THE CHILDREN’S LIBRARY

NATURAL WONDERS

The Robin Moth

THE CHILDREN’S LIBRARY

NATURAL WONDERS

By
EDWIN TENNEY BREWSTER

Garden City — New York
DOUBLEDAY, DORAN & COMPANY, INC.
1928

COPYRIGHT, 1912 BY DOUBLEDAY, PAGE & COMPANY.
ALL RIGHTS RESERVED.
PRINTED IN THE UNITED STATES AT
THE COUNTRY LIFE PRESS, GARDEN CITY, N. Y.

PREFACE

No small part of our fundamental knowledge concerning the world of nature has been put into shape for comprehension by children, time out of mind. “The Swiss Family Robinson” is half natural history, even if not always of an especially convincing kind; and science of all sorts, good and bad together, makes up no small portion of Jules Verne’s uncounted tales. “Cousin Cramchild’s Conversations,” if there had been such a book, would have embodied the Victorian idea of what every child should know about his universe; while of actual books, we elders recall at once Abbott’s “Science for the Young,” and the half dozen contributions to juvenile knowledge of John Trowbridge and “Arabella Buckley.” Even the great Ostwald, within the decade, has made a child’s book on chemistry after the old conversational form.

In school, moreover, between his geography and his nature study, the modern child becomes acquainted with not a little modern science, while in most of our states a detailed acquaintance, by no means always scientific, with his own physiology is required by law of every public school pupil. One thing with another, today’s child of eight or ten is supposed to know a little of physics and of biology, together with a good deal in a general way of earth science and the elements of human physiology.

Naturally, there are excellent texts and reading books in all these fields. So far as I am aware, however, the present work is the first attempt to set before young readers some knowledge of certain loosely related but very modern topics, commonly grouped together under the name, General Physiology. It is, in short, an attempt to lead children of eight or ten, first to ask and then to answer, the question: What have I in common with other living things, and how do I differ from them? Incidentally, in addition, I have attempted to provide a foundation on which a perplexed but serious-minded parent can himself base an answer to several puzzling questions which all children ask—most especially to that most difficult of them all: By what process of becoming did I myself finally appear in this world?

How far I have succeeded with either task, I leave to the mothers who shall read this book aloud.

E. T. B.

Andover, Massachusetts

NATURAL WONDERS

CONTENTS

ILLUSTRATIONS

Frontispiece

[The Robin Moth]

Full Page Illustrations

[How the Chicken Gets Inside the Egg]

[Seeds That Have Plumes and Wings]

[The Star-fish Has Eyes on His Arms; The Slug Also Has Eyes on His Horns; The Snail Has Eyes on His Two Longer Horns]

[Lymph Cells or White Blood Corpuscles]

[Extinct Reptiles Which Look Like a Mixture of Alligator, Rhinoceros and Kangaroo but Their Bones Were More Like the Bones of Birds]

In the Text

[A Sea-Urchin]

[Eggs of Perch After Egg Laying]

[Salmon with Yolk Sac]

[The Bean Egg Changes to a Bean Plant]

[Living Bricks Which Make the Skin of a Leaf]

[Cells of the Inner Tree Pulp]

[Cells of the Outer Skin of a Leaf]

[Cells of a Pond Scum Much Enlarged]

[Three Sorts of Infusoria Much Enlarged]

[Some Jelly-fish Grown on Stalks and Some Swim About in the Sea]

[The Cob Is the Mother of the Corn]

[Pollen Grains Much Enlarged]

[A Right-handed Person Has All His Thinking Spots on the Left Side of His Brain]

[A Sea-anemone]

[More Common Infusorians, Much Enlarged]

[The Leaf Has a Spiral Joint on Which to Turn]

[Optical Illusions]

[Optical Illusions]

[Optical Illusions]

[Optical Illusions]

[Optical Illusions]

[Ear of a Mole Cricket on the Front Leg]

[Back of the Frog’s Eyes Are the Ear Drums]

[A Newt]

[The Leaves Take in Air Through Breathing Holes]

[In Place of Lungs, Insects Have Breathing Holes]

[The Minute Animal Which Causes the “Sleeping Sickness”]

[The Caterpillar Changes into a Moth]

[Accidents to Growing Fish Eggs]

[A Two-headed Turtle, a Crab with an Eye on One Side and a Feeler on the Other, and a Child With Two Great Toes on Each Foot]

[The Fangs of a Rattlesnake]

[Early Man Scratched Pictures of the Mammoth on Pieces of Its Own Bones]

[The Elephant Has Lost the Front of His Face]

[Our Single-toed Horse Has Been Made Over from a Four-toed One]

I
How the Chicken Gets Inside the Egg

There is no more fascinating sight to be seen anywhere than an incubator full of eggs just as the chickens begin to hatch out. You look through the little glass window in the side and see, at first, only rows of clean white eggs, dozens upon dozens of them, looking as if they were all ready to go into the family ice-chest or to be made into omelets for breakfast.

But they are not. First you begin to hear faint scratchy sounds. Pretty soon, here and there, a hole breaks through the broad end of an egg, and a tiny bill sticks out. The little chick is packed so tightly into the egg that it can move only its head. So it pecks and pecks; and stops to rest; and pecks again; and the hole in the shell gets larger and larger; until by and by, the egg cracks open, and a brand-new chicken draws its first long breath and looks out into the world.

After that, the chick usually takes a long rest, for it is pretty tired. When it feels better, it begins to move its legs and wings, and a half-hour or more after it first began work, it gets clear of the shell and stands up on wabbly legs, wet, bedraggled, weary, as disconsolate looking a little object as can well be imagined. Shortly, however, the feathers, which at first were plastered tight to the skin, dry off and fluff out, the legs get steady, and soon there is running about a rolypoly yellow chick, seemingly at least twice as large as the egg which held him only an hour before. Truly it is a wonderful sight, five hundred eggs turning into little chicks in an incubator, for all the world like the kernels of corn changing to pop-corn in the popper.

But wonderful as it is to see the way a chick comes out of an egg, it is still more wonderful to see the way it gets in. A fresh, new-laid egg has no chick inside. After it has been kept warm three weeks, it has—all ready to come out. The question is how the chicken got there.

Many different men have studied this question. For the most part, they have started a dozen or more eggs at once, and then taken them one by one and two or three hours apart, and cautiously broken them open to see what was inside. Sometimes, however, a student of eggs carefully cuts away the shell on one side, until he has made a hole about the size of a ten-cent piece. Over this he cements a sheet of glass as thin as paper, so that he can look through this tiny window into the egg, and see the chick grow.

This is really easier than it sounds. The yolk, as everyone must have noticed in hard-boiled eggs, does not stay in the middle of the egg, but always floats to the upper side. The chick, too, always forms on the upper side of the yolk; and when the egg gets turned over, the yolk rolls round like a barrel in the water and brings the chick to the upper side. So the chick, until it grows big enough to be a tight fit, always lies crosswise of the egg, on the upper side of the yolk just under the shell.

At first, of course, there is no chick at all, but only a round white fleck hardly larger than the head of a large pin, on the side of the yolk where the chick is by and by going to be. Before the end of the first day after the egg is laid, this little fleck has become somewhat oval in outline and an eighth of an inch across. Through its center runs a whiter line, as thick as heavy basting cotton and a sixteenth of an inch long; about half as large, that is, as an “l” or a figure “1” in the type on this page.

This is the beginning of the chick. Only it has hardly yet begun to be a chick, for it has as yet neither head, tail, wings, legs, eyes, nose, mouth, heart, stomach, brain, nor any other parts. It is in short, only a tiny line of chicken substance, which is now to begin to be made into a chicken.

Early in the second day of incubation, the little white line begins to get thicker on the end where the head is going to be. The brain and spinal cord appear first; later in the day there is the first sign of eyes and ears. At about the same time, the heart begins to form, and the minute blood vessels to grow out into the yolk like the first roots of a tiny plant. Before the end of the second day, the heart has begun to beat, and the blood vessels have begun to absorb the yolk to feed the growing chick. The yolk, in its turn, feeds on the white; for as everybody knows, the yolk and the white of an egg are stored up food, on which the little bird can live and grow until it is old enough to get out of the egg and shift for itself.

At the beginning of the third day, or a few hours before, the chick, which has been lying on the yolk face down (only it hasn’t any face yet), turns over on its left side. It is getting to be a big bird now, a quarter of an inch long and as thick as a good sized pin. Next, the brain grows rapidly; and so do the eyes, though these are not so large as the eyes of the finest needles. Now too, the nerves begin to form; also the lungs, the stomach, liver, and other organs of digestion; and there are beginnings of a tail, though without feathers.

During the fourth day, there are signs of a mouth. Legs and wings, looking just alike, begin to bud out from the body. Another day, and one can tell which is which; while now there appear beginnings of the skull and of the place where the back bone is going to be. Meantime, the little bird has become more than a half-inch long—though it does not yet look the least bit like a bird, but more like a large “?” mark. There is still no front to the body, and the heart, beating merrily away, hangs out in the yolk.

With the second week, the little chicken does begin to look something like a real bird. The bones begin to harden; while on the tip of what has been just an ordinary nose appears a speck of chalk, which will by and by harden into a bill. The claws begin to grow; and there are signs of feathers, each one still enclosed in the little transparent sac in which it forms.

At the end of two weeks, the white of the egg is all used up; and the little bird, which has been lying crosswise of the egg, now turns to bring its head toward the broad end. The yolk, too, is getting small; and on the nineteenth day, the chick pulls the last remnant into its little tummy, and begins to close over the hole. At about the same time also, he pecks through into the large air space which one sees in the broad end of an egg, when he eats it, hard-boiled, at a picnic. For a week or more, he has been breathing by means of a sort of gill, much like that of a fish, only that instead of being on the side of the head like a fish’s it grows out from the middle of the stomach on a long stalk and spreads over the inside of the shell. So the chick breathes through the shell, which is full of minute holes almost too small to be seen. But after the last bit of yolk has been taken in, this gill shrivels up and drops off, and the chick breathes with its lungs like the rest of us.

