controls the voluntary 
 
 23 
 
NERVCff 
 
 FIG. 12. The nervous system. From the brain and spinal cord, nerves run 
 
 to all parts of the body. 
 
 24 
 
THE RULER OF THE BODY 25 
 
 muscles (those which we can move when we wish), and the 
 higher centers of the brain act as the organ of the mind. 
 
 The sympathetic nervous system controls the glands * of 
 the body and the involuntary muscles (page 226), the 
 muscles which we cannot control by the will, as those of the 
 stomach, intestine, heart, and blood vessels. 
 
 The Brain and the Spinal Cord. The brain has three divi- 
 sions, the cerebrum, the cerebellum, and the medulla oblon- 
 gata. The spinal cord is the soft white substance that you 
 
 CONVOLUTIONS 
 
 MEDULLA OBLONGAT 
 
 FIG. 13. The brain. 
 
 may have seen in the backbone of an animal. In man it is about 
 seventeen inches long and half an inch in diameter. At the 
 base of the skull is a great opening, through which the spina ? 
 cord enters the cranium (Fig. 14) and joins the brain. 
 
 The Membranes of the Brain and Cord. Around the brain 
 and cord are three connective tissue membranes. The 
 outermost membrane, which is thick and tough, is called 
 
 1 The salivary glands, glands of the stomach and intestine, the pancreas, liver, 
 kidneys, and sweat glands are some of the glands in the body. 
 
26 
 
 HUMAN PHYSIOLOGY 
 
 the dura mater. It lines the entire dorsal cavity of the 
 body, both the cavity of the cranium and the cavity in the 
 spinal column. The innermost membrane, which is thin and 
 delicate, is called the pia mater. It lies close to the surface 
 of the cord and brain and dips down into all the wrinkles 
 and folds in the surface of the brain. In it are the blood 
 
 vessels that nourish the outer parts 
 of the brain and cord. Between 
 the dura mater and the pia mater 
 is a third membrane, the arachnoid 
 membrane. These membranes * 
 hold the very soft and delicate 
 brain and cord in place and keep 
 them from being shaken about 
 within the dorsal cavity. 
 
 The Cerebro-spinal Fluid. The 
 brain and spinal cord are still 
 further protected by a layer of 
 liquid around them called the cere- 
 The base of the skull, bro-spinal fluid. This fluid is on 
 both sides of the arachnoid mem- 
 brane that is, between the dura 
 mater and the pia mater and en- 
 tirely surrounds the cord and brain. It acts as a cushion 
 inside the walls of the dorsal cavity and keeps the brain and 
 cord from striking against the walls of the cavity. 
 
 Nerves. From the under surface of the brain and from the 
 spinal cord, shining white nerves pass out to every part of 
 the body. If you should examine one of these nerves under 
 
 1 The three membranes taken together are called the meninges of the brain 
 and cord. Cerebro-spinal meningitis is a disease caused by germs growing in 
 these membranes and in the cerebro-spinal fluid 
 
 FIG. 14 
 
 showing the opening through 
 which the spinal cord enters the 
 cranium. 
 
THE RULER OF THE BODY 27 
 
 a microscope, you would find that it is made of many hun- 
 dreds of very fine fibers, bound tcg'ether by connective tissue. 
 Although these fibers are so slender that they cannot be seen 
 without a microscope, some of them are of great length, the 
 longest reaching from the spinal cord to the hands and feet. 
 In the larger nerve trunks the fibers are bound up in a 
 number of bundles, which are all wrapped together in a com- 
 mon sheath (Fig. 15). The larger nerves divide into smaller 
 
 BLOOD VESSELS 
 
 FIG. 15. A is a cross-section of a nerve, showing the bundles of nerve fibers that 
 make up the nerve, wrapped in the connective tissue sheath. B is one of the bundles 
 of nerve fibers shown in A, enlarged to show the individual fibers. 
 
 branches containing only a few bundles, or sometimes only 
 one bundle. In the finest nerve branches, the bundles of 
 nerve fibers finally break up into the separate fibers, many 
 thousands of which end in the skin and muscles, and in the 
 other organs of the body. 
 
 The Function of Nerves. The function of the nerves is to 
 carry messages between the different parts of the body and the 
 brain and spinal cord. 
 
 Some nerves carry messages to the brain and cord. By 
 these messages we learn when anything touches the body, 
 
28 HUMAN PHYSIOLOGY 
 
 when the body is hungry or thirsty, or hot or cold, when it 
 is in pain, and about the things that we see, hear, taste, and 
 smell. Other nerves carry messages outward from the brain 
 and cord, causing the muscles to move, and making all the 
 parts of the body to work together in harmony. The power 
 by which we feel, think, and will lies in the brain. The 
 commands that we send out, causing voluntary movements 
 of the muscles, start from the brain. The nerves are useful 
 only to carry to the cord and the brain messages which tell 
 us about the body and the outside world, and to carry com- 
 mands outward from the brain and cord to the muscles and 
 to the other organs of the body. 
 
 The Telegrapher and the Telegraph Wires. The brain and 
 spinal cord are often compared to a telegrapher in an office, 
 and the nerves in the body to telegraph wires that run out 
 in all directions from the office. Over the wires the teleg- 
 grapher receives messages that tell him what is going on 
 about him, and he sends out messages commanding that cer- 
 tain things be done. So through some of the nerves the 
 brain and cord receive messages which tell them about the 
 body and the things going on around it ; and over other 
 nerves they send messages out commanding the muscles to 
 move the body, and the different organs to do their work 
 according to the body's needs. 
 
 Necessity for a Nervous System. From this you will under- 
 stand that the nervous system connects all parts of the body 
 and causes all the organs to work together for the good of 
 the body as a whole. Without a nervous system, the human 
 body would not be one body at all, but a mass of flesh and 
 blood and bones, the different organs working not at all, or 
 working without plan or system, and the whole body certain 
 to die in a few minutes. With a nervous system it is the living. 
 
THE RULER OF THE BODY 29 
 
 moving, speaking human body, the most wonderful thing 
 in all the world. 
 
 Summary. The nervous system controls all parts of the 
 body and causes them to work together. The great divisions 
 of the nervous system are the central nervous system and the 
 sympathetic nervous system. The central system controls 
 the voluntary muscles; its chief center (the brain) is the 
 organ of the mind. The sympathetic system controls the 
 involuntary muscles and the glands of the body. 
 
 The brain has three divisions the cerebrum, the cere- 
 bellum, and the medulla oblongata. Around the brain and 
 cord, and protecting them, are three membranes the dura 
 mater, pia mater, and arachnoid membrane and a layer of 
 cerebro-spinal fluid. 
 
 Nerves are composed of nerve fibers. Nerve fibers carry 
 messages between the different parts of the body and the brain 
 and spinal cord. Some fibers take messages to the brain 
 and cord, and some fibers carry messages away from the 
 brain and cord. The nerve centers (brain and cord) may be 
 compared to a telegrapher, and the nerve fibers to telegraph 
 wires. The incoming messages bring information about the 
 body and the world "around the body, and the outgoing 
 messages are commands from the nerve centers to the 
 muscles, glands, and other organs. 
 
 Without a nervous system the different organs of the 
 human body would work without system, or would not work 
 at all, and the body would die. By the nervous system, all 
 the body parts are made to work harmoniously together, 
 all are united into one wonderful body. 
 
30 HUMAN PHYSIOLOGY 
 
 QUESTIONS 
 
 What is the function of the nervous system? Name the two 
 divisions of the nervous system. What are the chief centers of the 
 central nervous system ? What is one of the great functions of this 
 system ? With what part of the nervous system is the mind associ- 
 ated ? What is the function of the sympathetic nervous system ? 
 
 Name the three divisions of the brain. Name the three mem- 
 branes that are around the spinal cord and brain. What is the 
 function of these membranes? What is between the arachnoid 
 membrane and the pia mater ? What is its function ? 
 
 Describe the structure of a nerve. How long are the longest 
 nerve fibers in the body ? What is the function of a nerve ? 
 
 In comparing the nervous system to a telegrapher and a tele- 
 graph system, what part of the nervous system corresponds to the 
 telegrapher? What is the function of this part of the nervous 
 system ? What part of the nervous system corresponds to the tele- 
 graph wires? What is the function of this part of the nervous 
 system ? 
 
 To what part of the body are the incoming messages carried? 
 What is the effect of these messages ? To what organs are the out- 
 going messages taken ? What is the effect of these messages ? 
 
 Why is a nervous system necessary in the body? 
 
 Why is it possible for a tree to live without a nervous system, 
 when a man cannot do so ? If the cells in the human brain should 
 become cold, would they die ? Do the cells in the feet or ears die 
 if they become cold? If a fish should be frozen in the ice, would 
 the cells of its brain be killed ? Are little one-celled animals killed 
 by cold water? Ask a physician which cells in the body are most 
 affected by such poisons as strychnin, opium, nicotine (the poison in 
 tobacco), and alcohol. 
 
CHAPTER IV 
 
 THE SKELETON 
 
 THE skeleton is the framework on which the body is 
 built. The shape of the body, therefore, is determined prin- 
 cipally by the skeleton. Examine your own body, and you 
 will readily understand that this is true. Feel your head, 
 and under your hair and skin you will find the bones which 
 give the head its form In the fingers and toes are bones 
 which determine whether they shall be long and slender, or 
 short and thick. Down the middle of your back you can 
 feel a row of bones under the skin, and so through all the 
 body you will find bones under the skin and muscles, out- 
 lining the forms of the different parts. 
 
 The Functions of the Skeleton. The first function of the 
 skeleton is to support the body. Without a skeleton, the body 
 would be weak and soft, and the head, arms, legs, and trunk 
 would fall together in a confused mass. But the bones 
 are hard and stiff, and form a strong framework, so that 
 each part of the body stays in its proper place, and the whole 
 body can stand upright. 
 
 The second function of the skeleton is to protect parts of the 
 body that are easily injured. The bones of the head form 
 a strong box to protect the brain ; the spinal column holds 
 the spinal cord safe in the cavity in its center ; and the bones 
 of the chest protect the heart and lungs. 
 
 31 
 
6PINAL COLUMN 
 CLAVICLE- 
 
 TARSAL BONES 
 METATARSAL BONES 
 PHALANGES 
 
 FlG. 16. The skeleton of the human body. 
 32 
 
THE SKELETON 
 
 33 
 
 The third function of the skeleton is to provide a system of 
 levers, by means of which the body elm be moved. Moving the 
 body is the special function of the muscles, and we shall 
 take up this subject in the next chapter. But you can easily 
 understand that without a skeleton such movements as walk- 
 ing or raising the arm would be impossible. 
 
 THE PRINCIPAL BONES OF THE SKELETON 
 
 FIG. 17. The skull. 
 
 There are two hundred and six bones in the human skeleton 
 They are divided naturally into three groups. The first group 
 contains the twenty-eight bones of the head, the second group 
 the fifty-eight bones of the trunk, and the third group the one 
 hundred and twenty bones of the limbs. 
 
 The Skull. The twenty-eight bones of the head taken to- 
 gether compose the skull. Eight of these bones are solidly 
 
34 
 
 HUMAN PHYSIOLOGY 
 
 united to form a box (the cranium) for the protection of the 
 brain. Six little bones are in the ears (Fig. 120), and the 
 other fourteen bones of the skull form 
 the skeleton of the face. All the bones 
 of the face are in pairs except the lower 
 jawbone and the thin bone which forms the 
 partition between the two sides of the nose. 
 The Spinal Column. The spinal column 
 is composed of twenty-four vertebra (sin- 
 gular, vertebra), the sacrum, and the coccyx. 
 It supports the parts of the body above the 
 hips, and protects the spinal cord. When 
 it is broken, standing or walking is im- 
 possible, because the trunk has no support, 
 and because the spinal cord, through which 
 the muscles that keep the body erect are 
 governed, is injured. 
 
 To do its work, the spinal column must 
 have strength enough to carry the weight 
 of the trunk, head, and arms, and must 
 bend easily in all directions, yet not sharply 
 enough at any one point to crush the deli- 
 cate spinal cord within it. If it were com- 
 posed of long bones, either it would be stiff 
 and allow little movement of the upper 
 parts of the body, or it would bend sharply 
 at the joints as the arms do at the elbows 
 and the legs at the knees, and injure the 
 
 no. is. Thr sp inai cord at these P oints - But because the 
 
 column. spinal column is composed of many short 
 
 bones, and has many joints, it allows the body to bend freely 
 
 forward or backward, or from side to side, yielding a little at 
 
THE SKELETON 
 
 35 
 
 each joint, but not enough anywhere to crush the cord. Also, 
 because the spinal column is flexible, bending at so many 
 different points, it rarely happens that it is broken, as would 
 be the case if the trunk were carried on a stiff support. 
 
 FIG. 19. The bones of the trunk. 
 
 The Sternum and Ribs. The sternum, or breast bone, is 
 a flat bone lying in the front of the chest. The ribs are 
 long, slender bones, which curve around the chest. They are 
 twenty-four in number, twelve pairs. All the ribs are joined 
 
36 HUMAN PHYSIOLOGY 
 
 to the vertebrae at the back. The seven upper pairs are 
 joined to the sternum in front, and are called true ribs. 
 The five lower pairs of ribs are called the false ribs. The 
 three upper pairs of false ribs have their front ends attached 
 to the lowest pair of true ribs. The two lowest pairs of false 
 ribs are called floating ribs,' because their front ends are free. 
 The ribs protect the heart, lungs, stomach, liver, and other 
 organs lying in the upper part of the ventral cavity, and form 
 a framework to which the muscles that are used in breathing 
 are attached. 
 
 The Bones of the Shoulder. The clavicle (collar bone) 
 and the scapula (shoulder blade) form the skeleton of the 
 shoulder. The scapula lies in the back of the shoulder. In 
 its outer end is a socket for the upper end of the arm bone. 
 The weight of the arm, and of anything which is lifted by the 
 arm, pulls downward on the scapula. The scapula, therefore, 
 has powerful ligaments and muscles attaching it to the ribs 
 and to the vertebrae, and holding it in place. 
 
 T.he inner end of the clavicle is joined to the sternum, and 
 the outer end is propped against the point of the scapula, 
 thus bracing the shoulder. When the clavicle is broken, as 
 often happens when one falls on the shoulder, the point of 
 the shoulder drops downward and forward. By feeling your 
 own shoulder, you can easily locate the clavicle running 
 out from the sternum to the point of the shoulder, and the 
 scapula, with its bony ridge, in the back of the shoulder. 
 
 The Pelvic Bones. Place your hands on your sides, and 
 you will feel the two large, irregular, wide-spreading pelvic 
 bones. They are firmly joined to the sacrum behind and to 
 each other in front. These three bones with the coccyx form 
 the pelvis, which balances on top of the thigh bones, and gives 
 a firm support for the upper parts of the body. The lower 
 
THE SKELETON 37 
 
 abdominal organs lie within the bowl-shaped pelvis, and are 
 partly supported by it, and many great muscles are attached 
 to the sacrum and to the pelvic bones. 
 
 The Bones of the Limbs. Each limb has in it thirty bones, 
 and the bones of the arms and the legs are very similar (Fig, 
 33). Each has a large bone in the upper part, the humerus 
 in the arm, and \h.e femur in the thigh. Each has two bones 
 in the lower part, the radius and the ulna in the forearm, 
 and the tibia and fibula in the leg below the knee. In both 
 the wrists and the ankles we find a group of small bones, the 
 eight carpal bones in the wrist, and the seven tarsal bones in 
 the ankle. In the hand beyond the carpals are five meta- 
 carpal bones, each bearing a finger, and in the foot beyond 
 the tarsals are five metatarsal bones, each bearing a toe. In 
 the fingers are fourteen phalanges, and in the toes are four- 
 teen phalanges. The arms and legs have the same number of 
 bones in each, and in their general plan differ only in this, 
 the wrist has one more bone than the ankle, and at the elbow 
 there is no bone like the patella (knee-cap), which protects 
 the front of the knee. 
 
 SHAPES AND STRUCTURE OF BONES 
 
 Shapes of Bones. The bones of the human skeleton may 
 be classified as long and short, fiat and cylindrical, and irregu- 
 lar. This gives us a great variety of shapes, but it is usually 
 easy to see some connection between the shape of a bone and 
 its function. 
 
 Long bones give motion to distant parts of the body, and by 
 means of the long bones great rapidity of motion through 
 long distances can be brought about. The bones by which 
 the hands and the feet are moved so quickly and so far are 
 the best example of long bones. 
 
HUMAN PHYSIOLOGY 
 
 Short 
 through 
 
 bones give free movement in various directions 
 short distances, and at the same time give great 
 strength. The bones of the 
 wrists and ankles and the ver 
 tebrae are the best examples of 
 short bones. 
 
 Cylindrical bones are found 
 where supporting some portion 
 of the body is one of the main 
 functions of the bone. The 
 bones of the limbs, of the 
 hands and the feet, and the 
 clavicles are cylindrical bones. 
 Flat bones are usually either 
 protecting bones or bones to 
 which many muscles are at- 
 tached. The sternum and the 
 bones of the cranium are flat, protecting bones. The pelvic 
 bones and the scapulas are 
 bones which are spread out flat 
 to give room for the muscles. 
 Not only are the flat bones made 
 so as to give as much room as 
 possible for the muscles, but the 
 heads of the long bones are ex- 
 panded for the same purpose, 
 and nearly all bones have eleva- 
 tions and processes (Fig. 21) to 
 which muscles can be fastened. 
 This is necessary, for there are over five hundred muscles 
 in the body, most of which are attached to the skeleton. 
 Irregular bones usually have several functions. A good 
 
 FlG. 20. The scapula. This flat bone 
 has many muscles attached to it. The 
 ridge strengthens the bone and its end 
 provides a point against which the 
 clavicle can be propped. 
 
 FlG. 21. Vertebrae, 
 
THE SKELETON 39 
 
 example of a bone of this kind is a vertebra. This has a 
 round portion which supports the weight of the body ; it has 
 a flattened ring of bone inclosing and protecting the spinal 
 cord ; and it has a flat spine behind and processes on the 
 sides, to which the muscles of the back are attached. 
 
 Materials in Bone. A dead and dry bone is composed of 
 a great network of tough fibers and of hard mineral matter 
 that fills in the spaces between the fibers. A bone, there- 
 fore, has in it two kinds of matter, animal matter (the fibers) 
 and mineral matter. About two thirds of the weight of the 
 average bone is mineral matter and one third is animal mat- 
 ter. In childhood there is a smaller proportion of mineral 
 matter in the bones, and in old age the amount of animal 
 matter is very small. By the following experiments you can 
 find out for yourself the proportion of animal and of mineral 
 matter in a bone, and the function of each kind of material : 
 
 Weigh a piece of dry bone. Then burn it in a hot fire. Notice 
 the smell. The animal matter in the bone is 
 burning. When all the animal matter has been 
 burned out, the bone will have a grayish color. 
 When this is the case, take it out of the fire and 
 weigh it again. Of what kind of matter is the 
 bone now composed? What proportion of it 
 was animal, and what proportion mineral matter? 
 Try to bend the bone, and notice how easily it 
 crumbles and breaks. What do you think is the 
 function of the animal matter? 
 
 Dissolve the mineral matter out of the drum- 
 stick of a chicken or turkey by soaking it in 
 weak hydrochloric acid. 1 Then examine the bone, 
 and note that it is the same size and shape as be- 
 fore. Try to bend it and you will find that it is 
 as limber as a piece of rubber. Of what is the F . IG ; 22> . A , 
 
 r , .. , TT1 , P . - , with the mineral mat- 
 
 bone now composed ? What is the function of the ter removed 
 
 mineral matter of the bone ? 
 
 1 Any weak acid, or strong vinegar, may be used in this experiment, 
 
40 HUMAN PHYSIOLOGY 
 
 From these two experiments you will understand that the 
 mineral matter gives to the bones the stiffness and firmness 
 which enables them to support the body, and the animal 
 matter gives the toughness which keeps them from breaking. 
 
 Structure of Bones. The shafts of the long bones and a 
 thin layer on the surface of all the bones are composed of 
 
 FIG. 23. A is a portion of the shaft of a long bone. B is a cross-section of a small 
 portion of the same bone more highly magnified, showing more clearly the canals in 
 the compact bone and the small cavities (lacuna) in which the bone cells lie. 
 
 compact bone. The remainder of the skeleton is composed 
 of spongy bone. The spongy bone is filled with small cavi- 
 ties, like the holes in a sponge. The compact bone when 
 looked at with the unaided eye appears solid, but when 
 examined under the microscope even this hard bone is seen 
 to be full of very small canals. Through these canals the 
 
THE SKELETON 41 
 
 blood vessels reach to every part of the bone, carrying nour- 
 ishment to the bone cells. 
 
 The Cavities in the Long Bones. To provide room for the 
 attachment of all the muscles and to have sufficient strength 
 for the support of the body,, the bones must be large. At 
 the same time it would be objectionable to have very heavy 
 bones, for the muscles would find great difficulty in moving 
 them about. The small cavities in spongy and compact bone 
 assist in decreasing the weight of the skeleton. To lighten 
 
 FlG. 24. Experiment showing that a hollow cylindrical bone is strong. 
 
 it still more, large cavities are hollowed out in the long bones 
 of the limbs. That a hollow cylinder is stronger than the 
 same material in a solid form,' you can prove by the follow- 
 ing experiment : 
 
 Set a sheet of paper on end and lay a book on it. Will it 
 support the book? Fold the paper as tightly as possible, so that it 
 will be in the form of a small, solid bone. Will it now support the 
 book? Now roll the paper into a hollow cylinder and place your 
 book upon it. Will it support a heavier weight than it would before 
 it was rolled into this form ? Does it contain any more material or 
 is it any heavier? 
 
 Nature uses a hollow cylinder not only in the skeleton, 
 but in other structures where she wishes to combine strength 
 
4 2 
 
 HUMAN' PHYSIOLOGY 
 
 and lightness. Stalks of grasses and grains are hollow, and 
 so strong is a wheat stalk that it has a height four hundred 
 times as great as its diameter, and carries the heavy head of 
 grain without breaking, although it is blown about and bent 
 by the wind. Man also uses hollow tubes in the framework 
 of bicycles, and in other places where he wants strength 
 without great weight. 
 
 Bone Marrow. The large cavities of the long bones and 
 the smaller cavities of the spongy bone are filled with bone 
 marrow. The marrow in the larger cavi- 
 ties contains blood vessels, nerves, connec- 
 tive tissue, and fat. The marrow of the 
 spongy bone contains less fat, and in it the 
 red corpuscles of the blood are formed. 
 Because of the large quantity of fat which 
 it contains, the marrow of the larger cavi- 
 ties is yellow in color ; the marrow in the 
 spongy bone, because of the large number 
 of red corpuscles which it contains, usually 
 has a reddish hue. 
 
 The Periosteum. Pick the surface of a 
 fresh bone with the point of a knife, and 
 you can lift a thin covering or membrane. 
 This is the periosteum. It is made of a 
 network of connective tissue fibers, closely 
 woven together over the surface of the 
 bone. Among the fibers of the periosteum 
 section of the humenis. are many of the blood vessels which carry 
 nourishment to the bones, and if the periosteum is destroyed, 
 the bone under it will die}- 
 
 1 A bone grows in thickness by having layers of new bone material laid down 
 on the surface of the bone under the periosteum. 
 
 FIG. 25. Longitudinal 
 
THE SKELETON 43 
 
 Summary. The bones support the body, protect delicate 
 organs, and act as levers by means of which the muscles move 
 the body. There are 206 bones in the human skeleton, 28 
 in the skull, 58 in the skeleton of the trunk, and 120 in the 
 skeleton of the limbs. 
 
 In. respect to their shape, bones are classified as long and 
 short, flat and cylindrical, and irregular. Long bones give 
 rapid motion through long distances. Short bones combine 
 strength and freedom of movement. Cylindrical bones are 
 supporting bones, and flat bones protect delicate organs or 
 have many muscles attached to them. Irregular bones usually 
 have several different functions. 
 
 Bones are one third animal matter, which makes them 
 tough, and two thirds mineral matter, which gives them 
 their stiffness and rigidity. The cavities in the bones help to 
 lighten them and at the same time permit them to retain 
 sufficient strength to support the body. 
 
 Bone marrow contains fat, blood vessels, connective tissue, 
 and nerves. The yellow marrow has in it much fat. The red 
 marrow contains less fat, and in it the red blood corpuscles are 
 formed. The periosteum carries many of the blood vessels 
 that nourish the bone. 
 
 QUESTIONS 
 
 Give three functions of the skeleton. How many bones are in the 
 body? Into how many groups are they divided? How many bones 
 are there in each group ? 
 
 How many bones are in the skull? in the cranium? in the ears? in 
 the face? Name some of the bones of the skull. 
 
 How many and what bones are in the spinal column? Give two 
 qualities that the spinal column must have. Give two advantages 
 that come from having the spinal column composed of many parts. 
 
44 HUMAN PHYSIOLOGY 
 
 Where is the sternum ? How many ribs are there ? What is a 
 true rib ? a false rib ? a floating rib ? Give two uses of the ribs. 
 
 Name the shoulder bones. To what is the scapula attached? 
 What is the function of the clavicle ? What bones compose the 
 pelvis ? Give three functions of the pelvis. Compare the skeletons 
 of the arm and of the leg. 
 
 Give four shapes of bones, with the functions of bones having each 
 of these shapes. Give examples of bones of each shape. 
 
 What two kinds of material in bone ? What proportion of a bone 
 is mineral matter ? animal matter ? What is the function of the 
 mineral matter ? of the animal matter ? At what time of life is there 
 little mineral matter in the bones ? little animal matter ? 
 
 Where in the skeleton is the compact bone found ? spongy bone ? 
 How do compact and spongy bone differ? 
 
 Why is it necessary that the bones should have considerable size ? 
 What would be the objection to having large solid bones ? How 
 have the large bones been lightened without too greatly weakening 
 them? 
 
 Of what is bone marrow composed ? Where is red bone marrow 
 found ? yellow bone marrow ? How does one kind of marrow differ 
 from the other? What is the periosteum? What happens to the 
 bone when the periosteum is destroyed ? 
 
 Of what is the animal matter in a living bone composed (page 8) ? 
 Do the bones of an old person or of a little child bend more easily ? 
 Why? Which breaks more easily? Why? Which heals more 
 easily after it is broken ? Why ? 
 
 Is a hollow iron post as strong as a solid iron post of the same 
 size ? How many times as high as its own diameter is the tallest 
 smokestack or tower that you know ? 
 
 What part of the skeleton is incomplete in a little baby ? 
 
CHAPTER V 
 
 THE SKELETON (Continued) 
 JOINTS 
 
 EACH bone can support the part of the body in which it 
 is located, but to form a skeleton for the support of the body 
 as a whole, the bones must be joined together. The places 
 where the bones come together are the joints. These are 
 divided into two great classes, immovable and movable 
 joints. 
 
 Immovable Joints. Immovable joints are found in portions 
 of the body where movement between the bones is not neces- 
 sary, and where great strength and firmness are required in 
 the skeleton. In the cranium all the bones are solidly joined 
 to protect the brain, and the joints are immovable. The joint 
 between the two pelvic bones, and the joints between the 
 pelvic bones and the sacrum, are other examples of immov- 
 able joints. All the bones of the pelvis are thus firmly united 
 in one solid support for the body. In our own bodies we 
 overlook the immovable joints because there is no movement 
 at these places, but in a skeleton this kind of joint may easily 
 be observed. 
 
 Necessity for Movable Joints. Most of the joints in the 
 skeleton are movable. It is necessary that they should be, 
 for it is only at the movable joints that the body can bend. 
 Without movable joints you could not close your hand ; you 
 
 45 
 
46 HUMAN" PHYSIOLOGY 
 
 could not bring your hand to your mouth; you could not sit, 
 and you could not walk. Without movable joints it would 
 not be possible for one part of the body to be moved without 
 moving the whole body. You will understand, if you think 
 about it, that with the whole skeleton united solidly in one 
 piece, our muscles could not move the body at all. With a 
 skeleton having movable joints, they lift the body about, one 
 part at a time; but without the bending at the joints, the 
 muscles would have no more power of lifting the body than 
 you have of lifting a chair in which you are sitting. 
 
 Kinds of Movable Joints. Movable joints are of three 1 
 principal kinds, ball-and-socket joints, hinge joints, and 
 gliding joints. 
 
 In ball-and-socket joints a ball, or rounded end, of one bone 
 fits into a socket, or cup-like hollow, in the other bone. The 
 shoulder joint and the hip joint (Fig. 27) are good examples 
 of ball-and-socket joints. This kind of joint allows motion 
 freely in any direction, as you can observe by swinging the 
 arm about at the shoulder, or the leg at the hip. 
 
 Hinge joints do not allow motion in all directions, but only 
 in two opposite directions, the same movement that a knife 
 blade has in opening and closing. The elbow and knee joints, 
 the first two joints of the fingers and toes, and the joints of 
 the lower jaw are examples of hinge joints. What kind 
 of a joint is at the base of the metacarpal bone that bears the 
 thumb ? 
 
 In gliding joints the bones move or glide only a little 
 on each other. The joints between the small bones of the 
 ankles and the wrists are good examples of gliding joints. 
 
 1 The joints between the bodies of the vertebrae are intermediate between im- 
 movable and movable joints. In them the bones do not slide on each other, but 
 the thick and elastic cartilages (Fig. 21) permit considerable bending. 
 
THE SKELETON 
 
 47 
 
 CARTILAGE AND LIGAMENTS 
 
 Cartilage. By far the greater portion of the human skele- 
 ton is bone, but a small part of it is composed of cartilage^- and 
 ligaments. Cartilage (Fig. 26) is 
 a smooth white substance always 
 found covering the ends of the 
 bones at the joints. In a movable 
 joint each bone has its own carti- 
 lage, and the surfaces where the 
 two cartilages rub together are 
 kept moist by an oily liquid. The 
 smooth cartilage and the oily fluid 
 keep down friction in the movable 
 joints and cause them to work 
 smoothly and noiselessly. 
 
 In immovable joints, a piece of 
 cartilage grows in between the 
 two bones and firmly unites them. 
 Cartilage is found also in the front 
 portion of each rib (Fig. 19). This 
 makes the ribs more springy and 
 less likely to be broken by pressure 
 or by a blow on the chest. 
 
 Ligaments. Around the joints are tough bands of con- 
 nective tissue called ligaments. In parts of the body like the 
 
 1 When the skeleton is being formed in the body, it is at first composed of 
 cartilage. This changes to bone until only a thin layer of cartilage on the ends 
 of the bones remains. As long as a bone is growing, however, there is some 
 cartilage in it. Thus, in youth, there are in the shaft of a long bone one or more 
 narrow rings of cartilage. This cartilage grows and keeps turning to bone on 
 each side, causing the bone to increase in length. Finally the rings of cartilage 
 turn to bone and there is no more growth in the length of the bone. 
 
 FIG. 26. Cartilage. Cartilage 
 has a connective tissue covering 
 (a) similar to the periosteum on 
 a bone. The cartilage cells (6) 
 build around themselves a whitish, 
 elastic substance (c) which forms 
 the ground material of cartilage. 
 
4 8 
 
 HUMAN PHYSIOLOGY 
 
 knee, elbow, ankle, and wrist, 
 the number of ligaments about 
 the joints is astonishingly great. 
 Their function is to hold the bones 
 of the skeleton together. 
 
 HOW THE SKELETON PROTECTS 
 THE BRAIN 
 
 In all ordinary circumstances 
 the cranium shields the brain 
 FIG. 27. The ligaments of the hip from outside injury, and the 
 J mt - whole skeleton is arranged to 
 
 protect the brain from injury by jarring. This is necessary 
 because the brain is so soft and delicate an organ that not- 
 withstanding the protection given to it by the membranes 
 and fluid about it (page 26), it is shaken about and injured 
 by any violent jarring of the head. Serious results sometimes 
 follow a blow on the head, even when the skull has not been 
 fractured, and any one who falls asleep after such an injury 
 should be wakened from time to time to see that he is not 
 unconscious. 
 
 FIG. 28. Pressing on an arched stick. 
 
 FlG. 29. The arch of the foot. 
 
 If the head were jarred every time the feet strike the 
 ground in walking and running, it would surely be harmful 
 
THE SKELETON 
 
 49 
 
 to the brain. To prevent this jarring, the skeleton has in it 
 three devices that give springiness to- the whole frame. 
 
 The Arch of the Foot. Press on a curved stick or a piece 
 of barrel hoop as shown in Figure 28, and notice how much 
 springiness the arch gives it. The bones of 
 the human foot form an arch on which the 
 weight of the body falls when 
 the body is in a standing position. 
 In walking and running, there- 
 fore, the arch of the foot acts as 
 a spring under the body. 
 
 The Curves of the Spinal 
 Column. Strike the floor with 
 a straight stick held as in Figure 
 30 and your hand will be jarred. 
 But strike the floor with a curved 
 stick held in the same way, and 
 you will find that the curve will 
 give a springiness to the stick 
 that prevents the hand from being 
 jarred. The double curve of the 
 spinal column (Fig. 18) makes it 
 springy, and so protects the head 
 from the jar when the feet strike 
 the ground. You can get an idea 
 of the usefulness of these curves 
 by imagining how much worse 
 your brain would be shaken up 
 when you run and jump if your head were carried on the 
 end of a straight, stiff bone instead of on your spinal column. 1 
 
 1 Jump with the legs held straight and stiff. Then jump with the legs bent 
 at the knees, and notice the difference in the amount of jar the body receives. 
 
 FIG. 30. This 
 straight stick 
 jars the hand. 
 
 FIG. 31. This 
 curved stick 
 springs down 
 and does not 
 jar the hand. 
 
50 HUMAN PHYSIOLOGY 
 
 Cartilages. The cartilages between all the joints, but 
 especially the thick cartilages between the vertebrae (Fig. 21), 
 act like rubber pads in giving elasticity to the skeleton. If 
 you have worn shoes with rubber heels, or have walked on a 
 rubber mat, you will know at once how these cartilages pre- 
 vent jarring of the brain. 
 
 These three devices, along with the half-bent joints of the 
 legs, give springiness to the skeleton and protect the brain. 
 How well this work is done, you may know from the fact 
 
 that boys and girls in their play run 
 about and jump, and sometimes fall 
 so hard that the bones of the body 
 are broken, and yet it is not often 
 that the brain is injured. 
 
 THE SKELETONS OF OTHER VERTE- 
 BRATES 
 
 Similarity of Human and Other 
 Vertebrate Skeletons. In the skele- 
 tons of all vertebrates, a spinal 
 column and skull are found. All of 
 them except the amphibians have 
 ribs. Shoulder and pelvic bones to 
 which the limbs are attached are 
 found in almost all of them. The 
 limbs of vertebrates are built on the 
 same general plan, but they are used 
 
 Skeleton of'an^ang-utan. in so man y different ways that the 
 skeletons of the limbs may seem to 
 
 be very different. Certain bones may be much longer than 
 they are in man, as the phalanges in the wings of a bat. 
 
THE SKELETON 51 
 
 Often bones may be united as are the tibia and the 
 fibula in the frog, and the carpal and metacarpal, and the 
 tarsal and metatarsal bones of many animals. Sometimes 
 we have the wrong idea of a limb until we study it closely. 
 Thus, in the front limb of the horse, the foot corresponds 
 to one finger on our hand, the hoof to a finger nail, and the 
 one metatarsal is very long, so that what seems to be the 
 knee is really the wrist. In birds the tarsal and metatarsal 
 bones are united and elongated and in a chicken the ankle 
 joint is often thought to be the knee. In some ways the 
 limbs of these animals are very different from the limbs 
 of man, but all the principal bones in them correspond to 
 the principal bones in the human arms and legs. 
 
 Differences between the Human and Other Vertebrate 
 Skeletons. Of all the vertebrates, monkeys and apes have 
 skeletons most nearly like the skeleton of man. But although 
 an ape's skeleton has in it every bone that is found in the 
 human skeleton, yet there is no difficulty in distinguishing 
 between the two. 
 
 An ape has less intelligence than a man, and its brain and 
 cranium are much smaller. The jaws of an ape are much 
 longer and heavier than they are in man, the teeth are 
 larger, and the front teeth slant forward. 
 
 The human spinal column has a backward turn at the 
 top that causes the skull to balance on top of the spinal col- 
 umn when the body stands upright. The spinal column of 
 an ape lacks this backward curve, and when an ape stands 
 up its head sticks out forward. The muscles of the neck, 
 shoulders, and back, therefore, have heavy work to keep the 
 head from falling forward when the body stands erect. 
 
 The pelvis and femurs of man are also fitted for an upright 
 carriage of the body. Man is a very tall animal for his size, 
 
FIG. 33. Vertebrate limbs. A is the human leg; B, the human arm; C, the fore 
 leg of a horse ; D, the wing of a bird ; , the foot of a bird ; F, the hind leg of a frog ; 
 G, the wing of a bat; H, the fore leg of a tortoise. 
 
 5 2 
 
THE SKELETON 53' 
 
 and he has only two feet to balance himself on. The human 
 pelvis is, therefore, wide, and the heads of the femurs are 
 turned inward. The feet are thus spread apart, making it 
 easier to keep the balance of the body. Shut your eyes and 
 stand with your feet wide apart. Then shut your eyes and 
 stand with your feet close together, and you will understand 
 the advantage of this arrangement. 
 
 The arms of the ape are proportionately much longer than 
 the arms of man, and the legs are shorter. In man the arms 
 reach about halfway between the hip and the knee. In apes 
 they reach to the knee, and in some species even to the 
 ground. 
 
 In apes all the metacarpal and metatarsal bones are very 
 long except the first one, which is very short. This sets the 
 thumbs and great toes far down on the sides of the hands 
 and feet, and in reality gives the apes neither true hands 
 (with thumbs opposing the fingers) for grasping, nor feet for 
 walking, as we find in man; but long organs halfway between 
 hands and feet, with which the ape holds to large branches 
 as it climbs among the trees. 
 
 HYGIENE OF THE SKELETON 
 
 As the body grows, mineral matter is gradually deposited 
 in the bones and the skeleton becomes harder. During child- 
 hood the bones are flexible and it is easy to bend them and 
 change their shapes ; but after the skeleton has hardened, it 
 is exceedingly difficult to change the shape of the bones. 
 
 It is very important, therefore, that the skeleton be kept 
 in proper position during childhood and youth. The general 
 carriage of the body cannot be well understood until we 
 have studied the muscles, so here we shall point out only 
 
"54 HUMAN PHYSIOLOGY 
 
 a few ways in which different bones of the body may be 
 bent out of their proper shape. 
 
 Allowing a baby to stand up and walk too soon may cause 
 him to become bow-legged, and lifting or carrying heavy loads 
 may have the same effect on older children. Heavy work 
 done by the young is likely to pull the points of the shoulders 
 downward and forward, causing round shoulders. Anything 
 carried habitually on one side may cause the spinal column to 
 be bent over to that side. It has been found that many 
 school children have slight curvature of the spine from 
 always carrying their books on the same arm, and very 
 many people have one shoulder or hip a little higher than 
 the other. Boys sometimes wear belts that are drawn too 
 tight around the waist, instead of resting on the hips. These 
 or any tight clothing around the waist, may bend in the 
 lower ribs. This is very injurious, for it presses on the 
 organs which are packed in the abdominal cavity. 
 
 You should avoid all these unhygienic practices, and others 
 which you will think of for yourselves, such as stooping 
 over your desk, or sitting sideways in your seat with one 
 shoulder higher 1 than the other, while you study or write. 
 You should take especial care to form the habit of carrying 
 the body erect; for if the bones are permitted to harden in a 
 stooping position, it is almost certain that you will go through 
 
 lr To THE TEACHER: Much real damage as well as a great deal of discomfort 
 may be caused by having seats and desks that are too low or too high for the 
 pupils. Writing on desks that are too high will throw one shoulder higher than 
 the other and cause lateral curvature of the spine. Bending over a desk that is 
 too low will give a stooping carriage to the body. Sitting in seats so high that 
 the feet cannot touch the floor causes stooping and very great weariness. 
 Where the school authorities fail to provide proper desks, the teacher should see 
 that the younger children have foot rests and should do everything in his power 
 to have all his pupils properly seated. 
 
THE SKELETON 55 
 
 life with a stooping carriage, your sternum and ribs dropping 
 down and crowding your heart and lungs. If you have any 
 work that compels you to stoop as' you do it, stop once in a 
 while, straighten yourself up, and take several deep breaths ; 
 in addition, make a special point of holding the body erect 
 while not at work. 
 
 Broken Bones. If the two ends of a broken bone are 
 placed together, the bone cells soon cover the surface of the 
 broken ends with a jelly-like, white material. In a few days 
 this begins to harden, and soon the two parts are firmly 
 united. The only thing we can do to help nature in this 
 process is to put the broken ends together, and keep them 
 together until the fracture is healed. Of course a physician 
 must be called to set a broken bone, but the patient needs 
 intelligent care until the physician arrives. If an arm or 
 a leg is broken, stretch it out straight on a pillow. If the 
 person must be moved, tie a pillow about the limb, or wrap 
 a blanket or a coat around it, and then tie umbrellas or canes 
 about it to keep it straight. Often there are sharp points on 
 the broken ends of bones. In lifting the person, take care 
 that the limb is not bent at the fracture, or the sharp ends of 
 the broken bone may cut the muscles, blood vessels, or 
 nerves. 
 
 Dislocations and Sprains. When the ligaments (and some- 
 times the muscles and nerves also) around a joint are broken, 
 and the bones slip out of place, we have a dislocation. A 
 few people have some joints with sockets so shallow that the 
 bones may be dislocated without breaking the ligaments, but 
 such joints are not common. When a bone is dislocated, it 
 must be put back into its place and kept there until the liga- 
 ments grow again about the joint. Usually only a physician 
 can get a dislocated bone back into place without danger to 
 
HUMAN PHYSIOLOGY 
 
 the patient, and he should be called before the parts become 
 swollen. 
 
 When a joint is sprained, some of the ligaments around it 
 are broken and torn loose, but the bones are not dislocated. 
 
 Treatment of Dislocations and Sprains. Until a physician 
 can be called, both dislocated and sprained joints should be 
 bathed in either hot or cold water, or, better still, in hot and 
 cold water alternately. This will help to keep the injured 
 part from swelling and becoming painful. 
 
 A dislocated or sprained joint should not be rested all the 
 time, but should be exercised, even if the movement causes 
 great pain. If the joint is not exercised, it will become much 
 swollen with liquids from the blood, and will be very painful. 
 Exercise helps to keep up a good circulation of the blood 
 through the part, and this carries away the broken tissue and 
 dead cells, and helps in every way to hasten the healing of 
 the injury. But after a dislocation, great care must be used 
 that, in exercising, the injured parts are not again dislocated. 
 A dislocated joint should be well bandaged to keep the bones 
 in place, and then exercised in such a way that there will be 
 no danger of dislocating it again. 
 
 Tobacco and the Skeleton. The bones are built up and 
 grow through the manufacture of bone materials by the cells 
 (page 8). Tobacco seems to injure the cells which do this 
 work, for young persons who use tobacco are usually stunted 
 in their growth. We know that tobacco injures the heart and 
 the digestive organs, and it may be that it injures the bone cells 
 by preventing them from getting a good supply of food and 
 oxygen. Possibly the tobacco itself injures the bone cells. 
 However the harm is done, we are sure that it is done, for 
 the bones of young tobacco users do not grow as they should. 
 
 Summary. There are two great classes of joints, im- 
 
THE SKELETON 57 
 
 movable and movable. Immovable joints are found in the 
 skeleton where motion is not nepessary, but firmness and 
 strength are required. Movable joints are necessary that the 
 different body parts may have motion. The three principal 
 kinds of movable joints are ball-and-socket joints, hinge joints, 
 and gliding joints. 
 
 The ends of the bones are covered with a smooth, white 
 substance called cartilage. In the movable joints this is 
 kept moist with an oil-like liquid, which causes the joints to 
 work smoothly. At the joints the bones are tied together 
 with strong connective tissue ligaments. 
 
 The arch of the foot, the curves of the spinal column, and 
 the cartilages in the skeleton and the half -bent knee joints 
 keep the brain from being jarred as we walk and run. 
 
 The human skeleton resembles other vertebrate skeletons 
 in having a spinal column, skull, ribs, shoulder and pelvic 
 bones, and two pairs of limbs. The bones in other vertebrate 
 limbs often differ markedly from the bones in the human 
 limbs, but in all these limbs the same general plan of the 
 skeleton is present. Man's skeleton differs from an ape's in 
 the skull, spinal column, pelvis, and femurs, the length of 
 the arms, and in the hands and feet. 
 
 During childhood and youth the bones are easily bent, and 
 it is very important that they be kept in proper position. A 
 broken limb should not be allowed to bend at the fracture. 
 In a dislocation or a sprain the ligaments about the joint are 
 broken. A joint that has been injured in this way should be 
 treated with hot or cold water and carefully exercised. 
 
 Tobacco keeps the bones of the skeleton from reaching 
 their full growth. 
 
58 HUMAN PHYSIOLOGY 
 
 QUESTIONS 
 
 What is a joint ? What are the two great classes of joints ? Where 
 are immovable joints found? Give examples of immovable joints. 
 
 Why are movable joints necessary? Name three kinds of mov- 
 able joints. Explain what movement each kind of movable joint 
 allows. Give examples of each kind. 
 
 Where is cartilage found ? What is its use in the movable joints ? 
 What is a ligament and what is its function? 
 
 Why is it important that the skeleton should have springiness ? 
 Name three devices for giving springiness to the skeleton. 
 
 Mention some ways in which the human skeleton resembles other 
 vertebrate skeletons. Mention five ways in which the human skele- 
 ton differs from the skeleton of an ape. 
 
 Why is it important that the skeleton be kept in proper shape dur- 
 ing early life? Mention four ways in which parts of the skeleton 
 may be deformed. 
 
 How would you care for a person with a fractured limb ? What is 
 a dislocation ? a sprain ? What is the best treatment for a disloca- 
 tion or a sprain? 
 
 What effect has tobacco on the skeleton? 
 
 Carefully measure your height in the morning. Then measure it 
 again at night after you have been moving about all day. Are you 
 taller in the morning or in the evening? Why? 
 
 Do you know any animals that have the skeleton on the outside of 
 the body ? What great advantage is this to these animals ? What 
 do crabs, lobsters, crayfish, and many insects find it necessary to do 
 when the body increases in size? An earthworm has no skeleton. 
 How does it cause its body to move in crawling? 
 
CHAPTER VI 
 
 THE MUSCLES 
 
 THE skeleton supports the body. The muscles move it. 
 When we think of a living animal, we think of it as having 
 the power to move. Yet without muscles we and all the 
 animals we see about us would lie quiet, like dead matter. 
 It is by the power of the muscles that the giant whale is 
 driven through the sea, and the wild bird is carried through 
 the air. Muscles cause the wings of the mosquito to vibrate 
 faster than the eye can see ; they move the creeping snail. 
 The muscles carry our feet along, they lift our arms, they 
 keep our hearts beating night and day. The power by which 
 a muscle causes movement lies within its cells. 1 
 
 The Muscles. The skeleton is the framework of the body, 
 and the muscles are stretched on the framework, sliding 
 smoothly and noiselessly over one another in their move- 
 ments. They form the chief part of the flesh which rounds 
 
 1 The tissues that we have studied up to this time are the supporting tissues of 
 the body, and the pupil should get clearly in mind the difference between them 
 and the other tissues. The function of bone, cartilage, and connective tissue is 
 to support the body. Since this work is too heavy for soft cells, the cells of sup- 
 porting tissues become builders and construct a great framework to support the 
 body. The bone cells build bone fibers and hard mineral matter. The con- 
 nective tissue cells build tough connective tissue fibers, and the cartilage cells 
 build the groundwork of cartilage. Supporting tissues are composed of cells and 
 materials which the cells have built. Other tissues are composed entirely of cells. 
 Muscle tissue is composed of muscle cells, the largest and most active cells in 
 the body. 
 
 59 
 
FIG. 34. The outer muscles of the body. 
 60 
 
THE MUSCLES 6 1 
 
 out the body. They number more than five hundred, and 
 more than two fifths of the entire body weight is muscle. 
 The lean meat of animals is muscle, and by examining the 
 body of an animal in a butcher shop, you can see that a 
 great portion of the entire body is composed of muscles. 
 
 The Functions of Muscles. The first and chief function of 
 the muscles is to move the body. The muscles cause the move- 
 ments when we walk or run, when we turn the head or eyes, 
 when we swallow, when we breathe, or when the heart beats. 
 The body cannot move in any way except by means of the 
 muscles. 
 
 The second function of the muscles is to help the bones in- 
 close the body cavities^ and thus protect the delicate internal 
 organs. 
 
 The third function of the muscles is to assist the ligaments 
 in binding the skeleton together at the joints. Nearly every 
 muscle in the body stretches across a joint and is attached 
 on each side of it, and the strong muscles are a great aid in 
 holding the skeleton together. 
 
 How the Muscles move the Body. Muscle cells 1 are so 
 long that they are often spoken of as muscle fibers. They 
 have the power of contracting, or of drawing up and becoming 
 shorter and thicker, as a worm does in crawling. When the 
 
 1 The cells of voluntary and involuntary muscles are very different in appear- 
 ance. Involuntary muscle cells (Fig. 5) are spindle-shaped, and are several 
 times as long as the average body cell. Voluntary muscle cells (Fig. 35) are 
 slender fibers often two and a half inches long, which is many hundreds of times 
 longer than an ordinary cell (see footnote on page 4). An involuntary muscle 
 cell, like an ordinary cell, has only one nucleus. A voluntary muscle cell has 
 thousands of nuclei. The reason for this is that the nucleus is the part of the 
 protoplasm that enables the cell to take in and use food, and one nucleus would 
 not be enough for a cell containing the great amount of protoplasm found in a 
 voluntary muscle cell. 
 
62 
 
 HUMAN PHYSIOLOGY 
 
 PERIMYSIUM 
 
 BLOOD VESSEL 
 
 cells in a muscle contract, the whole muscle is shortened. 
 This causes a bending at the joint over which the muscle 
 passes, and a movement of some part of the body, since 
 the muscle pulls on the bones to which it is attached. From 
 Figure 39 you can understand how, when the biceps muscle 
 contracts, the arm is bent at the elbow and the hand raised. 
 
 Voluntary and Involuntary Muscles. Muscles are divided 
 into two great classes, voluntary and involuntary muscles. 
 Voluntary muscles are under the control of the will. They are 
 governed by the brain, and we can contract them when we 
 
 wish. Try to raise your hand 
 and you can do so, because it 
 is moved by voluntary muscles. 
 Nearly all the voluntary mus- 
 cles are attached to the skele- 
 ton. 
 
 Involuntary muscles are not 
 tinder the control of the will. 
 They are governed by the sympa- 
 thetic nervous system, and over 
 them the will has no control. If 
 food were started down your 
 throat, you would be compelled 
 to swallow it even though you 
 knew it contained poison, for the 
 muscles of the throat are invol- 
 untary muscles. The involun- 
 tary muscles are found chiefly in 
 the blood vessels, walls of the 
 heart, digestive organs, and in 
 other internal parts of the 
 body. 
 
 FIG. 35. A is a portion of a muscle 
 showing the connective tissue cover- 
 ing (perimysium) and the connec- 
 tive tissue partitions which divide 
 the muscles into bundles of muscle 
 cells (fasciculi). In B a part of a 
 bundle of cells is shown more highly 
 magnified. The length of the mus- 
 cle cells is so great that only a small 
 portion of an}' one cell can be shown. 
 
THE MUSCLES 
 
 The Connective Tissue Skeleton of Muscles. The muscles 
 are held together by connective tissue, and the arrangement of 
 this tissue in a voluntary muscle is very 
 similar to its arrangement in a nerve. 
 A muscle has a connective tissue 
 sheath, which covers it like a thin 
 skin (Fig. 35). Connective tissue 
 partitions l run in from the sheath all 
 through the muscle, dividing the mus- 
 cle cells into groups and tying them 
 up into bundles. Fine fibers of con- 
 nective tissue are woven in among the 
 individual muscle cells, so that the 
 muscle has around it, and running all 
 through it, a framework of connective 
 tissue. 2 The connective tissue passes 
 out at the ends of a muscle and, be- 
 coming entangled and interwoven with 
 the fibers of the periosteum, attaches 
 the muscle to the skeleton (Fig. 36). 
 
 Tendons. The connective tissue m ay 
 pass directly from the muscle into the 
 periosteum of the bone. Often, how- 
 ever, the connective tissue from a mus- 
 cle unites and forms a tough white 
 
 1 In a piece of meat cut "across the grain" (i.e. 
 across the muscle cells) the connective tissue parti- 
 tions in the muscle may easily be seen. 
 
 2 Not only the muscles, but the whole body has 
 a complete framework of connective tissue. If all 
 materials of the body except the connective tissue 
 were removed, there would still remain the form 
 of the whole with all the organs in place. 
 
 FIG. 36. Diagram show- 
 ing how the connective tis- 
 sue passes through a muscle 
 from bone to bone. The 
 muscle cells are shown 
 many times larger than they 
 would actually appear. 
 
6 4 
 
 HUMAN PHYSIOLOGY 
 
 cord called a tendon. The tendon passes to a bone some- 
 times to a bone at a considerable distance from the muscle 
 and attaches itself to the bone by spread- 
 ing out on its surface and sending its 
 fibers in among the fibers of the perios- 
 teum. 
 
 Uses of Tendons. Certain parts of the 
 body (the hands, for example) need to 
 have great strength and to be capable of 
 making a variety of movements, without 
 at the same time becoming so covered 
 with muscles that they will be large and 
 heavy. In such parts of the body, the 
 muscles are placed at a distance and 
 joined to the bones by tendons. There 
 are nearly thirty muscles for moving the 
 fingers of each hand. If all these mus- 
 cles were on the hand, it would not be 
 very beautiful, and would be too clumsy 
 to do any fine work. The muscles that 
 move the fingers are, therefore, placed 
 on the forearm, and only slender tendons 
 run down to the hand. Open and close 
 your hand, and you can see and feel the 
 muscles working in your forearm, and in 
 the wrist and back of the hand you can 
 see the movements of the tendons which 
 close and open the fingers. 
 
 Tendons held in Place by Ligaments. 
 In Figure 37 you can see that the tendons 
 pass under strong ligaments which surround the wrist. In 
 many other parts of the body there are ligaments forming 
 
 FIG. 37. The muscles 
 of the forearm and the 
 tendons and ligaments of 
 the hand and wrist. 
 
THE MUSCLES 65 
 
 bands and loops, which hold the tendons down close to the 
 bones. You can learn the necessity^ for these ligaments by 
 an experiment, and the same experiment will teach you 
 something about tendons. 
 
 Tie a piece of string about the tip of the first or second finger. 
 Run the string back along the front of the finger, across the palm, 
 and up the wrist to the forearm. This string is to represent a tendon. 
 Now get one of your schoolmates to tie strings around your finger, 
 hand, and wrist, as you see in Figure 38. These strings represent the 
 ligaments which hold the tendons in place. From up on the fore- 
 arm pull on the cord which represents the tendon. What effect has 
 it on the finger and hand? Cut the cords which represent the 
 ligaments, and pull on the cord representing the tendon as before. 
 Does the cord follow the curves of the fingers and hand, and lie 
 down flat along the bones ? What difficulty would we have in the 
 hand if the tendons were not tied down to the bones ? Now turn 
 the string about and run it down the back of the finger and hand, 
 and note how a tendon pulling on the back of the finger will open it. 
 
 From this experiment you will understand the use of the 
 ligaments in the hand and wrist; you will also realize that 
 without the ligaments around the 
 ankles, the tendons would rise and 
 run straight from the toes to the 
 muscles below the knees ; and that 
 all through the body it is very 
 necessary for the tendons to be tied 
 down close to the skeleton. 
 
 Constant Contraction of Muscles. 
 Lay the back of your hand on the 
 desk, stiffen your arm at the elbow, 
 and bear down on the desk. Now 
 feel the muscle on the back of your FlG ' 38 ' ^f in ? how a ten " 
 
 don bends a nnger. 
 
 upper arm. It is hard and con- 
 tracted. It is keeping your arm from bending by pulling on 
 
66 
 
 HUMAN PHYSIOLOGY 
 
 the point of the ulna at the elbow. Now stand on one leg 
 with the knee of that leg slightly bent, and feel the muscles 
 both above and below the knee. They are tightly contracted 
 because they are holding the knee and ankle joints from 
 giving way under the weight of the body. 
 
 You know that if a man goes to sleep 
 when sitting up> his head falls forward. 
 The muscles which support the head must 
 keep a constant contraction to hold it erect, 
 and when the man goes to sleep these 
 muscles relax. A dead body will not stand 
 up, but will give way at the joints. The 
 living body can stand up because the mus- 
 cles keep the body 
 from bending at 
 the ankles, knees, 
 hips, and in the 
 back. Not only 
 when the body 
 moves, but when 
 any part of it is 
 held erect or ex- 
 tended, the mus- 
 cles must be con- 
 tracted to hold it 
 
 in position. Try holding the arm extended for five minutes, 
 or standing perfectly still for some time, and you will soon 
 find that some of your muscles are doing heavy work, 
 although there is no movement of the body. 
 
 Antagonistic Muscles. Many of the muscles of the body 
 are in pairs, each muscle of the pair working against the 
 other. Muscles which oppose each other in this way are 
 
 FIG. 39- 
 
 The antagonistic action of the biceps and 
 triceps muscles. 
 
THE MUSCLES 6? 
 
 called antagonistic muscles. An excellent example of a pair 
 of antagonistic muscles is found in the upper arm. On the 
 front is the biceps, which lifts up the forearm. On the back 
 of the arm is the triceps, which straightens out the forearm. 
 In the leg, both above and below the knee, other antagonistic 
 muscles will be found, and as you study the muscles of the 
 body, you will note that nearly all of them are arranged 
 to work in .opposition to other muscles. This is necessary, 
 for a muscle cannot push, and if a part of the body is to 
 be moved back and forth, it must have a muscle to pull it 
 each way. 
 
 Accuracy of Motion given by Antagonistic Muscles. The 
 antagonistic action of muscles is very important in giving us 
 control of our movements. Suppose you wish to extend the 
 forearm to pick up something. You do this by contracting 
 the triceps. If there were no biceps, the forearm would be 
 thrown out with a jerk, and would probably go beyond the 
 object for which you were reaching. But as the muscles are 
 arranged, the biceps exerts a steady, even pull against the 
 triceps, and when the hand has been extended far enough, 
 the biceps gives a pull strong enough to balance the action 
 of the triceps, bringing the hand to a stop at just the right 
 place to grasp the object. The brakes on a street car or on 
 a railroad train make it possible to stop at the desired place. 
 In the same way, the antagonistic action of the muscles en- 
 ables us to check the movements of the body and keep them 
 from going too far. 
 
 The Nervous Control of the Muscles. The way in which 
 the nervous system controls all the muscles and makes them 
 move the body about, seems almost as wonderful as a story 
 from the Arabian Nights. You look at a book and wish to 
 read in it ; your hand reaches out and grasps the book, opens 
 
68 HUMAN PHYSIOLOGY 
 
 it at the place where you wish to read, and holds it up before 
 your eyes. You wish to go out of the room ; your body 
 rises, your feet carry you along, and out of the room you go. 
 You wish to throw a ball to one of your playmates; the 
 muscles of your legs and back, the muscles which draw back 
 the shoulder, arm, and hand, those which draw these parts 
 forward again, and the muscles which open the hand to re- 
 lease the ball, are all brought into action. Each one of this 
 great number of muscles must contract at exactly the right 
 time, with exactly the right force, and must not remain con- 
 tracted a moment too long, or the ball will go wide of the 
 mark, and you will make a poor throw. 
 
 All such movements are accomplished, not by each muscle 
 working independently, but only through the nervous system, 
 which controls them all. From the brain or spinal cord a nerve 
 goes to every voluntary muscle in the body, and a branch of 
 a nerve fiber goes to each muscle cell (Fig. 102). When 
 you wish to make a certain movement, the commands pass 
 through the nerves to the proper muscles, the muscle cells 
 contract, and the movement is made. 
 
 The voluntary muscle cells are controlled by the central 
 nervous system. Many commands are sent to them without 
 our thinking about it; many movements have been made by us 
 so often that the cord and brain send the right commands 
 without thought. But all of the voluntary muscles 1 are under 
 the control of the will, and when we desire to do so, we can 
 send a message from the brain to any one of these muscles 
 and make it contract. 
 
 1 The muscles that are used in breathing are in a sense intermediate between 
 the voluntary and involuntary muscles. We can control them for a short time ; 
 but if the breath is held, they soon act in spite of the will. Try holding your 
 breath and you will find that it is possible to do so for only a short time. 
 
THE MUSCLES 
 
 69 
 
 THE CARRIAGE OF THE BODY 
 
 It would be interesting and profitable l to locate a number 
 of the more prominent muscles of the body and to study their 
 action, but we have time 
 to take up only the mus- 
 cles that support the spinal 
 column. From your study 
 of the skeleton you already 
 understand that the entire 
 upper part of the body 
 stands up on the spinal 
 column as on a stem (Fig. 
 19), and that if the spinal 
 column droops, the head 
 and the whole framework 
 of the chest must stoop 
 forward. It is therefore 
 not necessary to explain 
 to you why these muscles 
 are so important from the 
 hygienic standpoint. 
 
 The Long Muscles of the 
 Back. Along the dorsal 
 side of the spinal column 
 are long muscles for supporting the spine and for keeping 
 the skull from falling forward. The muscles of the back are 
 heaviest in the lumbar region (the " small of the back"), 
 
 1 To THE TEACHER : If time will permit, some exceedingly valuable work may 
 be done by having the pupils learn the origin, insertion, and action of some of 
 the muscles shown in Figure 34. The most interesting and profitable part of the 
 work will be the location of these muscles on the body 
 
 FIG. 40. The muscles of the head. 
 
HUMAN PHYSIOLOGY 
 
 where the two large erectors of the 
 spine (erector spinae) may easily be 
 felt on either side of the spinous 
 processes (Fig. 2 1 ) of the vertebrae. 
 When the long muscles of the 
 back contract they straighten the 
 upper part of the spinal column, 
 as the tendons on the backs of 
 the fingers open the hand. When 
 the muscles of the back are weak 
 they allow the head and the upper 
 part of the spine to droop forward, 
 spoiling the appearance and allow- 
 ing the framework of the chest to 
 drop down and crowd the lungs 
 and heart. 
 
 The Abdominal Muscles. The 
 abdominal muscles are long, thin, 
 flat muscles lying in the abdominal 
 walls. These muscles connect the 
 ribs and sternum with the rim of 
 the pelvis and prevent the uppei 
 part of the trunk from being 
 drawn over backward by the long 
 muscles of the back. The abdom- 
 inal muscles also hold the internal 
 organs in place, and by forcing the 
 
 internal organs back against the dorsal wall of the abdominal 
 
 cavity, support the spinal column in front in the lumbar 
 
 region. 
 
 The Psoas Muscles. The heavy psoas muscles are attached 
 
 along the spinal column hi the lumbar region. These muscles 
 
 FIG. 41. The muscles that sup- 
 port the spinal column. It is these 
 muscles, and not the muscles of the 
 shoulders, that hold the body erect- 
 
THE MUSCLES 71 
 
 have two functions. They lift the thigh, or if the leg is held so 
 that it cannot be raised, they bend the body forward at the hips. 
 They also brace the spinal column on the front of the lumbar 
 curve, preventing too great a forward curvature at this point. 
 . How to acquire and kee0 an Erect Carriage. In bringing 
 the body to an erect position, the great thing is to straighten 
 out the curves of the spi- 
 nal column. Straighten 
 the upper curve, and the 
 head and chest will be 
 lifted. Straighten the 
 lower curve, and the ab- 
 domen will be drawn in. 
 Teach the muscles on 
 both sides of the spinal 
 column to keep the 
 proper contraction, and 
 
 the body will Stand erect. FIG. 42. A diagram of a cross-section through 
 TTi^ PJiftipQt wav nf train the lumbar region of the body. The erectors of 
 
 Ihe easiest way oi tram- the spine (erector gpinaj) and the psoas musdcs 
 
 ing the muscles to do this acting against each other keep the spinal column 
 
 work properly is to stand erect> 
 
 and walk as though you were hung by the top of the head, 
 a little back of the center. This will cause the spinal column 
 to be straightened out, pull in the abdomen, and bring up the 
 head until it balances on top of the spinal column. Stand in 
 this position, and note that your head is back and your chin 
 is close to your neck, your ribs and sternum are lifted off the 
 heart and lungs, and the muscles are tightened across the 
 abdomen, forcing the abdominal organs back and up. " Stand 
 tall" thrusting up the top of the head as high as possible, and 
 drawing the chin and abdomen in, is the best rule for position 
 in standing and walking. 
 
 ERECTOR SPIN/C 
 
72 HUMAN PHYSIOLOGY 
 
 Mistakes made in trying to stand Erect. The most com- 
 mon of all mistakes made in trying to acquire a good carriage 
 is to try to bring the head and neck to an erect position by 
 forcing back the shoulders. The true remedy is to straighten 
 out the spinal column on which the head rests. 
 
 Another common mistake made in trying to stand erect 
 is to throw the head and chest up and allow the abdomen to 
 be thrust forward. The trouble is that although the muscles 
 along the back are contracted, bringing up the upper part of 
 the spine, yet the psoas and abdominal muscles are allowed 
 to relax, and the spinal column bends inward in the lumbar 
 region. 
 
 A third mistake is to lift the shoulders and throw back- 
 ward the entire upper part of the body when trying to bring 
 the shoulders back. The shoulders should be drawn back- 
 ward by pulling the scapulas flat down against the back, and 
 this can be done without moving any other part of the 
 body. 
 
 Importance of acquiring a Correct Carriage in Youth. If 
 the body is not held erect in youth the bones will harden in a 
 stooping position, the cartilages between the vertebrae will 
 become wedge-shaped, and the muscles will develop in length 
 to fit a stooped skeleton instead of a straight one. Youth 
 is also the best time to build up and strengthen weak mus- 
 cles, and to teach all the muscles to keep a proper amount of 
 contraction. 
 
 The easiest way to acquire an upright carriage is to form 
 the habit of sitting, standing, and walking erect. " Stand 
 tall," and the muscles will fall into the habit of keeping the 
 spinal column upright. It is possible, however, by suitable 
 exercise, to develop and strengthen weak muscles, and if you 
 are inclined to stoop you should exercise especially the mus 
 
THE MUSCLES 73 
 
 cles that support the spine. A teacher who understands the 
 science of posture is a great aid in improving the carriage of 
 the body, for unless exercises are properly carried out they 
 may make worse the defects they are intended to remove. 
 
 The Body balanced over the Feet in Standing and Walking. 
 In the erect position the body must be balanced over the feet, 
 and if one part of the body is too far forward or backward, 
 some other part must be thrust out in the opposite direction to 
 balance it. If the head droops forward, or if the shoulders 
 are carried too far forward, so that the weight of the arms 
 pulls forward instead of straight downward at the sides, the 
 spinal column between the shoulders sinks backward in a 
 balancing curve. If any part of the body is out of position, 
 it will force other parts out of position also ; so for good pos- 
 ture each part of the body from head to feet must be in 
 place. Improper shoes and defective feet are frequent causes 
 of bad posture. The feet should point straight forward in 
 walking, and if the heels pound, the whole body should be 
 swayed forward at the ankles so that the chest will be over 
 the toes. 
 
 HYGIENE OF MUSCLES 
 
 All the cells of the body live together, and it is not possible 
 to have some of them in bad condition and the remainder of 
 them in good health. Whatever keeps the whole body in 
 health, therefore, benefits the muscles. Among these things 
 are plenty of good food, fresh air, and sleep. Other things 
 that are necessary, not only for the health of the muscles but 
 for the health of the whole body, are exercise and rest. 
 
 Importance of Exercise. Exercise benefits the body in 
 many ways. It quickens the breathing and starts the heart 
 to beating faster, and it stirs up the different organs of the 
 
74 HUMAN PHYSIOLOGY 
 
 body and causes more blood to flow through them. Without 
 exercise the muscles become weak and soft, and it is also true 
 that if the muscles are not exercised the whole body, espe- 
 cially the digestive organs, will get out of order. A whole 
 book could be written on this subject, but any one who 
 wishes to take healthful exercise knows how to do so, and 
 we will merely call your attention to the following important 
 facts : 
 
 The muscles should be exercised every day. Almost every 
 one who is lazy and neglects to do this suffers, for, generally 
 speaking, without exercise the body cannot keep in health. 
 Exercise should be stopped before one becomes too tired, for too 
 much exercise is worse than not enough. Whenever possible, 
 exercise should be taken outdoors. Outdoor games furnish en- 
 joyment, fresh air, and exercise all at the same time and are 
 the best of all forms of exercise. 
 
 Effect of Tobacco and Alcohol on the Muscles. Tobacco 
 weakens the muscles. Athletes who wish to have their 
 muscles in such condition that they will contract with the 
 greatest possible power are not allowed to use it. Alcohol 
 also weakens the muscles, especially in any long-continued 
 effort. In mountain climbing in the high Alps it was found 
 by experiment that a moderate amount of alcohol decreased 
 the power for work 20 per cent. 
 
 Summary. The muscles number more than five hundred 
 and make up more than two fifths of the body weight. They 
 move the body, help inclose the body cavities, and assist in 
 binding the skeleton together. The two classes of muscles 
 are the voluntary and involuntary. 
 
 A muscle has a framework of connective tissue by which 
 it is attached to the skeleton. In some cases the connective 
 tissue forms a tendon and runs to a bone at a distance from 
 
THE MUSCLES 75 
 
 v> 
 
 the muscle. The tendons are held down close to the skele- 
 ton by ligaments. The muscles o the body keep a certain 
 amount of contraction, as is shown by the fact that a dead 
 body will not stand up. Most of the muscles are arranged 
 in pairs, one muscle of the pair working in opposition to the 
 other. The nervous system controls the muscles and causes 
 them to work together in a wonderful manner. 
 
 In the carriage of the body, the muscles of the spinal 
 column are very important. The erectors of the spine, the 
 abdominal muscles, and the psoas muscles support the spinal 
 column and should be taught to keep a proper amount of 
 contraction. The best way to do this is to form the habit 
 of standing and walking erect. 
 
 A common mistake in trying to acquire an erect carriage 
 is to pull the shoulders back instead of straightening up the 
 spinal column. Another mistake is to allow the spinal column 
 to bend forward too much in the lumbar region. A third 
 mistake is to attempt to pull the shoulders back by raising 
 them and throwing back the entire upper part of the body. 
 In youth is the time to acquire a good carriage. 
 
 The body is balanced over the feet when in the upright 
 position, and one part out of position throws other parts out 
 of position also. Incorrect shoes and bad feet are common 
 causes of bad posture. 
 
 Exercise is necessary, not only for the health of the muscles, 
 but for the health of the other organs of the body as well. 
 
 QUESTIONS 
 
 How many muscles are in the body? How much of the body 
 weight is muscle? 
 
 Give three functions of the muscles. What causes a muscle to 
 contract? Explain how the biceps muscle bends the arm. Name 
 
76 HUMAN PHYSIOLOGY 
 
 the two classes of muscles. What is the difference between them? 
 To what are the voluntary muscles attached ? Where are the in- 
 voluntary muscles found? 
 
 ^Describe the connective tissue skeleton of a muscle. How is a 
 muscle attached to a boneP^Of what is a tendon composed? What 
 advantage is there in having tendons in the body?/' How are the 
 tendons kept close to the bones? 
 
 // Why does a man's head remain erect when he is awake and fall 
 forward when he goes to sleep ?/ 2AVhat are antagonistic muscles ? 
 Give an example. /^/Why are the muscles of the body arranged in 
 pairs? What effect have the antagonistic muscles on our move- 
 
 What has the nervous system to do with our movements? By 
 what part of the nervous system are the voluntary muscles con- 
 trolled ? y /Where are some of the muscles that are used in walk- 
 ing? /iWhen these muscles are used, do you think of the movements 
 causea by them? $ 
 
 f ^What part of the skeleton supports the head and trunk? ^hat 
 muscles keep the upper part of the spinal column erect? What fol- 
 lows if these muscles are weak or relaxed too much?-?3Give two 
 functions of the abdominal muscles ; two functions of the psoas 
 muscles. If these muscles are weak or relaxed, what effect has it on 
 the curves of the spinal column? What is the best method of train- 
 ing the muscles to hold the spinal column erect? Give the rule for 
 position in standing and walking. What mistakes are often made 
 in trying to stand erect? Why is it important to acquire a correct 
 carriage in youth ?2fWhy is it impossible to bend over when stand- 
 ing close against a wall?^What effect on the spinal column has 
 drooping the head? How should the feet be held in walking? 
 
 Name four things necessary to the health of the body. Mention 
 some of the effects of exercise on the body. What effect has lack 
 of exercise on the muscles? on the other organs of the body? Give 
 three important facts relating to exercise and health. What effect 
 have tobacco and alcohol on the muscles ? 
 
