May's anatomy, physiology, and hygiene; for use in primary and intermediate schools

Front matter

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Preface

In the following pages the author has endeavored to present, in as simple and clear a manner as possible, the most important facts relating to the anatomy, physiology, and hygiene of the human body.

Of late years physicians have laid great stress upon the study of the prevention of disease ; and, keeping pace with this improvement, the laity have become better informed about matters pertaining to the care of the body than formerly. The great utility of such knowledge has led to the enactment of laws in New York and other States making provision for the study of physiology and hygiene in the public schools, with special reference to the effects of stimulants and narcotics upon the human system. Such legislative provisions are very gratifying. Proper instruction to children on these subjects must do much to diminish the amount of sickness and raise the general standard of health.

The author has endeavored to use the simplest terms compatible with clearness.

The lessons will be made more interesting and valuable if illustrated by the various tissues obtainable at the butchers' ; thus, the heart of a calf will serve nicely to show the general shape and arrangement of cavities and valves in the human heart. In the same way other organs and tissues should be

IV PREFACE

utilized by the teacher to elucidate the various parts of the body. The skeleton and its different parts should be before the class in reciting upon the bones.

The synopsis given at the end of each chapter is intended to be of use in reviews and in guiding the teacher in a systematic presentation of the subject.

FOURTH EDITION.

In this edition the author has made a number of changes. The chapters on Alcoholic Drinks and Narcotics have been entirely rewritten, a new chapter on Physical Exercise introduced, and the whole work been remodelled.

S. E. J. 231 West Seventy-First Street, New York.

Contents

CHAPTEE I.

Introduction

The Vision of Mirzah and Its Allegorical Significance — The Bridge of Life— The Causes of Death — Anatomy and Physiology and Their Teachings— The Study of Hygiene— The Primary Constituents of our Bodies— Subdivisions of the Body— Its Different Parts — Their Gross Structure and Their Minute Structure — The Cells of the Body — The Anatomical Parts of the Body — The Head and Neck— The Trunk — The Upper Limbs— The Fingers — The Lower Limbs— Synopsis and Questions ... 13-22

CHAPTER n.

The Framework or Skeleton.

Position in the Higher Animals— Uses of Bone : Support, Protection, Strength, Motion— Number of Bones — Forms of Bones : Long, Short, Flat, Irregular — Structure of Bone : Surface, Interior, Periosteum, Spaces, Color — Composition of Bone — Variations in Composition in Early and in Advanced Life — Care of the Skeleton : Effects of Faulty Position, Tight Clothing, Improperly-shaped Shoes, Stimulants and Narcotics, Poor Health — Fracture of a Bone — Parts of the Skeleton : Head, Trunk, Upper and Lower Limbs — Bones of the Head : Cranium and Face — The Cranium : Frontal, Parietal, Occipital, Temporal, etc. ; Ragged Edges — The Face ; Orbits ; Nose ; Nasal and Malar Bones ; Upper and Lower Jaws — Mobility of the Skull — Bones of the Trunk — The Spinal Column ; Sacrum and Coccyx ; Canal for Spinal Cord v-The Pelvi3 — The Hip-Bon^— The CoUar-Bone— The Shoulder*

V

VI CONTEJN^TS.

Blade— The Breast^Bone— The Ribs: True, False, Floating— The Chest: Boundaries; the Diaphragm — The Bones of Upper Limb — The Humerus — The Bones of the Forearm; Radius, Ulna — The Bones of the Wrist and Hand : the Wrist, the Palm, the Fingers — The Bones of the Lower Limb— The Femur— The Patella — The Bones of the Leg : Tibia, Fibula — The Bones of the Foot : the Heel, Instep, Toes — Synopsis of Skeleton— Questions on the Skeleton 23 44

CHAPTEE III.

The Joints.

