Physiology of man and other animals

Front matter

m\

Class j Q p 3 3 Book Ml Copyright^!

COPTOIGHT DEPOSIT.

Chapter I Page

Organisms composed of living substance — Appearance of living substance — Meaning of the word cell — Importance of the cell — Irritability — Assimilation — Reproduction — Universal characteristics — Non-living matter in a living cell — Starch in the potato — Starch used for food — A question simplified — Matter — Heat — Diffusion — Osmosis — The question answered — Chemical action — Combustion — Characteristics of hydrogen, carbon dioxide, oxygen — Heat and chemical action — Manufacture of starch — Transfer of starch — Purification of air — Air, its composition and pressure — Summary 7

Chapter II

A universal process — The process defined — Necessary conditions — The law of gases — Passage of a gas through a membrane — Influence of pressure on rate of passage — Establishment of an equilibrium — Independent behavior of gases — Application to respiration — Free oxygen — Equilibrium of nitrogen — Respiration in specific animals — Lower animals — Higher animals — Respiratory organs in aquatic animals — Relation between the blood and the gill membrane — Situation of the moist membrane — Respiratory organs in land animals — Mechanism for bringing

ix x CONTENTS

PAGE

air in contact with the membrane — Respiratory muscles — Inspiration — Expiration — Effect of the elasticity of the lungs on the diaphragm — Phraseology — Hygiene of respiration — Summary 23

Chapter III

Steps in the process — Nature of the process — In one-celled animals — In many-celled animals — The complete digestive tract — Variations in development — Diet of animals — The five food substances — Water — Salts — Carbohydrates — Hydro-carbons — Proteids — Necessary proportions of food substances — Nutriment in foodstuffs — Digestion — Enzymes — Enzymes in the digestive juices — Reversible action of enzymes — Enzymes in the tissues — Passage of food through the canal — Absorption in the intestine — Excretory organs — The kidneys — Urea — The sweat glands — Hygiene of digestion — Summary 45

Chapter IV

Necessity for circulation — The system — In lower animals — In higher animals — Mechanical factors which control the circulation, 1 ) The heart, 2 ) The valves, 3 ) The closed system, 4) Elasticity, 5) Tone — Composition of the blood — The red corpuscles — Relation between ogyxen and hemoglobin — Oxygen can not establish an equilibrium — Origin and fate of the corpuscles — The white corpuscles — Coagulation — The serum — The lymph — The lymphatics — Vaso-motor nerves — Relation to the body temperature — Interference with the vaso-motor mechanism — Effect of alcohol on body temperature — Adaptation of the circulation to bodily need — Summary 67

Chapter V Eepeoduction

Origin of living matter unexplained — Reproduction — In one-celled animals — In many-celled animals — Restricted to

CONTENTS xi

PACK

Bpecial oells — Reproductive cells of the sea-urchin — Attraction of the sexual cells — Division of the fertilized egg — Differentiation of cells — The process universal — Protection of the cells in hunt animals — Sexual reproduction

of plants — Summary 87

Chapter VI

Protoplasmic motion — Ciliary motion — Muscular contraction — Theory of muscular contraction — Stimuli — Rhythmical contraction — Influence of the structure of muscles — Influence of arrangement of muscles — The function of a skeleton — The skeleton external in lower animals — Internal in higher animals — The structure of bones — The spinal column — The shoulder girdle — The pelvic girdle — The ribs — Appendages — Joints — Relation of muscles to bones — Relation of nerves to muscles — Structure of the nervous system — The work of nerves — The value of the nerves — Sense organs — Sympathetic system — Exercise — Effect of alcohol on the nervous system — Summary 99

Chapter VII

Habitat — The ameba — More highly specialized forms — Food substances — Wastes — Respiration — Reproduction — S u m - mary 128

Chapter VIII Ccelenterata

Many-celled animals — The primary layers — Tissues of the coelenterata — Distinguishing characteristics — Assimilaxii CONTENTS

