Chapter VIII: Part 8

Swim Bladder.--An organ of unusual significance, called the _swim bladder_, occupies the region just dorsal to the food tube. In young fishes of many species this is connected by a tube with the anterior end of the digestive tract. In some forms this tube persists throughout life, but in other fishes it becomes closed, a thin, fibrous cord taking its place. The swim bladder aids in giving the fish nearly the same weight as the water it displaces, thus buoying it up. The walls of the organ are richly supplied with blood vessels, and it thus undoubtedly serves as an organ for supplying oxygen to the blood when all other sources fail. In some fishes (the _dipnoi_, page 187) it has come to be used as a lung.

Circulation of the Blood.--In the vertebrate animals the blood is said to circulate in the body, because it passes through a more or less closed system of tubes in its course around the body. In the fishes the heart is a two-chambered muscular organ, a thin-walled _auricle_, the receiving chamber, leading into a thick-walled muscular _ventricle_ from which the blood is forced out. The blood is pumped from the heart to the gills; there it loses some of its carbon dioxide; it then passes on to other parts of the body, eventually breaking up into very tiny tubes called _capillaries_. From the capillaries the blood returns, in tubes of gradually increasing diameter, toward the heart again. The body cells lie between the smallest branches of the capillaries. Thus they get from the blood food and oxygen and return to the blood the wastes resulting from oxidation within the cell body. During its course some of the blood passes through the kidneys and is there relieved of part of its nitrogenous waste. Circulation of blood in the body of the fish is rather slow. The temperature of the blood being nearly that of the surrounding media in which the fish lives, the animal has incorrectly been given the term "cold-blooded."

Nervous System.--As in all other vertebrate animals, the brain and spinal cord of the fish are partially inclosed in bone. The central nervous system consists of a _brain_, with nerves connecting the organs of sight, taste, smell, and hearing, and such parts of the body as possess the sense of touch; a _spinal cord_; and _spinal nerves_. Nerve cells located near the outside of the body send in messages to the central system, which are there received as sensations. Cells of the central nervous system, in turn, send out messages which result in the movement of muscles.

Skeleton.--In the vertebrates, of which the bony fish is an example, the skeleton is under the skin, and is hence called an _endoskeleton_. It consists of a bony framework, the vertebral column which protects the spinal cord and certain attached bones, the ribs, with other spiny bones to which the unpaired fins are attached. The paired fins are attached to the spinal column by two collections of bones, known respectively as the _pectoral_ and _pelvic girdles_. The bones in the main skeleton serve in the fish for the attachment of powerful muscles, by means of which locomotion is accomplished. In most fishes, the _exoskeleton_, too, is well developed, consisting usually of scales, but sometimes of bony plates.

Food of Fishes.--We have already seen that in a balanced aquarium the balance of food was preserved by the plants, which furnished food for the tiny animals or were eaten by larger ones,--for example, snails or fish. The smaller animals in turn became food of larger ones. The nitrogen balance was maintained through the excretions of the animals and their death and decay.

The marine world is a great balanced aquarium. The upper layer of water is crowded with all kinds of little organisms, both plant and animal. Some of these are microscopic in size; others, as the tiny crustaceans, are visible to the eye. On these little organisms some fish feed entirely, others in part. Such are the menhaden[33] (bony, bunker, mossbunker of our coast), the shad, and others. Other fishes are bottom feeders, as the blackfish and the sea bass, living almost entirely upon mollusks and crustaceans. Still others are hunters, feeding upon smaller species of fish, or even upon their weaker brothers. Such are the bluefish, squeteague or weakfish, and others.

Footnote 33: It has been discovered by Professor Mead of
Brown University that the increase in starfish along certain
parts of the New England coast was in part due to
overfishing of menhaden, which at certain times in the year
feed almost entirely on the young starfish.

What is true of salt-water fish is equally true of those inhabiting our fresh-water streams and lakes. It is one of the greatest problems of our Bureau of Fisheries to discover this relation of various fishes to their food supplies so as to aid in the conservation and balance of life in our lakes, rivers, and seas.

Migration of Fishes.--Some fishes change their habitat at different times during the year, moving in vast schools northward in summer and southward in the winter. In a general way such migrations follow the coast lines. Examples of such migratory fish are the cod, menhaden, herring, and bluefish. The migrations are due to temperature changes, to the seeking after food, and to the spawning instinct. Some fish migrate to shallower water in the summer and to deeper water in the winter; here the reason for the migration is doubtless the change in temperature.

The Egg-laying Habits of the Bony Fishes.--The eggs of most bony fishes are laid in great numbers, varying from a few thousand in the trout to many hundreds of thousands in the shad and several millions in the cod. The time of egg-laying is usually spring or early summer. At the time of spawning the male usually deposits milt, consisting of millions of sperm cells, in the water just over the eggs, thus accomplishing fertilization. Some fishes, as sticklebacks, sunfish, toadfish, etc., make nests, but usually the eggs are left to develop by themselves, sometimes attached to some submerged object, but more frequently free in the water. In some eggs a tiny oil drop buoys up the egg to the surface, where the heat of the sun aids development. They are exposed to many dangers, and both eggs and developing fish are eaten, not only by birds, fish of other species, and other water inhabitants, but also by their own relatives, and even parents. Consequently a very small percentage of eggs ever produce mature fish.