Definition — Uses — Subdivision — Immovable Joints — Sutures — Slightly-movable Joints : General Arrangement, Ligaments, Varieties : Gliding, Hinge, Pivot, Ball-and-Socket — Accidents to Joints — Synopsis of Joints — Questions on the Joints 45-o0

CHAPTER IV.

The Muscles and Motion.

Function of Muscles — Description of Muscle-tissue — Tendons — Fat — Uses of Fat : Warmth, Protection, Food, Appearance — Kinds of Muscle-tissue — Voluntary Muscles — Involuntary Muscles — Mixed Muscles — How Muscles Act — Influence of the Brain and Nerves — Ordinary Muscular Movements very Complex — Groups of Muscles — Facial Expressions — Number of Muscles — Shape of Muscles — Size of Muscles — A Few Important Muscles : Biceps, Triceps, Pectoralis, Diaphragm — Tendon of Achilles — The Care of Muscles — Exercise : Necessity, Amount, Kind, Proper and Improper— Effects of Alcohol and Tobacco on Muscles — Changes in Muscle by Use of Alcohol — Synopsis of Muscles and Motion— Questions on Muscles and Motion 51-65

CHAPTEK V.

Physical Exercise.

Value of Physical Exercise— Effect of Exercise on the Muscles— Effects of Muscular Over-exercise— Effect of Exercise on the Skin— Effect of

COJ^TENTS. Vll

Exercise on the Lungs — Effect of Exercise on the Heart — Effect of Exercise on the Appetite — When to Exercise and When Not to Exercise — Different Kinds of Exercise — Gymnasium — Home — Different Kinds of Apparatus — Effect of Alcohol and Tobacco on Athletes — Synopsis and Questions 66-77

OHAPTEK VI.

Food and Drink.

Necessity for Eood and Drink — Essential to Life — Difference in Food of Plants and of Animals— Difference in the Food of Different Animals — Carnivorous Animals — Herbivorous Animals — Different Kinds of Food Required by Man— Fleshy Food — Vegetable Food — Starch — Green Vegetables— Fat and Fatty Food — Water — Tea and Coffee — Necessity for Combination of all Forms of Food and Water — Some of the Simplest Forms of Food — Meat and Fish— Bread — Milk: Cream, Butter, Cheese — Eggs — Variety in Food — Proper Food — Methods of Cooking : Boiling, Stewing, Frying, Broiling, Roasting, Baking — Cautions Regarding Eating — Drinking- Water — Dangers of Well-water — How Poisoning Occurs — How Avoided — Advantages of Mixed Diet — Beverages : Tea, Coffee, Cocoa, Kola, Coca — Their Useful and their Harmful Properties — Synopsis of Food and Drink — Questions on Food and Drink 78-94

CHAPTER VII.

Alcoholic Drinks.

Definition— How Made— Fermentation— Alcohol— Alcoholic Appetite- Prevention of Fermentation— Fermentation in Bread-making— Cider —Wine— Champagne— Malt Liquors— Root Beer—Distilled Spirits— Cordials— General Effects of Alcoholic Drinks -Effect of Alcohol on Food— Summary of Diseases Caused by Alcohol— Alcoholic Drinks and Expectancy of Life — Moral Effects of Alcoholic Drinks — Money Spent in Alcoholic Drinks — Alcoholic Drinks and Crime — Synopsis and (Questions , , , , 95-109

VUl CONTENTS.

CHAPTER VIII.

The Blood and the Circulation — The Heart and the Blood-vessels.