PAGE

tion — Irritability — Fixed forms — Nervous system — Colonial forms — Reproduction — Alternation of generations — Summary 135

Chapter IX Echinodermata

Characteristics — T h e starfish — Symmetry — Internal structure — Irritability — Mechanics of locomotion — Assimilation — Reproduction — Regeneration — Summary 147

Chapter X Mollusca

Shells — The living animal — Formation of the shell — The Clam — Gills — Circulatory system — Alimentary canal — Nervous system — Economic value — Characteristics of the group.. 154

Chapter XI

Irritability of the earthworm — Mechanics of locomotion — Surface characteristics — Assimilation — Increase of digestive surface — Circulatory system — A segment — Excretory organs — The nervous system — Reproduction — Classification — Flat worms — Round worms — Segmented worms — Molluscoidea 162

Chapter XII Arthropoda

External characteristics — Nervous system — Digestive system — Respiratory system — Excretory system — Circulatory system — S e n s e organs — Reproduction — Appendages — Classification — Crustacea — Locomotion of the lobster — External characteristics — Moulting of the shell — Digestive system — Other organs — Respiration — Reproduction — Segmentation — Acerata — Myriapoda — Insecta 173

CONTENTS xiii

Chapter XIII Verterrata

PAGE

Irritability — Assimilation — Respiration — Reproduction — General characteristics — Classification 185

Chapter XIV Plants

Irritability — Assimilation — Reproduction 189

Review Questions 201

Index 205

INTEODUCTION

Physiology is a study of activity. It deals with the activity by which a living plant or animal manifests the fact that it is alive, and the activity of the various parts of its body which do the work required to keep it alive.

Physiology is related to anatomy in very much the same way that the work that a machine is capable of doing is related to its structure. When we study the anatomy of an animal we study the structure of its body, and we may do this through dissection after it has been killed. But when we study physiology we study the manifestation of life, the curious incomprehensible thing which marks the infinite, possibly the infinitesimal, difference between inert matter and a sensitive organism.

It has been customary to devote a large amount of space in text-books of human physiology to a consideration of anatomy. Structure and function have been presented together and causal relations have been established between them. This has led to confusion of thought. Structure has come to be regarded by young students as the underlying cause of function ; and characteristics common to all animals as peculiar to human beings. This is fundamentally wrong. Structure can not initiate activity. It can only control or modify it. Although the activity of living organisms may be regu-

2 INTRODUCTION

latecl by their structure, it is dependent primarily on living matter itself. The functions of human beings are therefore not unique. They are but highly developed characteristics common to all animals.

We do not tat and breathe because we have a certain number of bones and a definite arrangement of muscles, though the manner of eating and breathing may be influenced by this arrangement. We might as well expect a steam engine to go because it has a certain number of wheels and pistons. These may determine the manner of its going, but without the steam it remains still. A dead man has the same gross anatomy as a living man. If anatomy were a determining cause of activity the functions of the body would not stop when death occurs.

Exactly what the difference between living and dead matter may be we do not know, but we do know the way in which living matter manifests the fact that it is alive ; and we know that wherever it is found, in the simplest animal or in the most complex, these manifestations are the same. The point of departure in the study of physiology should therefore be the activity of the living substance. In studying this activity and the causes that control it we find that physiology is related to physics and chemistry and that this relation is more vital than its relation to anatomy. Through physics and chemistry we may explain the activity of living matter; through anatomy we explain nothing but accidental modifications of its activity.

The human body, though the most complex and wonderfully efficient machine in existence, has in common with the simplest animals and plants only the functions

INTRODUCTION 3

that belong to living matter. Every organism assimilates food, substances circulate through all parts of its body, it breathes, it moves and it is able to produce its kind. These are the functions that we are to study. To explain their simple universal features we must have recourse to the principles of physics and chemistry. No adequate explanation can be made of any process without a knowledge of these principles, for in all purely physical operations the animal obeys certain natural laws, usually without knowledge on its part, of what it is doing and certainly without volition. But as the peculiar way in which the functions manifest themselves is dependent upon structure, to explain the manner of their occurrence in any particular animal we must have recourse to anatomy.