At the end of three weeks, there is nothing left of the egg but the shell and a tea-spoonful of water. The chick, which began life the size of a pin head, now fills the shell jam full, with only just room enough to peck the hole that lets him out. On the twenty-first day of his imprisonment, out he comes.

[How the Chicken Gets Inside the Egg]

II
Some Other Sorts of Eggs

All birds lay eggs. Some are brown or white like the hen’s egg; some are green, some buff, some blue; many are speckled. Some, like the eggs of the screech owl, are almost as round as marbles; not a few are so pointed at one end as to be fairly pear-shaped. The hummingbird’s egg is the size of one’s finger tip, the ostrich egg is as large as one’s head. But all alike they have shell and yolk and white; and by and by, a little bird inside. Only sometimes, like the chick, the little bird hatches out with feathers grown, and only needs to dry off and get its breath, before it is ready to run about and pick up a living for itself; and sometimes, like the little robin, it has no feathers, cannot stand up on its legs, and has to be fed by its parents, like a human baby.

Snakes and turtles have eggs also, very much like birds’ eggs. Like these, they have white and yolk; and the little reptile grows in the egg almost exactly like the little bird. For curiously enough the turtles, snakes, lizards and crocodiles, tho they look so very different from birds, are really very like them. They all have large eggs, with large yolks; and the little animal begins at a point in the side of the yolk, and does not, for a long time, fill the entire egg.

Oddly enough, there does not seem to be much connection between the size of an animal and the size of its egg. Big birds, to be sure, have big eggs; and little birds have little eggs. But a great crocodile, fifteen or twenty feet long and able to bite a man in halves, is hatched from an egg no larger than that of a goose. The little salt water minnow, or killifish, which is only as long as one’s finger, has very large eggs, for a fish, almost as large as small blue berries, and quite as large as the eggs of salmon and trout which grow to be a hundred times heavier. But cod fish, which sometimes are almost as large as a man, and the great sturgeons, which are as long as three men and as heavy as a horse, have eggs not much larger than the periods on this page, smaller even than those of a tiny ant. As for the little sea creatures, star-fish, sea-urchins, and the like (which to be sure, are quite as large as a hummingbird or a wren) their eggs are but fine dust, which cloud the water and are too small to be seen at all.

However, the smaller the eggs, the more of them there are, to make up. While some birds lay only two eggs at a time, and few more than a dozen, some fishes lay a hundred or more, the cod a hundred thousand, and the sturgeon two or three million.

[A Sea-Urchin]

Sometimes, when one is poking about in the brooks in the spring of the year—as every boy and girl should do, for it is great fun—one happens upon masses of transparent jelly half as large as one’s head, full of tiny black dots. These black dots, which are just about the size of the o’s in this book, are the eggs of frogs. If instead of being in round masses, they are in long strings, a yard sometimes in length, then they are almost always the eggs of toads; but if they occur neither in masses nor in strings, but separately, then they are the eggs of newts.

It seems strange that a frog should be able to lay a mass of eggs and jelly forty or fifty times larger than the frog itself. The real egg, however, is only the dark speck; and this when it is first laid has only a thin coating of jelly, hardly thicker than paper and nearly dry. As soon, however, as it touches the water, this dry jelly begins to swell, and goes on swelling and swelling for three hours until it is a hundred times larger than it was to start with.

These balls of frog’s eggs look, then, very much like tiny hens’ eggs with black yolks, broken into a bowl ready for cooking. They really are not quite this; because the frog’s eggs have no shell and no white, being simply yolk and nothing else. In fact, the only sorts of eggs that do have white are those of birds and reptiles; while few others have shells either. The jelly of frog’s eggs is not “white,” because it is not meant for the little frog to eat, but to keep other creatures from eating him. Besides this, it helps to keep the little chap warm.

You will recall that the little chick begins as a tiny dot on one side of the yolk, and keeps growing larger and larger until it uses up both yolk and white and fills the entire shell. Not so the little frog. Always, from the very beginning, it is as large as the egg. It is the egg, in fact. You can see that the egg is dark above and light below just as the tadpole will be, and the frog after him. At first, however, the baby tadpole does not have any parts or members. He gets in proper succession, eyes, ears, backbone, brain, skin, tail, and the rest; but he does not grow any larger until he hatches out, wriggles his way thru the jelly, and begins to eat.

At first the tadpoles are very tiny, only a quarter of an inch in length; and they cling in tufts to the under side of the water plants. After that, I suppose, everybody knows what happens.

There is still another curious difference between hens’ eggs and frogs’. When a frog lays an egg, that egg is nothing else but just egg—the little frog has not begun at all to form inside it. But when a hen lays an egg, while there is no little creature in that either, still the egg has already begun to get ready to turn into a chick. Some animals go farther than this, so that when their eggs are laid, the little creature is already formed inside, and so has only the last part of his growing left to be done outside. Certain fishes, certain reptiles, and various other animals besides, actually put off laying the eggs until so late that the young is all ready for hatching. Such eggs are laid and hatched at the same time, or even hatched first and laid afterwards.

All the four-footed creatures which have fur and hair, horses, cattle, dogs, cats, monkeys, and the like, manage in this way. And because this kind of egg doesn’t get knocked about, it does not need to have either hard shell nor thick jelly to protect it, but only a thin skin. For this reason, and because the egg hatches a few moments before it is laid, people are apt to miss it entirely, and so to get the idea that these animals have no eggs at all. But they have—one egg for each little animal.

We pretend that the bunny rabbits at Easter are hatched from the colored Easter eggs. They really are hatched out of rabbits’ eggs. No one notices the remnants of the rabbits’ egg, because what little there is soon dries up to almost nothing, or else the old mother rabbit eats it. Besides, one has all one can do to look at the new bunnies. Nevertheless, all little animals come out of eggs, puppies, colts, lambs, calves, kittens, every kind of living creature that is big enough for you to see, and a good many besides that are so small that you have to look for them with a microscope.

III
Little Fishes In The Brook

Of all eggs, the most interesting, I think, are the fishes’. Nearly all of these are pretty small, little round whitish globules like sugar pills. Some, like the eggs of trout and salmon which one finds in the gravel banks of rapid streams, are as large as fair-sized beads. Many, like the eggs of sea fish which float near the surface of the ocean, would go thru the eye of a darning needle.

The point, however, which makes them especially interesting is that so many of them are like tiny glass marbles. The membrane around them is so clear, and the substance of the egg itself so transparent, that with a magnifying glass, one can look right thru the egg, and see the little white fleck inside grow from nothing at all to a real fish, long enough to reach clear round the egg and lie with its tail almost in its mouth.

Some eggs are much clearer than others. The clearest are, at first, like clear glass, so that they can not be seen at all under water. Soon, however, a tiny vague white spot begins to form on the lower side. Then one can make out that the egg is covered with a rather thick membrane, that within this is a narrow, clear space filled with water, while within this and still smaller, floats the tiny yolk which is the real egg that is going to become the little fish.

[Eggs of Perch after Egg Laying.]
(From Bulletin of U. S. Fish Commission.)

The white spot on the yolk is not itself fish, but only fish stuff, which is being made ready to turn into fish by and by. The spot grows larger and thicker, until it looks like a round dab of putty stuck on the side of a marble. When this cap has grown until it is about half as much in diameter as the egg itself, it thins in the middle and thickens at the edges, until it forms a ring. A very strange thing, thereupon, happens to this ring. It begins to grow; and as it grows, it keeps slipping farther and farther round the egg. Soon it has become a band round the middle of the egg. Then as it moves along still farther to the other side of the egg, it has, of course, to grow smaller in order to fit. So it does, and the extra length taken in at one point in the ring, forms the body of the little fish. The head has already begun to form from a thickening at one side of the ring before it passed the middle of the egg. The two sides of the ring form the two halves of the body. But the tail being easier to make, does not grow out until much later.

Now there is a head and a body; but the only difference is that the head is bigger. Neither has any parts. There are no eyes, ears, nose, or mouth in one; nor any fins, backbone, stomach, nor scales in the other. These all appear later, much as in the chick—eyes, ears, brain, and heart early; fins and tail, scales and the whole front of the body not until long afterwards.

Many learned men have spent their entire lives in studying the way in which all these various parts form in the young animal, and a most strange and fascinating study it is, quite worth any man’s spending his life on. If I were to tell all that is known about the least part of one fish, the tale would fill up this entire book and leave no room for anything else. I shall, therefore, tell about the eyes only—partly because they are interesting and important organs; but more because they happen to be parts of the body which form in the same manner in all animals that have a backbone, whether they are fishes, frogs, birds, four-footed beasts, or human beings. The eyes with which you, my reader, are reading this page, grew in the way I shall describe, as I have myself seen it in the egg of cod and sea-bass.

In general, the part of the body to form earliest is the brain. Next after that come the eyes. These begin as two buds which grow out one on each side of the brain where the head is going to be. Each is a hollow, bubble-like affair on a short stalk; as much as anything, except for size, like a hollow rubber ball stuck on a pencil stub. One would think that this hollow ball would simply change into an eyeball; but it doesn’t, for Nature rarely does things simply. Instead, one side of the eye-bud folds in, as you might push in a hollow rubber ball with your finger, until it forms a cup. This cup is the eyeball. The sides grow out until the hole narrows down to the dark opening in the middle of the eye which we call the pupil. Various kinds of eye-stuff grow over the edge and form the interior parts of the eye; other tissues on the outside thicken the walls and form the transparent cornea in front; and while the pupil is still large, a portion of the substance which is later to become the skin, buds into the eyeball to form the lens of the eye. The reason, then, for this round-about process, this doubling in of the original eye bud to make a cup, which afterwards closes down to the eyeball we finally use, is to get various substances inside the eye, and finally to leave a pupil for the light to enter.

[“Salmon With Yolk Sac.”]

Thus far, like the little chick, the little fish has had no front to its body. It lies on the yolk, curled round it like a child with the stomach ache hugging a pillow. By and by the tail grows out free of the yolk. The head also lifts clear, and the lower jaw has room to form. Last of all, the sides of the body grow completely round the yolk, and put it where it will do the most good.