Importance of the Blood — Appearance of the Blood, Color — Composition of the Blood : Eluid, Globules — Blood-globules ; Number — Microscope — Red Blood-globules — White Blood-globules — The Plasma — The Blood of Other Animals — Use of the Red Blood-globules— Use of the Plasma — Difference between the Blood in Arteries and the Blood in Veins — Clotting of the Blood — Value of the Clotting of Blood — The Circulation : How Seen in the Frog — The Heart — Situation of the Heart— Form of the Heart — The Pericardium — Cavities of the Heart, Grooves, Auricles, Ventricles — Function of the Heart — Frequency of the Heart-beats — Course of the Blood — Circulation through the Lungs — Changes in the Blood while Passing through the Lungs and through the System : The Aorta — Valves of the Heart — The Blood-vessels : Arteries, Veins, Capillaries — The Arteries — The Pulse — The Capillaries — The Veins : Differences between Veins and Arteries — Valves of the Veins — Rapidity of the Circulation of the Blood — Fainting : Its Treatment — Bleeding : Its Treatment, Hemorrhage — How to Have a Good Circulation — Exercise — Effects of Alcohol upon the Heart and the Circulation— Effect of Alcohol upon the Arteries ; Apoplexy— Effects of Tobacco upon the Heart and Circulation, "Tobacco Heart"— The Lymphatics, Difference between them and Arteries, Use, Course; Lacteals— Synopsis of the Blood and the Circulation, the Heart and the Blood-vessels— Questions on Chapter 110-137

CHAPTER IX.

Digestion.

Definition— The Various Organs of Digestion— Alimentary Canal— The Mouth— Teeth : Temporary, Permanent— Parts of Teeth— Structure of Teeth— Names of Teeth— Care of the Teeth— The Salivary Glands : Parotid, Sublingual, Submaxillary— Saliva— Effects of Chewing Gum —The Throat— The Tongue— The Gullet— The Stomach : Description, Pylorus, Coats — Gastric Juice — Gastric Tubules — Pepsin- Function of Gastric Juice— Uses of Stomach : Digestion, Storehouse, f'ulverizer— Stomachs in Certain J^ower Auim^ls— Igffect of Tobacco

CONTENTS. IX

on Stomach — Effect of Alcohol on Stomach — Discovery of How the Stomach Acts— '^ Heavy " and '^ Light" Food— The Bowels: Subdivisions, Pylorus, Duodenum, Small Intestine, Large Intestine, Attachment to Backbone, Coats — The Peritoneum— Motion of Intestines — Projections on Inner Surface of Intestines — The Work of the Intestines : Digestion — Starchy, Fatty, Fleshy Food — Openings into Small Intestines: From Pancreas, From Liver — The Liver and ' Gall bladder : Position, Description — Uses of the Liver : Bile, Purify Blood, Remove Impurities — Liver Cells — Bile — Action of Bile — Purification of Blood by Liver — The Liver as a Storehouse for Nourishment — The Unhealthy Liver : Gout — The Drunkard's Liver — The Pancreas : Pancreatic Juice — Uses of Pancreatic Juice — Absorption— Method of Absorption by Blood-vessels — Lacteals — Habits which are Injurious to " Proper Digestion : Eating too Quickly, Eating too Much, Eating too Many Sweets and Sours, Chewing Gum, Ice-water in Large Quantity, Violent Exercise after Meals, Severe Brain-work after Meals, Bathing after Meals, Excitement, Alcoholic Drink, Smoking — The Spleen : Description, Position, Use, Enlargement — Synopsis of Digestion — Questions on Digestion 138-164

CHAPTEK X.

The Organs of Voice and Breathing.

Definitions — Course of the Inspired Air — The Organ of Voice — The Larynx — Form and Situation — Parts of Larynx — Triangular and Circular Pieces — The Epiglottis — The Vocal Cords— Their Protection of the Windpipe — The Vocal Cords in Breathing — How Sounds are Produced — The Varieties of Vocal Sounds — Speaking — The Trachea or Windpipe — Situation and Form— The Air - passage and the Food-passage — Rings of the Windpipe — Branching of the Wind-pipe — The Bronchi — The Lungs — Division and Situation— Shape of the Lungs — Structure of the Lungs — Subdivision of the Bronchi — The Air-vesicles — The Pleura — Breathing is Involuntary — Movements of the Chest in Breathing — Mouth-breathing — Frequency of Breathing — Changes which Breathing Produces in the Blood and Tissues — Changes Produced in the Air by Breathing — The Poisonous Gases — Effects of Impure Air — Purification of the Air — How Plants Live and Grow — Ventilation — Simple Means of Ventilating — Absence of praughts — Necessity for Sunlight— Effect of Tight Clothing upou

CONTENTS.