PAET I

Chapter I

Organisms Composed of Living Substance. — Every organism is composed mainly of living substance. Its characteristics, functions and powers are dependent on the nature of the living substance. If then we are to understand the physiology of any plant or any animal we must know something about this substance. We must study it, not in its most highly developed form, as it appears, for instance, in the muscles and nerves of human beings, but in its simplest state. We shall then find out what the characteristics are that distinguish it from everything else. These characteristics are few and always the same. They may become more complex as the result of some special development, but no matter how highly developed this substance may be, it can not take on new powers, it can only develop and modify those that belong to it simply because it is alive.

Appearance of Living Substance. — If we scrape a few hairs from the stamen of such a flower as the wandering jew and examine them with a compound microscope we can see what this substance looks like. Each hair is made up of a series of compartments which appear more or less transparent (Fig. 1, A). Within the transparent space in each compartment a shadowy, granular

M

U if fcMM mmmwmM

Fig. 1.— -4, a hair from the stamens of spiderwort ; i?, a single cell enlarged. The circulation of the protoplasm is indicated by the arrows; n, nucleus. (From Sedgwick and Wilson.)

substance slowly streams about (Fig. 1, B). This granular substance is the living substance, or protoplasm, as it is usually called. The most remarkable thing that we notice about it, is- that it moves apparently without

LIVING MATTEE 9

anything to make it move. The streams of protoplasm seem to flow from a spot of thickened protoplasm called the nucleus. This spot is always a center of activity. The transparent space around the protoplasm is called the vacuole; the enclosing wall, the cell-wall; and the entire structure, the cell.

Meaning of the word Cell. — The name cell was given to the structure when microscopes were very poor. Investigators saw only the w r alls and attached undue importance to them. The name now refers not to the walls but to the living substance which w 7 e know to be infinitely more important. A cell is a little mass of protoplasm which contains a nucleus. It may, or may not, be surrounded by a definite wall, and it may, or may not, contain other things.

Importance of the Cell. — A simple cell, or protoplasm in its simplest form, is the starting point of every plant and every animal. Some plants and animals never get beyond the starting point ; that is, they remain all their lives in the one-celled stage. Such single cells are able to do everything necessary to the life of an independent organism. By studying these one-celled forms, then, it is possible to discover the wonderful powers that characterize living substance and all living organisms.

Irritability. — If a drop of stagnant water is placed on a glass slide and examined with a compound microscope, minute, one-celled, transparent animals may be seen moving swiftly across the field. If one of them is quiet long enough, we may see in its body what we have already seen in the hair cell. The protoplasm is moving. But as we look, the animal scurries away.

This independent movement from place to place is merely a mechanical response to some form of motion within the cell. On the surface of some of these animals are tiny, hair-like projections called cilia (Fig. 2). The protoplasm inside moves in such a way that the cilia wave to and fro ; the animal then moves through the water like a boat propelled by oars. Still others have a tail-like projection which becomes fastened to something in the water (Fig. 3). Within the tail is a thread of protoplasm attached alternately first on one side

Fig. 2. — Paramecium

showing cilia. (From and then on the other. Ihis thread McMurrich.) contracts and the animal is pulled

away from anything that may happen

to touch it. Movement in response

to an outside stimulus, or irritation,

is called irritability.

Assimilation. — Another thing that

attracts the attention as we watch

these animals in the drop of water, is

that some are larger than others of

the same kind, just as cats are larger

than kittens, and men are larger than

boys. We may infer from this difference in size that they have the

power of growth, or the .power to

add new protoplasm to their bodies, and that in order to

get the materials for the manufacture of protoplasm,

Fig. 3.— Vorticella showing stalk of contractile protoplasm. (From McMurrich.)