Now the fish is ready to hatch. For some time it has been giving occasional wiggles inside the egg membrane; finally it breaks thru and floats out. It is a tiny helpless creature, still more than half yolk. It cannot swim, but floats, belly up, and mouth wide open, not yet able so much as to close its jaws.

From this time on, the fish grows rapidly, living on the yolk, which grows smaller and smaller. At first the little creature floating on its back can only give an occasional wiggle. As the yolk becomes more manageable, the fish wiggles more. Soon it turns for a moment on its side, then clear over; and by the time the last of the yolk has disappeared, it is swimming right side up and has begun to eat the still tinier water creatures which are its food. At this stage, if it is a fresh water fish, it begins to be visible in the shallows in schools of minute, but veritable, fishes a quarter inch long and mostly eyes.

IV
Of Plants’ Eggs

The plant’s egg is, of course, the seed. We commonly say that the plant grows from the seed. And so it does. Yet this is not exactly true either, because the ripe seed is already a little plant, folded up tight and packed away in a hard case, like a chick inside its shell.

If one takes, for example, an ordinary bean or a peanut, peels off the shell and opens it carefully, it separates into two halves, held together by a little nodule at one end. These two halves, which together form pretty much the entire bean, are really two fat leaves. They are the yolk of the bean egg, on which the new bean plant is going to feed until it has grown leaves and root, so that it can pick up a living for itself out of the earth and air.

The rest of the new plant is the little nodule which lies between these seed-leaves. Curled up against the outside of the seed, like a puppy’s tail between its legs, is a short fat root; while hidden away between the seed-leaves is the next pair, tiny leaves almost too small to see, but real leaves nevertheless.

So the bean is an egg. Not a new-laid egg, but an egg with a little plant inside, all ready to hatch out and grow.

[The bean egg changes to a bean plant.]

If instead of cooking and eating the bean, we plant it in the ground, or in wet sawdust or blotting paper, it soon hatches out. The shell drops off, the seed-leaves first take in water and swell and then shrink away to nothing as the growing plant eats them up. The little root grows down, the little leaves grow up, the whole plant turns green and begins to climb the bean pole.

All seeds, then, are eggs just ready for hatching. They are like fish eggs, however, rather than like birds’ eggs, because the little fish and the little plant both save most of their yolk to use in getting a start in the world after they are hatched out. But the birds, you will recall, because they have large eggs and plenty of room inside, keep on growing till the yolk is all gone, and then hatch.

The little plant, as you might expect, gets inside its seed almost exactly as the little bird or frog or fish gets inside its egg. The “string beans” which we eat in the summer are fat pods stuffed out with bean-stuff to be used in making seeds. There are tiny beans inside, which are new-laid bean eggs, and so have no little plant inside, but only bean-stuff. The little bean plant, starting from nothing, forms one part after another, like chick and fish.

But where does the egg come from in the first place? The bean egg forms in the pod, too small at first to be seen at all, and keeps growing until it is big enough to begin to form the new plant. In exactly the same way, the mother fish, and the mother frog, and the hen, have a sort of pod inside them. First this pod stuffs and fattens itself out with egg-stuff, like a string bean. Then some of it turns into little eggs, too small to be seen. These grow and grow, like the beans in the pod, while the pod shrinks away. Only after they have grown a great deal, do they begin to form little beans, or fish or chicks inside.

[Seeds that have Plumes and Wings]

First of all, in short, the bean pod begins as a minute speck and grows into a proper pod. Then the bean inside this pod begins as a minute speck, and grows into a proper bean. Then the new bean plant inside this bean begins as a minute speck and grows into a proper bean plant, ready to be hatched out and shift for itself. So part of the mother plant becomes pod, and part of the pod becomes bean, and part of the bean becomes little growing plant. So it is with little fishes and little birds and little rabbits and puppies and kittens and all the rest of the little animals that you know.

V
What Little Boys and Girls are Made Of

“What are little boys made of, made of?
What are little boys made of?
Snaps and snails and puppy dog’s tails;
That’s what little boys are made of.
What are little girls made of, made of?
What are little girls made of?
Sugar and spice and all that’s nice;
That’s what little girls are made of.”

So says the old nursery rhyme. It has this much truth in it, that little boys and little girls are far from being alike, and it isn’t worth while to try to make either one over into the other. What little boys and girls are really made of, and all other living things as well, is a much longer story.

Oddly enough one can tell this story more simply by telling first about little star-fish and sea-urchins, and what they are made of. Star-fishes’ and sea-urchins’ eggs (for the two creatures are really very much alike, for all they look so different) are much like the eggs of fishes. They are round and transparent, and so minute that they look like fine red dust in the water. Naturally, therefore, few people ever see them at all.

Each of these eggs is a tiny drop of fluid substance with a very thin skin round it. It is in fact, not unlike a toy rubber balloon, filled with thin jelly mixed with oil, and set floating in the water.

This then is the young egg, before there is any sign of a growing creature inside. One would perhaps expect to see the oil and jelly mixture change gradually into a star-fish. Instead of this, however, this little balloon-like affair splits squarely in two, and makes two little balloons just alike, which lie side by side and more or less flattened against one another, like two soap bubbles blown from the same pipe. In about a half hour, each of these balloons or bubbles, “cells” as they have come to be called, has divided again; so that now there are four. The four soon become eight; the eight, sixteen. In the course of a few hours, there are hundreds, all sticking together and all very minute; so that the whole mass looks like the heap of soap bubbles which one blows by putting the pipe under the surface of the soap suds.

So the first single cell of the new laid egg, small as it was, has become several hundred still smaller. These, however, are not yet star-fish, but only star-fish-stuff, arranged in a little pile like a heap of bricks, and all ready to build into a star-fish.

Now if a man is building a house out of bricks, he piles the bricks near where the house is going to be; and then he takes them, a few at a time, and cements them into his wall. Not so the star-fish house. This has to be built right in the living brick pile. It is as if we dumped a heap of bricks in a field, and then each brick of its own accord got up and went to its proper place in the house. The little ball of cells which is the egg, begins to swell, and fold, and move. It pushes out one part here, and doubles in another there. The cells divide rapidly in one place, and form a thick solid bunch; in another they spread to a thin sheet. By and by, there is a little creature; not indeed a star-fish, but something with a stomach and an outside skin, and between the two, certain nondescript cells, which later on are going to make the hard skeleton and the muscles. After this, the cells still keep on dividing, but instead of getting smaller and smaller, they wait each time they divide till they grow to full size again. Thus the baby star-fish grows. And by growing fast in some places, and slowly in others, and in still others not growing at all, it changes at length into a veritable star, altho no bigger than a grain of sand.

All eggs change into little animals in this same way. The hen’s egg yolk is such a cell—a thin skin filled with oil and jelly. The frog’s egg is another, with one side colored black. The fish egg is like the others, with an especially clear jelly that one can easily see into. Frog eggs and star-fish eggs and sea-urchin eggs, most sorts of eggs in fact, split fairly in two the first time they split at all, the whole yolk divides and the little animal, from the first moment when there is any at all, is always as large as the egg. But birds’ eggs, most fish eggs, and some other sorts too, are so loaded down with fat that the egg does not divide clear thru, but as I have already explained, only at a tiny spot on one side where the jelly is thickest. But whether this pile of minute cells which is the heap of little animal bricks, is a small spot on the side of a large egg or the whole of a small one, it all comes to the same thing in the end. When the proper moment arrives, the living cell bricks move to their appointed stations, and the new creature begins to form.

Now we know what little boys and girls are made of. They are built of enormous numbers of these living bricks which we call cells, just as other living creatures are. All of us, men or animals, trees, bushes, or grass, were once, each of us, just one single round cell which divided, and divided, and divided again, until it became a vast number. Out of this vast number the new plant or animal builds itself.

If it is an animal like ourselves, this body stuff, before it becomes a body, is a round ball. A furrow doubles in along the place where the back is to be, and becomes the spinal cord. A rod strings itself along underneath this, and becomes the backbone. The front end of the spinal cord grows faster than the rest, becomes larger, and is the brain. The brain buds out into the eyes. The outer surface of the body, not yet turned into skin, buds inward and makes the ear. Four outgrowths come down from the forehead to make the face. The limbs begin as shapeless knobs, and grow out slowly into arms and legs. Sometimes these make a mistake at their ends, and split into six fingers or toes instead of the customary five. Then if the little creature is a human baby, the Doctor has to cut one of these off; but if it’s a kitten we say it has double paws and will be a good mouser—tho really I don’t suppose it makes the least difference.

Most of our growing, then, is just the increase in numbers of these little living bricks. There is a spot at the bottom of each finger nail where the nail cells are dividing and pushing out the finger nail. The white spots in the nail do not mean that one has been telling white lies, as some people say. They come because one happens to bruise the soft “root” of the nail where the nail cells are new and easily hurt like the soft flesh of a little child.

When we were very much younger than we are now we had no teeth. As biting-time drew near, the cells of the thin skin which lines the mouth began to multiply so rapidly where the two gums touch one another that they soon formed a thick ridge growing back into the jaw. A little later, and this ridge continued to grow at twenty separate points while it stopped growing everywhere else. Soon these twenty growing points opened up into twenty pockets. From the bottom of each pocket grew up a tooth; while from the side of each there budded out another pocket in which, when the baby is eight years or more old, the second teeth form. But the three back teeth in each side of a man’s jaw, tho they come late and are the largest he has, really belong to the first milk set, the rest of which he lost as a child.

Even the hair grows by the division of cells at the inner end of the little bulb which you see on the end of the hair when you pull it out and look at it against white paper. Just between hair and skin is a spot which is neither hair nor skin, where all the growing of the hair is done.

So we are not built like a cement or a wooden house, but like a brick one. We are made of little living bricks. When we grow it is because these living bricks divide into half bricks, and then grow into whole ones again. But how they find out when and where to grow fast, and when and where to grow slowly, and when and where not to grow at all, is precisely what nobody has yet made the smallest beginning at finding out.

VI
More About Living Bricks

The largest of these living bricks is the yolk of an ostrich egg; since this is, of course, like all eggs before they begin to grow, a single cell. The smallest known are certain of the bacteria and germs which float about in the air, and are so minute that they cannot be made out even with the strongest microscopes. All one can see is that there is something there; something which if placed a thousand in a row, would still not reach across a grain of dust.