Breathing — The Deformed Chest — Effects of Tobacco Smoke upon the Lungs and Throat— Synopsis of Organs of Voice and Respiration — Questions on Organs of Voice and Respiration 165-183

CHAPTER XI.

The Heat or the Body.

Our Body may be Compared to a Stove — Fuel — Combustion — Work, the Result of the Combustion of Fuel — Refuse, another Result of the Burning of Fuel — The Results of the Combustion of Food — Casting off the Refuse Materials from the Body — Food and Oxygen Produce Heat and Work — Warm-blooded and Cold-blooded Animals — Heat of the Human Body in Health — Heat of the Human Body at the Surface — Heat of the Body in Sickness — Regulation of the Bodily Heat — Warm Clothing -How to Keep Warm in Winter — How to Keep Cool in Summer — How the Body is Kept Cool in Summer — Effects of the Passage of Moisture into the Air — Perspiration — Ice-water in Summer — Sunstroke — Effects of Cold — Synopsis of the Heat of the Body — Questions on the Heat of the Body 184-194

CHAPTER XII.

Narcotics.

Narcotics — Effects of — Examples — Tobacco— Origin of Name — History of Tobacco — Cultivation of Tobacco — Preparation of Tobacco — Composition of Tobacco — Nicotine— Effects of Tobacco upon the System — The Tobacco Habit — Tobacco as a Medicine— Injurious Effects of Tobacco upon the Adult — Smokers' Sore Throat— Tobacco Heart — Tobacco Blindness — Tobacco Nervousness — Inj urious Effects of Tobacco on the Young — Influence of Tobacco upon Muscular Strength and the Power of Endurance — Cigarette Smoking— Other Objections to the Tobacco Habit — Smoking is an Expensive Habit — Opium and Morphine — Preparation of Opium — Physical Properties of Opium and Morphine — Opiates - Laudanum — Dover's Powder — Paregoric — Effects of Opium and Morphine — Opium and Morphine Poisoning — The Opium and Morphine Habit — Pangs of — Results of— Chloral or Chloral Hydrate — Appearance of — Uses of — The Chloral Habit —Effects of— Absinthe— Effects of— The Absinthe Habit— Hashish — Chlorofprm— Uses of— The Chloroform Habit 195-210

CONTENTS. 2a

CHAPTER XIII.

The Nervous System.

Parts of the System Already Described — Functions Existing in both Animals and Plants — Similarity in the Structure of Plants and Animals — — Absence of Nervous System in Plants — Most Perfect Nervous System in Man — Function of the Nervous System — Subdivisions of the Nervous System— Brain — Spinal Cord — Nerves — Examples of the Action of the Nervous System— Rapidity of Action of the Nervous System — Coverings of the Brain — Size and Weight of the Brain — Divisions of the Brain: Cerebrum, Cerebellum, Medulla — The Cerebrum — Gray and White Parts of the Cerebrum — The Cerebellum—The Medulla — The Cranial Nerves : Twelve Sets — Functions of the Brain — Mind, Will, Thought, Memory, Intelligence — The Work of the Brain — Reason and Judgment — Intelligence — Training the Brain — The Spinal Cord — Interior of the Spinal Cord — The Spinal Nerves — Kinds of Nerves : Sensation and Motion — Functions of the Spinal Cord — Reflex Action — Examples of Reflex Action — Sleep — Amount of Sleep — Sleep of Children—Uses of Sleep — Time for Sleep — Nervousness — Wakefulness — Effects of Alcohol upon the Nervous System — Delirium Tremens — Effects of Tobacco upon the Nervous System — Effects of Coffee and Tea upon the Nervous System — The Sympathetic System of Nerves — Synopsis of the Nervous System — Questions on the Neivous System 211-237

CHAPTER XIV.