THE MUSCLES 77 
 
 REVIEW QUESTIONS 
 
 Chapter I. Of what are living things composed ? How do cells 
 originate? Why is it necessary that there should be a division of 
 labor among the cells of the body? Name some of the different 
 kinds of cells in the body and give their functions. 
 
 Define : protoplasm ; nucleus ; tissue ; organ ; anatomy ; physi- 
 ology; hygiene. 
 
 Chapter II. Name and locate the two body cavities. What is in 
 each? Where does man belong in the animal kingdom? Mention 
 some ways in which the bodies of all vertebrates are alike. How 
 does the human' body differ from the bodies of all other animals? 
 
 Chapter III. What is the function of the nervous system? Ex- 
 plain why some such system is necessary in the body. Name the 
 divisions of the brain. Describe a nerve. What is the function of 
 the nerves? 
 
 Define and give the function of the following: central nervous 
 system ; sympathetic ; dura mater ; arachnoid ; pia mater ; cere- 
 bro-spinal fluid. 
 
 Chapter IV. Give three functions of the skeleton. What part of 
 the skeleton forms a central axis to which all the other parts are 
 joined ? Name bones of different shapes, with their functions. What 
 materials are in bones, and what is the function of each kind of 
 material ? What advantage is there in the hollow structure of bones ? 
 
 Define : compact ; spongy ; marrow ; periosteum. 
 
 Chapter V. Name two classes of joints ; three kinds of movable 
 joints. Describe cartilage and tell where it is found. How is 
 friction kept down in the joints? What are ligaments? How is 
 the skeleton made springy? How does the human skeleton resemble 
 other vertebrate skeletons? How does it differ from the skeleton of 
 an ape? Mention some points in connection with the hygiene of 
 the human skeleton. How would you treat a broken bone? a 
 dislocation ? a sprain ? 
 
 Chapter VI. Give the functions of the muscles. How are muscles 
 attached to bones ? Explain how the muscles move the body. What 
 muscles are important in the carriage of the body ? How may an 
 erect carriage be acquired? What mistakes are made in trying to 
 stand erect? Why should the body be carried erect in youth? 
 Speak of the importance of exercising the muscles. What effect 
 does any part of the body that is out of position have on other 
 parts of the body ? 
 
CHAPTER VII 
 
 FOODS AND ENERGY 
 
 TO-DAY we take in food. To-morrow the food is gone and 
 we are hungry still. We eat again and the next day find our 
 need for food as great as it was at first. We spend our lives 
 working for food and eating food, and yet only a few short 
 hours behind, hunger is always following on our trail. 
 
 Why can we not forget all about food? What makes us 
 want to eat? Why do we spend our money for something 
 that we cannot keep ? Why not give up eating and have time 
 to rest and enjoy life? Because without food the life of the 
 cells and of the body comes to an end. 
 
 Why the Cells need Food. The living protoplasm in the 
 cells is continually wasting away. In certain parts of the 
 body the cells are constantly dying l and being replaced by 
 new cells. Other new cells are needed when the body grows 
 in size (page 10). New protoplasm, therefore, is constantly 
 being built up for the repair and growth of the cells, and 
 this protoplasm is formed from the materials that are in the 
 foods. Food is necessary to furnish material for the repair 
 and growth of the cells. 
 
 The cells get their energy their warmth and power to 
 work from the food. A muscle cell gets its strength, a 
 
 1 It is estimated that fourteen billion red blood corpuscles die in the body 
 every day. Great numbers of cells also die on the surface of the skin. 
 
 78 
 
FOODS AND ENERGY 79 
 
 bone cell gets its power to build bone, and all other cells, 
 whatever they do, get their power ^o work from the energy 
 which is in the food. Just as a .locomotive gets its energy - 
 its warmth and power to move from the fuel which is burned 
 under its boiler, so the cell gets its energy from the food 
 which is burned within the cell. Cut off the fuel from a 
 locomotive, and it will become cold and still. Cut off the 
 food from a cell, and it will lose its energy and become a dead 
 cell. Food is necessary to furnish energy to the cells. 
 
 THE CHEMISTRY OF FOODS 
 
 Molecules and Atoms. In the study of chemistry we learn 
 that everything that we can see, feel, taste, or smell is com- 
 posed of very small parts called molecules. Just as a house 
 is built of bricks, so are wood, stone, water, earth, air, and 
 other substances composed of molecules. 
 
 Molecules are so small that millions of them are required 
 to build the smallest object that can be seen with the most 
 powerful microscope. They are so small that we cannot 
 imagine how small they are. Yet chemists study molecules, 
 and they have discovered some very wonderful things about 
 them. One of the most wonderful of these discoveries is 
 that molecules are composed of still smaller particles called 
 atoms. There are about eighty kinds of atoms, all differing 
 in many ways. 
 
 Elements and Compounds. Elements are substances that 
 have only one kind of atoms in their molecules. Compounds 
 have two or more different kinds of atoms in their molecules. 
 Perhaps you do not understand what you have just read, but 
 if we play that we are building molecules, you will probably 
 
8o HUMAN PHYSIOLOGY 
 
 get a clear idea of the difference between an element and 
 a compound. 
 
 Suppose we have a pile of bricks of many different colors, 
 some purple, some red, some yellow, some green, some 
 blue, and some violet. Suppose we call these bricks atcms, 
 and of them decide to build molecules. Let us first build 
 a molecule using only red bricks. This is like the molecule 
 of an element, for it has only one kind of atoms in it. Let us 
 now build a molecule of yellow bricks. This also is like the 
 molecule of an element, for only one kind of atoms was used 
 in making it. Now let us build a molecule partly of yellow 
 and partly of red bricks. Is this like the molecule of an 
 element? No, for it has in it two kinds of atoms. It is like 
 the molecule of a compound. Let us now build a big mole- 
 cule and put into it all the different kinds of bricks that 
 we have. Is this big molecule an element or a compound ? 
 Read the. definition of a compound again, and you will see 
 that this is certainly a compound. 
 
 Some Common Elements and Compounds. Since there are 
 eighty kinds of atoms, there are about eighty elements. You 
 could tell that iron is an element from 
 the diagram of its molecule, for both 
 atoms are of the same kind. Gold is 
 
 F,G. 43 ~A molecule of iron. another element, the atoms in its mole. 
 
 iron is an element because ail cule being the same. Other common 
 the atoms in its molecule are elements are silver, copper, lead, tin, 
 
 of the same kind. ' ,, ' 
 
 zinc, sulfur, and carbon (the black sub- 
 stance of which charcoal and soot are composed, and which 
 you see on the burnt end of a match). Still other elements are 
 oxygen, the gas which is taken into the blood from the air when 
 we breathe; hydrogen, a very light gas used to fill balloons; 
 and nitrogen, a gas making up about four fifths of the air. 
 
FOODS AND ENERGY 
 
 81 
 
 Since the eighty different kinds of elements combine in 
 very many different ways, there are thousands of compounds 
 all about us. Wood, stone, water, 
 and earth are all compounds. 
 Rocks and the ores of metals are 
 compounds. Dynamite and gun- 
 powder are compounds whose 
 
 FIG. 44. A mclecule of water. 
 Water is a compound because it has 
 molecules fly to pieces with great more than one kind of atoms in its 
 
 force. Everything that you eat 
 
 and wear is a compound, and if you should pick up the thing 
 nearest your hand, you would probably find that you were 
 holding a compound. 
 
 Compounds Different from the Elements of which they are 
 formed. When blue and yellow paint are stirred together, 
 the mixture is neither blue nor yellow, but green. So a com- 
 pound may be very different from any of the elements of 
 which it is formed. Thus when carbon (a black solid) and 
 sulfur (a yellow solid) unite, they make a liquid. When oxy- 
 gen and iron unite, they make the red rust which you have 
 so often seen. This rust is not a gas like oxygen, nor is it a 
 tough and hard metal like iron. It is a compound, and very 
 different from each of the elements (oxygen and iron) of 
 which it is made. 
 
 Water is another compound which is different from either 
 
 of the elements in it. Hydrogen 
 and oxygen are both gases, but 
 when they unite, they form water, 
 a %"<* Carbon and oxygen also 
 form a compound very unlike 
 either of the elements entering 
 into it. A piece of charcoal is 
 a black solid which you can see and handle, and oxygen is 
 
 FIG. 45- A molecule of carbon 
 dioxid. This gas is a compound, its 
 
 tW 
 
82 HUMAN PHYSIOLOGY 
 
 the gas of the air which is so necessary to our lives. But 
 when carbon and oxygen unite (as they do when you burn a 
 piece of charcoal) the compound, carbon dioxid, is a poisonous 
 gas very different from the solid carbon, and also very 
 different from the life-supporting oxygen. 
 
 The Language of Chemists. Chemists do not write out the 
 whole names of the elements, but write H for hydrogen, O 
 for oxygen, S for sulfur, C for carbon, and other short signs 
 for the other elements. They have also a short way of writ- 
 ing out the kinds of atoms and how many of each kind are in 
 a compound. Thus they write H 2 O (read : H two O) for 
 water, meaning that in a molecule of water there are two 
 atoms of hydrogen and one atom of oxygen. For carbon 
 dioxid, the poisonous gas which we breathe out from the 
 lungs, and which is formed when anything containing carbon 
 is burned, they write CO 2 (read : CO two), meaning that in a 
 molecule of this gas there are one atom of carbon and two of 
 oxygen. 
 
 CLASSES OF FOOD 
 
 From plants and animals the people of the world obtain 
 many different foods. All these foods, however, can be put 
 into three great classes, the carbohydrates, fats, and proteins. 
 
 Carbohydrates. The carbohydrates include the starches 
 and sugars. Almost all of them come from plants. Nearly 
 every plant has its own kind of starch, and we have corn 
 starch, wheat starch, oat starch, potato starch, arrowroot 
 starch, and many other varieties of starch. All the grains, 
 and potatoes and most other vegetables, are starchy foods. 
 
 Sugar is an important food. Most of the sugar that we 
 use comes from sugar cane and the sugar beet. Besides what 
 
FOODS AND ENERGY 83 
 
 we purposely add to our foods to make them pleasant to the 
 taste, we get considerable amounts pf sugar in maple syrup, 
 molasses, honey, and fruits, and there is some sugar in corn, 
 sweet potatoes, milk, and many other foods. 
 
 Fats. There is no difference between fats and oils, except 
 that at ordinary temperatures fats are solid and oils are 
 liquid. For use as food they are the same, and are all called 
 fatty foods. 
 
 Among the common fatty foods are butter, taken from 
 milk ; lard and cotton-seed oil, used in cooking ; olive oil, used 
 in salads and dressings; and the fat that is always found in 
 meat. Besides the fats obtained from these foods we get 
 some fats in eggs, cheese, corn, chocolate, and in a great 
 many other foods. 
 
 Proteins. Most of the food that we get from animals con- 
 tains proteins. Lean meat, fish, eggs, milk, and cheese, all 
 contain protein matter. Wheat, corn, and other grains con- 
 tain a considerable proportion of protein ; but of all common 
 foods obtained from plants, peas and beans are the richest in 
 proteins. The table in the back of the book shows the pro- 
 portion of proteins, carbohydrates, and fats in many foods. 
 
 Chemical Composition of the Different Classes of Foods. 
 The carbohydrates contain the three elements, carbon, 
 hydrogen, and oxygen, and in the common carbohydrates, 
 as in water, there are always twice as many atoms of hydro- 
 gen as there are atoms of oxygen. Thus, common sugar is 
 Ci2H 2 2On, there being two atoms of hydrogen for one of oxy- 
 gen. Fats contain the same elements as the starches and 
 sugars, but in different proportions, having in them much 
 less oxygen than is found in the carbohydrates. Proteins 
 contain all the elements (carbon, hydrogen, and oxygen) 
 which are found in the other foods, and in addition they 
 
84 HUMAN PHYSIOLOGY 
 
 contain nitrogen and usually very small amounts of sulfur, 
 phosphorus, iron, and other elements. 
 
 All Foods come from Living Things. From what you have 
 already learned you will know that the principal elements in 
 food are very abundant in the world. Oxygen and nitrogen 
 make up nearly all of the air. Water is two thirds hydrogen, 
 as you could tell by counting the number and kinds of atoms 
 in its molecules. Carbon is abundant in wood ; coal is nearly 
 all carbon ; and there is much carbon in the rocks of the 
 earth. 
 
 But you could not live on water, coal, and air. They con- 
 tain all the chief elements of our food, but it is only when 
 these elements have been built up into the proper compounds 
 that they are useful in nourishing the body. These com- 
 pounds we find only in the bodies of living things, so all our 
 food must come from the bodies of animals or from plants. 
 " In building our house, we can use only bricks ripped 
 from the walls. of other houses." 
 
 Uses of the Different Classes of Foods. Protoplasm is living 
 protein matter ; it is always partially composed of nitrogen, 
 and any food which is used in cell building must contain 
 nitrogen. The proteins are therefore the building foods. 
 The fats and carbohydrates lack the necessary nitrogen, and 
 cannot be used in cell building. They &re fuel foods, useful 
 for burning in the cells to furnish energy. The proteins when 
 burned also furnish energy to the cells, but their main use 
 is to provide materials for building new protoplasm. 
 
 OTHER THINGS NECESSARY TO THE BODY 
 
 Oxygen and Water. Besides the three classes of foods that 
 we have studied, there are certain other substances which the 
 
FOODS AND ENERGY 85 
 
 body must have to keep it in health. Among these things 
 oxygen takes the first place. We breathe it in constantly, 
 and if the supply of oxygen is cut off for even a short time, 
 we die. Water is also absolutely necessary to the body. 
 Besides the water that we drink, we get a great deal of water 
 in our foods, as you can see by referring to the table of foods 
 in the back of the book. Potatoes are more than 80 per 
 cent water ; beef is more than half water ; and even in dry 
 foods like rice and beans there is water. 
 
 Minerals. Several minerals are needed by the body. Of 
 these salt is needed in the greatest quantity. During the 
 time of growth the body must have also a considerable quan- 
 tity of lime to build the skeleton. Iron in small amounts is 
 necessary for the formation of the red blood corpuscles, and 
 small amounts of several other minerals are needed by the 
 body. Some of these minerals we get in water, and others in 
 our food. Vegetables have a special diet value because of 
 the large amounts of lime, potassium, and other minerals that 
 they furnish the body. 
 
 Accessory Food Substances. Certain other substances 
 (sometimes called " vitamins ") are necessary for health or 
 even for life. Chemists do not yet know what these sub- 
 stances are, but by feeding-experiments on animals and by a 
 study of human diseases it has been determined that there are 
 at least three of them. The lack of one of these (the " anti- 
 neuritic " diet factor), which is especially abundant in the 
 outer layer of grains, causes a disease of the nervous system 
 called beriberi. Inflammation of the eyes, failure to grow, and 
 possibly rickets are due to a lack of a second accessory sub- 
 stance which is soluble in fat and is found in the green parts 
 of plants, the yolk of eggs, and in the fat of milk. The 
 third accessory food substance (the "antiscorbutic" sub- 
 
86 HUMAN PHYSIOLOGY 
 
 stance) is found especially in fresh fruits and vegetables, and 
 scurvy is caused by a diet that is deficient in it. 
 
 Among rice-eating peoples beriberi is common, but in our 
 country nearly every one has a sufficient supply of the anti- 
 neuritic substance. But it seems probable that a goodly num- 
 ber of our people, especially growing children, have an insuf- 
 ficient supply of the fat soluble substance, and it has been 
 proved that in many cases physical well-being is promoted by 
 adding foods rich in the antiscorbutic substance to the diet. 
 
 Summary. The human body constantly requires food. 
 This food is necessary to furnish building material and 
 energy to the cells. 
 
 All matter is composed of molecules that are built of still 
 smaller particles called atoms. Elements have only one kind 
 of atoms in their molecules. Compounds have two or more 
 kinds of atoms in their molecules. There are about eighty 
 elements and thousands of compounds. Compounds are 
 often very different from any of the elements of which they 
 are formed. 
 
 The three classes of foods are the carbohydrates (starches 
 and sugars), the fats, and the proteins. The carbohydrates 
 are obtained chiefly from plants. They contain carbon, 
 hydrogen, and oxygen, there being in them two atoms of 
 hydrogen for each atom of oxygen. Fats and oils contain 
 these same elements but in different proportions. Proteins, 
 in addition to the elements found in the other foods, contain 
 nitrogen. Lean meats, eggs, milk and cheese, grains, and 
 peas and beans are the principal protein foods. 
 
 The elements found in foods are very abundant in the 
 world, but only compounds built up by living plants and 
 animals can be used by man for food. The proteins give 
 energy to the body, and they are the only foods that can be 
 
FOODS AND ENERGY 87 
 
 used in building protoplasm, because only the proteins con- 
 tain nitrogen. The other foods furnish energy to the body. 
 Oxygen, water, and certain minerals are also necessary to 
 the body. The body obtains its minerals from water and 
 foods. Green vegetables are especially valuable for their 
 minerals. 
 
 QUESTIONS 
 
 Give two reasons why the body needs food. Why do the cells 
 need building material? Why do they need energy? 
 
 Of what is all matter composed ? Of what are molecules com- 
 posed? What is an element? What is a compound? Name some 
 elements ; some compounds. Name some compounds that are 
 different from the elements of which they are composed. Give 
 some examples of the short signs that chemists use. 
 
 What are the three classes of foods ? What two kinds of carbo- 
 hydrates are there? From what are they obtained? Mention some 
 starchy foods ; some foods that contain sugar. What is the differ- 
 ence between a fat and an oil ? Mention some fatty foods. Mention 
 a number of foods that are rich in proteins. 
 
 What elements are in carbohydrates? In what proportion are the 
 hydrogen and oxygen in them ? What elements are in fats ? Give 
 two uses of the proteins in the body. How are the carbohydrates 
 and fats used in the body? From what kind of objects are our 
 foods obtained? 
 
 Mention some other things that are needed by the body. Where 
 does the body obtain its oxygen? water? mineral matter? 
 
 When gas or oil is burned, what becomes of the atoms of which 
 its molecules were composed ? 
 
CHAPTER VIII 
 
 THE DIGESTIVE ORGANS 
 
 WE have now learned that the cells of our bodies must 
 have food. But before one of the cells in the brain, for 
 
 instance, can use the 
 beefsteak or the potato 
 that lies on your plate, 
 many changes must be 
 made in these foods. 
 We therefore have a 
 great system of organs 
 whose business it is to 
 work over and prepare 
 the foods for the cells. 
 These are the digestive 
 organs. Of all parts 
 of the body, it is the 
 most important to un- 
 derstand the digestive 
 system, for oftener 
 than any other part of 
 the body, these organs 
 fail in their work, and 
 interfere with the 
 health. 
 The Digestive Sys- 
 
 VERMIFORM AP 
 
 FIG. 46. The digestive organs. 
 
 tern. The digestive system includes the alimentary canal and 
 
 88 
 
THE DIGESTIVE ORGAN'S 
 
 8 9 
 
 certain accessory or assisting organs of digestion, the teeth, 
 salivary glands (Fig. 54), liver , and pancreas. The alimen- 
 tary canal is a long passageway through the body, into which 
 the food is taken while it is being digested. The teeth grind 
 the food into small pieces, and the other accessory organs of 
 digestion pour juices into the alimentary canal that assist in 
 digesting the food. Before beginning the study of* the diges- 
 tive organs it is well to have a general idea of the structure 
 and function of a gland, for 
 the whole digestive system is 
 in the main a collection of 
 glands. 
 
 A Simple Gland. In a simple 
 gland the cells are arranged 
 in the form of a hollow tube 
 (Fig. 47). On one side the 
 gland cells take in water and 
 other materials from the blood. 
 On the other side the gland 
 cells give off a liquid into the 
 hollow in the center of the 
 gland. When the gland cells 
 give off liquid 1 the liquid 
 flows out of the mouth 
 of the gland. The gland is then said to secrete , and the 
 liquid from a gland is called the secretion of the gland. 
 
 FIG. 47 . 
 
 A section through a simple 
 gland. 
 
 1 In some glands the cells merely take up on one side materials from the 
 blood, and on the other side give off the same materials into the central opening 
 of the gland. A sweat gland is an example of this class of glands. The water 
 and the salt of the perspiration merely flow from the blood through the cells of 
 the gland, and come out on the skin as sweat. Other glands build up new sub- 
 stances with the materials which they take from the blood. The glands of the 
 
CjO HUMAN PHYSIOLOGY 
 
 THE ALIMENTARY CANAL 
 
 The alimentary canal is almost thirty feet in length. Its 
 principal divisions are the mouth, pharynx (throat) , esophagus, 
 stomach, and the small and large intestine. In its walls are 
 muscles that contract on the food and force it onward through 
 the canal. Beginning with the lips, the alimentary canal 
 
 FIG. 48. The stomach, liver, and pancreas. 
 
 is lined throughout with a smooth mucous membrane. This 
 differs from skin in having a pink color and in being kept 
 moist with sticky mucus (Fig. 6), which causes the food to 
 move easily along in its course through the alimentary canal. 
 The Stomach. The food is taken into the mouth, passes 
 back through the pharynx, and goes down the esophagus. 
 
 stomach are examples of this kind of glands. The cells in these glands build up 
 and give forth in their secretion a substance called pepsin, which digests the 
 protein foods. 
 
THE DIGESTIVE ORGANS 91 
 
 At the bottom of the esophagus is the stomach. This holds 
 about three pints, and when full is About a foot long and four 
 inches through in the thickest part. When empty, however, 
 the stomach draws up and occupies much less space. The 
 function of the stomach is to serve as a storehouse for food so 
 that enough can be eaten at one time to supply the body for 
 several hours, and also to secrete gastric juice. 
 
 The Glands of the Stomach. In the inner coat of the 
 stomach wall are great numbers of gastric glands, which 
 
 INNER SURFACE OF STOMACH 
 
 OUTER CONNECTIVE 
 TISSUE COAT 
 
 OBLIQUE MUSCLES CIRCULAR MUSCLES LONGITUDINAL MUSCLES 
 
 FIG. 49. A section of the wall of the stomach, showing muscles and glands. B is one 
 of the glands more highly magnified. 
 
 secrete gastric juice for digesting the food and for killing 
 bacteria. Each gland is a little circular depression (like 
 a little well) in the wall of the stomach. If a handkerchief 
 be spread over the hand and thrust down into the hand 
 
9 2 
 
 HUMAN PHYSIOLOGY 
 
 FIG. 50. To illustrate how 
 a gastric gland is formed by 
 an infolding of the stomach 
 wall. 
 
 with a pencil as you see in Figure 50, the shape of a simple 
 gastric gland, and the way it lies in the stomach wall, will be 
 very well represented. Some of the 
 gastric glands branch in their lower 
 parts; but they are all formed by 
 folding the inner layer of the stomach 
 wall into deep narrow pockets. 
 Figure 49 shows how closely these 
 glands are packed together, and it 
 also shows how small they must be, 
 for they do not reach more than 
 halfway through the stomach wall, 
 although the wall itself is little 
 thicker than a piece of heavy cloth. 
 The Gastric Juice. From two and a 
 half to five quarts of gastric juice are secreted in a day. 
 Most of the gastric juice is water, but it contains pepsin for 
 digesting the protein food, and acid. The acid kills many 
 bacteria, thus keeping them from getting into the intestine 
 and causing trouble there. It is useful in digestion also, since 
 without the acid the pepsin is unable to digest the protein 
 foods. 
 
 The Muscles of the Stomach. The entire alimentary canal 
 from the top of the esophagus onward, has a circular and a 
 longitudinal layer of muscles in its walls. The stomach has 
 these two muscle layers, and has in addition a layer of oblique 
 muscles. There are, therefore, circular muscles running 
 around the stomach, longitudinal muscles running lengthwise 
 of the stomach, and oblique muscles running slantingly in the 
 stomach walls. These muscles force the food onward through 
 the stomach; and during digestion, especially in the lower part 
 of the stomach, the muscles keep contracting and mixing up 
 
THE DIGESTIVE ORGANS 
 
 93 
 
 the food in the gastric juice. At the pylorus, or point where 
 the stomach joins the small intestine, the circular muscles are 
 thickened into a strong ring, the pyloric muscle, which closes 
 the opening between the stomach and intestine while diges- 
 tion is going on in the stomach. After stomach digestion 
 has been finished, the circular muscles contract* above the 
 food, the pyloric muscle opens at the same time, and the food 
 is forced into the intestine (page 112). 
 
 The Small Intestine. The small intestine is coiled in the 
 abdominal cavity. It is much the longest part of the alimen- 
 tary canal, having a length 
 of nearly twenty-two feet. 
 In its walls are intestinal 
 glands, very similar to the 
 glands of the stomach. 
 They secrete the intestinal 
 juice, which aids in digest- 
 ing the food. The juices 
 of the liver and of the 
 pancreas are also emptied 
 into the small intestine, and 
 the digestion carried on 
 here is even more impor- 
 tant than the digestion in 
 the stomach. 1 
 
 The Villi. 
 
 INTESTINAL GLANO 
 
 FIG. 51. Villi and intestinal glands. 
 
 On the intestinal wall are many little finger- 
 like projections called villi (singular, villus), which stand up 
 in the digested food and absorb it, or take it into the body 
 through the intestinal wall. So abundant are the ,villi that 
 
 1 In a few cases the stomach has been removed and the esophagus connected with the 
 small intestine. Persons on whom this operation has been performed have lived, the 
 digestive work of the stomach being done by the small intestine. 
 
94 HUMAN PHYSIOLOGY 
 
 they give the inner surface of the intestinal wall an appear- 
 ance like velvet, and they absorb the food much more 
 rapidly 1 than a smooth, even wall could do. Digestion is 
 finished in the small intestine, and most of the liquids and 
 the digested food are absorbed before the large intestine is 
 reached. A little food, however, passes into the large intes- 
 tine and is there absorbed while the muscles in the walls of 
 the large intestine move onward the indigestible material. 
 
 The Large Intestine. The large intestine begins low 
 down in the right side of the abdominal cavity, passes up the 
 right side, then across under the diaphragm, and down the left 
 side. Just below where the small intestine opens into it there 
 is a small, worm-like structure (Fig. 46), the -vermiform 
 appendix? The large intestine has no villi. Its glands 
 secrete mucus and also throw off into the intestine some 
 waste products from the body. 
 
 THE ACCESSORY ORGANS OF DIGESTION 
 
 The Teeth. A tooth is composed of a crown, a neck, and 
 one or more roots. The roots stand in sockets in the jaw- 
 bones, and are covered by a layer of bone-like cement. 
 The outer coat of the crown is made of enamel, the hardest 
 material in the body. Under the enamel and forming the 
 main bulk of the tooth is the dentine? a substance harder 
 than the most compact bone, but not nearly so hard as 
 
 1 The villi give from four to eight times as much absorbing surface as the 
 smooth walls of the intestine would give. 
 
 2 The disease called appendicitis is caused by germs growing in the vermiform 
 appendix and causing inflammation. In severe cases of appendicitis, it may be 
 necessary to open the abdominal cavity and remove the vermiform appendix. 
 
 3 Ivory is dentine, usually obtained from the tusks of elephants, but. some- 
 times from the tusks of the walrus or the teeth of the hippopotamus. 
 
THE DIGESTIVE ORGANS 
 
 95 
 
 enamel. In the middle of the tooth is the pulp cavity, a little 
 chamber containing nerves and blood vessels. Get a tooth 
 from a dentist, or find the tooth of an animal, and break it 
 open, and you will have no difficulty in finding the enamel, 
 the dentine, the pulp cavity, and 
 the little root canals through 
 which the nerves and blood 
 vessels come up from the jaw- 
 bone into the tooth. 
 
 Different Kinds of Teeth and 
 their Functions. There are four 
 kinds of teeth, incisors, canines 
 or cuspids, bicuspids, and molars. 
 The incisors are flat and sharp 
 for biting off food. In the dog 
 and other flesh-eating animals 
 the canines' are tusks which are 
 used as weapons and hi tearing 
 
 flesh, but in man their principal use is to assist the incisors in 
 biting. The bicuspids and the molars have wide surfaces for 
 grinding the /food into small pieces and mixing it thoroughly 
 with the saliva. Examine a back tooth and notice the cusps, 
 or points, on it. Observe how the cusps of the upper and 
 lower teeth fit into each other when the jaws are tightly 
 closed. Then notice how the jaws move sidewise in chewing, 
 and you will readily understand how the food is crushed and 
 ground to pieces as the teeth slide across each other. 
 
 Temporary and Permanent Teeth. The jaws in childhood 
 are too small to hold the large teeth which we need in later life. 
 In early life we have therefore a set of twenty small tempo- 
 rary teeth, and hi later life a set of thirty- two larger permanent 
 teeth. The earliest permanent teeth to appear are the first 
 
 FIG. 52. Section of a tooth. 
 
9 6 
 
 HUMAN PHYSIOLOGY 
 
 molars, which come in behind the temporary molars about 
 the sixth or seventh year. 
 
 Care of the Teeth. Decay of the teeth is caused by bacteria, 
 which find a splendid place to grow in the moist, warm food 
 between the teeth. It is also thought that bacteria are the 
 
 FIG. 53. One half of the permanent leeth. 
 
 cause of tartar, a dark hard substance that collects on the 
 teeth of some persons. It is evident that the best way to 
 preserve the teeth and to keep them white and beautiful is 
 to keep them clean, so that bacteria will find no food 
 materials among them. They should be brushed with pure 
 soap or a good tooth powder after each meal, or at least in 
 the morning and at night before going to bed. Particles of 
 food should be removed from between the teeth with a wooden 
 or quill toothpick, or with a piece of thread. It is very 
 
 1 A common error is to mistake the first permanent molars for temporary teeth, 
 and to allow them to decay, thinking that they will be replaced by new teeth. 
 When there are three double teeth on one side of the jaw, the back one is a 
 permanent tooth. 
 
THE DIGESTIVE ORGAN'S 
 
 97 
 
 important not to break the enamel by biting on thread, nuts, 
 or other hard substances ; for where the enamel is broken and 
 the dentine exposed, decay soon follows. Tartar should be 
 removed by a dentist, for it causes the gums to shrink and 
 expose the necks of the teeth below the enamel. 
 
 When decay has begun in a tooth, the only remedy is to 
 have the cavity filled by a dentist. This should be done 
 before the cavity becomes large and gets down close to the 
 nerves in the pulp cavity of the tooth. The teeth are so 
 valuable that we cannot afford to lose them, and it is far 
 better to have a dentist look them over occasionally and fil) 
 all small cavities than it is to suffer later from toothache, 
 neuralgia, and indigestion, and to pay for crowns, bridge 
 work, or artificial teeth. 
 
 The Salivary Glands. There are six salivary glands, three 
 pairs. The two sublingual glands are under the tongue, the 
 submaxillary glands, are under 
 and behind the corners of the 
 lower jaws, and the parotid^- 
 glands are in front of the ears. 
 The saliva is carried from the 
 glands to the mouth through 
 circular canals called ducts. 
 The ducts of the submaxillary 
 and of the sublingual glands of 
 each side of the head unite 
 before they enter the mouth. 
 The ducts from the parotid 
 gland open on the inside of 
 
 SUBLINGUAL GLAND 
 
 FIG. 54. The salivary glands. 
 
 the cheeks opposite the second molars of the upper jaw. The 
 
 1 In mumps the parotid glands are swollen and inflamed. The other salivary 
 fitlands also are occasionally affected. 
 
9 8 
 
 HUMAN PHYSIOLOGY 
 
 saliva is secreted by the cells in the 
 small branches of the gland (Fig. 5 5 ) 
 and flows into the main duct and on 
 into the mouth. 
 
 Uses of the Saliva. The saliva 
 moistens food and makes it possible 
 to swallow dry food like crackers, 
 which without saliva would become 
 dust in the mouth. The saliva is 
 useful also because it contains a 
 substance called ptyalin, which di- 
 gests starch. 
 
 The Pancreas. The pancreas (Fig. 
 48) is a long gland, shaped something 
 like the tongue of a dog. The Ger- 
 mans call the pancreas the " abdomi- 
 nal salivary gland," and this is a very 
 good name for it, for it is composed 
 of many little branches, like a great 
 salivary gland, and the pancreatic 
 juice is very much like thin, watery 
 FIG. 55. Diagram of a longitu- saliva. The pancreas is the most 
 
 dinal section of a salivary gland. . r ,, ,, ,. . . , 
 
 A salivary gland is formed by important of all the digestive glands, 
 folding in the lining of the mouth for the pancreatic juice contains 
 
 in the same way that a gastric tfy p sin a substance which digests 
 gland is formed by folding in the Jjr 
 
 lining of the stomach. The dif- proteins, amylopsin f or digesting 
 ference in the plan of the two starches, and steapsin for digesting 
 
 glands is that a gastric gland r , , ,, .... ,. 
 
 branches only a few times, while fatS The PanCreatlC JU1C6 digests 
 a salivary gland has hundreds of all three classes of f Oods Very 
 
 branches. rapidly, and it is principally the 
 
 action of this juice that makes the digestion in the small 
 intestine so important. 
 
 TUBULE 
 
THE DIGESTIVE ORGANS 99 
 
 The Liver. The liver is the largest gland in the body; 
 it weighs from three and a half to ,f our pounds. It lies in 
 the right side of the abdominal cavity close up to the dia- 
 phragm, one lobe running down close to the body wall and 
 another extending across under the diaphragm and covering 
 the inner end of the stomach. The liver cells secrete bile, 
 and running all through the liver is a system of little ducts 
 that collect the bile and bring it all to one large bile duct. 
 This large duct empties into the upper part of the small 
 intestine. 
 
 On the under side of the liver is a little pear-shaped sac, 
 called the gall bladder (Fig. 48). When digestion is not 
 going on, the opening of the bile duct into the small intestine 
 closes, and the bile passes into the gall bladder, where it is 
 stored. Then when food passes into the small intestine for 
 digestion, the mouth of the bile duct opens and the walls of 
 the gall bladder contract, sending into the intestine a flood 
 of greenish-yellow bile. In a later chapter we shall study 
 about other important functions of the liver. 
 
 The Digestive System as a Whole. The alimentary canai 
 may be compared to a long channel through the body, and 
 the cells of the digestive organs to workers who are stationed 
 along the sides of the canal to prepare the foods for use by 
 pouring digestive juices over them as they pass along the 
 canal. 
 
 In the mouth the food is ground into fine pieces and mixed 
 with saliva, and the ptyalin in the saliva immediately starts 
 the process of digestion. Then the journey through the long 
 canal begins in earnest, the cells of the stomach, intestine, 
 pancreas, and liver pouring in their juices as the food reaches 
 their parts of the canal. On and on the food is moved, the 
 juices digesting it and the digested portion being absorbed. 
 
100 HUMAN PHYSIOLOGY 
 
 until finally only the indigestible matter of the food stuffs 
 remains. 
 
 The digestive juices can work outside of the body as well 
 as in the alimentary canal, and it might be possible to arrange 
 a digestive system according to a plan differing from that 
 which nature has used in our bodies. Yet you would have 
 difficulty in thinking of anything simpler or better for diges- 
 tion and absorption than a long tube through the body, into 
 which the foods can be taken and soaked in digestive juices 
 while they are slowly moved along. 
 
 The Nervous Control of the Digestive System. The diges- 
 tive organs, like other parts of the body, are controlled by 
 the nervous system. Most of the work of regulating these 
 organs is done through the sympathetic nervous system, and 
 it is carried on without our knowledge and without any atten- 
 tion from the mind. The salivary glands and the glands of 
 the stomach, however, are controlled to a certain extent by 
 the higher centers of the brain, and the mind has a very great 
 effect on them. You perhaps know how, when you are hun 
 gry, the sight or odor of food will " make the mouth water." 
 This means that at the mere thought of food the nervous 
 system starts the salivary glands to work. The gastric 
 glands also are influenced by the mind, as the following 
 experiments on a dog showed : 
 
 The esophagus of a dog was divided, and when the animal 
 was hungry, he was given some fresh beef. The dog thought 
 he was eating a good dinner, but a tube had been connected 
 to the esophagus in such a way that the beef did not go into 
 the stomach but into a dish beside the dog. Nevertheless, 
 the gastric glands promptly began to pour gastric juices 
 into the stomach. Merely showing the food to the dog was 
 enough to start the secretion of the glands. The experiment 
 
THE DIGESTIVE ORGANS lOi 
 
 showed clearly that the mind affects the glands pf the stcw-ack 
 as well as the salivary glands. 
 
 At another time a tube was fitted to the part of the esopha- 
 gus which was connected with the stomach, and beef was 
 introduced into the stomach without the dog's knowing that 
 he was being fed. In this case, the gastric juice was 
 secreted very slowly, and the meat lay in the stomach a long 
 time before it was digested. 
 
 These experiments show plainly that the nervous system 
 has a great effect on the digestive organs, since the taste or 
 smell of food, or even the sight of food, will start the 
 secretions to flowing from some of the digestive glands. 
 They teach us that it is very important for our food to be 
 pleasant to the taste, in order that a good supply of juices 
 may be secreted to digest it. They show how indigestion 
 may be caused by eating food which is distasteful, and by 
 eating when food is not wanted. They also explain some 
 things which have long been known, that a cheerful, happy 
 life brings with it a good digestion ; and that anger, quarrel- 
 ing, melancholy, sorrow, homesickness, and pain interfere 
 with the digestion of the food. Our food should therefore 
 be well cooked and served in an appetizing manner ; every 
 one should come to the table in a cheerful frame of mind, 
 and should avoid all disagreeable topics of conversation, and 
 all unpleasant thoughts should be laid aside until the meal is 
 over. " Laugh and grow fat " is a wise old saying which we 
 would do well to heed. 
 
 Alcohol and the Digestive Organs. Strong alcohol is ex 
 ceedingly injurious to living cells. The stomach and the 
 liver get in its strongest form the alcohol which is taken into 
 the alimentary canal, and these are the digestive organs most 
 injured by alcohol. Strong alcoholic drinks taken into the 
 
102 HUMAN PHYSIOLOGY 
 
 ; stomach cause inflammation of the lining of the stomach. If 
 taken often, they may cause catarrh of the stomach. They 
 are especially harmful if taken when the stomach is empty. 
 Alcohol taken at mealtime is diluted by the food and liquids 
 in the stomach, and its effect on the mucous membrane of 
 the stomach is therefore weakened. Practically all alcohol 
 taken into the alimentary canal is absorbed through the stom- 
 ach walls, and therefore the intestine is little affected by it. 
 After the alcohol is absorbed from the stomach it is car- 
 ried to the liver. The two chief diseases of the liver, due to 
 alcohol, are fatty degeneration, caused by beer, ale, and other 
 malt liquors, and hardening of the liver, caused by whisky, 
 gin, rum, brandy, and other distilled liquors. In fatty degen- 
 eration, the living protoplasm of the liver cell is replaced by 
 fat, and finally each cell becomes a little sac of fat, unable 
 to manufacture bile or to do the other work of a liver cell. 
 In hardening of the liver, the connective tissue of the organ 
 grows far too abundantly, and by contracting squeezes the 
 delicate blood vessels and liver cells. This greatly hinders 
 the work of the liver, and may even cause the liver cells to 
 waste away and die. Either one of these diseases may cause 
 death, hardening of the liver being a common cause of death 
 among excessive drinkers. 
 
 THE DIGESTIVE ORGANS OF OTHER ANIMALS 
 
 A starfish throws its stomach out of its mouth and wraps 
 it about the oyster or other animal that it wishes to eat. 
 A snake has jaws fastened together with ligaments so elastic 
 that it swallows whole animals thicker than its own body. 
 An elephant feeds itself with its trunk, which corresponds 
 to the nose in other animals. There are many other things 
 
THE DIGESTIVE ORGANS 103 
 
 connected with the digestive systems and food habits of ani- 
 mals that are very different from anything that is found in 
 man. 
 
 Teeth. Beetles, grasshoppers, and crustaceans 1 have no 
 teeth, but have horny jaws which work sideways instead of up 
 and down as our jaws work. Some fish have teeth, but many 
 have none. A frog has teeth in its upper jaw, and a toad 
 has no teeth in either jaw. All the reptiles have teeth ex- 
 cept the turtle tribe, which, like the birds, have horny, tooth- 
 less beaks. In the poisonous snakes, two of the salivary 
 glands secrete poison, or venom, instead of saliva, and two of 
 the teeth are long, hollow fangs through which the venom is 
 injected into whatever the snake strikes. 
 
 The teeth of mammals differ very much according to the 
 food which they eat. Rodents have long, chisel-like incisors 
 for gnawing. The carnivora have long canines for killing 
 their prey and tearing the flesh on which they feed. The 
 herbivora have broad back teeth for grinding the grass and 
 leaves which they eat. 
 
 Among the herbivorous animals are many interesting 
 differences in the number and arrangement of the teeth. An 
 elephant has ten teeth, two upper incisors (the tusks) and 
 eight molars. A cow has six incisors and two canines in the 
 lower jaw, and no incisors or canines in the upper jaw. A 
 horse has six incisors and two canines in each jaw, but the 
 canines do not come through until about the sixth year. You 
 can therefore tell something about the age of a horse by 
 looking at his teeth. If he has eight front teeth in each jaw, 
 he is over six years old. In both the cow and the horse there 
 is a wide space between the canines and the back teeth. 
 
 1 Hard-shelled animals with jointed legs, like the crab, crayfish, lobster, etc. 
 
104 HUMAN PHYSIOLOGY 
 
 Tongues. A frog's tongue is fastened near the front of the 
 mouth, and lies with its tip pointing backward in the mouth. 
 So quickly that the eye cannot follow it, the frog can throw 
 
 FIG. 56. A frog's tongue. 
 
 its tongue over forward and out of its mouth to catch an 
 insect. The lizard also catches insects by shooting out the 
 tongue. In this way some small lizards pick up from one 
 thousand to fifteen hundred ants at one feeding. A snake 
 uses its forked tongue for feeling, and possibly for frighten- 
 ing away those who might attack it; but a snake does no 
 
 FlG. 57. A chameleon catching a moth. The chameleons are closely related to the 
 lizards. The tongue can be extended six or eight inches with lightning-like rapidity. 
 
 harm with its tongue. The tongues of carnivorous mammals 
 are covered with sharp little points for cleaning the last 
 particles of meat from bones. The giraffe can stretch out 
 its tongue until it is eighteen inches long, to gather in the 
 leaves on which it feeds. 
 
THE DIGESTIVE ORGANS 
 
 105 
 
 Other Digestive Organs. Crustaceans have a gastric mill 
 in the stomach. On the inside of the stomach wall there are 
 bony plates which are rubbed together to grind up the food. 
 A chicken (like other birds) softens its food in a crop, or wide 
 place in the esophagus, and then, with small stones which it 
 swallows, grinds the food in the gizzard, or thick-walled back 
 part of the stomach. 
 
 The ruminants, or cud-chewing animals (cattle, sheep, 
 goats, deer, antelope, camels, and giraffes), have the stomach 
 
 FlG. 58. The stomach of a ruminant. 
 
 in four parts or divisions. They have also two openings from 
 the esophagus into the stomach, one a longitudinal slit in the 
 side of the wall opening into the first division of the stomach, 
 and the other the usual opening at the bottom of the 
 esophagus leading into the second stomach. The food is 
 first swallowed without much chewing, and the ball of grass 
 or other coarse material stretches the esophagus wall, opens 
 the slit in its side, and drops into the first division of the 
 stomach. It is either stored here or passed on into the sec- 
 ond division and stored there. Then, when the animal has 
 finished eating, the food is brought up, a mouthful at a 
 
I0 6 HUMAN PHYSIOLOGY 
 
 and rechewed. When it is swallowed the second time it is 
 so soft and pasty that it fails to open the slit in the esophagus 
 wall, but passes through the upper part of the second division 
 of the stomach into the third stomach. From there it is 
 quickly passed into the fourth or true stomach, where it is 
 digested. 
 
 In their wild state the cud-chewing animals are eaten by 
 the carnivora, and this kind of stomach is an advantage to 
 them, since they can gather their food quickly and swallow 
 it, and then hide in a safe place while they chew it at their 
 leisure. 
 
 In addition to the four divisions found in the stomachs of 
 other ruminants, the camel has little sacs, formed by folding the 
 stomach wall into pouches or pockets, in which water is stored. 
 A muscle runs around the mouth of each sac and closes it 
 tightly, holding the water in until it is needed. At the right 
 time the muscle closing the sac relaxes, letting the water flow 
 into the stomach. 
 
 The intestine of the carnivorous animals is short, and that 
 of the herbivorous animals long, the ox having an intestine 
 about one hundred and fifty feet in length. Judging from the 
 human teeth and other digestive organs, man seems to be mid- 
 way between the herbivorous and carnivorous animals. We 
 may therefore conclude that nature intends that man should 
 eat both vegetable and animal food. 
 
 Summary. Before the foods can be used by the cells they 
 must be digested. This work is done by the organs of the 
 digestive system, which is composed of the alimentary canal 
 and the accessory organs of digestion. In the main the 
 digestive organs are glands that take material from the blood 
 and manufacture digestive juices. 
 
 The alimentary canal is nearly thirty feet in length. It 
 
THE DIGESTIVE ORGANS 107 
 
 has muscles in its walls that move the food onward, and is 
 lined with mucous membrane. The stomach holds about 
 three pints. It serves as a storehouse for food, and the 
 glands in its wall secrete the gastric juice. The gastric juice 
 contains pepsin for digesting protein foods, and acid which 
 assists in digestion and kills bacteria. The small intestine 
 is about twenty-two feet in length. Its glands secrete the 
 intestinal juice, and the villi on its walls absorb the digested 
 food. The glands of the large intestine secrete mucus and 
 throw off wastes from the body. 
 
 The body of a tooth is composed of dentine. Its crown is 
 covered with hard enamel and it has a pulp cavity in its 
 center. The four kinds of teeth are incisors, canines, bicus- 
 pids, and molars. There are twenty teeth in the temporary 
 set and thirty-two in the permanent set. Decay of the teeth 
 is caused by bacteria that grow in the food material that clings 
 to the teeth. To prevent decay, keep the teeth clean. 
 
 There are three pairs of salivary glands, the sublingual, 
 submaxillary, and parotid. They secrete saliva which 
 moistens the food and contains ptyalin for digesting starch. 
 The pancreas pours pancreatic juice into the small intestine. 
 This juice contains trypsin for digesting protein, amylopsin 
 for digesting starch, and steapsin for digesting fat. The 
 liver secretes bile, which is stored in the gall bladder until 
 needed in the small intestine. 
 
 The alimentary canal is a long channel through the body 
 into which the food is taken and moved along, while diges- 
 tive juices are poured over it. As the food moves along it is 
 digested and absorbed. The salivary glands and the stomach 
 are greatly influenced by the mind, and a contented, happy 
 life greatly aids in keeping the digestive organs in good con 
 dition. 
 
108 HUMAN PHYSIOLOGY 
 
 Alcohol causes inflammation of the stomach and fatty degen 
 eration and hardening of the liver. It is exceedingly in- 
 jurious to the digestive organs and should not be taken into 
 the alimentary canal. 
 
 The digestive organs of some other animals are very dif 
 ferent from our own. 
 
 QUESTIONS 
 
 Why do we need a digestive system ? What does the digestive 
 system include? Name the accessory organs of digestion. Describe 
 the alimentary canal. What is the function of the teeth? of the 
 other accessory organs of digestion? Of what in the main is the 
 digestive system composed? 
 
 How are the cells arranged in a simple gland? What do these 
 cells do ? What is meant by the word secrete ? secretion ? 
 
 How long is the alimentary canal? Name its chief divisions. 
 How is the food moved through it ? With what is it lined ? How 
 does this differ from skin? 
 
 Locate the stomach (page 1 7). Trace the course of the food into 
 the stomach. How much will the stomach hold ? Give its dimen- 
 sions when full. What two functions has the stomach ? 
 
 What is the function of the gastric glands ? Show how a gland is 
 formed in the wall of the stomach. How much gastric juice is 
 secreted in a day ? What does it contain ? What is the use of the 
 pepsin ? Give two uses of the acid. Describe the muscles of the 
 stomach. What two functions have these muscles? What and 
 where is the pyloric muscle and what is its function? 
 
 How long is the small intestine? What do its glands secrete? 
 What juices are emptied into it ? Describe the villi. What is their 
 function? What and where is the vermiform appendix? What is 
 the function of the glands of the large intestine? 
 
 Name the parts of a tooth. What is the enamel? dentine? the 
 pulp cavity? What is in the pulp cavity? Name the four kinds of 
 
THE DIGESTIVE ORGANS 109 
 
 teeth. Give the function of each kind. How many teeth in the 
 temporary set? in the permanent set? , What causes decay of the 
 teeth? How can decay be prevented? After decay has started, 
 what should be done ? 
 
 Name the salivary glands. What is their function? What two 
 uses has saliva? Locate the pancreas (page 17). What does it 
 secrete? What three substances are in the pancreatic juice? What 
 does each digest? Locate the liver. How large is it? What does 
 it secrete ? Where is the gall bladder and what is its function ? 
 
 To what may the digestive system as a whole be compared? What 
 happens to food as it is moved through the alimentary canal? 
 
 What proof is there that the mind affects the secretion of the 
 salivary glands ? In the case of the dog, what effect on the gastric 
 glands had the idea that he was eating ? What happened when the dog 
 was fed without knowing it? What do these experiments show? 
 Name some of the conditions of the mind that may interfere with 
 digestion. 
 
 What effect has alcohol on the stomach ? on the liver ? 
 
 How does a starfish get its food into its stomach? What is peculiar 
 about the way a snake eats ? about the way an elephant eats ? Tell 
 something about the teeth of different animals. 
 
 What is peculiar about the tongue of a frog? Tell something 
 about the tongues of other animals. 
 
 What is peculiar about the treatment of the food in the stomach 
 of a crustacean ? of a bird ? Describe the stomach of a ruminant and 
 the course of the food through it. Of what advantage is this kind 
 of stomach to a ruminant ? Describe the stomach of a camel. 
 
 If the small intestine had a smooth wall, how long would it need 
 to be to have the same absorbing surface that it now has (see footnote, 
 page 94) ? Explain how folding the wall of the alimentary canal into 
 deep .glands greatly increases the secreting surface. 
 
CHAPTER IX 
 
 DIGESTION, ABSORPTION, AND OXIDATION OF FOODS * 
 
 Why Food must be digested. When food has been taken 
 into the alimentary canal, it has not yet really entered the 
 body, but is only in a passageway which leads through the 
 body. To get into the body, it must first pass through 
 the lining of the alimentary canal into the blood. Many of 
 our fcods must have changes made in them before they can 
 do this, and the following experiments will show one of the 
 changes which is necessary in many foods: 
 
 Drop a few grains of salt into a 
 glass of water and stir it up. Does 
 the salt dissolve ? Taste the water. 
 Are there salt molecules in all parts 
 of the water? 
 
 Stir some clean sand into another 
 glass of water. Does the sand dis- 
 solve? Do its molecules separate 
 and go out through the water as 
 do the salt molecules, or do they 
 remain together? 
 
 Fold a piece of soft paper in 
 the manner indicated in Figure 59. 
 Open it at the free corners and set 
 Pour the salt water into the paper. Does 
 
 FIG. 59. 
 it in the mouth of a glass. 
 
 1 To THE TEACHER : The whole subject of the nutrition of the human body is 
 far from elementary, and it takes careful teaching to give beginning classes any 
 comprehension of it. It is the central idea in physiology, however, and under- 
 
DIGESTION, ABSORPTION, AND OXIDATION III 
 
 the water pass through the paper? Does the salt pass through the 
 paper? Arrange another piece of paper the same way and pour into 
 it the water containing sand. Does the sand pass through the paper .' 
 
 When a substance dissolves in a liquid, its molecules 
 separate. When it does not dissolve, they remain clinging 
 together in a great mass. The single molecules of salt in 
 the water readily pass through the paper ; but the grains of 
 sand, with their molecules all in great clusters, are caught by 
 the paper and are not allowed to pass through. 
 
 Most of our solid foods are substances that do not dissolve 
 in water or in the juices of the alimentary canal. Meat, 
 butter, eggs, or bread would lie indefinitely in the alimentary 
 canal without dissolving if their molecules were not changed. 
 They must, therefore, be digested, or changed to substances 
 that will dissolve in the stomach and intestine. Digestion 
 is the process of changing foods into substances that will dis- 
 solve and pass through the walls of the alimentary canal into 
 the blood. 
 
 You will see at once the tremendous importance of diges- 
 tion, for if it is not properly performed, the food which should 
 nourish the body may simply pass through the alimentary 
 canal and never get to the cells which it should feed. 
 
 Changes in the Food during Digestion. The molecules of 
 food are large, as molecules go, a starch molecule having in it 
 four hundred and fifty atoms, while some of the great protein 
 molecules are composed of more than two thousand atoms. 
 During digestion these large molecules are split into smaller 
 molecules. Each molecule of starch is split into ten molecules 
 of malt sugar, and then each molecule of malt sugar is split 
 
 lies practically all hygiene. Additional material on this subject is given in the 
 Appendix, and where sufficient time is given to the subject, this material should 
 be used. 
 
1 1 2 HUMAN PHYSIOLOGY 
 
 into two molecules of grape sugar. Thus in digestion, starch, 
 which does not dissolve in water, has each of its great mole- 
 cules split up into twenty molecules of grape sugar, which 
 dissolve and pass through the intestinal wall. The great 
 protein molecules and the molecules of fat are also split in 
 digestion into smaller molecules which can be absorbed. 
 
 How the Molecules are split. In the digestive juices are 
 very peculiar substances called enzymes or ferments, the 
 ptyalin, pepsin, trypsin, amylopsin, and steapsin that have al- 
 ready been mentioned. These enzymes have the power of 
 splitting up l the food molecules. Each enzyme can split the 
 molecules of only one class of food, so there must be different 
 kinds of enzymes for digesting the carbohydrates, the pro- 
 teins, and the fats. 
 
 Digestion in the Mouth. When food is taken into the 
 mouth, the salivary glands begin to work more rapidly, and 
 the ptyalin in the saliva at once attacks the starch and begins 
 to change it to malt sugar. At the best there is not much 
 time for digestion in the mouth, and by eating slowly we not 
 only give the ptyalin more time to work on the starch, but we 
 also give the glands more time to secrete the ptyalin, and 
 we mix the ptyalin more thoroughly with the food. All this 
 increases starch digestion in the mouth. 
 
 Digestion in the Stomach. The food remains in the stom- 
 ach from one to four hours. The main digestion carried 
 on here is that of the proteins by the pepsin of the gastric 
 juice. This enzyme splits the protein molecules into smaller 
 molecules called peptones, which dissolve in the gastric 
 
 1 Enzymes are found only in living animals and plants, but they can work 
 outside of a living body as well as in it. If ptyalin is put into a dish with starch, 
 or pepsin with a protein, digestion will go on in the dish as it does in the alimen- 
 tary canal. 
 
DIGESTION, ABSORPTION, AND OXIDATION 113 
 
 juice. The stomach keeps working the food along, and espe- 
 cially in its lower part keeps mixing the gastric juice with it. 
 After about an hour the pylorus opens and lets the more 
 liquid part of the food pass on into the intestine. The pepsin 
 continues its work on the food remaining in the stomach, 
 and as this is sufficiently digested, it is passed on from time 
 to time into the intestine. The acid in the gastric juice stops 
 the action of the ptyalin on the starch, but in the upper part 
 of the stomach the acid sometimes takes an hour or more to 
 work through the food. Much starch is, therefore, digested 
 by the ptyalin after the food leaves the mouth. 
 
 Digestion in the Small Intestine. When the food passes 
 into the small intestine, the glands of the intestine secrete 
 their juices, the gall bladder contracts and sends the stored-up 
 bile into the intestine, and the pancreas begins to send in the 
 pancreatic juice with its three powerful enzymes, trypsin, 
 amylopsin, and steapsin. Then the following enzymes finish 
 the digestion of the foods : 
 
 Amylopsin changes the starches which escape the ptyalin 
 into malt sugar. Then each molecule of malt sugar, and also 
 the cane sugar (ordinary sugar) that we take in our food, is 
 split by enzymes in the intestinal juice 1 into grape sugar. 
 Thus all the starches and sugar are finally changed by diges- 
 tion into grape sugar. 
 
 Trypsin digests the proteins which have escaped the pepsin. 
 
 Steapsin digests the fats Bile is not a digestive juice, for 
 it contains no enzymes; but it assists in destroying the acids 2 
 
 1 The enzyme that digests malt sugar is called maltase. The enzyme that 
 digests cane sugar is called invertasc. 
 
 2 The intestinal and pancreatic enzymes, like the ptyalin, cannot work when 
 strong acids are present. Both the bile and the pancreatic juice contain mineral* 
 that unite with and destroy the acid of the gastric juice. 
 
1 14 HUMAN- PHYSIOLOGY 
 
 of the gastric juice, it in some way assists the steapsin in the 
 digestion of the fats, and it greatly hastens the absorption of 
 the fats. 
 
 Absorption. The liquids and the digested foods in the ali- 
 mentary canal pass through the wall of the canal into the 
 blood. This process is called absorption and takes place 
 chiefly from the small intestine. After absorption the blood 
 carries the foods all through the body, and each cell takes 
 from the blood the food that it needs. 
 
 The Foods within the Cells. A part of the protein food 
 taken into a cell is used for building purposes. The remainder 
 of the food is oxidized (burned) within the cell. In this 
 process, the food molecules are torn down and the atoms that 
 were in these molecules unite with atoms of oxygen the food 
 molecules are destroyed and new kinds of molecules are 
 formed. Therefore, in the oxidation (burning) of the foods 
 within the cells, the foods are destroyed and new substances are 
 formed. These substances are the body wastes. You must 
 get clearly in mind that the same materials (atoms) that go 
 into the cells in the form of foods come out of the cells as 
 wastes, that the foods are changed to wastes within the cells. 
 
 The Body Wastes. When sugar and fat are burned in the 
 body, the waste products are carbon dioxid and water. When 
 protein foods are burned or when the protoplasm of the cells 
 breaks down, carbon dioxid and water are given off, and in 
 addition uric acid and many other waste products are formed. 
 The carbon dioxid and the protein wastes are poisonous and 
 pass out of the body through the lungs and kidneys. 
 
 What a Cell gains by burning Food. If the foods simply 
 go into a cell and then come out again as wastes, what does 
 a cell gain by taking in and burning food ? A cell gains 
 energy by the oxidation of the foods. 
 
DIGESTION, ABSORPTION, AND OXIDATION 11$ 
 
 When on a cold day you put coal into the stove, you do not 
 care anything about whether or not there is coal in the stove. 
 What you are interested in is the heat ....*.. .:..-...... 
 that you will get when the coal burns. 
 
 J 
 
 So when a cell burns food, it is not 
 profited by the atoms and molecules 
 of the food, but by the energy the 
 heat and strength and power to work 
 that is given to the cell by the 
 burning. In this connection it would 
 be well to read again pages 78 and 79. 
 The Storage of Foods in the Body. 
 Our cells must have a constant sup- Lv^/'rX"A : T 
 ply of food, and it is necessary to FlG> ^ The 
 
 have a Store Of food in the body that a cell and are changed to wastes 
 
 can be used in times of sickness or Wlthin the celu 
 starvation. When sugar is abundant, a few ounces of it can 
 be stored by the liver until it is needed by the cells. The 
 great store of food in the body, however, is in the form of fat. 
 The fat is deposited about the intestines, kidneys, and other 
 internal organs, it is packed among the muscles and in other 
 tissues, and a layer of fat is laid down under the skin. The 
 fat under the skin is useful not only for feeding the body in 
 times of food scarcity, but to retain the body heat. 
 
 Fat in Animals. Animals that hibernate go into their win- 
 ter quarters fat in the autumn, use up their fat during theii 
 winter's sleep, and come out thin in the spring. The camel 
 has a store of fat in the hump on its back, which enables it 
 to go for many days without food. Seals, whales, and other 
 warm-blooded animals that live in cold waters have a thick 
 layer of fat under the skin to keep in the body heat. In a 
 whale this layer of blubber is sometimes two feet thick. 
 
1 6 HUMAN PHYSIOLOGY 
 
 ALCOHOL AND DIGESTION 
 
 Alcoholic Drinks and Digestion. Alcohol taken with food 
 causes an increase in the amount of saliva and gastric juice 
 secreted, but it seriously interferes with the work of the pepsin 
 if more than five per cent of the contents of the stomach is 
 alcohol. Alcohol also checks stomach digestion by paralyzing 
 the muscles of the stomach, and beer and wine contain acids 
 and other substances that very greatly hinder the work of the 
 ptyalin. On the whole, the rate of protein digestion is not 
 much changed by alcoholic drinks in small quantities, but 
 the digestion of the starch is greatly hindered. The whole 
 question of the effects of alcohol on the process of digestion 
 is of little practical importance, however, for alcohol so fre- 
 quently causes diseases of the digestive organs that it would 
 be unwise to take it into the alimentary canal, even though 
 it greatly aided digestion. 
 
 Effects of Alcohol on the Work of the Liver. The liver 
 manufactures bile and stores up sugar. It has besides a 
 third function, one connected with the uric acid and other 
 protein wastes of the body. The uric acid is poisonous to 
 the body, and if it is not removed from the blood, rheuma- 
 tism, gout, and other serious troubles follow. The liver 
 changes a considerable part of the iiric acid to urea^ which is 
 taken out of the body by the kidneys. 
 
 Alcohol not only produces the diseased condition of the 
 liver so commonly found in alcohol users (page 102), but it 
 sometimes interferes especially with the manufacture of urea 
 in the liver. In some persons alcohol even in very small 
 amounts (the amount that one would get in a glass of beer) 
 seriously hinders the liver in its work of changing uric acid to 
 
DIGESTION, ABSORPTiON, AND OXIDATION \\J 
 
 urea. A large part of the uric acid is then left in the blood 
 to bring about its evil consequences^ 
 
 Summary. Foods are digested, or split by enzymes, to 
 make them dissolve and pass through the walls of the alimen- 
 tary canal. 
 
 Starch is split into malt sugar by ptyalin in the mouth and 
 stomach and by amylopsin in the intestine. The malt sugar 
 and the sugar that we eat are split in the intestine into 
 grape sugar. This grape sugar is then absorbed and carried 
 to the liver, where it is stored until it is needed by the cells. 
 Within the cells the grape sugar is burned, and water and 
 carbon dioxid come out of the cells as wastes. The cells 
 obtain energy from the sugar. 
 
 Proteins are split into peptones by pepsin in the stomach 
 and by trypsin in the intestine. They furnish energy and 
 building material to the cells, and are broken up into water, 
 carbon dioxid, and uric acid, and into a number of other 
 substances which contain the nitrogen of the protein molecule. 
 
 Fats are digested in the small intestine. They are burned 
 to carbon dioxid and water in the cells, to which they give 
 energy. 
 
 After digestion the foods are absorbed and carried by 
 the blood to the cells. Within a cell, part of the protein 
 food is used in building new protoplasm and the remainder 
 of the food is oxidized. In this process the food molecules 
 are torn down and new substances (the body wastes) are 
 formed from the atoms of these molecules. By the oxidation 
 of foods a cell gains energy. 
 
 Cells must have a constant supply of food, and there is in 
 the body a great store of fat for use in times of sickness or 
 when food cannot be obtained. 
 
 Alcoholic drinks increase secretion but hinder the action of 
 
1 1 8 HUMAN PHYSIOLOGY 
 
 the enzymes, and on the whole make the process of digestion 
 slower. They also produce serious results by keeping the 
 liver from changing uric acid to urea. 
 
 QUESTIONS 
 
 Why must foods be digested? What is digestion ? What kind of 
 changes do the food molecules undergo during digestion? What is 
 an enzyme? Name some of the digestive enzymes. 
 
 What enzyme is in the saliva and what kind of food is digested in 
 the mouth ? To what is this foo'd changed ? Give three reasons for 
 eating slowly. What enzyme is in the stomach? What kind of 
 foods are digested in the stomach? To what are they changed? 
 How long does food remain in the stomach ? What do the stomach 
 muscles do during this time? What effect has the acid of the 
 stomach on the ptyalin? 
 
 What digestive juices work on the foods in the small intestine? 
 Name the three enzymes in the pancreatic juice. What does the 
 amylopsin do? To what are all the starches and sugars finally 
 changed in digestion? What does the trypsin do* the steapsin? 
 What is the function of the bile ? 
 
 What is absorption ? Where are the foods taken after absorption ? 
 In what way does a cell use part of the protein food? What is done 
 with the remainder of the food ? What is oxidation ? What happens 
 to the food molecules during oxidation? What becomes of the atoms 
 that were in the food molecules? 
 
 What wastes are formed when sugar and fat are burned within the 
 cell ? when proteins are burned in the cell ? Which of these wastes 
 are poisonous? How do they leave the body? What does a cell 
 gain by burning food? 
 
 Why is it necessary to have food stored in the body? Where is 
 sugar stored? In what form is the chief store of food in the body? 
 Where in the body is the fat deposited? How is fat used by animals 
 that sleep through the winter? Where does the camel have a store 
 
DIGESTION, ABSORPTION, AND OXIDATION 119 
 
 of fat and why does it need this fat? Why do animals that live in 
 cold climates need a layer of fat on the body? ' 
 
 What effect has alcohol on the secretibn of saliva and gastric juice? 
 on the rate of digestion of proteins? of starch? Why is it unwise 
 to take alcohol into the alimentary canal? What are the three func- 
 tions of the liver? What effect has alcohol on one of these functions ? 
 What diseases are caused by this? 
 
 If a cell had fats and carbohydrates, could it live without proteins? 
 Why? If it had proteins and fats, do you think it could live without 
 carbohydrates, or if it had proteins and carbohydrates, could it live 
 without fats ? Give a reason for your answer. 
 
 A man had trouble in digesting fatty food. What enzyme was 
 weak in his digestive juices? 
 
 Malt contains an enzyme that does the same work as ptyalin and 
 amylopsin. A man who had stomach indigestion took malt to relieve 
 the difficulty. What mistake did he make ? What enzyme should he 
 have taken? 
 
 Suppose there is trouble in digesting starch. What other food can 
 be eaten that will give the cells grape sugar ? 
 
 What enzyme is lacking when there is trouble in digesting sugar, or 
 sweet materials like candy and cake that contain much sugar? Would 
 the use of malt or pepsin relieve the trouble? Is it possible to furnish 
 the cells with grape sugar without eating sugar? How? 
 
 What enzymes are mainly employed in digesting the following 
 foods : potatoes ; maple syrup ; butter ; cheese ; beans ; lean meat ; 
 fat meat ? 
 
 Find out what enzymes you can buy in a drug store. Do any ani- 
 mals have enzymes that we do not have ? Do plants have enzymes ? 
 
CHAPTER X 
 
 DIETETICS 
 
 A food may be defined as a substance that can be di- 
 gested ; l that can furnish the cells with either building material 
 or energy ', or with both building material and energy ; and that 
 does not injure the cells. Coal contains energy, and dyna- 
 mite contains great quantities of energy ; but the diges- 
 tive enzymes cannot split the molecules of coal and dynamite, 
 so these substances are of no use for food. Opium can be 
 burned in the cells, and of course must furnish heat to the 
 cells. Yet opium is not a food but a poison, because the 
 injury done by it to the cells is many times greater than 
 the good done by the little energy which it yields. A true 
 food not only must furnish energy, but also must not injure 
 the cells. 
 
 In dietetics we have, therefore, two problems. For our 
 food we must choose substances that can be digested without 
 injury to the digestive organs^ and substances that will supply 
 the needs of the body ivithout injuring it. 
 
 THE CARE OF THE DIGESTIVE ORGANS 
 
 Most digestive troubles are related to infections of the 
 tonsils, teeth, or other parts of the digestive system ; to de- 
 rangement of the nervous control of the digestive organs ; or 
 to the putrefaction or fermentation of food in the alimentary 
 
 1 A few foods, e.g. grape sugar, and some of the ingredients of soups, are in 
 such a form when eaten that they can be absorbed without digestion. These, of 
 course, need no digestion. 
 
 1 20 
 
DIETETICS 
 
 121 
 
 canal. Much of the hygiene of these organs is, therefore, 
 connected with the treatment of other parts of the body, and 
 less of it than was formerly supposed relates to eating habits 
 and the selection and preparation of food. 
 
 Infections with Pus-forming Bacteria. In many persons the 
 gums, teeth, or the bones of the jaw about the roots of the 
 teeth are infected with pus-forming bacteria. The tonsils also 
 are infected with these bacteria in an amazing number of 
 persons. In many of these cases the stomach and intestine 
 are deranged by the pus and germs that are constantly swal- 
 lowed, and by the toxins that are absorbed into the blood, 
 and relief from the digestive troubles can come only from the 
 removal of the infection in the mouth and throat. Chronic 
 infections of the appendix and gall bladder are also often 
 responsible for the failure of the digestive organs to function 
 as they should. 
 
 Defective Nervous Control of the Digestive Organs. If the 
 nervous system is deranged, the digestive organs that are 
 under its control often fail to function properly. Living at a 
 high tension, lack of sleep, fatigue, worry, anger, sorrow, 
 eye-strain, a chronic infection in some part of the body, or 
 anything else that upsets the nervous system may therefore 
 cause trouble with the digestion of the foods. When digestive 
 ailments are due to the general condition of the nervous 
 system, the remedy of course lies in the restoration of the 
 nervous system to a proper working condition. 
 
 On the other hand, a deranged condition in the digestive 
 organs may cause nervous. troubles or intensify them. Hard 
 or coarse food like raw vegetables or unripe fruits may so 
 irritate the nerves of the stomach and intestine as to cause 
 convulsions or even death in a young child, and one promi- 
 nent investigator believes that, in certain persons with hyper- 
 
122 HUMAN PHYSIOLOGY 
 
 sensitive nervous systems, the retained intestinal wastes 
 produce their evil effects by over-stimulation of the intestinal 
 nerves, that the bulky solid masses so irritate the nerve 
 endings that they cause the entire nervous control of the 
 digestive system to be upset and that in this way they pro- 
 duce the headaches and other symptoms that often accom- 
 pany a constipated condition. 
 
 Putrefaction and Fermentation of the Food in the Alimen- 
 tary Canal. If there is a lack of acid in the gastric juice, 
 bacteria may grow in the stomach and upper intestine and 
 cause trouble by fermenting the carbohydrates and fats. 
 Putrefaction of the proteins is an even more common cause 
 of trouble, if the wastes are not moved along the intestine 
 and promptly eliminated from the body. 1 
 
 The possibility that in some cases the chief evil resulting 
 from the retention of the intestinal wastes is the irritation of 
 the nervous system has been referred to above, and some 
 physicians advise against large quantities of coarse foods for 
 certain persons with very sensitive nervous systems. 
 
 1 The importance to the health of the prompt movement of the food along 
 the alimentary canal cannot be too strongly emphasized. It has generally been 
 taught that if the intestinal muscles are slow in their work, the bacteria that are 
 always present in the alimentary canal will produce offensive gases that will be 
 carried to the lungs and given off in the breath, and that substances that will 
 poison the whole body will be absorbed from the intestine. 
 
 Coarse vegetables, fruits (especially if the skins are eaten), corn meal, oatmeal, 
 and whole wheat bread furnish considerable amounts of indigestible matter which 
 stimulate the muscles in the walls of the alimentary canal and cause them to move 
 the food along. Drinking plenty of water softens the intestinal contents and 
 makes it easier for them to move onward, and exercise is beneficial to most per- 
 sons whose intestinal muscles are less active than they should be. Most im- 
 portant of all, however, is regularity in emptying the bowel. If this is done at a 
 certain time each day, the nerves and muscles of the intestine fall into a rhythmic 
 activity that insures a regular removal of the body wastes. 
 
DIETETICS 123 
 
 Keeping the Digestive Organs in Health. The following 
 rules may be helpful in keeping /the digestive organs in 
 health : 
 
 1. Eat slowly and chew the food well. This helps in giving 
 the nervous system an opportunity to settle down and control 
 the digestive organs as it should. It is, of course, only one 
 phase of a quiet, orderly life as contrasted with a life of 
 worry and strain. 
 
 2. Eat a reasonable amount at each meal. The body must 
 have a certain amount of food, and if only a little is eaten at 
 one meal too much is likely to be eaten at another. Break 
 fast is the meal that is most likely to be too scant. 
 
 3. Eat different kinds of food at each meal. If only one 
 kind of food is eaten, all the work is thrown on one enzyme. 
 Too much fat may give the steapsin more work that it can 
 do, while the amylopsin is entirely idle because no starchy 
 food was eaten. Eating a great amount of candy at one 
 time gives the sugar-digesting enzyme more sugar than can 
 be digested for hours, while the other enzymes have nothing 
 to do. This has exactly the same effect as eating too much, 
 for in either case digestion will be long delayed. School 
 children often injure their digestive organs by eating such 
 foods as candy, pickles, and pastry. Some of these foods are 
 injurious because they are taken in too great quantities, and 
 some are indigestible and injurious in any quantity. 
 
 4. Eat only at meal time. After digestion, the glands of 
 the alimentary canal should have time to rest and prepare a 
 supply of enzymes for the next meal. Eating between meals 
 also dulls the appetite at mealtime, and we have already 
 seen (page 100) how hunger and a good appetite assist in 
 causing an abundant flow of digestive juices. 
 