Few cells, however, are as small as bacteria on the one hand, nor anything like as large as the yolks of birds’ eggs on the other. Many are just comfortably visible to the unaided eye. But the great mass of cells which make up our own bodies, the bodies of other animals, and of plants are a little too small to be made out with a common pocket lens, tho an ordinary microscope shows them with ease.

While the egg yolk is dividing to form the first hundred or more living bricks out of which the little animal is to be built, the cells are all about alike, generally round except where they are flattened against one another. As soon, however, as they begin to move about into place to build the new animal, they begin themselves to change. Some remain small; others grow large. Some grow out into long strings, and become muscle fibers or nerve. At one point, many thousands together swell up with oil and become fat. At another, more thousands build themselves about with hard lime phosphate, and become bones and teeth. Those which form within them little brown granules, give the color to hair and skin. The blood is colored red by the coin-shaped cells which float in it. In certain parts of the eye, on the other hand, the cells have to remain perfectly clear and colorless, else the light could not come thru and we should never see truly.

When an animal is very young indeed, long before it is ready to leave the egg, the whole outer surface of its body is covered with a single layer of these cells. They are packed closely together, and flattened against their neighbors so that the sheet of cells is not unlike, on a small scale, the marble floor of a public building or the block pavement of a city street. Like other living cells, these grow, and divide. They cannot grow sidewise, for the space is already filled; nor inward for that way lies the entire body. So they split off a piece of their outer ends. Then they do it again, and yet again; until the outer skin of the body, from being one layer of cells in thickness has become many.

Only the original inner layer, however, grows and divides. The split off ends dry up to a roundish cracker shape, grow hard and homy, and become the thin outer skin of the body, which we run pins and needles under, and pull off or scrape off when we “bark” our shins, without hurting. This part of the skin is dead. It gets rubbed off by our clothes, or soaks off in the bath tub and has to be scrubbed off the sides. But as fast as it is removed on the outer surface, it grows again from the living bottom layer. No matter how old one gets, this lower layer of the skin continues to split off the outer ends of its cells, just as it did before there was any proper skin at all. Most parts of the body grow thruout their mass; but the skin grows only on the inner side.

On the palms of the hands and the soles of the feet the skin grows very rapidly and is especially horny. When one works with his hands more than he is accustomed, the first effect is to wear the skin thin and sore, or to pull it loose from the bottom layer and make blisters. In the end, however, the rubbing only makes the live skin work faster, until it builds great homy callouses that no work can wear thru. But when our boots do not fit and rub in one spot, this also starts up the live skin to working hard. First thing we know, we have a corn. For a corn is only an especially hard and thick callous, where the living skin made a mistake and grew too much in one little spot.

Each finger nail and toe nail is a sort of corn. It grows from a fold of skin, forming from the bottom layer like any skin, but it is especially homy, even more horny than the hardest callous. The hair, also, is a sort of corn. The skin doubles in to form a minute pocket; and at the bottom of this pocket this same living under layer of the skin grows into a narrow shaft of cells, dry and dead and homy like skin and nails.

The horns of animals, too, are only thick hard skin. Sometimes they have a core of bone inside, but the outside is just a special sort of skin. Wherever we go in the body, there we find some special sort of cell. They may be large, small, thick, thin, long, round, soft, hard. They may build this, that, or the other thing around them. They may have this, that, or the other thing inside. But in one way or another the whole body, from head to heels, is built of these cells and their products.

[Living bricks which make the skin of a leaf. Five pairs of these are the lips of breathing holes.]

It is the same way with the plants. They too are built of these living bricks. Each leaf and blade of tree or grass is covered with a sheet of colorless cells one layer deep, which one can often peel off from the green pulp underneath. The green pulp, in turn, is a rather loose pile a half dozen thick, of roundish brick-shaped cells, each containing scattered grains of green coloring matter. The solid wood of a tree is only the thick walls of long slender cells, overlapping at the ends and packed tightly together. These cells lie lengthwise of the tree; that is why wood splits with the grain so much easier than it cuts across it.

[ Cells of the inner tree pulp. The rings show that the tree is three years old. ]

[ Cells of the outer skin of a leaf. At the bottom is the mouth of a breathing hole. ]

I have already said that at the time of year when the tree is growing rapidly, these woody cells are large; but when the tree is growing slowly, they are small. So each year there is a change from large cells formed in the spring to smaller ones grown in the fall. The next year, the living substance of the cell moves off to the growing region next the bark, and leaves the old wood cells empty. These, therefore, never change; and because the large cells and the small ones do not look quite alike, we see the annual rings of wood in the tree trunk, as thick as card board, which give us the light and dark lines in our furniture and our hard wood floors. From these one can tell, not only how old the tree is, but also what were its good years when it grew rapidly, and what its poor seasons when it hardly grew at all. If a drought came along any summer, or if insects one year ate off all the leaves, that too shows in the wood. But trees which grow in the tropics, where they keep growing the whole year thru, do not have annual rings.

While some cells of the tree form wood and some green pigment, others in the bark produce cork, as one can see nicely in the thin layers of cork in the bark of an elm. The cells of juicy fruits swell up with water, and form sugar and various flavoring matters and pleasant acids. Where the animal cells swell up with oil and become fat, the plant cells swell up with starch grains and become a potato or the thick seed-leaves of a bean. But other cells form gum, rosin, turpentine, pitch, and the various oils and the like, pleasant or bitter, which we use for food and medicines.

So the plant, like the animal, is just a great mass of different sorts of these living bricks, and of the various substances which they form within and around them.

Naturally it takes millions upon millions of these living bricks to build up the body of a man or an apple tree, still more of a whale or one of the giant redwood trees of California. Many humbler creatures, on the other hand, both animals and plants, contain comparatively few. Our common green pond scums, for example, which tho they are plants, have neither leaves nor stems nor roots, are like single long lines of tiny green barrels set end to end. Our common sea-lettuce is a sheet of cells only one layer thick; while other sea-weeds and water plants are but bundles of a score or more. Often the fewer such bricks there are, the larger they are; even at times, to a half-inch in thickness and an inch or more in length.

[ Cells of a pond scum much enlarged. The green living substance flowing from one to another unites to form an egg or spore. ]

A vast number of plants and animals, moreover, are single cells. Such among plants are the yeasts with which most of us make our bread, and a few of us brew our beer. Such also are the hundreds of different sorts of bacteria, which tho some of them are the germs of various catching diseases, are for the most part useful enough. But of these we shall learn more by and by. The green spots and patches on the bark of old trees and fences, and sometimes even on damp earth, are due to enormous numbers of minute plants, green with the same green pigment as the leaves of the largest tree; while the green tint of the gray lichens on rocks and tree trunks is caused by similar single-celled plants which grow among the white fibers of the lichen proper. Besides these, there are many like plants which float about in fresh water, each a single cell.

[ Three sorts of infusoria much enlarged. ]

The diatoms which one finds in the mud at the bottom of ditches and mud-puddles, tho they have shells and move about, are usually counted among plants; but the water of most ditches and puddles swarms with amoebas, infusoria, animalcules of various sorts, most of them large enough to be made out with the unaided eye when seen in a tumbler against the light, and each a single cell.

Many animals, then, and many plants are just one single cell and no more. Many others, like pond scums and sea-lettuces,—which are plants,—and sponges and jelly-fishes,—which are animals,—are composed of many cells, but all pretty much alike. But the animals and plants which we know best, kittens and oak trees and horses and grass, and the creatures we know best of all which are ourselves, are made up of many cells, and many different sorts—skin and bark and wood, flesh and fat and leaves and hair and all the rest, so many that it would take half an hour merely to write them all down.

[ Some jelly-fish grow on stalks and some swim about in the sea. ]

These “cells” then, are the living part of every plant and animal. Each of them became by the splitting in halves of an older cell; each of these in turn by the splitting in halves of a still older cell, until we get back to the egg which is the great-great-great-grandfather of them all. But the egg itself arose by the splitting of still another cell, which, of course, was part of the parent’s body. This came from yet another, and so on back to the beginning of life on this earth, tho nobody knows how long ago that was.

So the living flesh of us has always been alive. Most of it will die; but some of it will live on in our children and our children’s children, until the and of the world.

VII
How Much of Us Is Alive

How much of a tree is alive? Certainly not the outer bark. That falls off in dry scales, or can be scraped off down to the white layers within, and the tree be none the worse. Certainly not the wood. One often comes across old trees that have lost limbs or been carelessly pruned, which are entirely decayed out on the inside, so that nothing is left but a thin shell next the bark. Yet these trees grow as vigorously as ever, and bear leaves and fruit like a solid tree. The bark is dead; and the wood is dead. Between the two is a thin layer, perhaps a quarter inch thru, which is alive. On one side, it is changing into dead wood. On the other side, it is changing into dead bark. The new wood is alive, and the new bark. Between them is something neither wood nor bark, but just living tree-stuff. The green leaves also are alive, and the green twigs, and the blossoms, and the growing buds. But at least half of every living tree is already dead; while the larger and longer lived a tree is, the smaller proportion of it is alive at one time.

How much of a hen’s egg is alive? Not the shell, for that is mostly just chalk. Not the white, for that is merely the little chicken’s pantry shelf where it keeps the food on which it is to grow. The living part of the egg is the yolk—unless somebody boils the egg and so kills it. Sometimes, too, the egg dies, as any living thing may; then we usually find it out.

Even we ourselves are not all alive. I have already pointed out that our hair and nails are not alive at all, and that our outer skin, the thin skin, that is, which we tear off when we bark our shins, is fully alive only on the inside. Our “bark” in fact, is very like a tree’s. Each has a soft, thin, living layer on the inside, which grows, hardens, dies, forms a water-tight layer over the rest of the body, cracks into scales, and drops off. Where one forms cork, the other forms horn. Indeed the cork stoppers of our bottles are made from nothing more than an especially thick corky bark of a certain kind of oak, like the especially thick and homy soles of all bare-footed savages and some bare-footed little boys.