LIVING MATTEE 11

they must take in fond. [f we watch patiently we

may see them eat. They do this in a primitive way. They simply engulf another organism smaller than themselves. The parts of this organism which are unfit for the building up of new protoplasm they eject from their bodies. The nutritious material they retain and manufacture into protoplasm. This process is called assimilation.

Reproduction. — If we continue to watch, we may notice that when one of these animals has attained its full growth it splits into two small ones. (Fig. 4).

jNtir ] ^§mh fy

Fig. 4.— Ameba dividing by fission. (From Sedgwick and Wilson, after Leidy.)

Each of these assimilates food, grows to maturity and in turn divides. The number of animals is thus rapidly increased. This is the simplest form of reproduction.

Universal Characteristics. — Irritability, assimilation, and reproduction are universal characteristics of living matter and of all organisms composed of it. The study then of any organism means the study of the specific way in which these characteristics manifest themselves.

Non-Living Matter in a Living Cell. — Suppose we look at a cell which differs from those we have seen in

Fig. 5.— A section of potato showing starch grains within the cells.

that it contains other substances besides the living substance. Such a cell may be obtained by cutting a very thin section of a potato. (Fig. 5). When we look at

the section with the compound microscope we see two things ; the walls of a series of irregular boxes, and enclosed by them a great many transparent globules.

Starch in the Potato.

— What are these globules ? Doubtless in the beginning chemists tried many tests before they found out, but now that we know the test to apply, it is a very simple matter to prove that the globules are made of starch. Iodine stains brown whatever it touches except starch and this it stains blue. We may test this by putting a few drops on a lump of starch and on something which we know contains no starch. If we put a drop of iodine on the potato cell the protoplasm and the cell walls turn brown and the globules turn blue. The globules are therefore made of starch. After this we will refer to them as starch grains.

Starch Used for Food. — What are the starch grains in the potato for ? The starch is made and stored for the sake of furnishing the living substance of the potato with something with which it can repair wear and tear. It is one of the substances out of which new protoplasm is made.-

LIVING HATTER 13

A Question Simplified. — If we understand how the starch grains are made and how they get into the cells of the potato it will simplify the attempt to explain similar processes in the human body. Starch is manufactured inside the plant of water and carbon dioxide. The water enters the plant through its roots, the carbon dioxide through its leaves. How? We may consider the root and the leaf as more or less hollow structures covered with a thin, moist membrane. The membrane is a solid, the water is a liquid, and the carbon dioxide is a gas. How do a gas and a liquid pass through a solid ? In order to explain this, we must know something about the nature of a gas, a liquid, and a solid.

Matter. — Every substance, everything in the world that can be called matter, is made of very tiny particles. These little particles are constantly rotating, or vibrating very rapidly, and they have more or less power to move away from each other.

If they move very slightly so that they do not change their relative positions, the substance has a definite shape and a definite volume and we call it a solid. If they move freely but not entirely away from each other the substance has a definite volume but no definite shape and we call it a liquid. If their motion is unrestricted so that they may fly entirely away from each other the substance has neither definite shape nor definite volume and we call it a gas.

Heat. — The word heat means rapidity of vibration. In response to heat a substance may change from a solid to a liquid, or from a liquid to a gas. As it grows hot its particles move more rapidly and push farther and farther apart. They do not change in size or in number but the spaces between them become larger and the substance occupies more space than it did before. (Fig. 6).

A B

Fig. 6.— A diagram illustrating expansion. A bit of matter, A, before ; B, after the application of heat. The particles have not changed, but as they are farther apart they occupy more space.

When butter melts, it expands until it becomes a liquid. When water evaporates, it expands until it becomes a gas. In both cases the increased motion of the particles represents an increase in heat, and the increase is the same whether the process takes place quickly or slowly. The increase of heat, or motion, on the part of one substance means a corresponding loss of heat, or motion, on the part of some other substance, thus there can be no evaporation unless something is cooled in the process. If a hot substance is brought in contact with a cold substance, the more rapidly moving particles transfer their motion to the more slowly moving ones as a bat does to a ball, and as the one substance grows warmer the other grows colder until the temperature of both is the same. If a substance evaporates from the surface of the body, it takes heat from the body in so doing and we feel cooler.