 5. Drink plenty of water both at mealtime and between 
 
124 HUMAN PHYSIOLOGY 
 
 meals. Water, either hot or cold, stimulates the secretion of 
 the gastric juice and hastens the digestion of the food. It 
 softens the intestinal contents and helps in their onward 
 movement. At least 4 pints of water a day are considered 
 advisable for an adult. 
 
 6. Do not talk about unpleasant things at mealtime. This 
 interferes with the secretion of the digestive juices (page 101). 
 
 7. Exercise regularly. Any one who does not exercise is 
 almost certain to surfer from indigestion (page 74). 
 
 8. Do not overwork or overstudy. Either overwork or 
 overstudy will bring on indigestion. Probably the nervous 
 system is first injured, and the trouble with the digestive 
 organs comes from a lack of proper -nervous control. 
 
 9. Give tJie eyes proper care. Many cases of headache and 
 stomach trouble are cured at once by fitting the eyes with 
 proper spectacles or eyeglasses. Probably bad eyesight, like 
 overwork, injures the nervous system, and the nervous sys- 
 tem then fails properly to regulate the digestive organs. 
 Fitting the eyes with glasses is of course far more important 
 for those who do close work than for those whose work puts 
 no strain on the eyes. 
 
 10. See that the intestinal wastes are promptly removed 
 from the body (page 122). 
 
 AMOUNTS AND KINDS OF FOOD NEEDED 
 
 An adequate diet must supply the energy needs of the 
 body ; it must furnish the protein needed for building mate- 
 rials ; it must contain the minerals and vitamins necessary to 
 the cells; and it should have sufficient bulk to cause the 
 wastes to be moved promptly along the intestine. It is very 
 easy to select a diet that will be lacking in some of these 
 
DIETETICS 125 
 
 particulars. Therefore, a study of foods and diets usually 
 yields great returns in health. The protein supply is one of 
 the important elements in the diet, and we shall first discuss 
 certain important dietetic facts relating to the proteins of the 
 food. 
 
 Proteins of Different Value for Building Purposes. When 
 proteins are digested, they are broken into proteoses and pep- 
 tones, and before they are absorbed the peptones are split 
 into still smaller molecules called amino-acids, many differ- 
 ent kinds of which are known. Different proteins yield 
 these acids in different proportions when they are broken up, 
 and some proteins yield only certain ones of them. It is 
 now known that we need for the nourishment of our bodies 
 not a certain amount of protein, but certain amounts of these 
 different amino-acids. It has long been known that gelatin 
 alone will not nourish the body, and recent experiments have 
 shown that other proteins differ in their power to supply the 
 needs of the cells. 
 
 In these experiments, rats were fed with a suitable mixture 
 of minerals, carbohydrates, fats, and some single protein. 
 It was found that a certain protein (zein), which was obtained 
 from corn and which lacks certain amino-acids, would not 
 support life. Other proteins (gliadin and hordein), which 
 were obtained from wheat, rye, and barley, kept young rats 
 alive but did not enable them to grow. The proteins from 
 peas and beans when fed alone supported life, but were also 
 inadequate for growth. Other proteins (casein from milk, 
 glutenin from wheat, lactalbumin from milk, vitellin . from 
 the yolk of eggs) proved adequate for both the maintenance 
 and growth of animals. 
 
 These experiments clearly indicate that for building pur- 
 poses some proteins are more valuable than others. The 
 
126 HUMAN PHYSIOLOGY 
 
 proteins of meat, milk, and eggs are of good quality ; speak 
 ing generally, the proteins of grains, peanuts, and soy beans 
 are worth, for building purposes, about half as much as those 
 of meat and milk; and the proteins of peas and beans are 
 about half as valuable as those of grains. 
 
 Amount of Protein needed by the Body. From what has 
 been said above, it will be evident that it is impossible to say 
 that any definite amount of protein is required by the body 
 unless the kind of protein is specified. But where a mixed 
 diet is taken, so that the proteins come from various sources, 
 men have usually eaten daily about 4 ounces of dry protein, 
 or enough to yield about 460 Calories l of heat. 
 
 But notwithstanding all the feeding experiments that have 
 been carried on with men and lower animals, and in spite of 
 all the mass of human experience with different diets, food 
 authorities still disagree as to the amount of protein that the 
 diet should contain. From the results of recent studies, 
 one investigator concludes that pellagra is due to a lack of 
 the high-quality proteins furnished by meat, eggs, and milk. 
 It has been announced also, as the result of investigations on 
 animals, that the " war edema " common in European coun- 
 tries where there was a shortage of food is due to a lack of 
 protein and not to a lack of vitamins or other elements in 
 the diet ; and it has been found difficult to increase the weight 
 of persons emaciated from starvation without liberal protein 
 feeding. 
 
 1 A Calorie is the amount of heat required to raise the temperature of one 
 liter of water i C. Not all the energy of the foods is used in warming the body, 
 part of it being used in building protoplasm, enzymes, and other substances, and 
 part of it by the muscles doing work. But the easiest way of measuring the 
 aiiount of energy in food is to try how much heat it will give off when it is 
 burned. The amount of energy in food, therefore, is always given in Calories, 
 or the amount of heat which it yields when burned. 
 
DIETETICS 12; 
 
 On the other hand, many authorities on foods believe that 
 a sufficient amount of protein is provided in any normal diet 
 and that a high-protein diet causes putrefaction in the in- 
 testine, overloads the system with protein wastes, and is a 
 cause of disease of the kidneys and other parts. 1 Persons 
 taking a diet high in protein are usually heavy eaters of meat, 
 and from the present state of our knowledge it would seem 
 wise to eat only moderately of this food and to take daily 
 not more than enough protein to yield from 350 to 400 Calo- 
 ries of heat (page 353). 
 
 Amount of Energy needed by the Body. The body not 
 only requires building material, but it must have energy. 
 This is secured by the oxidation of the food within the cells. 
 A man doing moderately heavy work needs food enough to 
 furnish about 3000 Calories. Women need somewhat less 
 than men, a twelve-year-old child as much as an adult, and 
 young people from fourteen to eighteen more than at any 
 other time in life. 
 
 Only the proteins supply building materials, but all the 
 different classes of foods yield energy to the body. After 
 the building wants of the body are supplied, it is better to 
 use, for energy, carbohydrates and fats rather than protein, 
 as these foods are cheaper and leave no wastes except 
 water and carbon dioxid. After the building wants are 
 supplied, there are no exact proportions in which protein, 
 carbohydrate, and fat must be used, but a reasonable amount 
 of each is advisable. A fairly liberal supply of fat seems to 
 
 1 One investigator divided rabbits into two lots and fed them the same, except 
 that one lot had additional protein in the form of milk casein. Those on the 
 high-protein diet developed kidney disease, while the others remained free from 
 it. When the experiment was repeated and the additional protein given in the 
 form of soy beans, the results were the same. 
 
128 HUMAN PHYSIOLOGY 
 
 be conducive to health, and those who have had experience 
 in feeding consumptives believe it raises the resistance of 
 the body to germs. A given amount of fat will yield more 
 than twice as much energy as the same amount of protein or 
 carbohydrate. 
 
 Minerals in the Diet. Minerals are required in the body 
 only in small amounts, but these small amounts are as neces- 
 sary for health as a proper supply of , protein or other foods. 
 Among the minerals most frequently lacking in our foods are 
 calcium, phosphorus, and iron. 1 In general, these minerals 
 are found in vegetables, fruits, eggs, milk, 2 and the outer 
 layer of grains. They are lacking in meat, and persons who 
 live chiefly on meat and white bread are especially likely to 
 suffer because of a lack of minerals. Boiling vegetables in 
 water removes much of the mineral matter from them, and 
 vegetable soups are valuable for the minerals they contain. 
 Baking potatoes and other vegetables retains the minerals in 
 them, and this method of cooking should be more commonly 
 employed. 
 
 The whole question of minerals in the diet is an important 
 one, for recent studies indicate that many persons fail to get 
 sufficient mineral matter in their food, and according to one 
 estimate one half the people in the United States are suffer- 
 ing from calcium starvation. In limestone regions this min- 
 
 1 There is much evidence to indicate that goiter, which is common in some 
 regions and rare or unknown in others, is due to a lack of iodine in the food and 
 water. It has been reported from Switzerland that this disease can be prevented 
 in goitrous regions by using salt from regions where the disease does not occur, 
 and experiments made by the United States Public Health Service in Akron, 
 Ohio, seem to prove that goiter can be kept from developing in school children 
 by giving small weekly doses of iodine. 
 
 2 Milk contains only small quantities of iron, and babies that are kept on an 
 exclusive milk diet too long lack this important mineral. 
 
DIETETICS 129 
 
 eral is supplied by the water, but in other regions a liberal 
 supply of leaf vegetables and milk 'is needed to make sure 
 that a sufficient amount of it will be secured. Milk is par- 
 ticularly rich in calcium, and children who are deprived of 
 milk are almost sure to lack this element. 
 
 Vitamins. The existence of vitamins has only recently 
 been discovered, and our knowledge of them and of their dis- 
 tribution in the various foodstuffs is as yet far from complete. 
 Nearly all of us get an ample supply of the antineuritic 
 vitamin, but it is advisable to plan the diet so that a fair 
 supply of the others will be insured. This can be done by 
 including fresh fruits, fresh vegetables (especially leaf vege- 
 tables), and fresh milk in the diet. More home gardens and 
 more milk cows and milk goats would greatly improve the 
 diets of many families. On page 352 a table showing the 
 distribution of vitamins in some common foodstuffs is given. 
 In canning and drying fruits and vegetables, the vitamins are 
 usually partially destroyed. Heating with an alkali (as in 
 baking biscuit or corn bread with soda, or boiling vegetables 
 with soda to make them tender) destroys the vitamins almost 
 entirely. 
 
 Some Suggestions as to Diet. No hard and fast rules can 
 be given for selecting a diet, but the following suggestions 
 may be of aid : 
 
 1. Eat meat y but only in moderation. This will give the 
 body some of the less common amino-acids furnished by 
 meats and at the same time will permit other foods to be 
 taken that will furnish bulk, minerals, and vitamins. 
 
 2. Use plenty of milk. This will supply high-grade pro- 
 tein, lime, and the fat-soluble vitamin. 
 
 3. Eat vegetables, especially leaf vegetables. These supply 
 minerals, vitamins, and bulk. A varied diet is more likely to 
 
130 
 
 HUMAN PHYSIOLOGY 
 
 FlG. 61. Starch grains in the cells 
 of a potato. Raw starch is in hard 
 little grains that are almost indiges- 
 tible, but cooking causes the grains to 
 soften and burst. 
 
 supply all the materials needed 
 by the body than a restricted 
 one, and the vegetables are the 
 foods most likely to be eaten in 
 insufficient amounts. 
 
 4. Avoid an excess of sugar. 
 This not only deranges the di- 
 gestion of many persons, but it 
 supplies no protein, minerals, 
 vitamin, or bulk. If much sugar 
 is taken, other foods needed for a 
 good diet are likely to be omitted. 
 
 5. Eat enough food. Enough 
 should be eaten 
 
 to keep up the 
 weight and vigor of the body. It is esti- 
 mated that about 30 per cent of children 
 fail to take enough food (pages 353-355). 
 
 The Cooking of Foods Cooking breaks 
 up the cell walls of plants and the con- 
 nective tissue of meats, thus causing these 
 foods to fall to pieces more easily, so that 
 the digestive juices have a better opportu- 
 nity to do their work. Raw starch is in 
 hard little grains that the enzymes can 
 hardly penetrate and which are almost in- 
 digestible. Cooking causes these grains to 
 soften, swell, and burst, making the starch 
 readily digestible. Thorough cooking of 
 meat is important to kill certain parasites that 
 may be in it. Pork may contain a very tiny 
 worm called the trichina, and the young of 
 
 FIG. 62. A trichina 
 lying among the mus- 
 cle cells. It is found 
 in pork, and pork 
 should be thoroughly 
 cooked before it is 
 eaten. 
 
DIETETICS 
 
 the tapeworm is found in both pork and beef. If trichinae 
 
 are swallowed alive, they breed in the intestine and the young 
 
 bore through the intestinal walls 
 
 and reach the muscles, causing 
 
 the disease called trichinosis. The 
 
 young of the tapeworm fastens 
 
 itself to the intestinal wall, absorbs 
 
 the digested food, and grows into a 
 
 long worm. 
 
 ALCOHOL AS A FOOD 
 
 FIG. 63. Tapeworm. The young 
 
 of * ^P 6 1 is found in both 
 
 pork and beef. 
 
 The question is often asked 
 whether or not alcohol is a food. 
 
 On this point people Continually 
 
 disagree. One reason for the dis- 
 agreement is that different defini- 
 tions of the word " food " are used. A food is often defined 
 as a substance which can be burned in the body and will give 
 energy to the body. In this sense alcohol is a food, for in 
 moderate amounts it is oxidized in the body and gives heat and 
 strength to the muscles. The other definition of a food is that 
 given on page 120. This definition insists that a food not only 
 must furnish building material or energy, but also must not 
 injure the cells. According to this definition, it is certain 
 that alcohol in any but very small quantities is not a food, 
 for it works great harm to the cells, especially to the nerve 
 cells. 
 
 Whether or not alcohol in very small doses injures the 
 cells, is very uncertain. If you took a drop of alcohol into 
 your body, its effect would be so slight that you could not 
 notice it. Even if it injured your cells, you would never 
 
I 3 2 HUMAN PHYSIOLOGY 
 
 know it. If you took a spoonful of alcohol, probably you 
 still could not notice any effect on yourself. But if you 
 began the habit of drinking beer or wine or other alcoholic 
 drinks, it is certain that you would get enough alcohol to 
 injure your body decidedly. We do. not discuss whether a 
 very, very small amount of a poison like opium or belladonna 
 would injure the cells, and whether these drugs give energy 
 to the cells and are, therefore, foods. There is little more 
 reason for discussing whether or not alcohol is a food ; for, 
 used in the amounts taken by any one who drinks alcoholic 
 liquors, it is not a food but a poison. 
 
 Patent Medicines. Often we read, in advertisements, of 
 medicines that will cure cancer, consumption, dyspepsia, and 
 many others of our worst ills. These medicines will not do 
 what is claimed for them. If there were any medicines that 
 would cure cancer or consumption, the skillful physicians 
 and scientists who are at the heads of our medical colleges 
 and hospitals would know it, and they would be using them 
 and telling every one about these wonderful remedies. 
 
 Some patent medicines contain opium, which is soothing 
 and causes pain to be unnoticed, so that a person sometimes 
 thinks he is better, when his disease has not been affected at 
 all. Other patent medicines are very strong in alcohol, 
 as strong as, or stronger than, the most powerful alcoholic 
 drinks. A dose of some of these medicines contains enough 
 alcohol to affect the body decidedly, and the strengthening 
 effect that persons sometimes think they feel when they use 
 these " tonics " is nothing but the effect of the alcohol. Many 
 patent medicines of course contain useful drugs, but without 
 the advice of a physician it is unwise to take in among the 
 delicate little cells of our bodies any strong medicine whose 
 effects we do not understand. 
 
DIETETICS 133 
 
 QUESTIONS 
 
 Define a food. Why cannot coal be used for food ? opium ? 
 What two points must we keep in mind in choosing our foods ? 
 
 Name three causes of digestive disturbances. Discuss each of 
 these. Give some rules for keeping the digestive organs in health. 
 
 What must an adequate diet supply ? Into what are the proteins 
 split before absorption ? How do proteins differ as to the amino- 
 acids they yield ? Compare certain proteins as to their value for 
 building purposes. 
 
 Discuss conflicting ideas as to the advantages and disadvantages 
 of low- and high-protein diets. What article of food is usually eaten 
 in abundance by those living on a high-protein diet ? About how 
 much protein is it probably wisest to take daily ? 
 
 How much energy does a man doing moderate work require ? 
 At what time of life is most food needed ? Why should carbo- 
 hydrates and fats be used to supply the energy needs of the body ? 
 
 What minerals are most frequently lacking in the diet ? What 
 foods supply minerals in greatest amounts? In what foods are 
 minerals lacking ? What method of cooking conserves the minerals 
 in vegetables ? What foods supply particularly large amounts of 
 calcium ? What foods should be included in the diet to make sure 
 of a supply of vitamin ? 
 
 Give four rules for the selection of food. How does cooking 
 make foods more digestible ? Why should pork and beef be thor- 
 oughly cooked before eating ? 
 
 What two definitions are sometimes given for a food ? Accord- 
 ing to which of these definitions is alcohol, except possibly in the 
 very smallest quantities, not a food? Why is the discussion of 
 whether or not alcohol is a food of little practical importance ? 
 
 What injurious substances do some patent medicines contain? 
 Why is it not advisable to take medicine without the advice of a 
 physician ? 
 
134 HUMAN" PHYSIOLOGY 
 
 REVIEW QUESTIONS 
 
 Chapter VII. Give two reasons why the body needs food. Ol 
 what is all matter composed ? Of what are molecules composed ? 
 What is an element? a compound? Name the three classes of 
 foods. Give examples of foods of each class. How do these food 
 classes differ in chemical composition ? Mention some other things 
 that are necessary to the body. 
 
 Chapter VIII. Explain how a gland is formed and how it works. 
 Draw a diagram of the digestive system and label the different diges- 
 tive organs. What is the function of the stomach ? of the gastric 
 juice ? How long is the small intestine ? Name three secretions 
 that are emptied into it. Describe the villi. What is their function r 
 Name the accessory organs of digestion. Define : dentine ; enamel ; 
 pulp cavity ; incisor ; canine ; bicuspid ; molar. 
 
 Name and locate the salivary glands. What is the use of the 
 saliva ? What glands of the digestive system are known to be 
 affected by the nervous system ? What mental condition is favor- 
 able to a good digestion ? What trouble does alcohol cause in the 
 stomach ? in the liver ? 
 
 Chapter IX. Why must food be digested ? How are the food 
 molecules changed in digestion ? By what are they changed ? Tell 
 where the following enzymes are found, and what food each one 
 digests : ptyalin ; pepsin ; trypsin ; amylopsin ; steapsin. To what 
 are the proteins changed in digestion ? the starches and sugars ? 
 Why must a cell have protein ? What happens to the food mole- 
 cules when the foods are oxidized within the cells ? What becomes 
 of the atoms that were in the food ? What does a cell gain by 
 burning food ? What use is the fat in the body ? What effect has 
 alcohol on digestion ? on the work of the liver ? 
 
 Chapter X. Give some rules for keeping the digestive organs in 
 health. Define a. food. Give some causes of indigestion. How 
 much energy is needed by the body daily ? What foods supply 
 minerals in greatest abundance ? Give some rules for selecting a 
 diet. How much protein is needed daily ? Why, according to our 
 definition of a food, is alcohol not a food ? Why are patent medi- 
 cines dangerous ? 
 
CHAPTER XI 
 
 THE CIRCULATORY SYSTEM 
 
 FROM the time we are born until we die, the heart beats. 
 Day and night the blood flows through the body, passing out 
 from the heart, streaming in among the cells, and hastening 
 back to the heart. If because of disease or injury to the 
 body the heart stops, the body dies. If the blood is weak 
 and thin, the health of the body suffers, and if the blood is 
 allowed to escape from the body, life at once ceases. 
 
 Why does the heart beat? Why is the blood kept flowing 
 through the body? How does it help the cells to have the 
 blood passing by them ? Why are physicians so anxious that 
 the blood be kept strong and pure and that nothing be done 
 that will injure the heart ? Why could not the body continue 
 to live even though the heart should stop beating and the 
 blood should cease to flow? To answer these questions 
 intelligently, we must first of all understand the great laws 
 according to which the body lives. Our bodies must have 
 food and water, they must have oxygen, they must get rid of 
 their poisonous wastes, and they must have an even tempera- 
 ture, neither too hot nor too cold. Our bodies are composed 
 of cells, and each cell must have all of these things. 
 
 The Function of the Blood. The human body is a great 
 colony of cells. The food and water for all the cells in the 
 colony are taken in through the alimentary canal ; but there 
 must be some arrangement so that a cell in the brain or in 
 
 135 
 
136 HUMAN PHYSIOLOGY 
 
 the foot can get the food that has been prepared for it by the 
 digestive organs. Oxygen is taken in through the lungs ; 
 but the oxygen must be distributed all through the body to 
 the cells. The poisonous wastes leave the body through the 
 lungs and kidneys ; but the wastes that are produced in the 
 cells must be moved from the cells to the lungs and kid- 
 neys before they can be thrown out of the body. The heat 
 of the body is produced by burning food within the cells ; 
 but in certain inner parts of the body, like the liver and 
 muscles, there is too much heat, while in the outer parts of 
 the body there is not enough heat. There must, therefore, 
 be some way of distributing the body heat so that none of 
 the cells will be either too hot or too cold. 
 
 The function of the blood is to carry food, water, and oxyger* 
 to the cells, to carry wastes away from the cells, and to carry 
 heat from the warmer to the cooler parts of the body. As the 
 blood flows among the cells it feeds them and gives them 
 oxygen, picks up and carries away their wastes, cools the hot 
 cells, and warms the cells that are too cold. The body may 
 be very quickly killed by stopping the flowing of the blood 
 among the cells. 
 
 THE CIRCULATORY ORGANS 
 
 The flowing of the blood through the body is called the 
 circulation. The organs concerned in keeping up the circu- 
 lation are the circulatory organs. These are the heart (Fig. 
 70), the blood vessels (arteries, veins, and capillaries}, and the 
 lymphatic vessels (Fig. 66). 
 
 The Heart. The heart 1 is usually about the size of the 
 closed hand of the person to wham it belongs. It lies in the 
 
 J The heart is inclosed in a double-walled sac called $&& pericardium. (Fig. 
 82.) 
 
THE CIRCULATORY SYSTEM 137 
 
 thoracic cavity with its apex (point) to the left of the center 
 of the body. The walls of the heart are composed of muscle 
 cells, and within the heart are four cavities, two upper 
 cavities called auricles, and two lower cavities called ventri- 
 cles. The auricles have thin walls, for their task is the small 
 one of sending the blood down into the ventricles. The ventri- 
 
 DESCENDINQ 
 VENA CAVA DESCENDING VENA 0*V* 
 
 PULMONARY ARTEW 
 
 PULMONARY 
 VALVE CLOSED 
 
 FIG. 64. Diagram of the right side of the heart showing the working of the valves. 
 When the ventricle relaxes, the valves are as shown in A. When the ventricle con- 
 tracts, the valves are as shown in B. 
 
 cles, on the other hand, have thick walls because they have 
 the heavy work of forcing the blood through the body. The 
 function of the heart is to keep the blood circulating through 
 the body. 
 
 The Action of the Heart. Place your hand on your chest 
 and you can feel the heart beat. 1 What is it doing when it 
 beats ? It is pumping the blood through the body. 
 
 The walls of the auricles first contract and draw inward on 
 
 1 When the ventricles contract, the apex of the heart is pressed more forcibly 
 against the wall of the chest. This causes the beat, which can be felt by placing 
 the hand on the chest over the heart. The pulse that is felt in the arteries is a 
 wave that travels out in the blood within an artery when the ventricles force the 
 blood out of the heart. 
 
CAPILLARIES OF 
 CHEST AND ARMS 
 
 DESCENDING VENA 
 
 PULMONARY 
 
 RIGHT 
 
 DESCEND! NO 
 AORTA 
 
 CAPILLARIES OF 
 
 STOMACH, INTESTINE 
 
 AND SPLEEN 
 
 CAPILLARIES 
 OF LEGS 
 
 FIG. 65. Diagram of the circulation of the blood in the body. 
 138 
 
LYMPHATIC VESSEL 
 
 THORACIC DUCT 
 
 LYMPHATIC VESSEL 
 FROM INTESTINE 
 
 FIG. 66. The heart and the principal vessels of the body. 
 539 
 
140 
 
 HUMAN PHYSIOLOGY 
 
 the blood, forcing the blood into the ventricles. The auricles 
 then relax and the powerful walls of the ventricles contract, 
 squeezing the blood out into the arteries. The ventricles 
 now relax and for a moment the heart rests. Then the 
 auricles again contract, completing the filling of the ventricles ; 
 the ventricles squeeze the blood out into the arteries, and so 
 the process is repeated again and again. In one day the heart 
 does as much work in sending the blood through the body as 
 its owner would do in walking eight and one half miles on a 
 level road. 
 
 FIG. 67. These gates work like the valves of the heart. When the boy pushes on 
 them one way, they open, but when he pushes on them the other way, the chains hold 
 them so that they will not open. 
 
 The Rate of the Heart Beat. In an adult the heart usually 
 beats from seventy to eighty times a minute. It is faster in 
 women than in men, and varies in different individuals, some 
 persons naturally having a faster heart beat than others. 
 The rate of the heart beat varies also with age, 1 with rest and 
 exercise, and with health and disease. You should count 
 your own heart beat several times so that you will know its 
 average rate. Then in sickness you will know how much it 
 varies from its natural beat. 
 
 1 The heart beat at different ages is about as follows: at birth, 130-140; first 
 year, 115-130; second year, 100-115; third year, 90-100; seventh year, 85-90; 
 fourteenth year, 80-85; adult life, 70-80; old age, 60-70; extreme old age, 
 75 -8o. 
 
THE CIRCULATORY SYSTEM 141 
 
 The Valves of the Heart. In the heart are four valves, 
 two between the auricles and the ventricles (Fig. 64), and two 
 at the openings of the great arteries (aorta and pulmonary 
 artery), which lead out from the ventricles. All four valves 
 are made of connective tissue, and their function is to keep the 
 blood from flowing backward. 
 
 The valves between the auricles and ventricles work like 
 little doors (Fig. 67) which open only downward into the 
 ventricles. Little ligaments hold the valves so that they 
 cannot be pushed upward into the auricles. The blood can 
 therefore flow from the auricles into the ventricles, but 
 when the ventricles contract, the blood pushes up under 
 the valves and lifts them so that the openings between the 
 auricles and ventricles are closed. Since the blood cannot 
 pass back into the auricles, it must flow out into the arteries 
 when the ventricle walls contract. 
 
 Each of the valves at the entrance 
 to the great arteries is made of three 
 loose pockets on the wall of the 
 artery. The pockets open upward, 
 and as the blood leaves the ventricles 
 it readily flows over them. But when 
 the ventricles relax and the blood 
 starts to run back into the heart, the FlG - 68 - The ba se of the aorta 
 pockets fill with blood and hang out in ^h^s,^ ? 
 
 the Opening of the artery SO that they backward into the heart it catches 
 
 touch each other. They thus close in the pockets, which then swing 
 
 out and close the opening in the 
 
 the passageway and keep the blood aort a. see also Figure 6 4 . 
 from flowing back into the heart. 
 
 Blood Vessels. Arteries are blood vessels in which 
 the blood flows away from the heart. Veins are blood 
 vessels in which the blood flows to the heart. Capillaries 
 
142 
 
 HUMAN PHYSIOLOGY 
 
 are small vessels through which the blood flows from the 
 arteries to the veinsl The two great arteries (aorta and 
 pulmonary artery) that leave the heart divide into smaller 
 arteries. These smaller arteries divide again and again, 
 until finally they end in exceedingly small capillaries, which 
 
 FIG. 69. The blood flows from the arteries through the capillaries into the veins. 
 
 are everywhere among the cells. After running in among 
 the cells the capillaries begin to unite. More and more 
 of them flow together and form small veins. The small 
 veins continue to unite and form larger veins until they 
 are joined into the large veins, the vena cavce and the 
 pulmonary veins, which empty into the heart (Fig. 65). You 
 must clearly understand that in the circulation the blood does 
 not get out of the blood vessels, but passes through the capil- 
 
 1 To THE TEACHER : If a microscope can be procured, the teacher should 
 not fail to have his pupils observe the fascinating sight of the blood corpuscles 
 shooting along in the capillaries. One of the best places to see this is in the 
 tail of a tadpole. Lay the tadpole on a flat piece of glass, and it will usually 
 become quiet enough in a little while to allow the microscope to be focused on 
 the capillaries. 
 
THE CIRCULATORY SYSTEM 
 
 143 
 
 laries from the arteries to the veins (Fig. 69). So abundant 
 are the capillaries that the finest needle thrust into the body 
 tissues cuts and breaks many of them. 
 
 JUGULAR VE 
 (FROM HEAD) 
 
 SUBCLAVIAN ARTERY. 
 (TO ARM) 
 
 SUBCLAVIAN VEIN.^'/; 
 (FROM ARM) 
 
 DESCENDING VENA 
 
 ARTERV 
 (TO ARM) 
 
 'DESCENDING AORTA 
 
 FIG. 70. The heart and the bases of the great wssels. 
 
 The Walls of the Blood Vessels. The walls of the arteries 
 are composed chiefly of connective tissue and of muscle 
 fibers which are placed circularly about the vessels. When 
 the muscle fibers in the wall of an artery contract, they make 
 the opening of the artery smaller, and a less amount of 
 blood passes through it. By changing the size of the 
 
144 HUMAN PHYSIOLOGY 
 
 arteries, some of the blood 1 can be cut off from a part of the 
 body that is resting and needs only a little blood, and can be 
 sent to a part of the body that is working and needs a larger 
 blood supply. 
 
 The walls of the veins are thinner than the walls of the 
 arteries, and have in them more connective tissue and less 
 muscle. The walls of the capillaries are very thin, con- 
 sisting of only one layer of thin flat cells and a few fibers of 
 connective tissue. 
 
 The Course of the Circulation. The heart is a double organ. 
 The right ventricle sends the blood through the lungs to the 
 left auricle. The left ventricle sends the blood through the 
 body to the right auricle. In a complete circulation the blood 
 therefore passes twice through the heart. By studying the 
 diagram on page 138, you will find that the course of the 
 blood, beginning with the right auricle, is as follows : 
 
 From two great veins (the venae cavae) into the right 
 auricle. 
 
 From the right auricle into the right ventricle. 
 
 From the right ventricle into the pulmonary artery and its 
 branches. 
 
 From the branches of the pulmonary artery into the 
 capillaries of the lungs. 
 
 From the capillaries of the lungs into four pulmonary veins. 
 
 From the pulmonary veins into the left auricle. 
 
 From the left auricle into the left ventricle. 
 
 From the left ventricle into the aorta and its branches. 
 
 From the branches of the aorta into the capillaries of 
 the body. 
 
 1 It is estimated that the capillaries of the intestine can hold all the blood in 
 the body, and that if all the vessels in the body should relax at one time, it would 
 take several times as much blood as there is in the body to fill all of them. 
 
THE CIRCULATORY SYSTEM 145 
 
 From the capillaries of the body into the smaller veins. 
 
 From the smaller veins into the two great veins 1 called the 
 ascending and descending venae cavae, and then back into 
 the right auricle. 
 
 Day and night the blood circulates through the body, pass- 
 ing out from the heart through the arteries, flowing through 
 the capillaries and returning to the heart by way of the veins. 
 Day and night the heart pumps away, 2 keeping the current 
 of blood flowing through the vessels. No other organ of the 
 body is so hard-worked as the heart, which pauses to rest 
 only between its beats. 
 
 The Nervous Control of the Circulation. The heart has two 
 sets of nerves, one set quickening its beat and the other 
 set causing it to beat more slowly. Through these nerves, 
 the rate of the heart beat is controlled. 
 
 The muscles in the walls of the arteries are also supplied 
 with two sets of nerves. One set of nerves causes the 
 muscles in the arterial walls to contract, and one set causes 
 
 1 From the diagram on page 1 38 it can be seen that the portal circulation, or 
 the circulation through the liver, is peculiar in that the blood passes through two 
 sets of capillaries. The blood that has passed through the capillaries of the 
 stomach, intestine, pancreas, and spleen is collected into one great vein (the 
 portal vein) and taken to the liver, where it again spreads out in the capillaries 
 among the liver cells. It is then collected into the hepatic vein and goes on 
 to the heart. Sugar is stored in the liver, and the advantage of this arrange- 
 ment is that the blood carrying the absorbed sugar passes through the liver 
 before it goes to the rest of the body. The blood that comes to the liver through 
 the portal vein has lost its oxygen in the first set of capillaries, so the liver has 
 another supply of blood coming to it through the hepatic artery (page 138) to 
 furnish it with oxygen. 
 
 2 The circulation time of the blood through the body (from left ventricle to 
 right auricle) is on an average something like a minute. The circulation time 
 through the lungs (from right ventricle to left auricle) is about twelve or fifteen 
 seconds. This means that twice in eyery minute and a quarter the heart must 
 pump all the blood in the body through itself. 
 
146 
 
 HUMAN PHYSIOLOGY 
 
 them to relax. The size of tl>e openings in the arteries, 
 and the amount of blood going to the different parts of the 
 body, can thus be regulated by the nervous system. 
 When a person blushes, the little arteries in the skin of the 
 
 FIG. 71. The vessels of the foot. Only a few of the arteries are shown. 
 
 face open and allow a larger quantity of blood to come into 
 them. From this you can understand how quickly the size 
 of the arteries can be changed, and, when you think of the 
 cause of blushing, you will know that the muscles in the 
 blood vessels can be affected by the nervous system. 
 
 THE BLOOD AND LYMPH 
 
 The blood makes up about one nineteenth of the body 
 weight. It is composed of a liquid part, the plasma, and 
 of red and white blood corpuscles that float in the plasma. 
 On an average about five million red corpuscles and 
 ten thousand white corpuscles are found in a drop of 
 blood the size of the head of a pin. There are, there- 
 
THE CIRCULATORY SYSTEM 147 
 
 fore, about five hundred red corpuscles to one white cor- 
 puscle. 
 
 The Plasma. The blood plasma is composed mainly of 
 water. Dissolved in the plasma are the different foods, aalts, 
 and other materials used by the cells. 
 The function of the plasma is to carry 
 foods and wastes, and to form a 
 liquid in which the corpuscles can float 
 about in the blood vessels. 
 
 The White Corpuscles. The white 
 corpuscles can change their shape. 
 They are the only cells of the body, 
 except the muscle cells, that have 
 the power of movement, 1 and more FlG ' 72 ' Red and white blood 
 
 corpuscles. 
 
 than any other of our cells they re- 
 semble the little one-celled animals about which we studied in 
 the first chapter. They often escape from the capillaries 
 by passing through between the cells of the capillary wall 
 (Fig. 73). For a long time it was thought that the white 
 corpuscles had no definite work to do, but roamed about 
 while the other cells were busy, each at its particular 
 task. Now it is known that the function of the white cor- 
 puscles is to kill the disease germs which get into the body 
 among the cells (Fig. 137). 
 
 The Red Corpuscles. The red corpuscles are small, cir- 
 cular disks with a hollow in each side, as you see in Figure 72. 
 Most of them are formed in the marrow of the spongy bone 
 (page 42). Here 1 some of the cells lose their nuclei, take 
 on the shape of corpuscles, and by and by float away in 
 the blood stream as red corpuscles. For some time they 
 circulate through the blood vessels, but finally die and 
 
 1 On ciliated cells (Fig. 6) the cilia move, but the cells as a whole do not. 
 
148 
 
 HUMAN PHYSIOLOGY 
 
 are broken up, chiefly in the spleen. Part of the broken 
 down materials of the red corpuscles leave 
 the body as the coloring matter of the 
 bile. It is estimated that every day 
 about fourteen billions of red corpuscles 
 die in the body, and as many new ones 
 are formed. 
 
 The Function of the Red Corpuscles, 
 The function of the red corpuscles is to 
 carry oxygen and to assist the plasma in 
 carrying carbon dioxid. The way in which 
 the red corpuscles carry oxygen is very 
 interesting. They have within them a 
 substance called hemoglobin. When this 
 is exposed to oxygen, as it is in the lungs, 
 each molecule of the hemoglobin unites 
 with a molecule of oxygen and carries the 
 oxygen away with it. Then, when the 
 corpuscle goes out in the capillaries among 
 the cells, the hemoglobin 1 gives up its oxy- 
 gen to the cells (Fig. 74). 
 
 The carbon dioxid is dissolved in both 
 the plasma and the corpuscles. It does 
 not, however, unite to any extent with the 
 FIG. 73- A white cor- hemoglobin of the corpuscles, as the oxy- 
 
 puscle escaping from a J 
 
 capillary. gen does, and a corpuscle can carry both 
 
 1 The way the oxygen is carried in the blood may be represented by compar- 
 ing the blood to a stream, the red corpuscles to little boat's in the stream, and 
 the hemoglobin molecules to little jars in the boat. In the lungs a molecule of 
 oxygen is placed in each of the jars ; out in the cap-illaries of the body the 
 oxygen is emptied out of the jars, and the little boat floats around to the lungs, 
 where each jar is again loaded with a molecule of oxygen. 
 
THE CIRCULATORY SYSTEM ^ 149 
 
 carbon dioxid and oxygen at the same time. 1 The carbon 
 dioxid injures the cells because it/ is itself poisonous, and 
 not by keeping the corpuscles from carrying oxygen to 
 them. 
 
 The Color of the Blood. Blood containing oxygen is bright 
 red in color, and blood without oxygen is dark, appearing 
 blue in the veins under the skin. This you can see by look- 
 ing at the veins in your forearm, which bring the blood from 
 the hand back to the heart. The blood gets its oxygen in the 
 lungs (Fig. 81) and loses it in the capillaries of the body. The 
 blood is therefore red in the pulmonary veins, in the left side 
 of the heart, and in the aorta and all its branches. It is 
 dark in the veins bringing the blood from the body to the 
 heart, in the right side of the heart, and in the pulmonary 
 artery. The same thing can be said more briefly thus : The 
 blood is red while going from the lungs to the body capil- 
 laries, and dark while going to the lungs from the body 
 capillaries. 
 
 The Lymph. The blood plasma soaks through the thin 
 walls of the capillaries and passes out among the body cells. 
 After the plasma gets outside the capillaries it is called 
 lymph. The lymph surrounds all the cells in the body and 
 fills all the little spaces between the cells. A fresh supply 
 of lymph is constantly escaping from the blood, and the 
 amount of lymph in the body is several times as great as the 
 amount of blood. 
 
 The Function of the Lymph. The function of the lymph is 
 to receive food and oxygen from the blood and pass them on to 
 the cells, and to receive the wastes from the cells and pass them 
 
 1 In suffocation from gas, death is usually caused by a gas called carbon mon- 
 oxid (CO) . This unites very firmly with the hemoglobin, and when the blood 
 comes to the lungs, the corpuscles cannot take up the oxygen. 
 
150 
 
 HUMAN PHYSIOLOGY 
 
 FIG. 74. As the blood flows through the capillaries 
 it gives food and oxygen to the cells and takes wastes 
 from the cells. The lymph acts as a middleman be- 
 tween the cells and the blood. 
 
 to the blood. The cells of the body, except the blood corpus- 
 cles, lie outside the 
 blood capillaries. 
 The food and oxy- 
 gen must pass out 
 of the blood capil- 
 laries before they 
 can reach the cells. 
 This the food arid 
 oxygen do by pass- 
 ing out through the 
 capillary walls into 
 the lymph, and then 
 through the lymph 
 to the cells. In 
 
 the same way the wastes reach the blood, passing out of 
 
 the cells into the lymph, and from the 
 
 lymph into the blood. The lymph is 
 
 therefore a middleman between the cells 
 
 and the blood. 
 
 The Cells in the Body surrounded by 
 
 Liquid. Each cell of the body lives in a 
 
 liquid (the lymph) as truly as does a little 
 
 one-celled animal that lives in a pond of 
 
 water. The one-celled animal takes its 
 
 oxygen and food from the water, and its 
 
 wastes pass out into the water. The cells 
 
 of the body take their food and oxygen 
 
 from the lymph, and discharge their wastes 
 
 into it. In the pond, however, there is an 
 
 abundance of food and oxygen for the 
 
 little animal, and the amount of water in the pond is so great 
 
 FIG. 75. Muscle 
 cells and the blood 
 capillaries that nourish 
 them. These cells are 
 surrounded by lymph 
 as are the cells in Figure 
 74- 
 
THE CIRCULATORY SYSTEM 
 
 that the wastes have little effect, on its purity. In the 
 body, on the other hand, the cells are so closely crowded 
 that they would in a very short time use all the food and 
 oxygen in the lymph, and fill it with poisonous wastes. 
 There must therefore be some way of constantly sending into 
 the lymph a fresh supply of food and oxygen, and of con- 
 stantly carrying away the wastes; and this, as we have seen, 
 is done by the blood. 
 
 THE LYMPHATIC SYSTEM 
 
 Since the plasma is continually 
 escaping from the blood capillaries, 
 there must be some way of carrying 
 the lymph away from among the 
 cells; otherwise too much lymph 
 would collect in the tissues and the 
 body would become swollen with 
 liquid. 1 The lymph cannot go back 
 into the blood capillaries against the 
 current of escaping plasma, so there 
 is another system of vessels (Fig. 78) 
 to drain it away from among the 
 cells. The vessels that do this are 
 called the lymphatic vessels, and their 
 function is to collect the lymph from 
 among the tissues and carry it again 
 to the blood. 
 
 The Lymphatic Vessels. The 
 lymph flows into the lymph capil- 
 laries, which form a thick network 
 
 MUCOUS 
 CELL 
 
 FIG. 76. A villus and its 
 vessels. The lymphatic vessels 
 (lacteals) are in black. 
 
 1 In dropsy the lymph collects in the tissues and causes great swelling. 
 
1 5 2 HUMAN PHYSIOLOGY 
 
 among the cells. The capillaries unite and form larger 
 vessels, which finally empty the lymph back into the blood. 
 The lymphatic vessels from the right arm and the upper 
 part of the right side of the body empty into a vein in 
 the right shoulder (Fig. 66). The lymphatic vessels of the 
 remainder of the body empty into the thoracic duct. This 
 
 INCOMING LYMPHATIC VESSELS 
 
 CORPUSCLES 
 CONNECTIVE TISSUE CAPSULE 
 
 FIG. 77. A lymph node. The lymph niters through among the white corpuscles in 
 
 the node. 
 
 vessel is about the size of a slender pencil and runs up the 
 back of the ventral cavity, bending over at the top, and empty- 
 ing into a large vein deep in the left shoulder. Thus the 
 lymph that escapes from the blood capillaries is taken up by 
 the lymphatic vessels and brought back to the blood. 
 
 The Lymphatics of the Small Intestine. Besides taking 
 up the escaped plasma from among the cells, the lymphatic 
 vessels 1 in the small intestine do another work. The digested 
 foods sugars, proteins, and fats all pass through the 
 walls of the villi (page 93), but to get into the blood the fats 
 
 1 The lymphatics of the small intestine are called lacteals. 
 
THE CIRCULATORY SYSTEM 153 
 
 travel a different road from the others. The sugars and 
 proteins pass into the blood capillaries of the villi (Fig. 76). 
 The fat enters the lymph capillaries, and is carried to the 
 thoracic duct, which empties it into the blood. 
 
 The Lymph Nodes. Scattered through the body are many 1 
 white bodies, called lymph nodes. The largest of them are 
 perhaps as large as an ordinary 
 sized marble, though somewhat 
 flattened. If you should examine 
 a lymph node, 'you would find that 
 
 it has a connective-tissue coat and that 
 it is filled with white corpuscles. The 
 lymphatic vessels pour the lymph into 
 these nodes, where it filters through FlG> ?8> The i ymph atic 
 
 among the Corpuscles in the node much vessels and nodes of a part of 
 
 as water filters through sand grains. * 
 After passing through the node, the lymph is taken up 
 and carried on by other lymphatic ' vessels. The lymph 
 from many parts of the body passes through several nodes 
 before it reaches the blood. 
 
 The Function of the Lymph Nodes. The lymph nodes have 
 two functions : they furnish breeding places for the white cor- 
 puscles, and they filter out disease germs that get in among the 
 cells and are taken up by the lymphatic capillaries. 
 
 1 There are six or seven hundred lymphatic glands in the body lar^e enough to 
 be seen without a microscope (Fig. 66). 
 
154 HUMAN PHYSIOLOGY 
 
 The white corpuscles that escape from the blood enter the 
 lymphatic capillaries and are carried to the lymph nodes. 
 Inside the nodes they divide and form new corpuscles. The 
 corpuscles reach the blood again by passing into the vessels 
 that flow from the nodes and floating in the lymph to the 
 blood. 
 
 Many diseases are caused by germs that live and grow 
 among the cells. Some of these germs are taken up by the 
 lymph capillaries and carried into the lymph nodes. The 
 nodes stop the germs, and the corpuscles in 'the nodes kill 
 them. Thus the germs are kept from getting into the 
 blood and being carried all through the body. 1 
 
 HYGIENE 
 
 The heart is a muscle, and it is by far the hardest worked 
 of all the muscles of the body. It is especially hard-worked 
 at that period in life when growth is very rapid, when a 
 boy or girl, in a single year, becomes almost as large as a 
 man or a woman. Any extra strain put upon the heart at 
 this time is very likely to cause trouble. The heart also be- 
 comes weak in old age, and old persons should take care not 
 to overwork their hearts. The following are the chief causes 
 of injury to the heart : 
 
 Severe Exercise. Exercise of the muscles greatly increases 
 the work of the heart. Hard work causes any muscle to en- 
 large, and the extra work thrown on the heart by severe 
 exercise may cause " athletic heart." In this condition the 
 
 1 In cancer, " cancer cells " are carried into the lymph nodes that receive the 
 lymph from the diseased tissue, and set up their growth there. It is impossible 
 to treat the disease successfully after the cancer cells have reached the lymph 
 nodes that lie deep in the body. It is important, therefore, that a physician be 
 consulted at the earliest possible moment. 
 
THE CIRCULATORY SYSTEM 155 
 
 heart is enlarged, sometimes to several times its natural size. 
 This enlarging of the heart is frequently followed by a re 
 laxation of the heart and of the arterial walls. The openings 
 where the valves are placed are enlarged until the valves 
 do not completely close them. The valves then leak and part 
 of the blood flows backward in the circulation. This blood 
 must be pumped twice, so the work of the heart is in- 
 creased. Very hard work may also cause fatty degeneration 
 of the heart. 
 
 Boys often injure their hearts by bicycle riding. Football 
 sometimes injures the heart, requiring too long-continued and 
 too severe exercise for any but those with naturally strong 
 hearts. Too much playing of tennis may also overtax the 
 heart, and any other severe and long-continued exercise may 
 do the same. It is well to keep in mind that the time of 
 life when the heart is most frequently injured is in youth. 
 
 Headache Remedies. A great number of headache reme- 
 dies are manufactured from coal tar. They are powerful 
 depressors of the heart, and many people have injured their 
 hearts with them. They are useful medicines, but very dan- 
 gerous to take except under the advice of a physician. 
 
 Alcohol. The effects of alcohol on the heart and blood 
 vessels are very serious. It sometimes causes a paralysis of 
 the muscles in the small vessels, so that they are always dis- 
 tended with blood, as you may have seen in the face and 
 eyes of one who uses alcohol excessively. It weakens the 
 arteries by causing a fatty degeneration and a hardening 
 of the arterial walls. Apoplexy (the bursting of a blood 
 vessel in the brain) is therefore more frequent among alco- 
 holics than among abstainers from alcohol. Alcohol also 
 sometimes causes great quantities of fat to be deposited upon 
 the heart, thus interfering with its work; it so affects the 
 
1 56 HUMAN PHYSIOLOGY 
 
 nervous control of the heart that the action of the whole 
 organ is weakened. 
 
 The use of alcohol also overworks the heart. It takes 
 more force to pump the blood out of the heart into hard, stiff- 
 walled vessels than is required to pump it into vessels with 
 elastic walls. The work of the heart is therefore increased 
 when the arterial walls are hardened by the use of alcohol. 
 This, like hard exercise, overworks the heart, and brings on 
 enlargement of the heart, trouble with the valves, and fatty 
 degeneration. Beer drinkers in particular suffer from heart 
 disease, because in addition to enduring all the evil 
 effects of alcohol, a beer drinker's heart is required to 
 pump through the system the great quantities of water 
 taken in the beer. 
 
 Of course, from reading the above you are not to understand 
 that every one who takes alcohol into his body must have all 
 these diseases of the heart. You are to understand, however, 
 that the effects of alcohol on the heart are bad, and that heart 
 disease is much more common among those who use alcohol 
 than among those who abstain from alcohol. With such an 
 important organ as the heart, no one can afford to take the 
 chance of weakening it in any way, for even though in health 
 it may seem to be doing its work without difficulty, in an 
 attack of pneumonia or other severe illness, when everything 
 depends on the heart's holding out for a few days longer, it 
 may suddenly fail. Statistics from a European hospital show 
 that 1 6 per cent of all deaths in the hospital were due to 
 "beer drinker's heart," the weakened hearts failing under the 
 strain of disease. 
 
 Tobacco. Tobacco so affects the heart nerves that the 
 action of the heart becomes unsteady, sometimes beating 
 very hard and fast, and sometimes with a weak, fluttering 
 
THE CIRCULATORY SYSTEM 157 
 
 beat. This trouble is known as " tobacco heart," and is very 
 common among young cigarette snookers. 
 
 Summary. The body cannot live without the circulation 
 of the blood, because it is the blood that carries the food, 
 oxygen, and water to the cells, takes away the wastes from 
 the cells, and distributes the body heat. 
 
 The blood is pumped through the body by the heart. It 
 leaves the heart through the arteries, passes through the 
 capillaries, and comes back to the heart through the veins. 
 As it passes through the capillaries it gives food and oxygen 
 to the cells and takes up the cell wastes. 
 
 The blood is composed of corpuscles and plasma. The 
 plasma escapes through the capillary walls and passes out 
 among the cells. It is then called lymph. The lymph is 
 taken up by the lymphatic vessels and returned to the 
 blood. 
 
 The heart is sometimes injured by too severe exercise, 
 headache remedies, alcohol, and tobacco. 
 
 QUESTIONS 
 
 Give three great laws according to which the body lives. What is 
 the function of the blood ? Explain why the circulation of the blood 
 is necessary. 
 
 What are the circulatory organs ? Locate and describe the heart. 
 Of what are the walls of the heart composed ? How many cavities 
 are in the heart, and what are they called ? Why are the walls of 
 the ventricles thicker than the walls of the auricles ? What is the 
 function of the heart? 
 
 Describe a contraction of the heart. What is the average rate of 
 the heart beat? How fast does your own heart beat? 
 
 Where are the valves in the heart? What is their function? 
 
158 HUMAN PHYSIOLOGY 
 
 Describe the way the valves in the heart close the openings between 
 the auricles and the ventricles ; the way they close the openings 
 from the arteries into the heart. 
 
 What is an artery? a vein? a capillary? How does the blood 
 flow in each of these vessels? How does it get from the arteries 
 into the veins ? 
 
 How do the walls of arteries, veins, and capillaries differ ? How 
 is the size of the opening in an artery changed? What advantage 
 is this to the body? 
 
 Trace the course of the blood from right auricle to right auricle. 
 How long does it take the blood to make this circuit ? 
 
 What two sets of nerves are connected with the heart? with 
 the arteries ? What proof can you give that the blood vessels are 
 controlled by the nervous system? 
 
 How much of the body weight is blood ? Of what is blood com- 
 posed? What is the liquid part of the blood called? What two 
 kinds of corpuscles are in the blood? How abundant are the red 
 corpuscles ? the white ? 
 
 What is the function of the plasma ? Where are the white cor- 
 puscles formed (page 153)? Explain how they escape from the 
 capillaries. What is the function of the white corpuscles ? 
 
 What shape has a red corpuscle ? Where are the red corpuscles 
 formed? What becomes of them ? What is their function ? What 
 substance in them carries the oxygen? Explain how it does this. 
 How is carbon dioxid carried in the blood ? Why is carbon dioxid 
 injurious to the cells? 
 
 Where in the body is the blood red? Where is it dark? What 
 is lymph ? What is the function of lymph ? How does the life of 
 one of the body cells resemble the life of a small animal in a pond of 
 water ? 
 
 What is the function of the lymphatic vessels? Where do the 
 vessels from the upper part of the right side of the body empty into 
 the blood ? What vessel drains the lymph from the remainder of the 
 body? Where does this vessel empty into the blood? How do 
 
THE CIRCULATORY SYSTEM 159 
 
 the absorbed sugar and proteins reach the blood? How do the 
 absorbed fats reach the blood ? 
 
 Describe a lymph node. How is the lymph carried into and 
 through it ? What two functions have the lymph nodes ? 
 
 At what times of life is the heart especially likely to be injured? 
 Why does too severe exercise hurt the heart? In enlargement of 
 the heart, what trouble is there with the valves ? What effect has 
 this on the amount of work the heart must do ? Name some of the 
 forms of exercise that are likely to injure the heart. 
 
 What effect have headache remedies on the heart ? What effect 
 has alcohol on the small vessels? on the wal's of the arteries? 
 What does this sometimes cause? What does alcohol cause to be 
 deposited about the heart? How does alcohol increase the work of 
 the heart ? What additional work does a beer drinker's heart have ? 
 Why is it unsafe to risk injuring the heart ? What per cent of deaths 
 in a European hospital were due to beer drinker's heart? What 
 is the effect of tobacco on the heart ? 
 
 Press on a vein in your wrist with one finger. On the side of the 
 finger toward the heart empty the vein by rubbing another finger 
 along it. Does the blood flow back into the vein ? On the other side 
 of the finger that is pressing the vein, rub the blood away from the 
 heart. Does the blood flow back into the vein ? Explain. 
 
 Explain why a steady stream of water comes out of the end of a 
 long rubber hose into which water is being pumped'with intermittent 
 strokes. The blood in the arteries flows in spurts, and in the capilla- 
 ries and veins it flows in a steady stream. Explain why it does this. 
 Why does it require more force to pump water into an iron pipe than 
 into a rubber hose with elastic walls ? 
 
 Does a wave on a river travel with the same speed as the water in 
 the river ? Do the blood and the wave in the blood that causes the 
 pulse in an artery, travel with the same speed? 
 
CHAPTER XII 
 
 RESPIRATION 
 
 WATCH the chest of some one who is near you, and you 
 will see that it alternately rises and falls. As the chest 
 rises, air is taken into the lungs. This is called inspiration. 
 When the chest falls, the air is driven out of the lungs. 
 This is expiration. The whole process of taking the air into 
 the lungs and sending it out of them is called breathing, or 
 respiration. Like the circulation of the blood, respiration 
 goes on night and day as long as the body lives. 
 
 The Object of Respiration. The object of respiration is to 
 take oxygen into the body and to give off carbon dioxidfrom the 
 body. When the blood passes through 
 the lungs, it takes up a new oxygen sup- 
 ply for the cells, and loses the carbon 
 dioxid which it has carried away from the 
 cells. Without respiration, the circulation 
 of the blood would be useless, for the 
 blood could not obtain oxygen, and it 
 would carry through the body again and 
 again the poisonous carbon dioxid which 
 it takes up from the cells. 
 
 Why Oxygen is Necessary to the Cells. 
 When the foods are oxidized (burned) 
 within the cells, the atoms of the foods unite with atoms of 
 oxygen. By this process, energy is given to the cells (page 
 
 160 
 
 FIG. 79. Burning low for 
 lack of oxygen. 
 
RESPIRATION l6l 
 
 1 14). If there are no oxygen atoms in the cells for the food 
 atoms to unite with, it is evident tjiat the oxidation of the 
 foods within the cells must come to a stop. The cells will 
 then be unable to get energy, and they will die. Without 
 oxygen they cannot use the food, and without oxygen they 
 starve to death for lack of energy as surely as if no food had 
 reached the cells. Oxygen is necessary that the foods may be 
 burned within the cells. As oxygen is necessary for the burn- 
 ing of the foods within the cells, so it is necessary for the 
 burning of all substances everywhere. Cover a candle by set- 
 ting a glass vessel over it (Fig. 79). In a few moments the 
 candle will go out because there is no more oxygen in the 
 vessel. 
 
 THE ORGANS OF RESPIRATION 
 
 The organs of respiration include the framework of the 
 chest, the muscles that are used in breathing, the hmgs, and 
 the air passages. The lungs are the most prominent of these 
 organs, and it is in them that the blood gives off its carbon 
 dioxid and takes up its oxygen. Most of the diseases of the 
 respiratory organs are caused by germs that grow on the 
 warm, moist lining of the air passages, and in the air sacs of 
 the lungs. 
 
 The Lungs. The lungs (Fig. 84) are composed chiefly of 
 a great mass of air passages and air sacs. They therefore 
 have a light and spongy structure. In the lungs blood ves- 
 sels are very abundant, for at each beat of the heart as much 
 blood goes to them as goes to all the remainder of the body. 
 The lungs are hung in the thoracic cavity by the trachea 
 (Fig. 82), through which air passes into and out of them. 
 Each lung is surrounded with a thin connective tissue sac 
 -called a pleura (plural, pleura). 
 
1 62 
 
 HUMAN PHYSIOLOGY 
 
 The Thoracic Cavity. 
 
 The thoracic cavity (Fig. 8) lies 
 within the framework of the chest, 
 and the diaphragm 1 forms its floor. 
 It is divided longitudinally into three 
 chambers (Fig. 80). In each side 
 chamber lies a lung. In the central 
 chamber the heart and the bases of 
 the great blood vessels, the trachea, 
 and the esophagus are found. The 
 central chamber is wider in its lower 
 
 FIG. 80. The divisions of the front portion where the heart lies, and 
 
 thoracic cavity. narrower above and behind the heart. 
 
 The Pleurae. The pleura are two 
 
 thin, double-walled sacs. The outer 
 
 layer of a pleura is attached to 
 
 the chest wall and diaphragm, and 
 
 stretches as a partition across the 
 
 thoracic cavity from top to bottom. 
 
 The inner layer incloses the lung. 
 
 This layer of the pleura is very 
 
 delicate, and forms a thin coat over 
 
 FIG. 81. Air sacs and blood 
 
 the surface of the lung. In Figure vessels in the lungs. The blood 
 
 80 yOU Can See how the Chest capillaries lie in the thin walls 
 
 cavity is divided into three parts 
 by the pleurae, and in Figure 82 
 
 trace a pleura entirely out mto tn f air f ' ana * y - 
 
 \ J gen passes from the sac into the 
 
 lung 
 
 you can 
 around a 
 
 of the air sacs. As the blood 
 passes through the capillaries 
 carbon dioxid and water pass 
 out into the air sac, and oxy- 
 
 - , . K C " | 
 
 and around the blood. 
 
 1 The diaphragm (Fig. 8) is a thin sheet of muscle with a connective tissue 
 center. It is dome-shaped, the stomach and liver fitting into the hollow in its 
 lower surface. Viewed from above, the diaphragm appears as a ring of muscle 
 with a connective tissue center. It is attached all around by its outer edge to the 
 body wall, specially heavy bands of muscles running down and attaching them- 
 
RESPIRATION 
 
 163 
 
 cavity in which the lung lies. 1 The surfaces of the pleurae 
 are kept moist with a thin yellowish liquid. 2 This prevents 
 friction when the two layers of the pleura move on each 
 other in breathing. 
 
 FIG. 82. The pleurae. 
 
 How the Chest is enlarged in Inspiration. In inspiration 
 the chest is enlarged in two ways. The ribs and sternum are 
 lifted up and out, widening the cavity of the chest. The dia- 
 phragm is drawn downward, causing the bottom of the chest 
 cavity to sink, and thus increasing the size of the cavity. The 
 
 selves to the front of the spinal column. When the muscles of the diaphragm 
 contract and shorten, they draw its top (center) downward. 
 
 1 The pupil should also trace out the course of the pericardium and note 
 that it is a double-walled sac enveloping the heart as a pleura envelops a lung. 
 
 2 The disease called pleurisy is inflammation of the pleurae. In this disease 
 considerable quantities of liquid may collect between the two layers of the pleune. 
 
164 HUMAN PHYSIOLOGY 
 
 chest walls and the diaphragm are thus drawn away from the 
 lungs, leaving a vacuum, or empty . space, between the two 
 layers of the pleurae. The air then rushes down into the lungs, 
 and expands them until they fill the enlarged thoracic cavity. 
 So promptly do the lungs expand and follow up the chest 
 walls and diaphragm in inspiration that there is no noticeable 
 space between the two layers of the pleurae. 
 
 Expiration. In ordinary expiration, the muscles do little 
 work. The ribs and sternum sink chiefly from their awn 
 weight, and the diaphragm is pushed 1 up by the liver, stomach, 
 and other abdominal organs below it. This with the elasticity 
 of the lungs drives out the air ; for just as the stretched walls 
 of a blown-up football or of a toy balloon expel the air, so the 
 stretched walls of the air sacs and of the small bronchial tubes 
 help to force the air out of the lungs. 
 
 The Nasal Passages and the Pharynx. 'When air is taken 
 into the lungs, it first enters the nasal passages (Fig. 83). 
 These are two narrow chambers that run up in the head as 
 high as the eyes and backward about four inches. An open- 
 ing in the floor of each nasal chamber at the back leads down 
 into the pharynx. 
 
 The pharynx is a funnel-shaped cavity lying behind the 
 mouth. It curves around the base of the tongue, with its 
 mouth opening forward. Hanging down in front of the 
 openings from the nasal chambers and helping to separate the 
 mouth from the pharynx is a little curtain-like structure called 
 
 1 When the diaphragm comes down in inspiration, it forces the organs below it 
 downward and pushes the abdominal walls outward. In expiration the stretched 
 abdominal walls come inward partly because of their elasticity, and partly because 
 of the contraction of the abdominal muscles, and drive the diaphragm upward. 
 In a forced expiration, the abdominal muscles contract forcibly, pulling in the ab- 
 dominal walls and driving the diaphragm far upward. At the same time they 
 draw down the ribs and sternum, to which they are attached at their upper ends. 
 
RESPIRATION- 165 
 
 the uvula, or soft palate. In swallowing, the uvula is pushed 
 back over the openings from the nose so that it covers them 
 and prevents food and water from entering the nose (Fig. 83). 
 
 In the side walls of the pharynx, directly under the corners 
 of the lower jawbone, the two tonsils 1 are located. When 
 viewed from the inside of the pharynx, the tonsils appear 
 like gentle, rounding elevations lying under the mucous mem- 
 brane which lines the pharynx walls. At the bottom of the 
 pharynx are two openings, one leading into the esophagus 
 and one into the larynx. 
 
 The Larynx. The larynx is the enlarged upper part of 
 the trachea. It has a framework of cartilages, which you 
 can easily feel in the front of your neck. In swallowing, the 
 food and drink would fall down into the larynx if it were not 
 for the epiglottis (Fig. 83). This flap-like structure stands 
 in front of and above the opening to the larynx, and in swal- 
 lowing the larynx is drawn up and forward, 2 so that its mouth 
 is pushed up in under the epiglottis. The food or water 
 then passes over the larynx into the esophagus. During 
 breathing the larynx drops down, leaving its mouth open, and 
 allowing the air to pass into and out of the lungs. The vocal 
 cords, which produce the sound of the voice, are in the larynx. 
 
 The Trachea and its Branches. The trachea divides into 
 two great branches, one of which goes to each lung. Within 
 the lung these branches divide again and again, until finally 
 they end in little air sacs. The branches of the trachea are 
 
 1 When germs get into the tonsils and cause inflammation, the disease is 
 called tonsillitis. 
 
 2 Feel your larynx while you swallow, and note how it rises. If one laughs 
 when eating or drinking, the larynx is lowered and food or water may fall down 
 into the trachea. When food or liquid is driven upward through the pharynx in 
 laughing or by vomiting, it may pass in behind the uvula and enter the nasal pas- 
 sages from the rear. 
 
1 66 
 
 HUMAN- PHYSIOLOGY 
 
 called the bronchial tubes. In the walls of the trachea and 
 of all the larger bronchial tubes are rings of cartilage to keep 
 
 the air passages from 
 closing and shutting 
 off the supply of air * 
 from the air sacs in 
 the lungs. 
 
 The Air Sacs. Each 
 small bronchial tube 
 at the end widens out 
 and becomes a thin- 
 walled sac. The walls 
 of this sac are thrown 
 into little sac-like 
 folds, so that the end 
 of a bronchial tube is 
 a larger sac 2 made up 
 of a great number of 
 
 FIG. 83. The air follows the path indicated by little SaCS, all Opening 
 
 inward toward the 
 center. So abundant 
 are the air sacs in the lungs that their estimated number is 
 725,000,000, and if they were all opened and spread out side 
 by side, they would cover 2150 square feet of space. 
 
 Changes in the Air in the Air Sacs. The walls of the air 
 sacs are exceedingly thin. They contain a very great 
 
 1 In asthma the muscles in the walls of the small bronchial tubes contract so 
 that the greatest difficulty is experienced in getting the air to pass in and out of 
 the air sacs. In pneumonia the small air passages and the air sacs are stopped 
 up with mucus and blood. 
 
 2 The larger air sacs at the ends of bronchial tubes are called infundibula 
 (singular, infundibuluni}. The smaller air sacs of which an infundibulum is 
 composed are called alveoli (singular, alveolus). 
 
 TRACHEA 
 
 the blue arrows, and the food follows the path indi- 
 cated by the red arrows. 
 
RESPIRATION 
 
 16 7 
 
 number of delicate blood capillaries through which all the 
 blood in the body passes every minute and a quarter (page 
 145). As the blood flows through the capillaries in the walls 
 of the air sacs, oxygen from the air passes in through the 
 walls of the sacs and enters the blood, and carbon dioxid 
 
 FIG. 84. The trachea and the lungs. B and Cshow the way the small bronchial 
 tubes end in air sacs (infundibula) which are made up of a large number of smaller sacs. 
 
 passes out from the blood into the air (Fig. 81). Water also 
 passes out of the blood into the air, as you can prove by 
 breathing on a cold window pane, and the air is warmed 
 while in the lungs. The air in the lungs, therefore, loses 
 oxygen, and gains carbon dioxid, water, and heat. 
 
 Perhaps what is going on in the lungs would be made more vivid 
 to you, if, in imagination, you could make a trip down into the lungs 
 and see what is happening there. Following down the trachea and 
 the bronchial tubes, you would come into one of the larger air sacs. 
 
1 68 HUMAN PHYSIOLOGY 
 
 There you would see all about you the mouths of the little air sacs 
 opening into the chamber in which you were standing. Going up to 
 the mouth of a small sac and looking in, you would see the blood 
 shooting along in the capillaries in the walls. As the blood enters 
 the capillaries, it is dark in color, but as it moves along it gradually 
 takes on a redder and redder hue until it is a bright scarlet when it 
 gets through the capillaries and starts to the heart. 
 
 Peering still more closely into the sac, you would see a great mul- 
 titude of little oxygen molecules flying from the air into the blood, 
 where they unite with the hemoglobin of the red corpuscles and are 
 carried away. You would also see the carbon dioxid and water 
 molecules flying out from the blood into the air in the little sac, and 
 then passing out into the larger sac and up into the bronchial tubes, 
 to pass out of the lungs in the breath. 
 
 Mucus and Cilia. The entire respiratory tract is lined with 
 mucous membrane and is kept moist with sticky mucus. 
 In all parts of it except in the pharynx and air sacs and over 
 the vocal cords, the walls are covered with cilia (Fig. 6). 
 
 The mucus on the walls of the air passages catches dust 
 and germs that are in the air, and the cilia sweep the mucus 
 and matter which is caught in the mucus out of the air pas- 
 sages. The air is thus cleansed, and irritating dust particles 
 and dangerous disease germs are in a great measure prevented 
 from getting down into the delicate air sacs of the lungs. 
 
 The nasal passages are especially fitted for purifying and 
 warming the inhaled air. The nostrils are guarded by hairs 
 for straining out dust, the mucus on the walls of the long and 
 narrow nasal passages catches much dust and many germs, 
 and air inhaled through the nose is warmed before it reaches 
 the throat and lungs. Any trouble in the nasal passages 
 
 1 Nasal polyps close the passage through the nose, and adenoids (spongy 
 growths above and behind the uvula) block the openings from the nose to the 
 throat. The teacher should report to the parents all children who have trouble 
 in breathing through the nose (pages 253, 270). 
 
RESPIRATION 169 
 
 that interferes with breathing through the nose should 
 receive medical attention at once,, for in mouth breathing, 
 cold and dusty air is taken into the throat and lungs. This 
 brings on many diseases of those parts. 
 
 RESPIRATION IN OTHER ANIMALS 
 
 An insect has no lungs, but it takes in air through a great 
 number of little tracheae, or air tubes, which open along the 
 sides of its body. A fish has very thin gills through which 
 the blood flows. The fish takes water into its mouth and 
 sends it backward over the gills and out through the gill slits 
 on the sides of its neck. As the water passes over the gills, 
 the oxygen from the water passes into the blood, and the 
 carbon dioxid from the blood is given off into the water. 
 A fish cannot live in boiled water, because when water is 
 boiled, the air is driven out. It cannot live in the air, 
 because when taken out of the water, its gills stick together, 
 and the oxygen cannot get in among the gills to pass into 
 the blood. 
 
 The frog, instead of making a vacuum in his chest and thus 
 causing the air to pass into the lungs, takes air into the mouth, 
 and by drawing in the skin under its chin, forces the air 
 downward. Watch a frog breathing, and note how the throat 
 works out and in. When under water, the frog gives off car- 
 bon dioxid and absorbs oxygen through its thin, moist skin. 
 It may interest you to know that a frog does not drink water, 
 but absorbs this also through the skin, the water passing into 
 the blood which flows in the capillaries of the skin. 
 
 A bird has no diaphragm and the lungs run far back in the 
 body. In many birds branches from the lungs go out even 
 into the hollow bones, 
 
I/O HUMAN PHYSIOLOGY 
 
 HYGIENE 
 
 Five points connected with the hygiene of the respiratory 
 system are worthy of notice. The first is in regard to the 
 effects of tight clothing about the body. This interferes with 
 the respiratory movements, and is a great evil, for it leads to 
 shallow breathing, in which the air passes into and out of the 
 trachea and larger bronchial tubes without sending much oxy- 
 gen into the air sacs or taking much carbon dioxid out of them. 
 
 The second point is in regard to the danger of breathing 
 dust. Large numbers of people die every year from consump- 
 tion, pneumonia, diphtheria, and grip, and many more suffer 
 from catarrh and other diseases of the respiratory organs. 
 
 All these diseases are carried by germs, and persons who 
 breathe dusty air suffer greatly from them. The reason for 
 this is that the dust particles cut and wound the air passages, 
 and the germs are able to gain an entrance into the tissues 
 at these points and set up their growth. Every effort should 
 be made, therefore, to keep from breathing dust. Streets 
 should be kept sprinkled, and when floors are swept, as little 
 dust as possible should be raised. Dust should be wiped 
 from walls and furniture with a damp cloth, and not stirred 
 up into the air. Everything possible should be done to pre- 
 vent the inhalation of dust, for most respiratory diseases are 
 germ diseases, and the germs are frequently able to attack 
 these parts because of the wounds made by particles of dust. 
 
 The third point which we wish to mention is the value of 
 deep breathing exercises. 1 It is an excellent plan for every 
 one, several times a day, to stand erect, as directed on page 
 71, fill his lungs to their utmost capacity, hold the air for a 
 
 1 It is well to" know that breathing exercises are very injurious to any one who 
 is suffering from consumption. 
 
RESPIRATION- 1 71 
 
 few moments, and then slowly and steadily exhale it. This 
 takes the oxygen deep into the lungs, brings out the carbon 
 dioxid, and quickens the heart beat, thus starting the blood 
 more swiftly through the whole body. 
 
 Outdoors, in the fresh air, is the best place to take these 
 breathing exercises, and you can practice them as you walk 
 to and from school. But a better time to practice them is 
 when you have become tired from sitting over some task for 
 a considerable time. Then you will find that it will rest and 
 refresh you to go to a window, open it, and take several deep 
 breaths of fresh air. In school, when every one has been 
 sitting quietly until the respiration has become shallow and 
 the heart beat slow, it is very beneficial to throw the win- 
 dows wide open and have everybody stand up and take 
 several deep breaths, along with some stretching exercises 
 to relieve the cramped muscles. A couple of minutes spent 
 in this way takes very little time, and sets everybody to work 
 again with renewed vigor. You must take care, however, not 
 to practice breathing exercises so vigorously that you make 
 yourself dizzy, or you may do yourself more harm than good. 
 
 The fourth point to which we would call your attention is in 
 regard to the use of alcohol. Users of alcohol are particularly 
 liable to attacks of pneumonia, catarrh of the pharynx, larynx, 
 and bronchial tubes, and to other respiratory diseases. The 
 chief reason for this seems to be that alcohol weakens the power 
 of the body to kill germs. We shall take up this whole subject 
 in a later chapter, but you should know now that when pneu- 
 monia or grip is abroad, and every one is trying to keep himself 
 in the best possible health so that he will be able to kill any germs 
 that get into his body, drinking alcohol, even in small amounts, 
 will greatly lessen the power of the body to resist germs. 
 