“The blood,” we say, “is the life.” And yet the blood itself is dead. The watery part is just soup; water and salt and fat and jelly. The minute, coin-like, red blood corpuscles carry the oxygen of the air from the lungs all over the body. But there are similar oxygen-carriers, likewise dead, in bottles in the drug-stores. The corpuscles are dead cells alive once, and like the hard skin cells, a great deal more useful dead than alive.

As for our teeth, the hard white enamel on the outside is just about as much alive as a clam shell. The baby tooth, as I have already explained, is formed in a little pocket in the gum. The inner part of the tooth grows up from the cells at the bottom, very much as a hair grows out from the bottom of the still smaller pocket where it starts. In fact, the tusks of pigs and the long front gnawing teeth of squirrels and rats are still more like hairs, for they keep growing from the root, and wear off at the outer end. The tooth pushes thru the gum; and as it goes by, the cells at the sides of the pocket and on top plaster it with a coating of enamel. Therefore, as most of us find out to our cost, this enamel once destroyed, can never grow again. Once clear of the pocket where it was formed, it has to last us the rest of our lives; and little boys and girls who don’t keep their teeth clean when they are young, have to put up with something not nearly so good when they are grown up.

The inside of the tooth is not quite so dead as the outside—one sometimes gets the impression during a visit to the dentist that it isn’t dead at all. The tooth, inside the enamel, is mostly bone; and bone is mostly lime, like clam-shells, mortar and chalk, plaster, and the great boulders and ledges of rock in a limestone country. The rest of the bone is living substance, scattered cells far apart from one another with long roots, that look as if they had grown out into the bone like tree roots into the soil. Really, however, it is the other way. Before there were bones, there were bone cells. These build themselves round with the hard bone substance, pushing their neighbors away and leaving only the long root-like strands of living substance. It is thru these root-like living strands that we feel the dentist’s auger bore into the solid tooth. But cutting the outer enamel does not hurt at all simply because no part of that is alive.

We are, then, built of living bricks, but of living bricks set in dead mortar. We saw that the great trees, complex and long lived, have more wood and bark and other dead substances in them than the shrubs, herbs, and grass. These in turn are less alive than the lowly water plants and yeasts and molds which have no wood or bark at all. The same is true of animals. The jelly-fishes and infusoria have neither skin, hair, bones, nails, nor blood, and are pretty much all alive. So the more a creature’s life is worth, the less of it is alive.

Even the living cells themselves are not wholly alive. The thin living jelly always contains water and salt, which are—just water and salt. Fat cells contain drops of oil, which are simply stored up food material, no more alive than the oil in an oil can. Plants, on their side, store up their food largely as starch, no more alive than that in a package from the grocers. Besides oil and starch, some cells contain gum or rosin or saliva or milk or sweat, which they pour out from time to time. These substances, too, can hardly be considered more alive while they are in the body than when they are outside.

So the living substance is the cell jelly. Everything outside the cell is dead; many cells even are dead, while not a few, even while alive, contain so much dead stuff within them, that there is more oil in a young hen’s egg than there is chick, and more starch than corn-plant in a grain of corn.

VIII
How We Grow

By “we” I mean all living things, trees and grass and dogs and cats and boys and girls. For as you, my reader, have I hope already discovered, we who have the breath of life in us are a good deal alike, whether we are oaks or men. We don’t look much alike, to be sure. But when we consider the things that are not alive—the stones and stoves and bats and balls and such—and see how very different we are from these, then we get some idea of what being alive is, and understand how being alive makes us blood-brothers with everything else that is alive also.

Now things that are alive usually do more or less growing. We have already learned something of this growing of little creatures in the egg—how the eye buds out as a ball and afterwards folds into a cup, how the limbs sprout out from the body as shapeless lumps which only gradually turn into hands or feet or wings. We have learned something of the way the bones grow, and the skin, and the hair, and the nails. Now we have to learn something more about the way a little child or a little tree grows up to be a big one.

The tree, we already know, grows larger round only between bark and wood. It grows taller only at the tips of its branches. The solid wood, once formed, does not change. If then, you drive two nails into the trunk of a little tree, say a foot apart and one above the other, even if that tree should grow to be a hundred feet high, those two nails would remain just where they were, a foot apart and just the same height from the ground as before. The little tree looks so much like the big one, that one cannot help thinking that it has simply grown thruout, so that the same branch which was once at the height of one’s head has now been lifted to the height of the house eaves. But this is not the fact. The lower branches of the little tree have died and dropped off; what are now the lower branches of the large tree, were once the top twigs of the little one, which have always been at the same level where they now are. The top branches of the large tree, as the tree grows still larger, will in their turn become, first the middle branches, then the lower ones, then will drop off entirely.

Now this growing at one end which looks like growing thruout is pretty common in our own bodies. We have seen how the hair grows at the inner end only, and the nails likewise, and the skin. Ignorant people will tell you that cutting off the ends of your hair, or singeing the ends; and that smearing various messes on the outside of your skins will change the quality of either. Don’t you believe them. After wood and skin and hair and teeth are once grown, all we can do is to protect them. Really to affect their growth for good or ill, we have to do something to the growing end.

The bones also grow in spots. The child’s leg bones and arm bones and finger bones do not simply swell up to become the man’s. The head of each bone, the rounding end, that is, where it touches the next, grows on the outside. But the shaft does its growing chiefly at two spots, one at each end where the shaft joins the head.

The bony part of the tooth, on the other hand, starts as a paper-thin sheet, but full sized. The living cells which build the hard bone, lie on the inside of this shell. They keep building on more bone on the inner surface, pushing themselves toward the middle of the tooth, until the tooth wall is so thick that only a narrow space is left in the center. But their long roots which they leave behind, still reach thru to the outer surface of the bone, ready to ache when there is occasion. Meantime, the outside of the tooth pocket, as we have learned, has been plastering on enamel on the outside of the shell, and pushing itself farther and farther away.

A plant’s roots, like its branches, grow at the tips; and the nerves in our own bodies grow in somewhat the same way, beginning at the inner end, and somehow finding their way thru and around the other tissues of the body, till they find the place to which they were sent. But the muscles and the fat grow thruout their mass, like dough being raised for bread. Most of the hollow tubes of the body—the blood vessels, for example, and the red lane down which our breakfast goes—grow in this way. But the hollow bones, as they grow, are taken down on the inside to enlarge the hollow, and built up again on the outside with old material and new to enlarge the shaft.

Even the blood grows, the watery portion coming from the food we eat and the water we drink; but the red and white corpuscles which float in the watery part, are made in special factories in the body (some of them in the marrow of the bones) and turned loose in the blood stream.

Growing, you see, tho easy to do, is by no means so simple as it appears.

IX
How We Grow Up

Ten years from now, you who are reading these sentences will be grown up. Once you were little pink and white babies, all soft and sweet and clean. And because you were soft and unresisting, you grew at a tremendous rate. At first you probably doubled your weight in six months. Then it took three years; then six or eight. By the time you are twelve, you probably will be half as heavy as you ever will be. In all the rest of your lives, you will do no more growing than you did in the first 180 days of them.

You will grow, too, as you have grown, by fits and starts. Sometimes you will shoot up like sunflower stalks. Sometimes, again, you will stop growing large, and begin growing hard. You will not seem to be getting bigger; but you will be getting stronger. Then, when you start growing again, you will perhaps find that you really can’t do so much as you could when you were a year younger, nor do it so well.

So you will keep on, sometimes growing large and sometimes growing hard, but almost never both at once, until you come to the full stature of men and women, and your soft baby flesh that couldn’t lift its head from the pillow has changed to tough muscle and hard bone. That is, of course, supposing that you have taken care of yourselves. If you haven’t—why then it may be different.

This growing up is so common an affair, so many of us do it, puppies and calves and kittens and little rabbits and baby birds, that we usually forget how wonderful a matter it is. Wonderful indeed it is; yet hardly less strange is it that after we have grown a while, then we stop. Yet our hair, as we know, doesn’t stop, nor the skin, nor the nails. Sometimes parts of the body which have hardly grown at all in youth, start up and grow in middle life. But the parts of the body which count, the parts which if they did grow would make us larger, these somehow know enough to stop.

It is not so with some other living creatures. A tree does not stop growing so long as it lives; nor does a fish. The big oak or the big trout may have grown faster than the little one; most likely it has simply been growing longer. We call any creature adult when it is large enough to have children of its own. But the oak bears acorns and the trout lays eggs, and then keeps on growing till it is ten, twenty, fifty times bigger than it was when it first had little ones. It is as if the cat, when her kittens were growing up, kept on growing along with them; and next year when there were more kittens kept on growing nearly as fast as they; and kept on year after year as long as it lived until it got to be as large as an elephant. And still its kittens would be just kittens, no larger than before.

Many animals manage their growing this way. The star-fish egg, you remember, is for size like a minute grain of dust, and the baby star when he first hatches out is hardly bigger. After that, he eats all he can get and grows as fast as he can, like any other kind of baby.

But suppose the little star-fish, as large say as a pin head, doesn’t find enough to eat. Does he then starve? Not a bit. He simply doesn’t grow. The eggs hatch out in the late spring within a few weeks of one another, and the little stars which do not happen upon a good boarding place, go practically without food all summer long. They remain perfectly healthy; but they scarcely grow at all, so that at the end of the summer they are still the pin heads that they were six months before.

On the other hand, when a star-fish happens to be born where he can find plenty of barnacles or small clams or mussels, he doesn’t do much but eat, and grows to match. It may happen, then, that of two stars, hatched on the same day, the one which has been well fed will be no less than five thousand times larger than the other which has gone hungry. Now a grown man is only about fifteen times as large as a new-born babe. But this is as if two babies, each six months old, should be, one no heavier than at birth, while the other weighed twenty-five tons and was as large as a whale.

So you can’t judge by appearances. The star-fish that you pick up at the shore may be a very young animal which has been well fed, or a very old one which has gone on short rations, while a young star, still growing, may be twenty times larger than his own great-grandfather.

X
How We Grow Old

After we grow up, we grow old. People say that we first grow up to men and women; then we continue adults; then we grow old. Really, however, we begin to grow old the day we are born; while we shall never again grow old so fast as we did when we were babes in arms.