Diffusion. — Water apparently disappears when it evaporates. When 1 does it go? As it becomes a gas, the particles on the surface move away from their fellows and pass into the nearest space that is open to receive them. If the water is in contact with air, this space is between the particles of the air. (Fig. 7, A). The air

B

Fig. 7.— A diagram illustrating diffusion. Two substances in contact, A, before; B, after diffusion has begun.

particles are also moving rapidly and they pass into the spaces between the particles of the water. (Fig. 7, B). The particles of each substance then continue to move from space to space in the other until each holds as much of the other as it can, or until one of them is entirely taken up by the other. This process is called diffusion.

Osmosis. — If the water were separated from the air by a moist membrane, diffusion would take place through the membrane. As the membrane is a solid, its particles do not move away from each other, but through the spaces between them the particles of air and of water pass to the other side and the two substances become intermingled. (Fig. 8). This process is called osmosis.

The Question Answered. — Through the process of osmosis a liquid or a gas can pass through such a solid as a moist membrane. A cell-wall is a moist membrane. If the particles of a liquid or a gas come in contact with it they pass into the spaces between the particles of the

A B

Fig. 8.— A diagram illustrating osmosis. Two substances separated by a membrane, A, before ; B, after osmosis has begun.

cell-wall and get through to the other side. In this way water and carbon dioxide pass into the root and leaf, starch into the potato cell, and substances pass from cell to cell in the bodies of organisms.

Chemical Action. — How are starch grains made? Water and carbon dioxide enter the plant by a physical process which involves no change in their nature. In the plant they are manufactured into starch, an absolutely different substance. This is done by a chemical process. In chemical action two or more simple substances unite to form a complex substance, or a complex substance splits into the simple substances of which it is composed.

Combustion. — Carbon dioxide is a colorless gas, and as its name indicates it is made of two substances, carbon and oxygen. Oxygen is a colorless gas and as far as appearance goes it is not to be distinguished from carbon dioxide. Carbon is a black solid best known in the form of charcoal.

When oxygen unites with a substance, the substance is said to burn. When wood burns oxygen from the air unites with two substances in the wood, carbon and hydrogen, a colorless gas. The union of oxygen with carbon produces carbon dioxide; with hydrogen, water. The substances in wood that do not unite with oxygen are left unburned in the form of ashes.

When a substance burns its weight is increased by the weight of the oxygen that unites with it. It may be hard to realize that an invisible gas has weight and that a thing weighs more after it is burned than before, but the fact is easily proved. When magnesium wire is burned, the resulting product is a white powder called magnesium oxide. The weight of the powder is greater than that of the original piece of wire by the amount of oxygen which has united with it.

Characteristics of Hydrogen, Carbon Dioxide, Oxygen. — If a burning splinter is thrust successively into three jars containing hydrogen, carbon dioxide and oxygen its behavior in the three cases is markedly different. In the jar of hydrogen, it goes out, but the hydrogen itself begins to burn at the mouth of the jar with a blue flame. The heat of the burning splinter raises the hydrogen to the kindling temperature and it unites with oxygen from the air. The water that is formed appears in drops on the side of the jar.

In the jar of oxygen the splinter burns for a moment much more freely than it does in the air; then it goes out. In the carbon dioxide, it instantly goes out.

If a small amount of clear lime water, which is a test for carbon dioxide, is now put into these two jars, it turns milky in both, showing that in the one case oxygen united with carbon from the splinter to form carbon dioxide, and that in the other the carbon dioxide was unchanged. Carbon dioxide does not burn because it can not hold any more oxygen; it does not allow anything to burn in it because it will not allow the oxygen w T hich it holds to unite with anything else. It is therefore inactive.

Oxygen is very active. It burns, or unites with, almost everything with which it comes in contact if the temperature is raised to the kindling point. Even iron burns in it, forming iron oxide or rust.