 The last point which we would ask you to note in connec- 
 
172 
 
 HUMAN PHYSIOLOGY 
 
 tion with the hygiene of the respiratory organs is the effect of 
 cigarette smoking on the lungs and on the health of the whole 
 body. Users of cigarettes very commonly inhale the smoke. 
 This smoke is irritating to the air passages and has a very 
 injurious effect on the lungs. In addition to the poisonous 
 substance that is in the tobacco, cigarette smoke contains a gas 
 called carbon monoxid (page 149, footnote). Both the poison 
 of the tobacco and the carbon monoxid pass into the blood in 
 the capillaries of the lungs and injure the cells of the body. 
 
 THE VOICE 
 
 The Cartilages of the Larynx. 
 
 FIG. 85. The cartilages of the larynx. 
 A and B show the cartilages as seen from the 
 front. C is the back of the cartilages in their 
 natural position. D is a longitudinal section 
 of the larynx showing the vocal cord stretched 
 from the thyroid cartilage in front to the vocal 
 process of the arytenoid cartilage at the back. 
 
 The walls of the larynx are 
 mainly composed of two 
 great cartilages, the thyroid 
 and the cricoid. The thyroid 
 cartilage is the "Adam's ap- 
 ple" which you can feel in 
 the front of your throat. It is 
 somewhat V-shaped, with the 
 opening behind. Set upon 
 end a partially opened book, 
 and it will represent fairly 
 well the shape of the thyroid 
 cartilage. 
 
 The cricoid cartilage forms 
 a complete ring, but it is much 
 narrower in front than be- 
 hind (Fig. 85 B\ In front, 
 the cricoid lies in the larynx 
 wall below the thyroid (Fig. 
 85.0), but at the back its 
 
RESPIRATION 173 
 
 wide part stands up between the two wings of the thyroid 
 and forms the back wall of the larynx (Fig. 85 C). 
 
 On top of the cricoid, at the back, stand up the two little 
 arytenoid cartilages. Each one is loosely hinged at its base, 
 so that to a certain extent it can slide outward toward the side 
 wall of the larynx or inward toward the other arytenoid. It 
 has on the inner side of the base a small projection called 
 the vocal process (Fig. 85 /?), to which the back end of the 
 vocal cord is attached. 
 
 The Vocal Cords. The vocal cords are insignificant little 
 bands of connective tissue that run along the side walls of 
 
 FlG. 86. The mouth of the larynx viewed from above. A shows the position of 
 the vocal cords (c) in deep breathing ; B is their position in ordinary breathing ; and C 
 shows them brought together for speaking or singing, a is the epiglottis. 
 
 the larynx from the front to the back. They are attached 
 to the thyroid cartilage in front and to the vocal processes 
 of the arytenoid cartilages at the back. They are buried in 
 the mucous membrane that lines the larynx, and are therefore 
 attached to the side wall of the larynx by one edge. If you 
 will gather up and draw out a fold of skin on the back of the 
 hand, you will have something that in a way represents a 
 vocal cord. 
 
 The Vocal Cords in Action. In ordinary breathing the vocal 
 cords lie close to the walls of the larynx and are not affected 
 by the air as it passes out of and into the lungs. In talking 
 or singing the cords are drawn out from the walls and stretched 
 
174 
 
 HUMAN PHYSIOLOGY 
 
 across the opening of the larynx, until there is only a narrow 
 slit between the cords. The air passing out over the tightly 
 stretched cords causes them to vibrate and produce the sound 
 of the voice. To make a gentle sound, a slight current of 
 air is passed over the vocal cords. To make a loud sound a 
 heavy current of air is sent out. 
 
 How the Vocal Cords are thrown into and out of Action. 
 The vocal cords are thrown into and out of action by mus- 
 
 FlG. 87. Diagram illustrating how the vocal cords are brought into action. When 
 the points of the arytenoid cartilages (represented by the gates in the diagram) to which 
 the cords are attached are turned forward, the cords lie close to the wall. When the 
 cartilages swing out, as in D, the cords are drawn out from the walls, as in C. 
 
 cles that are attached to the arytenoid cartilages. When a 
 sound is to be produced, the arytenoid cartilages are made 
 to slide inward toward each other and are rotated (Fig. 87 D\ 
 so that they draw the vocal cords out from the walls (Fig. 
 87 C). The cords are thrown out of action by sliding the 
 arytenoid cartilages outward and rotating them so that the 
 vocal processes point forward (Fig. 87 B). This allows the 
 cords to lie close to the larynx walls (Fig. 87 A). 
 
 The Pitch of the Voice. The heavy strings of a guitar or 
 of a violin give a low tone, and the light strings give a high 
 tone. In strings of the same weight, a tight string gives a 
 
RESPIRA TIOIT 1 75 
 
 higher tone than a loose string, and a short string' a higher 
 tone than a long string, as you can tell by tightening the 
 strings on a stringed instrument, and changing their lengths 
 by fingering them. The pitch of the sound depends, there- 
 fore, on the weight, the length^ and the tightness of the string. 
 
 Persons who have long and heavy vocal cords have low 
 voices, and persons with short and light vocal cords have 
 high voices. The larynx of a man is larger than the larynx 
 of a woman, his vocal cords are larger and longer, and his 
 voice has, therefore, a lower pitch. 1 
 
 Change of pitch in the voice is brought about by the mus- 
 cles of the larynx tightening and loosening the vocal cords. 
 When a low tone is to be produced, the cords are loosened. 
 When a high tone is to be produced, the cords are tight- 
 ened. When one thinks how many notes a singer makes 
 in a few minutes, tightening the vocal cords just enough to 
 give the right pitch to each one, he realizes how rapidly and 
 accurately the muscles of the larynx must work. 
 
 Summary. Respiration is necessary to take in oxygen and 
 give off carbon dioxid. The lungs are in the thoracic cavity. 
 This cavity is enlarged and air drawn into the lungs by 
 lifting up the framework of the chest and by pulling down 
 the diaphragm. 
 
 The air passes through the nasal passages and pharynx, 
 enters the larynx, and goes down the trachea and its 
 branches into the air sacs of the lungs. In the air sacs it 
 gives up its oxygen to the blood and takes up carbon dioxid 
 and water from the blood. The air passages are lined with 
 
 1 When male and female voices sing in unison, the male voices are an octave 
 lower than the female. At the time when a boy's voice changes, the larynx sud- 
 denly grows very much larger, and the vocal cords are lengthened. While the 
 voice is changing it should not be given any severe use. 
 
176 HUMAN PHYSIOLOGY' 
 
 mucous membrane, and in most parts the walls are covered 
 with cilia. The mucus catches dust, and the cilia sweep it 
 out of the air passages. 
 
 Tight clothing about the body interferes with breathing; 
 many diseases of the respiratory organs come from breathing 
 dust ; deep breathing exercises are very valuable ; alcohol 
 brings on lung diseases; and cigarette smoking injures the lungs. 
 
 The cartilages of the larynx are the thyroid, cricoid, and 
 arytenoids. The vocal cords are attached to the thyroid in 
 front and to the arytenoids behind. In speaking or singing, 
 the vocal cords are thrown out from the wall, and the voice 
 is produced by passing a current of air over the cords. The 
 pitch of the voice depends on the weight, length, and tight- 
 ness of the cord. 
 
 QUESTIONS 
 
 What is inspiration? expiration? respiration? By observing the 
 breathing of some person who does not know what you are doing, find 
 out how many times he breathes in a minute. 
 
 What is the object of respiration ? Why is oxygen necessary to 
 the body? Of what are the lungs chiefly composed? How much 
 blood goes to the lungs? What is the covering of a lung called? 
 Into how many parts is the thoracic cavity divided? What is in the 
 side chambers of the thoracic cavity? the middle chamber? Make a 
 drawing showing the location of a pleura. 
 
 In what two ways is the chest enlarged ? How is the air forced 
 out of the lungs? Trace the air down into the lungs, naming the 
 different parts of the air passages. Describe the nasal passages. 
 How does the air get from the nasal chambers into the mouth? 
 
 Describe the pharynx. What separates the pharynx from the 
 mouth? What is its use? Where are the tonsils? How are food 
 and water kept from falling into the larynx? 
 
 Describe the branching of the trachea. What are the branches ol 
 
RESPIRA TION 1 77 
 
 the trachea called ? How are the trachea and bronchial tubes kept 
 open? Describe an air sac. In what^ength of time does all the 
 blood in the body pass through the lungs ? What passes from the 
 air into the blood ? from the blood into the air ? 
 
 With what is the respiratory tract lined ? How is it kept moist ? 
 What parts of the respiratory tract are covered with cilia ? What is 
 the use of the mucus? of the cilia? What are the nasal passages 
 especially fitted to do ? Why is mouth breathing harmful ? 
 
 How does an insect breathe ? a fish ? Why cannot a fish live in 
 boiled water ? in the air ? How does the frog take air into its lungs ? 
 How does it respire while under water ? How does a frog take water 
 into its body? What is peculiar about a bird's lungs? 
 
 Why is tight clothing harmful? Name five germ diseases of the 
 respiratory organs. How does dust cause these diseases? What 
 measures are useful in keeping down dust? 
 
 What effect have deep breathing exercises on the heart beat and 
 circulation? Where should such exercises be taken? when? To 
 what respiratory diseases are users of alcohol particularly liable ? 
 
 Name the two large cartilages in the larynx. Describe the thy- 
 roid cartilage ; the cricoid. Where are the ary tenoid cartilages ? 
 How can they be moved ? Describe the vocal cords. To what are 
 they attached at the front ? at the back ? along the edge ? 
 
 What is the position of the vocal cords in ordinary breathing? 
 in talking or singing? How is the voice produced? How is a 
 gentle sound produced? a loud sound? How are the vocal cords 
 thrown into action ? out of action? 
 
 Upon what does the pitch of a sound depend? What kind of 
 vocal cords have persons with low voices ? persons with high voices ? 
 Why has a man's voice a lower pitch than a woman's voice? How 
 is the pitch of the voice changed? 
 
 When a bucket is lowered in water, what causes the water to rush 
 into it? We live at the bottom of an ocean of air. What causes 
 the air to be drawn into the lungs when the chest cavity is enlarged? 
 
CHAPTER XIII 
 
 VENTILATION 
 
 OF all the evils that befell man when he came to live 
 within walls and doors, the lack of fresh air is the greatest. 
 By its own activity, the body is constantly rendering great 
 quantities of air unfit for use, and the necessity of securing a 
 fresh supply is always upon us. As long as man dwelt in the 
 great outdoors, all that was necessary was for the lungs to 
 expel the stale air and it was carried away. But indoors the 
 air is imprisoned and is often breathed again and again. In 
 this chapter the problem of securing a supply of fresh air 
 will be considered. 
 
 The Air. The air consists of about four fifths nitrogen 
 and one fifth oxygen, with small amounts of several other 
 gases which vary at different times and places. Among the 
 gases that exist in small quantities in the air is carbon dioxid. 
 The nitrogen is not used in the body, but passes into and out 
 of the lungs unchanged. 
 
 The Supply of Oxygen. Twenty-one per cent of the air is 
 oxygen. It is absolutely necessary for life, but under ordi- 
 nary circumstances the air and the blood always contain 
 enough oxygen for the cells. As long as more than ic per 
 cent of the air is oxygen, a person lives as well as if he were 
 breathing pure oxygen. Expired air still contains 1 5 per cent 
 of oxygen, so there would be no lack of oxygen in the body, 
 even though the air were breathed twice. 
 
 Carbon Dioxid. Air contains a little less than 4 parts in 
 10,000 of carbon dioxid. Expired air contains about 430 
 
 178 
 
VENTILATION- 179 
 
 parts in 10,000 of carbon dioxid. Stating it in another way, 
 ordinary air is .04 per cent carbon cjioxid, and expired air is 
 4.3 per cent carbon dioxid. The air that leaves the lungs, 
 therefore, contains more than a hundred times as much car- 
 bon dioxid as the air that enters them. Under extreme con- 
 ditions enough carbon dioxid may collect in crowded buildings 
 to be harmful, but it is now believed that the amounts found 
 in rooms that are ordinarily well ventilated are without harm- 
 ful effects. 1 An oil stove or a gas stove that is not connected 
 with a chimney gives off great quantities of carbon dioxid and 
 is very injurious to the health. 
 
 Three Important Points in Ventilation. The whole subject 
 of ventilation is not well understood, but the following points 
 are known to be important : 
 
 The humidity of the air. Dry air evaporates the perspira- 
 tion from the skin very rapidly, which gives a sensation of 
 chilliness. Living in such an atmosphere also causes irrita- 
 tion of the eyes, nose, and throat, and a tendency to restless- 
 ness and nervousness. When the occupants of a room feel 
 cold with the thermometer at 68 degrees, moisture should be 
 added to the air (page 356). 
 
 In moist atmospheres the perspiration evaporates very 
 slowly from the skin and the excess body heat is not removed. 
 Drowsiness, overheating, and headache are apt to follow sit- 
 ting in an atmosphere of fhis kind. Water vapor is given off 
 from the lungs, and the atmosphere of crowded rooms is usu- 
 ally heavily laden with moisture. 
 
 Motion in the air. When the air is still, a blanket of moist 
 
 1 The " choke damp " of coal mines is carbon dioxid, and this gas sometimes 
 collects in dangerous quantities in silos and in wells. By lowering a lighted 
 lantern its presence in a silo or well can be detected. The flame will die out if 
 dangerous quantities of carbon dioxid are present. 
 
180 HUMAN" PHYSIOLOGY 
 
 air forms about the body, which in warm rooms quickly causes 
 overheating. One of the important points in ventilation, 
 especially in hot, moist atmospheres, is that air currents be 
 set up that will blow away this wet air blanket and allow the 
 body heat to be removed. 
 
 The temperature of the air. The proper temperature for 
 indoor air depends on its humidity and on the amount of 
 motion in it. When the air of a room is very dry the occu- 
 pants will be uncomfortable unless the temperature is raised 
 to 75 degrees. When the air is quiet and very moist, over- 
 heating will follow if the temperature rises above 65 degrees. 
 When the air is properly humidified and has gentle air 
 currents in it, the thermometer should stand at about 68 
 degrees. 
 
 Amount of Fresh Air Needed. According to accepted stand- 
 ards of ventilation, a man must have 3000 cubic feet of fresh 
 air every hour. If he is working, he will need twice this 
 amount. An eight-year-old boy needs one half as much as a 
 man. 
 
 Usually it is not possible to change the air of a room more 
 than five times an hour without causing drafts. Changing it 
 five times an hour, each person must have 600 cubic feet of 
 air space in a room to get his 3000 cubic feet of fresh air. 
 Public buildings, therefore, should have 600 cubic feet of air 
 space for each person, and in the living and sleeping rooms 
 of private dwellings each member of the family should have 
 1000 cubic feet of space. Of course, even with this much 
 space, the air will become bad unless there is some way of 
 constantly changing it. 
 
 Principles of Ventilation. A room will hold only a certain 
 amount of air, and if fresh air is brought in, part of the air 
 already in the room must pass out. In any system of venti- 
 
VENTILATION- l8l 
 
 (ation there must, therefore, be an opening through which the 
 air can enter the room, and an openipg through which it can 
 escape. The cold air in a room sinks to the floor and the 
 warm air rises to the top of the room. The opening by which 
 the air is drawn off from the room, should, therefore, be near 
 the floor. 
 
 In ordinary buildings some air finds its way through crevices 
 around windows and doors and through the floors. Opening 
 and closing doors, and persons passing in and out of a room, 
 also create a circulation of the air. Air may pass both out 
 and in through the same opening, as you can show by the 
 following experiment : 
 
 Hold a lighted candle near the top of an open doorway. The candle 
 flame will be blown to one side, showing that a current of air is passing 
 in or out through the top of the doorway. Now hold the candle in the 
 doorway close to the floor. The air current here will usually be found 
 to be passing in a direction opposite to the direction of the current 
 of air in the top of the doorway. By holding the candle at different 
 heights, find a stationary layer of air lying between two layers of air 
 that are moving in opposite directions. Open or close some other 
 door of the room and note the effect on the candle flame. Have 
 some one walk through the doorway past the flame and note the 
 effect. 
 
 Ventilating Public Buildings. In many public buildings it is 
 impossible to hav.e satisfactory ventilation, because the builders 
 did not provide any special arrangements for drawing off the 
 used air and for sending in a supply of fresh air. Windows 
 were put in houses, not to be used as ventilators, but to 
 admit light, and it is very difficult to use them as ventilators 
 without causing drafts. In schoolhouses, churches, theaters, 
 and other buildings, where many people collect, some way of 
 forcing in fresh air and of drawing off the air which has 
 been used, should be provided. Unless this is done, it is 
 
1 82 HUMAN PHYSIOLOGY 
 
 almost impossible in cold weather to change the air rapidly 
 enough to prevent carbon dioxid from accumulating in the 
 building. 
 
 Heating Systems and Ventilation. Heating with a hot-air 
 furnace 1 constantly sends a supply of fresh but very dry 
 air into the room. A fireplace gives considerable ventila- 
 
 FiG. 88. How a fireplace helps to ventilate a room. A current of air passes up 
 the chimney, and this causes the fresh air to be drawn into the room. 
 
 tion by causing a draft of air up the chimney. Stoves give 
 some ventilation in the same way, but not so much as an 
 open fire. Radiators heated by hot water 'and steam give 
 no ventilation. 
 
 Avoiding Drafts. One great problem connected with venti- 
 lation is how to get the fresh air into the room without causing 
 cold drafts. One of the most satisfactory ways of doing this 
 is to have warm air sent in by the heating system. Some 
 
 1 Some cheap iron furnaces, when they become red hot, allow gas from the 
 coal to pass through them. Breathing this gas is exceedingly unhealthful. 
 
VENTILATION 
 
 183 
 
 very useful devices for ventilating are made, by which air is 
 
 drawn in behind a fireplace or intq a jacket around a stove 
 
 and warmed before it comes into 
 
 the room. A board set under a 
 
 window sash allows the air to come 
 
 in between the two sashes and go 
 
 upward without causing a draft on 
 
 those sitting in the room. Muslin 
 
 fronts, which admit air without 
 
 causing drafts, have long been used 
 
 in poultry houses, and cloth window 
 
 screens are now in use as ventilators 
 
 in many schools. 
 
 Even when buildings have been 
 constructed with no ventilating sys- 
 tem, it is possible to do much to 
 secure fresh air without causing 
 harmful drafts. Several windows 
 may each be opened a little, when to open one wide would cause 
 great trouble. Schoolrooms and churches should be filled with 
 fresh air while they are empty. At noon and during recesses 
 schoolroom windows can be opened and a great deal done in 
 a very short time toward getting out the stale air. 
 
 Importance of ventilating Sleeping Rooms. A great deal 
 of time is spent in the atmosphere of the sleeping room, and 
 at night the air of sleeping rooms is not set in motion by the 
 opening and closing of doors and by persons passing out and 
 in. For these reasons the ventilation of the room where you 
 sleep deserves special attention. 
 
 If your sleeping room is not ventilated in some other way, 
 you should open one or more windows each night. If the 
 windows are so arranged that they cannot be opened without 
 
 FIG. 89. Ventilating by placing 
 a board under a window. 
 
184 HUMAN PHYSIOLOGY 
 
 causing a draft over the bed, fit boards under the sashes, 
 or get fresh air in some other way. Do not sleep in a 
 closed room breathing again and again the stale air that 
 has come off from your own lungs, and do not be afraid 
 to admit the night air to your room, for the same atmos- 
 phere that surrounds houses during the day surrounds them 
 at night. 
 
 Outdoor Sleeping. Every year more and more people are 
 sleeping outdoors. It was long ago noticed that people who 
 lived much in the open air were not troubled with consumption 
 as were those who lived indoors. Then it was found that 
 sleeping outdoors often helped to cure consumption. People 
 began to wonder why anything that helped to cure sick- 
 ness might not also help to keep them from getting sick, 
 so more and more of them are building upper porches 
 and other places where they can conveniently sleep in the 
 open air. 
 
 It is probable that the benefits of outdoor sleeping come 
 from spending the long time when one is in bed in an 
 atmosphere that is fresh, cool, and constantly in motion. 
 With this amount of time spent in the pure outdoor air, 
 the body becomes so well and strong that it can kill off 
 the disease germs that get into it. A well-ventilated house 
 helps to preserve the health; walking and other exercises 
 that require spending time in the open air are also healthful ; 
 but outdoor sleepers think their way of obtaining fresh air is 
 the best of all, because in this way most of them spend more 
 time in the outdoor air than they could possibly do in any 
 other way. 
 
 Summary. The lack of fresh air is the greatest evil that 
 accompanies indoor life. Oxygen and carbon dioxid are the 
 important gases of the air from the standpoint of the health, 
 
VENTILATION- ^5 
 
 but the important points in ventilation are the humidity, mo- 
 tion, and temperature of the air. Each person should have 
 600 cubic feet of room space and 3000 cubic feet of fresh air 
 per hour. It is especially important that the sleeping room 
 be well ventilated, because much time is passed in the atmos- 
 phere of this room. Outdoor sleeping is a healthful practice 
 which is probably beneficial because it furnishes the sleeper 
 with plenty of fresh air. 
 
 QUESTIONS 
 
 Of what two gases is the air chiefly composed? Name one other 
 gas that is found in small quantities in the air. What per cent of 
 the air is oxygen ? What per cent of expired air is oxygen ? What 
 per cent of carbon dioxid is in ordinary air ? in expired air ? 
 
 Name three important points in ventilation. How does dry air 
 ; ocl che body ? What bad effects has dry air on the health ? What 
 effects follow sitting in a hot, moist atmosphere? Why is motion in 
 the air desirable? Discuss the question of the proper temperature 
 of the air. 
 
 How much fresh air is needed by a man when he is at rest? by a 
 working man? by a boy? In public buildings, how much space 
 should there be for each person? in sleeping rooms? 
 
 In ventilating, why should the opening by which the air passes out 
 be near the floor? What is necessary for the satisfactory ventilation 
 of crowded public buildings? What systems of heating ventilate a 
 room? What systems give no ventilation? Explain how a fireplace 
 or stove brings fresh air into a room. Give some ways of avoiding 
 drafts in ventilation. What should be done while schoolrooms and 
 churches are empty? Why should sleeping rooms be especially well 
 ventilated? Is night air unhealthful? From what do the benefits 
 of outdoor sleeping probably come ? 
 
CHAPTER XIV 
 
 RENAL ARTERY 
 
 THE KIDNEYS AND THE BODY WASTES 
 
 SOMETIMES the body is well; sometimes it becomes ill. 
 Why is it strong and abounding in health at one time and at 
 another time weak and ill? Usually not because it lacks 
 food or oxygen, or because it is too hot or too cold, but be- 
 cause there are poisons in the body that injure the cells. 
 
 Sometimes the poisons that cause 
 sickness are produced by disease 
 germs (page 285). Frequently they 
 come from our own cells. Our 
 bodies constantly produce carbon 
 dioxid and poisonous protein wastes 
 (urea and uric acid), 1 and without 
 organs for throwing off these sub- 
 stances, life for us would not be 
 possible for even an hour. We 
 have already learned how the car- 
 bon dioxid is excreted from the 
 body. In this chapter we shall 
 study the kidneys, the organs that 
 remove the uric acid and urea from 
 the blood. 
 
 The Kidneys. . The kidneys are 
 two bean-shaped organs. They are 
 fastened to the back wall of the 
 
 FlG. 90. The kidneys and 
 the bladder as seen from behind. 
 
 1 There are other protein wastes besides the urea and uric acid, but for the 
 sake of convenience the others will be disregarded here. 
 
 1 86 
 
THE KIDNEYS AND THE BODY WASTES 187 
 
 abdominal cavity, one on either side of the spinal column. 
 Stored around the kidneys are great quantities of fat The 
 function of the kidneys is to excrete urea, uric acid, and water. 
 As the lungs purify the blood by removing from it carbon 
 dioxid, so the kidneys purify the blood by taking out of it 
 urea and uric acid. 
 
 FlG. 91. A is a longitudinal section of a kidney, showing how the kidney tubules 
 empty into the branches of the ureter. B is a kidney tubule enlarged to show the cor- 
 puscle at its upper end, and the long, winding course the tubule follows before it 
 empties into the ureter. C is a small portion of a tubule, showing how the walls of the 
 tubule are built of cells. 
 
 The Tubules of the Kidneys. The kidneys are composed 
 chiefly of an enormous number of very fine winding tubes 
 (tubules). The tubules rise in little sacs (Fig. 91 E) and flow 
 
i88 
 
 HUMAN PHYSIOLOGY 
 
 together, forming larger tubules. These larger tubules all 
 run to the inner side of the kidney, where they empty into 
 the branches of the ureter (Fig. 91 A). 
 
 The Renal Corpuscles. The corpuscle on the end of a 
 kidney tubule consists of a double-walled sac and a tuft of 
 blood vessels. The structure of a corpuscle is most easily 
 learned by studying its development. 
 
 When the kidney is being formed in a very young animal, 
 the kidney cells arrange themselves so as to form tubes 
 
 WALL OF 8*C 
 
 FIG. 92. The development of a renal corpuscle. The corpuscle is formed by a 
 blood vessel pushing in the end of a kidney tubule. (After Bailey.) 
 
 (Fig. 91 C). A small blood vessel grows up close against the 
 end of a tube (Fig. 92 A) and begins to push it in (Fig. 92 B). 
 The end of the tube then broadens out and forms a small round 
 sac, which grows up around the blood vessel (Fig. 92 C). 
 Meanwhile, the blood vessel twists about and divides up into 
 capillaries, and continues pushing in the wall of the sac 
 (Fig. 92 D and E\ until at last the corpuscle consists of a 
 bunch of little blood vessels buried in a narrow-mouthed 
 pocket in the end of the sac. This pocket almost fills the 
 sac (Fig. 91 B\ 
 
THE KIDNEYS AND THE BODY WASTES 189 
 
 How the Wastes are excreted from the Kidneys. When 
 the blood is flowing through the capillaries in a renal cor- 
 puscle, the wastes escape through the capillary walls. They 
 then pass on through the inner walls of the sac into the tubule, 
 and flow down the tubule to the ureter. Also, blood capilla- 
 ries are abundant all through the kidneys, and along the 
 course of the tubules, wastes from the blood pass into the 
 tubules through the tubule walls. Drop by drop the millions 
 of kidney tubules separate the wastes from the blood and 
 empty them into the ureters, which carry the wastes to the 
 bladder^ 
 
 Alcohol and the Kidneys. More commonly, probably, than 
 any other organs of the body, the kidneys become diseased 
 from alcohol drinking. The cells in the corpuscles and 
 tubules of the kidneys should allow the wastes to pass 
 through them, and at the same time they should hold back 
 the food that is dissolved in the blood. Alcohol may cause 
 the kidney cells to become diseased and to allow the foods to 
 escape with the wastes. Sometimes the cells suffer from 
 fatty degeneration, and still more commonly the connective 
 tissue in the ^kidney increases greatly (page 102) and stran- 
 gles the cells of the tubules. In Bright's disease, which is 
 much more common among alcohol drinkers than among 
 abstainers, whole tubules die and the protein foods are 
 allowed to escape with the wastes. 
 
 Summary. Ill health is often the result of poisoning 
 the cells. The kidneys are organs for removing the 
 poisonous protein wastes and water from the body. A 
 kidney is composed of many fine tubules, each of which ends 
 
 1 The amount of water excreted by the kidneys depends, of course, on the 
 amount of liquid taken into the body and on the amount of water lost by perspi- 
 ration. On an average, it is a little over three pints per day for an adult man. 
 
1 9 HUMAN PHYSIOLOGY 
 
 in a renal corpuscle. A tuft of blood capillaries is buried in 
 each of the corpuscles and the wastes pass out from the 
 blood into the tubules and down to the ureters. Alcohol 
 causes kidney trouble, Bright's disease being very common 
 among drinkers. 
 
 QUESTIONS 
 
 To what is ill health frequently due? Where do these poisons 
 come from ? Locate the kidneys. What is deposited around them ? 
 What is their function ? 
 
 Of what is a kidney chiefly composed? Describe the course of 
 the tubule. In what does a tubule rise ? Describe the development 
 and structure of a renal corpuscle. How do the wastes get from the 
 blood into the tubules? 
 
 What should the cells of the kidney tubules do with the wastes and 
 with the foods ? What two diseased conditions of the kidneys does 
 alcohol cause? What disease of the kidneys is common among 
 drinkers? 
 
CHAPTER XV 
 
 THE SKIN AND THE BODY HEAT 
 
 The Functions of the 
 Skin. The skin has four 
 functions. It forms a 
 protective covering for the 
 body, which keeps the 
 more delicate tissues from 
 being injured, and pre- 
 vents disease germs from 
 getting in among them. 
 // is an organ of feeling, 
 for most of the nerves of 
 touch end in the skin. It 
 regulates the heat of the 
 body, permitting the body 
 to cool off when it be- 
 comes too warm, and 
 keeping in the heat when 
 the body becomes cold. 
 Its other function is to 
 assist the lungs and kid- 
 neys in excreting water 1 from the body. 
 layers, the epidermis and the dermis. 
 
 A The lungs, kidneys, and skin give off so much water that we are compelled 
 to drink liquids to give the body a sufficient supply of water. You should under- 
 stand, therefore, that when the skin excretes water, the object is to cool the body 
 and not to get rid of the water. 
 
 191 
 
 FIG. 93. A section of the skin. B is a small 
 portion of a sweat gland, and C is a cross-section 
 of a sweat gland enlarged to show that these 
 glands are hollow tubes with walls composed 01 
 cells. 
 
 The skin has two 
 
192 
 
 "HUMAN PHYSIOLOGY 
 
 Thickening of the Epidermis. The 
 
 epidermis is the protective layer of the 
 skin, and wherever unusual pressure 
 comes on the skin, as on the soles of 
 the feet or on the palms, the epider- 
 mal cells multiply very rapidly and 
 cause a great thickening of the outer 
 layer of the epidermis. When con- 
 stant pressure falls on a small area 
 of epidermis, as sometimes happens 
 when a tight shoe is worn, a corn, or 
 little mound of epidermal cells, is built 
 up. This can be relieved only by re- 
 moving the pressure that caused the 
 growth. It is much easier to prevent 
 corns than it is to cure them, and only 
 properly fitting shoes should be worn. 1 
 A wart is a place where the epidermal 
 cells grow and multiply more than is 
 natural, but the cause of warts is not 
 known. In cancer, either the epider- 
 mal cells or the connective tissue cells 
 increase enormously and feed on the 
 other body tissues. 
 
 The Color of the Skin. The color 
 of the skin is due to pigment in the 
 cells of the lower layers of the epidermis. The outer epider- 
 mal layers are partially transparent, and we look through 
 these and see the coloring matter in the lower cells. Expos* 
 
 1 It is estimated that 58 per cent of Americans have corns, ingrowing nails, the 
 bones of the feet bent out of shape, or other foot troubles. The question of 
 properly fitting shoes is, therefore, one of considerable importance. 
 
 FlG. 94. A section of the 
 epidermis. The epidermis 
 grows by the division of the 
 iower cells. Its outer cells dry 
 and scale off. A papilla con- 
 taining a touch corpuscle is 
 shown. The skin pigment is in 
 the lower cells of the epidermis. 
 
THE SKIN AND THE BODY HEAT 
 
 193 
 
 The subcutaneous 
 
 ure to the sun or wind causes the coloring matter to become 
 more abundant in the skin, and the skin, as we say, becomes 
 tanned. A freckle is a spot in the epidermis where the pig- 
 ment is especially abundant. It is probable that the use of 
 the skin pigment is to protect the nerves and other delicate 
 structures beneath the epidermis from the light of the sun. 
 
 The Dermis and the Subcutaneous Layer. The second 
 layer of the skin is the dermis. It is composed of connec- 
 tive tissue in which there are blood vessels, lymphatic vessels, 
 and nerves. The upper surface of the dermis is thrown into 
 papilla that stand up like little mountain peaks under the 
 epidermis. Some of the papillae contain blood vessels, and 
 some of them contain touch corpuscles. In the lower part 
 of the dermis considerable fat is stored 
 layer lies under the dermis. It is a 
 layer of loose connective tissue in 
 which large quantities of fat are found. 
 
 Sweat Glands. With a magnifying 
 glass small pores can be seen in the 
 skin, in some portions of the body as 
 many as twenty-five hundred to the 
 square inch. They are the mouths of 
 sweat glands, which are little tubes 
 composed of epidermal cells (Fig. 93). 
 A sweat gland runs down through the 
 epidermis and ends in a coil in the 
 lower part of the dermis, or in the 
 subcutaneous layer. 
 
 The Function of the Sweat Glands. 
 The function of the sweat glands is to 
 cool the body by pouring out perspiration on the skin. Around 
 the lower part of a sweat gland are many fine blood capillaries 
 
 MOUTHS OF SWEAT GLANDS 
 
 FIG. 95. The surface of 
 the skin of the finger-tip, mag- 
 nified to show the mouths of 
 the sweat glands. In some 
 parts of the skin the papillae 
 are arranged in rows, giving 
 the surface of the skin a 
 ridged appearance. 
 
194 HUMAN PHYSIOLOGY 
 
 from which an abundant supply of lymph escapes. The water 
 of the lymph passes on through the walls of the sweat gland 
 into the opening in the center of the gland, and flows out on 
 the skin. A little perspiration passes out through the sweat 
 glands at all times, but usually the amount is so small that it 
 passes off into the air as vapor without being noticed. On a 
 hot day, however, or when the body becomes hot from 
 exercise, the sweat glands work so rapidly that the water 
 accumulates on the skin. 
 
 How the Body is cooled by the Perspiration. The body is 
 cooled by the evaporation of the perspiration on the skin. 
 Pour alcohol or ether on your hand and allow it to evaporate 
 and your hand will feel cold. This shows that a liquid in 
 evaporating takes up heat. You can have the same fact 
 proved to you by visiting an ice factory and seeing water 
 frozen by the evaporation of ammonia, or by performing the 
 following experiment : 
 
 Note the height at which the mercury stands in a thermometer. 
 Then cover the bulb of the thermometer with cotton, and wet the 
 cotton with ether, chloroform, gasoline, alcohol or water. Swing 
 the thermometer through the air and then note the height of the 
 mercury. What causes it to fall ? 
 
 The Sweat Glands controlled by the Nervous System. The 
 sweat glands are controlled by the nervous system, which 
 causes them to work rapidly or slowly according to the heat 
 of the body. That the sweat glands are connected with the 
 nervous system is shown by the way embarrassment or pain 
 may bring out the perspiration. 
 
 The Hair. A hair grows in a small, deep pocket in the 
 skin, called the hair follicle. At the bottom of the follicle is 
 the hair papilla. This is a little mound of connective tissue, 
 belonging to the upper layer of the dermis. The follicle is 
 
THE SKIN" AND THE BODY HEAT 
 
 195 
 
 lined with and the hair papilla is covered over by cells which 
 have been folded in from the 
 epidermis. The hair rests 
 on the papilla, and grows by 
 the epidermal cells at the 
 base of the hair multiplying 
 and pushing the cells above 
 them upward. A hair, like 
 the epidermis, contains nei- 
 ther nerves nor blood vessels. 
 In the connective tissue of 
 the papilla, however, is a rich 
 blood supply, which brings 
 food to the growing cells at 
 the base of the hair. 
 
 The Sebaceous Glands and 
 the Muscles of the Hair. 
 Opening off from the sides 
 of the hair follicles are the 
 sebaceous glands, which man- 
 ufacture a clear, odorless oil 
 for the hair. Small muscles 1 
 are attached to the hair folli- 
 cle in such a way that when 
 they contract, the hair is made to stand on end. Doubtless 
 you have seen the hairs on a cat's tail or on a dog's neck stand 
 on end, and you probably know that in man great fright may 
 cause these muscles to contract and make the hair stand up. 
 
 1 The upper ends of these muscles are attached in the connective tissue just 
 below the epidermis. Under certain conditions they contract and draw the epi- 
 dermis down in little depressions, producing the condition that is called " goose- 
 flesh." 
 
 BLOOD VESSEL 
 
 FlG. 96. A hair in its follicle. 
 
I9 6 HUMAN PHYSIOLOGY 
 
 Care of the Hair. Brushing the hair is very beneficial to it 
 because it spreads the oil from the sebaceous glands all along 
 the hair. Brushing the hair also causes a good circulation of 
 blood in the scalp, thus providing the growing cells of the 
 hair with an abundance of food and oxygen, and promptly 
 carrying away their wastes. The hair and scalp should be 
 washed occasionally with good soap to remove dust and oil. 
 A little ammonia or borax in the water is useful when the 
 hair is very oily, but if this treatment causes the hair to 
 become dry and brittle, only soap and water should be used. 
 
 Dandruff and Baldness. It is thought that dandruff is 
 caused by a germ that grows in the sebaceous glands and 
 the scalp, and that this disease may be spread by hair brushes 
 and combs. It is, therefore, safest not to use the combs and 
 brushes that are found in public places. 
 
 Baldness is supposed usually to be caused either by dan- 
 druff or by tight hats that cut off the blood from the scalp. 
 This is little more than a guess, however, for the subject is 
 not well understood, and there are many cases in which neither 
 of these explanations holds. When a hair falls out, a new hair 
 will take its place, provided the epidermal cells that line the lower 
 part of the hair follicle and cover 'the hair papilla are not de- 
 stroyed. If these are destroyed, the hair will not be renewed. 
 
 The Nails. A nail is formed from the upper horny layer 
 of the epidermis. Its growth is chiefly at the base, as you 
 will know if you have seen a spot x grow forward on a nail 
 until it reached the tip. The nail cells turn to a horny sub- 
 stance, and the nails have a pink appearance because the rich 
 blood supply below can be seen through them. Where the 
 cells are young, the blood cannot be seen so plainly through 
 
 1 A black spot on a nail is caused by injuring the blood vessels under the nail, 
 thus allowing the blood to flow out and form a clot. 
 
THE SKIN AND THE BODY HEAT 
 
 them, and there is, therefore, a white area at the base of each 
 nail. y 
 
 When a nail is injured, or lost through accident, it will 
 grow again, provided the bed of epidermal cells on which the 
 nail rests and from which it grows is not destroyed. But if 
 the " roots of the nail " are destroyed, the nail will not be re- 
 placed. The nails protect the fingers, and assist in picking 
 up small objects. 
 
 THE BODY HEAT 
 
 A man in the cold Arctics loses much more heat than does 
 a man living in the warm tropics. Yet the temperature of the 
 human body all over the world is the same. A man who is 
 violently exercising produces five or six times as much heat 
 as a resting man produces. Yet the temperature of the 
 human body in exercise and rest is nearly the same. In 
 health, the human body keeps a temperature of about 98^ 
 degrees, varying from a little above this point to about a 
 degree below it. 
 
 The Regulation of the Body Heat. On a cold day we can 
 close the doors and windows of a room and with a small fire 
 keep the temperature of the room at 70 degrees, or we can 
 open a window and still keep the temperature of the room at 
 70 degrees by firing up and producing more heat. We can 
 control the temperature of the room either through the 
 amount of heat that is lost, or through the amount of heat 
 that '^produced. So the temperature of the human body can 
 be kept at 98^ degrees either by regulating the amount of 
 heat that escapes from the body, or by regulating the amount 
 of heat produced in the body. Both of these methods are 
 used in our bodies. 
 
198 HUMAN" PHYSIOLOGY 
 
 Regulating the Escape of Heat. The skin governs the 
 escape of heat from the body in two ways. The first way 
 is by regulating the amount of blood that comes out into the 
 skin. When the body is cold, the blood vessels of the skin 
 contract and keep the blood in the warm internal parts of 
 the body. When the body is hot, the vessels in the skin open 
 up and allow a larger amount of blood to come to the outside 
 of the body where it will be cooled. 
 
 The other method of regulating the escape of the heat is 
 through the sweat glands. When the heat of the body rises, 
 the sweat glands cool the body by pouring out perspiration 
 on the skin. Both the vessels of the skin (page 145) and the 
 sweat glands are governed by the nervous system, so it is the 
 nervous system that regulates the amount of heat that escapes 
 from the body. 
 
 Regulating the Amount of Heat produced. When the body 
 is exposed to severe cold, much heat escapes from it, and the 
 cells burn an extra supply of food to keep the body tempera- 
 ture up to 98^- degrees. For this reason, men living outdoors 
 in cold weather require great quantities of food (page 124). 
 For the same reason, an animal that is kept outdoors in the 
 winter needs more food than the same animal requires when 
 it is kept in a warm stable. 
 
 The Temperature of the Body in Illness. When one is weak 
 and ill, the body temperature sometimes falls below normal, 
 not enough heat being produced or too much heat being lost. 
 Sometimes the sweat glands work when they should not do 
 so, as in the night sweats which accompany consumption and 
 other weakening diseases. More commonly the temperature 
 rises above 98^ degrees, when one is said to have fever. 
 
 The Cause of Fever. In fever there is usually a greater 
 breaking down of the tissues and a greater production of 
 
THE SKIN AND THE BODY HEAT 199 
 
 heat than is natural. Not nearly so much heat is produced 
 in fever, however, as in violent exercise, and the main cause 
 of a fever is that not enough heat is 'lost. Usually the trouble 
 is that the sweat glands refuse to work. The crisis or turn 
 of a fever is usually marked by the sweat glands beginning 
 their work, the surplus heat escaping and the fever going 
 down from that time. 1 
 
 Chills. In illness the skin usually is hot and flushed with 
 blood, but sometimes the blood vessels of the skin are tightly 
 closed and the blood is kept from coming to the outside of 
 the body where it will be cooled Then the skin has no 
 warm blood, and the person has a chill and feels cold, even 
 when the inner parts of the body are in a hot fever. 
 
 The Extremes of Body Temperature. The human body is 
 very sensitive indeed to changes in temperature, and will die 
 if its heat falls far below or rises much above normal. One 
 hundred and two degrees is warm fever, and 104 degrees is 
 a hot fever; 105 degrees, if it continues for long, is danger- 
 ous, and when a fever rises to 109 or no degrees, it is almost 
 surely fatal. How far below normal the temperature can 
 fall without fatal results depends on how long-continued the 
 decline is, but 91 or 92 degrees will cause death in a very 
 short time. 
 
 1 Sometimes, in slight fevers, a hot bath, followed by an extra heavy covering 
 of the body for a time, will start the sweat glands and lower the fever. Rubbing 
 with alcohol quickly cools the body, because the alcohol evaporates very rapidly. 
 Sponging with water cools the skin in the same way, but not so rapidly. Some- 
 times, in long-continued illness, where the temperature goes so high that there is 
 danger of death from the fever, it is best to take the heat out of the body with 
 ice-packs or an ice-cold bath. But this (as well as rubbing with alcohol) is a 
 shock to the nervous system, and it drives the blood inward and checks instead 
 of starting the sweat glands. It should be used only when a physician advises it, 
 or when the fever runs so high that it must be quickly lowered. Sponging with 
 warm or tepid water is safer> and is often sufficient. 
 
200 HUMAN PHYSIOLOGY 
 
 BATHING 
 
 Dead epidermal cells of the skin and oil from the seba^ 
 ceous glands become mixed with perspiration and dust and 
 form a considerable amount l of waste matter on the skin. 
 This should be removed, or it will form a breeding place for 
 many germs,' which may get down into the hair follicles and 
 cause pimples and other skin troubles. 2 It is important, 
 therefore, to keep the skin clean, and to do this, soap should 
 be used on the skin to dissolve the oily matter. For purposes 
 of cleanliness, a moderately warm bath is best, but aside from 
 cleansing the skin, bathing has little effect on the body except 
 through the temperature of the water. A hot or cold bath, 
 however, may have a decided effect on the nervous system, 
 and through it, on the whole body. 
 
 Cold Baths. When a cold bath is taken, the blood vessels 
 of the skin contract and send the blood to the heart, lungs, 
 brain, and other internal parts of the body. This quickens 
 the circulation and respiration, and causes more food to be 
 oxidized in the body, thus producing more body heat. After 
 the bath, the reaction (the return of the blood to the skin) 
 usually comes, warming and reddening the skin, and giving 
 the bather a fresh and pleasurable feeling. Rubbing the 
 skin helps to bring on the reaction. Sometimes when the 
 water is very cold, or the person taking the bath is weak or 
 unaccustomed to cold baths, the reaction does not follow, and 
 the bather is left weak and shivering. This is decidedly 
 injurious. A person should train himself gradually to a cold 
 bath, and should always be sure that the temperature of the 
 water is not so low, and the time spent in the bath not so 
 
 1 It has been estimated that a pint of epidermal cells scale off one arm and 
 hand in a month. 2 Blackheads are hair follicles that have become stopped up. 
 
THE SKIN AND THE BODY HEAT 2OI 
 
 long, that the reaction will not come promptly. Some indi- 
 viduals do not seem able to accustom themselves to cold baths 
 without too great a shock to the nervous system, and these 
 persons should bathe only in warm or tepid water. 
 
 Warm Baths. Most of the effects of a hot bath are exactly 
 opposite to the effects of a cold bath. A hot bath opens the 
 vessels in the skin, and draws the blood to the surface of the 
 body and away from the muscles and the internal organs. 
 
 Time for bathing. Since a cold bath sends the blood to 
 the brain and causes a greater amount of food to be oxidized 
 in the body, the best time to take such a bath is in the morn- 
 ing, when we wish to have our energies aroused and to wake 
 up for the work of the day. It should not be taken when one 
 is very hot or tired. The best time for a warm bath is just 
 before bedtime, after the work of the day is done. Persons 
 who are troubled with insomnia (sleeplessness) sometimes 
 find that a warm bath enables them to go to sleep. One who 
 has been engaged in very hard exercise will find that a hot 
 bath draws the blood away from the muscles to the skin. 
 A warm bath should not be taken immediately before or 
 after eating, because it draws the blood from the digestive 
 organs. Tepid baths have no particular effect on the body, 
 and may be taken at any time. Unless the water is cold, a 
 swim, like other exercise, may be taken at almost any time 
 except just before and for a time after eating. 1 
 
 1 It is well to know that " cramps," with which swimmers are occasionally 
 seized, is believed to come on more frequently after eating. Just what the trouble 
 is in cramps is not well understood. One theory is that when the diaphragm is 
 hindered in its downward movement by a full stomach, the severe exercise of 
 swimming and the force required to push out the body walls in the water, throws 
 so heavy a task on the respiratory muscles that these muscles suddenly fail in 
 their work and the breathing stops. Whether or not this theory is correct, it is 
 probably best to follow the old rule of not taking a swim for two hours after eating. 
 
202 HUMAN PHYSIOLOGY 
 
 THE HEATING OF BUILDINGS 
 
 The lower animals depend on the food which they burn in 
 their bodies to keep up their heat, but man has learned the 
 use of fire, and in the colder portions of the earth heats his 
 houses. This has many advantages, but it has certain dis- 
 advantages ; for when we pass from a warm house into cold 
 winter air, there is suddenly a very great change in the 
 amount of heat that is lost from the body. 
 
 Overheated Rooms. Many rooms both in private dwell- 
 ings and in schoolhouses and other public buildings are kept 
 too hot. This is injurious for the following reason: 
 
 In a warm room the skin is moistened with perspiration 
 and the blood is drawn to the surface of the body. When a 
 person passes from a warm room to the cold outside air, the 
 perspiration on the skin continues to evaporate and take heat 
 out of the body, and large amounts of heat are lost before 
 the blood can be cut off from the skin. An overheated 
 room is injurious because on leaving it too much heat is lost 
 from the body, and the body is chilled. Sitting down to rest 
 in the cold outside air when one is hot from exercising may 
 in the same way cause the body to be chilled. 
 
 Underheated Rooms. Cold rooms are injurious because in them 
 the body loses too much heat and becomes cold and chilled. Cold 
 floors are common, and little children, especially, suffer from 
 them. The temperature of the air at the floor of a room is often 
 20 degrees lower than the temperature of the air a few feet 
 above the floor. When small children get down to play on the 
 floor they may be passing from a warm to a cold atmosphere, and 
 they often suffer from cold in a room that in some parts is suffi- 
 ciently heated. Fires should be built on cold days in the spring 
 and fall, or colds will follow staying in rooms that are too cool. 
 
THE SKIN AND THE BODY HEAT 203 
 
 How chilling the -Body injures it. The most common 
 result of chilling the body is a cold. It is practically certain 
 that a cold is a germ disease,. and it is thought that allow- 
 ing the body to become too cold weakens it, so that the 
 germs can grow in it and cause the cold. One great ad- 
 vantage that is claimed for cold baths is that by training 
 the vessels of the skin to close quickly they prevent the 
 body from becoming chilled and give those who take them 
 marked freedom from colds. 
 
 The Use of the Thermometer. In keeping a room at the 
 proper temperature, a thermometer is a very great aid. The 
 temperature of different parts of the room should be tested 
 and some method of heating used that will warm all parts of 
 the room as evenly as possible, so that some of the people in 
 the room will not be too hot while others are too cold, or one 
 part of the body be warm while another part of it is cold. 
 Where rooms are heated with stoves, it will be found that a 
 large stove gives a more steady, even heat than a small stove 
 gives. Having one part of the body hot and another part 
 cold is decidedly injurious, so cold floors and cold drafts are 
 to be avoided wherever possible. From 65 to 70 degrees is 
 the proper temperature for a room in which people are sit- 
 ting, and when it is necessary to raise the temperature 
 above 70 degrees to make a room comfortable the air is too 
 dry and some means of adding moisture to it should be pro- 
 vided. 
 
 CLOTHING 
 
 Birds have feathers and most mammals have a coat of hair 
 to retain the body heat, but in man the hair on the body is so 
 fine and thin that it is of little use as a protection from the 
 cold. In the colder regions of the earth, man has, therefore, 
 
204 HUMAN PHYSIOLOGY 
 
 been compelled to clothe himself to krep up his body heat. 
 The chief physiological use of clothing is to retain the body heat. 
 Clothing also saves the body from wounds and bruises and 
 protects it from the heat and light of the sun. 
 
 How Clothing retains the Body Heat. Heat passes with 
 great difficulty through dry air, and clothing prevents the 
 escape of the body heat chiefly through holding air in the 
 little crevices in the cloth. The fur of animals forms a very 
 warm body covering, and in a number of animals (including 
 the cat, rabbit, and sheep) it has been found that on an average 
 about 2 per cent of the fur is hair, and 98 per cent of it is 
 air that is held in the little spaces between the hairs. 
 
 The Best Materials for Clothing. Woolen clothing is 
 warmer than cotton or linen. Wool is therefore the best 
 material for winter clothing, but in hot summer weather, cot- 
 ton and linen clothing may be superior to woolen. Woolen 
 clothing is warmer than the others because it has many little 
 air spaces between the threads; in cotton and linen cloth 
 the threads are harder, and are woven more solidly together, 
 so that a smaller amount of air is held in the cloth. 
 
 Wool is superior to cotton and linen for winter clothing for 
 another reason, also. It will absorb more water than either 
 of the others, and therefore does not become dampened so 
 quickly by the perspiration. Cold water or cold, wet clothing 
 touching the skin takes the heat out of the body with great 
 rapidity, and if a person clothed in cotton or linen exercises 
 until he perspires, his clothing becomes damp ; then if he 
 rests in a cold atmosphere the heat may escape too rapidly 
 from the body, and a cold follow. 
 
 Tight-fitting and Insufficient Clothing. Tight clothing, by 
 interfering with the circulation of the blood, may cause cold- 
 ness in some parts of the body. Cold feet are often caused 
 
THE SKIN AND THE BODY HEAT 205 
 
 by tight shoes, which prevent the circulation of the blood. It 
 is important that sufficient clothing/be worn in cold weather to 
 keep up the body heat ; for allowing the body temperature to 
 fall below normal at once lowers the resistance to germs and 
 makes one more susceptible to colds, pneumonia, influenza, 
 and other respiratory diseases. It is also important that the 
 clothing be so distributed on the body that all parts of the body 
 will be kept warm, and it should be loose enough to allow 
 freedom of motion to the parts beneath it. 
 
 Other Hygienic Points connected with Clothing. Wet cloth- 
 ing takes the heat out of the body and is especially likely to 
 cause colds. Damp feet are a common cause of sickness, and 
 when rubbers are needed to keep the feet dry they should 
 always be worn. 
 
 Wearing heavy clothing indoors has the same effect as 
 staying in an overheated room. An overcoat should not 
 be worn in the house, but should be put on before going out- 
 doors, to protect the body from the sudden change to the cold 
 of the outside air. 
 
 Heavy clothing should be worn in the spring and fall when 
 the weather demands it. If in the spring the weather turns 
 cool after heavy clothing has been taken off, the heavy cloth- 
 ing should be put on again. The clothing and the heating 
 of buildings should be adapted to the weather, and if thin 
 clothing is worn and fires are allowed to go out on cold days 
 in the spring and fall, colds and sickness will follow. 
 
 Summary. The skin forms a protective covering for the 
 body, is an organ of feeling, regulates the body heat, and 
 excretes water. The outer layer of the skin is called the 
 epidermis. The dermis is a layer of connective tissue under 
 the epidermis, and the subcutaneous layer lies below the 
 dermis. Fat is stored in this layer. 
 
206 HUMAN PHYSIOLOGY 
 
 The sweat glands take water from the blood and pour it 
 out on the skin as perspiration. By the evaporation of the 
 perspiration the body is cooled. The sweat glands are under 
 the control of the nervous system. 
 
 A hair grows in a hair follicle and rests on a hair papilla. 
 It grows from the epidermal cells at its base. The sebaceous 
 glands secrete a clear oil for the hair. Brushing and a clean 
 scalp are beneficial to the hair. Dandruff is in all probability 
 a germ disease and may be contracted from brushes and 
 combs that other persons have used. Baldness is usually 
 supposed to be due to dandruff or tight hats. 
 
 The nails grow from the epidermis. They protect the 
 fingers and are useful in picking up small objects. 
 
 The temperature of the healthy human body is always near 
 98^ degrees. The skin regulates the escape of heat from the 
 body by controlling the amount of blood that comes to the 
 skin and by the action of the sweat glands. The amount 
 of heat produced in the body is regulated by the amount of 
 food that is oxidized, extra food being burned when the body 
 is cold. 
 
 In sickness the temperature of the body may rise too high 
 or fall too low. The chief trouble in fever is that not enough 
 heat is lost, the sweat glands usually failing to work. In a 
 chill the blood is cut off from the skin. 
 
 The skin should be kept clean so that germs will not find 
 food on it. 
 
 A cold bath is best taken in the morning and a warm bath 
 at bedtime. Cold baths are injurious when they are not 
 promptly followed by the reaction. 
 
 Overheated rooms cause the body to be chilled after leav- 
 ing them ; underheated rooms cause the body to be chilled 
 while in them ; and chilling of the body is followed by colds. 
 
THE SKIN AND THE BODY HEAT 207 
 
 A thermometer should be used to determine whether rooms 
 have the proper temperature. 
 
 Clothing retains the heat by holding air in its pores. 
 Wool is a warmer material for clothing than cotton or linen. 
 Tight-fitting clothing causes coldness of parts of the body by 
 interfering with the circulation. Wet clothing, wearing heavy 
 clothing indoors, and insufficient clothing during cold weather 
 in the spring and fall are causes of sickness. 
 
 QUESTIONS 
 
 Give the four functions of the skin. Name the kyers of the skin. 
 What is a corn? What gives the color to the skin? What is a 
 freckle? 
 
 Of what is the dermis composed? What is a papilla? Where 
 is the subcutaneous layer? Of what is it composed, and what is 
 deposited in it? 
 
 What are the pores in the skin? Describe a sweat gland. What 
 is the function of the sweat glands? Where does the water of the 
 perspiration come from ? Why do we not see the perspiration on 
 the skin at all times? How does perspiration cool the skin? What 
 controls the sweat glands ? 
 
 What is a hair follicle? a hair papilla? With what is the follicle 
 lined and the papilla covered ? When the hair grows, where do the 
 cells multiply ? From what layer of the skin is the hair formed ? How 
 does a hair get food ? Where are the sebaceous glands ? What is 
 their function ? What causes the hair to stand on end ? 
 
 Give two reasons why brushing benefits the hair. What is the 
 cause of dandruff? How may this disease be contracted? What 
 causes baldness? 
 
 From what layer of the skin are the nails formed ? What causes 
 their pink color? What causes the white spot at the base of a nail? 
 What is the function of the nails ? 
 
208 HUMAN PHYSIOLOGY 
 
 What is the temperature of the body in health ? Give two ways by 
 which the body heat is regulated. In what two ways does the skin 
 regulate the escape of the heat from the body ? How do the cells 
 regulate the amount of heat produced? Why must persons living 
 outdoors have more heat than those who live indoors? 
 
 What is fever? What is its cause ? What causes a chill? 
 
 Why should the skin be kept clean? Give the effect of a cold 
 bath on the blood vessels of the skin. Give some other effects of 
 a cold bath. When is a cold bath injurious? 
 
 Give the effect of a warm bath on the vessels of the skin ; on the 
 distribution of the blood. When should a cold bath be taken? a 
 warm bath? Why is a warm bath harmful immediately before or 
 after eating? What is the effect of a tepid bath? Why should one 
 not take a swim immediately after eating ? 
 
 Why are overheated rooms injurious ? underheated rooms ? How 
 does chilling the body injure it? How do cold baths prevent this? 
 What is the proper temperature for a living room ? Why is the use 
 of the thermometer important ? 
 
 What is the chief physiological use of clothing ? How does clothing 
 retain the body heat? Which is the warmest material for clothing? 
 Why? Which material absorbs moisture best? What is the effect of 
 tight clothing on the heat of the body? Why should the feet be kept 
 dry? What is the effect of wearing heavy clothing indoors? At what 
 time of the year should especial care be taken to wear sufficient 
 clothing? 
 
THE SKIN AND THE BODY HEAT 209 
 
 REVIEW QUESTIONS 
 
 Chapter XI. Why is the circulation of the blood necessary? 
 Trace the blood from right auricle to right auricle. What does the 
 blood lose and gain in the capillaries of the body? of the lungs? 
 How is the oxygen carried in the blood? What is lymph? How is 
 it returned to the blood? What is the function of a lymph node? 
 Mention some common causes of injury to the heart. 
 
 Define :* auricle ; ventricle ; artery ; vein ; capillary ; hemoglobin ; 
 plasma ; thoracic duct. 
 
 Chapter XII. What is the object of respiration? Why is oxygen 
 necessary to the body? Why must the body get rid of its carbon 
 dioxid? What does the air gain and lose in the lungs? Why does 
 mouth breathing cause disease? Name five points connected with 
 the hygiene of the respiratory organs. What kind of diseases chiefly 
 affect these organs? How is voice produced? How are the vocal 
 cords thrown into and out of action ? 
 
 Define : pleura ; diaphragm ; uvula ; larynx ; epiglottis ; bronchial 
 tubes ; mucus ; cilia ; thyroid ; cricoid ; arytenoid. 
 
 Chapter XIII. Why is ventilation necessary? How much fresh 
 air does a person need in an hour? How much air space for each 
 person should there be in a public building? in a private house? 
 Explain how a fireplace or stove ventilates a room. Why is the ven- 
 tilation of sleeping rooms especially important ? 
 
 Chapter XIV. What is the usual cause of illness? How are the 
 poisons that are in the body produced ? What is the function of the 
 kidneys? Explain how the wastes get from the blood into the 
 ureters. What diseases of the kidneys are caused by alcohol? 
 
 Define : uric acid ; renal corpuscle. 
 
 Chapter XV. Give four functions of the skin. Explain how the 
 perspiration gets from the blood to the surface of the skin. Draw a 
 diagram of a hair in its follicle. What is the temperature, of the 
 human body? How is the escape of the heat from the body con- 
 trolled ? When is a cold bath injurious ? What is the danger from 
 an overheated room? from a cold room? Mention some hygienic 
 points connected with clothing. 
 
 Define : epidermis ; dermis ; papilla ; follicle ; sebaceous. 
 
CHAPTER XVI 
 
 THE NERVOUS SYSTEM * 
 
 THE first great work of the nervous system is to cause all 
 the parts of the body to work harmoniously together, The 
 second is to act as the organ of the mind. 1 In a former chap- 
 ter we learned something of the way the body is ruled, and 
 we have seen in a general way how the different organs are 
 controlled and kept at work. In this chapter we shall take 
 up in more detail the structure and the function of the ner- 
 vous system. 
 
 Nerve Cells and Nerve Fibers. Nerve tissue contains nerve 
 cells and nerve fibers. The nerve cells are much branched, 
 are larger than most of the body cells, and have a gray colon 
 Most of them are found in the brain 2 and spinal cord, but 
 small groups of nerve cells called ganglia 3 (singular, gang- 
 lion) are found in various parts of the body. 
 
 1 A simple and easy way of treating of the relation between the brain and the 
 mind is to say that the mind is in the brain, and that it is the cells of the brain 
 that think and feel. It may be objected, however, that we do not know where 
 the mind is; that if can exist apart from the body altogether; and that while the 
 function of the muscle cells is to contract, and the function of gland cells is to 
 secrete, it is perhaps not allowable to say that the function of the brain cells is to 
 think. The brain, however, is in some way closely associated with the mind, and 
 we have therefore spoken of it as the organ of the mind. 
 
 2 It is estimated that there are 1,200,000,000 cells in the gray matter on the 
 surface of the cerebrum. 
 
 3 There is a ganglion on the root of each spinal nerve (Fig. 103), but most of 
 the ganglia belong to the sympathetic system (Fig. 106). They are found chiefly 
 
 210 
 
THE NERVOUS SYSTEM 
 
 211 
 
 OEU 
 
 A nerve fiber contains a gray central axis cylinder, which 
 is a branch of the cytoplasm of a 
 nerve cell. A nerve fiber is there- 
 fore always connected with a nerve 
 cell and may almost be considered 
 as a branch of a cell. A nerve cell 
 and nerve fiber taken together are 
 called a netiron. The nerve mes- 
 sages, which are also called stimuli 
 and nerve impulses, travel through 
 a fiber in the gray central axis 
 cylinder. 
 
 Efferent and Afferent Nerve 
 Fibers. 1 The nerve fibers in which 
 the impulses travel from the brain 
 and cord are called efferent fibers. 
 They take messages to the muscles 
 which cause the muscles to contract, 
 and to all the glands and organs 
 of the body, causing each to work. 
 The fibers which carry impulses 
 from the different parts of the 
 body to the brain and cord are 
 called afferent fibers. 
 
 The Nervous System as a Con- 
 nector of the Body Parts. As you 
 
 in the internal parts of the body, and are not 
 found in the limbs, or to any extent among the 
 voluntary muscles. Many of them are micro- 
 scopic. 
 
 1 Efferent and afferent nerve fibers are often 
 called motor and sensory fibers. FIG. 97. A neuron. 
 
212 
 
 HUMAN PHYSIOLOGY 
 
 will understand better after studying reflex actions, a great 
 portion of the work of the nervous system in governing the 
 body is done by putting the different body parts into com- 
 munication with each other. In a former chapter (page 23) 
 we have spoken of the nervous system as the ruler of the 
 body. In reality, it resembles a telephone system as much 
 
 FlG. 98. A shows the number of wires necessary to connect twelve houses by tele 
 phone without a central office. B shows the number of wires necessary to connect the 
 same number of houses through a central office. The number of nerve fibers that 
 would be necessary to connect all parts of the body without a brain and spinal cord 
 to act as a central office can hardly be imagined. 
 
 as it does a monarch. As on a telephone system the dif- 
 ferent houses are put into connection with each other 
 through a central office, so the different parts of the body 
 are connected through the brain and spinal cord. In many 
 parts of the body each cell is supplied with a nerve fiber 
 (Fig. 102) and the body has in it a perplexing network of 
 nerves. By examining Figure 98, you can understand what 
 a hopeless tangle the nervous system would become if an 
 attempt were made to connect all the cells of the body with- 
 out a brain and spinal cord to act as a central office. 
 
THE NERVOUS SYSTEM 
 
 213 
 
 THE CENTRAL NERVOUS SYSTEM 
 
 The central nervous system consists of the brain, the spinal 
 cord, and the nerves arising from the brain and cord. Twelve 
 pairs of nerves pass out from the brain, and thirty-one pairs 
 from the cord, putting these nerve centers in connection with 
 all the body parts. 
 
 The Brain. The spinal cord is only a little thicker than a 
 lead pencil. The brain fills the whole cranial cavity. The 
 
 / MEDULLA -OBLONGATA 
 
 FIG. 09. Longitudinal section of the brain. 
 
 spinal cord of a man weighs about an ounce. The brain 
 weighs about fifty ounces. The brain, therefore, composes 
 by far the greatest part of the central nervous system. Its 
 three main divisions are the cerebrum, the cerebellum, and 
 the medulla oblongata. 
 
 The Cerebrum. The cerebrum comprises more than three 
 fourths of the entire brain. It is divided by a deep groove in 
 
214 
 
 HUMAN PHYSIOLOGY 
 
 its upper surface into a right and a left hemisphere. The sur- 
 face of the cerebrum is thrown into a great number of folds 
 and wrinkles called convolutions (Fig. 13). 
 
 A layer on the surface of the cerebrum is composed of 
 nerve cells, and therefore has a gray color. This is the gray 
 matter of the brain, with which the mind is associated. The 
 inner and lower parts of the cerebrum are chiefly composed 
 of nerve fibers. 
 
 The Fibers of the Cerebrum. A great network of fibers 
 connects all the different parts of the cerebrum with 
 
 each other. Other fibers connect 
 the cerebrum and the cerebellum, 
 and countless fibers run through the 
 medulla into the spinal cord, and 
 connect the cerebrum with the body 
 parts below. In the medulla most 
 of the fibers from the cerebrum cross 
 so that the right hemisphere of the 
 cerebrum is connected with the left 
 side of the body, and the left hemi- 
 sphere is connected with the right 
 side of the body. If, because of 
 injury or of apoplexy, a blood clot 
 forms on the right side of the cere- 
 the left side of the body that will be 
 
 FTG. ioo. The cerebrum 
 from above, showing the hemi- 
 spheres. 
 
 The cerebrum has three func- 
 
 brum, it will be 
 paralyzed. 
 
 Functions of the Cerebrum. 
 tions : 
 
 The cerebrum is the seat of the mind. When the cerebrum 
 of a pigeon or of a dog is removed, life may go on, but all 
 memory and reason are lost, and the animal is hopelessly 
 idiotic. Removing the gray matter on the surface of the 
 
THE NERVOUS SYSTEM 215 
 
 cerebrum has the same effect on the intelligence as re- 
 moving the whole cerebrum. 
 
 The cerebrum is the seat of the sensations. Nerve messages 
 from all parts of the body come into the cerebrum and 
 cause the sensations of light, sound, taste, smell, touch, heat, 
 cold, hunger, fatigue, and other sensations. Without a 
 cerebrum an animal has no mind, and without a mind there 
 could, of course, be no knowledge of the afferent nerve 
 impulses and no such thing as a sensation 'of pain, cold, 
 hunger, or any other kind of sensation. 
 
 The cerebrum originates and sends out impulses that cause 
 voluntary movements. When we decide to move, the cere- 
 brum can start out impulses which cause the muscles to con- 
 tract. We have, therefore, the power of voluntary movement 
 the power to make the muscles work when we wish them 
 to do so. 
 
 The Cerebellum. The cerebellum lies behind and above 
 the medulla, and is covered over by the back lobes of the 
 cerebrum. Many nerve fibers connect the two sides of the 
 cerebellum with each other. The cerebellum is also con- 
 nected with the cerebrum, and through the medulla and cord 
 with most of the body. The cells in the cerebellum are 
 mainly in a layer on the surface, and the fibers in its central 
 lobe are arranged so that they form a tree-like mass of white 
 matter, called the arbor vita ("tree of life "). 
 
 Function of the Cerebellum. There is much dispute about the 
 function of the cerebellum, but it seems to be about as follows : 
 
 The cerebellum causes all the muscles to keep a proper 
 amount of contraction. When the cerebellum is injured, all 
 the muscles are relaxed, instead of keeping a certain amount 
 of contraction as they usually do. The result is trouble in 
 the movements, because when the cerebrum causes a muscle 
 
2i6 HUMAN PHYSIOLOGY 
 
 to contract, the antagonistic muscle does not work in opposi- 
 tion and steady the motion. This causes jerky movements 
 and movements that often go too far (page 67). 
 
 The second function of the cerebellum is to assist in coor- 
 dinating the movements of the muscles of locomotion. When 
 a man's cerebellum is injured, he staggers about as though 
 he were intoxicated. His muscles are not paralyzed, but 
 some of them contract too powerfully, some not powerfully 
 enough, and often they fail to contract at the right moment. 
 The cerebellum seems to cause the muscles that are used in 
 standing, walking, and running to act in an orderly manner, 
 and thus keeps the body from falling. 
 
 The Pons. The pons lies in the pathway between the dif- 
 ferent parts of the brain, and it is composed chiefly of fibers 
 that connect the cerebrum, cerebellum, and medulla. There 
 are also in the pons many fibers that connect the two sides of 
 the cerebellum. From one side of the cerebellum the fibers 
 pass forward to the pons, cross over in it, and turn backward 
 into the other side of the cerebellum. The word " pons " 
 means a bridge, and the pons is a bridge connecting all parts 
 of the brain. 
 
 The Medulla. The medulla contains many nerve fibers 
 that connect the higher parts of the brain with the spinal 
 cord and the body. The greater part of the head and many 
 of the internal organs, including the heart and lungs, are sup- 
 plied by nerves that rise from the medulla. When the cere- 
 brum is removed from an animal, the intelligence is lost, but 
 life may go on; when the cerebellum is injured, the control 
 of the muscles is lost; but when the medulla is injured, death 
 comes at once because the breathing stops. 
 
 The Function of the Medulla. The medulla conducts stimuli 
 to and from the higher parts of the brain, and */ acts as a reflex 
 
THE NERVOUS SYSTEM 21 J 
 
 center for the parts of the body that receive nerves from it. 
 To understand what is meant by a reflex center we must 
 know what a reflex action is. Before taking up this subject 
 we shall discuss the spinal cord, for like the medulla the 
 spinal cord is a reflex center. 
 
 The Spinal Cord. The inner part of the spinal cord is 
 composed of gray matter (cells) and the outer part of white 
 matter (fibers). All the skin and the voluntary muscles of 
 the body parts below the neck are supplied by the thirty-one 
 pairs of spinal nerves, and through the sympathetic system 
 the spinal cord is connected with the internal organs, the 
 sweat glands, and the blood vessels. 
 
 Functions of the Spinal Cord. The spinal cord has the same 
 two functions as the medulla. The first of these functions is 
 to conduct impulses to and from the brain. The nerve impulses 
 that come in through the spinal nerves pass up to the brain 
 through the cord, and the nerve impulses sent out by the 
 brain to the glands and muscles come down through the 
 cord. For this reason, if the spinal cord be cut across, all 
 parts of the body supplied by nerves from below the cut 
 lose their feeling and are paralyzed. The impulses from 
 these parts cannot get up to the brain to cause sensations 
 of feeling, and the commands of the brain cannot get to the 
 muscles below the cut to cause them to move. The other 
 function of the spinal cord is to act as a reflex center. 
 
 Reflex Actions. Reflex actions are actions that are caused 
 by impulses which start in afferent nerves. An example 
 will give the clearest idea of a reflex. 
 
 Suppose you burn your finger by touching a candle flame 
 (Fig. 101). The heat starts an impulse up the afferent nerve 
 fibers. The impulse passes into the spinal cord, then into 
 the efferent nerve, and traveling down to the muscles of the 
 
218 
 
 HUMAN" PHYSIOLOGY 
 
 arm, causes them to contract and jerk the hand away. An 
 impulse also goes on up to the brain, and causes a sensation 
 of pain, but the hand is moved before the pain is felt. 
 
 An action like this is a reflex action. It differs from the 
 action when you voluntarily move your hand in the place in 
 which the nerve impulse starts. In the voluntary action, the 
 brain originates and starts out the impulse. In the reflex 
 
 FIG. 101. Diagram illustrating reflex action. The impulse starts in the finger and 
 passes through the spinal cord to the muscle of the arm. B shows the way the con- 
 nections between the neurons are made in the cord. 
 
 action, the impulse starts in the outer ends of the nerves, goes 
 into the cord, and comes back down the nerves to the muscles. 
 In this action the spinal cord makes the connection between the 
 afferent and efferent neurons. 
 
 Could a reflex be carried on without thought ? Could the 
 spinal cord carry on reflexes without the brain ? If nothing 
 disturbed the outer ends of the afferent nerves, would a reflex 
 center ever cause movement ? Think out these problems, and 
 you will read the next paragraphs more intelligently. 
 
THE NERVOUS SYSTEM 
 
 219 
 
 The Spinal Cord as a Reflex Center. The spinal cord can 
 carry on reflexes in a wonderful w,ay without the aid of the 
 brain. A shark with its head cut off, swims in a very natural 
 manner. A turtle can walk about after it has lost its head. 
 If a drop of weak acid or strong vinegar is put on the back 
 of a brainless frog, the frog 
 will wipe the acid or vinegar 
 off with its foot. If the foot 
 that the frog is using is held, 
 the other foot will then be used. 
 The spinal cord, without the 
 brain, can carry on reflex ac- 
 tions for any part of the body 
 that is supplied by the spinal 
 nerves. 
 