The Relation of the Spawning Habits to Economic Importance of Fish.--The spawning habits of fish are of great importance to us because of the economic value of fish to mankind, not only directly as a food, but indirectly as food for other animals in turn valuable to man. Many of our most desirable food fishes, notably the salmon, shad, sturgeon, and smelt, pass up rivers from the ocean to deposit their eggs, swimming against strong currents much of the way, some species leaping rapids and falls, in order to deposit their eggs in localities where the conditions of water and food are suitable, and the water shallow enough to allow the sun's rays to warm it sufficiently to cause the eggs to develop. The Chinook salmon of the Pacific coast, the salmon used in the Western canning industry, travels over a thousand miles up the Columbia and other rivers, where it spawns. The salmon begin to pass up the rivers in early spring, and reach the spawning beds, shallow deposits of gravel in cool mountain streams, before late summer. Here the fish, both males and females, remain until the temperature of the water falls to about 54 deg. Fahrenheit. The eggs and milt are then deposited, and the old fish die, leaving the eggs to be hatched out later by the heat of the sun's rays.

Need of Conservation.--The instinct of this and other species of fish to go into shallow rivers to deposit their eggs has been made use of by man. At the time of the spawning migration the salmon are taken in vast numbers, for the salmon fisheries net over $16,000,000 annually.

But the need for conservation of this important national asset is great. The shad have within recent time abandoned their breeding places in the Connecticut River, and the salmon have been exterminated along our eastern coast within the past few decades. It is only a matter of a few years when the Western salmon will be extinct if fishing is continued at the present rate. More fish must be allowed to reach their breeding places. To do this a closed season on the rivers of two or three days out of each seven while the shad or the salmon run would do much good.

The sturgeon, the eggs of which are used in the manufacture of the delicacy known as _caviar_, is an example of a fish that is almost extinct in this part of the world. Other food fish taken at the breeding season are also in danger.

Artificial Propagation of Fishes.--Fortunately, the government through the Bureau of Fisheries, and various states by wise protective laws and by artificial propagation of fishes, are beginning to turn the tide. Certain days of the week the salmon are allowed to pass up the Columbia unmolested. Closed breeding seasons protect our trout, bass, and other game fish, also the catching of fish under a certain size is prohibited.

Many fish hatcheries, both government and state, are engaged in artificially fertilizing millions of fish eggs of various species and protecting the young fry until they are of such size that they can take care of themselves, when they are placed in ponds or streams. This artificial fertilization is usually accomplished by first squeezing out the ripe eggs from a female into a pan of water; in a similar manner the milt or sperm cells are obtained, and poured over the eggs. The eggs are thus fertilized. They are then placed in receptacles supplied with running water and left to develop under favorable conditions. Shortly after the egg has segmented (divided into many cells) the embryo may be seen developing on one side of the egg. The rest of the egg is made up of food or yolk, and when the baby fish hatches it has for some time the yolk attached to its ventral surface. Eventually the food is absorbed into the body of the fish. The development of the fish is direct, the young fish becoming an adult without any great change in form. The young fry are kept under ideal conditions until later, when they are shipped, sometimes thousands of miles, to their new homes.

NOTE TO TEACHER.--It is suggested that in the spring term the frog be studied, but if animal biology be taken up during the fall term the fish only might be used.

THE FROG

Adaptations for Life.--The most common frog in the eastern part of the United States is the leopard frog. It is recognized by its greenish brown body with dark spots, each spot being outlined in a lighter-colored background. In spite of the apparent lack of harmony with their surroundings, their color appears to give almost perfect protection. In some species of frogs the color of the skin changes with the surroundings of the frog, another means of protection.

Adaptations for life in the water are numerous. The ovoid body, the head merging into the trunk, the slimy covering (for the frog is provided, like the fish, with mucus cells in the skin), and the powerful legs with webbed feet, are all evidences of the life which the frog leads.

Locomotion.--You will notice that the appendages have the same general position on the body and same number of parts as do your own (upper arm, forearm, and hand; thigh, shank, and foot, the latter much longer relatively than your own). Note that while the hand has four fingers, the foot has five toes, the latter connected by a web. In swimming the frog uses the stroke we all aim to make when we are learning to swim. Most of the energy is liberated from the powerful backward push of the hind legs, which in a resting position are held doubled up close to the body. On land, locomotion may be by hopping or crawling.

Sense Organs.--The frog is well provided with sense organs. The eyes are large, globular, and placed at the side of the head. When they are closed, a delicate fold, or third eyelid, called the _nictitating membrane_, is drawn over each eye. Frogs probably see best moving objects at a few feet from them. Their vision is much keener than that of the fish. The external ear (_tympanum_) is located just behind the eye on the side of the body. Frogs hear sounds and distinguish various calls of their own kind, as is proved by the fact that frogs recognize the warning notes of their mates when any one is approaching. The inner ear also has to do with balancing the body as it has in fishes and other vertebrates. Taste and smell are probably not strong sensations in a frog or toad. They bite at moving objects of almost any kind when hungry. The long flexible tongue, which is fastened at the front, is used to catch insects. Experience has taught these animals that moving things, insects, worms, and the like, make good food. These they swallow whole, the tiny teeth being used to hold the food. Touch is a well-developed sense. They also respond to changes in temperature under water, remaining there in a dormant state for the winter when the temperature of the air becomes colder than that of the water.