For growing old is simply growing hard. We begin life as squashy little babies. Our bones are like green sticks. Our flesh is like dough, only the softest cloth must touch our skins, and Nurse has to hold her hand under our poor backs to keep our heads from dropping off. Children are not squashy, but they are still soft. You can pinch children. Sometimes you do. But you can’t pinch a grown man, any more than you can pinch a board. Children are of course, much harder than babies. All the same, if you put your fingers in your mouths, or stand too much on one leg or slouch over your books or shrug your shoulders up beside your ears when you play first base, or sit on one foot when you curl up in the big chair in the library, or do any other of the forty-leven things that somebody has to tell you forty-leven times a day not to do, then you will pull your bones all out of shape as if they were so much India rubber; and when you grow up and your bones and muscles set, then you can’t get back into shape again—tho you’ll wish you could.

For get hard you will. Then you will be grown up. When you are just hard enough, you will be in the prime of life, able to work as easily as you now play, and liking it, I hope, even better. But still you will keep on getting hard; and when you get too hard, then you are old.

So growing old is growing hard. And since the younger you are, the faster you grow, you never grew old so fast as when you were a tiny baby, and you never again will grow old so fast as you are growing old now.

And the moral is, as the Duchess used to tell Alice, that since we stay young and soft only a very short while, and grown-up and hard most of our days, we’d better, as much as we possibly can, make the short end of our lives help out the long one.

What I mean is this. While we are young, we are soft and plastic and teachable. As we grow older, not only do our bodies harden, but our minds also. We can do a great deal more after we are grown up than we can while we are children; and I think we are, if less light-hearted, on the whole quite as happy. But we shall be a great deal less able to take up anything new. Let us, therefore, practice while we are young those things which will bring us most happiness, after we are too old to change.

For example, suppose a boy is fond of out-door games, as every normal and healthy boy ought to be. He plays baseball all the spring, tennis all summer, football thruout the autumn, and what there is left of the year goes into ice hockey. He plays expertly, has a glorious time; and he grows up manly and strong. This is as it should be—so far.

But suppose the same boy, thru school and college and at work. There is no more football for him, and no more ice hockey. For a few years he may get an occasional game of baseball; if he is very lucky he will get a little tennis. But tell me, boy who is reading this page, how many of your father’s friends and associates ever play at all the games at which you spend your spare time?

Now while we are supposing, let us suppose that this boy of ours, instead of spending all his spare time at games, spent only half. The other half he shall devote to sports which are not games. He shall learn to ride a horse, to fish, to handle a sail boat, to swim, row, paddle, to climb mountains, to take care of himself in the woods, and above all to walk thru level country and enjoy the sight of all he sees. By and by, this boy will grow up. In the natural course of things, he will put away bat and ball and hockey stick before he is thirty, but rod and saddle and oar will bring him happiness and health almost to the end of his days.

There is a difference too in games. One plays football thru school and perhaps in college—eight years at the outside. But one world’s champion tennis player was well by forty; he must have played thirty years. A golfer gets forty or fifty years of pleasure for the trouble of learning his game. You may think you will learn the boy’s game now, and the man’s game later. But you won’t. You will learn the man’s game now along with the boy’s, or else you won’t learn it at all. You will be too old to learn, and go gameless to your grave.

Or suppose a girl is fond of music, and learns to play, very nicely, the banjo. It will be charming enough, summer evenings on the porch—so long as one is young and has only a girl’s soul to express in music. But by and by she will grow up to be a woman, and have little children of her own. Will she get out her banjo Sunday evenings and play for them hymns and solemn songs, or tinkle coon melodies for them when they are sick? Indeed she will not. She will put that banjo on the top shelf of the spare bed room closet, and wish she had spent her effort learning some other instrument more worth while.

So it is with everything else. If, while we are young, we train our ears to enjoy good music, and our eyes to love good pictures and good furniture, cloudy landscapes and great trees, and our minds to care for the important things of life, literature and religion and art and science and politics and history, we shall still possess growing sources of happiness longer after we have ceased to care to read stories or to be able to play ball. A wise child will study the happiest adults whom he knows, and learn to like and to do whatever most helps to make them blessed.

However, I meant to tell about how we grow old, rather than how we can best get ready to be so.

Oddly enough, most living creatures do not grow old. They simply live along till some other creature comes along and eats them up, or till the cold weather comes on and they freeze. A fresh egg is so soft that it hardly holds together; a young chicken is as tender as you please; while an old hen has to be boiled for days in order to be eaten at all. But an old fish isn’t tough; neither is an old lobster. Who ever heard a cook asking for little oysters, for the sake of getting them tender and juicy, or a fisherman preferring small fish? We like these the better, the older and larger they are. All animals, before they hatch out of the egg, are very soft. Afterwards they all grow larger and harder. But some stop growing big and continue to grow hard; and some stop growing hard and continue to grow big. The first sort grow old; the second do not.

Now when you come to think of it, about the only animals that grow old are the four-footed beasts, ourselves, and the birds. But the rate at which these various creatures grow old may be very different indeed.

Let us take a new-born human baby, and a new-born puppy, and a new-born mouse. All these are helpless little babies; and all three start immediately growing up and growing old. But while it takes six months for the human baby to grow to be twice as large as it was at birth, the puppy doubles its weight in nine days; while the little mouse, in the first twenty-four hours doubles its weight twice, so that at the end of its first day of life it is already four times as large as at the beginning.

At six months, the human baby, if he is very much up and coming, as you no doubt, my reader, were, can just begin to sit up without a pillow at its floppy back; it cannot walk a step, and it hasn’t a tooth in its head. But a six months puppy is a wiggly little beast, who runs away miles when he gets lost, chews up the family overshoes, and is well on the way toward losing his milk teeth. Meanwhile the mouse has grown up to be as large as he ever will be, has children of his own and probably grandchildren.

At five years the mouse is dying of old age. The puppy has become a sedate and middle-aged dog; but the baby is still a little child, just beginning to go to school, and still some years from losing its first tooth. At ten years, the child is young, the dog is old, and the mouse has become ancient history.

You musn’t think that the larger animals live longest. A horse is as large as six or eight men, but it is old long before a man first votes, and the birds, which are in general much smaller than the beasts, also in general live three, four, and five times as long. Even the elephant, thought to be longest lived of all beasts, lives no longer than we. But fish and turtles and crocodiles and shell-fish and the like, which are neither beasts nor birds and grow big without growing old, may outlive even parrots, elephants and men.

I dwell upon this at some length because there is no doubt that just as the dog grows old more slowly than the mouse, and the man grows old more slowly than the dog, so some men grow old, more slowly than others. Some people have used up their lives and are old at fifty or sixty; some are still young and hard at work at seventy and eighty. Now it rests partly with ourselves which we shall be. Five is not a large number to multiply by. But five times your present age, my reader, will take you well up to middle life. In no small degree, it is for you to choose whether you will come to five times your present age with the best part of your lives over and done with, or with the best part still to come. What, in general, your fathers and mothers are telling you is right and teaching you to do, will contribute to the one result; what in general they are telling you is unwise and wrong will doom you to the other. That indeed is how we know that some things are right and others things are wrong. People have tried, many times over, and found out, to their profit or to their cost.

XI
Why We Grow At All

Did you ever stop to think how extremely convenient it is to have two parents? Mama stays at home and takes care of the little children, reads and sings to them, tells them stories, puts them to bed, spanks them when they are naughty and kisses them when they are good. Indeed, you couldn’t get on very well without Mama. Neither could you get on very well without Daddy. Daddy doesn’t seem so important as Mama; but if Daddy didn’t go to work every day, and earn money for Mama and their little boys and girls, where would house and food and clothes and birthday parties and music lessons all come from?

Suppose there were no Mamas at all, but only just Daddies. Then of course there would be no aunties, nor nurses nor cooks nor big sisters nor kind ladies in the next house. There would be only just men; and half the men would have to stay home from the office to take care of the little boys of the other half, and then their work wouldn’t get done, and there would be no end of trouble.

It would be almost worse if there were only Mamas and no Daddies. For then all the Mamas would have to go out to work; and even when they could earn enough to hire a nurse, which I am afraid would not be often, the best of nurses isn’t like Mama. So it is really much better as it is, when we have both fathers and mothers, one to work abroad, and the other to work at home and take care of the children.

In fact, this arrangement is so much better than any other that pretty much all the living world has adopted it. You know the ears of corn which we buy in August and September and eat off the cob. You know too how it comes from the shop, all wrapped up in soft green husks, with the long silk hanging out of the end, that little girls in the country use for dolls’ hair, and ridiculous little boys try to smoke in pipes. The ear is the mother corn, and the kernels wrapped snugly away in the green husk are her children. Or rather they are her eggs, with the little corn plants inside, almost ready to be dried over winter and be planted and start life for themselves. Each kernel of corn has one fibre of silk, which is joined to it at one end and hanging out of the ear at the other.

[ The cob is the mother of the corn. Its father is the tassel. ]

The ear, then, is the mother of the corn. Its father is the tassel at the top of the stalk. From each branch of the tassel hang many tiny brown bags, each about as large as a grain of rice, and each filled with a very fine brown dust. This dust is called pollen. And unless a grain of this pollen falls on each thread of silk of each ear, then the kernel at the other end of the thread will never grow to full size and never become a seed; but will always remain small like the undersized kernels at the end of the ear. If the tassel is cut off; or the silk pulled out; or the ear tied up in a paper bag, then the ear forms no proper seed.

Sometimes, on an ear of sweet corn, one finds a few kernels, or a single kernel only, that instead of being white like the rest, is yellow. This means that somewhere in the neighborhood, it may be miles away, somebody has planted a field of common yellow corn, which we make into corn meal, but do not eat off the cob because it isn’t sweet. A grain or two of pollen from this yellow corn has been carried by the wind and fallen on the silk of an ear of sweet corn. So the father of that particular kernel is yellow and its mother white, and the kernel is colored just as if a white woman had married a Negro or an Indian.