 What the Spinal Cord does 
 in Reflexes. The spinal cord 
 not only acts as a connector 
 between the afferent and the 
 efferent neurons, but it makes 
 the right connections so that 
 the proper muscles will be FlG I02 The efferent nerve ending 
 
 moved. // also arranges and in the voluntary muscle cells. 'Through 
 
 sets in order the impulses that the nerve fibers 'w** com ? into the 
 
 muscle cells and cause them to contract. 
 
 come to tt, hurrying them on to 
 
 some muscles, holding them back from others, making some of 
 the stimuli strong and others weak, so that in a movement like 
 the swimming of the shark, which involves almost the whole 
 body, each muscle gets its stimulus so that it will contract at 
 exactly the right moment and with the proper force. Yet 
 the spinal cord has no intelligence; for a brainless frog will 
 sit and dry up beside the water that would save its life, and 
 
220 HUMAN PHYSIOLOGY 
 
 all memory is gone from an animal that has only a spinal 
 cord. 
 
 Other Reflex Actions. Reflex centers are found not onty 
 in the cord but also in the medulla and in the lower part of 
 the brain in front of the medulla, and to a large extent the 
 body is governed through its reflex centers. If the eye is 
 touched, the eyelids will close. Tickling the inside of the 
 nose causes sneezing, and tickling the inside of the larynx 
 causes coughing. Cold water thrown on the face causes the 
 breath to be drawn in suddenly, while a sharp odor, as of 
 ammonia, stops the inspiration. Water starting into the nose 
 also checks the breath, and in diving birds, water poured 
 across the nostrils will for a long time hinder inspiration. 
 Heat on the skin makes the vessels relax, and cold causes 
 them to contract. The passing of digested food into the 
 intestine causes the pancreas to secrete its juice and the gall 
 bladder to be emptied. Almost the entire government of 
 the internal organs is carried on by reflexes of which we are 
 not even conscious, but when one of these organs gets into 
 trouble, the impulses that the afferent nerves carry up to the 
 brain give us the sensation of pain and let us know that some 
 of our organs need attention. 
 
 The Body Self-governing through the Reflexes. A close 
 study of the reflexes shows that they are all purposeful. 
 Even those which are carried out without intelligence or con- 
 sciousness are all beneficial to the body. In studying them, 
 one also becomes impressed with the fact that the body itself 
 brings these reflexes about, and through them largely regu- 
 lates itself. For example, when the heart beats hard and the 
 arteries are tightly stretched with blood, it takes a forcible 
 contraction to squeeze the blood out of the ventricles into the 
 arteries. The pressure of the blood within the heart then 
 
THE NERVOUS SYSTEM 221 
 
 starts impulses up the afferent nerves of the lining of the 
 heart. These pass to the medulla, and impulses which slow 
 up the beat of the heart come down the efferent nerves 
 Thus the heart largely regulates itself, the high blood pres 
 sure causing it to slow its beat. By the effects of heat and 
 cold on the skin, the blood vessels are largely controlled, and 
 many other parts of the body are also, to a certain extent, self- 
 governing. We must not give too much credit to the nervous 
 system for its wonderful wisdom in regulating the body, for 
 usually the impulses which cause the action of the muscles 
 and glands are not started by the nervous system at all, but 
 by some other part of the body, and all that the nervous sys- 
 tem does is to make the proper connections between the 
 afferent and efferent nerves. 
 
 Acquired Reflexes. Besides these natural reflexes, there 
 is another set of reflexes that is acquired by practice. In 
 skating, riding a bicycle, rowing, boxing, fencing, playing a 
 piano, and in almost any kind of activity, movements are 
 made without thought. The eye of the piano player sees a 
 certain note, and his finger strikes the right key. The bicycle 
 rider feels a slight leaning of his wheel to the side, and he 
 shifts his body so as to keep the balance. These movements 
 have been made so often that they become reflex, and are 
 carried out without thought. 1 
 
 Habit. The performance of any act with which the mind 
 is connected makes easier a further performance of that act. 
 For instance, the fingers of the pianist move slowly and awk- 
 wardly at first, since the mind requires time to decide where 
 
 1 The acquired reflexes are all associated with the mind, and their seat is in 
 the outer layer of the cerebrum. When this is removed, all the acquired reflexes 
 are lost, while the natural reflexes that are carried on by the lower parts of the 
 brain and by the cord remain. 
 
222 HUMAN PHYSIOLOGY 
 
 each finger shall be placed. But after long practice the 
 fingers move rapidly and without thought. By practice the 
 skilled swordsman has trained his nervous system so that 
 without thought so quickly that there is not time for 
 thought his sword follows that of his antagonist and turns 
 aside the thrust. 
 
 As a physical habit can be formed by the repetition of an 
 act, so mental and moral habits can be formed habits of 
 good work and of poor work ; of honesty and dishonesty ; of 
 neatness and accuracy, and of carelessness and untidiness ; 
 habits of preparing lessons and of leaving them unprepared. 
 All kinds of habits are formed most readily in youth, and 
 it is seldom that, after the age of twenty-five or thirty, long- 
 established habits are broken. Indeed, it is difficult at any 
 time of life to break a habit that has once been thoroughly 
 formed. The pupil who is idle in the third grade is usually 
 an idler still in the sixth grade. The trifler in the sixth grade 
 is usually a trifler still in the high school ; and it would be 
 almost a miracle to find a high school drone who had become 
 a capable and industrious college student 
 
 Just what it is in the nervous system that makes it want 
 to keep doing the same things over again, is not known. But 
 it is well known that what a person does in youth determines 
 very largely what that person will both do and be in his later 
 life. The character is largely formed by the habits, and there 
 is much truth in the old proverb which says, "Sow an act 
 and reap a habit ; sow a habit and reap a character." 
 
 Summary. The nervous system controls the body and is 
 the organ of the mind. 
 
 Most of the nerve cells are in the brain and spinal cord, but 
 a few of them are in ganglia. A nerve cell and its fiber are 
 called a neuron. Nerve fibers that carry impulses outward 
 
THE NERVOUS SYSTEM 
 
 223 
 
 are efferent fibers, and those that carry them inward are 
 afferent fibers. The nervous system does a great part of 
 its work by acting as a connector of the body parts. It is 
 arranged like a telephone system in which the spinal cord 
 and brain correspond to the central office. 
 
 The cerebrum is the largest division of the brain. It is 
 divided into hemispheres and has many convolutions on its sur- 
 face, to give room for the cells that are associated with the mind. 
 The fibers from it cross in the medulla, so that the two hemi- 
 spheres of the cerebrum are connected with opposite sides of 
 the body. The cerebrum is the seat of the mind and of the 
 sensations, and originates impulses that cause voluntary motion. 
 
 The cerebellum causes the muscles to keep a proper amount 
 of contraction and coordinates the movements of the muscles 
 of locomotion. The pons is a bridge between the different 
 parts of the brain. The medulla connects the brain and spinal 
 cord and gives rise to nerves that supply the head and many 
 internal organs, including the heart and lungs. The function 
 of the medulla is to transmit stimuli and act as a reflex center. 
 The spinal cord gives rise to many nerves. It conducts 
 stimuli and is a reflex center. 
 
 In a reflex action the impulse starts in an afferent nerve, 
 passes inward to the brain or cord, and comes out again along 
 an efferent nerve. Reflexes are carried on without thought, 
 and through them the body is in a great measure self -regu- 
 lating. Certain reflexes may be acquired by practice, and 
 habits are easily formed. To a large extent the habits formed 
 in youth determine what the character will be. 
 
 QUESTIONS 
 
 Give two functions of the nervous system. Where are most of the 
 nerve cells found ? What is a ganglion ? an axis cylinder ? a neuron ? 
 
224 HUMAN PHYSIOLOGY 
 
 What is an afferent nerve fiber ? an efferent nerve fiber ? How is 
 an important part of the work of governing the body done by the 
 nervous system? What is the advantage in having the nervous 
 system arranged with a central portion through which all the body 
 parts are connected? 
 
 What are the parts of the central nervous system ? How large is 
 the brain as compared with the spinal cord? Name the three 
 divisions of the brain. How large is the cerebrum? How is it 
 divided? What are the convolutions? Where is the gray matter 
 of the cerebrum? Of what is it composed? With what is it as- 
 sociated? With what part of the body is the right hemisphere of 
 the cerebrum connected ? Where do the fibers from the cerebrum 
 cross? Give three functions of the cerebrum. 
 
 What is the arbor vitae? Give two functions of the cerebellum. 
 What is the result of injury to the cerebellum ? Where is the pons? 
 Of what is it composed and what does it do ? What part of the body 
 is supplied with nerves from the medulla? Why does injury to the 
 medulla cause death ? Give two functions of the medulla. 
 
 Where are the fibers in the spinal cord? the cells? What two 
 functions has the cord ? What is a reflex action ? Give an example 
 of one. What is the great function of the spinal cord in a reflex 
 action ? 
 
 Mention some reflexes that can be carried on without the brain. 
 What does the spinal cord do in these reflexes in addition to making 
 the connections? Does it have intelligence? Where are some 
 other reflex centers ? What are some of the reflexes that are carried 
 on by them ? Give some examples of how the body regulates itself 
 through reflexes. 
 
 What is an acquired reflex? Give examples of acquired reflexes. 
 How are habits formed ? Why is it important that correct habits be 
 formed early in life ? 
 
CHAPTER XVII 
 
 EFFERENT ROOTS 
 
 FIG. 103. 
 
 The spinal cord and the roots of a pair of spinal 
 nerves. 
 
 THE NERVOUS SYSTEM (Continued) 
 NERVES 
 
 The Cranial Nerves. The twelve pairs of cranial nerves 
 rise from the brain. The first pair are the nerves of smell, 
 and the second pair are the nerves of sight. The nerves of 
 taste and of hear- 
 ing are also cra- 
 nial nerves. In 
 general, the cra- 
 nial nerves sup- 
 ply the head, 
 but one pair of 
 nerves from the medulla goes to the internal organs of the 
 body (page 216). 
 
 Spinal Nerves. Thirty-one pairs of spinal nerves pass out- 
 ward from the spinal cord through openings between the 
 vertebrae. Each spinal nerve has a ventral and dorsal set of 
 roots. The ventral roots come from the front of the cord and 
 the dorsal roots from the back of the cord. The ventral 
 roots contain the efferent fibers, and the dorsal roots the 
 afferent fibers. Outside of the spinal cord the roots unite 
 to form one nerve, which contains both efferent and afferent 
 fibers. 
 
 Effect of cutting and stimulating a Spinal Nerve. The affer- 
 ent impulses pass into the cord through the dorsal roots of a 
 
 225 
 
226 HUMAN PHYSIOLOGY 
 
 spinal nerve; the efferent impulses pass out of the cord 
 through the ventral roots. What effect would it have on the 
 part that is supplied by a spinal nerve, if the nerve were 
 cut as in A (Fig. 104)? If it were cut as in Bt as in C1 
 
 AFFERENT ROOT 
 
 AFFERENT ROOT AFFERENT ROOT 
 
 EFFERENT ROOT A EFFERENT ROOT D EFFERENT ROOT 
 
 FIG. 104. A is a spinal nerve that has been cut; B is a spinal nerve, with the 
 efferent root cut ; C is a spinal nerve with the afferent root cut. 
 
 A nerve impulse started in the wrong direction in a nerve 
 produces no effect. Suppose thaj: by pinching the cut end 
 of the nerve or by touching it with an electric wire you stimu- 
 lated it and started an impulse in it. What effect would it 
 have to stimulate the cut end at a (Fig. 104)? at ? at cl 
 at*/? at*? at/? 
 
 THE SYMPATHETIC NERVOUS SYSTEM 
 
 Nearly all the cells of the central nervous system are in the 
 brain and spinal cord. They are collected in great centers. 
 The cells of the sympathetic nervous system are in ganglia, 
 which are scattered through the body. This system consists 
 chiefly of two chains of ganglia, one on either side of the 
 spinal column ; of scattered ganglia in many of the internal 
 organs, especially the intestine and other abdominal organs ; 
 of a great network of fibers that connect all these ganglia 
 with each other and with the spinal cord and brain ; and of 
 the sympathetic nerves that supply various organs. 
 
 From some of the cranial nerves and from all of the spinal 
 nerves, branches run to and from the sympathetic ganglia. 
 Every part of the sympathetic nervous system is thus con- 
 
THE NERVOUS SYSTEM 
 
 227 
 
 nected with the central nervous system, the 
 medulla and the sympathetic system being 
 especially closely connected. Thus the central 
 nervous system is able, through the sympa- 
 thetic system, to reach the parts of the body 
 that are not supplied with nerves directly from 
 the brain and cord. 
 
 The Function of the Sympathetic System. In 
 general the sympathetic system controls the in- 
 
 ternal organs (heart 
 and blood vessels, di- 
 gestive organs, kid- 
 neys, etc.) and the 
 sweat glands and ves- 
 sels of the skin. It 
 controls these organs 
 chiefly through reflex 
 actions, yet the 
 sympathetic system is 
 not an independent 
 system. It cannot do 
 its work without the 
 central nervous sys- 
 tem, as you will un- 
 derstand when you 
 have learned how 
 sympathetic reflexes 
 
 are Carried OUt. 
 
 FIG. 106. Side view of the sym- .4Ji^i : K 
 
 patheticnervoussystem. Note the Sympathetic Re- *! 
 chain of ganglia lying beside the flexCS. A Sympathetic ganglion 
 spinal column, and the great net- ^ ^ the power to turn an 
 work of fibers running to the in- 
 
 temai organs. 
 
 , FlG -'S; Th< | 
 
 two chains ok 
 sympathetic gan- 
 
 . 
 
 bacR and cause a reflex action, but 
 
228 HUMAN PHYSIOLOGY 
 
 when the ganglion receives an afferent impulse, it sends the 
 impulse on into the spinal cord or brain, where it is started 
 back down an efferent nerve. The impulses go through 
 ganglia on their way to and from the cord and brain, 
 but the reflex centers lie in the central system. Although 
 the central nervous system takes part in the sympathetic 
 reflexes, yet we have no consciousness of these reflexes. 
 Neither is it possible for us by a voluntary effort to 
 influence the internal organs through the sympathetic sys- 
 tem. This system is connected with the spinal cord and with 
 the lower centers of the brain, and not with the higher cen- 
 ters of the brain, with which the mind is associated. 
 
 FlG. 107. In the sympathetic system the nerve impulses pass through ganglia on 
 their way to and from the cord and brain. 
 
 The Sympathetic a Part of the Central Nervous System. 
 The entire nervous system works together in governing the 
 body, and it gives a wrong impression to speak of two 
 systems. The sympathetic is, after all, only a branch of 
 the central nervous system that is ruled without our knowl- 
 edge by the cord and by the lower centers of the brain. 
 It contains such a network of fibers that almost all the 
 internal parts of the body are connected the one with the 
 other, so that it is impossible for one of these organs to 
 become deranged without affecting the other organs. The 
 organs thus " sympathize" with each other, and for this reason 
 the nerves to these parts are called the sympathetic system. 
 
THE NERVOUS SYSTEM 
 
 229 
 
 THE NERVOUS SYSTEMS OF OTHER ANIMALS 
 
 The great difference in the nervdus systems of the higher 
 and lower vertebrates is in the cerebrum. In the lower 
 forms, as in the fishes, frogs, and 
 reptiles, the cerebrum is small 
 and smooth, and contains on its 
 surface only a few of the nerve 
 cells (gray matter) that in man 
 are associated with the mind. 
 In the higher animals, the cere- 
 brum is greatly increased in 
 size, and its surface becomes 
 convoluted, making room for a 
 great number of nerve cells on 
 its surface. As a general state- 
 ment, it is true that intelligence 
 increases with the development 
 of the cerebrum. The lower forms with small cerebrums are 
 stupid, and higher animals with larger and more convoluted 
 cerebrums are more intelligent. The cerebrum of man is the 
 most highly developed of all, and man is the most intelligent 
 of all animals. 
 
 HYGIENE OF THE NERVOUS SYSTEM 
 
 The nervous system is so closely connected with all parts of 
 the body that it is of the utmost importance to keep it in 
 health. Good food and fresh air are necessary to the nerve 
 cells, as they are to all other cells. In the special hygiene of 
 the nervous system, the following points should be noted : 
 
 Sleep. Sleep is absolutely necessary to the nervous sys- 
 tem. During sleep the nerve cells rest and prepare them- 
 
 FlG. 108. The brain of a snake (A) t 
 and ol a cat (B). 
 
230 HUMAN PHYSIOLOGY 
 
 selves for further work, and the idea that it is possible to 
 sleep too much is probably incorrect. Babies should sleep 
 from fifteen to twenty hours out of the twenty-four, older 
 children from ten to fourteen hours, and adults from seven to 
 ten hours. Occasionally a person is found who keeps in good 
 health on five or six hours of sleep, and other persons are 
 found who must have eleven or twelve hours. Most people 
 under twenty years of age are better off with ten hours of 
 sleep than with eight or nine hours, and most older persons 
 keep in better health when they sleep nine full hours than 
 when they sleep seven or eight hours. 
 
 There is no surer way to undermine the health than to stay 
 up late at night and get up early in the morning, thus cutting 
 short the hours of sleep. One who is doing this may think 
 he is in good health, but if he will enter an athletic contest or 
 do something else that will really put his nervous system to 
 the test, he will find that he is not in the best condition. A 
 runner who has been losing sleep has not the slightest chance 
 of winning from others who have had long and regular hours 
 of sleep. His nervous system cannot control his muscles 
 quickly and accurately enough to prevent his falling behind 
 in the race. 
 
 Tobacco. The evil effects of tobacco on the nervous system 
 are generally recognized. Its weakening effect on the mus- 
 cles has already been noted (page 74), and it seems to produce 
 this effect more by interfering with the nervous regulation of 
 the muscles than by injuring the muscle cells themselves. 
 
 Persons who use tobacco are often troubled with a restless- 
 ness and a jerkiness of movement, so that they cannot remain 
 long in any one position. They are also subject to more or 
 less constant trembling of the extremities, especially of the 
 hands. Men who use tobacco seldom have the steadiness of 
 
THE NERVOUS SYSTEM 231 
 
 nerve required to make expert marksmen, and athletes who 
 are training for contests of strength, endurance, or skill are 
 not allowed to use tobacco in any form. 
 
 The effects of tobacco on the mind are more pronounced 
 than its effects on the nervous control of the muscles, One 
 class at Yale University was divided into four grades accord- 
 ing to scholarship. Only 25 per cent of those in the highest 
 division used tobacco, while 85 per cent of those in the lowest 
 division were tobacco users. In another class 90 per cent of 
 the first honor men were non-users of tobacco. 
 
 In young pupils the effects of tobacco on the mind are 
 much more marked than are its effects in older persons. In a 
 Chicago school, out of 125 boys who smoked, only two were 
 able to keep up with their class. Nine tenths of these 125 
 boys belonged to educated, intelligent families; they had 
 Deen given excellent school advantages; yet among them 
 were found nearly all the boys who were from two to four 
 /ears older than the average age of the children in their 
 grade. In all, there were reported in Chicago 2402 pupil* 
 who were cigarette smokers, and only 6 per cent of them 
 were able to do the school work of their grade. It is reason- 
 able to believe that the use of tobacco had dulled the minds 
 of these boys and had changed many of them from bright, 
 active pupils into idling incompetents. 
 
 Tobacco also often leads to moral degeneration. Nothing 
 is more fatal to ambition than tobacco, and to an extent it 
 destroys the will power. A boy begins smoking a few cigar- 
 ettes, and soon the habit has fastened itself on him so firmly 
 and his will has been so weakened that he cannot break the 
 habit, even when he realizes that he is injuring himself. The 
 great majority of boys who smoke cigarettes are irritable, per- 
 verse, and careless of the rights of others. Our prisons and 
 
232 
 
 HUMAN PHYSIOLOGY 
 
 reformatories are filled with those who began smoking cigar- 
 ettes in youth. What would have been the fate of each of 
 these persons if he had not used tobacco, is of course im- 
 possible to say; but there is no doubt but that many of 
 them would have led successful lives if it had not been for 
 cigarettes. 
 
 So well known are the effects of tobacco on the young, that 
 in nearly all our states and in many foreign countries, stringent 
 laws have been passed making it a crime to sell or give 
 tobacco to boys under a certain age. One state has even 
 prohibited the use of cigarettes in any form by old or young. 
 
 FlG. 109. At the left is a healthy nerve cell from a sympathetic ganglion. The 
 others are nerve cells from one of the sympathetic ganglia of a man who died of alco- 
 holic paralysis. Note the breaking down of the cells that the alcohol has caused. 
 
 Employers often favor those who do not use tobacco, and 
 many employers will have nothing to do with tobacco-using 
 boys. The evil effects of tobacco are known to the world, 
 and this evil effect falls most heavily on the nervous system. 
 
 Alcohol. To tell the exact effect of a very small amount 
 of alcohol on the nervous system is no more possible than to 
 tell the exact effect of a small amount of alcohol on any 
 other part of the body. When any considerable amounts of 
 alcohol are taken, however, the entire nervous system is 
 deranged. The following effects are very noticeable when 
 alcohol is used to excess : 
 
 If enough alcohol is given to an animal to produce intoxi- 
 
THE NERVOUS SYSTEM 
 
 233 
 
 cation, in from ten to forty minutes the branches of some of 
 the nerve cells will be found to be shrunken and gathered 
 into little knots, and certain granules that are found in the 
 protoplasm of nerve cells will have broken down. In long- 
 continued excessive use of alcohol, many of the cells die, and 
 it is also common for nerve fibers to degenerate and die, 
 causing paralysis. Continued use of alcohol also causes a 
 thickening of the connective-tissue membranes of the brain, 
 and of the supporting tissue within the gray matter of the 
 brain, so that the brain of a confirmed alcoholic contains 
 fewer nerve cells and more supporting tissue than does a 
 normal brain. In delirium tremens, some changes that are 
 not at all understood occur in the nerve cells generally. 
 With such changes in structure of the nervous tissue, we 
 should naturally expect the great disturbances of function 
 which alcohol causes. 
 
 Almost every one is familiar with the way the nervous 
 system loses control of the muscles when it is under the in- 
 fluence of alcohol. The weakening of the muscles that fol- 
 lows the use of alcohol (page 74) seems to be due more to 
 its effect on the nervous system than to the effect on the 
 muscles themselves. The nervous system is as greatly in- 
 fluenced by alcohol in its other work, as in its work of regu- 
 lating the muscles ; the mind of an intoxicated person works 
 no more accurately than his muscles work. Drunkenness 
 may very properly be considered as temporary insanity, 
 caused by the poisoning of the nerve cells by alcohol. De- 
 lirium tremens is a condition in which the cells have been so 
 repeatedly poisoned that ideas are associated in the most 
 grotesque and frequently terrifying manner. 
 
 The effects of alcohol on animals are very marked. Kittens 
 that were daily intoxicated with alcohol lost al\ interest in 
 
234 
 
 HUMAN PHYSIOLOGY 
 
 FlG. no. These are normal kittens, and they are playing as healthy kittens do. 
 
 play, cleanliness, and mice, and showed no fear of dogs. 
 They ate and slept, but took no interest in anything else, 
 acting strikingly like animals from which the cerebrum had 
 been removed. Dogs that had been given alcohol daily in 
 moderate amounts showed the most extreme fear, howling 
 
 FlG. in. These kittens have been given alcohol. They are stupid and sleepy, 
 and have lost all interest in play. (From a photograph by Dr. C. F. Hodge.) 
 
THE NERVOUS SYSTEM 235 
 
 and cringing when a bell was rung or when the floor was 
 struck, and awakening from their sleep to cower in terror or 
 run and howl in an agony of causeless fear. This timidity 
 continued after the giving of alcohol had been stopped, show- 
 ing that the mental workings of the brain had been perma- 
 nently injured. 
 
 The results of these experiments show the very great effect 
 of alcohol on the mind. It is estimated that 20 per cent of 
 insanity comes from this cause, and it is proper to conclude 
 that just as alcohol injures the liver and kidneys, so it injures 
 the nerve tissue ; and as it interferes with the workings of 
 the liver and kidneys, so it interferes with the function of the 
 nervous system, both in governing the body and in its work 
 as an organ of the mind. 
 
 Summary. The twelve pairs of cranial nerves rise from 
 the brain. They supply the head and many of the internal 
 organs. The thirty-one pairs of spinal nerves rise in the 
 spinal cord. Each nerve has a set of ventral roots that con- 
 tain the efferent fibers and a set of dorsal roots that contain 
 the afferent fibers. 
 
 The sympathetic nervous system consists of a network 
 of ganglia and fibers. It controls by reflexes the internal 
 organs, the blood vessels, and the sweat glands. It is con- 
 nected with the central nervous system and cannot carry on 
 its work alone. It is called the sympathetic system because 
 by it all the internal organs are connected and through it 
 they " sympathize " with each other. 
 
 Intelligence increases with the development of the cere- 
 brum. The lower vertebrates have small, smooth cerebrums 
 and the higher vertebrates have larger and more convoluted 
 cerebrums. The human cerebrum is the most highly devel- 
 oped of all. 
 
236 HUMAN PHYSIOLOGY 
 
 Because the nervous system is directly connected with all 
 parts of the body, it is very important to keep it in health. 
 The special need of the nervous system is sleep, without 
 enough of which we cannot have good health. 
 
 Tobacco interferes with the nervous control of the muscles. 
 It also dulls the mind. It is especially harmful to the young, 
 as is shown by the fact that only 6 per cent of 2402 cigarette 
 smokers in the Chicago public schools were able to do their 
 school work. Another effect of tobacco is a weakening of 
 the moral nature. 
 
 Alcohol affects the structure of nerve tissue, the excessive 
 use of alcohol causing many of the nerve cells and fibers tu 
 die. It also affects the function of nerve tissue, intoxication 
 causing the nervous system to lose its control of the muscles 
 and its mental power. The minds of animals are perma- 
 nently injured by alcohol, and among human beings about 
 20 per cent of insanity is caused by it. 
 
 QUESTIONS 
 
 How many pairs of cranial nerves are there? Where do they rise ? 
 What part of the body do they supply? 
 
 How many pairs of spinal nerves are there? Where do they rise? 
 What kind of fibers are in the dorsal roots ? the ventral roots ? 
 
 Of what does the sympathetic nervous system consist ? How is the 
 central nervous system connected with it ? What part of the body 
 does it control? Explain how a sympathetic reflex is carried out. 
 Are we conscious of these reflexes ? Can we .control them ? Why is 
 this part of the nervous system called the sympathetic system ? 
 
 What is the great difference in the nervous systems of the higher 
 and lower vertebrates ? What increases with the development of the 
 cerebrum ? 
 
THE NERVOUS SYSTEM 237 
 
 How much sleep is needed by persons of different ages ? What is 
 said of the importance of sleep? y 
 
 What effect has tobacco on the muscles? How does it produce 
 this effect? What did investigations at Yale University show in 
 regard to the effects of tobacco on the students? How many of the 
 125 cigarette smokers in one Chicago public school kept up their 
 school work? What per cent of the cigarette smokers in all the 
 schools investigated did so? What effect has tobacco on the am- 
 bition ? on the will power ? As a rule, are cigarette smokers worried 
 about their own condition and anxious to do better? Why have laws 
 been made against selling cigarettes? Why do employers favor boys 
 who do not use tobacco? 
 
 What is the effect on the nerve cells of an animal of sufficient alco- 
 hol to cause intoxication ? How quickly does it produce this effect ? 
 What effect has long-continued and excessive use of alcohol on nerve 
 tissue ? on the supporting tissue of the brain ? What effect has alcohol 
 on the nervous control of the muscles ? on the mental workings of the 
 nervous system? 
 
 What effect had daily intoxication on kittens? What effect had 
 moderate amounts of alcohol on the minds of dogs ? 
 
 A reflex movement (Fig. 101) is quicker than the movement 
 would be if the impulse had to go to the brain. Explain why. What 
 advantage is there in having the body governed by reflexes that 
 require no attention from the mind? 
 
 When the " funny bone " is struck, a nerve in the arm is crushed 
 against the bone. What part of the body is affected? Explain why. 
 Persons who have had a limb amputated sometimes complain of 
 pain in the limb. What causes this sensation ? Where is the 
 trouble in a paralytic stroke ? 
 
CHAPTER XVIII 
 
 THE EFFECTS OF ALCOHOL ON THE HUMAN BODY 
 
 THE question of the use of alcoholic drinks is one that con- 
 tinually agitates our nation, and indeed has been receiving, 
 for many years, the serious attention of the whole civilized 
 world. The opponents of alcohol insist that it is the chief 
 cause of poverty and crime, and they urge against alcohol 
 the physiological argument that it injures the body. Other 
 persons maintain that alcohol, in moderate quantities, is 
 beneficial to the body. 
 
 We have already learned something of the effects of alcohol 
 on many of the different organs of the body. The human 
 body, however, is more than a collection of organs. It is 
 one whole, and any physiological question must be looked at 
 from the standpoint of the body as a whole. In this chapter 
 we shall take up the effects of alcohol on the body from a 
 more general view point. 
 
 What is Alcohol? Alcohol is a substance formed from 
 
 sugar by a small plant called 
 yeast. When yeast grows in 
 water in which sugar is dissolved, 
 it digests or ferments the sugar, 
 breaking it up into water, carbon 
 dioxid, and alcohol. The alcohol, 
 like the carbon dioxid, is poisonous to the yeast if present in 
 large quantities. 
 
 Alcoholic Drinks. The most common alcoholic drinks are 
 wine, cider, beer, and distilled liquors. Wine and cider are 
 
 238 
 
 FIG. 112. Yeast plants. 
 
EFFECTS OF ALCOHOL ON THE HUMAN BODY 239 
 
 made by allowing yeast to ferment the sugar in fruit juice. 
 If it is apple juice that is fermented, the product is cider. If 
 grape juice is fermented, the product is wine. Beer is made 
 by allowing the yeast to ferment sugar from grain. The 
 starch in the grain is first changed to sugar by sprouting 
 the grain, after which it is ready to be fermented by the yeast. 1 
 
 Brandy is manufactured by distilling fermented fruit juice. 
 Whisky is made by distilling the fermented material from 
 grain or potatoes, and rum by distilling fermented molasses. 
 Beer contains on an average about 5 per cent of alcohol, 
 wine contains about 10 per cent of alcohol, and distilled 
 liquors contain about 50 per cent of alcohol. 
 
 Alcohol and Length of Life. If alcohol as it is commonly 
 used is beneficial to the body, drinkers should live longer 
 than those who abstain from alcohol. If alcohol injures the 
 body, we should expect abstainers to be longer lived than 
 drinkers. The best possible way, therefore, of settling the 
 question as to whether alcohol injures or benefits the body is 
 to compare the death rates of drinkers and of abstainers. 
 
 The United Kingdom Temperance and General Provident 
 Institution is a life insurance company of London, England. 
 For more than fifty years this company has kept separate 
 lists of the moderate 2 drinkers and abstainers among its policy 
 
 1 In distilling liquors, the liquid (the fruit juice or the water in which the 
 grain has been soaked) that contains the fermented sugar is heated, and the 
 vapor that comes from it is caught and condensed. The alcohol in the liquid is 
 changed to vapor more easily than the water, and the liquors that are manufac- 
 tured in this way are strong in alcohol. 
 
 2 All insurance companies refuse to accept heavy drinkers, and they reject 
 many persons who are very moderate drinkers indeed. The above statistics, 
 therefore, apply only to those who were moderate drinkers at the time they were 
 insured. Some of them may later have become excessive drinkers, but if all 
 drinkers were included in the statistics, the death rate among the alcohol users 
 would be very much higher than is here shown. 
 
240 
 
 HUMAN PHYSIOLOGY 
 
 holders. Its records show that for every 74.3 deaths among 
 abstainers, there are 100.4 deaths among the drinkers. The 
 death rate is, therefore, 35 per cent higher among the 
 users than among the non-users of alcohol. Many other life 
 insurance companies have kept similar records, and in every 
 case the death rale is from 25 to 50 per cent higher 
 among the drinkers than among the abstainers. These 
 averages have been made up from records including many 
 thousands of lives, and there is no doubt of their correct- 
 ness. They have been examined with great care to see 
 if there was any reason other than the use of alcohol why 
 the drinking man should die earlier than the non-drinker. 
 No such reason can be found, and it is certain that the 
 users of alcohol fail to live as long as those who do not use 
 alcohol, because the alcohol weakens and injures the body. 
 
 Alcohol and Tuberculosis, We have already seen (page 171) 
 ,that alcohol lowers the power of the body to resist disease 
 germs. The relation of alcohol to tuberculosis deserves 
 special mention. 
 
 In France, the districts drinking 12.5 liters of wine per capita 
 had annually 3.3 deaths from tuberculosis for each one thou- 
 sand inhabitants. The districts drinking 35.4 liters of wine per 
 capita had annually 10.8 deaths from tuberculosis for each one 
 thousand inhabitants. In the sanatoria for consumptives at 
 Loslau, Germany, in 1899, 30 per cent of the patients were 
 avowed alcoholics, 37 per cent were moderate drinkers, 27 per 
 cent were occasional drinkers, and only 6 per cent were total ab- 
 stainers. According to estimates made in France, 10.3 per 
 cent of the children of drunkards suffer from tuberculosis, 
 while only 1.8 per cent of the children of total abstainers 
 have tuberculosis. 
 
EFFECTS OF ALCOHOL ON" THE HUMAN BODY 241 
 
 Statistics like these show clearly that alcohol users are 
 especially subject to tuberculosis. ,So thoroughly established 
 and so important is this fact, that in Paris, in 1905, the Inter- 
 national Tuberculosis Congress, whose members include the 
 most learned bacteriologists and physicians in all the world, 
 adopted the following resolution : " We strongly emphasize 
 the necessity and importance of combining the fight against 
 tuberculosis with the struggle against alcoholism." 
 
 The Relation of Alcohol to Insanity. The great increase in 
 recent years of the number of the insane has excited alarm, 
 and considerable time has been devoted to studying the causes 
 of insanity. From a careful study of the causes bringing on 
 insanity in the patients in all the asylums in England, Wales, 
 and Ireland, it is estimated that alcohol causes about 20 
 per cent of all insanity. In England, personal intemperance 
 (intemperance of the insane person himself) causes nearly 
 15 per cent of insanity, and intemperance of the parents 
 causes enough more to bring the total to about 20 per cent. 
 When one thinks of the very great effect that alcohol has on 
 nerve tissue, and of the way it affects the working of the 
 mind, it does not seem at all strange that continued drinking 
 should bring on insanity. 
 
 Alcohol and Heredity. Whether or not the children of 
 those using alcohol are affected by the drinking of their par- 
 ents is a question that cannot be neglected. That children 
 are very greatly affected by drunkenness in their parents, the 
 following facts make certain : 
 
 Two pairs of dogs, as nearly alike as possible, were selected. 
 One pair was given alcohol in their food, and the other pair 
 had the same food and care, without alcohol. Of twenty- 
 three puppies of the pair of dogs that had alcohol, nine were 
 deformed, ten were born dead, and only four lived. The 
 
242 HUMAN PHYSIOLOGY 
 
 other pair of dogs in the same time raised forty-five puppies, 
 four of which were deformed and forty-one of which lived. 
 Thus, only 17.4 per cent of the puppies born to the alcoholic 
 dogs lived, while 90.2 per cent of the much larger number 
 born to the other dogs lived. 
 
 Much the same effect is produced in human families by 
 alcohol. In ten alcoholic families investigated, there were fifty- 
 seven children. Of these children, ten were deformed, six 
 were idiots, six were epileptics, twenty-five failed to live, and 
 only ten of the fifty-seven, or 17 per cent, were normal 
 and healthy. In ten families not using alcohol that were in- 
 vestigated, there were sixty-one children. Of these, two were 
 deformed, five failed to live, and fifty-four, or 88.5 per cent, 
 were normal and healthy. One investigator estimates that 
 only about 17.5 per cent of the children of drunkards are 
 physically sound; another places the percentage at 11.7 per 
 cent ; and still another reports that of the children of drunken 
 parents examined by him, not more than 6.2 per cent were 
 strong and well. These facts show that the bodies of children 
 are affected by the intemperance of their parents. 
 
 The minds of children are also affected by the drinking of 
 parents, as the following facts show : 
 
 Of 8624 children of drunken parents, 53 per cent were 
 mentally defective, while of 13,323 children of sober parents, 
 only i o.i per cent were unable to keep up with their school 
 work. Of children whose ancestors had been free from 
 alcoholic taint for three generations, 96 per cent were pro- 
 ficient in school work, while of those who had three gen- 
 erations of alcoholic ancestors, only 23 per cent were able to 
 keep up with their classes, and 76 per cent had some 
 nervous trouble. 
 
 We thus see that the evil effects of alcohol on both mind 
 
EFFECTS OF ALCOHOL ON" THE HUMAN BODY 243 
 
 and body are inherited. Professor Welch of Johns Hopkins 
 University says, " The brunt of the evil heritage of alcohol 
 falls on the nervous system of the second generation." 
 
 Alcohol and Character. The relation of the body to the 
 mind is not understood. We do not know, therefore, how 
 drugs affect the mind and character of a person, but we do 
 know that drugs can do this. The continued use of opium 
 will change an upright and honorable person into a shameless 
 falsifier. Cocaine sometimes turns mere boys into desperate 
 criminals, who do not shrink from robbery and murder. 
 Alcohol also has a great effect on the character. By intoxi- 
 cation, some mild and kind men are changed into cruel and 
 dangerous persons, and the breaking down of the will power 
 and character in confirmed drunkards is something with 
 which many people are familiar. 
 
 The following facts show that, in the opinion of business 
 men, drinking renders men on the whole less faithful, honest, 
 and efficient. Bonding companies are suspicious of drinking 
 men, and often refuse to furnish bonds for men who frequent 
 saloons. The Fifth Avenue National Bank of New York 
 City has for thirty years forbidden even its clerks and mes- 
 senger boys to drink in saloons and barrooms. Many large 
 railroads refuse to employ drinking men in their operating 
 departments, and some of them refuse to employ drinkers 
 even as bookkeepers or ticket agents. Shrewd business 
 men everywhere, in employing men, give the preference to 
 abstainers over drinkers. Any young man seeking employ- 
 ment in a responsible position will soon learn that one of 
 the first questions asked an applicant is whether or not he 
 drinks. 
 
 Conclusion. We find that alcohol shortens life; that it 
 makes the users of it more susceptible to germ diseases, the 
 
244 HUMAN PHYSIOLOGY 
 
 relation of alcohol drinking to tuberculosis showing this in 
 a striking way ; that alcohol causes a considerable amount of 
 insanity, and that the drinking of parents has a very inju- 
 rious effect on the bodies and minds of their children. We 
 also find that alcohol has a tendency to destroy the will 
 power and the character of those who use it. 
 
 These are facts that must be faced by any one investi- 
 gating the effects of alcohol on the human body. The only 
 answer that can be made to these facts is that it is the abuse 
 and not the use of alcohol that works all this evil. This is a 
 question that need not be discussed here, for practically every 
 one who uses alcohol at all uses too much of it (page 131). 
 When it is used as mankind uses it, its effects are the evil 
 effects given above. 
 
 QUESTIONS 
 
 How is alcohol formed? What is cider? wine? beer? How are 
 distilled liquors manufactured? How much alcohol is in wine? in 
 beer? in distilled liquors? 
 
 What figures are given as to the death rates of drinkers and 
 abstainers? Why must these figures be regarded as reliable? 
 
 What reasons are there for thinking that in France wine drinkers 
 are especially subject to tuberculosis? What facts from Europe 
 indicate that alcohol increases consumption? What effect has 
 alcohol drinking on the amount of tuberculosis among the children 
 of the drinkers? What is the opinion of the International Tuberculosis 
 Congress in regard to the connection between alcoholism and 
 tuberculosis ? 
 
 What per cent of insanity, according to estimates made in England, 
 is due to alcohol ? Tell something of the effects of alcohol on the 
 children of the drinkers. What effect does alcohol often have 
 <on the character ? What facts show that business men consider 
 alcohol users less trustworthy than non-drinkers? 
 
CHAPTER XIX 
 
 THE SPECIAL SENSES : Touch, Taste, Smell, and Hearing 
 
 PART of the nerve impulses that are carried into the brain 
 cause reflex actions ; part of them cause sensations. It is 
 difficult to describe a sensation, but we have all experienced 
 sensations of light, sound, touch, heat, cold, and hunger. 
 There is, therefore, no difficulty in understanding the mean- 
 ing of the term. 
 
 General Sensations. Hunger is caused by afferent im- 
 pulses from the stomach, and thirst by impulses from the 
 pharynx. Afferent impulses from the muscles (for every 
 muscle has great numbers of afferent as well as efferent nerve 
 fibers ending in it) cause the sensation of tiredness, and other 
 impulses give rise to feelings of pain, nausea, and other sen- 
 sations. These impulses rise within the body; they originate 
 because of some condition of the body, and they cause what 
 are called the general sensations. Most (but not all) of the 
 general sensations are caused by impulses that come from all 
 parts of the body. 
 
 Special Sense Organs. In some parts of the body are 
 special sense organs. In these the afferent nerve fibers end 
 in such a way that they are stimulated from without the body. 
 The sense organs are the eye, the ear, the nose, the epithelium 
 of the tongue and mouth, and the skin. The nerves in the 
 eye are stimulated by light ; the nerves in the ear by sound 
 waves in the air ; the nerves of smell by odors ; the nerves of 
 
 245 
 
246 
 
 HUMAN PHYSIOLOGY 
 
 taste by substances dissolved in the mouth ; and the nerves 
 in the skin by touching objects, and by heat and cold. The 
 impulses that are thus started in these nerves travel up to 
 the brain and cause sensations of light, sound, smell, taste, 
 and touch. Seeing, hearing, smelling, tasting, &&& feeling are 
 the five special senses, and by these senses we learn all that 
 we know of the world about us. 
 
 TOUCH 
 
 Afferent Nerve Endings in the Skin. The upper surface 
 of the dermis is thrown into papillae that stand up like little 
 
 FlG. 113. Afferent nerve endings. A shows a nerve fiber in the skin ending at 
 the bases of tactile cells. B shows a nerve fiber with free endings among the cells of 
 the skin. The nerves of glands and of involuntary muscles, and the afferent nerves 
 of voluntary muscles, end in this way. C shows a nerve fiber ending in a bulb of 
 connective tissue. Many nerve endings of this kind are found in the lower layers of 
 the skin, and in the internal parts of the body. 
 
 mountain peaks under the epidermis. Some papillae of the 
 skin (Fig. 93) contain only blood vessels, but in other papillae 
 
THE SPECIAL SENSES 247 
 
 tactile corpuscles (Fig. 94) are found. These are small, oval 
 bodies, in which one or several nerves of touch end. The 
 tactile corpuscles are especially abundant in the fingers and 
 toes. 
 
 Other nerves of touch branch at the ends, and have on the 
 tip of the branch a little saucer-like expansion that fits 
 around the base of an epidermal cell. Such a cell is called a 
 tactile cell. Still others of the afferent nerve fibers of the 
 skin end in many small free branches among the epidermal 
 cells. 
 
 How we feel. When we touch anything, the epidermis is 
 pressed down on the ends of the nerves of touch. This 
 starts an impulse; up the nerve to the 
 brain, and causes a sensation of feeling. 
 If all the nerve endings in the skin that 
 is being touched have the same amount 
 of pressure on them, we know that we 
 are feeling a smooth surface. If some 
 of them are being pressed harder than 
 
 others, we know that the surface is 
 FIG. 114. 
 
 rough. We know what part of the body 
 it is that is touching an object because we know which 
 nerves are bringing the impulses. We know whether the 
 object is large or small by the amount of skin that is touching 
 it, and by the distance that we must move the hands to pass 
 them over it. The mind is thus able to judge of many things 
 by the nerve impulses that come to it through the nerves of 
 touch. That it may form mistaken judgments from these 
 impulses, you can prove by crossing your fingers (Fig. 114) 
 and rubbing the point of your nose so that it will touch the 
 outer edge of one finger and the inner edge of another finger. 
 It will seem as though you had two noses, because ordinarily 
 
248 HUMAN PHYSIOLOGY 
 
 it takes two objects to touch the fingers on their edges as the 
 nose is touching them, and the mind has come to think that 
 there are two objects when impulses come from these points 
 at the same time. 
 
 Different Kinds of Afferent Nerves in the Skin. In the skin 
 are nerves that are stimulated by touch, others that are stim- 
 ulated by heat, and others that are stimulated by cold. 
 Whether there are special nerves of pain, or whether any 
 afferent nerve fiber, if stimulated in the wrong way, will 
 cause pain, is not known. When the epidermis is removed, 
 as by a burn, all sensations of touch, heat, and cold are lost, 
 and only sensations of pain come from the part. That the 
 nerves in the skin do not all do the same kind of work you 
 can easily prove by the following experiment : 
 
 Fill a small test tube with warm water, or warm the end of a wire 
 or other piece of metal, and pass it slowly over the skin of the fore- 
 arm. In certain spots you will feel a sensation of warmth. Mark 
 these places by small drops of ink, and then pass a cold object over 
 the same area of skin. Note that the nerves for feeling cold are not 
 in the same place as the heat nerves. Also note that nerves of touch 
 are found where there are neither heat nor cold nerves. 
 
 Where the Sense of Feeling is Best. In some parts of the 
 skin the nerve endings are very abundant, and in these 
 places the sense of touch is acute. In the 
 tip of the tongue it is most acute of all. It 
 is also very highly developed in the lips, in 
 the tip of the nose, and in the finger tips. 
 Thrust two pins through a thin piece of 
 cork (Fig. 115) and touch them to the fin- 
 ger tip. Here you can feel the two points 
 when they are only one twelfth of an inch 
 apart. But if you touch them to the back 
 of the hand or forearm, they will feel like one point unless you 
 
THE SPECIAL SENSES 249 
 
 place them much farther apart. On the tip of the tongue we 
 can distinguish two objects that are only one twenty-fifth of 
 an inch apart, while on the back of the body two objects must 
 be separated by two and one half inches before we can tell 
 whether one or two points are touching us. The following 
 is an interesting experiment : 
 
 Thrust two pins through a piece of cork, and while some member 
 of the class is blindfolded, or looking the other way, touch his skin on 
 the finger tips, back of the hand, forearm, lips, cheek, neck, etc. 
 Sometimes use one pin and sometimes two, and measure how far 
 apart the two must be separated before they can be distinguished on 
 the different parts of the body. 
 
 TASTE' 
 
 The nerves of touch are all over the body, but the nerves 
 of taste end only in the tongue and in the epithelium l of the 
 back part of the mouth. The taste nerves branch out and 
 end free among the epithelial cells, and in some places in the 
 tongue they end in a special way in little 
 bodies that are called taste buds. A taste 
 bud is composed of an outer circle of long 
 cells, set edge to edge, as the staves are 
 arranged in a barrel. It is buried in the 
 epithelium of the tongue, and at the tip of 
 the bud is a small opening out into the 
 mouth. Within the bud are long, slender FIG. n6. A taste bud. 
 taste cells, the tips of which stand up out 
 of the opening in the end of the bud. Within the taste bud 
 the nerves of taste are connected with the taste cells. 
 
 Before anything can be tasted, it must first be dissolved. 
 Then the little molecules of the substance work down in 
 
 1 The outer layer of cells in a mucous membrane is called the epithelium, 
 It corresponds to the epidermis of the skin. 
 
250 
 
 HUMAN PHYSIOLOGY 
 
 among the taste cells and so affect them that they start im. 
 pulses in the nerve fibers behind them. These impulses go 
 to the brain and cause sensations of taste. 
 
 SMELL 
 
 The olfactory nerves, or nerves of smell, end in the lining of 
 
 the upper front part of the nasal cavities. In the mucous 
 
 membrane of these parts are long, 
 slender cells called olfactory cells. 
 They lie between the epithelial 
 cells, and their outer ends are di- 
 vided into fine cilia-like processes. 
 From the inner end of the olfactory 
 cells nerve fibers pass to the brain. 
 The olfactory cells are in reality 
 
 FIG. n 7 . The olfactory nerves. ne rve cells that have grown down 
 
 from the brain above, and they are the only 
 
 nerve cells in the body that are exposed to 
 
 the outside world. 
 
 How we smell. From anything that has 
 
 an odor, molecules are flying off into the 
 
 air. These molecules pass into the nasal 
 
 chamber, come into contact with the olfac- 
 tory cells, and there cause changes that 
 
 start impulses up the olfactory nerves. 
 
 Drawing the air up into the nose brings 
 
 the molecules up to the olfactory cells, and 
 
 we therefore sniff the air when we wish to 
 
 smell anything. 
 
 In certain animals the sense of smell is 
 
 much more highly developed than it is the ciiia-iike processes 
 
 J r on them are the olfac- 
 
 m man. Some kinds of dogs can follow tory ceils. 
 
 FIG. 118. A por- 
 tion of the olfactory 
 mucous membrane. 
 The slender cells with 
 
THE SPECIAL SENSES 25 1 
 
 the track of an animal or man many hours after the trail has 
 been made, and bees and some pther insects are also far 
 more keen-scented than is man. 
 
 Care of the Olfactory Organ. Inflammation destroys the 
 delicate olfactory cells, and when they have been destroyed 
 they are not renewed. Inhaling dust is a common cause of 
 inflammation of the mucous membrane of the nose, and taking 
 cigarette smoke into the nose is very injurious to the olfactory 
 cells. Catarrh should have medical treatment, for by it the 
 sense of smell is partially destroyed in many persons, and it 
 may lead to more serious diseases. 
 
 HEARING 
 
 Hearing is caused by waves of air striking against the ear. 
 In order to understand this subject, it is necessary to under- 
 stand something of the nature of air. In solid bodies, the 
 molecules cannot move about from one place to another. In 
 liquids, the molecules move about and slip over each other, 
 but they do not separate. In gases, the molecules are not 
 held together, but separate and fly off from each other. 
 
 The air is a mixture of gases (page 178), and if the air 
 molecules were visible, you would see the molecules of the 
 different gases dancing and flying about and striking against 
 each other. When the wind blows, the molecules are flying 
 along. When the wind pushes against you, the many little 
 molecules of which the air is composed are flying against you 
 and striking you. In a great gale the air may be traveling 
 at the rate of a mile a minute, and in very great storms it 
 may even have a speed of two miles a minute. With a 
 speed like this, its molecules strike objects in their path with 
 tremendous force, uprooting trees, carrying away houses, and 
 overturning large and heavy objects. 
 
252 
 
 HUMAN PHYSIOLOGY 
 
 Sound Waves. When you throw a stone into water, the 
 stone strikes against the molecules of water and sets them in 
 motion. The molecules which are set in motion by the stone 
 strike against those next to them ; these in turn hit the next 
 set, and a wave runs out in the water. When a bell is rung, 
 the bell vibrates and strikes the air molecules next to it, set- 
 ting them in motion. These strike the next molecules, and 
 so on, and a wave runs out through the air. When these air 
 waves strike the ear, they start impulses in the auditory nerve, 
 the impulses are carried to the brain, and we hear the bell ring. 
 Big air waves cause loud sounds, and small waves cause slight 
 sounds. Great sound waves may strike the ear with such force 
 as to break the tympanic membrane (Fig. 119), and they may 
 also break windows and jar houses. 
 
 The , Ear. The ear is an organ so constructed that when 
 the sound waves strike it, the afferent nerves in it will be 
 
 stimulated. It is divided into 
 
 TEMPORAL BONE , , ., , 
 
 three parts, the external, 
 middle, and internal ear. 
 
 The External Ear. The ex- 
 ternal ear includes the part 
 that we see and the canal 
 (auditory canal) leading in 
 to the middle ear. The ex- 
 ternal ear is composed of a 
 piece of cartilage covered 
 with skin. Its function is to 
 catch the sound waves and 
 turn them down the canal to 
 the middle ear. When animals are listening intently, they 
 hold up their ears to catch as much of the sound waves as 
 possible, and a man sometimes holds his hand behind his 
 
 FIG. 119. The ear. 
 
THE SPECIAL SENSES 
 
 253 
 
 ear to help in turning the sound waves down the canal to the 
 middle ear. 
 
 The Middle Ear. The middle ear is a little cavity in the 
 temporal bone of the skull. The cavity is shaped like a 
 drum, and is often called the tympanum, or ear drum. At 
 the inner end of the auditory canal is the tympanic mem- 
 brane. This stretches like a piece of thin skin across the 
 bottom of the canal, and separates the external ear from the 
 tympanum. The cavity of the tympanum is filled with air. 
 
 The Bones of the Ear. In the middle ear are three very 
 small bones, the malleus (hammer), the incus (anvil), and 
 the stapes (stirrup). The malleus 
 is fastened to the tympanic mem- 
 brane, the stapes fits into an open- 
 ing that leads into the internal ear, 
 and the incus is between the mal- 
 leus and the stapes. These three 
 bones stretch across the middle 
 ear from the tympanic membrane 
 to the inner wall. 
 
 The Eustachian Tube. The 
 Eustachian tube is a narrow pas- 
 sageway that leads from the mid- 
 dle ear to the pharynx. It enters 
 the pharynx high up in the side 
 wall, opening almost into the back part of the nasal cham- 
 ber. Through the Eustachian tube the air passes out of 
 and into the middle ear, and keeps the pressure of the aii 
 within the tympanum the same as the outside air pressure. 
 If a Eustachian tube becomes closed, 1 the varying pressure 
 
 1 In colds, catarrh, scarlet fever, measles, pneumonia, and in some other dis- 
 eases, inflammation may extend up the Eustachian tubes and cause deafness 
 
 FIG. 120. Bones of the ear. 
 
254 
 
 HUMAN PHYSIOLOGY 
 
 OPENING FOR STAPES 
 
 of the atmosphere caused by changing conditions of the 
 weather and by passing to the lighter atmospheres of higher 
 altitudes or the heavier atmospheres of lower altitudes, 
 causes an unequal pressure on the two sides of the tympanic 
 membrane. This causes deafness. 
 
 The Internal Ear. The internal ear lies deep in the tem- 
 poral bone, and is divided into three parts. The central 
 
 part is the vestibule ; the front 
 part, which is coiled like a snail 
 shell, is the cochlea; and the 
 back part is the semicircular 
 canals. The entire internal ear 
 is filled with fluid. Standing 
 out in this fluid from the 
 walls are slender, hair-like cells, 
 that at their inner ends are 
 connected with the fibers of 
 the auditory nerve. The im- 
 pulses that cause us to hear 
 come from the cochlea. 
 How a Sound is heard. The external ear catches the sound 
 wave and turns it down the auditory canal, at the bot- 
 tom of which the wave strikes the tympanic membrane. 
 The membrane swings out and in, and sets the chain of 
 bones in motion. The malleus pushes on the incus, and the 
 incus on the stapes. The stapes is thus forced in against the 
 fluid in the vestibule and in this fluid waves are set up which 
 run through the internal ear, striking against and moving the 
 hair-like cells that project into the fluid. This starts im- 
 
 by closing the tubes (page 270). Adenoid growths often close the Eustachian 
 tubes and start inflammation in them. Probably two. thirds of all deafness and 
 ear trouble comes from this cause. 
 
 FIG. 121. The internal ear. B shows 
 the natural size of the internal ear. 
 
THE SPECIAL SENSES 
 
 255 
 
 pulses that travel up the auditory nerve to the brain, and 
 causes a sensation of sound. 
 
 Function of the Semicircular Canals. The semicircular 
 canals are not concerned in hearing, but their function is to 
 assist in retaining the equilibrium of the body. One canal 
 lies behind the vestibule in a vertical plane, and if the head 
 moves forward or backward in the way that it moves in nod- 
 ding, the fluid in this canal is set in motion. Another canal 
 runs outward from the vestibule in a horizontal plane; when 
 the head is turned to the side, as when one turns the head to 
 look over the shoulder, the fluid in this canal is set in motion. 
 The other canal runs up and outward from the vestibule in 
 a vertical plane, so that if the head moves toward the side in 
 the way it does when it is bent over toward the shoulder, the 
 fluid in this canal moves. 
 
 If the body leans in any direction, the fluid in one or more 
 of these canals is always set in motion, and impulses are sent 
 to the brain, bringing information in regard to the direction in 
 which the body is beginning to fall. Impulses are then sent 
 out from the brain that cause the proper muscles to contract 
 and bring the body again to the upright position. Sometimes 
 the semicircular canals become diseased, and then there is 
 great difficulty in retaining the equilibrium of the body, be- 
 cause it is not noticed that the body is beginning to fall. 
 Sight and impulses from the muscles assist in keeping the 
 equilibrium, but a prominent part of this work is done by the 
 semicircular canals. 
 
 Care of the Ears. A blow on the side of the head is danger- 
 ous, for it may send such a strong air wave down the auditory 
 canal that the tympanic membrane will be ruptured. Live 
 insects in the ear may cause great distress by buzzing and 
 moving about. They can be drowned by pouring oil or water 
 
256 HUMAN PHYSIOLOGY 
 
 into the ear. No one but a physician should attempt to re- 
 move these or other objects from the ear, 1 because in doing so 
 there is great danger that an unskilled person will injure the 
 lining of the auditory canal or break the tympanic membrane. 
 
 The hearing may be injured by quinine, and this should be 
 taken for any considerable time only under the advice of a 
 physician. Earaches and deafness are caused by various 
 troubles, very often by catarrh that has spread up the Eusta- 
 chian tube and affected the middle ear. Earache may some- 
 times be prevented at night by wearing a hood or nightcap 
 while sleeping, but wearing cotton in the ears and pouring 
 oil and other liquids into them often brings on serious trouble, 
 and should not be practiced. Children with ear trouble should 
 have the prompt attention of a skilled physician or they will 
 often suffer great pain needlessly, and perhaps will have the 
 hearing permanently impaired. Among adults about one 
 third have the hearing affected in one or both ears largely 
 because of neglect in youth. 
 
 Summary. Some of the afferent nerve impulses cause sen- 
 sation. General sensations are produced by impulses that 
 arise within the body. In the special sense organs the 
 nerves end in such a way that they are stimulated from out- 
 side the body. Seeing, hearing, smelling, tasting, and feel- 
 ing are the special senses. 
 
 The afferent nerves of the skin end in tactile corpuscles, at 
 the bases of tactile cells, and in free nerve endings. In feel- 
 ing objects, stimuli are started in the nerves by pressure ; 
 and from these stimuli the brain forms many judgments in 
 
 1 The bitter wax in the auditory canal is secreted by small glands in the skin. 
 It is a protection against insects. Scraping the wax out of the ears with the head 
 of a pin or other piece of metal may cause the lining of the auditory canal to be- 
 come inflamed, and greatly increase the quantity of wax secreted. 
 
THE SPECIAL SENSES 
 
 regard to the things that we touch. In the skin are nerves 
 of touch, heat, and cold, and possibly nerves of pain. The 
 sense of touch is acute in the tip of the tongue, lips, and fin- 
 ger tips, and much less acute in some other parts of the body. 
 
 Many of the fibers of the nerves of taste end free in the 
 mucous membrane of the tongue and of the back part of the 
 mouth. Other fibers end in taste buds. Before anything 
 can be tasted it must be dissolved. 
 
 The olfactory cells are nerve cells in the nasal mucous 
 membrane. Impulses are started in these cells by odors. 
 The olfactory cells are delicate nerve cells, and if they are 
 destroyed, the sense of smell is permanently lost. 
 
 A sound wave is produced by setting in motion the mole- 
 cules of the air. When these waves strike the ear, they 
 cause us to hear. 
 
 The ear is composed of the external, internal, and middle 
 ear. The external and middle ears are separated by the 
 tympanic membrane. The middle ear contains the malleus, 
 incus, and stapes. The Eustachian tube puts the air in the 
 middle ear into communication with the outside air. The 
 internal ear is composed of the vestibule, cochlea, and semi- 
 circular canals. The canals assist in preserving the equilib- 
 rium of the body. 
 
 When a sound wave strikes the external ear, it is turned 
 down the auditory canal and sets in motion the tympanic 
 membrane. This moves the chain of bones in the middle 
 ear, and they set up waves in the fluid in the internal ear. 
 These waves start impulses in the nerves of hearing that 
 are carried to the brain, and cause sensations of sound. The 
 ear should have intelligent care, for many cases of defective 
 hearing come from neglecting ear troubles in children. 
 
258 HUMAN PHYSIOLOGY 
 
 QUESTIONS 
 
 What causes sensations? Name some of the general sensations. 
 Where do the nerve impulses that cause these sensations originate? 
 Name the special sense organs. How are the nerve endings in each 
 one stimulated? 
 
 Give three ways in which the afferent nerves end in the skin. 
 How are impulses started in these nerves when we touch an object? 
 Explain how we are able to judge of certain properties of objects by 
 touching them. What different kinds of nerves end in the skin? 
 Where is the sense of feeling acute? Where is it least acute? 
 
 Give, two ways in which the nerves of taste end in the tongue. 
 Describe a taste bud. How is the nerve of taste stimulated? Does 
 a chicken taste corn when it eats it ? 
 
 Where is the organ of smell located ? Describe the olfactory cells. 
 What kind of cells are they? What is an odor? How are impulses 
 started in the olfactory cells? In what ways may these cells be injured ? 
 
 Of what is air composed? Explain how a bell starts waves in the 
 air. How do these waves cause the sensation of sound ? 
 
 Name the three divisions of the ear. What is the function of the 
 external ear? What is the middle ear called? Why? What and 
 where is the tympanic membrane? Name the bones of the ear 
 Where are the Eustachian tubes? What is their use? 
 
 Name the parts of the internal ear. With what is it filled ? Ex- 
 plain how a stimulus is started in the auditory nerve. What is the 
 function of the semicircular canals ? How are the impulses started 
 in the nerves that are connected with these canals ? W T hen one whirls 
 himself rapidly about and then stops, what causes him to have a sen- 
 sation of dizziness? 
 
 How may a blow on the ear injure the hearing ? How may an 
 insect in the ear be killed? What is a common cause of earache and 
 deafness? Why should ear troubles in children receive attention? 
 
CHAPTER XX 
 
 THE SPECIAL SENSES (Continued): SEEING 
 
 ALL space is filled with an invisible substance called ether, 
 and light is waves in the ether. The eye is so constructed 
 that when the ether waves enter it, they stimulate the affer- 
 ent nerves and start impulses to the brain that cause the 
 sensation of sight. 
 
 Protection of the Eyes. The eyes are very important and 
 very delicate organs, and must therefore be well protected. 
 The deep bony eyesockets are a great protection from blows. 
 The inside of the eyesocket is lined with a layer of fat which 
 forms a soft cushion for the eyes to rest and turn on, and if 
 the eye is struck, the fatty layer between it and the bone 
 assists in preventing injury. 
 
 The eyelids, eyelashes, and eyebrows also assist in protect- 
 ing the eyes. The eyelids screen them from dust and light, 
 and close if a blow is threatened. The eyelashes guard the 
 eyes from dust and light, and the eyebrows keep the sweat 
 from running down from the forehead into the eyes. 
 
 The Lachrymal Glands. In the outer corner of each upper 
 eyelid is located a lachrymal gland, very similar in structure to 
 a small salivary gland. These glands secrete the tears and 
 pour them into the eyes at the upper outer corners. The tears 
 flow down across the eye to the inner corner, where they enter 
 the lachrymal duct, which carries them down into the nasal 
 chamber. In their passage across the eyes, the tears cleanse 
 
 259 
 
26o 
 
 HUMAN PHYSIOLOGY 
 
 FIG. 122. 
 
 The lachrymal gland and 
 duct. 
 
 the eye, washing' away dust and germs. The workings of the 
 lachrymal glands give us another illustration of the effect of 
 
 the mind on the body; for 
 sorrow, pain, and sometimes 
 anger cause them to secrete so 
 abundantly that the tears cannot 
 all be carried away by the lach- 
 rymal ducts, but overflow on the 
 cheeks. 
 
 The Meibomian Glands. In 
 the eyelids are small glands 
 called the Meibomian glands. 
 They are very similar to sebaceous glands, and empty out 
 an oily secretion along the edges of the eyelids. Water 
 does not flow freely over an oiled surface, and the secretion 
 from the Meibomian glands prevents the tears from over- 
 flowing the eyelids. When the 
 eyelids are inflamed and con- 
 gested, the Meibomian glands 
 sometimes become diseased, 
 and the secretion from them 
 dries around the roots of the 
 eyelashes, forming scales very 
 similar to dandruff. 
 
 The Muscles of the Eyes. 
 There are six muscles to move 
 each eye. The back ends of 
 these muscles are attached to the walls of the eyesocket. The 
 front ends are attached to the ball of the eye. By these 
 muscles, the eyes can be turned in any direction, so that it is 
 not always necessary to turn the head toward the object at 
 which we are looking. 
 
 FIG. 123. The muscles of the eye. 
 
SEEING 
 
 26l 
 
 The Structure of the Eye. The eye has three coats. The 
 outer one is the sclerotic coat, the middle one is the choroid 
 coat, and in the back part of the eye is a third inner coat 
 called the retina. The optic nerve enters the eye at the back 
 and spreads out in the retina. 
 
 FIG. 124. A diagram of a section of the eye. 
 
 The interior of the eye is divided by the lens and the 
 ligaments that support the lens into a small anterior cham- 
 ber and a larger posterior chamber. The posterior chamber 
 is filled with a transparent, jelly-like substance, called the 
 vitreous humor. The small anterior chamber is filled with 
 the aqueous humor, a watery fluid similar to tears. 
 
 The Sclerotic Coat. The sclerotic coat, or white of the 
 eye, is composed of dense, closely woven connective tissue. 
 It has a white color, except in front, where it is transparent. 
 This transparent part is called the cornea, and through it the 
 
262 HUMAN PHYSIOLOGY 
 
 light passes into the interior of the eye, as light passes 
 through a window into a house. 
 
 The Choroid Coat and the Iris. The choroid coat is a loose 
 connective tissue coat. It contains pigment that gives it a 
 rich, dark color similar to the inside of a grape skin. The 
 front part of the choroid is called the iris. This contains a 
 circular opening, the pupil, in its center. The iris lies behind 
 .the transparent cornea, and being seen through the cornea, 
 gives the color to the eye. A person is black-eyed, brown- 
 eyed, or blue-eyed, according to the pigment in his iris. 
 
 The Function of the Iris. The function of the iris is to 
 regulate the amount of light that enters the eye. In the iris 
 
 are circular muscle fibers, run- 
 ning around the pupil, and 
 when these contract, they 
 make the pupil smaller. 
 Other muscle fibers run in 
 from the outer edge of the 
 iris to the pupil, and when 
 FIG. 125. One cat has been in the dark; these contract, they enlarge 
 
 the other has been in the light. , . . 
 
 The control of the size of the pupil is carried on by invol- 
 untary reflexes. When a strong light enters the eye, the 
 circular fibers in the iris contract and diminish the size of the 
 pupil. When the light is weak, the pupil is enlarged and 
 more light is admitted to the eye. When you step out of a 
 brightly lighted room into the dark, you cannot see, because 
 the pupil is too small to allow enough light to enter. But if 
 you remain out in the dark, the pupil will be enlarged and 
 admit more light, and your vision will become better. When 
 you step from a darkened room out into the bright sunshine, 
 the light dazzles the eyes, because the opening in the pupil 
 
SEEING 263 
 
 is too wiae and lets in too much light. After a few minutes, 
 the muscles of the iris contract and diminish the size of the 
 pupil, thus adapting the eye to the bright light. 
 
 The eye of a cat shows very distinctly the changes in the 
 size of the pupil. In the dark the pupil is large and round, 
 and in a bright light it is narrowed to a slit. This you can 
 easily see for yourself by examining the eye of a cat that has 
 been in the light, and then shutting the cat in a dark room 
 or closet and examining its eye again, or you can see the 
 expansion and contraction of the pupil in your own eye by 
 the following experiment : . 
 
 Stand facing a window and examine the pupil of your eye in a 
 mirror. Now cover the eye for a few moments with your hand, re- 
 move the hand quickly, and watch the pupil. When a person is in 
 health, the pupil should promptly expand when the eye is covered 
 and contract when the eye is exposed to the light. 
 
 The Lens. The lens (Fig. 129) lies close against the back 
 of the iris. It is thin at the edges and thicker in the 
 middle, and is composed of a clear, jelly-like substance. 
 The lens is inclosed in a circular sac, and both the sac 
 and the material in it are transparent, so that the light 
 can pass through them to the retina in the back of the 
 eye. The lens is attached to the choroid coat by the suspen- 
 sory ligament, which runs out all around from the outer edge 
 of the lens. Figure 124 shows the lens and the suspensory 
 ligament as they appear when cut across, but you must 
 understand that the lens is circular like a coin, and that the 
 suspensory ligament is a ring with the lens fitted into the 
 opening of the ring. 
 
 The Function of the Lens. The junction of the lens is to 
 form images of the objects that we see, and to accommodate the 
 eye to near and distant objects. In forming images in the 
 
264 HUMAN PHYSIOLOGY 
 
 eye, the lens is assisted by the curved surface of the cornea, 
 On the ground glass in the back of a camera, you can see 
 an image formed by the lens in the front of the camera. 
 The lens and cornea of the eye form images on the retina 
 in the same way that the image on the camera is formed. 
 
 How a Lens forms an Image. Hold a convex lens 1 so that 
 sunlight will pass through it. You will find that the lens 
 brings the rays of light to a focus, that is, it bends them so 
 that they all meet in one point. It does this by changing the 
 
 FlG. 126. Image formed by a convex lens. 
 
 directions in which the light waves are running, causing 
 them all to run toward one point. The lens of the eye 
 bends all the rays of light that come from one point, so that 
 they meet in one point on the retina of the eye. In Figure 126 
 you can see how all the rays of light from the point of the 
 arrow meet in one place and form an image of the arrow 
 point. In the same way, an image of the other end of the 
 arrow is formed, and of every other point in the arrow, and 
 all these points together make an image of the arrow. So, 
 in. looking at a landscape, an image of the whole landscape 
 's formed in the eye, all the rays of light that come from any 
 one part of the scene in front of the eye meeting in one 
 point and forming an image of that point on the retina. The 
 
 1 This experiment can be performed with the lens in a pair of convex 
 spectacles. 
 
SEEING 
 
 26 5 
 
 images that are formed in the eye, like the images in a 
 camera, are upside down, and the right 
 and left sides are reversed. 
 
 The Retina. The retina contains slen- 
 der, pointed cells that are affected by 
 light. These cells are connected with 
 the optic nerve, and when light strikes 
 the retina an impulse is started which 
 passes back through the optic nerve to 
 the brain. 
 
 The Function of the Brain in seeing. 
 Impulses are started in the eye by the 
 images that fall on the retina, but these 
 impulses must be carried to the brain be- 
 fore the sensation of sight is produced. 
 From the impulses that come into the 
 brain from the eye, we form judgments 
 in regard to the form, size, color, and 
 smoothness or roughness of objects. 
 
 J FIG. 127. When light 
 
 From these impulses we can judge also str ikes the retina, impulses 
 
 Of the distance Of Objects from US, Of are started in the long, slen- 
 . . , ,_. ... , f ,, . der cells (a and 6) of the 
 
 their relative positions, and of their retina T v hese are carried 
 movements. That the mind does not to the brain, and cause the 
 always form correct judgments from sensation of sight, 
 the impulses that come from the eye, you can easily dem- 
 onstrate by looking at the two lines 
 NW / of the same length in Figure 128. 
 
 X" %^ The Accommodation of the Eye. 
 
 - -^ The shape of the lens must be 
 
 ^_ -^ changed according to the distance 
 
 NV / from the eye of the object that we 
 
 FIG. 128. are looking at. When the object is 
 
266 
 
 HUMAN PHYSIOLOGY 
 
 close to the eye, the lens must be 
 made more convex; for a distant 
 object the lens needs to be flat- 
 tened. This change in shape of 
 the lens is called the accommoda- 
 tion of the eye and is brought 
 about by the ciliary muscles. 
 
 How the Eye is accommodated. 
 The suspensory ligament is at- 
 tached to the choroid coat as is 
 shown in Figure 129. The front 
 ends of the ciliary muscles are 
 attached to the sclerotic coat. 
 Their other ends are attached to 
 the choroid coat. When these 
 muscles contract, they stretch the 
 choroid and draw it forward. 
 This loosens the suspensory liga- 
 ment, and the lens of itself rounds 
 FIG. 129. When the ciliary mus- out and becomes more convex, 
 cies contract they draw forward the when the ciliary muscles relax, 
 
 choroid coat, loosen the suspensory 
 
 ligament, and allow the lens to be- the stretched choroid returns to its 
 come more convex. former position, thus tightening 
 
 the ligament again and flattening the lens. 
 
 The change in shape of the lens can be illustrated with a 
 small sac, or with the swimming bladder of a fish, filled with 
 air or water. Pull on the ends of the sac, and you will flatten 
 it. Decrease the pull, and of itself the sac will round up, as 
 does the lens when the ligament is loosened by the choroid's 
 coming forward. You should take especial care to note 
 that the contraction of the ciliary muscles loosens the 
 ligament, and does not tighten it, for pupils who are 
 
 CILIARY 
 MUSCLES 
 
SEEING 
 
 26 7 
 
 studying the eye often get an incorrect idea in regard to this 
 point. 
 