The Senses.

Definition — Enumeration — Special Senses.

The Sense of Touch and the Skin — Thickness— Uses of the Skin — Protection — The Skin as the Organ of Sensation — Throwing Off Water, Salts, and Poisonous Matters — Regulating the Bodily Warmth — Structure of the Skin — Scarf-Skin — True Skin— Color of the Skin— Markings of Skin — Attachments of Skin — The Perspiration-tubes — The Pores — Perspiration — Sensible and Insensible Perspiration— Uses of the Perspiration — The Oil-tubes — The Hair — The Nails — Care of the Skin— The Results of Uncle anliness and Filth — Bathing — Warm

XU CONTENTS.

Baths — Cold Baths — Turkish and Russian Baths — Clothing — Exercise — Cosmetics — Care of the Hair— Care of the Nails— Synopsis of Sense of Touch aijd the Skin— Questions on the Sense of Touch and the Skin 238-250

The Nose and the Sense of Smell — Functions of Nose — Breathing Channel and Smelling Channel — Parts of the Nose — Nerves of Smell— Sense of Smell in Lower Animals — Cold in the Head — Use of Smell— Sweet Scents— Synopsis of Nose and Sense of Smell— Questions on Nose and Sense of Smell 250-254

The Tongue and the Sense of jTas^e— Structure of Tongue— Uses of Tongue —Uses of Sense of Taste— Abuse of Sense of Taste— Synopsis of Tongue and Sense of Taste— Questions on Tongues and Sense of Taste 254-257

The Eye and the Sense of Sight — Protections to the Eye— The Eyelids — The Eyebrows and Eyelashes— Parts of the Eye— Interior of the Eye — the Iris— The Muscles of the Eye— How we See— Resemblance of the Eye to the Photographer's- Camera— The Nerves of the Eye — Blindness— Images — The Tears — Care of the Eyes : Rest for the Eyes, Fine Print, Direction of the Light, Reading while Lying Down, Reading in the Cars, Contagious Eye Disease, Stooping in Reading — Weak Sight — Old Sight — Synopsis of Eye and Sense of Sight — Questions on the Eye and Sense of Sight 257-268

The Ear and the Sense of Hearing — Parts of the Ear — The Outer Ear — The Middle Ear— The Bones of the Ear— The Eustachian Tube— The Internal Ear — The Nerve of Hearing — Sound — How we Hear^Deaf Mutes— Cr.re of the Ear— Synopsis of the Ear and the Sense of Hearing — Questions on the Ear and the Sense of Hearing 268-274

Index 275

Chapter I. Introduction

Theee is a beautiful allegory upon human life, by Addison, called " The Vision of Mirzah." Mirzah, who had ascended the hills of Bagdad to spend a day in quiet meditation, says, " And behold as I sat there, I heard a sound as of sweet music, and looking up I saw a genius clad in shepherd's garments, who beckoned me and said, ' I have heard thy musings on the life of man,' and he commanded me to look eastward. I did so and beheld a great valley with a foaming tide rushing through it. Spanning it was a bridge, composed of threescore-and-ten arches, which, added to some broken ones near one end, made up the number to nearly one hundred. At either end was a thick mist. I turned to the genius in surprise. * "What does this mean ? ' I asked.

" Then he told me that the mist was the mist of eternity, and the bridge, the bridge of life. And as I looked I noticed many people passing over it, and also that there were numerous trap-doors in the bridge, more numerous at the ends than in the middle, which opened as they were stepped upon, and let the people fall through into the rushing tide beneath, which bore them quickly away into the mist. I noticed some of the people pushing others on trap-doors that they otherwise would not have trodden on, and also that many others were busy in the pursuit of bubbles which broke almost as soon as they grasped them. I noticed that very few got past the middle part of the bridge, though some did keep up a kind of hobbling march through the broken arches, though they looked tired and weary from the long walk."