Different plants manage these things differently. The ancient Egyptians, who lived on dates much as we live on corn and wheat, used to plant orchards of date palms as we plant orchards of our fruits. Every year, at the time when the cultivated date trees were in blossom, the Egyptian farmers used to go out into the desert, cut branches from certain wild palms which never bore fruit, and carry them in procession thru their date orchards. They did not know why they did this. They only knew that if they omitted the ceremony for a single year, that year they got no fruit. We know now, of course, that the date-bearing palm is the female tree; and the wild palm which doesn’t bear anything is the male. The procession with branches thru the orchards simply brought in the pollen.

Most plants, on the other hand, not to take any chances, have seed and pollen in the same flower. Many too, instead of relying on accident and the wind to carry one to the other, are arranged so that insects and humming-birds, in seeking food, shall make the transfer. Some, few, however, like the willows, have seed and pollen on separate trees.

[ Pollen Grains much enlarged. ]

The water plants manage in much the same way. They, for the most part, turn loose in the water what in them corresponds to the pollen, and waves and currents carry it to the young seeds. The simpler water animals, sponges and sea-anemones and shell-fish do much the same. While the female sea-urchin or star-fish produces eggs as small as dust, the male produces a still finer pollen-dust, which we call milt or sperm. If one grain of this happens to float against an egg, the egg at once begins to change to a young animal. Otherwise after a week or so the egg dies and that is the end of it. Of course, under these conditions, the chance of egg and milt getting together is pretty slim, and the waste of eggs is enormous. So the fishes, which can move about, have a much better plan. When the female salmon, for example, swims up the rivers to leave her eggs among the gravels in the swift water, the male goes along with her. After she has laid her eggs and gone away, along comes her mate and scatters milt over them. So the salmon egg is pretty sure to grow; and the salmon can afford to have few eggs and larger, and so give her little ones more yolk to live on and a better start in the world.

The bees have a still better device. The single queen bee, as everybody is supposed to know, lays all the eggs of the hive. When the queen is young and the new swarm is just starting, she annexes enough of this pollen-milt-sperm to last her the rest of her life, and stores it up in a little sack. Then whenever she lays an egg, all she has to do is to give this sack a squeeze, press out a little of the contents, and start the egg growing into a new bee.

Strangely enough, however, altho this practice of having two parents is so very common among both animals and plants, and so universal among human beings, it is not, so far as we can see, at all necessary. Potatoes are thick underground branches, and not seeds at all. Yet we plant them and they answer exactly as well. Many lowly creatures, like the yeasts, the bacteria, the infusorians of stagnant water, and the like, never have anything resembling seeds or eggs. There is a parent. The parent splits in halves. There are two children. And where is the parent?

Among the common green plant-lice which swarm on the leaves in the summer, the males all die early in the season. After that the females go on laying eggs, and these hatch more females which lay more eggs, for ten and twelve generations, before the cold weather comes on and some of the eggs begin to hatch out males once more. They get along exactly as well when each insect has only one parent, as when it has two.

In the case of the queen bee, if while the egg is being laid she squeezes the sack, then the egg hatches out a worker, which has therefore, two parents. But if she does not, then the egg hatches out a drone, which has only one. There are many other strange facts of this sort, which have been known for a long time, but which nobody has yet been able quite to understand.

Some facts still stranger have recently come to light. It has found that in the case of many sea creatures, star-fish, sea-urchins, shell-fish and others, that if the eggs are kept in common sea water, but kept carefully away from any milt, they soon die, and never grow up at all. But if any one of a considerable number of substances is added to the water, sugar, salt, acids, and other things, then the eggs, tho they still have only one parent, proceed to grow into the proper sort of little sea creatures, just as if they had two.

It is really a great mystery; the most that any one can say is that the eggs are there, but something in the water, or the absence of something, stops their growing. Add sugar, salt, acid, or milt and they grow. In the case of the land animals, this something is probably in the blood—for as you know, the blood is salt like the sea, and in many other ways much like it.

At any rate, this is practically a most convenient arrangement. A mother bird, for example, is herself born with all the eggs she is ever going to lay already formed inside her. But something in her blood keeps those eggs from growing bigger than pin heads. They don’t grow into proper eggs, that can hatch into little birds, until the mother bird gets a mate to help her build the nest, and to feed the little birds when they come, and sometimes to feed her too. Then some of them do grow up and hatch; and the two old birds take care of them.

But as I said, it is all a very great mystery, which the wisest men do not yet completely understand, and little boys and girls can hardly expect to understand at all.

XII
Things That Do Not Have To Be Learned

So far in this book, we have been learning about the body. We know something about the wonderful life-jelly of which all living things are made—how it is itself the soft parts of plants and animals, and how it builds for itself the hard shell and bones and wood, which are its supports and its tools. We know, also, something about how each particular animal or plant or human being starts as a minute fleck of this life-jelly, grows to be, first a seed or an egg, and then a full grown animal, a man, or a tree. We know, too, something of the living bricks which build the bodies of living creatures; and something of the difference between young creatures and old ones. More than this, I trust, we have learned that all this curious information is not to be looked at merely as something interesting or amusing; but that like all the teachings of science, it is something that will help us to live wisely. For as we come to know, we ought also to learn to do; and while we are finding out something about living things, we ought also to be finding out something about living.

We have, I say, thus far been learning about our bodies. Now we shall turn to a still more important part of us, and try to learn something about our minds. Our bodies, we found, are very much indeed like the bodies of animals and even of plants. Perhaps we shall find that our minds also are like those of other living things. Perhaps we shall find them to be something very different indeed.

Most of us, I suppose, have seen at least one little baby. I don’t mean a small baby merely, one that sits up in its carriage with a pillow behind its back, and smiles up at you when you look in under the hood. I mean a real little baby, a week or two old, that can’t turn its head over on the pillow or put its hands anywhere in particular, and instead of being nice and pink, is as red as a little beet—for the little baby’s skin is so very thin that it uses it to breath thru, to help out its poor little lungs, just as the frogs and other water creatures which have lungs breath thru the skin also. You know the size of baby I mean; if you haven’t had any younger brothers and sisters, there must at least have been something like it in the next house.

Now there are several very strange facts about such little babies, of which by no means the least strange is this: If you take such a very weak and tiny creature, just able to move its arms and legs, and put a finger or a small stick across the palm of its hand, the little one will grip so hard that you will have no small difficulty in getting its fingers loose again. In fact, some babies will actually allow themselves to be lifted in this way; and will hang by their hands a minute or more before they will flop down again into a helpless heap.

So here is one thing that the wee baby can do better than he can when he gets to be older and a good deal stronger, and better sometimes than he will ever be able to do it again. It is something, too, that he did the first time he tried, didn’t have to learn, didn’t have to practice, didn’t have to do anything but just be born knowing how. Pity we can’t all get our geography lessons and our piano practice done this easy way!

There are not a few other things which we all did exactly right the first time, without ever being shown how, or practicing, or seeing anyone else. For instance, when we were very young indeed, and very small, about as young and small, in fact, as people ever get, somebody gave us our first drink of water. We were not a day old then; and we didn’t even know enough to look at the same point with both eyes at once, but let them straggle off, one eye looking at one thing and the other at another, so that both got generally mixed up and couldn’t make out much of anything. But we knew all about drinking. We shut our little mouths tight round the stopper of our bottle, and sucked away like little steam pumps. The water went down the front of our throats, crossed over to the back, and went into our thirsty tummies. Meanwhile, our breath went in at our noses, down into the back of our throats, crossed over to the front, and went down our wind-pipes. But tho wind and water had to go crosswise of the same passage, we never made a mistake, and opened or shut the wrong lid for the wrong fluid, so as to let the air into our stomachs or the water into our lungs. Which really, when you consider how young we were, and how this was the first drink we ever took, was decidedly clever of us.

An act of this sort, which we are born knowing how to do and do right the first time without ever practising or being taught, is called an instinct. Mighty handy, too, they are, these instincts. Think what would happen to a baby that didn’t have the sucking instinct, and couldn’t take a spoonful of water nor a drop of milk till somebody had explained about drinking and showed him how to swallow without letting it run down the wrong way. I don’t believe there would be much chance of that baby’s ever growing up. To be sure, the other instinct that makes the little baby grip so hard on one’s finger, really, isn’t any particular use to him in these days. Long, long ago, nevertheless, when our ancestors were wild men and only half human, the little baby had to cling to its mother when she ran thru the forest with the wild beasts chasing her. Then if the little baby couldn’t hang on tight, it was pretty likely to get eaten up. But the babies that clung to their mothers, while their mothers were climbing a tree with both hands, and so couldn’t hold on to them, these babies lived to grow up, and the memory of that far away time still lingers in each little baby’s grip.

Some things are so important that one really has to know them. Did you ever think why girls like to play with dolls and boys do not? Why, on the other hand, boys can throw stones and girls cannot? Girls like to play with dolls, because when they grow up to be women and have real babies of their own, these babies have got to be dressed and fed and washed and tended and taken care of when they are sick. All this is very hard work indeed, about as hard and trying work as anybody ever has to do; so that if your own particular mama did not have a natural and instinctive love in her heart for all babies, she would not have jumped up at night every time you cried, no matter how cold and sleepy she was. If taking care of little babies were just plain work, to be done no better than other sorts of work are done, it would be pretty unpleasant for the babies. So women are made to love babies so much that even when they are little girls they like to play at taking care of doll babies, in default of real ones. But boys and men, they don’t count; so they do not have this taking-care-of-babies-and-dolls instinct.

But the boys and men can throw things, because before the invention of guns (which really was not very long ago) and before men lived in cities and planted crops, about the only way to get anything to eat was to get out and throw something at an animal and kill it. Then, too, when there was a war (and this often used to be most of the time) the fighting had to be done with spears and swords, which had to be thrown, or else used to strike and thrust with, which is pretty much the same thing as throwing. So it happened that for ages upon ages before our ancestors became civilized, while the women stayed at home and took care of the children, the men went out and threw things. And that is why today, girls like to play with dolls, but boys like to hunt and fish; and why boys can throw stones, and girls can’t.