 Near-sightedness. The image in the eye must fall exactly on 
 the retina, or vision cannot be distinct. In some persons, the 
 eyes are long from the front 
 to the back. In such persons, 
 the rays of light meet before 
 they reach the retina. This 
 makes an indistinct image, as 
 does a camera, microscope, or 
 field glass, when it is out of 
 focus. In B( Fig. 130) you can 
 see how the rays of light from 
 the head of the arrow meet in 
 front of the retina, and how, 
 when they reach the retina, 
 they have crossed and sepa- 
 rated again, scattering the 
 image on the retina instead of 
 making it clear and distinct at 
 one point. In such an eye, 
 the images of the different 
 points overlap, and a blurred, 
 indistinct image of the whole object is the result. Near- 
 sighted persons usually have prominent eyes, and the cornea 
 usually is more convex than it is in the normal eye. 
 
 Far-sightedness. A far-sighted eye is too short from front 
 to back. In such an eye, the retina is so close to the lens 
 that the rays of light have not been brought together when 
 they get to it, and the image is blurred (Fig. 130 C). Per- 
 sons with eyes of this kind see distant objects best, because 
 the rays from these objects meet more quickly than do those 
 
 FIG. 130. A, normal; , near-sighted; 
 and C, far-sighted eye. 
 
268 HUMAN PHYSIOLOGY 
 
 from near objects. In a far-sighted eye, the cornea is usually 
 flatter than it is in the normal eye, and in far-sighted per- 
 sons the eyes are not so prominent as they are in near-sighted 
 persons. 
 
 Astigmatism. In astigmatism, the curvature of the cornea 
 is uneven, some parts being flatter than other parts. The 
 rays of light that pass through the flatter places on the 
 cornea are not brought to a focus as soon as the rays passing 
 through the more convex parts. A distinct image cannot be 
 formed in such an eye, for the lens cannot be so shaped that 
 all the rays from one point will come together in a single 
 point on the retina. 
 
 Eyes of Old Persons. In old persons, the material of which 
 the lens is composed becomes harder and less fluid, and when 
 the suspensory ligament is slackened, the lens fails to change 
 its shape. The power of accommodation is thus lost. One 
 of the most wonderful things about the eye is the way it 
 accommodates itself to objects at different distances, and in 
 old persons this power is to a certain extent lost. 
 
 Spectacles. If a sharp, clear image is not formed on the 
 retina, eye trouble is certain to result. Near-sighted, far- 
 sighted, and astigmatic eyes need spectacles or eyeglasses 
 to assist in forming distinct images on the retina. The kind 
 of lenses that are needed in the spectacles depends on where 
 the image falls in the eye, each particular eye needing to be 
 fitted with a lens that will cause the image to fall exactly on 
 the retina. 
 
 Concave lenses spread the rays of light farther apart. If a 
 concave lens is placed before a near-sighted eye, the lens will 
 spread the rays of light and cause them to meet farther back 
 in the eye (Fig. 131). A person Vho is very near-sighted 
 will need a strongly concave lens, and a person who is only 
 
SEEING 
 
 269 
 
 a little near-sighted will need 
 only a slightly concave lens. 
 Each eye needs a lens that 
 will bring the rays to a focus 
 on the retina. 
 
 Convex lenses bend the rays 
 nf light together and cause 
 them to meet more quickly. 
 In far-sighted eyes, the rays 
 have not yet met when they 
 reach the retina, and by plac- 
 ing a Convex lens before SUch FIG. 131. How glasses cause the rays 
 
 an eye, the rays can be of light to meet on the retina, 
 brought together and made to meet on the retina. 
 
 In astigmatic eyes, the lens must be ground to suit the eye. 
 Where there is a little hill on the cornea, a concave place 
 must be ground out in the lens, and where there is a flat 
 place on the cornea, the lens must be convex. Old persons 
 need one pair of glasses for seeing distant objects, and another 
 pair for seeing near objects. 
 
 CONVEX LENS 
 
 HYGIENE OF THE EYES 
 
 It is a great mistake to think of the eye as a separate part 
 of the body, doing its work without connection with the other 
 body parts. Like all the other organs, it is intimately related 
 to the rest of the body, and any defect or trouble in the eye 
 is likely to affect other organs, the nervous system, and the 
 general health. It is, therefore, important to care for the eyes, 
 not only to relieve pain in the eyes themselves and to have 
 good vision, but for the purpose of keeping the entire body in 
 health. 
 
2/0 HUMAN PHYSIOLOGY 
 
 Care of the Eyes. Spectacles or eyeglasses should be worn 
 when they are needed. These should always be secured from 
 a reliable physician or eye specialist, and not from some un- 
 skilled person or traveling optician, for it requires considerable 
 skill and care to examine an eye, and to tell exactly the kind 
 of lens that is suited to it. Also, the eye sometimes changes 
 very rapidly, so that the lenses of the spectacles need to be 
 changed, and it is always better to deal with some one who 
 can examine the eyes from time to time, and change the 
 lenses as changes are needed. 
 
 The importance of having the eyes properly fitted with 
 glasses cannot be too strongly insisted on, for many cases of 
 nervousness, headache, indigestion, nausea, and mental dull- 
 ness vanish as if by magic when glasses are adjusted to the 
 eyes. 1 If a person has any signs of eye trouble, or if he has 
 headaches and stomach trouble for which there seems to be 
 no reason, the eyes should be examined at once. 
 
 A good light should always be used in reading or in doing 
 other close work. To read by a dim light, as when one reads 
 on into the twilight, is exceedingly injurious. A dazzling, 
 bright light is also injurious, especially if it shines directly 
 into the eye. In reading, one should sit so that the light will 
 
 1 To THE TEACHER : A considerable proportion of the children who are re- 
 garded as dull in school fall behind their classes because of defective hearing or 
 vision. The teacher should carefully watch his dull pupils for symptoms of 
 trouble in the nasal passages, test the hearing by some such device as trying how 
 far the child can hear the ticking of a watch, and note if the child holds his 
 book close to his eyes or shows other symptoms of eye trouble. The attention 
 of parents should be called to any defects that may be discovered, and the parents 
 should be made to understand the importance of medical attention for such 
 cases. Any close work is injurious to the eyes of young children, and kinder- 
 garten teachers especially should take .care to see that the eyes of the children 
 in their charge are not injured by too much sewing, weaving, or other similar 
 work. (See also page 308, note i."i 
 
SEEING 2/1 
 
 fall on the book, but not into the eyes. Facing a window in 
 the daytime is injurious, and it is also injurious to read on a 
 dark day in a corner of a room far from a window. 
 
 Reading while lying down is a bad practice, because in this 
 position, too great a blood supply comes to the eyes, and they 
 become congested with blood. Then, too, the book or papei 
 is often held in a very awkward position, which strains the 
 eyes. 
 
 Resting the eyes occasionally is very helpful. In reading, 
 the eye is accommodated for near objects, and the ciliary 
 muscles must be held contracted to round up the lens. In 
 reading for long periods of time, these muscles become ex- 
 hausted. It is, therefore, a good idea to stop occasionally 
 while reading, and to close the eyes or look out of a window 
 at a distant object, allowing the ciliary muscles to relax and 
 rest. This advice applies of course when one is doing any 
 work that is hard on the eyes. 
 
 Dust is exceedingly injurious to the eyes. It always causes 
 irritation by scratching the surface of the eye and the lining 
 of the eyelids, thus allowing the entrance of germs that may 
 cause inflammation. For congestion and redness of the 
 eyes, bathing in cold water is helpful. A little boracic acid 
 dissolved in water (the exact strength of the solution is not 
 important) and dropped into the eyes at night on retiring 
 has a very soothing effect on the eyes, and helps to kill 
 germs that get into them. But in any serious or long-con- 
 tinued trouble with the eyes, a physician or oculist should 
 always be consulted. 
 
 Effect of Tobacco and Alcohol on the Eyes. In a few per 
 sons, tobacco affects the nerves of sight so that distinct vision 
 and the power of distinguishing between colors are lost. 
 Tobacco smoke is irritating to the eyes, and in a considerable 
 
2/2 HUMAN PHYSIOLOGY 
 
 number of persons, smoking brings on a congestion and red- 
 ness of the eyes and eyelids. Alcohol congests the vessels 
 of the eyes, as it does those of other parts of the body, but 
 the effects of alcohol and tobacco on the eyes in most cases 
 are not very serious, as compared with their effects on some 
 of the other organs of the body. 
 
 Summary. The eye is protected by the eyesocket, the eye- 
 lids, eyelashes, and eyebrows. It is cleansed by tears that are 
 secreted by the lachrymal gland and are drained off into the 
 nose by the lachrymal duct. The edges of the eyelids are 
 kept oiled by the Meibomian glands so that the tears will 
 not overflow on the cheeks. 
 
 The eye is moved by six muscles. It has three coats, 
 the sclerotic coat, choroid coat, and retina. Its interior is 
 divided by the lens and the suspensory ligament into an ante- 
 rior and a posterior chamber. The anterior chamber contains 
 the aqueous humor ; the posterior chamber contains the vitre- 
 ous humor. 
 
 The .transparent front portion of the sclerotic coat is called 
 the cornea, and the front portion of the choroid coat is the 
 iris. The iris gives the color to the eye. In the center of 
 the iris is an opening called the pupil. The muscles in the 
 iris open and close the pupil and in this way regulate the 
 amount of light that enters the eye. 
 
 The lens and cornea form images on the retina of the eye. 
 The images start impulses to the brain that give us the sensa- 
 tion of sight. The eye is accommodated for near and far 
 objects by changing the shape of the lens. 
 
 It is essential to clear vision that the image fall on the 
 retina. Eye troubles cause headaches and a derangement of 
 the digestive and nervous systems. When spectacles are 
 needed, they should be worn. A good light should be used 
 
SEEING 2/3 
 
 in reading, and occasionally the eyes should be rested. Dust 
 is harmful to the eyes and tobacco and alcohol may in- 
 juriously affect them. 
 
 QUESTIONS 
 
 What is light ? What does light do when it enters the eye? 
 
 How is the eye protected? Where are the lachrymal glands? 
 the lachrymal ducts ? the Meibomian glands ? What is the function 
 of the Meibomian glands ? 
 
 How many muscles move each eye? Where are these muscles 
 attached? Name the coats of the eye; the two chambers of the 
 eye. What separates the two chambers? Where is the vitreous 
 humor? the aqueous humor? 
 
 Of what is the sclerotic coat of the eye composed? What does 
 the choroid coat contain? What is the cornea? iris? pupil? 
 What is the function of the iris? How is the size of the pupil 
 changed? Under what conditions does it enlarge and contract? 
 
 Describe the lens. How is it held in place? What is its func- 
 tion? Explain how an image is formed by a lens. Describe the 
 cells in the retina and tell how nerve impulses from these cells 
 reach the brain. What part has the brain in seeing? 
 
 Where are the ciliary muscles attached? Explain how the eye is 
 accommodated. 
 
 What is the trouble in a near-sighted eye? in a far-sighted eye? 
 in an astigmatic eye? in the eyes of old persons? 
 
 What effect have concave lenses on light waves that pass through 
 them ? convex lenses ? What kind of lenses are needed in specta- 
 cles for near-sighted eyes? for far-sighted eyes? for astigmatic 
 eyes? 
 
 What are some of the ailments brought on by eye trouble ? Why 
 is it important to wear spectacles when they are needed ? r rom 
 whom should they be procured ? Mention three points that should 
 be kept in mind in caring for the eyes. Why is dust injurious to 
 the eyes? What effect has tobacco on the eyes? alcohol? 
 
CHAPTER XXI 
 
 ACCIDENTS 
 
 IN cases of accidents and emergencies it is often very im- 
 portant that something be done at once. Some of the best 
 measures to be employed in such cases will be discussed in 
 this chapter. When the time comes for putting these measures 
 into use, a cool head and quick action are absolutely neces- 
 sary. Therefore, at such times, keep cool, think quickly, and 
 act sensibly and at once. 
 
 How to keep Afloat in Water. It requires very little force 
 to keep the human body afloat in water. In trying to keep 
 afloat, therefore, keep your body low in the water. A small 
 board is enough to keep you afloat if you will do this. If 
 thrown into the water by the upsetting of a small boat, do 
 not try to climb upon the boat, or you may sink it. Keep 
 your body low in the water and support yourself by taking 
 hold of the boat with your han(t If you break through the 
 ice, keep your body low in the water 
 and take hold of the edge of the ice 
 with your hand. Every one should learn 
 to swim, for knowing how to swim 
 even a few yards will often save life. 
 
 How to revive a Person who has 
 FIG. 132 Draining the been under Water. In drowning, the 
 water from the lungs. ^vti** is that the air is cut off from 
 the lungs by the water. The great point, therefore, is to get 
 air into the lungs as quickly as possible. 
 
 274 
 
ACCIDENTS 
 
 275 
 
 The first thing is to drain the water from the lungs. Turn 
 the patient on his face and lift him as is shown in Figure 132. 
 Lift him up two or three times, jerking the body, so that all 
 the water will come out of the lungs. Do this quickly (in 
 about thirty seconds). 
 
 After the water is out of the lungs, turn the patient on his 
 back. Put something a pillow, clothes, anything at hand 
 under the shoulders to throw the chest out. Loosen the 
 clothing at the neck and waist. The tongue must be drawn 
 out of the mouth and 
 either held or fastened by 
 having a pin thrust through 
 the tip. Otherwise it will 
 drop back and close the 
 throat. All this must be 
 done quickly r , for life often 
 depends on starting respi- 
 ration at once. 
 
 The next step is to start 
 artificial respiration. To 
 do this, grasp the patient's 
 arms and pull them up far 
 over his head (Fig. 133 A) 
 while you count one, two, 
 
 FIG. 133. 
 
 piration. 
 
 Two ways of starting artificial res 
 The way shown in B is the better, 
 
 three. Then bring the 
 arms down to the sides and 
 press as hard as possible 
 
 on the sides of the chest to force the air out of the lungs. 
 Do this about twelve or fifteen times a minute. If the 
 patient does not begin to breathe in three or four minutes, 
 turn him over and try if any more water can be drained form 
 the lungs, 
 
276 HUMAN PHYSIOLOGY 
 
 When there are two persons to care for the patient, they 
 should take the positions shown in Figure 134, and when 
 
 the arms are brought 
 down to the sides, one 
 should press on the 
 abdomen and chest 
 in such a way as to 
 force in the ribs and 
 drive the abdominal 
 organs and diaphragm 
 upward. Keep up 
 artificial respiration 
 for two hours, if 
 necessary, for per- 
 
 FIG. 134. Artificial respiration carried on by two persons. i* i 
 
 after showing no signs of life for this length of time. 
 
 A newer and better method is shown in Figure 133 B. 
 About fifteen times a minute the weight of the body is 
 thrown forward on the hands and then the pressure is re- 
 moved without lifting the hands. In this method the tongue 
 requires no care, and more air passes through the lungs than 
 passes through them .when the patient is laid on his back. 
 
 Other treatment is useful when there is help enough to give 
 it without interfering with the artificial respiration. The limbs 
 should be rubbed upward to make the blood in the veins flow 
 to the heart, and, if possible, the wet clothing should be re- 
 moved and the body wrapped in warm blankets. Often the 
 easiest way of warming the patient is to pour warm water 
 over his clothing and then cover him with a blanket. Hot- 
 water bottles or other warm objects will help to keep up the 
 heat. In cold weather the warming of the patient is a very 
 important part of the treatment. After the patient begins to 
 
ACCIDENTS 
 
 277 
 
 breathe, he should be kept warm, the head being warmed as 
 well as the body. Hot water or hot coffee is useful. A little 
 alcohol or 15 drops of ammonia in one third of a glass of 
 water every fifteen minutes is also helpful. 
 
 Suffocation. In suffocation the trouble is lack of oxygen, 
 and artificial respiration is the remedy. 
 
 Bleeding. When a large artery is cut, the blood flows from 
 it in spurts. When a vein is cut, the blood comes from it in a 
 steady stream. Sometimes the bleeding can be stopped by 
 pressing on the cut vessel with 
 the fingers. If an artery has 
 been cut, the pressure must be 
 applied between the wound and 
 the heart. If a vein has been 
 cut, the pressure should be ap- 
 plied on the side of the wound 
 away from the heart. Can you 
 explain why this is the case ? 
 When the wound is in a limb, 
 a handkerchief or other piece 
 of cloth should be knotted and 
 tightly twisted about the limb, 
 as shown in Figure 135. The 
 knot in the handkerchief should 
 be placed over the cut blood 
 vessel, and if this does not 
 stop the bleeding, a small stone or a piece of wood should be 
 slipped under the knot. The best place to close an artery in 
 the leg is on the inside of the thigh, or behind the' knee, 
 because at these points the arteries can be pressed against 
 the bones. The upper arm is the easiest place to cut the 
 blood off from the arm. When the wound is in a part of the 
 
 FIG. 135. Stopping bleeding from 
 an artery in the leg. 
 
2/8 
 
 HUMAN PHYSIOLOGY 
 
 FlG. 136. Stopping bleeding 
 from an artery in the arm. 
 
 body around which something cannot be twisted, cloths should 
 be folded and pressed down on the wound. Any part of the 
 
 body from which blood is escaping 
 should be raised, for the blood al- 
 ways flows more easily to a part of 
 the body that is lowered. 
 
 Fainting. Fainting is caused by a 
 lack of blood in the brain. In treat- 
 ing a person who has fainted, it is 
 most important to lay him flat and 
 loosen all clothing about the neck so 
 that the blood can readily flow to 
 the head. Fresh air is beneficial, 
 and sprinkling the face with cold 
 water or causing the patient to smell 
 ammonia salts may assist in bring- 
 ing him back to consciousness. ' When fainting is followed by 
 weakness, a few drops of ammonia in a little water (15 drops 
 of ammonia in one third of a glass of water for an adult) 
 will prove a helpful stimulant. 
 
 Sunstroke. Lay the patient in the shade and pour cold 
 water on or apply ice to the head, back of the neck, and 
 spine. 
 
 Foreign Bodies in the Eye. Foreign particles may be re- 
 moved from the eye by turning back the eyelid over a match 
 or similar object, and wiping off the foreign body. The eye 
 should not be rubbed or the particle may become embedded 
 in the lining of the eyelid or in the outer surface of the eye. 
 Holding up the eyelid while the eye is moved about sometimes 
 brings the particle down to where it can be removed. Some- 
 times the offending body may be washed out by bathing 
 the eye. 
 
ACCIDENTS 279 
 
 Burning Clothing. If your clothing should take fire, do 
 not start to run. Lie down and wrap yourself in a rug, 
 blanket, or anything you can lay hands on, to smother the 
 flames. If no rug or blanket is at hand, lie down and roll 
 over and over. In any case be sure and lie down to prevent 
 the flames from coming up around your face, for inhaling a 
 flame is often fatal. 
 
 When the clothing of another person is on fire, wrap him 
 in something to smother the flames, and throw him down. 
 Protect your own face as much as possible while doing this. 
 In a burning building hold something before your face when 
 near a flame. 
 
 Treatment of Burns. Moisten the clothing with water and 
 clip it away from the wound. Do not tear the skin. Rather 
 than do this, leave patches of clothing sticking to the wound. 
 Blisters should not be broken, but the liquid in them should 
 be drained off by making small holes with a needle in the 
 sides of the blisters. The treatment for burns made with hot 
 water is the same. 
 
 Shut the air off from the burn. The following are conven- 
 ient methods of doing this : 
 
 Cover the wound with clean cotton cloths that have been 
 dipped in olive (sweet) oil. If carbolic acid and glycerin are 
 at. hand, add a teaspoonful of each to a pint of the oil before 
 it is used. 
 
 Stir baking soda into vaseline and cover the wounds with 
 cloths on which this has been spread. 
 
 Soak cloths in water in which as much soda as possible 
 has been dissolved, and spread them over the wound. 
 
 When nothing else is at hand, cover the wound with white 
 of egg, wet starch, or wet flour. Do not cover a burn with 
 cotton, or the cotton will stick to the flesh and cause trouble. 
 
280 HUMAN PHYSIOLOGY 
 
 Great care should be used to keep a burn from becoming 
 infected with germs (page 312). Unless it does become in- 
 fected, it is best not to open it for some time, but to keep the 
 cloths with which it is covered moist with sweet oil in which 
 there is a little carbolic acid and glycerin. 
 
 Poisoning. When any poison except an acid has been 
 swallowed, vomiting should be induced at once. To cause 
 the vomiting, stir a tablespoonful of mustard in a glass of 
 water, take half of it, drink a large quantity of hot water, 
 and follow it with the remainder of the mustard. Large 
 amounts of warm salt water or simply warm water may be 
 used when no mustard is at hand. Tickling the throat with 
 a feather or thrusting the finger down the .throat will often 
 bring on the vomiting. 
 
 Acids. Give soda, chalk, old mortar, or soap in plenty of 
 warm water, and then cause vomiting. Oil and milk are also 
 useful For carbolic acid alcohol, oil, or milk should be used. 
 
 Arsenic. Cause vomiting and give hydrated sesquioxid of 
 iron. This compound may be formed by adding tincture of 
 iron to baking powder. Give some of the brown powder 
 that is formed to the patient every few minutes. The poison 
 in Paris green, Fowler's solution, and Rough on Rats is 
 arsenic, and the treatment for poisoning with them is the 
 same as the treatment for poisoning with arsenic. 
 
 Belladonna. This is the poison in nightshade. Use the 
 treatment for it that is given below for opium. 
 
 Mercuric Chlorid. (Also called bichlorid of mercury and 
 corrosive sublimate.) Give milk and white of egg or both. 
 Flour or starch with milk and eggs is also a good remedy. 
 
 Phosphorus. Magnesia and chalk in water and the white 
 of egg are good remedies. Do not give oil or milk. Phos- 
 phorus is in the substance on the ends of matches, and phos 
 
ACCIDENTS 28l 
 
 phorus poisoning usually comes from allowing children to 
 play with matches. 
 
 Opium. Give strong coffee or ammonia (15 drops in one 
 third of a glass of water every fifteen minutes or oftener). 
 Walk the patient about, slap him, throw cold water on him, 
 and do not allow him to go to sleep. Morphine, laudanum, 
 cholera mixtures, paregoric, and soothing syrups are ail either 
 forms of opium or contain it. 
 
 Strychnin. Inhaling chloroform or ether will quiet the 
 patient. Give five grains of sodium bromid every half hour. 
 Ammonia (see under Opium) or camphor in water is useful. 
 Throw cold water over the patient and use artificial respira- 
 tion if necessary. 
 
 Stramonium. This is the poisonous substance in Jimson 
 weed. The treatment for poisoning with it is the same as 
 the treatment for opium poisoning. 
 
 It is to be remembered that in poisoning with any of the 
 above substances except acids, one of the most important 
 things is to cause vomiting promptly. In acid poisoning it 
 is usually best to give something to destroy the acid (page 
 280) before the vomiting is induced. 
 
 Summary. In accidents and emergencies a cool head and 
 prompt action are important. 
 
 It is much easier for a person to keep afloat when his 
 body is low in the water than when he tries to climb up 
 out of the water. To revive a person who has been under 
 water, the water should be drained from the lungs and artificial 
 respiration started at once. This should be kept up for at 
 least two hours. It is also important to keep the patient 
 warm. 
 
 Suffocation is due to lack of oxygen, and artificial respira- 
 tion is the treatment for it. 
 
282 HUMAN PHYSIOLOGY 
 
 Bleeding from a large* vessel may be stopped by pressing 
 on and closing the vessel. Fainting persons should be laid 
 flat so that the blood will flow to the head. In sunstroke 
 the patient's head and spine should be cooled. 
 
 Running when the clothes are on fire fans the flames. In 
 such an emergency one should lie down and smother the 
 flames with a rug or blanket, or put them out by rolling over 
 and over. In all cases of fire, care should be taken not to 
 inhale the flame. In a burn the skin should not be torn, but 
 the wound should be covered from the air. 
 
 In poisoning, vomiting to get the poison out of the stomach 
 is a very important part of the treatment. In acid poison 
 ing it is best to give something to destroy the acids before 
 vomiting is caused. Other treatment should be given accord- 
 ing to the poison. 
 
 QUESTIONS 
 
 In trying to keep afloat, where should the body be allowed to 
 remain ? What causes death in drowning ? In attempting to re- 
 vive an apparently drowned person, what is the important thing to 
 do? 
 
 What is the first thing to do in attempting to revive a person who 
 has been under water ? How is this done ? In what position should 
 the patient then be laid? Why must care be exercised in regard to 
 the tongue? Explain how artificial respiration may be carried on 
 by one person ; by two persons. How long should it be continued \i 
 the patient does not sooner revive ? Describe another method that 
 one person may use in causing artificial respiration. What is the 
 advantage of this method? What other treatment should be given 
 where possible? 
 
 What causes death in suffocation? What treatment should be 
 given? 
 
ACCIDENTS 283 
 
 When a large artery is cut, how does the blood flow from it? 
 How does the blood flow from a vein? Where should pressure be 
 applied to close a cut artery? a vein? Explain how bleeding from 
 a cut in a limb may be stopped. Where is the best place to apply 
 pressure to shut off the blood from the leg ? from the arm ? How 
 may bleeding from a cut in some other part of the body be stopped? 
 
 What causes fainting ? How should a fainting person be treated ? 
 What treatment should be given in sunstroke ? 
 
 What should one not do if his clothing takes fire ? What are the 
 best ways of extinguishing the flame ? Why is it important to pro- 
 tect the face from flame? 
 
 What two important points should be kept in mind in dressing a 
 burn ? How may the air be kept from a burn ? 
 
 What is an important part of the treatment in poisoning? 
 
284 HUMAN PHYSIOLOGY 
 
 REVIEW QUESTIONS 
 
 CHAPTER XVI. How does the nervous system resemble a -telephone 
 system? Give the functions of the cerebrum; of the cerebellum ; 
 of the pons j of the medulla ; of the spinal cord. Explain how a 
 reflex action is carried out. Define ; ganglion ; neuron j afferent ; 
 efferent ; convolutions ; arbor vitae ; acquired reflex. 
 
 CHAPTER XVII. How many pairs of cranial nerves are there ? of 
 spinal nerves ? Which roots of the spinal nerves contain the afferent 
 and which the efferent fibers? (This may be fixed in the mind by 
 remembering that the first letters of the wurds dorsal and afferent, 
 and of ventral and efferent, spell Dave?) What is the function of the 
 sympathetic system ? Explain how a sympathetic reflex is carried 
 out. How much sleep is needed by a person of your age ? What 
 are the effects of tobacco on the nervous system? of alcohol? 
 
 CHAPTER XVIII. How is alcohol formed? What is its effect on 
 length of life? on the death rate from tuberculosis? What per cent 
 of insanity is caused by alcohol? Give some facts that show that the 
 evil effects of alcohol are inherited. Speak of the effects of alcohol 
 on the character. 
 
 CHAPTER XIX. Name the special senses. How is the sensation 
 of feeling caused? of taste? of smell? How may the olfactory cells 
 be injured ? How does a wave in the air cause a sensation of sound ? 
 Mention some ways in which the ears may be injured. Define : 
 auditory canal ; tympanic membrane ; tympanum ; malleus ; incus ; 
 stapes ; Eustachian tube ; vestibule ; cochlea. 
 
 CHAPTER XX. How is the eye protected ? Draw a diagram of a 
 longitudinal section through the eye. Explain how an image is 
 formed on the retina. Explain how the eye is accommodated. 
 What is the trouble in a near-sighted eye ? in a far-sighted eye ? in 
 an astigmatic eye ? In each case what kind of spectacles is needed ? 
 Mention some points connected with the hygiene of the eye. 
 
 Define : lachrymal gland ; retina ; vitreous humor ; aqueous humor ; 
 cornea ; iris ; pupil ; suspensory ligament ; ciliary muscles. 
 
 CHAPTER XXI. Tell how to revive a person who has been under 
 water. What should be done in cases of suffocation ? of bleeding ? 
 of fainting ? of sunstroke ? when the clothing is on fire ? in treating a 
 burn? in cases of poisoning? 
 
CHAPTER XXII 
 
 DISEASE GERMS 
 
 DISEASE germs cause the death of over 50 per cent of the 
 human race. In addition to this great loss of life, they are 
 responsible for an amount of suffering so great that it can 
 hardly be imagined. Every year millions of dollars' worth of 
 time is lost by persons suffering from diseases caused by 
 germs; great amounts of time and money are constantly 
 being spent in caring for these sufferers; and every year 
 hundreds of thousands of people rise from beds of sickness, 
 weakened for life by diseases caused by these small enemies 
 of mankind. 
 
 A great part of this suffering and loss of money, time, and 
 life is unnecessary, for germ diseases are, in the main, pre- 
 ventable. 1 The most useful facts of all science, therefore, 
 are the facts that give us a knowledge of disease germs and 
 how to avoid them. 
 
 What are Disease Germs? One-celled animals are called 
 protozoa (singular, protozob'n), and one-celled plants of a cer- 
 tain kind are called bacteria (singular, bacterium). The prin- 
 cipal breeding places of protozoa and bacteria are in water 
 and in the earth. To most kinds of them we pay no attention, 
 for they are harmless. A few kinds, however, grow in the 
 bodies of man and other animals, and cause sicknes^. When 
 
 1 " It is within the power of man to cause all parasitic diseases to disappear 
 from the world." PASTEUR, 
 
 285 
 
286 HUMAN PHYSIOLOGY 
 
 we speak of disease germs, we are referring to the little ani- 
 mals and plants that grow in the bodies of men and animals 
 and cause disease. 
 
 The Multiplication of Disease Germs. All that most disease 
 germs do when they multiply is to grow longer and pinch in 
 two. Then there are two germs. A cholera germ may be- 
 come full-grown and divide in twenty minutes, and all disease 
 germs multiply with astonishing rapidity. If one germ and 
 the germs that come from it should divide at the rate of once 
 an hour, in twenty-four hours they would increase to more 
 than seventeen millions. 
 
 Where Disease Germs come from. The germ of typhoid 
 fever may be in water, the smallpox germ on clothes, the 
 diphtheria germ on a pencil or a drinking cup, and the germs 
 of many different diseases may at times be found in milk. 
 These germs, however, do not originate in the water, on the 
 clothes or pencil, or in the milk, but in nearly all cases they 
 come front some human body in which they are growing. In 
 the prevention of germ diseases, nothing is so important, 
 therefore, as to keep germs from the bodies of persons who 
 have these diseases from being scattered about. 1 The follow- 
 ing experiments will show that disease may be spread by 
 allowing the little plants and animals that cause them to get 
 into new locations where they can grow : 
 
 1 It is important to realize that germs are plants and animals, and that a germ 
 can grow only from another living germ of the same kind. It is unsafe to have 
 dirt and unclean matter about, only because such matter may contain germs, and 
 any germs in it may remain alive ; but the idea that germs originate in such 
 matter is not correct. As we shall see later, a few germ diseases may occasion- 
 ally be contracted from animals, and people who are not themselves sick may 
 sometimes carry certain kinds of disease germs in their bodies. In most cases 
 of germ diseases, however, the germ comes from another person who is suffering 
 with the disease. 
 
DISEASE GERMS 28? 
 
 Thrust a needle into a rotten apple and then into a sound apple. 1 
 Lay the sound apple away for a few days and wait for the appearance 
 of the disease in it. Cut it open and note how the rot has spread 
 out from the needle path. The disease will probably develop more 
 quickly if you will bore a small, deep hole in the side of the apple 
 and pack some of the rotten material from the apple into it. 
 
 Inquire among greenhouse owners and find a carnation that is 
 suffering from stem rot. Cut into the diseased stem, and then with 
 the same knife cut a healthy stem half in two. Tie a cloth about the 
 wounded stem, and keep it moist until the disease develops. The 
 disease may be more surely produced by putting into the wound a 
 little matter from the diseased stem. 
 
 How Disease Germs enter the Body. Sometimes disease 
 germs enter the body through the skin, working down 
 through the hair follicles and sweat glands, or getting into 
 wounds. The germs of a number of diseases are introduced 
 into the body by the bites of insects. More commonly, germs 
 enter the mouth or nose and grow in the walls of the air 
 passages, the walls of the alimentary canal, or in the lungs. 
 A knowledge of how a germ enters the body often helps us 
 to avoid the disease that it causes. 
 
 How Germs cause Sickness. When disease germs grow in 
 the body, they produce substances called toxins. The toxins 
 are very violent poisons, and cause illness by poisoning the 
 cells of the body. You should get clearly in mind the fact 
 that it is not the germs themselves, but the toxins that the 
 germs produce, that cause the disease. Almost all fevers are 
 caused by the toxins of disease germs. 2 
 
 1 Rots are caused by fungi (Fig. 151) that are much larger than the bacteria 
 and protozoa that cause diseases in our bodies. The fungi are living plants, 
 however, and closely related to the bacteria; and rots are spread by the spreading 
 of the fungi that cause them, just as our diseases are spread by the spreading of 
 the bacteria and protozoa that cause them. 
 
 2 Within the body, substances called antitoxins are produced to destroy the 
 toxins. These are discussed on page 307. 
 
288 
 
 HUMAN PHYSIOLOGY 
 
 How the Body kills Germs. Germs that get into the body 
 are killed in two ways by the white corpuscles of the blood 
 and by a germicidal (germ-killing) substance that is in the 
 blood. The white corpuscles flow around the germs and 
 take them in, or swallow them. Then the corpuscles 
 attempt to digest and kill the germs, and the germs try to 
 grow in the corpuscles and use them for food. If the cor- 
 puscles triumph, the germs will be killed and the disease 
 
 FIG. 137. A white corpuscle taking in disease germs, a is a germ that has been killed 
 and partially broken up by the corpuscle. 
 
 will be checked. If the germs are victorious, the corpuscles 
 will be destroyed, the disease will go on, and the patient will 
 finally die. 
 
 Just what the germicidal substance of the blood is or where 
 it comes from is not certainly known, but there is something 
 dissolved in the blood that kills germs that get into the body. 
 The blood of a healthy person always has some germicidal 
 substance in it and some power of killing germs. When 
 disease germs get into the body, more of this substance is 
 manufactured and thrown off into the blood, where it power- 
 fully aids the white corpuscles in the fight against the germs. 
 The turn of the fever in germ diseases comes when the 
 corpuscles and the germicidal substance begin to get the 
 better of the germs. 
 
 Different Germicidal Substances. There is a different ger- 
 micidal substance for each different kind of disease germ, and 
 
DISEASE GERMS 289 
 
 after recovery from an attack of a disease, a large amount 
 of the germicidal substance for the germ of that disease will 
 be found in the blood. The germicidal substance for some 
 germs remains in the blood for years, and there are many 
 diseases that people usually have but once. This is because 
 after an attack of one of these diseases the germicidal sub- 
 stance remains in the blood through life and promptly 
 kills any germs of that kind that may get into the body. 
 In other diseases the germicidal substances quickly disap- 
 pear from the blood, and we may have them again and again. 
 Inherited Diseases. It is often said that diseases (e.g. con- 
 sumption, leprosy, cancer) are inherited. By this, it is not 
 meant that the germs of a disease are inherited, but that 
 little power of killing those germs is inherited. If the 
 parent has little power of killing a certain germ, the child 
 will also be likely to have little power of killing it. The 
 germ may get into the body of the parent, and, finding little 
 resistance, attack him. At another time it gets into the 
 body of the child, and the germicidal power of the blood 
 being slight, the child is also attacked. Certain families are 
 weak in their power of resistance to certain germs, and 
 therefore suffer from the diseases caused by these germs. 
 Races of men differ in their power to kill germs, the Mon- 
 golians particularly being attacked by leprosy, and the 
 negro race having little resistance to the germ that causes 
 consumption. The germicidal power of the body is inherited 
 in races as well as in families, but it is the lack of power to 
 kill the germ, and not the germ itself t that is inherited. A 
 member of a family that suffers from a certain disease should 
 take special care to keep himself free from the germs of that 
 disease, for as long as he can keep these germs out of liis 
 body, he may be as healthy as any one. 
 
290 HUMAN PHYSIOLOGY 
 
 Keeping up the Germicidal Power of the Body. The seeds 
 of plants lie in the earth through the cold winter, waiting for 
 the warmth of spring to enable them to grow; so disease 
 germs often lie in the body, ready, if a favorable time comes, 
 to start their growth. Germs capable of producing disease 
 are usually in the body, and the germs of most dangerous 
 diseases often enter the body at times unknown to us. The 
 only safe way, therefore, is always to keep the body in 
 health, so that it may be able to repel any attacks that may 
 be made upon it. Overwork, hunger, exposure to cold, wet 
 feet, insufficient sleep, bad ventilation, bad food, lack of exer- 
 cise, alcohol all of these things injure the body and lower 
 its germicidal power. It is a duty that every one owes to 
 himself to keep his body in good condition, and to fail to do 
 so is no more sensible than it would be for a garrison in a 
 hostile country to go to sleep with the gates of the fortress 
 open. 
 
 Alcohol and Germ Diseases. We have already learned that 
 the world's greatest authorities on tuberculosis state that al- 
 cohol drinking renders the body more susceptible to the 
 germ that causes that disease (page 240). Physicians have 
 observed that a drunken spree sometimes brings on an attack 
 of pneumonia, and it has long been the opinion of medical 
 men that alcohol drinkers are more liable to the attacks of 
 germ diseases than are non-users of alcohol. 
 
 More recently it has been definitely proved by experiments 
 on animals that alcohol lowers the germicidal power of the 
 body, and it has been discovered that alcohol paralyzes the 
 white corpuscles and renders them unable to take up and 
 destroy disease germs. Knowing this, it is easy to understand 
 why drinking may bring on an attack of a germ disease. 
 When pneumonia germs are already in the body waiting for 
 
DISEASE GERMS 291 
 
 a chance to attack it, and the white corpuscles are paralyzed 
 by drinking alcohol, we need not be surprised if the disease 
 develops. 
 
 Summary. Disease germs cause the death of over one half 
 of the human race. They are small plants and animals that 
 grow in the body and multiply with great rapidity. They 
 are spread from the bodies of those who are suffering with 
 germ diseases, enter the body in various ways and cause dis- 
 ease by producing a poisonous toxin. 
 
 The body kills germs by its white blood corpuscles and by 
 a germicidal substance in the blood. The germicidal sub- 
 stance is increased during an attack of a disease, and after 
 recovery may remain in the blood, so that the person will be 
 protected against that disease for life. Certain families and 
 races of men are particularly weak in their power to kill cer- 
 tain germs. It is of the greatest importance to keep up the 
 germicidal power of the body. This is lowered by alcohol. 
 
 QUESTIONS 
 
 What are disease germs ? How do they multiply ? Where do the 
 germs that cause our diseases come from ? How do they enter the 
 body? How do they cause sickness? How does the body kill them? 
 Why do we usually have certain diseases only once ? What is meant 
 by an inherited disease ? Why is it important to keep up the germi- 
 cidal power of the body? Mention some ways in which the resist- 
 ance of the body to germs may be lowered. How does alcohol reduce 
 the power of the body to kill germs ? 
 
CHAPTER XXIII 
 
 DISEASES CAUSED BY PROTOZOA 
 
 THE protozoa (page 285) are the smallest of all animals. 
 The largest of them can barely be seen with the naked eye, 
 and under the most powerful microscope the smallest of them 
 look like tiny specks. Some of those living in the ocean have 
 shells, and so abundant are they that great beds of chalk and 
 limestone are built by them. Others are phosphorescent, 
 and in the warmer seas the waves at night are often fringed 
 with light from the multitude of protozoa in the water. 
 They are abundant in fresh water also, every pool and pud- 
 dle containing great numbers of them, and they grow as 
 parasites in almost every animal from worms and insects up 
 to man. Some of our worst diseases are caused by protozoa. 
 
 MALARIA 
 
 Malaria is one of the worst diseases that afflict mankind. 
 No community or portion of a country can reach its highest 
 state of development as long as malaria is prevalent in it ; 
 for the disease affects a large number x of the inhabitants, 
 and persons so affected do not have and cannot have the 
 strength, energy, and ambition necessary to carry on great 
 
 1 In malarial countries the germ is sometimes found in the blood of from 20 to 
 30 per cent of the inhabitants. In many instances the disease takes a slow 
 chronic form in which the patient does not have chills and fever, and often does 
 not know that he is suffering from the disease. The germ may remain in the 
 
 body for years. 
 
 292 
 
DISEASES CAUSED BY PROTOZOA 
 
 293 
 
 enterprises. Many of the most backward portions of our 
 country would m a very few years be centers of industry, 
 education, and leadership, if malaria could be eradicated from 
 them. 
 
 The Cause of Malaria. Malaria is caused by protozoa that 
 live in the red corpuscles of the blood. The protozoon in- 
 creases in size until it almost 
 fills the corpuscle. Then 
 it divides into a number of 
 parts, each of which is a 
 young germ. These break 
 out of the corpuscle into 
 the blood, and then each 
 one settles upon and en- 
 ters a fresh red corpuscle. 
 Within the corpuscle the 
 germ grows and the young 
 break forth in due time to 
 repeat the process. 
 
 During their growth 
 within the corpuscles the 
 malaria germs produce 
 toxin. At the time when 
 the young break down the 
 
 corpuscles and come out into the blood, a great amount of 
 this toxin is liberated in the blood at once, and the result is a 
 chill and fever. In addition to injuring the body with its 
 toxin, the malaria germ destroys millions of the red blood 
 corpuscles, thus interfering with the oxygen-carrying power 
 of the blood. 
 
 Kinds of Malaria Germs. There are several different va- 
 rieties of the malaria germ, some of which produce a more 
 
 FIG. 138. The malaria germ in a red blood 
 corpuscle. A, B, and C show the growth of 
 the germ ; D shows it dividing into a number 
 of young germs; E shows the corpuscle 
 broken down and the young germs escaping 
 into the blood. 
 
294 HUMAN PHYSIOLOGY 
 
 severe form of the disease than others. In one form of the 
 disease the germ requires seventy-two hours to complete its 
 growth and break out of the corpuscles. In this kind of 
 malaria, the chill comes every third day. In other forms, the 
 germs require forty-eight hours for their development, and 
 in these kinds of malaria the chill comes every other day. 
 It is quite possible, however, to have more than one crop of 
 the germs in the blood at one time. One set of germs may 
 break out of the corpuscles one day and a different set the 
 next day, so that the affected person may have a chill every 
 day. In some cases of malaria the germs may keep coming 
 out all the time and the patient may have a continuous fever. 
 Usually a malarial fever rises and falls, and for this reason 
 a continuous malarial fever is often called remittent fever. 
 
 How the Malaria Germ enters the Body. The malaria germ 
 is introduced into the body by a certain species of mosquito 
 (Fig. 152). A mosquito feeds on man by inserting its pro- 
 boscis through the skin and sucking out the blood. When a 
 mosquito draws blood from a person who is affected with 
 malaria, it takes malaria germs into its stomach. The germs 
 enter the wall of the mosquito's stomach, and multiply there, 
 and many of them finally reach the mosquito's salivary 
 glands. 
 
 The opening in the proboscis of a mosquito is too fine 
 to allow red blood corpuscles to pass through it. The mos- 
 quito, therefore, when it thrusts its proboscis through the 
 skin to feed, injects saliva down through its proboscis into 
 the wound to break up and digest the red corpuscles. If 
 the mosquito is infected with malaria, the germs will be 
 injected into the wound with the saliva. The germs thus 
 introduced into the body enter the red blood corpuscles, and 
 about a week later the disease develops. 
 
DISEASES CAUSED BY PROTOZOA 295 
 
 Curing Malaria. After the germs of most diseases get 
 into the body, it is impossible to kill them by taking medi- 
 cines. The germs are harder to kill than our own cells, and 
 we cannot poison them with medicines without poisoning our 
 own bodies. Fortunately, the human body can endure an 
 amount of quinine that will poison and kill the germ of mala- 
 ria. 1 Malaria is, therefore, one of the few germ diseases that 
 can be successfully treated by taking medicine to kill the 
 germ. It is far better, however, to prevent the disease than 
 to try to cure it. 
 
 The Prevention of Malaria. Man gets the malaria germ 
 from the mosquito, and the mosquito gets it from man. If we 
 could destroy all mosquitoes, the disease, of course, would die 
 out. If we could destroy all the germs that are in the blood 
 of malaria patients, the mosquitoes would not become infected, 
 and the disease would cease to be spread. The following 
 suggestions for the -prevention of malaria are in accordance 
 with these principles, and by following them out much can be 
 done to check the disease : 
 
 Screening Malaria Patients. It is very important to keep 
 a malarial patient under mosquito netting until the germs dis- 
 appear from his blood. Where this is not done, it has been 
 found that the mosquitoes in the house become infected by 
 biting him, and that other persons in the house usually 
 contract the disease. In regions where there is only an 
 occasional case of malaria, or where only a few persons are 
 living close together (as in a country farmhouse), this pre- 
 caution will do much to prevent the spread of malaria. 
 
 Avoiding Unnecessary Exposure to Mosquitoes. Persons 
 
 1 Malaria germs are killed much more easily by quinine while they are free in 
 the blood than when in the corpuscles. The quinine should be taken so that it 
 will be in the blood at the time when the germs come out of the corpuscles. 
 
296 HUMAN" PHYSIOLOGY 
 
 living in malarial regions should keep their houses carefully 
 screened and should sleep under mosquito nets during the 
 mosquito season. They should * not expose themselves to the 
 attacks of mosquitoes very early in the morning or late in the 
 day, and should take care to avoid the haunts of the mosqui- 
 toes on cloudy days when mosquitoes are flying. Judgment 
 should be exercised in selecting places to be visited in camping 
 and fishing excursions, for one night spent among mosquitoes 
 may start an attack of malaria that will last for months. 
 
 The Use of Quinine. Quinine frees the blood from malaria 
 germs, and thus prevents mosquitoes from becoming infected. 
 A little quinine in the blood will also kill any malaria 
 germs that may be introduced into the body by an infected 
 mosquito, and thus prevent the development of 
 the disease. In malarial regions it is sometimes 
 advisable to take small doses of quinine daily 
 as a preventive measure. 
 
 Destroying Mosquitoes. This is the most 
 effective of all the measures that are employed 
 in fighting malaria. The subject will be dis- 
 cussed in a later chapter (page 323). 
 
 FIG. 139. DYSENTERY 
 
 The ameba 
 
 of dysentery. Chronic dysentery is usually caused by a pro- 
 
 The three dark tozoon, an ameba, that is similar in many ways 
 
 iJe^ameba to a l ar g e white blood corpuscle. The disease 
 
 are red blood is most common in the tropics, but is found in 
 
 corpuscles on our own CO untrv. The ameba of dysentery lives 
 
 which it has . . , ,, 
 
 been feeding, m water, and when swallowed, enters the wall 
 of the large intestine and grows there. The 
 disease comes from impure water, and the best methods of 
 preventing it will be taken up in another chapter. 
 
DISEASES CAUSED BY PROTOZOA 
 
 SMALLPOX 
 
 297 
 
 Smallpox is probably caused by a small protozoon that 
 lives in the cells of the skin and of certain other parts of the 
 body. 1 The germs may be carried on 
 clothing or anything that a smallpox pa- 
 tient touches, and there are great numbers 
 of germs in the dried scales that come from 
 the skin during recovery from the disease. 
 As smallpox germs may remain alive for FIG . 
 months after being dried and scattered, smallpox in the ceils of 
 the disease is very easily spread. For this the skm - 
 reason a person suffering from smallpox should be quaran- 
 tined, and everything that has been about him should be 
 burned or disinfected (page 332). The incubation period of 
 smallpox (the time between the entrance of the germs into 
 the body and the appearance of the disease) is usually from 
 seven to twenty-one days. 
 
 Vaccination. Before vaccination was discovered, smallpox 
 was one of the hardest of all diseases to control. Up to a 
 little over one hundred years ago, about 95 per cent of all 
 persons were attacked by it, and the number of deaths from 
 smallpox was enormous. 'About the year 1800 vaccination 
 began to be practiced, and in all civilized countries it is now 
 more or less compulsory. Where vaccination is thoroughly 
 carried out, smallpox has almost ceased to exist, but in coun- 
 tries where the people are not vaccinated, or where only part 
 
 1 There is still some uncertainty in regard to the germ of smallpox, some of 
 those who have studied the bodies shown in Figure 140 holding that they are not 
 the germs that cause the disease. It is certain, however, that smallpox is a 
 germ disease, and we have learned how to control it even if we are not certain 
 as to the exact germ that causes it. 
 
298 HUMAN PHYSIOLOGY 
 
 of them are vaccinated, it is still impossible to prevent the 
 spread of the disease. 1 
 
 How Vaccination protects against Smallpox. The germ of 
 smallpox flourishes in man. It grows in cattle also, causing 
 the disease called cowpox. After growing in the cow this 
 germ seems to be weakened and changed so that it grows 
 feebly in man and has only a slight power of producing 
 disease. 
 
 In vaccination, germs from a cow are put into the human 
 body. Here they grow and begin to produce the mild inflam- 
 mation that follows vaccination. The body now works up the 
 germicidal substance for these germs and kills them out 
 before they can make much growth and spread through the 
 body. After this is done, the germicidal substance remains 
 in the blood, and if any smallpox germs get into the body, the 
 germicidal substance is there to kill them. 
 
 From this you will understand that a person who has been 
 successfully vaccinated is in very much the same condition 
 as a person who has had a light attack of smallpox. After 
 
 1 In the United States, Canada, and the other countries with which we 
 are njost familiar, vaccination has been extensively practiced and in conse- 
 quence in these parts of the world smallpox has been rare and most cases of 
 it are mild. Because of this fact, many persons have come to believe that it 
 has lost its old-time malignancy. This notion is incorrect, as is shown by the 
 history of smallpox in other parts of the world in recent times. From 1893 * 
 1898, Russia had over 275,000 deaths from the disease, Spain nearly 24,000, 
 Hungary over 12,000, and Italy and Austria each over 11,000. Before the 
 American occupation of the Philippine Islands, only a part of the inhabitants of 
 the Islands had been vaccinated, and thousands of deaths from smallpox occurred 
 every year. The people have now been thoroughly vaccinated, and in 1907 there 
 was not a single death from the disease in seventeen provinces of the Islands. 
 There is no doubt that the decrease in the death rate is due to vaccination, for 
 quarantining has failed to prevent a considerable amount of certain other diseases 
 (diphtheria, scarlet fever, etc.) that are much less infectious than smallpox. 
 
DISEASES CAUSED BY PROTOZOA 299 
 
 vaccination, as after recovery from an attack of many germ 
 diseases, the germicidal substance in the blood becomes 
 weaker and weaker, but never entirely disappears. Just when 
 it becomes so weak that revaccination is necessary, it is im- 
 possible to say. A successful vaccination usually protects 
 from smallpox for several years. Sometimes the germicidal 
 substance in the blood is fairly strong after seven, eight, 
 nine, or ten years. Two successful vaccinations usually 
 protect against smallpox for life, but in a very few persons 
 the germicidal substance disappears so rapidly after vaccina- 
 tion that the disease may be contracted in nine months. The 
 safest way is to be vaccinated every few years, and when 
 smallpox is prevalent, to be revaccinated if more than nine 
 months have passed since the last vaccination. There can 
 r-be no mistake in this, for if the germicidal substance is still 
 strong in the blood, all the germs put in by vaccination will 
 be killed, and the vaccination will not take. If the vaccina- 
 tion does take, it is a sure sign that the germicidal power of 
 the body had run low and that revaccination was needed. 
 
 RABIES (HYDROPHOBIA) 
 
 Rabies is believed to be caused by a protozoon that grows 
 in the nerve tissue. This germ attacks not only man, but 
 also many of the lower animals. It is found in the saliva of 
 animals suffering from the disease, and usually gets into the 
 human system through the bites of rabid animals. Practically 
 all the rabies in our country comes from the bites of dogs, 
 and it would be possible by properly muzzling dogs to stamp 
 out the disease entirely, as has been done in several Eu- 
 ropean countries. It is a mistake to think that rabies de- 
 velops in dogs because of hot weather, for they get the 
 
300 HUMAN" PHYSIOLOGY 
 
 germ from the bites of other dogs and may have the disease 
 at any time of the year. 
 
 In man the germ of rabies grows very slowly. At least 
 two weeks are required after the germs are introduced 
 into the body before the disease shows itself. Usually the 
 disease does not develop for five or six weeks, and some- 
 times not for a year. There is no cure for rabies after the 
 disease develops, but a preventive treatment, founded on the 
 same principles as vaccination, was discovered by a great 
 French scientist named Louis Pasteur. The Pasteur treat- 
 ment is successful in nearly all cases in which it is com- 
 menced in time. Where the materials for this treatment can 
 be delivered within thirty-six hours, they can be sent by mail 
 and the treatment given to the patient by his home physician. 
 No time should be lost in beginning the treatment. V^ 
 
 The Treatment of Wounds made by Rabid Animals. A 
 very great safeguard against this disease is to treat promptly 
 wounds made by the teeth of animals with something that 
 will kill the germs in the wounds. Any disinfectant (page 
 334) is useful, but burning with nitric acid is the most effec- 
 tive remedy. This should be done by a physician to make 
 sure that it is thoroughly done, and to guard against too great 
 injury to the flesh by the acid. The best method is to apply 
 at once to the wound any disinfectant that may be at hand 
 and then have it treated as soon as possible by a physician. 
 Treatment of the wound even after twenty-four hours is 
 useful. An animal that has bitten any one should not be 
 killed, but should be confined until it is known whether or 
 not it has hydrophobia. If the animal remains in health for 
 nine or ten days, there will then be no occasion for worry. 
 
 Other Protozoan Diseases. In the tropics many diseases of 
 man are caused by protozoa. Among these diseases are the 
 
DISEASES CAUSED BY PROTOZOA 301 
 
 slow and fatal sleeping sickness of Africa, which is commu- 
 nicated to man by a fly. It is thought that scarlet fever, 
 measles, and yellow fever may be /caused by protozoa, but 
 the germs of these diseases are not known. Rocky Moun- 
 tain or " spotted " fever, a disease of the Rocky Mountains, 
 which is caused by the bite of a tick, may also be a protozoan 
 disease. A protozoon that is carried by a tick causes the 
 " Texas fever " or " tick fever " that is prevalent among cattle 
 in our Southern states, and in the tropics many fatal diseases 
 of animals are caused by protozoa. 
 
 Summary. Protozoa cause many diseases of man. Among 
 them are malaria, dysentery, and perhaps smallpox, and 
 rabies. Malaria germs are carried by mosquitoes, and the 
 disease may be escaped by avoiding mosquitoes. Dysen 
 tery usually comes from impure water. The germ of 
 smallpox is easily spread, and few persons naturally have 
 the power to resist it. By vaccination the germicidal 
 power of the body toward the smallpox germ may be 
 raised and the disease controlled. Rabies comes from the 
 bites of dogs. Generally the disease can be prevented 
 from developing by the Pasteur treatment. Wounds made 
 by the teeth of animals should be disinfected. Protozoa 
 cause other diseases of animals and men. 
 
 QUESTIONS 
 
 Why is malaria an important disease? Describe the life history 
 of the malaria germ. What causes the chill in malaria? How 
 does the malaria germ enter the body? How long is it after the 
 germ gets into the body before the disease appears ? How may the 
 malaria germ be killed in the blood? How may malaria be pre- 
 vented ? Where does the germ of dysentery grow in the body ? How 
 
302 HUMAN PHYSIOLOGY 
 
 does it get into the body ? How may smallpox germs be spread ? 
 What is the incubation period of the disease ? What per cent of 
 people had smallpox before vaccination was practiced? Explain 
 how vaccination protects the body. How often should one be 
 vaccinated ? 
 
 How does the germ of rabies enter the body ? How may the 
 disease be stamped out? What is the incubation period of 
 rabies? How may the development of the disease be prevented? 
 How should wounds made by the teeth of animals be treated? 
 Name some other diseases that are thought to be caused by pro- 
 tozoa. 
 
 In some parts of our country there is no malaria. Why is this the 
 case ? Sometimes persons who have been living in a malarial region 
 have chills and fever when they move into a region where there is no 
 malaria. In such cases, where do the germs come from that cause 
 the disease ? People sometimes have chills and fever in the winter 
 or spring when no mosquitoes are flying. Where do the malaria 
 germs come from in these cases? 
 
 When persons who have been vaccinated take smallpox, they 
 usually have a light attack of the disease. Why should you expect 
 this to be the case ? Ask a physician to explain to you the Pasteur 
 treatment for hydrophobia. How does the principle underlying this 
 treatment resemble the principle on which vaccination is founded ? 
 
 With a microscope examine a drop of dirty water for protozoa. 
 
CHAPTER XXIV 
 
 DISEASES CAUSED BY BACTERIA 
 
 BACTERIA are so extremely small that millions of them 
 have plenty of room to swim about in a drop of water, and 
 a drop of sour milk commonly contains about fifty million 
 bacteria. It would require twenty-five thousand of them, 
 placed side by side, to make a row an inch long. Examined 
 under a microscope that would cause a man to appear as 
 high as Mount Washington or Mount Mitchell, bacteria look 
 about as large as the periods and commas in ordinary print. 
 So exceedingly small are these little plants that they can 
 pass through the pores in a brick as easily as a man passes 
 through the doorway of a house. 
 
 Another remarkable thing about bacteria is their power of 
 multiplication. It has been calculated that if all the bacteria 
 in the world could get food, warmth, and moisture so that 
 they could multiply as fast as they are capable of doing, in 
 two days they would fill all the oceans and cover all the land 
 fifty feet deep. Fortunately for us, most of them are held in 
 check by lack of the right conditions for growth. Yet they 
 show what they can do when they get into such favorable 
 places as warm milk ; for a quart of milk, before it sours and 
 thickens, usually contains eight or nine hundred billions of 
 bacteria. 
 
 The Distribution of Bacteria. Bacteria are everywhere 
 about us in the water, in the soil, and clinging to the small 
 
 303 
 
304 HUMAN PHYSIOLOGY 
 
 particles of matter that are always floating about in the air. 
 About three million bacteria are ordinarily found in an ounce 
 of cultivated soil, and they are much more abundant than 
 this in the earth around houses and barns. The water from 
 most wells contains more than one million bacteria to the 
 quart. Millions of bacteria are always growing on the hu- 
 man skin, and in the mouth, the intestine, and the respiratory 
 passages. Some kinds of bacteria are useful ; most kinds are 
 harmless, and to them we pay no attention ; but a few kinds 
 produce toxins in the human body that cause some of our 
 worst diseases. 
 
 Shapes of Bacteria. Bacteria are cylindrical, spherical, or 
 spiral shaped like a firecracker, a marble, or a corkscrew. 
 
 The cylindrical bacteria are called 
 bacilli (singular, bacillus). The 
 spherical bacteria are called cocci 
 
 FIG. 141. "Bacteria. A is a ba- (singular, coccus\ and the spiral 
 ciiius, B is a coccus, and c is a forms are called spirilla (singular, 
 spirillum - spirillum). The shapes of bac- 
 
 teria have nothing to do with the diseases which bacteria 
 cause, but often give a convenient way of distinguishing 
 between different kinds. 
 
 BACTERIAL DISEASES OF THE RESPIRATORY ORGANS 
 
 Diphtheria. The diphtheria germ grows usually in the 
 pharynx, but is also commonly found in the larynx and 
 mouth, is sometimes found on the lips and in the nose, and 
 may grow in other parts of the body. It does not usually 
 grow outside of the human body, but it can remain alive for 
 several weeks in matter that has come from the throat of 
 a diphtheria patient. On slate pencils that have touched the 
 
 A 
 
DISEASES CAUSED BY BACTERIA 305 
 
 lips of a person who has diphtheria, living diphtheria bacilli 
 have been found for several days. The incubation period 
 of the disease is usually from two 'to seven days, but may 
 be less. 
 
 Sometimes attacks of diphtheria are so severe that death 
 comes in a day or two. In other cases, the germs make only 
 a slight growth before the body gets the upper hand of them, 
 and the attack is so light that it is often mis- 
 taken for a simple case of sore throat. In f 
 
 A 
 
 still other cases, the diphtheria bacillus lives j 
 in the throat without causing illness at all. 1 I 
 Where the germs remain in the throat without J 
 causing sickness, the body is able to hold them FIG. 142. The 
 in check and keep them from making enough jjjP htheria bacil ' 
 grovvth to harm it, but is not able to kill them 
 out entirely. After recovery from an attack of diphtheria it 
 is not uncommon for virulent germs to be found in the throat 
 for four or five weeks, and in one case they were found eight 
 months after recovery from the disease. The disease called 
 membranous croup is the same as diphtheria. 
 
 How Diphtheria is contracted. Diphtheria is usually con- 
 tracted by getting the germs on the hands and then from 
 the hands into the mouth. Sometimes germs that have 
 been coughed out into the air 2 are inhaled. Dried sputum 
 
 1 Most healthy persons who have the diphtheria germs in their throats have 
 been about some one who is suffering from the disease. 
 
 2 In coughing, sneezing, laughing, and to a certain extent in talking, small 
 droplets of liquid are sent out into the air. These may fly to a distance of three 
 feet, and some of them are so very fine that they are said to float in the air for as 
 long as twenty minutes. When a person is suffering from a disease like diphthe- 
 ria, pneumonia, or consumption, these droplets are of course filled with the germs 
 of the disease. One should not stand near a person who is coughing, and a sick 
 person should hold a handkerchief before his face when he coughs. 
 
306 HUMAN PHYSIOLOGY 
 
 may contain living diphtheria germs, but dust is not an 
 important carrier of the disease. The germs are almost 
 certain to get on the handkerchiefs and hands of persons 
 having the disease. They may be left on a drinking cup 
 or on a pencil, on a toy or a piece of candy that has been 
 handed about among children, and in many other ways 
 they may be transferred from one person to another. They 
 sometimes get into the body from milk (page 330) and they 
 are often carried by flies and left where they reach the 
 respiratory passages. 
 
 Quarantining in Cases of Diphtheria. The diphtheria germ 
 is sometimes found in the throats of healthy persons, in the 
 throats of diphtheria patients who have long since recovered 
 from the disease, and in mild diphtheria cases where the disease 
 has not been recognized. Persons are therefore going about 
 who are themselves perfectly well, or at least only slightly ill, 
 but who nevertheless carry diphtheria germs that are exceed- 
 ingly dangerous to others. These persons often object to 
 being quarantined, and health officials have great difficulty in 
 preventing the spread of diphtheria. The only way by which 
 the disease can really be controlled is to shut up in quarantine 
 every one who has virulent diphtheria germs in his throat, 
 whether or not he is himself ill. This often involves quaran- 
 tining for long periods of time both diphtheria patients and 
 members of families in which there is diphtheria. 
 
 Diphtheria Toxin and Antitoxin. The diphtheria germ may 
 cause death by closing the throat, but usually the cause of 
 death is the very powerful toxin which the germ produces. 
 This toxin attacks the nervous and the muscular systems, 
 and the direct cause of death often is that the nerve and 
 muscle cells of the heart are so injured that the heart stops. 
 
 We have already studied about how, when germs get into 
 
DISEASES CAUSED BY BACTERIA 307 
 
 the body, the body begins to work up its power of killing 
 them. So when toxin is produced in the body, the body 
 works up a substance called antitoxin that neutralizes, or 
 destroys, the toxin. If the body can produce enough anti- 
 toxin to keep the toxin from poisoning the cells, the germi- 
 cidal power of the blood will rise, and finally the germs will 
 be killed out. But if the toxin is not destroyed, it will poison 
 the body and take away its power of killing germs, the bac- 
 teria will triumph, and death will come. The antitoxin does 
 not kill the germs, but protects the body from the toxin until 
 the white corpuscles and the germicidal substance in the blood 
 can overcome the germs. 
 
 The Antitoxin Treatment. It was found that the horse 
 has a very great power of producing antitoxin, and the anti- 
 toxin now constantly used in the treatment of diphtheria is 
 secured from the horse in the following way : 
 
 Diphtheria germs are placed in beef broth, where they 
 grow and multiply, and produce great amounts of toxin. A 
 little of this toxin is then injected into the blood of a horse, 
 and the horse works up antitoxin to destroy it. Then a 
 larger dose of toxin is given the horse, and still more anti- 
 toxin appears in the blood. This is kept up until the blood 
 is made as strong in antitoxin as possible. Then the horse 
 is bled, and the blood allowed to coagulate, or clot. The 
 thin, yellowish serum that appears around the clot contains 
 the antitoxin, and it is this which is placed in sealed bottles 
 and sold as antitoxin after it has been freed from certain 
 slightly injurious substances which it contains. 
 
 When a person has diphtheria, and the germs begin to 
 manufacture toxin and poison the cells, some of the antitoxin 
 from the horse is injected into the blood. This unites with 
 the toxin and saves the body cells from being poisoned, thus 
 
308 HUMAN PHYSIOLOGY 
 
 giving the body time to kill the germs and so stop the 
 
 disease. When antitoxin is used in the early stages of 
 
 diphtheria, practically all deaths from this disease are 
 
 prevented. But it is very important to use it before the 
 
 toxin has poisoned and destroyed the cells. 
 
 v^'^8&: : -- Antitoxin is often given as a preventive to 
 
 '^^ : :'*^-'-v- those who have been exposed to the germs. 
 
 : : ';i^. ; * : '- } -^- Pneumonia. In some of the Northern 
 
 ''-&'-;*&-;^:'^ states pneumonia leads even tuberculosis 
 
 as a cause of death. It may be due to 
 
 FIG. I43 The pneu- m that wg j n tfae j fe t ^ - 
 
 monia germ. * * p 
 
 usually caused by a small coccus (Pneumo- 
 coccus]. This germ causes not only pneumonia, but also colds, 
 inflammation of the middle ear, 1 and meningitis (page 317). 
 The germs are in the secretions from the mouth and nose, and 
 they are transferred from one person to another in the same 
 manner as the germs of other respiratory diseases. 
 
 Recent studies indicate that one very important method of 
 infection in all the saliva-borne diseases is through the eating 
 utensils and glasses in public eating places and in soda foun- 
 tains and ice-cream parlors. In certain army cantonments 
 and among the workers in a number of public eating places 
 investigated, there was, during a given time in the 1918 epi- 
 demic, less than one fifth as much influenza where the dishes 
 were washed with boiling water as where they were washed 
 by hand. 
 
 1 Inflammation of the middle ear is caused by many different kinds of germs. 
 It is very serious, for incurable deafness will follow the breaking down of the 
 chain of bones, and there is danger of the inflammation spreading. Sometimes 
 the germs get into the cavities that are in the bone above the middle ear (Fig. 1 19), 
 producing the disease called mastoiditis, and sometimes they work through into 
 the cranial cavity and cause meningitis, or a brain ulcer. Running ears and other 
 diseases of the ear from which children especially suffer should not be neglected. 
 
DISEASES CAUSED BY BACTERIA 309 
 
 Varieties of the Pneumonia Germ. There are many differ- 
 ent varieties of the pneumonia germ. Some of these are 
 exceedingly virulent ; some are perhaps not dangerous at all. 
 Three races, or types, that are responsible for about 80 per 
 cent of all pneumonia cases and 90 per cent of the deaths from 
 the disease are now distinguished. A serum that is useful in 
 treating cases due to one of these races is now used. 
 
 Preventing Pneumonia. Perhaps the most important meas- 
 ure in the prevention of pneumonia is the isolation of cases 
 of the disease. Many healthy persons are carriers of germs 
 of the milder races, but the virulent kinds are not widespread. 
 
 A second important factor in the prevention of pneumonia 
 is rest in bed when attacked by colds, influenza, and measles. 
 Many cases of pneumonia begin as colds, the germs later 
 working downward into the lungs, while nearly all deaths in 
 connection with measles and influenza are due to pneumonia 
 following these diseases. 
 
 Anti-pneumonia vaccination has been tried with very en- 
 couraging results in the United States Army, and some 
 health officers advise every one to be vaccinated against the 
 pneumonia germ. This is done by injecting killed cultures 
 of the germ beneath the skin, as is done in vaccination 
 against typhoid fever. 
 
 Avoiding undue fatigue and exposure to cold and wet are 
 other important means of keeping up the body resistance to 
 the pneumonia germ. 
 
 Influenza. It was formerly believed that the cause of in- 
 fluenza is a small bacillus found in many cases of the disease, 
 but investigations made during recent epidemics indicate that 
 probably it is due to an undiscovered germ. It is supposed 
 that the germs pass from one person to another in the secre- 
 tions from the mouth and nose. The disease is a dreaded 
 
310 HUMAN PHYSIOLOGY 
 
 one, because so many persons are attacked and because of its 
 severity and the danger that pneumonia will follow it. 
 
 Influenza is one of the most easily com- 
 municable of all diseases. Good health and 
 physical vigor give no immunity, and one 
 \l attack does not protect against another. 
 \ N Medical authorities are agreed that a person 
 
 FIG. 144. The w j t | 1 m fl uenza should 2fo to bed at once and 
 
 bacillus that was . . 
 
 formerly believed remain m bed until he is thoroughly recov- 
 to be the cause of ered. This not only lightens and shortens 
 the influenza attack, but it greatly reduces 
 the risk of pneumonia, which is the chief danger with the 
 disease. 
 
 Colds. Many different kinds of germs (the pneumonia 
 germ among them) are found in the respiratory passages of 
 those who have colds. It is probable, however, that the 
 primary cause of epidemic colds is a germ that is as yet un- 
 discovered, and that the bacteria found in the respiratory tract 
 are secondary invaders that appear after the tissues have been 
 weakened by the first germ. Against epidemic colds no pro- 
 tection is known except keeping away from those who have 
 them. Care of the health, the removal of adenoids ' and 
 diseased tonsils, and the remedying of nasal defects are im- 
 portant in the treatment of chronic colds. 
 
 Whooping Cough. Whooping cough is caused by a bacillus 
 that grows in the trachea and bronchial tubes. About 10,000 
 deaths are due to it each year in the United States. It is 
 especially severe in small children, and great care should be 
 exercised to protect children under five years of age from it. 
 By vaccination the disease can in some cases be prevented, 
 and in other cases the vaccination usually shortens the course 
 of the disease and lessens its severity. 
 
DISEASES CAUSED BY BACTERIA 
 
 Consumption. Consumption is so important a disease that 
 it will be discussed in a separate chapter (chapter XXVI). 
 
 DISEASES CAUSED BY BACTERIA THAT ENTER THE BODY 
 THROUGH THE SKIN 
 
 The Pus-forming Bacteria. Several different kinds of 
 bacteria are included in this group. They are found in earth 
 around the habitations of men 
 and animals and in polluted 
 water, and are always found 
 on the human skin, where 
 they feed on the dead cells 
 and other matter on the skin. 
 When they grow in the tissues, 
 they cause inflammation and 
 form pus, or the thick liquid 
 matter that is found in boils 
 and infected wounds. 
 
 Diseases caused by the Pus- 
 forming Bacteria. The pus-forming bacteria cause boils, 
 carbuncles, erysipelas, blood poisoning, and inflammation in 
 wounds and sores. They may also cause inflammation in the 
 internal parts of the body. Tonsillitis and appendicitis are 
 usually caused by these germs, and meningitis may be caused 
 by them. It thus appears that the' same germ that makes a 
 wide-spreading growth in the skin and causes erysipelas, can 
 make a deep, localized growth and cause a boil or carbuncle, 
 spread through all the body and bring on blood poisoning, 
 or produce meningitis by growing in the membranes and 
 fluid around the brain and cord. The pus-forming germs 
 found in cases of erysipelas and abscesses are often very 
 malignant, and care should be used to prevent their spread. 
 
 FIG. 145. Three pus-forming bac- 
 teria. A causes the bluish-green pus 
 sometimes found in wounds; B is the 
 most common cause of boils ; and C 
 causes erysipelas and often is the cause 
 of boils and of blood poisoning. 
 
312 HUMAN PHYSIOLOGY 
 
 The Pus-forming Germs Injurious to the Body. A strange 
 idea that is very prevalent is that boils are beneficial to us. 
 Probably this belief arises from the fact that so much 
 offensive matter comes from a boil. It is exceedingly im- 
 portant to open up infected wounds, boils, and carbuncles, 
 and get the matter in them out of the body, for it is injurious 
 and dangerous to allow it to be carried through the body by 
 the blood. The pus, however, is composed chiefly of germs, 
 dead tissue cells, and dead white corpuscles which the germs 
 have killed. It no more benefits the body to have pus- 
 forming germs kill patches of the tissue and poison the 
 whole system with their toxins than it benefits the body to 
 have diphtheria, typhoid, or any other disease germs in it 
 
 Care of Wounds. For our protection against pus-forming 
 germs, it is very important to know how to care for small 
 wounds. If the wound has been made by a clean instrument, 
 and bleeds freely, the blood will wash the germs outward, 
 and by its germicidal power will probably kill any bacteria 
 remaining in the wound. In such a case, the best thing is to 
 tie the wound up " in the blood," and not open it until it 
 is healed, unless inflammation sets in. A good plan is to 
 wrap the wounded part in a thin, clean inner cloth, and out- 
 side of this tie a second cloth. The outer cloth can be changed 
 from time to time when it becomes soiled, while the innei 
 cloth is left undisturbed to keep germs from getting into the 
 wound. 
 