Heat and Chemical Action. — There is a very close relation between heat and chemical action. We use a burning match to light the fire because heat is necessary to bring about chemical action, and we sit near the fire to get warm because chemical action gives rise to an increase in heat. Heat, then, becomes an evidence that a chemical action which may be invisible is taking place. Heat will be given off whether the action takes place quickly or slowly, but if the action takes place slowly, as in the rotting of wood, or in the rusting of iron, it is not evident to the senses.

Manufacture of Starch. — When starch is made, six parts of carbon dioxide and six parts of water unite chemically to form one part of starch. Twelve parts of oxygen are left over. (6CO 2 +6H 2 O=C 6 H 12 O 6 +120). The process takes place in the leaf in the presence of sunlight, through the activity of chlorophyll^ the sub-

LIVI.NC MATTER stance which gives plants their greeD color. If green water plants are placed in a jar of water in the sunlight, hubbies of gas may be seen passing away from them. If this gas is caught in a test tube and touched with a lighted splinter Its behavior proves at once that it is oxygen. Its presence is a sign that the plant is rapidly making starch. (Fig. 9).

Transfer of Starch. — As starch is a solid that does not dissolve in water it cannot pass out of the leaf where it is made until it is changed to a soluble form. Through the activity of certain complex substances (see enzymes) which w T ill be described later it becomes converted into sugar. In this form it passes into the sap, which carries it throughout the plant. When the sugar reaches the potato the complex substances reverse their action and turn the sugar into starch, in which form it is stored for future use. Though there is an obvious advantage to the plant in this transformation it takes place not for this reason but as a result of chemical activity.

Purification of Air. — The work that plants do in keeping alive is of inestimable benefit to man. In making

Fig. 9.— Alga giving off oxygen. (After Bailey.)

starch they not only provide him with a large proportion of his food, but by taking in carbon dioxide and giving off oxygen, they purify the air, so that it is fit for him to breathe.

Air, its Composition and Pressure. — Air is a physical mixture, not a chemical compound. When pure, it is composed largely of two gases, oxygen and nitrogen, with small traces of water vapor and carbon dioxide. Besides furnishing gases that living organisms need, it affects them in many other ways, chiefly through its weight, which is enormous. It presses upon all sides of us in every direction with a force of fifteen pounds for every square inch of surface. This force represents the weight of a column of air with a base of one square inch stretching from the earth to the limit of the atmosphere. One would think this weight enough to crush a delicate little organism, but the external pressure is so nicely adjusted to the pressure within the body that it does no harm, and it regulates many functions. In the hair cell the streams of protoplasm are separated by large, transparent spaces which seem empty. They are, however, filled with a transparent liquid which by pressing back upon the wall with a force of fifteen pounds to the square inch neutralizes the air pressure, which would otherwise crush out the spaces and prevent their existence. This liquid is sap, or water containing dissolved substances, one of which is sugar.

Summary. — Every organism has a definite cellular structure, that is, it is made up of one or more cells, or little masses of protoplasm, each of which contains a nucleus and is surrounded by a cell-wall. It is further distinguished by physiological qualities dependent upon the peculiar characteristics of the protoplasm, or living substance of which it is composed.

This substance is distinguished from non-living substances by three qualities: irritability, or the power to move ; assimilation, or the power to use food substances ; and reproduction, or the power to form new protoplasm. These qualities of living matter are responsible for the behavior of organisms as independent beings.

Living matter responds to a stimulus with some form of motion. This motion may take the form of a circulation within the cell, or of a contraction. If the contractions are organized they will result mechanically in a movement of the whole, or of some part, of the independent organism from place to place. Food substances are used by independent organisms in such a way that new protoplasm is formed, endowed with the power of becoming differentiated into the specific tissues of a specific organism. Food that a sheep eats is never transformed into the muscles of a fish. Reproduction of independent organisms involves the formation of a cell endowed with the power to become a new individual like the parent.