Boys, then, are born with the throwing instinct. Throwing is as easy for them to learn as walking. But girls haven’t it. For them learning to throw is as hard as learning to walk on the hands. So we see how both with walking and throwing, the inborn instinct makes learning easy, tho it does not altogether take the place of practice.

XIII
Why We Like Certain Things

We have seen that the reason why all proper little girls like to play at taking care of dolls is that their mothers, and their grandmothers, and their great-grandmothers, and their great-great-grandmothers, and all other sizes of grandmothers for a thousand generations, and after that for another thousand, and after that nobody knows how many more, have all been taking care of real babies, until anything that looks like a baby has become about the most interesting and precious thing there is. We have seen also that boys learn to throw things easily, and like to throw things because all the while that their many times great-grandmothers have been taking care of the children, their many times great-grandfathers have been throwing spears and javelins at other people’s ancestors, or at things to eat running about on four legs.

Every proper boy likes to hunt and fish and camp out and play Indian because the most of mankind, up to a few centuries ago, have spent their entire time in hunting, fishing, living in huts, and generally playing Indians. Indians themselves, of course, play Indians all the time; and up to the beginning of the Christian era, our own ancestors, living in the wilds of northern Europe, were about as wild as Indians, and did little except play Indians all their lives. Who knows but that, a thousand years from now, after men have been civilized for a long while, and been getting their livings many years standing at benches or sitting at desks, all proper boys will think it great fun to study out of a book indoors? Perhaps they may; but I think it will be a long time first!

Every proper boy, too, when he gets old enough (and that is not so very old) likes to play at games. Now pretty much all these games, when you come to think of it, baseball, cricket, hockey, tennis, golf, I don’t know how many more, all involve hitting a ball with a stick. If we like to throw balls with our hands because our wild forebears threw javelins and spears with theirs, can you not guess at once that the reason why we like to strike balls with sticks is that these same wild forebears had for so many ages been striking things with clubs and swords? We like what our ancestors had to do. If we cannot cut and thrust and hack and throw and strike at wild animals in the chase or at other men in battle, at least we can do it with a ball. So bat and ball are the boy’s dolls. He plays with them for the same excellent reason that his sister plays with hers.

But why does every proper boy like to climb, and every proper girl too, if she has lived in the country and had a proper chance? About the first thing most of us did, as soon as we learned to creep, was to head for the nearest stairs, and try to climb up. When we get a little older, we cannot so much as set eyes on a fence or a shed roof without wanting to be on top of it; while as for trees, who of us, at a certain age, is satisfied until he has been to the top of every tree in the neighborhood. As for climbing mountains, that is one of the greatest games there is. So there is a climbing instinct in us, as well as a throwing instinct and a hit-something-with-a-bat instinct.

Now our wild ancestors who fished and hunted and played Indians for a living probably did not do much climbing. But long before their day we had certain still more ancient ancestors who were only half human and lived in the trees; and long before these, in turn, were still older ancestors who were not human at all, but regular apes who had hands in place of feet, and could climb like monkeys. These spent their lives in the trees; and in memory of them, each of us in turn, before he is quite old enough to play bat and ball games, is possessed to climb like a monkey, and climbs almost as surely and well.

Some people say, too, that the reason why a drowning person throws up his hands (the very worst thing he possibly could do under the circumstances) is that, being quite crazy with fear, he forgets completely his surroundings, remembers only the dim and far off time when the tree-folk escaped danger by climbing up out of the way, and reaches up for an imaginary branch which hasn’t been there these many thousand years. Perhaps this is so; for my part, I believe it is. At any rate, there is the wonderful grip of the new-born babe. Where did he get it if not by climbing trees, or clinging to his mother when she fled with him thru the branches?

Some people say also that the reason why we like to play hide-and-seek is that our ape ancestors, and our half-human ancestors, and our wild ancestors, and our half civilized ancestors, down to considerably after the time when the school histories begin, have spent no small part of their days stealing softly upon their enemies and the wild creatures they were hunting for food, or else hiding all mousey quiet while some enemy or wild beast is hunting after them.

There are a few people even who say that the reason why we like to go in swimming (we do like it, do we not?) is that in some sort of dim way we remember a still more ancient forebear who lived all the time in the water, who in short, was a veritable fish and did nothing else but swim. I don’t believe this myself. Not that we did not have such an ancestor—there doesn’t seem to be much doubt about that. But it all happened so very, very long ago that it doesn’t seem possible that there should be any trace of those days left. Still who can tell?

At any rate, we like to do a vast number of things that our forebears had to do whether they liked them or not; and if you can think of any other reason than this why you like baseball and hide-and-seek and climbing and dolls, I wish you would tell me.

XIV
Animals’ Games

Now that we know why boys play with balls and bats, and girls play with dolls, let us see if we can make out why kittens play with strings and puppies bark after wagons.

Perhaps you have already guessed. The grown up house cat and wild cat get a living all or in part by hunting birds and mice. They crouch close to the ground, creep slowly upon their prey; then seize it with a rush. That is just what the kitten does when you drag some small object slowly across the floor. The kitten doesn’t know why it chases a spool on a string. Really, however, it is playing at hunting small creatures, as its ancestors have hunted them in reality for a million generations.

Puppies are different from kittens. They don’t care much about spools and strings; but they like to run about over the fields and chew up their owner’s shoes. Now the wild dogs, and their cousins the wolves, do not go out alone and hunt small animals as the cats do. They go in packs; and they hunt large animals, wild sheep, wild oxen, deer, which they chase, sometimes, for days at a time. Spools and strings, therefore, are too small potatoes for the puppy; he chases wagons, automobiles and trolley cars, playing he is hunting big game. He doesn’t creep up cautiously on a ball of yarn, not to frighten it. Instead he barks at the top of his voice to call the rest of the pack. He runs away to play with other dogs, because the dogs and wolves are social animals; and when he chews up a rubber boot, he is playing that the pack has killed a moose and he is gnawing the great leg bone.

Of course, the puppy and the kitten do not know that they are playing at hunting when they chase spools and bark at carriages, any more than a boy knows why he likes to climb trees or hit a ball with a bat. But you can see for yourselves that the difference between the play of puppies and the play of kittens is just the difference between the work of a grown cat who hunts small creatures alone, and the work of a grown up dog who hunts large creatures in company.

Not many young creatures, such as we commonly see, do so much playing as puppies and kittens, tho boys and girls do a great deal more. In fact, the wiser any animal is when it grows up, and the more it is able to do then, the more playing it does, and the more interesting games it plays, when it is small. Calves and colts and lambs do not play especially interestingly, because wild cows and horses and sheep do not do much except eat, sleep, and run away from something that threatens to eat them up. But young squirrels, kept in cages, sometimes play at burying nuts in the floor of their cages for their winter supply of food; and young beavers, kept as pets in the house, have been said to play at building dams of chairs, canes, and umbrellas, across the parlor floor. Always, however, no matter how tame the grown animal is, the kitten plays at being a wild cat, and the puppy plays at being a wild dog, and the little boy plays at being a wild Indian; all because cats and dogs and men have been tamed and civilized for only a short while, but ran wild for ages.

There is one game that we all play, children, kittens, puppies, monkeys, and I don’t know how many other young creatures—and that is make-believe fights. We do it with sticks and snow balls and wooden swords; the little animals chase one another back and forth, and pretend to bite and scratch in the fiercest manner, as if they were fighting for their lives. Most animals do have to fight for their lives, many times over; so did most men in earlier times, before we had policemen and jails, and when everybody had to look out for himself.

Did you ever notice that a kitten is ticklish in just the same places that you are? You stroke the kitten’s back or head or legs, and it is as pleased as can be. But you touch it along the front of the body, or around the front of the neck, and at once it begins to bite and scratch and protest its best. All creatures that can be tickled at all are ticklish in the same places; and all these places happen to be precisely the spots where the great blood vessels and other important vital organs are close to the surface, and where, therefore, a wound would be most deadly. So when little animals play at fighting and pretend to bite one another, they bite hard enough to tickle. They don’t like to be tickled any more than you do. So they learn to protect those ticklish places in their play, and when they get to be grown up and fight in earnest, they have already learned not to get bitten in those spots where the bite would do most damage.

So the young animal’s instinct is to play at doing whatever his ancestors have been doing for work; and he has this instinct in order that he may like to do when young what he must do when old; and so have practice in doing it, and learn to do it well. Unfortunately, as men become more and more civilized, they have continually to do more and more new things, while they still persist in liking to do the old ones. That, I suppose, is why some boys and girls do not like to work.

XV
Some Instincts of Chicks and Kittens

It certainly is a most fortunate circumstance that all animals are born with a natural instinct for doing the particular things which they will have to do to make a living in the world. It would certainly be most inconvenient if moles and rats had an instinct to fly, and birds wanted to hide in drains and cellars; if cows thought they must dive into the water to catch fish, and seals tried to come ashore and graze in the pastures. As it is, each creature has the particular set of instincts which make it want to do the things which it can do best.

You remember what I told you in first pages of this book about the little chick inside the egg. It lies quietly and grows, until it is twenty-one days old. On the twenty-first day of its fife, for the first time, the chick feels the instinct to peck. It has no idea why it wants to peck, nor what will happen if it does. He only knows that pecking against the inside of his shell is precisely the one thing that he wants to do. So he pecks away—until, presto! out he comes into a new and very much larger world.

By and by, after the chick has got rested and dried off, he staggers up on his legs, and begins to look around him. His eye catches some small object—peck! he goes again, and catches the bit in his mouth the first time he tries, unerringly. It took you weeks to learn to put your hand where you wanted it; in fact you couldn’t so much as put your fingers in your mouth till you had tried many times. But the chick is born with the pecking instinct, and hits at the very first shot.

Yet the chick does not know what to peck at. He simply lets drive at whatever chances to catch his eye—a bit of gravel it may be, or something very nasty, or even a fleck of light on a blade of grass. What is good to eat and worth pecking at, he has to learn by trying just at you do. Neither does he know anything about drinking. In the course of time, as he goes about pecking at all sorts of things, he snaps at a dew drop on the grass or a sparkle of sun light on the water in his drinking vessel. So he gets his first drink; and in the course of time, he learns what water looks like.