 When a wound has been made with anything unclean, it 
 should be washed with a disinfectant (page 335) to kill germs 
 in it, before it is tied up. After being bandaged, a wound 
 should be carefully watched, and if pain, redness, and swelling 
 show that germs have got into it, it should be opened at 
 once and disinfected. A salve containing carbolic acid is 
 
DISEASES CAUSED BY BACTERIA 313 
 
 very useful in dressing small wounds and sores, because the 
 carbolic acid kills germs. Turpentine is an excellent agent 
 with which to treat a wound, and one that is often at hand. 
 
 Rheumatism. Acute rheumatism is a germ disease. Some 
 think that it is caused by pus-forming bacteria growing in the 
 joints, and others hold that it is caused by a very tiny germ 
 of its own. When this disease attacks the valves of the 
 heart, it is often fatal. 
 
 Tetanus (lockjaw). Tetanus is caused by a bacillus that is 
 commonly found in the earth about dooryards and gardens, 
 in the dust of streets, and in great abundance 
 about stables where horses are kept. It affects = ^i ^ 
 
 ^* g ' "T 6 ^ 
 
 chiefly man and the horse and gets into the 
 
 body through wounds, often through wounds 
 
 so small and insignificant that no attention 
 
 is paid to them. The tetanus germ by itself FIG. 146. 
 
 cannot grow except when it is shut off from The bacillus of 
 
 tetanus. 
 
 the air. With other germs, however, it can 
 grow in an open wound. 
 
 The tetanus bacillus grows especially in wounds made by 
 unclean instruments, because such wounds are likely to be 
 infected with this germ, and because pus-forming germs and 
 particles of dirt are left in such wounds. It grows best of 
 all in small, deep wounds like those caused by an unclean 
 nail, because wounds of this kind readily close over and 
 leave the tetanus germ with other germs and foreign matter 
 buried deep in the flesh and away from the air. The percus- 
 sion caps used on toy pistols also make dangerous wounds. 
 The germs are in the dust on the skin, and the very small, 
 sharp, flying particles of the caps cut deep into the flesh and 
 drive down tetanus germs along with other bacteria and dust. 
 
 The bacillus of tetanus is so common that it undoubtedly 
 
3 1 4 HUMAN PHYSIOLOGY 
 
 gets into many wounds in which it never grows, but it is 
 always wise to look after and protect every wound. Wounds 
 made by unclean instruments should be carefully sterilized, 
 and wounds on the feet of barefooted children should re- 
 ceive special attention, because these come in contact with 
 the earth and are exposed to infection. Wounds of a kind 
 that are especially liable to cause the development of the 
 disease should be looked after by a physician. 
 
 The Toxin of Tetanus. The tetanus germ makes only a 
 very slight growth in the body, but it produces a toxin of tre- 
 mendous power. This toxin for man .is a poison nineteen 
 times as strong as dried cobra venom, and two hundred and 
 fifty times as strong as strychnin. It produces its effects 
 by poisoning the nervous system, and through this so affects 
 the muscles that they are all thrown into contraction. The 
 muscles of the jaw, esophagus, and neck are often affected 
 before the other muscles in tetanus. 
 
 Tetanus Antitoxin. An antitoxin for tetanus has been pre- 
 pared, but this is successful only when used in large doses 
 very soon after the disease develops. It is very useful, how- 
 ever, in preventing tetanus, and when a person has received 
 a wound that is likely to bring on this disease, many physi- 
 cians make a regular practice of giving a dose of tetanus anti- 
 toxin to keep the disease from developing. 
 
 Leprosy. Leprosy is caused by a slow-growing bacterium, 
 similar in some ways to the tuberculosis germ. It produces 
 little toxin, and may exist in great numbers in the tissues of 
 the body for years before death results. Leprosy is slightly 
 contagious, though not so contagious as consumption. It is 
 believed that a cure for leprosy has been discovered. 
 
 Bubonic Plague. Bubonic plague is the disease that was 
 called the Black Death in the Middle Ages. In 1907 there 
 
DISEASES CAUSED BY BACTERIA 315 
 
 were 860,000 deaths from it in India. It is caused by a 
 bacillus that attacks rats and mice and gets into the bodies of 
 men from fleas that have lived on infected animals. The dis- 
 ease is carried from one country to another by sick rats, and 
 the way to fight it is to destroy the rats. It is now in all the 
 continents, and our seaports are in constant danger from it. 
 
 BACTERIAL DISEASES OF THE ALIMENTARY CANAL 
 
 Typhoid Fever. This disease is caused by a bacillus that 
 is taken into the body through the mouth. Usually it is a 
 very severe disease, and often it leaves the 
 sufferer weakened in some organ for life. 
 But sometimes an attack of typhoid fever 
 is so light that the patient does not realize 
 that there is much the matter with him. 
 The excretions from the intestines and kid- FIG. i 47 . The 
 neys of a typhoid patient are filled with the bacillus of t yP hoid 
 
 , _,, .. . fever. This germ is 
 
 germs. 1 These germs can live in water and fitted for life in the 
 in refuse matter outside of the body, but water and swims 
 if they are dried, they die in a short time. 
 By vaccination with dead germs typhoid fever can be almost 
 entirely prevented, and the discovery of this fact has helped 
 greatly in controlling the disease. 
 
 How Typhoid is contracted. Since the typhoid germ dies 
 from drying, it is not carried about in the air, but must get 
 
 1 About one person in every thirty who has typhoid fever carries the typhoid 
 bacillus through life. The germs remain in the gall bladder and intestine with- 
 out seeming to affect the person in whom they are growing A cook in New 
 York City infected twenty-six persons in a period of five years, and the germs 
 have been found in the excretions from the body forty-two years after recovery 
 from the disease. 
 
3l6 HUMAN PHYSIOLOGY 
 
 to the mouth without being dried out. Persons in the same 
 house with a typhoid patient may contract the disease from 
 the dishes, by getting the germs on the hands, from han- 
 dling the bedding, or in any of the many ways by which it is 
 possible for such small bodies as bacteria to be carried about 
 Flies will carry the germs about in great numbers, if all 
 wastes from typhoid patients are not carefully destroyed. 
 Occasionally the germ is in oysters that have been grown in 
 polluted waters, and for this reason, cooked oysters are safer 
 than raw oysters. In a large number of cases, the typhoid 
 germ has been carried in milk where some one having the 
 disease had prepared or handled the milk, 1 or where the milk 
 vessels had been washed in water containing the germs. 
 If a single typhoid germ should get into a can of milk, it 
 could produce thousands or perhaps millions of germs before 
 the milk was used, so the milk supply must be carefully 
 watched. In a great many cases, however, 
 typhoid is contracted direct from water. In 
 the next chapter we shall discuss the subject 
 of disease germs in drinking water. 
 
 Cholera. Cholera is caused by a germ that 
 grows with great rapidity in the intestines, 
 
 FIG. 148. The r J 
 
 cholera germ, and produces a strong toxin, sometimes causing 
 
 death within a few hours. Like the typhoid 
 
 germ, it gets into the alimentary canal through water and foods. 
 
 Other Bacterial Diseases of the Alimentary Canal. There 
 
 is a group of germs closely related to the typhoid germ that 
 
 cause intestinal diseases. The worst of these are the germs 
 
 that cause so much sickness among small children during the 
 
 summer months'(Appendix). 
 
 1 In the spring of 1908 one milkman in Boston who was suffering from typhoid 
 caused an epidemic of about 400 cases. 
 
DISEASES CAUSED BY BACTERIA 317 
 
 OTHER BACTERIAL DISEASES 
 
 Epidemic cerebro-spinal meningitis is caused by a germ that 
 grows in the membranes and fluid around the brain and spinal 
 cord. The germ is found in the nasal secretions 
 of those suffering from the disease. It is thought 
 that spinal meningitis is contracted by inhaling 
 the germ into the nose, whence it finds its way 
 to the brain. The disease is infectious and care 
 should be used to prevent its spread. The pneu- 
 monia germ, the typhoid germ, the germ of 
 
 tuberculosis, and the pus-forming and other germs cerebro- spinal 
 may also grow around the brain and cord and meningitis, 
 cause meningitis, but the common infectious form of the dis- 
 ease is caused by the germ shown in Figure 149. 
 One form of sore eyes is caused by a bac- 
 terium. The germs are carried by flies and 
 mav b e wiped on books, doorknobs, or any- 
 thing which a sufferer from the disease 
 >tl^^ touches. Children with this disease should 
 not be allowed to attend school, for it is 
 
 FIG. 150. The . . , . . .. _ . 
 
 bacillus that causes hl g hl y infectious. It is never quite safe to 
 infectious sore eyes, wash the eyes in a public basin, or to wipe 
 
 them on a towel that the public has used. 
 Yellow fever, chicken pox, mumps, measles, and German 
 measles are certainly germ diseases, but the germs that cause 
 them have not been discovered. 1 Many tropical diseases are 
 due to either bacteria or protozoa. 
 
 1 The incubation periods of some of the more common infectious diseases are 
 as follows : chicken pox, usually 13 to 14 days, but may be 1 8 or 19 days ; mumps, 
 1 3 to 21 days, though it may be shorter; measles, about 10 days; German measles 
 from 2 to 3 weeks; scarlet fever, 2 to 5 days; whooping cough, I to 2 weeks. 
 
HUMAN PHYSIOLOGY 
 
 Bacteria affecting Animals. Among bacterial diseases of 
 animals are chicken cholera, pink eye, distemper and glanders, 
 
 in horses, blackleg in cattle, an in- 
 testinal disease of parrots, and many 
 other animal diseases that we cannot 
 mention here. The germs of the 
 parrot disease, when inhaled by man, 
 produce a very severe form of pneu- 
 monia, and the glanders germ attacks 
 man and is often fatal to him. 
 
 Diseases caused by Other Organ- 
 isms. Many diseases of plants 
 (rusts, smuts, mildews, rots, etc.) are 
 caused by fungi that are related to 
 the molds and mildews. These are 
 much larger than bacteria, their 
 bodies being composed of long, 
 thread-like filaments. A few of 
 these fungi attack man, a number 
 of them entering the hair follicles 
 and growing in the skin. Among 
 the diseases caused by them are ring- 
 worm, barber's itch, and in tropical 
 
 countries, an itch which attacks any part of the body. Thrush, 
 which is found in the mouths of young babies, is also due to a 
 fungus, and a few kinds of yeasts occasionally attack the 
 human body. 
 
 QUESTIONS 
 
 Give some facts that show the extreme smallness of bacteria. 
 Where are bacteria found ? What shapes have they ? 
 
 Where does the bacillus of diphtheria grow? How long can the 
 germ remain alive outside the body ? What is the incubation period 
 
 FIG. 151. The fungus that 
 causes ringworm. 
 
DISEASES CAUSED BY BACTERIA 319 
 
 of diphtheria ? How is it contracted ? How strict a quarantine is 
 necessary to control diphtheria ? How does diphtheria cause death ? 
 What is antitoxin ? Explain the antitoxin treatment for diphtheria. 
 Why should the antitoxin be used in the early stages of the disease ?. 
 
 In what parts of the body does the pneumonia germ grow ? How 
 is the germ transferred from one person to another? Give some 
 ways by which the disease may be in a measure prevented. Why 
 is influenza a dreaded disease ? How may most of the dangers of 
 an influenza attack be avoided ? Mention some of the important 
 factors in the treatment of chronic colds. Why should young chil- 
 dren have especial protection from whooping cough ? 
 
 Name some of the diseases caused by pus-forming germs. Of 
 what is pus composed ? How should a wound made by anything 
 clean be treated ? a wound made by anything unclean ? 
 
 Where is the tetanus bacillus found ? Under what conditions can 
 it grow and under what conditions can it not grow ? What kind of 
 wounds are especially dangerous ? How does the tetanus germ in- 
 jure the body ? What germ does the leprosy bacillus resemble ? 
 How is plague spread ? 
 
 How does the typhoid germ enter the body ? What excretions 
 from a typhoid patient contain the germs ? What discovery has 
 helped greatly in controlling this disease ? Name some of the ways 
 in which typhoid fever may be contracted. How does the cholera 
 germ enter the body ? 
 
 By what germs may cerebro-spinal meningitis be caused ? Where 
 do the germs grow in this disease ? In what secretion of the patient 
 is the germ found ? How does the germ probably enter the body ? 
 
 How may the germ that causes sore eyes be spread ? Name 
 other germ diseases ; some germ diseases of animals ; some dis- 
 eases caused by larger fungi. 
 
 When one has been infected with diphtheria or tetanus germs, 
 antitoxin helps to keep the disease from developing. How does it 
 do this ? Are typhoid germs killed by freezing them in ice ? 
 
CHAPTER XXV 
 
 PREVENTING THE SPREAD OF DISEASE GERMS 
 
 AFTER most kinds of disease germs begin their growth in 
 the body, medicines are of very little use except to keep up the 
 body strength. In our warfare with germs, we must there- 
 fore depend chiefly either on keeping the germs out of the 
 body, or on the natural power of the body to kill them after 
 they enter it. Keeping up the germicidal power of the body, 
 and preventing the germs of infectious diseases from being 
 scattered about, are, therefore, the most important points in 
 the prevention of disease. In a former chapter (page 290) 
 we have discussed the necessity of keeping up the resist- 
 ance of the body to germs. We shall now study the best 
 methods of keeping the germs that come from the bodies 
 of sick persons from being spread abroad. 
 
 DANGERS FROM INSECTS 
 
 Fleas spread the germs of plague ; mosquitoes carry many 
 diseases ; the house-fly is a great carrier of germs ; and ticks 
 and certain tropical flies are known to carry disease. 
 The bedbug also is suspected of being responsible for the 
 spread of certain diseases. Any insect that bites us has an 
 excellent opportunity to introduce germs into the body, and 
 any insect that crawls over our food, as do flies and cock- 
 roaches, may easily spread the germs of many diseases. We 
 shall do well, therefore, to guard ourselves as much as 
 possible from insects. 
 
 320 
 
PREVENTING THE SPREAD OF DISEASE GERMS 321 
 
 Mosquitoes. The mosquito, more than any other one agency, 
 has driven man from the warmer and more fertile portions 
 of the earth to the colder and more barren regions. Not 
 only does it carry the germs of malaria, but it carries yellow 
 fever and dengue, or " breakbone fever," a disease com- 
 mon in the tropics and found to a certain extent in some 
 of our Southern states. The germs of several diseases of man 
 not found in our country, and of certain diseases of birds, 
 
 FlG. 152. The life history of the mosquito. A is the malaria-carrying mosquito 
 (Anopheles) , and B, the common mosquito (Culex). a is the eggs; 6, the wiggler; 
 c t the tumbler; and d t the adult mosquito. 
 
 are also carried by mosquitoes. Where it is possible to 
 do so, the best way to end these diseases is to destroy the 
 mosquitoes. To work at this intelligently it is necessary 
 first to know the life history of the mosquito. 
 
 The Life History of the Mosquito. The mosquito lays its 
 eggs on water. In about a day the egg hatches into a wig- 
 gler that swims actively about, feeding on protozoa and other 
 small animals that are in the water. The wiggler takes in 
 air through a breathing tube, which it thrusts out through the 
 surface of the water to the air, as shown in Figure 152. 
 
 In from seven to fourteen days the wiggler changes its 
 
322 
 
 HUMAN PHYSIOLOGY 
 
 form. The head and the fore part of the body become much 
 heavier, and the breathing tubes shift to the back of the body. 
 In this stage it is called a tumbler, because instead of wig- 
 gling as it swims, it tumbles over and over. In from two to 
 five days ten to twenty days from the time the egg was 
 laid the tumbler splits down the back, and the adult 
 mosquito comes out and flies away. How long a mosquito 
 lives in the adult form is not known, but one has been kept 
 
 FIG. 153. A is the malaria mosquito (Anopheles) and B is the common mosquito 
 
 (Culex). 
 
 for seventy-six days, and enough of them always live through 
 the winter to furnish a plentiful supply for the next summer. 
 Anopheles. The kind of mosquito that carries the germ 
 of malaria is called Anopheles. It is a small, almost silent 
 mosquito, that does most of its biting in the early part of the 
 night. It can readily be distinguished from other mosquitoes 
 by the black spots on its wings, and by its habit of elevating 
 the back part of the body, or standing up on its head, when 
 sitting and biting. The wiggler of Anopheles can be dis- 
 tinguished from the wiggler of other mosquitoes by its 
 position while breathing. The Anopheles wiggler lies almost 
 parallel to the surface of the water (Fig. 152 A), and the 
 other wigglers take a" position almost perpendicular to the 
 surface of the water (Fig. 152 B). 
 
PREVENTING THE SPREAD OF DISEASE GERMS 323 
 
 Other mosquitoes are often carried considerable distances 
 by the wind, but the Anopheles has a habit of clinging to 
 weeds, shrubs, and bushes when the wind blows, and is 
 not often found far from the place where it is hatched. The 
 mosquitoes that give people malaria are usually raised by 
 those same people, or by their near neighbors. 
 
 How to destroy Mosquitoes. The first thing in the fight 
 with mosquitoes is to deprive them of breeding places near 
 human dwellings. An old fruit can may catch and hold 
 enough rain water to breed a large number of mosquitoes ; 
 in the course of a summer, an almost unlimited number can 
 come from a water barrel or an open cistern ; and an un- 
 drained ditch by the roadside may supply enough mos- 
 quitoes to torment and infect with malaria all the people in 
 the vicinity. 
 
 Old cans and pans should be cleared away ; water barrels, 
 tanks, and cisterns should be screened so that the mosquitoes 
 cannot get to them to lay their eggs ; sagging eave troughs 
 should be braced up so that no water will stand in them, for 
 wigglers may start here in a very small quantity of water 
 and be washed down into the cistern, where they will com- 
 plete their development. All pools and puddles about houses 
 should be drained, and weeds and shrubbery in which the 
 mosquitoes can find a dark, cool place to hide during the hot 
 part of the day, or when the wind blows, should be cut down. 
 
 When pools of water cannot be drained, it is an easy 
 matter to kill all young mosquitoes in them by pouring a little 
 kerosene on the water. This forms a film over the water, 
 shutting the wigglers off from the air, and killing them in a 
 few minutes. If the kerosene is washed away by rains, it 
 must be renewed within ten days, for this is about the time 
 it takes a mosquito egg to grow into a mosquito. Minnows 
 
324 HUMAN PHYSIOLOGY 
 
 feed on the mosquito wigglers, so by introducing these into a 
 pond, the number of mosquitoes that breed there may be 
 greatly lessened. 
 
 The work of destroying mosquitoes in cities and towns 
 must be taken up by public officials who have authority 
 to compel every one to put his premises in sanitary con- 
 dition. Otherwise enough persons will keep breeding places 
 for mosquitoes to infect the whole town. When the work 
 is undertaken in this way, it is a simple and not at all expen- 
 sive matter entirely to eradicate mosquitoes and malaria from 
 a town, as has been done in many places. 
 
 The Danger of Flies. There is a belief among some people 
 that flies are useful scavengers. No greater mistake could 
 be made, for they light in and walk over 
 all manner of unclean matter, and then fly 
 into the house and spread germs and un- 
 cleanness over dishes, food, milk vessels, 
 and everything that they come in contact 
 with. 1 Not only do they carry germs on 
 their feet, but when a fly feeds on the 
 FIG. 154 The foot sputum o f a consumptive or the wastes 
 
 of a fly. A fly usually A 
 
 has great numbers of from a typhoid patient, the germs of these 
 germs clinging to its diseases are found alive ki the matter from 
 
 feet. .. . 
 
 its alimentary canal. 
 
 Flies may carry almost any kind of disease germs, so a 
 sick person should be carefully screened away from them, and 
 all matter from the body of a sick person should be destroyed 
 immediately. Otherwise, every one in the vicinity is in 
 danger of contracting the disease through the flies. 
 
 1 A fly was caught and made to walk over a plate of gelatine for two minutes. 
 In that time it left 289 germs in the gelatine. Another fly has been reported as 
 having 100,000 germs on its legs. 
 
PREVENTING THE SPREAD OF DISEASE GERMS 325 
 
 FIG. 155. The house-fly. A is the 
 egg which is laid in manure; B is the 
 larva or maggot ; C is the pupa or rest- 
 ing state ; and D is the adult fly. 
 
 Keeping Free from Flies. It is possible to do much in 
 the way of avoiding danger from flies by using screens and 
 flypaper, by covering food and 
 dishes, and by removing all 
 materials that attract them to 
 the house. A far easier and 
 more effective way is to re- 
 move the breeding places of 
 the flies. The egg of the 
 house-fly is laid in manure 
 about stables, in garbage, or in 
 dry closets. In a day or less, 
 this hatches into a small, white, 
 footless maggot, which in nine or ten days from the time the 
 egg was laid changes into the adult fly. 
 
 It is estimated that as many as 300 flies may hatch in 
 a cubic inch of manure, and if the breeding places of the 
 flies are left undisturbed, they will hatch faster than it is 
 possible to kill them. It is a simple matter, however, to 
 stop their increase by removing, once a week, all matter in 
 which they breed, burying it, or spreading it on the fields 
 where it will dry and the eggs and young will be killed. 
 
 Flies can also be prevented from hatching by covering the 
 matter in which they breed with lime. Full directions for 
 preventing the hatching of flies in manure by the use of borax 
 or hellebore may be obtained from the United States Depart- 
 ment of Agriculture. 
 
 DANGER FROM DUST 
 
 In a cubic yard of ordinary air, there are from a hundred 
 to a thousand bacteria. These bacteria are attached to float- 
 ing particles of matter of one kind or another. Air that 
 
326 HUMAN PHYSIOLOGY 
 
 is absolutely free from dust is also free from bacteria, and by 
 stirring up dust the number of bacteria in the air can be in- 
 creased to countless multitudes. 
 
 It was formerly believed that disease germs were blown 
 about in dust, and that the germs of respiratory diseases 
 were frequently carried into the air passages in dust. It is 
 possible that indoor dust, which contains pulverized sputum, 
 may at times have in it living disease germs, but as a carrier 
 of germs dust is of little importance ; for the germs of all our 
 ordinary diseases are killed by light and thorough drying, and 
 in outdoor dust their lives quickly come to an end. 
 
 Nevertheless, it remains true that dust is highly danger- 
 ous ; for it wounds the walls of the air passages and allows 
 any germs that may be in these parts to set up their 
 growth. Every possible effort should, therefore, be put 
 forth to prevent dust. Streets should be cleansed and 
 sprinkled, houses should be swept with carpet sweepers or 
 damp brooms, and some damp material 1 should be used in 
 sweeping public schoolrooms and other public buildings. 
 Schoolrooms should be swept after school so that there 
 will be time for the dust to settle before the pupils assemble 
 the next morning, and other public buildings should be 
 
 1 The Michigan State Board of Health recommends the following for use in 
 sweeping the floors of public buildings : 
 
 (i) To a pailful of sawdust wet with hot or cold water, add one half pint of 
 kerosene and a tablespoonful of sulpho-naphthol or formaldehyde. This ma- 
 terial can be prepared some days in advance of its use. 
 
 (2) Heat one third part sand, and add two thirds part sawdust. To a pailful 
 of this mixture add one half pint of paraffin oil and mix thoroughly. This prepa- 
 ration produces excellent results. 
 
 (3) Boil one pound of salsoda and one pound of chlorid of lime in a gallon 
 of water. Dampen sawdust to be used for sweeping with this solution. This 
 preparation is excellent for restoring the natural color of floors. 
 
PREVENTING THE SPREAD OF DISEASE GERMS 327 
 
 swept some time before they are to be used. Dusting 
 should be done with a damp cloth that will wipe off the dust 
 and take it away, for it is foolish simply to stir up the dust 
 into the air, where it will be inhaled or will settle again on 
 objects in the room. In rooms that are much used, hard 
 floors, rugs, and plain furniture are more hygienic than heavy 
 carpets and plush-covered furniture, because it is easier to 
 keep them free from dust. Vacuum cleaners are recom- 
 mended by health officials, because they remove dust and do 
 not stir it up where it will be breathed into the lungs. 
 
 DANGERS FROM WATER AND FOOD 
 
 Typhoid, dysentery, and diarrhea are the main diseases 
 that are carried by water. All over our country, every year, 
 many persons contract these diseases from the water, and 
 occasionally the water supply of a city will be so infected 
 that an epidemic will occur. The way water may be poi- 
 luted is shown by the history of the typhoid epidemic from 
 which Butler, Pennsylvania, suffered in the summer and 
 autumn of 1903. 
 
 Butler was then a city of about 16,000 inhabitants, supplied 
 with water from an artificial lake. A family living on the 
 banks of a small stream that flowed into the lake was stricken 
 with typhoid, and the wastes from the sufferers were thrown 
 out on the ground near the creek. The germs found their 
 way into the creek, and into the water that was used in 
 the city, and soon great numbers of the inhabitants were 
 stricken with typhoid, about 1200 cases developing before the 
 epidemic was over. One section of the city was supplied 
 with water from artesian wells, and the people using this 
 water did not suffer from the disease, which shows that the 
 germs were carried by the polluted water from the lake. 
 
328 HUMAN PHYSIOLOGY 
 
 Epidemics like the one in Butler are, of course, uncommon, 
 but if you will investigate, you will probably find that in 
 the town or community in which you live, several persons 
 die each year from these water-borne diseases. 
 
 Freeing Water from Disease Germs. By filtering through 
 beds of sand, a city can take almost all dangerous germs out 
 of its water supply. Many cities fail to do this, however, and 
 when one must use impure city water or water from an 
 ordinary well, the best plan is to boil it. Bringing it to a 
 boil will kill all dangerous germs, most of them dying if ihe 
 water is heated to 160 or 170 degrees. Most house filters are 
 almost useless, for they catch matter in which the bacteria 
 breed and multiply, and the bacteria pass through the pores 
 in most of them. Filters made of fine porcelain do keep 
 back bacteria if they are carefully cleaned and attended to, 
 but this is a great deal of work, and it is easier to boil water 
 than to look after a filter. It is always to be remembered 
 that to wash fruits, vegetables, dishes, or milk vessels in 
 impure water may be as dangerous as to drink the water. 
 
 Disease Germs in Natural Waters. Any water that comes 
 from the surface of the ground is likely to contain disease 
 germs, typhoid fever being a very common disease in 
 the country and in mountainous regions, where the people 
 drink from the most beautiful, clear springs. Shallow wells, 
 springs, and small streams are the most dangerous of all 
 waters. Cistern water, .where the cistern is closely cemented 
 and kept clean, is much safer. Water caught from a roof 
 and stored in a tank above ground is safe, and deep arte- 
 sian water is also free from dangerous germs. It is never 
 safe to use water from a shallow well, no matter how cool 
 and clear the water may be, for experience shows that people 
 who use such water suffer greatly from typhoid fever and 
 
PREVENTING THE SPREAD OF DISEASE GERMS 329 
 
 other intestinal diseases. Some wells are much worse than 
 others, an occasional well giving typhoid to almost every 
 family that uses water from it. Such a well should be filled 
 up, and if water from a suspicious source must be used for 
 drinking, it should be boiled. 
 
 Keeping Bacteria out of Wells. Very few bacteria live 
 deeper than five or six feet 1 in the soil. The pollution 
 
 
 FiG. 156. B shows how surface water enters a well, carrying with it germs from 
 the surface of the soil. A is a well arranged to keep out surface water and germs. 
 The water must not be allowed to run down behind the wall, the platform should be 
 double and water tight, and water should not be allowed to run back into the well 
 around the pump. 
 
 of wells comes from surface water getting into them when 
 it rains, and carrying with it bacteria from the upper layers 
 of the soil. . 
 
 To keep out bacteria, a well should first of all be located 
 on a high place and away from all pigpens, stables, or out- 
 buildings that may drain into it. Around the mouth of the 
 
 1 Where the soil is very coarse gravel or where it is underlaid by sloping, 
 cracked layers of rock, germs may travel considerable distances underground. 
 
330 HUMAN PHYSIOLOGY 
 
 well a tough clay should be spread and packed in thoroughly, 
 so as to form a water-tight layer over the soil. This should 
 slope so as to carry all surface water away from the well. 
 A sound, clean, water-tight platform, large enough to extend 
 out over the walls, should be built, so that no surface water 
 whatever will run in behind the wall and get into the well. 
 
 The whole task is to keep the surface water out of the 
 well. Cementing the upper part of the well and laying a 
 circle of cement over the surface of the earth above the 
 mouth of the well is the surest way of doing this. Where 
 there are disease germs in the ground, some of them are 
 likely to get into the water, but their number can be greatly 
 lessened by taking proper care of a well. Also a great deal of 
 the food materials on which the germs in the water grow and 
 multiply is kept out of the well by these precautions. No 
 one who is nursing a case of infectious disease should come 
 about the well, or if he does so, at least should use great care, 
 for it is an easy matter, by handling well-buckets or by work- 
 ing around a pump, to leave germs where they will get into 
 the well. 
 
 Dangers from Milk. The great danger from milk is due 
 to the fact that most kinds of germs multiply rapidly in it. 
 Tuberculosis is sometimes caused by milk, and the sickness 
 that is so common among young children in summer is 
 often due to germs in the milk. Typhoid fever, scarlet fever, 
 and diphtheria may also be contracted through milk. Again 
 and again it has t>een found that along the route of a cer- 
 tain milkman the people were suffering from one of these 
 diseases, and on investigation it would be proved that a case 
 of the disease existed among those handling the milk or in 
 their families ; or that the bottles had been taken back from 
 families where the disease was, or, in epidemics of typhoid 
 
PREVENTING THE SPREAD OF DISEASE GERMS 331 
 
 fever, that the milk vessels had been washed in water from 
 wells containing the typhoid germ. One article in a medical 
 journal reported 330 epidemics traceable to milk, of which 195 
 were typhoid epidemics, 99 were epidemics of scarlet fever, 
 and 36 were diphtheria epidemics. It is difficult for a private 
 citizen to guard himself against these dangers, and in all well- 
 governed cities and towns a health officer looks after the 
 milk supply. 
 
 Keeping Milk Free from Germs. All milk vessels and feed- 
 ing bottles for babies should be thoroughly scalded every day 
 to kill the germs in the milk that adheres to them. Other- 
 wise these germs will multiply in the new milk, and soon 
 it will be filled with them (page 303). Milk vessels should 
 never be rinsed in any but boiled .water, the purest of rain 
 water, or artesian water, for one dangerous germ that gets 
 into the milk from the water remaining on the vessels may 
 grow into a multitude. Milking should be done in a clean 
 building that has fly screens on it, and everything possible 
 should be done to keep dust and hairs out of the milk, for 
 these are swarming with germs. The milk should be cooled 
 as quickly as possible, and kept cool to prevent the germs 
 from multiplying so rapidly (page 130). It should be used 
 before it becomes old, for milk that at first has only a mod- 
 erate number of germs in it may soon be filled with countless 
 myriads of them. It is also necessary for a medical officer 
 to examine the cows from which the milk comes, or there 
 will frequently be living tuberculosis germs in the milk 
 (page 341). 
 
 Killing Germs in Milk. When it is impossible to obtain 
 clean fresh milk, it is often advisable to heat milk to 170 
 degrees or a little higher for a few minutes, or to heat it to 
 155 degrees for half an hour. This destroys most of the 
 
332 HUMAN" PHYSIOLOGY 
 
 germs in the milk, and a person using the milk has fewer ot 
 them to kill out. A few children, however, do not digest the 
 heated milk so well as raw milk, and heating does not render 
 wholesome very old milk, in which the germs already have 
 produced large quantities of toxins and acids. In the sum- 
 mer, however, ordinary milk is in most cases greatly im- 
 proved by heating. . 
 
 Dangers from Other Foods. Almost any food may be a 
 carrier of disease if it has been exposed to flies or placed 
 where the public may handle it. The intelligent citizen buys 
 his food from the groceryman who keeps a clean store and 
 screens his fruit and vegetables from flies. 
 
 DISINFECTION 
 
 It cannot be too strongly emphasized that nearly all our 
 germ diseases come from other persons who are diseased, 
 and that insects, water, and milk are sources of danger be- 
 cause they may become contaminated with germs from the 
 body of some person. In preventing the spread of germ dis- 
 eases, the destruction of the germs in sputum and in the 
 other discharges from the bodies of the sick is therefore more 
 important than any other precaution. It is well for every 
 one to know some of the ways of killing germs. 
 
 Drying. Disease germs, like other plants and animals, are 
 killed by too great loss of water. Even the tuberculosis germ 
 is killed by sufficient drying, and in disinfecting a house the 
 important thing is not to fumigate the walls with a gas but to 
 scrub the floor with a strong disinfectant, thus reaching the 
 germs in the crevices and removing mucus or other matter 
 that may protect them. A damp house tends to keep alive the 
 
PREVENTING THE SPREAD OF DISEASE GERMS 333 
 
 germs that are in it, and consumption, pneumonia, and other 
 diseases are more likely to develop in a damp house than in 
 a dry house. 
 
 Light. Light is injurious to bacteria, bright sunlight kill- 
 ing many germs in a few minutes, and a moderately strong 
 light assisting in checking their growth. It is an excellent 
 practice to expose bedclothes and rugs to the sun, and to 
 throw up the shades and allow the light to enter houses. In 
 rooms' occupied by consumptives, or by pneumonia, diph- 
 theria, or grip patients, this is especially valuable. Besides 
 the effect which light itself has on the bacteria, admitting the 
 light dries out a room, and assists in this way in killing the 
 germs. Dirt and dust, mingled with sweat and oil from 
 the skin, on doorknobs, banisters, and furniture, protect 
 germs from light and drying, thus keeping them alive. For 
 this reason the doorknobs and desks in schoolrooms should 
 be cleaned occasionally with soap and hot water. 
 
 Heat Boiling water kills the germs of all common dis- 
 eases, and handkerchiefs, dishes, and clothing that have be- 
 come infected can be made safe again by thoroughly boiling 
 them. Articles of little value, and sputum from patients 
 sick of respiratory diseases, may often be most conveniently 
 disposed of by burning (page 342). The surfaces of dishes 
 contain tiny crevices in which germs lodge, and in disin- 
 fecting dishes with hot water, it is necessary to leave them 
 for a few minutes in boiling water, so that the heat will reach 
 the germs in the crevices. 
 
 Chemical Disinfection. Certain chemicals are so poison- 
 ous to germs that they are extensively used in disinfecting. 
 A physician should always be consulted as to which disin- 
 fectant is best for a particular purpose, and exactly how to 
 use it, for some of them are better for one purpose than 
 
334 HUMAN PHYSIOLOGY 
 
 for another. Since most of these disinfectants are very poi- 
 sonous, an excellent plan is to add a little red ink or other 
 coloring matter to them so that they will not be mistaken 
 for water. The following are some of the most commonly 
 used disinfectants : 
 
 Bichlorid of mercury (corrosive sublimate) dissolved in 
 water, with one part of the bichlorid to a thousand parts of 
 water (i dram to I gallon of water), kills nearly all kinds of 
 germs in two or three minutes, and all kinds in fifteen min- 
 utes. This can be purchased in tablets of the right size to 
 make a pint or half pint of the disinfectant of the proper 
 strength. It is convenient, and an excellent disinfectant for 
 the hands, for washing floors and furniture, and for disinfect- 
 ing clothing that can be soaked in it. It cannot be used on 
 metal, as it destroys it, and is not good for disinfecting where 
 there is much organic matter present, as there is in dis- 
 charges from persons sick with typhoid and other intestinal 
 diseases. 
 
 Biniodid of mercury is more than twice as powerful as 
 bichlorid of mercury, and need be made only half as strong. 
 It is one of the best general disinfectants, and is especially 
 useful in disinfecting the hands, since it does not injure the 
 skin as do most other disinfectants. 
 
 Carbolic acid, made up in a 2^ per cent solution (3^- ounces 
 of liquid carbolic acid to I gallon of water), is as strong as 
 the bichlorid of mercury solution described above. This is a 
 very reliable disinfectant, good for almost any purpose. For 
 disinfecting sputum and other discharges from the body it is 
 well to use a 5 per cent solution. 
 
 Lysol is about the same strength as carbolic acid. It often 
 destroys the colors in clothing. 
 
 Formalin is about one half as strong as carbolic acid, a 5 
 
PREVENTING THE SPREAD OF DISEASE GERMS 335 
 
 per cent solution being equal to a I to 1000 solution of 
 bichlorid of mercury. It loses its strength if exposed to the 
 air. By heating formalin, a gas called formaldehyde is driven 
 off. This is the best of all gaseous disinfectants. 
 
 Chlorid of lime, made by adding i^ ounces of chlorid of lime 
 to i gallon of water, is a cheap and powerful disinfectant. 
 
 Milk of lime is a powerful disinfectant. It is made by 
 adding one part of freshly slaked lime by weight to four 
 parts of water. This is a cheap disinfectant, and, for certain 
 purposes, is as effective as anything that can be employed. 
 It should not be used in sinks, for it will cause trouble with 
 the traps. Air-slaked lime is worthless. 
 
 Special Points in disinfecting. Any one who is waiting on a 
 person sick with an infectious disease should frequently and 
 thoroughly disinfect his hands, holding them for several 
 minutes in the disinfectant. Washing the hands thoroughly 
 with soap assists very greatly in freeing them from germs. 
 Keeping the nails trimmed and the skin smooth makes the 
 hands easier to disinfect. 
 
 For treating an infected wound or a sore, peroxid of hydro- 
 gen and iodin are often used. A weak solution of carbolic 
 acid or a carbolic salve is also good, and washing with warm 
 salt water is useful (page 312). In vaccination the skin 
 should be cleansed, clean instruments used, and the wound 
 protected ; for the greatly swollen arms and running sores 
 that sometimes follow vaccination are caused by pus-forming 
 germs that get into the wound. 
 
 In typhoid fever, the germs are in the discharges from the 
 bowels and the kidneys, and should be received in vessels 
 containing disinfectants. Strong limewater is excellent for 
 this, and carbolic acid is also good. It is necessary to see 
 that the disinfectant is thoroughly mixed with the waste 
 
336 HUMAN PHYSIOLOGY 
 
 matter, and it should be allowed to stand for several hours to 
 make sure that all germs are killed. 
 
 In diphtheria, pneumonia, consumption, grip, measles, 
 scarlet fever, and spinal meningitis, the germs are in the dis- 
 charges from the throat and nose. It is best to receive these 
 discharges in strong disinfectants, carbolic acid being good 
 for this purpose. Above all, do not allow the discharges to 
 infect articles in the room. All handkerchiefs, dishes, and 
 other infected articles should be placed at once in boiling 
 water or soaked in carbolic acid or bichlorid of mercury. 
 These substances are poisonous, and must afterwards be 
 rinsed off dishes. Additional instructions in regard to the 
 disinfection of sputum will be found in the chapter on con- 
 sumption (page 342). 
 
 Where a whole room or house is to be disinfected, it is 
 usually done by fumigating. Formaldehyde, or sometimes 
 sulphur, is used for this purpose. Special directions are 
 necessary for this work if it is to be effectively done. Quick- 
 lime is a good disinfectant for cellars and closets, and the 
 germs in any matter that is buried in quicklime will be 
 killed. 
 
 Mistaken Ideas in Regard to Disinfection. The idea that 
 there is some connection between the smell of a substance 
 and its power as a germ killer is prevalent. Odoriferous 
 substances are sometimes burned in rooms containing sick 
 persons, or a little carbolic acid exposed in a saucer stf that 
 it will scent the air of the room. It need hardly be pointed 
 out that germs are not injured by anything of this kind. 
 
 Unhygienic Habits. There are numerous ways by which 
 germs can get into the body, and we will call attention to 
 a few habits which give them a special opportunity to do 
 so. One of these is the habit of putting pencils and other 
 
PREVENTING THE SPREAD OF DISEASE GERMS 337 
 
 objects into the mouth, often after these same objects have 
 been in the mouths of other people. Another is the habit 
 of drinking from the same cup that others use. Germs may 
 easily be left on a cup by any one who has them in his mouth, 
 and each child in school should have his own cup, and in 
 traveling one should carry a private cup. When it is neces- 
 sary to drink from a public cup, it is better to put both lips 
 into the cup and drink without taking the edge of the cup 
 into the mouth. One other habit that we would mention is 
 that of allowing the fingers to touch the face, eyes, or lips. 
 In many ways from books, doorknobs, pencils, seats and 
 straps in street cars, and from the hands of other persons 
 we get germs on our hands. It is, therefore, advisable to 
 form the habit of keeping the hands away from the face. 
 Especial attention should be given to this point when sore 
 eyes are prevalent. A good habit to form is that of washing 
 the hands with soap before eating (page 335). 
 
 Freeing the Country Farmhouse from Disease. By intel- 
 ligent effort, families living in the country can greatly de- 
 crease the risk of exposure to germs. If they will clear 
 away weeds and dense shrubbery from around their homes 
 and look after the breeding places of mosquitoes, they can do 
 much to protect themselves against malaria. By removing 
 the breeding places of flies and guarding their own milk and 
 water supplies, they can in a great measure free themselves 
 from typhoid fever. Sunlight admitted to the house is a 
 great aid in keeping the atmosphere free from germs, and 
 the fresh country air admitted freely to the sleeping rooms 
 at night will do much to build up the body and increase its 
 germicidal power. Germ diseases are almost as prevalent in 
 the country as in the city, but with a little care a family in 
 the country can, to a great extent, avoid them. 
 
338 HUMAN PHYSIOLOGY 
 
 City and Village Improvement. If the inhabitants of cities 
 and towns will work together, they can do much that will give 
 them more healthful and also more pleasant and beautiful 
 places to live. Sprinkling the streets and sodding with grass 
 along the sidewalks will help to keep down the dust. Clean 
 sidewalks are pleasanter than sidewalks that are covered 
 with sputum, and a street car that has been soiled by persons 
 spitting on the floor is neither inviting nor sanitary. By 
 cutting down the weeds and looking after the breeding 
 places of mosquitoes, the town is made more beautiful and 
 attractive as well as freed from malaria, and killing out the 
 flies saves us from annoyance as well as from disease. The in- 
 telligent citizen favors the improvement of his town because 
 it gives him a more pleasant place to live, and because he 
 knows that it costs far less to make a town clean and health- 
 ful than to have all the djsease that comes from insects, 
 unclean streets and sidewalks, dust, bad water, and impure 
 milk. 
 
 The Necessity for Public Health Officials. There are 
 always some careless persons who will spread disease if 
 they are permitted to do so, and in a town or city, it is 
 impossible for a person to protect himself against germ 
 diseases by his private efforts. He has no control of his 
 neighbor's flies and mosquitoes, and he cannot prevent con- 
 sumptives from scattering germs about where he is likely 
 to inhale them. If he lives in a city, he has no water ex- 
 cept that which comes to him through the city water mains, 
 and no milk supply except that which the milkman furnishes 
 him. His children may go to school and there be kept in 
 an unclean, badly ventilated schoolroom, and seated beside 
 some one who has just recovered from diphtheria, and who 
 is still carrying virulent diphtheria germs in his throat. With- 
 
PREVENTING THE SPREAD OF DISEASE GERMS 339 
 
 out public health officers, a private citizen will be exposed 
 in a hundred ways to danger from disease germs. It is, 
 therefore, the duty of every good citizen to uphold the 
 health officials and to work with them, and every one should 
 realize that it is a great moral crime to scatter abroad 
 germs that may cause sickness and death. 
 
 Summary. Disease germs are carried by insects, dust, 
 water, and food, and in other ways. They come from per- 
 sons who have germ diseases. By destroying the germs that 
 come from these persons, more can be done to prevent sick- 
 ness than in any other way. Country people may protect 
 themselves against germs, but in cities and towns health 
 officials are necessary. 
 
 QUESTIONS 
 
 What insects carry disease germs ? What diseases are carried by 
 mosquitoes ? Give the life history of the mosquito. How may the 
 malaria-carrying mosquito be distinguished from other mosquitoes? 
 How may mosquitoes be destroyed? How do flies carry germs? 
 How may flies be destroyed? Mention some measures that assist 
 in the prevention of dust. 
 
 Name some diseases that are carried by water. Tell of the 
 Butler typhoid epidemic. How may water be kept safe from 
 germs? What natural waters contain disease germs? What kinds 
 are safe ? Tell how to protect a well from germs. What diseases are 
 carried by milk? What measures are necessary to keep milk safe 
 from germs? How may disease germs in milk be killed? What 
 precautions should be taken to keep germs from foods? 
 
 Name four ways in which germs may be killed. Name some 
 common chemical disinfectants. How should sputum be disposed 
 of ? Mention some unhygienic habits. What measures will assist 
 in freeing a farmhouse from disease? in freeing cities and towns 
 from disease? Why are health officials necessary? 
 
CHAPTER XXVI 
 
 TUBERCULOSIS 
 
 ABOUT one seventh of the human race and one tenth of the 
 inhabitants of the United States die of tuberculosis. Each 
 year this disease claims in Europe about one million vic- 
 tims, and in our own country about one hundred and fifty 
 thousand. This means that each day four hundred of our 
 countrymen die of tuberculosis, and that eight millions of 
 the people now living in the United States will die of the dis- 
 ease. It is estimated that tuberculosis costs our nation in 
 money $1,003,000,000 a year, an annual sum that, if properly 
 expended, would free the land from the disease. 
 
 The Bacillus of Tuberculosis. Tuberculosis is caused by a 
 slender bacillus that attacks most vertebrate animals as well 
 as man. It may grow in almost any part of 
 the body and cause tuberculosis of the part 
 affected. When it grows in the intestine, it 
 causes tuberculosis of the intestine. When it 
 grows in the bone, it causes tuberculosis of 
 the bone. When it grows in the lymphatic 
 FIG. 157. The glands, it causes the disease formerly known 
 
 bacillus of tuber- r , , . ., A \ 
 
 cuiosis. as scro f u l a > an d when it grows in the lungs, 
 
 it causes tuberculosis of the lungs, or con- 
 sumption. The germ of tuberculosis may also grow in the 
 skin, kidneys, liver, or larynx, but it most frequently attacks 
 the lungs. 
 
 34<> 
 
TUBERCULOSIS 341 
 
 The bacillus of tuberculosis is slow-growing, but it is so 
 hardy that it often resists all efforts of the body to kill it, and 
 grows steadily on and on until it causes death. Outside of 
 the bodies of men and animals, it does not grow at all in 
 nature, and under the influence of light and drying, it finally 
 dies. Yet in the sputum of a consumptive, it often lives for 
 two or three months sometimes even for a whole year. 
 Pulverized sputum in indoor dust may therefore be a source 
 of danger to all who breathe it in. Away from the habita- 
 tions of men and animals, the tuberculosis germ is not found, 
 but it is frequently present in rooms that have been occupied 
 by careless consumptives. 
 
 HOW TUBERCULOSIS IS CONTRACTED 
 
 Tuberculosis is contracted from men and animals that have 
 the disease. The germ gets into the body usually either from 
 the milk of diseased cattle or, more commonly, from the 
 sputum of a consumptive. 
 
 Tuberculosis Germs in Milk. A great number of cattle are 
 affected with tuberculosis. Occasionally the ge/ms are in 
 meat, but more frequently they are in milk. 1 It is known 
 that the germs of tuberculosis can pass through the wall of 
 the alimentary canal, be carried by the blood to the lungs, 
 and there start consumption. Since no one wants to drink 
 living tuberculosis germs in his milk, dairy cattle should 
 certainly be properly inspected to see that they are free from 
 this disease. Yet the Alaska Indians, the Filipinos, and 
 many other peoples who do not use milk suffer greatly from 
 
 1 From examinations of milk made in Washington, B.C., it was estimated 
 that almost 7 per cent of the milk sold in the city contained living tuberculosis 
 germs. The germs are also found in butter that is made from infected milk, and 
 will remain alive and virulent in butter for weeks and months. 
 
342 HUMAN PHYSIOLOGY 
 
 tuberculosis, and it is probable that most tuberculosis comes 
 not from milk, but from persons who have consumption. 
 
 Dangers from Sputum. In the advanced stages of con- 
 sumption, the sputum that is brought up from the lungs 
 each day contains several billion germs. This sputum 
 should never be swallowed, for if this is done, there is danger 
 that the disease will be started in the walls of the alimentary 
 canal, or that the germs will get into the blood and be carried 
 to parts of the body that have not yet been infected. It is 
 also unsafe to spit the sputum out where it will be exposed 
 to flies, or to let it dry and blow about, for it may cause 
 other people to contract the disease. The germs in the 
 sputum should therefore be destroyed. 
 
 Disposal of Sputum. The sputum from a consumptive 
 should be received in a vessel that contains a disinfectant 
 (carbolic acid or chlorid of lime is good for this purpose), or 
 in pasteboard cups that may be burned. Sometimes the 
 sputum is received in vessels that contain water, and is then 
 disinfected with boiling water or buried in lime, but it is 
 safer to receive it in a . disinfectant. When the consumptive 
 is away from home, he may use pieces of cloth and seal them 
 up in waterproof envelopes that are made for the purpose, 
 until they can be destroyed. 
 
 Other Precautions to be taken. A consumptive should 
 always hold a handkerchief before his face when he coughs, 
 and these handkerchiefs should be placed in disinfectants, or 
 should be thoroughly boiled. He should learn to keep his 
 hands away from his face and mouth, and should occasionally 
 wash his hands in a disinfectant. He should have his own 
 dishes, and these should never be washed with those of the 
 family, nor allowed to come in contact with them until they 
 have been boiled for at least five minutes. His bedclothes, 
 
TUBERCULOSIS 343 
 
 clothing, and furniture ought occasionally to be disinfected, 
 or at least exposed to the bright sunshine as much as possible, 
 and his clothing should be boiled before it is washed with 
 other clothes. A consumptive should have a sleeping room 
 to himself, and this room should be kept bright and well 
 ventilated, to help kill any germs that may be free in it. 
 A house in which a consumptive has lived should be dis- 
 infected before any one else moves into it. 
 
 Danger from a Consumptive. Recent studies indicate that 
 there is little danger from a brief contact with a consumptive, 
 but that the long-continued and heavy infection that comes 
 from living with a careless consumptive is highly dangerous. 
 A consumptive should, therefore, live apart from other mem- 
 bers of the family, and in every way he should strive to save 
 o-thers from infection with the germs. If possible, he should 
 go to a sanatorium where he can have proper treatment for his 
 disease. 
 
 THE TREATMENT OF CONSUMPTION 
 
 Probably every one takes in tuberculosis germs at some 
 time, and in the lungs of most persons there are scars show- 
 ing where the tubercle bacilli have started to grow, but have 
 been destroyed. It is, therefore, a great mistake to think 
 that consumption is incurable. 
 
 Importance of Early Treatment. Any one who has symp- 
 toms of consumption 1 should not try to persuade himself 
 that his symptoms have no existence, for this will not stop 
 the growth of the germs. He should not lose valuable time 
 experimenting with patent medicines, for there is no medi- 
 
 1 The most common symptoms of consumption are cough, loss of appetite, 
 gradual loss of flesh and strength, fever, night-sweats, and blood-spitting. The 
 cough is often absent in the early stages of the disease. Only an examination by 
 a reliable physician should satisfy one. 
 
344 HUMAN PHYSIOLOGY 
 
 cine known that will cure consumption. The only sensible 
 thing for him to do is to be examined at once by a physician 
 who thoroughly understands the disease. Then, if he finds 
 that the germs have gained a foothold in his lungs, he should 
 give himself the best possible treatment at once, for every- 
 thing depends on starting the treatment early. 
 
 Important Factors in Treatment. In the successful treatment 
 of consumption, the following are the more important factors : 
 
 Rest. If a consumptive can be kept quiet, much of the 
 toxin that is produced by the germs will be thrown off in the 
 sputum. Anything that causes the breathing to be quick- 
 ened and deepened causes more of the toxin to be carried 
 from the lungs through the body, and increases the fever. 
 
 A consumptive should therefore have rest. If he has 
 fever, he should have absolute rest, not even walking about 
 his room. Laughing and loud talking should be avoided, 
 and coughing should be refrained from as much as possible. 
 When there is no fever, a little exercise may be taken, but it 
 should be taken with care. 
 
 Food. A consumptive should have an abundance of food, 
 especially of protein and fatty foods. Meats, eggs, milk, 
 and any other good foods that he can eat and digest should 
 be taken. Lunches should be eaten between meals and on 
 retiring. The foods must be well prepared and served in 
 different ways, or the patient will become tired of them. 
 
 Outdoor Life. Nothing in the treatment of consumption is 
 more important than fresh air, and the disease has been most 
 successfully treated where the patients have lived and slept 
 in the open air, summer and winter. Usually an upper porch 
 can be arranged with little expense, so that the patient can 
 sleep on it. In outdoor sleeping in winter, it is necessary to 
 have warm clothing and to wear some kind of hood to protect 
 
TUBERCULOSIS 345 
 
 the head and neck, and in many places in summer it is neces- 
 sary that the patient be screened from mosquitoes. 
 
 Other Important Points. Warm and dry clothing is of 
 course important, and if a consumptive lives indoors, he 
 should, above ail else, be sure to have plenty of fresh air. 
 Consumption is much more frequent in damp houses and on 
 wet soils, than it is in dry houses and on sandy soils. A con- 
 sumptive should not remain in a damp house, and if he 'lives 
 outdoors, he should locate- himself on a dry soil. He should 
 not worry about his disease being inherited, but should be 
 cheerful and hopeful, for if he takes his disease in time, he 
 has every reason to hope for recovery. The great importance 
 of early treatment must be understood, however, and early 
 symptoms like languor and loss of weight must be recognized ; 
 for after the cough has become established and the germs 
 appear in the sputum, a portion of the lungs has already 
 been destroyed. 
 
 Sanatoria for Consumptives. Many states have established 
 sanatoria to which consumptives can go, and, at a slight ex- 
 pense, remain until they recover from the disease. 1 This is 
 sensible, for in a sanatorium a consumptive can have proper 
 food and care at much less expense than he can have them 
 at home, and the physicians in the sanatorium know how to 
 disinfect so that there is no danger of the spread of the 
 disease. It is much more economical for the people of a 
 state to care for their consumptives in sanatoria than out of 
 them, and it is much pleasanter both for the consumptives 
 and for those who have not the disease. 
 
 1 Many state and city boards of health publish circulars giving very full and 
 detailed information in regard to the treatment of consumption. A consumptive 
 should write to the health board of his state for these circulars, for they will 
 enable him to care for himself much more intelligently. 
 
346 HUMAN PHYSIOLOGY 
 
 The Effect of Climate on Consumption. It was formerly 
 supposed that climate was very important in the treatment 
 of consumption, but consumptives are now being cured in 
 all our states, and it has been found in treating this disease, 
 that rest, food, and fresh air are of much more importance 
 than climate. Unless a consumptive has money enough to 
 support himself without work and to give himself proper 
 care, he should not leave his home for a distant state. For 
 in many places consumptives are not welcomed, and it is 
 better to be at home and have the proper care than to be 
 without money or friends in the best climate in the world. 
 A hot climate or a high elevation, however, is injurious to con- 
 sumptives, for in such a place the respiration is quickened. 
 
 Summary. Tuberculosis costs us 150,000 citizens and 
 $1,000,000,000 annually. It is sometimes contracted from 
 milk, but usually from the sputum of consumptives. Con- 
 sumption readily yields to treatment when taken in the early 
 stages. Rest, an abundance of food, and fresh air are the 
 most important factors in the successful treatment of the 
 disease. 
 
 QUESTIONS 
 
 Give some facts that show the importance of tuberculosis. Tell 
 something about the bacillus of tuberculosis. How does it get into 
 the body? How do tuberculosis germs that are swallowed in milk 
 get to the lungs ? Why is there reason to think that sputum is a 
 more common cause of consumption than milk? Why should sputum 
 be destroyed? How may this be done? What other precautions 
 should be taken in consumption? When is a consumptive to be 
 feared? Give three important factors in the treatment of consump- 
 tion. Mention some other points that are to be looked after. What 
 advantages come from having sanatoria for consumptives? How 
 important is climate in the treatment of consumption ? 
 
APPENDIX 
 
 A. FOODS 
 
 WHEN the foods are oxidized in the cells, and when a piece of 
 wood is burned in the fire, the process is the same, the molecules 
 are broken down, and their atoms are united with oxygen. What 
 happens to the foods within the cells may perhaps be made clearer, 
 therefore, by considering what happens in the burning of a piece of 
 wood or coal in a fire. 
 
 The Burning of a Piece of Wood. Lay a piece of wood in the fire, 
 and in a little while the wood is all gone. A few ashes may remain, 
 but these are only a little mineral matter that was in the wood and 
 did not burn. What has become of the wood ? 
 
 The answer is that the wood has been changed to gases 1 which 
 you cannot see, and has passed off into the air. The wood mole- 
 cules, like starch and sugar molecules, are built up of atoms of car- 
 bon, hydrogen, and oxygen. In the fire these large molecules are 
 broken to pieces, and the atoms in them unite with the oxygen of 
 the air. The carbon, when it unites with oxygen, forms carbon 
 dioxid. The hydrogen of the wood goes off in water vapor, which 
 is invisible when it is hot. By holding a cold 2 glass vessel over a 
 burning piece of wood or over a burning candle, you can catch and 
 condense on the inside of the vessel the water that is given off. 
 Of what elements is the fat of a candle composed? (Page 83.) 
 Is the water in the candle, or is it formed when the fat burns? 
 
 1 Smoke is composed of fine pieces of carbon that fly off into the air with- 
 out being burned. Only a very small part of wood or coal passes off in this way. 
 
 2 The vessel must be held over the flame only a very short time, or it will 
 become so hot that the water will not condense on the glass. A tall vessel made 
 of heavy glass should be used. 
 
 347 
 
348 APPENDIX 
 
 Energy set Free by Oxidation. Energy is stored in wood mole- 
 cules, and in the fire we get heat and light from these molecules .; 
 energy is stored in the molecules of coal, and an engine gets its 
 heat and its power to move from burning coal ; in the food mole- 
 cules, too, energy is stored, and by burning these molecules the cell 
 gets its heat and its power to work. By oxidation, the energy in 
 the molecules is set free. 
 
 The amount of energy the body needs depends on size, age, sex. 
 and the work done. 1 In proportion to their weight young persons 
 need more food than older ones, and women and girls require 
 somewhat less than men and boys. 
 
 Effects of Too Little Food. A group of young men placed on a 
 diet too low in energy value grew thinner until they had lost a little 
 more than 10 per cent of their weight. After that their bodies con- 
 tinued to live at this lower level without further loss of weight. 
 They did not become ill, but they lacked vigor, and when they 
 attempted severe muscular exercise they lacked the strength for it. 
 
 In this undernourished condition, the tissues are poor in fat and 
 
 1 An average-sized man needs daily enough food to yield the following num- 
 bers of Calories : 
 
 Absolute rest in bed without food , : * . . 1680 Calories 
 
 Absolute rest in bed with food ..... .'-* -i* . . . T . 1840 Calories 
 
 Office work or other light work, about . . . : v . . ... . 2500 Calories 
 
 Light muscular work 2700 Calories 
 
 Moderately active muscular work, as work of farmer or mechanic 3400 Calories 
 
 Hard muscular work 4000 Calories 
 
 Very hard muscular work 6000 Calories 
 
 The food requirements for boys are about as follows : 
 
 Under 2 years. , . .... . 900-1200 Calories 
 
 5-6 years . . . 1300-1600 Calories 
 
 9-10 years 1700-2000 Calories 
 
 14-15 years 2600-3100 Calories 
 
 16-17 years 2700-3400 Calories 
 
 In a boys' school where most of the pupils were from 13^ to 16 years of age, 
 the food used had a value of almost 5000 Calories for each pupil. 
 
APPENDIX 349 
 
 protein and the percentage of water in them is high ; there is little 
 resistance to infections ; a feeling of lassitude and weakness is 
 present ; and, in the young, growth is not as rapid as it should be. 
 In Europe during and since the war, great numbers of persons 
 have been living on insufficient diets, and there is no doubt of the 
 evil effects of undernourishment on the health. 
 
 Undernourishment Common. Investigations seem to indicate that 
 about 30 per cent of children fail to eat enough to supply their 
 energy needs, and in consequence are in a state of low vitality. 
 These children are found in the families of both rich and poor, 
 and the difficulty is that they either eat too little, or they are over- 
 active, causing the body to consume the food too rapidly. Usually 
 the trouble is that they eat only certain of the articles of food that 
 are on the table. Appetite cannot be taken as a guide in eating, 
 for many of those who habitually undereat are not troubled by 
 hunger. 
 
 Symptoms of Undernourishment. Thinness is the surest symptom 
 of lack of food, and a person who is thin should eat more or rest 
 and sleep more. 
 
 Other symptoms of a lack of sufficient nourishment are languor, 
 lack of mental alertness, lack of strength, and a general lack of 
 vigor and energy. A child who is suffering from partial starvation 
 often stands in the "fatigue position," the head and shoulders 
 drooping forward and the scapulas standing out on the back. It 
 seems probable that the incorrect posture of many children would 
 correct itself if these children would eat enough food to make them 
 vigorous and to cause them to lay on flesh. A person who wishes 
 to increase his weight should take special care to eat a full meal 
 three times a day. 
 
 Denmark's War Experiences with Food Regulation. In connec- 
 tion with a study of nutrition, the results of the food regulations 
 in Denmark during the late war are of interest. The persons reg- 
 ulating the food supply of the country had previously satisfied 
 themselves by careful experiment that whole-grain bread, if prop- 
 
350 APPENDIX 
 
 erly made, is a healthful food for man, and they believed that bran 
 yields proteins very valuable for human nutrition. They also be- 
 lieved that if food is provided in sufficient amount, the supply of 
 protein will take care of itself ; and they believed that fat is not 
 necessary if dairy products and green vegetables are used. 
 
 Accordingly, they refused to allow the feeding of potatoes or 
 bran to meat animals, as was done in other countries, with the 
 result that meat practically disappeared from the diet of the people. 
 After living for a year on whole-grain bread, potatoes, vegetables 
 (especially cabbage), milk, butter, and cheese, it was found that 
 the death rate had been reduced 34 per cent, and it was estimated 
 that the food blockade of Denmark in one year saved more than 
 6300 lives. 1 The per capita supply of food in Denmark was very 
 small, and the Danes claim that they escaped the suffering that 
 overtook the people of the central European countries only because 
 they managed their food matters more scientifically. 
 
 Diets for Hot and Cold Weather. Proteins increase the oxidation 
 of foods within the cells, experiments on a dog having shown that 
 the heat production of the body can be increased 20 per cent by 
 feeding protein. A diet rich in meat, therefore, enables one to 
 resist the cold better in winter ; but it is heating in summer, and a 
 diet including liberal amounts of fruits and vegetables is better 
 for hot weather. 
 
 The weight of the body may also be affected by the amount of 
 protein in the diet. Since proteins accelerate the oxidizing process 
 which consumes the food and tissues and thus lightens the body 
 weight, persons who wish to reduce their weight are advised to eat 
 protein rather than sugar, starches, and fats. Those who wish to 
 increase their weight need to include in the diet liberal amounts of 
 carbohydrates and fats, but, of course, sufficient protein for build- 
 ing purposes must be taken. 
 
 1 The 1918-19 influenza epidemic made it impossible to compare vital statis- 
 tics satisfactorily after the first year. 
 
APPENDIX 
 FOOD VALUES 
 
 351 
 
 NAME OF FOOD 
 
 INEDIBLE 
 PORTION 
 
 EDIBLE PORTION 
 
 PER CENT OF AVAILABLE 
 PROTEIN FAT AND CAR- 
 BOHYDRATE IN FOOD 
 AS PURCHASED 
 
 FUEL VALUES 
 OF FOOD AS 
 PURCHASED 
 
 1 
 
 Available nutrients 
 
 c 
 '3 
 1 
 
 PH 
 
 
 
 II 
 
 d 
 
 
 
 I 
 
 i! 
 
 35 
 
 A 
 
 8* 
 
 ll 
 
 CU Sc 
 
 
 % 
 
 % 
 
 % 
 
 % 
 
 % 
 
 % 
 
 % 
 
 % 
 
 Cals. 
 
 Cals. 
 
 Apples . . . 
 
 25 
 
 84.6 
 
 3 
 
 5 
 
 12.8 
 
 .225 
 
 375 
 
 9 .6 
 
 198 
 
 43 
 
 Bananas . . . 
 
 35 
 
 75-3 
 
 I 
 
 
 19.9 
 
 .65 
 
 325 
 
 12.9 
 
 265 
 
 58 
 
 Heans (dried) 
 
 
 12.6 
 
 I 5 .8 
 
 1.6 
 
 59.9 
 
 I 5 .8 
 
 1.6 
 
 59-9 
 
 
 3 2 5 
 
 Beef (round) 
 
 7.2 
 
 65.5 
 
 I 9 .7 
 
 12.9 
 
 
 18.2 
 
 11.9 
 
 
 840 
 
 185 
 
 Bread (white) . 
 
 
 35-3 
 
 7- 1 
 
 1.2 
 
 52.3 
 
 7.1 
 
 1.2 
 
 52.3 
 
 "55 
 
 254 
 
 Bread (graham) 
 Breakfast food l . 
 
 ~ 
 
 35-7 
 9.6 
 
 6.9 
 9-3 
 
 1.6 
 1.6 
 
 74 
 
 6.9 
 
 9-3 
 
 1.6 
 1.6 
 
 5i-3 
 
 74 
 
 1150 
 1617 
 
 253 
 356 
 
 Butter .... 
 
 
 
 ii 
 
 i 
 
 80.8 
 
 
 i 
 
 80.8 
 
 
 3427 
 
 755 
 
 Cabbage . . . 
 
 15 
 
 9L5 
 
 1.2 
 
 3 
 
 5-5 
 
 i 
 
 2 5 
 
 4.675 
 
 116 
 
 2 5 
 
 Candy .... 
 
 
 
 
 
 
 
 
 
 95 
 
 
 
 
 95 
 
 1767 
 
 389 
 
 Cheese . . . 
 
 
 
 34.2 
 
 25.1 
 
 32 
 
 2.4 
 
 25.1 
 
 32 
 
 2.4 
 
 1861 
 
 410 
 
 Corn meal 
 
 
 
 12.5 
 
 7-5 
 
 
 73-5 
 
 7-5 
 
 
 73-5 
 
 1578 
 
 347 
 
 Corn (canned) . 
 
 
 
 76.1 
 
 2.1 
 
 i.i 
 
 
 2.1 
 
 i.i 
 
 
 426 
 
 94 
 
 Eggs (boiled) . 
 Filberts . . . 
 
 II. 2 
 
 S 2 
 
 73-2 
 3-7 
 
 12.8 
 
 13-3 
 
 11.4 
 
 58.8 
 
 11.7 
 
 ! 6.3 
 
 10 
 28.2 
 
 5-6 
 
 632 
 1411 
 
 139 
 3" 
 
 Fish 2 .... 
 
 54-8 
 
 76.7 
 
 20 
 
 1.6 
 
 
 
 9 
 
 .72 
 
 
 
 198 
 
 43 
 
 Fowl 3 . . . . 
 Milk (whole) . 
 
 25-9 
 
 63-7 
 87 
 
 18.7 
 
 3-2 
 
 15-5 
 3-8 
 
 5 
 
 13-8 
 3-2 
 
 11.48 
 3-8 
 
 5 
 
 312 
 
 ^8.9 
 
 Milk (skimmed) 
 
 
 
 90-5 
 
 3-3 
 
 3 
 
 
 3-3 
 
 
 
 169 
 
 37-2 
 
 Mutton (loin) . 
 
 16 
 
 50.2 
 
 15-5 
 
 
 
 
 13 
 
 26.3 
 
 
 
 
 298 
 
 Oatmeal (dry) . 
 
 
 
 7.8 
 
 13-4 
 
 6.6 
 
 65.2 
 
 13-4 
 
 6.6 
 
 65.2 
 
 1740 
 
 383 
 
 Peanuts . . 
 
 2 5 
 
 .9.2 
 
 21.9 
 
 34-7 
 
 22 
 
 16.4 
 
 26 
 
 16.5 
 
 1710 
 
 376 
 
 Peas (green) 
 Pork (fresh loin) 
 
 45 
 19.7 
 
 74.6 
 S- 2 
 
 52 
 
 
 16.7 
 
 2.86 
 12.9 
 
 2 75 
 22.96 
 
 9.18 
 
 1208 
 
 & 
 
 Pork (salt ham) 
 
 13-6 
 
 40-3 
 
 15.8 
 
 36-9 
 
 
 
 13-6 
 
 31-88 
 
 
 
 1598 
 
 352 
 
 Potatoes (white) 
 
 20 
 
 78.3 
 
 1.7 
 
 .1 
 
 17.7 
 
 1.36 
 
 .08 
 
 14.16 
 
 292 
 
 64 
 
 Potatoes (sweet) 
 
 20 
 
 69 
 
 1.3 
 
 .6 
 
 26.2 
 
 1.04 
 
 .48 
 
 20.9 
 
 428 
 
 94 
 
 Prunes (dried) . 
 
 I 
 
 22.3 
 
 1.6 
 
 
 
 66.1 
 
 1.36 
 
 
 
 56.1 
 
 1070 
 
 235 
 
 Raisins (dried) . 
 
 10 
 
 14.6 
 
 2 
 
 3 
 
 68.7 
 
 1.8 
 
 2.7 
 
 61.8 
 
 1296 
 
 285 
 
 Rice .... 
 
 
 
 12.3 
 
 6. 5 
 
 3 
 
 76.9 
 
 6.5 
 
 3 
 
 76.9 
 
 1564 
 
 344 
 
 Strawberries . . 
 
 5 
 
 90.4 
 
 .8 
 
 5 
 
 6.8 
 
 .76 
 
 475 
 
 6.46 
 
 154 
 
 33 
 
 Sugar . . 
 
 
 
 
 
 
 
 100 
 
 
 
 100 
 
 1860 
 
 410 
 
 Tomatoes . . . 
 
 
 
 94-3 
 
 7 
 
 4 
 
 3-8 
 
 7 
 
 4 
 
 3-8 
 
 IOO 
 
 22 
 
 Watermelos . . 60 
 
 92.4 
 
 3 
 
 .2 
 
 6 
 
 .12 
 
 .08 
 
 2.4 
 
 50 
 
 II 
 
 Wheat. 
 
 * Black bass, whole. 
 
 8 Chicken, feathers removed. 
 
352 APPENDIX 
 
 DISTRIBUTION OF VITAMINS IN SOME COMMON FOODS 
 
 NAME OF FOOD 
 
 FAT SOLUBLE 
 VITAMIN 
 
 ANTI-BERIBERI 
 VITAMIN 
 
 ANTI-SCORBUTIC 
 VITAMIN 
 
 Foods of Animal Origin 
 
 Lean meat beef, mutton, etc. . x 
 
 Liver xx 
 
 Canned meats 
 
 Sweetbreads x 
 
 Fish, white o 
 
 Fish, fat salmon, herring, etc. xx 
 
 Eggs, fresh xx 
 
 Eggs, dried xx 
 
 Milk, whole raw xx 
 
 Milk, condensed, sweetened . . x 
 
 Butter, cod-liver oil, beef fat . . xxx 
 
 Lard o 
 
 Cheese, whole milk x 
 
 Foods of Vegetable Origin 
 
 Whole grain wheat, rye, maize x 
 
 White wheat flour ..... o 
 
 Polished rice o 
 
 Olive, cottonseed, coconut oil . o 
 
 Cabbage, fresh raw xx 
 
 Lettuce xx 
 
 Turnips (Swedes), raw juice . . 
 
 Carrots, fresh, raw x 
 
 Potatoes, raw x 
 
 Orange juice, fresh 
 
 Bananas x 
 
 Tomatoes, canned 
 
 Nuts . x 
 
 XX 
 
 very slight 
 
 XX 
 
 very slight 
 
 XXX 
 XXX 
 
 X 
 X 
 
 o 
 
 
 
 
 
 XXX 
 XX 
 
 XXX 
 
 X 
 
 less than x 
 
 XXX 
 
 very slight 
 
 XX 
 
 XX 
 
 xxx = very abundant, xx = moderately abundant, x = smaller amount. 
 
APPENDIX 
 
 353 
 
 ONE-HUNDRED CALORY FOOD PORTIONS, WITH CALORIES 
 IN PROTEIN, CARBOHYDRATE, AND FAT 1 
 
 NAME OF FOOD 
 
 " PORTION " CON- 
 TAINING 100 CALO- 
 RIES ROUGHLY 
 DESCRIBED 
 
 WEIGHT OF 100 
 CALORIES 
 
 CALORIES FROM 
 
 i 
 2 
 o 
 
 & 
 
 _d 
 
 
 
 2 
 
 I! 
 
 Cooked Meats 
 Beef, round, boiled (med. fat) . 
 Chicken as purchased, canned . 
 
 Small serving . 
 One thin slice . 
 Ordinary serving 
 Ordinary serving 
 ^arge serving . 
 
 Twelve to six- 
 teen 
 
 Ordinary serving 
 
 Dne dozen 
 Two small serv- 
 ings . . . 
 Two small serv- 
 ings . . . 
 