This allegory is unfortunately true, and few people who are born into the world live past middle life, and such are apt to be less strong and well than in youth. Very many die when they are little children of diseases or accidents which are the trap-doors of the vision. Others are ''pushed through/* which means that they are killed in battle or starved by the greediness of others, or that they are led by their companions on the dangerous trap-door of drink, which every year opens for more people to drop through than are killed in all the battles all over the world.

The bubbles which many chase are riches and pleasure. But if one has not health to enjoy them they are of no value. In olden times people were always seeking for the Elixir of Life, which would make them live forever. They never found it. But to-day wise men realize that the nearest thing to the Elixir is knowledge — knowledge of how to make our bodies large and strong, how to prevent sickness, and how to live as long as possible.

We look with wonder upon some of the machines made by men, the steam-engine, the printing-press, or the telephone ; but the human body, with its power to move, to talk, to see, to hear, and to think, is far more complicated and wonderful than any machine ; and it requires something more than ordinary intelligence to keep it in perfect running order.

Pain is the signal to us that we must stop for repairs, but it is a poor engineer who waits until his engine breaks down before he puts it in order ; so it is an unwise man who overworks or over-indulges himself until sickness tells him he must stop. There is always some one part of the body that will give out first. One may have inherited some w^eakness of heart or lungs ; another may have from childhood overtaxed his stomach by rapid eating, while a third may have injured his eyes by late reading, and so toward middle life something begins to wear out, and coughs, indigestion, or headache give warning of danger. It is therefore well worth

INTRODUCTIOIT. 15

our while to learn how each of us can develop our bodies to their fullest possibility of physical and mental culture.

There can be no study more fascinating than the study of our bodies. We listen to the music of an organ that is made by blowing wdnd through long pipes, but we have in our own throats the '* organ" of speech which can make far more beautiful music, and a pair of lungs which act as bel- Iqws and which work of themselves day and night. What do they look like ?

We marvel that the fine hair- spring of a watch can keep it ticking for twenty-four hours, and yet we have a heart that will keep on beating for seventy years without winding up. How does it do it ?

But the most wonderful thing about man is his mind, which in some mysterious w^ay is connected with the soft gray brain inside his skull. With his mind he studies, he calculates, he loves, he does business, he plans for the future ; and yet if he treats his brain badly, as by exciting it with strong drink, the clear mind is lost and the man becomes like a beast of the field. What can one do to prevent this?

The three combined studies of Anatomy, Physiology, Hygiene, will teach us everything we want to know about our bodies.

Anatomy is the study of the form and structure of the different parts of the body. It teaches us the size and shape of the bones, the kinds of muscles that move them, as well as the shape and position of the various Organs of the body. An Organ is some part, like the heart or stomach, which has some special work to do. This work is called its Function.

Physiology is the study of how we live. It explains how the lungs breathe, how the blood circulates, and how the stomach digests its food ; in short, what is the special function of each organ.

Hygiene, so-called after Hygeia, the goddess of health, is the science that teaches us how to keep all the organs of the

16 AINTATOMY, THYSIOLOGY, AKD HYGIENE.

body performing ttieir functions; in other words, how to| keep well.

Before we begin to study our bodies let us see where we | stand in the universe. Man is called the lord of creation, because he is the noblest work of the Creator ; he is the highest I of all animals, and yet he is very closely related to some of the lowest forms of life, and is wholly dependent on all the | animal and vegetable life around him.