 Small side dish . 
 Five servings 
 Three servings . 
 Two servings 
 One side dish 
 Two servings 
 One large-sized 
 Half of average 
 potato . 
 
 Ordinary pat or 
 ball . . . 
 \\ glass . . 
 i^ cubic inches 
 | ordinary glas 
 Small glass . 
 
 44 
 
 2^ 
 50 
 32.5 
 67.5 
 
 2IO 
 
 57 
 193 
 
 100 
 
 33 
 
 480 
 
 2 J5 
 164 
 
 99 
 
 178 
 
 102 
 
 49 
 
 12.5 
 
 275 
 23 
 49 
 140 
 
 1.6 
 .96 
 1.8 
 i.i 
 2.4 
 
 7-4 
 
 2. 
 
 6.8 
 3-6 
 
 1.2 
 
 2.66 
 1 6.66 
 
 & 
 S 
 
 3.62 
 i-7 
 
 .44 
 9-7 
 .82 
 
 i*7 
 
 4-9 
 
 60 
 
 23 
 40 
 28 
 73 
 
 56 
 5 
 49 
 80 
 29 
 
 21 
 
 15 
 2 
 10 
 13 
 
 2 5 
 II 
 
 6 
 
 5 
 34 
 25 
 5 
 19 
 
 4 o 
 
 77 
 60 
 
 72 
 27 
 
 8 
 5 
 
 22 
 20 
 7 1 
 
 18 
 
 48 
 23 
 
 34 
 
 10 
 
 3 
 
 i 
 
 9 
 99-5 
 
 12 
 
 11 
 
 5 2 
 
 00 
 
 oo 
 
 00 
 
 oo 
 
 00 
 
 36 
 
 00 
 
 29 
 
 00 
 00 
 
 61 
 37 
 
 75 
 56 
 77 
 
 11 
 85 
 
 00 
 
 54 
 
 2 
 
 9 
 29 
 
 Pork ham boiled 
 
 Veal leg boiled . . . 
 
 Uncooked Meals 
 Clams, round, in shell, edible 
 
 Mackerel (Spanish), whole, edi- 
 ble portion, average . . . 
 Oysters, in shell, edible portion, 
 
 Trout, brook, whole, edible por- 
 
 Turkey, edible portion, average 
 
 Vegetables 
 Beans, baked, canned .... 
 Beans, string, cooked .... 
 Beets, edible portion, cooked . 
 Carrots cooked 
 
 Corn, sweet, cooked .... 
 Peas, green, canned .... 
 Potatoes boiled . ... 
 
 Potatoes, sweet, cooked . . . 
 
 Dairy Products 
 Butter, as purchased .... 
 
 Buttermilk, as purchased . . . 
 Cheese, full cream, as purchased 
 
 Milk, whole, as purchased . . 
 
 1 Abridged from tables published in The Journal of the American Medical Association, 
 1907, xlviii, page 1320. These tables were compiled by Dr. Irving Fisher of Yale University. 
 
354 
 
 APPENDIX 
 
 ONE-HUNDRED CALORY FOOD PORTIONS, ETC. Continued 
 
 NAMB OF FOOD 
 
 "PORTION" CON- 
 TAINING ioo CALO- 
 RIES ROUGHLY 
 DESCRIBED 
 
 WEIGHT OF ioo 
 CALORIES 
 
 CALORIES FROM 
 
 tn 
 
 
 
 2 
 O 
 
 6 
 
 3 
 
 
 
 i| 
 
 31 
 
 Fruits (Dried} 
 Dates, edible portion, average . 
 Figs, edible portion, average 
 Prunes, edible portion, average 
 Raisins, as purchased .... 
 
 Three large . 
 One large . . 
 Three large . . 
 
 2S 
 
 31 
 32 
 31 
 
 206 
 131 
 
 IOO 
 
 243 
 
 120 
 
 37 
 270 
 290 
 173 
 
 260 
 
 28 
 25 
 
 122 
 
 38 
 
 108 
 
 30 
 32 
 
 24 
 35 
 15 
 
 99 
 i.i 
 1.14 
 i.i 
 
 7-3 
 4.61 
 
 3-5 
 
 8.6 
 4.2 
 
 i-3i 
 9-4 
 
 10. 
 
 5-40 
 9.1 
 
 4.29 
 3^5 
 
 1.05 
 i.i 
 
 .86 
 
 1.2 
 
 53 
 
 2 
 
 5 
 3 
 3 
 
 6 
 
 5 
 
 6 
 o 
 
 2 
 
 6 
 7 
 4 
 
 10 
 
 7 
 26 
 
 5 
 
 i 
 
 i 
 i 
 
 
 
 o 
 13 
 
 7 
 
 
 
 o 
 9 
 
 7 
 o 
 
 5 
 o 
 
 
 
 91 
 
 3 
 
 2 
 
 7 
 15 
 
 22 
 
 2 5 
 56 
 
 32 
 
 i 
 
 
 
 84 
 
 
 
 o 
 
 77 
 
 91 
 
 95 
 97 
 88 
 
 90 
 94 
 
 90 
 94 
 
 IOO 
 
 7 
 91 
 9i 
 89 
 
 75 
 
 
 
 18 
 
 63 
 98 
 
 99 
 15 
 
 IOO 
 IOO 
 
 IO 
 
 Fruit (Fresh or Cooked} 
 Apples, as purchased .... 
 Apricots cooked . 
 
 Two apples . 
 Large serving . 
 
 One large . . 
 Half ordinary 
 serving . . . 
 Small glass , . 
 About seven 
 olives . . . 
 One very large . 
 Three ordinary . 
 One large pear . 
 
 Two servings 
 
 Half ordinary 
 square piece . 
 Small piece . . 
 Ordinary cup 
 One-third ordi- 
 nary piece 
 Ordinary serving 
 
 Four teaspoon- 
 fuls .... 
 Seven olives . . 
 Three teaspoon- 
 fuls or \\ 
 lumps . . 
 Four teaspoon- 
 fuls .... 
 
 About eight . 
 
 Bananas, yellow, edible portion, 
 
 
 Grape juice . . .... 
 
 
 Oranges, as purchased, average 
 Peaches, as purchased, average . 
 Pears . . 
 
 Strawberries, as purchased, 
 
 Cakes, Pastry, Pudding and 
 Desserts 
 Cake, chocolate layer, as pur- 
 chased 
 
 Cake, sponge, as purchased . . 
 Custard milk ... . 
 
 Pie, apple, as purchased . . , 
 
 Sweets and Pickles 
 Honey, as purchased .... 
 
 Olives, green, edible portion 
 Sugar granulated 
 
 Sirup, maple 
 
 Nuts 
 Almonds, edible portion, average 
 
APPENDIX 
 
 355 
 
 ONE-HUNDRED CALORY FOOD PORTIONS, ETC Continued 
 
 NAME OF FOOD 
 
 " PORTION " CON- 
 TAINING ioo CALO- 
 RIES ROUGHLY 
 DESCRIBED 
 
 WEIGHT OF ioo 
 CALORIES 
 
 CALORIBS FROM 
 
 I 
 2 
 O 
 
 & 
 
 a 
 
 t 
 A 
 
 il 
 
 S 
 
 Nuts Continued 
 Brazil nuts, edible portion . . 
 
 Filberts, edible portion, average 
 Peanuts, edible portion, average 
 Pecans, polished, edible portion 
 Walnuts, California, edible por- 
 
 Three ordinary 
 size .... 
 Ten nuts . . . 
 Thirteen double 
 About eight . 
 
 About six . . 
 
 Small square 
 Ordinary thick 
 slice . . 
 Two crackers 
 Large serving . 
 Ordinary serving 
 i serving 
 Ordinary cereal 
 dish . . . 
 
 14 
 
 H 
 18 
 
 13 
 14 
 
 38 
 
 38 
 23 
 
 120 
 1 10 
 159 
 
 87 
 28 
 
 23 
 
 58 
 15 
 
 180 
 230 
 
 .49 
 .48 
 .62 
 .46 
 
 .48 
 
 1-3 
 
 1.3 
 
 .82 
 
 % 
 
 5- 6 
 
 3-1 
 
 97 
 
 .81 
 
 2.1 
 
 5-4 
 
 6-3 
 8.25 
 
 10 
 
 9 
 20 
 6 
 
 10 
 
 12 
 
 13 
 
 9 
 ii 
 
 14 
 18 
 
 10 
 12 
 
 9 
 32 
 
 20 
 
 16 
 17 
 
 86 
 84 
 63 
 
 87 
 
 83 
 
 16 
 
 6 
 20 
 
 2 
 15 
 
 7 
 i 
 
 21 
 
 68 
 
 20 
 
 47 
 18 
 
 4 
 7 
 17 
 
 7 
 
 7 
 
 72 
 
 81 
 71 
 87 
 7i 
 75 
 
 89 
 87 
 
 70 
 
 00 
 
 60 
 
 37 
 65 
 
 Cereals 
 Bread, corn (johnnycake), as 
 purchased, average .... 
 Bread, white, home-made, as 
 purchased . . . 
 
 Crackers, graham, as purchased . 
 Hominy, cooked 
 Macaroni, average, cooked . . 
 Oatmeal, average, boiled . . . 
 Rice, boiled, average .... 
 
 Spaghetti, average 
 
 Zwieback 
 
 Size of thick slice 
 of bread . . 
 
 One large egg . 
 Very large plate 
 
 Two plates . . 
 Two plates . . 
 
 Miscclla neo us 
 Eggs, hen's, boiled 
 
 Soup, bean, as purchased, average 
 Soup, cream of celery, as pur- 
 chased, average 
 
 Clam chowder, as purchased . . 
 
 REFERENCES. Locke's Food Values (D. Appleton & Co.) gives the chemical 
 and energy values of average helpings of foods, which makes it easy to calculate 
 the value of a given diet. Gephart and Lusk's Analysis and Cost of Ready-to* 
 Serve Foods is very instructive and is of especial value to those who eat in restau- 
 rants. It may be purchased from the Journal of the American Medical Associa- 
 tion, Chicago, for 15 cents. 
 
356 
 
 APPENDIX 
 MINERALS IN CERTAIN FOODS 
 
 
 
 1 
 
 i 
 
 
 PERCENTAGE OF CERTAIN MINERALS IN 
 
 i 
 
 s 
 
 
 ASH OF EDIBLE PORTION 
 
 8 g - 
 
 la- 
 
 NAME OF FOOD 
 
 
 JSi 
 
 < tfl K 
 
 
 Calcium 
 (CaO) 
 
 Potas- 
 sium 
 (K 2 0) 
 
 Phos- 
 phorus 
 (P 2 5 ) 
 
 Iron 
 
 Sulphur 
 
 ww 
 
 ui 5(J 
 
 M 3 
 
 ww2 
 
 
 
 
 
 
 
 
 c.o 
 
 Beans (dried) . . 
 
 .22 
 
 1.40 
 
 I.I4 
 
 .007 
 
 .22 
 
 
 2.9-6.8 
 
 Cabbage .... 
 
 .068 
 
 45 
 
 .09 
 
 .0011 
 
 .07 
 
 
 10.0-13.6 
 
 Celery . . 
 
 .10 
 
 37 
 
 .10 
 
 .OOO5 
 
 .025 
 
 
 40 
 
 
 Corn (whole) . . 
 
 .015 
 
 17 
 
 30 
 
 ,0011 
 
 .116 
 
 
 0.4 
 
 Ep"p"s 
 
 093 
 
 .165 
 
 37 
 
 .003 
 
 .19 
 
 9.0 
 
 
 
 Milk 
 
 .168 
 
 .171 
 
 .215 
 
 .0002 
 
 
 
 3-3 
 
 
 Oatmeal .... 
 
 13 
 
 .458 
 
 .872 
 
 .0036 
 
 
 
 3-2 
 
 Peas (dried) . . . 
 
 .14 
 
 i. 06 
 
 .91 
 
 .0056 
 
 23 
 
 
 1.9 
 
 Potatoes (white) . 
 
 .Ol6 
 
 53 
 
 .14 
 
 .0013 
 
 03 
 
 
 9.0-12.0 
 
 Prunes (dried) . . 
 
 .06 
 
 1.20 
 
 .25 
 
 .0029 
 
 03 
 
 
 7-9 
 
 Rice 
 
 .012 
 
 .084 
 
 .203 
 
 .0009 
 
 .105 
 
 2.4 
 
 
 
 Steak (round) 2 . . 
 
 .Oil 
 
 42 
 
 .50 
 
 .0038 
 
 .20 
 
 6.7 
 
 
 Turnips .... 
 
 .089 
 
 .40 
 
 .117 
 
 .0005 
 
 .07 
 
 
 6.6-12.5 
 
 Wheat (whole) . . 
 
 .061 
 
 .519 
 
 .902 
 
 .0053 
 
 17 
 
 2.6 
 
 
 Wheat (flour) . . 
 
 .025 
 
 .146 
 
 .20 
 
 .0015 
 
 17 
 
 2.7 
 
 
 1 Equivalent to cc. normal acid or normal alkali. 2 Lean. 
 
 REFERENCES. Bulletin No. 28 of the United States Department of Agriculture, 
 which may be purchased for 10 cents from the Superintendent of Public Docu- 
 ments at Washington, contains a very complete list of American foodstuffs, show- 
 ing the protein, carbohydrate, fat, and energy values. Sherman's Chemistry oj 
 Food and Nutrition (Macmillan) contains a good treatment of the theory of 
 nutrition and tables that are especially valuable in showing the mineral elements 
 in foods. 
 
APPENDIX 357 
 
 QUESTIONS AND PROBLEMS 
 
 i gram protein = 4.1 Calories. I kilogram = 2.. 2. pounds. 
 
 i gram carbohydrate = 4.1 Calories. i pound = 453.6 grams. 
 i gram fat = 9.3 Calories. I ounce = 28.3 grams. 
 
 To walk i ///*? M* /^<?/ requires for a man of average weight (154 
 pounds} energy equal to 59 Calories. 
 
 To ascend 100 /<?/ (<z.y z'w climbing a hill or a flight of steps) requires 
 energy equal to 15.4 Calories. 
 
 One hundred grams of dry protein per day is about an average allowance. 
 
 Sixty grams is a very low protein diet. Fifty to 60 grams of fat is a 
 normal daily allowance. 
 
 A man is too fleshy and wishes to reduce his weight. Suppose that he 
 eats just enough to support his body without exercise. How far must he 
 walk to take off five pounds of fat? 
 
 A six-year-old boy needs about half as much food as a man. What 
 would be a fair amount of carbohydrate for a boy of this age? If a six- 
 year-old boy bought half a pound of candy and ate it all in one day, in 
 addition to his usual food, how much carbohydrate would he get that day? 
 
 Suppose that in walking you use the same energy in proportion to your 
 weight as does the average man. How much energy will you use in walk- 
 ing a mile? 
 
 How much energy would you use in climbing to the top of the tallest 
 building that you know? 
 
 How much energy would be required to bring you from your home to 
 your place in the schoolroom ? 
 
 How much potatoes would. a man need to eat to get 100 grams of protein ? 
 
 How much beef would he need to eat to get 3000 Calories of energy ? 
 How much protein would this give him? 
 
 In balancing diets, it is more convenient to use as a basis for computa- 
 tion the Calories derived from each of the different classes of foods than to 
 find the amount of protein, fat, and carbohydrate in grams. For persons 
 doing moderate work, about \ of the Calories should come from protein. 
 From the table on pages 353-355 make up a diet that will yield approx- 
 imately 3000 Calories of heat with 375 Calories from the protein, 500 from 
 fat, and the remainder from carbohydrate. 
 
 As nearly as possible, estimate the total Calory content of your food for 
 a day and the Calories derived from each class of food. 
 
358 APPENDIX 
 
 If a man eats 100 grams of protein and 100 grams of fat a day, how 
 much carbohydrate will he need to give him 4000 Calories of heat ? 
 
 Look up the analyses of white bread (or white flour) and meat in all the 
 tables. Would a diet composed chiefly of these be low or high in miner- 
 als? in vitamins? 
 
 Would a diet of bread and milk be an improvement on a bread and 
 meat diet? 
 
 A boy lost 1 1 pounds on a day when he attended a school picnic and all 
 the children had lunch together. What was the probable cause of the 
 loss in weight? 
 
 Would a person be more likely to gain in weight if he lay down for a 
 rest each day? Why? 
 
 B. VENTILATION 
 
 Notwithstanding all the studies of ventilation that have been made, 
 there yet seems to be something about the subject that is not under- 
 stood, " We are still undecided as to why bad air is bad." It has 
 been found, however, that our heat-regulating mechanism is not so 
 effective as has been supposed ; that the temperature of the body may 
 rise a degree or more in a heated room ; and that one important point 
 in ventilation is the control of the body heat. All the recent researches 
 on the subject indicate that in crowded rooms the chief difficulty is 
 overheating, and that in the solution of the problems of ventilation, 
 the thermometer must play an important part. 
 
 The Humidity of the Air. When the bulb of a thermometer is 
 wet, the mercury in the thermometer at once falls, because it is cooled 
 by the evaporation of the water. The amount it falls depends on how 
 rapidly the water evaporates, and this depends on the dryness of the 
 air, dry air taking up the water more rapidly than moist air. By not- 
 ing how much a thermometer is cooled when the bulb is wet, the 
 humidity of the air can be learned, as you will understand by per- 
 forming the following experiment : 
 
 Take the temperature of the air in your schoolroom with a ther- 
 mometer, and let us suppose that you find it to be 70 degrees. Then 
 wrap a piece of thin cloth about the bulb of the thermometer, moisten 
 
APPENDIX 359 
 
 the cloth with water that is near room temperature, and either fan 
 the thermometer vigorously for two or three minutes or swing it 
 through the air, taking care that the heat of the body does not affect 
 it. Read the thermometer again. For convenience, we will suppose 
 that the wet-bulb temperature is 59 degrees, which will give a differ- 
 ence between the dry-bulb and wet-bulb temperatures of. 1 1 degrees. 
 
 Now turn to the table on page 360, and find 1 1 degrees in the row of 
 figures across the top. Come down the column to the number opposite 
 70 degrees in the left-hand column, and you will have the relative hu- 
 midity of the air, 5 2 per cent in this instance. In this way you can at any 
 time find the humidity of the air if you know the wet-bulb and dry-bulb 
 temperatures. You can also by the use of the table find the wet-bulb 
 temperature of the air when the humidity and the dry-bulb temperature 
 are given. For example, to find the wet-bulb temperature when the 
 dry thermometer registers 90 degrees and the humidity is 81 per cent, 
 you find 90 degrees in the column on the left of the table, move to 
 the right to 81 per cent, and then look at the top of the column for 
 the difference between the wet and dry thermometers, 5 degrees in 
 this instance. Subtracting this from 90 degrees, we find that the 
 wet-bulb temperature is 85 degrees. Find the wet-bulb temperature 
 when the air is no degrees and the humidity is 32 per cent. 
 
 Importance of the Wet-bulb Temperature. The human body acts 
 like a wet-bulb thermometer, and it is the wet-bulb and not the dry- 
 bulb temperature of the air that is important. An understanding of 
 this point will make plain to you at once why it is that the summers 
 in humid regions are oppressive, even when the temperature of the 
 air is not excessively high, and why in the "dry heat" of arid re- 
 gions people retain their vigor and working power in an astonishing 
 manner. It will also enable you to understand why the temperature 
 of the moisture-laden atmosphere in crowded rooms must not be 
 allowed to rise, and why in the atmosphere of a furnace-heated build- 
 ing, where the air humidity may be only 20 or 30 per cent, one may 
 feel cold unless the temperature is raised to 75 degrees. The proper 
 humidity for indoor air is from 40 to 50 per cent. 
 
APPENDIX 
 
 RELATIVE HUMIDITY TABLE 
 
 DIFFERENCE BETWEEN WET AND DRY THERMOMETERS 
 
 TEMPERATURE OF AIR 
 
 
 1 
 
 3 
 
 5 
 
 7 
 
 9" 
 
 n 
 
 13 
 
 15 
 
 17 
 
 19 
 
 2I C 2 3 
 
 25 
 
 27 
 
 29 
 
 60 
 
 94 
 
 84 
 
 73 
 
 63 
 
 53 
 
 44 
 
 34 
 
 26 
 
 18 
 
 10 
 
 2 
 
 
 
 
 
 65 
 
 95 
 
 85 
 
 75 
 
 65 
 
 56 
 
 48 
 
 39 
 
 3i 
 
 24 
 
 17 
 
 10 
 
 3 
 
 
 
 
 70 
 
 95 
 
 86 
 
 77 
 
 68 
 
 60 
 
 5 2 
 
 44 
 
 36 
 
 29 
 
 23 
 
 16 
 
 10 
 
 4 
 
 
 
 75 
 
 95 
 
 87 
 
 78 
 
 70 
 
 62 
 
 55 
 
 47 
 
 40 
 
 34 
 
 27 
 
 21 
 
 16 
 
 10 
 
 5 
 
 
 80 
 
 96 
 
 87 
 
 79 
 
 72 
 
 64 
 
 57 
 
 5i 
 
 44 
 
 38 
 
 32 
 
 26 
 
 20 
 
 15 
 
 10 
 
 6 
 
 85 
 
 96 
 
 88 
 
 80 
 
 73 
 
 66 
 
 60 
 
 53 
 
 47 
 
 4i 
 
 36 
 
 30 
 
 25 
 
 20 
 
 15 
 
 ii 
 
 90 
 
 96 
 
 00 
 00 
 
 81 
 
 75 
 
 68 
 
 62 
 
 56 
 
 50 
 
 44 
 
 39 
 
 34 
 
 29 
 
 24 
 
 20 
 
 15 
 
 95 
 
 96 
 
 89 
 
 82 
 
 76 
 
 69 
 
 63 
 
 58 
 
 5 2 
 
 47 
 
 42 
 
 37 
 
 32 
 
 28 
 
 23 
 
 19 
 
 100 
 
 97 
 
 90 
 
 83 
 
 77 
 
 7i 
 
 65 
 
 59 
 
 54 
 
 49 
 
 44 
 
 39 
 
 35 
 
 3? 
 
 27 
 
 23 
 
 105 
 
 97 
 
 90 
 
 84 
 
 78 
 
 72 
 
 66 
 
 61 
 
 56 
 
 5i 
 
 46 
 
 42 
 
 38 
 
 33 
 
 30 
 
 26 
 
 110 
 
 97 
 
 90 
 
 84 
 
 78 
 
 73 
 
 67 
 
 62 
 
 57 
 
 53 
 54 
 1* 
 
 48 
 
 44 
 
 40 
 42 
 44 
 
 36 
 
 32 
 
 28 
 
 115 
 
 97 
 
 91 
 91 
 
 85 
 85 
 
 79 
 80 
 
 74 
 
 75 
 
 69 
 
 70 
 
 64 
 65" 
 
 59 
 60 
 
 50 
 5i 
 
 46 
 
 47 
 
 38 
 40 
 
 34 
 36 
 
 3' 
 33 
 
 120 
 
 97 
 
 RELATIVE HUMIDITY OF AIR IN PERCENTAGES 
 
 Cooling the Body by Air Currents. Place a wet-bulb thermometer 
 in still air and note the reading. Then fan it vigorously and take a 
 second reading. What causes the mercury to fall ? The importance 
 of ventilating systems and fans in hot weather for cooling the body by 
 sending air currents over it is only beginning to be understood, and 
 they will be much more extensively used in the future. This will 
 prove to be an economy, for by these devices the health of workers 
 is preserved and their productive powers are greatly increased. 
 
APPENDIX 361 
 
 Clothing and Over-heating of the Body. Most of us understand 
 the importance of heavy clothing in cold weather, but during the 
 heated season many persons, especially men, do not wear clothing 
 adapted to the weather. On hot days, thin clothing that will allow 
 the air to penetrate to the skin and the perspiration to evaporate from 
 the surface of the body should be worn. Bare arms, low-cut shoes, 
 and clothing open at the neck, all allow the escape of body heat and 
 help to keep the body temperature from rising. A light diet is also 
 advisable in hot weather ; for a heavy protein diet increases the oxi- 
 dation of food and releases more heat in the body. These measures 
 are important ; for overheating of the body is very injurious, and we 
 should give the same attention to keeping cool in summer that we 
 give to keeping warm in winter. 
 
 C. ALCOHOL AND LENGTH OF LIFE 
 
 In 1909 forty-three of the leading life insurance companies of the 
 United States and Canada decided to investigate collectively the 
 death rates among different classes of their policyholders. The in- 
 vestigation included the histories of over 2,000,000 lives, and was the 
 most extensive study ever undertaken by life insurance companies. 
 Among other figures collected were the following in regard to the 
 mortality rates among users of alcoholic drinks : 
 
 MORTALITY 
 
 Moderate users (2 glasses of beer, one glass of whisky, or 
 
 their equivalent, a day) 118% 
 
 Liberal users (steady, free, but not immoderate use) . . 187% 
 
 These figures indicate that 1 18 moderate users of alcoholic drinks and 
 187 liberal users of them die where the number of deaths that would 
 naturally be expected is loo. 1 It should be understood, however, that 
 
 1 Insurance companies from their long experience are able to calculate about 
 how many deaths may be expected to occur among a given number of persons of 
 given ages. This average number is taken as 100%, and the rate among users of 
 alcohol was compared with the average rate. It should be understood that the 
 above comparisons are not between drinkers and abstainers, but between drinkers 
 and all classes of the insured drinkers and abstainers taken together. All 
 companies reject applicants who are heavy drinkers. 
 
362 APPENDIX 
 
 the information as to the consumption of alcohol, was obtained when 
 the policy was applied for, and a portion of those included in the above 
 results probably changed their habits later. Some of them doubtless 
 came to drink more freely and some became total abstainers. 
 
 In the above-mentioned investigation, no study of the mortality 
 rate among abstainers was made, but one American company that 
 made such a study secured the following data : 
 
 MORTALITY 
 
 Total abstainers 59 % 
 
 Rarely use 71% 
 
 Temperate 84% 
 
 Moderate 125% 
 
 These figures show a mortality rate among abstainers of less than 
 half that among moderate drinkers. 
 
 D. INTESTINAL DISEASES 
 
 The long intestinal tract affords a favorable place for the growth of 
 parasites, and the parasites find an easy mode of entrance to this 
 tract in the food and water that are taken in through the mouth. 
 Children, especially, suffer from intestinal diseases, and because these 
 diseases cause so much sickness and so many deaths, it is important 
 that their cause and the means of prevention be understood. 
 
 Diarrhea. Diarrhea may be caused by several different bacteria, 
 all of which grow in the intestine, and most of which are closely 
 related to the typhoid germ. One of these germs causes the very 
 severe form of diarrhea that runs in epidemics, and is sometimes 
 called flux. Poisoning from meats, fish, old milk, and ice cream is 
 often due to germs related to the diarrhea bacteria. The germs 
 grow in the food either before or after it is eaten, and produce the 
 toxins that cause the poisoning. 
 
 Infant Diarrhea. Summer complaint, from which so many young 
 children die, is caused usually by germs belonging to this same group. 
 The disease may easily be started in a little baby by giving it impure 
 water, and nothing but boiled water, pure rain water, or artesian 
 water should ever be given to a little child or put into its milk. 
 
APPENDIX 363 
 
 Nearly all milk contains germs that, when taken in large enough 
 numbers, will cause the trouble, and the milk supply is mainly respon- 
 sible for the disease. The disease is worse in summer because in 
 warm weather the germs multiply more rapidly in milk, and also 
 because the heat weakens the children so that they have not much 
 power of killing germs. The disease is infectious, and in some cities 
 great progress in preventing it has followed isolating the cases and 
 disinfecting the wastes, as is done in cases of typhoid fever. 
 
 How the Germs of Intestinal Diseases are Spread. The germs 
 of diarrhea, dysentery (page 296), and typhoid fever are usually 
 swallowed either in food or water. They are carried about and 
 get into the food and water in various ways (page 315), but one 
 especially important precaution in the prevention of all these dis- 
 eases is to keep discharges from the intestines away from flies. 
 
 Hookworms. The hookworm is a slender white worm, not quite 
 half an inch in length. It grows in the intestines, and causes a pro- 
 found anemia (lack of red blood corpuscles). Hookworms are found 
 in the warmer parts of all the continents ; they formerly caused one 
 third of all the deaths in Porto Rico, and it is estimated that in our 
 own country south of the Potomac River from 20 to 25 per cent of 
 the poorer white people suffer from hookworms. 
 
 How Hookworms get into the Body. The eggs of the hookworm 
 pass out of the body in the excreta from the alimentary canal. If 
 they are allowed to get into the soil, they develop into worms so small 
 that there may be fifty of them in a piece of earth the size of a pea. 
 These worms may enter the body through the skin (in which they 
 cause "ground itch"), be carried in the blood to the lungs, break 
 through into the air sacs and crawl up the trachea, and then reach 
 the intestines by being swallowed ; or they may be taken into the 
 alimentary canal in water or in food. The disease is more common 
 among children than among adults, because children go barefooted, 
 and sometimes eat with unwashed hands after playing in the earth , 
 it is more common among agricultural laborers and brickmakers than 
 among those who do not come in contact with the soil ; and the dis- 
 
364 APPENDIX 
 
 is more severe (though not more common) in the white than in 
 the colored race. 
 
 The Prevention of Hookworm Disease. The eggs of the hookworm 
 get into the soil only from persons who have the disease. Away 
 from the air the eggs die, and the disease may be entirely prevented 
 by the use of closets. In hookworm regions great care, there- 
 fore, should be exercised to prevent the pollution of the soil about 
 houses. To a certain extent, children may be saved from infection 
 by the wearing of shoes, but keeping the soil free from pollution 
 is the important measure in the prevention of hookworm disease. 1 
 
 Preventing Disease in Rural Regions. Intestinal diseases like 
 typhoid fever, dysentery, and hookworm are especially prevalent in 
 rural regions, and every county needs a health officer who will give his 
 time to showing the country people how to free themselves from these 
 diseases. The one thing above all others that is needed to check 
 them is a sanitary closet on every farm in the land. Such a closet 
 must be fly-tight ; for as long as flies are allowed to spread the germs 
 of intestinal diseases over foods and dishes, not even a beginning in 
 sanitation has been made. 
 
 In this connection it is of interest to note that from 1900 to 1912 
 in the United States the death rate in cities fell 21.2 per cent, and 
 that during the same years in the rural regions it fell only 8.6 per 
 cent. The reasons for this are that in cities the schools have physi- 
 cians and nurses to look after any children that need medical care ; 
 cases of diphtheria, measles, and typhoid fever are quarantined ; and 
 skilled health officers devote their whole time to guarding the people's 
 health. In the country there is no one to do this work, and the 
 country people are not getting the benefit of recent scientific and 
 medical discoveries. 
 
 1 Often it is not realized that hookworm victims are diseased, and they are con- 
 sidered lazy and ambitionless. Many cases of hookworm trouble are mistaken for 
 malaria. The symptoms of hookworm disease are paleness, thinness, dull skin and 
 eyes, dry hair, continued weakness, and sometimes an appetite for such sub- 
 stances as earth, tobacco ashes, and paper. The worms may readily be killed and 
 the disease cured by the use of very simple medicines. 
 
GLOSSARY 
 
 This glossary is intended chiefly to help the pupil in the pronunciation of the more 
 difficult terms. Words are defined only where no exact definition is found in the text. 
 The numbers refer to the pages on which definitions are found. 
 
 afferent (af fe-rent), carrying to. 
 
 ameba (am-e'ba), 296. 
 
 amylopsin (a-mM6p'sin), 98. 
 
 Anopheles (an-6fel-ez), 321. 
 
 aorta (a-or'ta), 141. 
 
 aqueous (a'kwe-us), watery. 
 
 arachnoid (a-rak'noid), like a cob- 
 web ; as, arachnoid membrane. 
 
 arbor vitae (ar'bor vi'te), 215. 
 
 arytenoid (a-rT-te'noid), 173. 
 
 bacillus (ba-sll'lus), 304. 
 
 bacteria (bak-te're-a), 285. 
 
 biceps (bi'seps), 67. 
 
 bronchial (bron'ke-al), 166. 
 
 canine (ka-nm'), 95. 
 
 capillary (cap'il-la-re), 141. 
 
 carbohydrate (kar-bo-hi'drat), 82. 
 
 cartilage (kar'til-aj), gristle. 
 
 cerebellum (ser-e-beTlum), 25. 
 
 cerebro-spinal (ser'e-bro-spT'nal), 26. 
 
 cerebrum (ser'e-brum), 25. 
 
 choroid (ko'roid), 261. 
 
 cilia (sll'e-a), plural of cilium; 
 minute, hair -like projections, 
 
 coccus (kok'us), 304. 
 
 coccyx (kok'six), 34. 
 
 cochlea (kok'le-a), 254. 
 
 corpuscle (kor'pusl), a cell of the 
 blood or lymph (page 147), or a 
 
 group of cells, as a renal corpuscle 
 
 (page 1 88). 
 cricoid (kri'koid), 172. 
 Culex (kyu'lex), 321. 
 cytoplasm (si'to-plazm), 4, footnote 
 dentine (den'tln), 94. 
 diaphragm (di'a-fram), 17. 
 dietetics (dl-e-tet'iks), the science or 
 
 study of the regulation of the diet. 
 diphtheria (dif-the're-a), 304. 
 dura mater (du'ra ma'ter), 26. 
 efferent (ef fe-rent), carrying from. 
 enzyme (en'zlm), 112. 
 epiglottis (ep-t-glot'tis), 165. 
 esophagus (e-sofa-gus), 90. 
 Eustachian (yu-stak'e-an), 253. 
 fasciculus (fas-slk'yu-lus), a bundle. 
 femur (fe'mer), 37. 
 fibula (fib'yu-la), 37. 
 formaldehyde (for-mal'de-hld), 335. 
 fungus (fun'gus), plural fungi (fun' 
 
 J0 3i8. 
 
 hemoglobin (hem-6-glo'bin), 148. 
 hepatic (\\G-^i'\\<i), pertaining to tht 
 
 liver ; as, hepatic vein. 
 hydrogen (hi'dro-jen) , 80. 
 incisor (in-si'sor), 95. 
 infundibulum (in-fun-dlb'yu-lum), 
 
 166. 
 
 365 
 
366 
 
 GLOSSARY 
 
 invertase (in-ver'tas), 113, footnote. 
 
 lachrymal (\ak'n-ma.Y), pertaining to 
 the tears; as, lachrymal duct. 
 
 lacteal (lak'te-al), 152. 
 
 larynx (lar'inks), 165. 
 
 lymph (limf), 149. 
 
 lymphatic (lim-fat'ik). 
 
 malleus (mal'le-us), 253. 
 
 medulla oblongata (med-ul'la ob- 
 lon-gah'ta), 25. 
 
 Meibomian (ml-bo'mi-an), 260. 
 
 membrane (mem'bran), a thin layer 
 of tissue. 
 
 meningitis (men-in-ji'tis), 308. 
 
 molecule (mol'e-kyul), 79. 
 
 mucus (myu'kus), 168. 
 
 neuron (new'ron), 211. 
 
 nitrogen (ni'tro-jen), 80. 
 
 nucleus (new'kle-us), 4. 
 
 olfactory (ol-fak'to-re), pertaining to 
 the sense of smell. 
 
 pancreas (pan'kre-as), 98. 
 
 papilla (pa-pil'la), 193. 
 
 parotid (pa-rot'id), 97. 
 
 patella (pa-tel'la), 37. 
 
 peptone (pep' ton), 112. 
 
 perimysium (per-e-mlz'e-um), 62. 
 
 periosteum (per-e-6s'te-um), 42. 
 
 phalanges (fa-lan'jez), 37. 
 
 pharynx (far'inks), 90. 
 
 pia mater (pfa ma'ter), 26. 
 
 process (pro'sess), a slender, pro- 
 jecting point. 
 
 proteins (pro'te-ins), 83. 
 
 protoplasm (pro'to-plazm), the living 
 substance of the cell. 
 
 protozoon (pro-to-zo'6n), plural pro- 
 tozoa (pro-to-zo'a), 285. 
 
 psoas (so'as), 70. 
 
 ptyalin (tl'a-lin), 98. 
 
 pulmonary (pul'mo-na-re), having t& 
 
 do with the lungs. 
 pylorus (pT-lo'rus), 93. 
 rabies (ra/be-ez), 299. 
 renal (re'nal), pertaining to the kid* 
 
 neys; as, renal corpuscle. 
 retina (ret'i-na), 261. 
 sacrum (sa/krum), 34. 
 salivary (sal'i-va-re), 89. 
 scapula (skap'yu-la), 36. 
 sclerotic (skle-rot'ik), 261. 
 sebaceous (se-ba'shus), 195. 
 spirillum (spi-ril'lum), 304. 
 stapes (sta'pez), 253. 
 steapsin (ste-ap'sin), 98. 
 subcutaneous (sub-kyu-ta/ne-us), 193. 
 submaxillary (sub-maks'il-la-re), 97. 
 tetanus (tet'a-nus), 313. 
 thoracic (tho-ras'ik), connected with 
 
 the chest, from thorax, chest. 
 thyroid (thi'roid), 172. 
 trachea (tra/ke-a), the windpipe. 
 trapezius (trap-e'ze-us), 60. 
 triceps (tri'seps), 67. 
 trichina (tri-ki'na), 129. 
 trichinosis (trlk-I-no'sis), 129. 
 trypsin (trip'sin), 98. 
 tuberculosis (tu-ber-kyu-lo'sis), 340. 
 tympanic (tTm-pan'ik), 252. 
 tympanum (tim'pan-um), 253. 
 urea (yu're-a), 116. 
 ureter (yu-re'ter), 188,, 
 uvula (yu'vyu-la), 165. 
 vena cava (ve'na ka'va), plural 
 
 venae cavaB (ve'ne ka've), 142. 
 vitreous (vlt're-us), like glass. 
 
INDEX 
 
 A star (*) after a page number indicates that an illustration of the subject appears 
 
 on that page. 
 
 Abdominal cavity, 1 6, * 1 7 ; muscles, 60, * 70. * 
 
 Absorption, 93, no 119. 
 
 Accidents, 274-283. 
 
 Acid, in gastric juices, 91,* 92, 107, 113; 
 uric, 114, 116; poison, 280. 
 
 Afferent nerves, 211, 217, 218,* 225,* 226,* 
 245, 246,* 248. 
 
 Air, 80, 178, 180, 229, 344. See also Oxygen 
 and Carbon dioxid. 
 
 Air sacs, 161, 162,* 166, 167.* 
 
 Alcohol, as a food, 131, baths, 199 (n. i); 
 how formed, 238 ; and length of life, 239 ; 
 and tuberculosis, 240; and insanity, 241; 
 and germ diseases, 290. 
 
 Alcohol, effects of: on the human body, 
 238-244, 361; muscles, 74, 233; di- 
 gestive organs, 101, 102, 116; heart, 
 155 ; arteries, 155 ; respiratory system, 
 171. kidneys, 189; nervous system, 
 232*; animals, 233, 234,* 241; character, 
 243; eyes, 271. 
 
 Alimentary canal, 88,* 287, 315, 362. 
 
 Amino-acids, 125. 
 
 Amylopsin, 98, 113. 
 
 Anatomy, denned, 13. 
 
 Animal kingdom, 17, 19.* 
 
 Animals, composed of cells, 4, 5, n; one- 
 celled, 5, 6,* 7, 150. 
 
 Antitoxins, 287 (n. 2), 306, 307. 
 
 Aorta, 138,* 141, 143,* 186.* 
 
 Appendix, vermiform, 88,* 94, 94 (n. 2). 
 
 Aqueous humor, 261.* 
 
 Arachnoid membrane, 26. 
 
 Arbor vitae ("tree of life"), 213,* 215. 
 
 Arch of foot, 48,* 49. 
 
 Arsenic, 280. 
 
 Arteries, pulmonary, 138,* 141, 143*; 
 hepatic, 138*; aorta, 138,* 141; circula- 
 tion in, 140, 142*; denned, 141; bleeding 
 from, 277,* 278.* 
 
 Arytenoid cartilages, 172,* 173, 174.* 
 
 Atoms, 79-81. 
 
 Auditory canal. See Hearing. 
 
 Auricles, 137,* 140, 141, 143.* 
 
 Bacilli, 304." See also Bacteria. 
 
 Bacteria, defined, 285 ; diseases caused 
 by 303-318; shapes of, 304*; of various 
 diseases 305,* 308,* 310,* 311,* 313,* 
 3i5,* 316,* 317,* 340* ; in foods, 316, 327, 
 
 330, 362. 
 aths, 
 
 Baths, 200-203. 
 
 Belladonna, 280. 
 
 Beriberi, 85, 86. 
 
 Bichlorid of mercury, 334. 
 
 Bile, duct, 90*; in the liver, 99. 
 
 Biniodid of mercury, 334. 
 
 Bladder, gall, 88,* oo * 99: of kidneys, 
 186,* 189. 
 
 Bleeding, 277,* 278.* 
 
 Blood, cells of, 7, ip,* 147* (see also Cor- 
 puscles) ; circulation of, 135-157. 
 
 Blood vessels, 17, 26, 27,* 42, 91,* 93,* 
 136, 138,* 141, 143,* 146,* 161, 162,* 
 191,* 195,* 198. 
 
 Body, human, a colony of cells, 3-15, 135; 
 plan of, 16-22; cavities of, 16,* 17; con- 
 trolled by nervous system, 28, 210; car- 
 riage of, 53, 69-72; laws governing, 135; 
 heat of, 135, 191, 194, 197-199, 202 ; effects 
 of alcohol on, 238-244, 361 ; equilibrium 
 of, 255 ; westes of, see Wastes. 
 
 Bone, cells of, 7, 8,* 56; materials in, 39, 
 40*; marrow, 40*, 42, 147. 
 
 Bones, of the human skeleton, 31-43*; 
 number of, 33; structure of, 37-38,* 
 40-43*; materials in, 39.* 
 
 Brain, 8,* 17,* 23, 24,* 25,* 48, 210, 210 
 (n. i), 213,* 265. 
 
 Bright's disease, alcohol and, 189. 
 
 Bronchial tubes, 166, 167.* 
 
 Bubonic plague, 314-315. 
 
 Burns, treatment of, 279. 
 
 Calories, 126 (n. i), 127, 348 (n. i), 353-355. 
 Capillaries, 138,* 141, 142,* 144 (n. i), 
 
 148,* 150,* 151.* 
 
 Carbohydrates, 82, 83, 125, 127, 350. 
 Carbolic acid, 334. 
 Carbon dioxid, 81,* 148, 150,* 160, 179, 
 
 Cartilage, 35,* 38,* 42,* 47,* 50; thyroid, 
 172*; cricoid, 172*; arytenoid, 172,* 
 i73~, 1 74-* 
 
 Cat, brain of, 229*; eyes of, 262.* 
 
 Cell, the, 3-15; structure of, 3,* 4; division 
 of, 5,* 6.* 
 
 Cells, kinds of, ^* 8,* 9,* 10,* 59,* 61,* 
 62,* 89,* 91,* 188,* 191..* 192,* 193,* 
 195* ; ciliated, 9,* 147 (n. i) ; growth of, 
 78, 84; energy in, 78, 84, 114; wastes of, 
 115,* 149, 150*; foods of, 7, 78, 79, 114, 
 115,* 150*; poison in, 186, 287. 
 
 Cerebellum, 25,* 213,* 215, 229.* 
 
 367 
 
368 
 
 INDEX 
 
 Cerebro-spinal fluid, 26 ; meningitis, 26 
 
 (n. i), 3I7-* 
 
 Cerebrum, 25,* 213,* 214,* 229.* 
 Chemistry of foods, 79, 80,* 81,* 82. 
 Chest (thoracic) cavity, 16,* 17, 162.* 
 Chicken pox, 317. 
 Chills, 199, 202, 203, 293. 
 Chlorid of lime, 334. 
 Cholera, 316.* 
 
 Choroid coat of the eye, 261,* 262, 266. 
 Cigarettes. See Tobacco. 
 Cilia, 6,* 9,* 147 (n. i), 168. 
 Ciliary muscles, 266.* 
 Circulation of the blood, 135-159. 
 Clavicle (collar bone), 32,* 35,* 36. 
 Cleanliness, importance of, 200-202. 
 Climate and tuberculosis, 346. 
 Clothing, 170, 204, 205; on fire, 279. 
 Cocci (sing, coccus), 304.* 
 Coccyx, 34.* 
 Cochlea, 254.* 
 Colds, 203, 310. 
 Compounds, 79-81. 
 Connective tissue, 8,* n, 25, 27,* 42, 47,* 
 
 62,* 63,* 89,* 91,* 143, 191.* 
 Consumption. See Tuberculosis. 
 Contraction, of muscles, 61, 65, 66*; of 
 
 auricles and ventricles, 137, 140; gov- 
 erned by the cerebellum, 215. 
 Convolutions of the brain, 25,* 214. 
 Cooking, 130. 
 Cornea, 261,* 266.* 
 Corpuscles, red, 7, 10,* 42, 85, 147,* 148, 
 
 293*; white, 10,* 147,* 148,* 153, 288*; 
 
 renal, 187,* 188*; touch (tactile), 191,* 
 
 246,* 247. 
 
 Cranial nerves, 225. 
 Cranium, 25, 26,* 34, 48. 
 Cricoid cartilage, 172.* 
 Cytoplasm, 4 (n. 2). 
 
 Dermis, 191,* 193, 195.* 
 
 Diaphragm, 16,* 17,* 18,* 162 (n. i), 163,* 
 
 164 (n. i). 
 Diarrhea, 362. 
 Dietetics, 120-133. 
 Digestion, 7, 9, 110-119, 121-123; organs 
 
 of, 88-109, 88,* 90*; alcohol and, 101, 
 
 116; juices in, 91, 93, 100; hygiene of, 
 
 120-123. 
 
 Diphtheria, 304307; germ of, 305.* 
 Disease germs, 285290*; and lymph nodes, 
 
 I 53> X S4; defined, 285; alcohol and, 290; 
 
 in water, 315,* 327-329; in milk, 316 
 
 (n. i), 330. See also Bacteria, Protozoa, 
 
 etc. 
 Diseases, intestinal, 362-364. 
 
 Disinfectants, 334-335. 
 
 Disinfection, 312, 332-338. 
 
 Dislocations, 55 ; treatment of, 56. 
 
 Dorsal cavity, 16.* 
 
 Drowning accidents, 274,* 275,* 276*. 
 
 Ducts. See Salivary, Thoracic, etc. 
 
 Dura mater, 26. 
 
 Dust, 170, 271, 325-327- 
 
 Dysentery, 296.* 
 
 Ear, bones of, 34, 253*; divisions of, 252- 
 
 254* ; care of, 255. 
 Ear drum (tympanum), 253. 
 Efferent nerves, 211, 218,* 219,* 226.* 
 Elements, 79-81. 
 Energy, foods and, 78-87, 114, 124, 348 
 
 in the cells, 78, 84, 114; oxidation and, 
 
 114, 1 60, 348. 
 
 Enzymes (ferments), 112, 113. 
 Epidermis, 191,* 192,* 195.* 
 Epiglottis, 165, 1 66,* 173.* 
 Epithelium, 249 (n. i). 
 Erector spinse, 70,* 71.* 
 Erysipelas, 311.* 
 Esophagus, 17,* 88,* 90, 166.* 
 Eustachian tube, 252,* 253. 
 Exercise, 12, 73, 124, 154, 170. 
 Eyes, 250-273; and digestion, 124; effects 
 
 of tobacco on. 271-272; foreign bodies 
 
 in, 278. 
 
 Fainting, 278. 
 
 Fat, 8,* 10, 42, 115, 191.* 
 
 Fats as food, 83, 113, 127-128, 153. 
 
 Ferments (enzymes), 112, 113. 
 
 Fever, 198, 293. 
 
 Fibers. See Muscles, Nerves, etc. 
 
 Flies, dangers from, 324,* 325.* 
 
 Follicle, hair, 194, 195,* 200. 
 
 Foods, for the cell, 7, 78, 79, 114, 115.* 
 150*; and energy, 78-87, 114, 124, 348; 
 chemistry of, 79-82; classes of, 82-84; 
 digestion of, no 119, 121-123; oxidation 
 of, 114, 160, 348; amount and kinds 
 needed, 124-128, 350; alcohol and, 131- 
 132; for consumptives, 344; tables 
 of, 351-356. 
 
 Foot, 48,* 49, 146.* 
 
 Formalin, 334. 
 
 Fungi, 287 (n. i), 318.* 
 
 Gall bladder, 88,* 90,* 99. 
 
 Ganglia, 210, 226, 227,* 228.* 
 
 Gastric glands and juice, 91,* 92. 
 
 Germicidal substance, 288, 290. 
 
 German measles, 317. 
 
 Germs. See Bacteria, Disease germs, etc. 
 
INDEX 
 
 369 
 
 Glands, stomach, 7,* 25, 25 (n. i), 91*; 
 cells of, 7,* 89,* 91*; salivary, 25 (n. i), 
 89, 97,* 98*; pancreas, 25 (n. i), 98; liver, 
 25 (n. i), 09; kidney, 25 (n. i); sweat, 
 25 (n. i), 89 (n. i), 191,* 193,* 194; 
 simple, 89* ; secretions of, 89, 89 (n. i) ; 
 gastric, 91*; intestinal, 93*; sublingual, 
 97*; submaxillary, 97*5 parotid, 97*; 
 sebaceous, 195; lachrymal, 259, 260*; 
 Meibomian, 260. 
 
 Goiter, 128 (n. i). 
 
 Grape sugar, 112, 113. 
 
 Gray matter (nerve cells), 214, 217, 229. 
 
 Hair, 194, 195,* 196. 
 
 Hand, u, 37, 64,* 65.* 
 
 Health officials, importance of, 338. 
 
 Hearing, 251-256. 
 
 Heart, location of, 17,*^ 18,* 137, i39*J 
 function of, 137;' auricles, 137*; ven- 
 tricles, 137*; valves of, 140,* 141*; 
 nerves of, 145; hygiene of, 154-156; 
 alcohol and, 155; tobacco and, 156. 
 
 Heat. See Body. 
 
 Heating and ventilation, 182, 197, 202. 
 
 Hemispheres of the cerebrum, 214. 
 
 Hemoglobin, 148. 
 
 Hepatic, vein and artery, 138,* 145 (n. i). 
 
 Heredity, and tuberculosis, 240, 345; and 
 alcohol, 241. 
 
 Hookworms, 363. 
 
 Hydrophobia. See Rabies. 
 
 Hygiene, denned, 13; of the skeleton, 53- 
 56; muscles, 73~745 digestive organs, 
 120-123; heart, 154-156; respiratory 
 system, 170-172; nervous system, 
 229-235. 
 
 Impulses, nerve, 211, 215, 217, 245. 
 
 Incus (anvil), 253.* 
 
 Influenza, 309, 310.* 
 
 Insects, as disease carriers, 287, 320-325, 
 
 321,* 322,* 324,* 325.* 
 Intestinal diseases, 315,* 316,* 362. 
 Intestine, 17*, 18*; large, 88,* 94; small, 
 
 88,* 93,* 113, 152. 
 
 Involuntary muscles, 25, 61 (n. i), 62. 
 Iris, 261,* 262,* 266.* 
 Iron, an element, 80*; in the blood, 85. 
 
 Joints, 45, 46, 48*; muscles and, 61. 
 Juices, digestive, 91-93, 98, 100, 112. 
 
 Kidneys, 7, i?,* 25 (n. i), 186,* 187*; am 
 the body wastes, 186-190; alcoholand, 189 
 Knee-cap. See Patella. 
 
 Lachrymal, bone, 33*; glands, 259, 260. 
 
 acteals, 151,* 152 (n. i). 
 .arynx, 165, r66,* 167,* 172,* I73-* 
 .ens of the eye, 261,* 263, 264,* 266.* 
 .eprosy, 314. 
 -igaments, 47, 48,* 55; and tendons, 64,* 
 
 65*; suspensory, 263, 266.* 
 ,ight, and the sense of sight, 262-267, 270 ; 
 
 and disease germs, 333. 
 iver, n, 17,* 18,* 25 (n. i), 88,* 89; and 
 
 alcohol, 102, 116; circulation in, 138,* 
 
 145 (n. i). 
 umbar region, 69. 
 ungs, 7, 9, ii, 17,* 18,* 148 (n. i), 161, 
 
 163,* 167*; circulation in, 138,* 162*; 
 
 air sacs in, 161, 162,* 106, 167*; in 
 
 drowning accidents, 274. 
 ^ymph, 149, 150,* 151, 194; nodes, 139,* 
 
 152,* 153*; and disease germs, 154, 
 
 154 (n- i). 
 Lymphatic, system, 151-154; vessels, 139, 
 
 151,* 152. 
 Lysol, 334. 
 
 lalaria, 292-296, 321,* 322,* 323. 
 
 Malleus (hammer), 253.* 
 
 Malt sugar, in, 113. 
 
 Mammals, 18, 19.* 
 
 Vlan, in animal kingdom, 17, 18, 19.* 
 
 Measles, 301, 317. 
 
 Medicines, patent, 12, 132, 343. 
 
 Medulla, 25,* 213,* 216, 229.* 
 
 Meibomian glands, 260. 
 
 Membranes, of brain and cord, 25, 26; 
 
 mucous, 90, 91,* 151,* 168. 
 Meninges, 26 (n. i) ; disease of, 317. 
 Mercuric chlorid, 280. 
 Milk, germs in, 330-332, 341. 
 Milk of lime, 334. 
 
 Mind, the seat of, 25, 210 (n. i), 214. 
 Mineral matter, in bone, 39; foods, 85, 
 
 128, 356. 
 
 Molecules, 79, 80,* 81,* no, in, 114. 
 Mosquitoes and malaria, 294-296, 321,* 
 
 .322,* 323- 
 
 Motor nerves. See Efferent. 
 
 Mucous membrane, 90, 91,* 151,* 168, 
 250,* 257. 
 
 Mucus, 9,* 90, 94, 1 68. 
 
 Mumps, 317. 
 
 Muscle, cells, 7, 8,* 10, 61 (n. i), 62,* 150,* 
 2ii*; tissue, 10, 59 (n. i). 
 
 Muscles, the, 59-77,* voluntary, 23-25, 
 61 (n. i), 62, 68, 215; involuntary, 25, 
 61 (n. i), 62, 228*; contraction of, 61, 
 65, 66,* 215; antagonistic, 67; of head> 
 69*; of spinal column, 69-72* ; effects 
 of alcohol and tobacco on, 74; of 
 
370 
 
 INDEX 
 
 stomach, 92 ; of the hair, 195,* 195 (n. i) ; 
 of the eye, 260*; ciliary, 266.* 
 
 Nails, the, 196. 
 
 Nasal, bone, 33*; passages, 164, 166,* 
 1 68; cavity, 260.* 
 
 Nerves, cells (gray matter), 8,* 210; tissue, 
 10, 210; of brain, 10, 26, 210 (n. i), 214, 
 229; fibers, 27,* 192,* 210, 211,* 218,* 
 219*; function of, 27-29; in bone, 42; 
 of the heart, 145 ; of the skin, 191,* 192* ; 
 cranial, 225; of touch, 246-248,* 256; of 
 taste, 249,* 257; of smell, 250,* 257; of 
 hearing, 252,* 254, 257; optic, 260,* 261,* 
 265. See also Afferent and Efferent. 
 
 Nervous system, 23-30,* 210-237*; central, 
 23, 213-224; sympathetic, 23, 226-228*; 
 like a telegraph system, 28; and the 
 muscles, 68 ; and the sweat glands, 194 ; 
 like a telephone system, 212* ; of other 
 animals, 229* ; hygiene of, 229-235 ; to- 
 bacco, alcohol, and, 230-235*. 
 
 Neurons, 211,* 218. 
 
 Nitrogen, 80, 84. 
 
 Nodes. See Lymph. 
 
 Nucleus, of cells, 4, 5,* 61 (n. i), 211*; 
 division of, 5,* 6.* 
 
 Olfactory organs. See Smell. 
 
 Opium, 120, 132, 281. 
 
 Optic nerve, 260,* 261,* 265. 
 
 Organs of the body, n, 17,* 18,* 23. 
 
 Outdoor sleeping, 184. 
 
 Oxidation of foods, 114-115,* 160,* 348. 
 
 Oxygen, and the cells, 7, 9, 114-115,* 148, 
 148 (n. i), 161 ; carried by red corpuscles, 
 7, 148, 148 (n. i) ; in air, 178, 179. See 
 also Oxidation. 
 
 Pancreas, 17,* 25 (n. i), 88,* 89, 90,* 98, 
 
 113; juices of, 98, 113. 
 Papillae, 191,* 192,* 193, 195.* 
 Pasteur treatment, 300. 
 Patella (knee-cap), 32,* 37, 60.* 
 Patent medicines, 12, 132, 343. 
 Pelvis, bones of, 32,* 35,* 36. 
 Pepsin, 90 (n.), 92. 
 Peptones, 112, 125. 
 Pericardium, 163,* 163 (n. i). 
 Periosteum, 40,* 42,* 63, 64. 
 Perspiration, function of, 194. 
 Pharynx (throat), 90, 164, 166.* 
 Phosphorus, 280. 
 Physiology, defined, 13. 
 Pia mater, 26. 
 Plasma, 146, 147, 149. 
 Pleura, 161, 162,* 163.* 
 Pneumonia, 308-309; germ of, 308.* 
 
 Poisoning, treatment for, 280-281. 
 
 Poisons, in cells, 120, 186, 287 ; in air, 178-179. 
 
 Pons, 213,* 216. 
 
 Portal circulation, 138,* 145 (n. i). 
 
 Posture, 60-73.* 
 
 Processes, bone, 38*; vocal, 172.* 
 
 Proteins, 83, 113, 124, 125, 153, 353. 
 
 Proteoses, 125. 
 
 Protoplasm, 4, n, 12, 13, 61 (n. i), 78, 84. 
 
 Protozoa, 285, 292-302.* 
 
 Ptyalin, 98, 112. 
 
 Pulmonary, artery, 138,* 141, 143*; veins, 
 
 138,* 142. 
 
 Pus-forming bacteria, 311-314.* 
 Pylorus, 90,* 93, 113. 
 
 Quarantine, 306. 
 Quinine, 256, 295, 296. 
 
 Rabies (hydrophobia), 299-300. 
 
 Reflex, centers, 217, 219; actions, 217-221,* 
 227. 
 
 Renal, artery, 186*; vein, 186*; cor- 
 puscles, 187,* 1 88.* 
 
 Respiration, 160-177*; organs of, 161-168*; 
 artificial, 274,* 275,* 276.* 
 
 Rest, 12, 73, 344. 
 
 Retina, 261,* 265,* 267,* 269. 
 
 Rheumatism, 313. 
 
 Ribs, 32,* 35,* 36. 
 
 Ringworm, 151.* 
 
 Sacrum, 34,* 35.* 
 
 Salivary glands, 25 (n. i), 89, 97,* 98.* 
 
 Scapula, 32,* 35,* 36, 38-* 
 
 Sclerotic coat of the eye, 261,* 266. 
 
 Sebaceous glands, 195.* 
 
 Semicircular canals, 254,* 255. 
 
 Sensations, 215, 245. 
 
 Senses, the special, 245-273. 
 
 Sensory nerves. See Afferent nerves. 
 
 Shoulder blade. See Scapula. 
 
 Skeleton, the human, 31-43*; principal 
 
 bones of, 33-37*; hygiene of, 53~57; of 
 
 other vertebrates, 5Q-53-* 
 Skin, the, 8,* 191-193,* 246*; and the 
 
 body heat, 191-208. 
 Skull, 32,* 33-* 
 Sleep, 183-184, 229-230. 
 Sleeping, outdoor, 184. 
 Sleeping sickness, 301. 
 Smallpox, 297-299.* 
 Smell, the sense of, 250-251.* 
 Sore eyes, 317.* 
 Spectacles, 268, 269,* 270. 
 Spinal column, 16,* 17, 31, 32,* 34,* 49, 
 
 54, 69, 71. 
 
INDEX 
 
 371 
 
 Spinal cord, 16, 17,* 24,* 25, 26,* 28, 217, 
 
 219, 225,* 226,* 227,* 228.* 
 Spinous processes, 38,* 70. 
 Spirilla, 304.* 
 
 Spleen, 17,* 1 8,* 88,* 138.* 
 Sprains, 55; treatment of, 56. 
 Sputum, 305, 326, 342. 
 Stapes (stirrup), 253.* 
 Starch, 82, in, 113, 116. 
 Steapsin, 98, 113. 
 Sternum (breast bone), 32,* 35.* 
 Stimuli, nerve (impulses), 211, 216. 
 Stomach, 7,* g, 17,* 18,* 88.* 90-93; of 
 
 ruminants, 105.* 
 Stramonium, 281. 
 Strychnin, 281. 
 Subcutaneous layer, 191,* IQ3- 
 Sugar, a carbohydrate, 82; digestion of, 
 
 in, 112, 113, 145 (n. i), 152-153. 
 Sunstroke, 278. 
 
 Suspensory ligament, 263, 266.* 
 Sweat glands, 25 (n. i), 89 (n i), 191,* 
 
 193,* 194, 198, 227. 
 Sympathetic nervous system, 23, 62, 226- 
 
 229-* 
 
 Tactile (touch) corpuscles, 246-247.* 
 
 Tapeworm, 131.* 
 
 Taste, 246, 249.* 
 
 Teeth, 89, 94-96*; in other animals, 103. 
 
 Temperature. See Heating. 
 
 Tendons, 63-65.* 
 
 Tetanus (lockjaw), 313*; toxin and anti- 
 toxin of, 314. 
 
 Thoracic (chest), cavity, 16,* 17, 162*; 
 duct, 152, 153. 
 
 Throat. See Pharynx. 
 
 Thyroid cartilage, 172.* 
 
 Tissues, 10, 59 (n. i). 
 
 Tobacco, effects of, 56, 74, 156-157, 172, 
 230-232,* 271-272. 
 
 Tongue, 97*; of other animals, 104.* 
 
 Tonsillitis, 165 (n. i). 
 
 Tonsils, 165. 
 
 Touch, 191,* 246-248.* 
 
 Toxins, 287, 293, 306, 307. 
 
 Trachea, 9,* 17,* 161, 163,* 165, 166.* 
 
 Trichina, 130.* 
 
 Trichinosis, 131. 
 
 Trypsin, 98, 113. 
 
 Tuberculosis, 240, 340-346.* 
 
 Tympanic membrane, 252,* 253.* 
 
 Tympanum (ear drum), 253. 
 
 Typhoid fever, 286, 315-316,* 324, 327, 328. 
 
 Urea, 116, 186, 187; alcohol and, 116. 
 Ureter, 186,* 187,* 188. 
 Uric acid, 114, 116, 150,* 186, 187. 
 Uvula (soft palate), 165, 166.* 
 
 Vaccination, against smallpox, 297-299: 
 pneumonia, 309; typhoid fever, 315. 
 
 Veins, 89,* 138,* 141-143,* 186*; bleeding 
 from, 277. 
 
 Venae cavae, 137,* 138,* 142,* 143.* 
 
 Ventilation, 178-185,* 358-360. 
 
 Ventral cavity, 16,* 17. 
 
 Ventricles, 137,* 140, 143.* 
 
 Vertebras, 34,* 38.* 
 
 Vertebrates, man one of, 18-20*; other, 50- 
 
 Villi, 93,* 94 (n. i), 151,* 152. 
 Vitamins, 85, 129, 352. 
 Vitreous humor, 261.* 
 Vocal cords, 165, 172-175.* 
 Voluntary muscles, 23, 61 (n. i), 62, 215. 
 
 Wastes, 7, 17, 114, 115,* 136, 149, 150.* 
 Water, chemical composition of, 81*; 
 
 function of, in body, 187, 191, 191 (n. 
 
 i); and disease germs, 286, 315, 327-330. 
 Whooping cough, 310. 
 
 Yeast, 238.* 
 
 Yellow fever, 301, 317. 
 
tninniiiiniiVHiirniiifiiniiitiiiiiiiiiiitiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiniiiiiiiiiimniiiiiiiiiiiiiiiiiiiiiiitiiiiiiiiiiiiiiinHniiin 
 
 NEW-WORLD SCIENCE SERIES 
 Edited by John W. Ritchie 
 
 EXERCISE AND REVIEW 
 BOOK IN BIOLOGY 
 
 By J. G. BLAISDELL 
 
 A Combined Laboratory Guide, Notebook 
 and Re-view Book for Students' Use 
 
 IN submitting the manuscript of this manual to the 
 publisher, the author wrote: 
 
 "As a teacher of biology, I have for several years felt the 
 need of a laboratory guide and notebook that would lighten the 
 labor and economize the time of both teacher and pupil in con- 
 nection with their laboratory work. In this age of cheap printing 
 it seems a needless waste of time and strength to compel teachers 
 to prepare laboratory outlines and to mimeograph or copy them 
 on the blackboard, and it ought to be possible to permit the 
 pupil, when he enters the laboratory, to begin work at once with 
 his laboratory directions, questions, needed outline drawings, and 
 space for his notes and sketches all on one neatly printed note- 
 book page. I have found the loose-leaf, blank-page, ring-cover 
 notebook, and separate laboratory directions method both waste- 
 ful of time and unsatisfactory in other respects, and have used 
 careful thought and my experience as a teacher in planning a 
 letter way." 
 
 Mr. Blaisdell has solved the problem with this book. His manual 
 bears '.he same relation to laboratory study as a well-ordered 
 text bears to the recitation, and cannot fail to conserve the time 
 of both teacher and pupil. 
 
 It contains 100 laboratory exercises, with space for more, cover- 
 ing a year's work in general biology, planned to meet the re- 
 quirements of the syllabus issued by the Regents of the Uni- 
 versity of the State of New York, and to accompany any high- 
 school text in general biology in common use. 
 
 Review exercises are provided, and a series of Regents' ques- 
 tions are so arranged as to give a review of the year's work. 
 
 viii + 152 pages. Price $1.20 
 
 WORLD BOOK COMPANY 
 
 YONKERS-ON-HUDSON, NEW YORK 
 2126 PRAIRIE AVENUE, CHICAGO 
 
IIIIIIIIII1IIMIIIII1IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIMIIIIIIIIIIIIIIIIIIIIIII 
 
 NEW-WORLD SCIENCE SERIES 
 
 Edited by John W. Ritchie 
 
 PERSONAL HYGIENE 
 AND HOME NURSING 
 
 A Practical Text for Girls and 
 Women for Home and School Use 
 
 By LOUISA C. LIPPITT, R. N. 
 
 Assistant Professor of Corrective Exercises, 
 University of Wisconsin 
 
 THE purpose of Miss Lippitt's book is to explain the 
 means by which girls and women may attain health 
 and happiness in the present and lay the foundations for 
 sane and vigorous lives in after years. In clearest terms 
 it lays down practical instructions for the conduct of their 
 daily lives. Not only are the rules set out, but the reasons 
 which underlie them are made clear. Directions are 
 given for preventing the spread of infection from cases 1 
 of communicable disease ; and instructions are furnished 
 for the care of one's self and one's family in cases of 
 accident or sickness. The author has desired to keep the f 
 book rather brief, and for this reason has introduced 
 only those topics on which women and girls seem par- | 
 ticularly to need instruction. 
 
 The text is* adapted for use as a beginner's book for 
 classes in hygiene and home nursing in high schools, 
 colleges and schools for nurses. 
 
 Cloth. Profusely illustrated. 
 
 vii -f 256 pages. Price $1.4.0 
 
 WORLD BOOK COMPANY 
 
 YONKERS-ON-HUDSON, NEW YORK 
 2126 PRAIRIE AVENUE, CHICAGO 
 
 IIIIIIIIIIIIIIIIIMIIIIIII Illllllllllllll Illllllll Illllllllll II MIMIIIIIIIIIII 
 
^iinmiimiiiiimiiimimiiiiiiiiiiniimiiimm 
 3 
 
 I HEALTH THROUGH > 
 PREVENTION &P CONTROL 
 OF DISEASES 
 
 By THOMAS D. WOOD, M.D. 
 
 and HUGH GRANT ROWELL, M.D. 
 
 Teachers College, Columbia University 
 
 /npHis book presents a definite, systematic plan or pro- 
 J. gram of prevention and control of contagious diseases 
 
 | in schools. The authors have had unusual opportunity to 
 
 | develop a system of health control in schools, and they 
 have combined their rich experience with that of other 
 workers in the field to produce a handbook for every one 
 concerned with health among school children. 
 The summing up in this compact book of the whole prob- 
 
 | lem of prevention of contagious diseases, makes available 
 in usable form material nowhere else accessible under one 
 cover. The various details of everyday procedure, of 
 health inspection, of application of preventive and cor- 
 
 | rective measures are given clearly and simply. Models of 
 the few necessary reports, requiring a minimum of clerical 
 work, are included. The plan and methods advocated 
 are based upon the latest scientific data; they have been | 
 tried out and have proved effective and necessary. 
 Everything has been included to make the book most 
 helpful to the teacher, while at the same time its scholarly 
 and important content makes it useful to the trained 
 specialist in school health work. It is a practical and 
 constructive book. Every teacher and school official, every 
 student preparing to teach, will find in it the information 
 
 | needed to control contagious diseases in schools and 
 promote the health of school children. 
 
 Cloth, vi+122 pages. Price $1.00 
 
 WORLD BOOK COMPANY 
 
 YONKERS-ON-HUDSON, NEW YORK 
 2126 PRAIRIE AVENUE, CHICAGO 
 
 ^llllllllllllltllllllllllllllllllllllllllllllllllMIIMIIIIIIMIIIIIIMIIIIIIIIIIIIIIIIIIIIIIIUIIillllllMIIIIIIMIIIIIIIMIIIIIUIIIIIIIMUUIMIMIIIIIIIIMIMIliT 
 
1 
 
 THE EARTH AND 
 ITS LIFE 
 
 By A. WADDINGHAM SEERS 
 
 THIS book contains a clear account of the origin of 
 our planet in the light of modern science. It recounts 
 the story of evolution, culminating in the origin of man, 
 and relates man's struggles against the animal world 
 with his eventual triumph, and his conquest of the earth 
 through the discovery of the means of locomotion. 
 
 Many facts and hypotheses in the fields of geology, 
 paleontology, botany, and ethnology are presented in a 
 clear, vivid, instructive way. The book covers the history 
 of the earth from the earliest days to the dawn of our 
 present civilization, and forms a useful introduction to 
 biology and anthropology. 
 
 The story is told simply and fascinatingly, and will appeal 
 strongly to old and young readers alike. It is as engross- 
 ing as any fairy tale, and at the same time makes a strong 
 appeal to the scientific spirit. 
 
 The subjects considered are not often dealt with in 
 elementary books, but are of great value from a cul- 
 tural as well as a scientific point of view. Children above 
 twelve years of age can not fail to derive from this vol- 
 ume a keen sense of the mystery and wonder of the world. 
 
 Cloth. Illustrated. Price $1.20 
 
 WORLD BOOK COMPANY 
 
 YONKERS-ON-HUDSON, NEW YORK 
 
 2126 PRAIRIE AVENUE, CHICAGO 
 
Head of the Science Department, State Normal College of 
 
 NEW- WORLD SCIENCE SERIES 
 Edited by John W. Ritchie 
 
 TREES, STARS and BIRDS I 
 
 A BOOK OF OUTDOOR SCIENCE 
 
 = 
 
 By EDWIN LINCOLN MOSELEY 
 
 e Department, State Normal ( 
 Northwestern Ohio 
 
 5 
 
 3 
 
 THE usefulness of nature study in the schools has been | 
 seriously limited by the lack of a suitable textbook. 1 
 It is to meet this need that Trees, Stars, and Birds is 
 issued. The author is one of the most successful teach- 
 ers of outdoor science in this country. He believes in 
 field excursions, and his text is designed to help teachers 
 and pupils in the inquiries that they will make for them- 
 selves. 
 
 The text deals with three phases of outdoor science that 
 have a perennial interest, and it will make the benefit 
 of the author's long and successful experience available 
 to younger teachers. 
 
 The first section deals with trees, and the discussion of 
 maples is typical: the student is reminded that he has 
 eaten maple sugar; there is an interesting account of its 
 production ; the fact is brought out that the sugar is really 
 made in the leaves. The stars and planets that all should 
 know are told about simply and clearly. The birds 
 commonly met with are considered, and their habits of 
 feeding and nesting are described. Pertinent questions 
 are scattered throughout each section. 
 
 The book is illustrated with 167 photographs, 69 draw- 
 ings, 9 star maps, and with 16 color plates of 58 birds, 
 from paintings by Louis Agassiz Fuertes. 
 
 It is well adapted for use in junior high schools, yet the 
 presentation is simple enough for pupils in the sixth grade. 
 
 Cloth, vtii + 404. + xvi pages. Price $1.80. 
 
 WORLD BOOK COMPANY 
 
 YONKERS-ON-HUDSON, NEW YORK 
 2126 PRAIRIE AVENUE, CHICAGO 
 
i BOOK TS 
 
V.B 65542 
 
 UNIVERSITY OF CALIFORNIA LIBRARY