For instance, there is a little animal, so small that it cannot be seen without a microscope. It is called Amoeba. It lives in stagnant water, and sometimes strays into our drinking-water, without doing it any harm. This amoeba is a soft, shapeless mass of pulp, called protoplasm, without any skin to hold it in shape. It is the lowest kind of animal that lives ; it has no mouth, no stomach ; it simply absorbs water, and rolls itself around little particles of food. It can divide in half and become two amoebae. The amoeba and man stand at the opposite extremes of the animal kingdom, and yet man has in his body countless cells that look and act almost exactly like the amoeba. In fact, man is largely made of different kinds of minute cells.

A cell is a bit of protoplasm surrounded by a covering or wall, and containing a body in the middle which is called the nucleus. Every living cell has, or has had the power to divide and make two new cells. This is the secret of life. It is the cause of all growth in animals and plants, and the thing that makes them different from the stones and water of the mineral kingdom.

To get the idea of a cell, think of a grape, with its soft pulp, like protoplasm ; its thin skin, like the wall, and its cluster of stones in the centre, like the nucleus. There are many kinds of cells in the body, some are long fibres, like threads, such as the nerves ; others are flat, like scales, as in the skin. The cells in the bones have hard walls, and those of the blood, which are called corpuscles, are like the amoeba, without any mTEODtJCTION. 17

walls at all. Each cell has its own term of life, and its own duties ; those in the liver secrete bile, those in the muscles produce motion. As soon as they have lived their day, they are seized upon as waste matter, and hurried away and cast out of the body, while new ones are formed to take their places.

Thus we see that the health of our bodies depends on the nourishment and health of each separate cell. If we burn our hands some of the cells are destroyed, and those lying near go to work to form new cellular tissue to take their place. If we eat too much candy the liver becomes overloaded with sweet and does not properly purify the blood, and the impurities work through the skin in the form of blotches and pimples.

The cells of the body are constantly demanding food, but all they want is a few mineral substances such as salt and lime to make the bones hard, iron to give vigor to the blood, and four elements. Carbon, Hydrogen, Oxygen, and Nitrogen. Carbon is like the soot that a flame gives off. Oxygen is that part of the air that gives us life. Hydrogen and Oxygen together make water, and Nitrogen is the gas that dilutes the Oxygen in the air. If we were the only living things in the universe we could not get at these foods, for our bodies are not made to take them in their pure form.

Plants, however, can absorb them from the water and air and soil ; they turn them into starch and sugar and other foods and store them up in their cells. Animals eat the plants, and make these four elements over into fat and muscle. When we eat vegetables and meat we are giving our cells the same Carbon, Ox^^gen, Hydrogen, and Nitrogen that has been worked over into food for the plants and animals.

But not all plants or animals are helpful to man. The savages fear wild animals and certain plants, with which their enemies poison their arrow-tips, so that a dart causes death ; but civilized man has discovered in the last fifty years a class

18 ANATOMY, PHrSIOLOay, AND HYGIENE.

of very minute plants and animals, which are the cause of a great many diseases, as well as of much benefit to man.

These are generally called germs, though the term bacteria may be applied to most of them. The bacteria are infinitesimal one-celled plants that divide to form new ones, and that increase by the thousands and millions. There are as many kinds as there is variety in the results they produce. One kind, growing in cheese, gives it its flavor ; another kind growing in milk makes it sour. Some grow on meat and cause it to decay. Some grow in our bodies, when they can find a lodgement, and make us ill. Diphtheria, consumption, cholera, and many other diseases are caused by bacteria which attack the cells and infuse poisons into the blood.

The life of man is thus an endless struggle of cells against cells. If the cells that make up his body get sufficient food so that they can grow and form new ones, then his body grows and thrives ; but if they do not get enough food, many of them perish, and his body becomes pale and thin and sick.

In the study of Anatomy, Physiology, and Hygiene, there will be many technical names to remember, and many scientific facts to learn ; but the successful students will not be those who merely get high per cents in their recitations, but those who by learning to take care of their bodies are able to walk with firm steps over many arches of the bridge of life.