Breathing.--The frog breathes by raising and lowering the floor of the mouth, pulling in air through the two nostril holes. Then the little flaps over the holes are closed, and the frog swallows this air, forcing it down into the baglike lungs. The skin is provided with many tiny blood vessels, and in winter, while the frogs are dormant at the bottom of the ponds, it serves as the only organ of respiration.

The Food Tube and its Glands.--The mouth leads like a funnel into a short tube, the _gullet_. On the lower floor of the mouth can be seen the slitlike _glottis_ leading to the lungs. The gullet widens almost at once into a long _stomach_, which in turn leads into a much coiled intestine. This widens abruptly at the lower end to form the _large intestine_. The latter leads into the _cloaca_ (Latin, _sewer_), into which open the _kidneys_, _urinary bladder_, and reproductive organs (_ovaries_ or _spermaries_). Several _glands_, the function of which is to produce digestive fluids, open into the food tube. These digestive fluids, by means of the ferments or enzymes contained in them, change insoluble food materials into a soluble form. This allows of the absorption of food material through the walls of the food tube into the blood. The glands (having the same names and uses as those in man) are the _salivary glands_, which pour their juices into the mouth, the _gastric glands_ in the walls of the stomach, and the _liver_ and _pancreas_, which open into the intestine.

Circulation.--The frog has a well-developed heart, composed of a thick-walled muscular ventricle and two thin-walled auricles. The heart pumps the blood through a system of closed tubes to all parts of the body. Blood enters the right auricle from all parts of the body; it then contains considerable carbon dioxide; the blood entering the left auricle comes from the lungs, hence it contains a considerable amount of oxygen. Blood leaves the heart through the ventricle, which thus pumps some blood containing much and some containing little oxygen. Before the blood from the tissues and lungs has time to mix, however, it leaves the ventricle and by a delicate adjustment in the vessels leaving the heart most of the blood containing much oxygen is passed to all the various organs of the body, while the blood deficient in oxygen, but containing a large amount of carbon dioxide, is pumped to the lungs, where an exchange of oxygen and carbon dioxide takes place by osmosis.

In the tissues of the body wherever work is done the process of burning or oxidation must take place, for by such means only is the energy necessary to do the work released. Food in the blood is taken to the muscle cells or other cells of the body and there oxidized. The products of the burning--carbon dioxide--and any other organic wastes given off from the tissues must be eliminated from the body. As we know, the carbon dioxide passes off through the lungs and to some extent through the skin of the frog, while the nitrogenous wastes, poisons which must be taken from the blood, are eliminated from it in the kidneys.

Change of Form in Development of the Frog.--Not all vertebrates develop directly into an adult. The frog, for example, changes its form completely before it becomes an adult. This change in form is known as a _metamorphosis_. Let us examine the development of the common leopard frog.

The eggs of this frog are laid in shallow water in the early spring. Masses of several hundred, which may be found attached to twigs or other supports under water, are deposited at a single laying. Immediately before leaving the body of the female they receive a coating of jellylike material, which swells up after the eggs are laid. Thus they are protected from the attack of fish or other animals which might use them as food. The upper side of the egg is dark, the light-colored side being weighted down with a supply of yolk (food). The fertilized egg soon segments (divides into many cells), and in a few days, if the weather is warm, these eggs have each grown into an oblong body which shows the form of a tadpole. Shortly after the tadpole wriggles out of the jellylike case and begins life outside the egg. At first it remains attached to some water weed by means of a pair of suckerlike projections; later a mouth is formed, and the tadpole begins to feed upon algae or other tiny water plants. At this time, about two weeks after the eggs were laid, gills are present on the outside of the body. Soon after, the external gills are replaced by gills which grow out under a fold of the skin which forms an operculum somewhat as in the fish. Water reaches the gills through the mouth and passes out through a hole on the left side of the body. As the tadpole grows larger, legs appear, the hind legs first, although for a time locomotion is performed by means of the tail. In the leopard frog the change from the egg to adult is completed in one summer. In late July or early August, the tadpole begins to eat less, the tail becomes smaller (being absorbed into other parts of the body), and before long the transformation from the tadpole to the young frog is complete. In the green frog and bullfrog the metamorphosis is not completed until the beginning of the second summer. The large tadpoles of such forms bury themselves in the soft mud of the pond bottom during the winter.

Shortly after the legs appear, the gills begin to be absorbed, and lungs take their place. At this time the young animal may be seen coming to the surface of the water for air. Changes in the diet of the animal also occur; the long, coiled intestine is transformed into a much shorter one. The animal, now insectivorous in its diet, becomes provided with tiny teeth and a mobile tongue, instead of keeping the horny jaws used in scraping off algae. After the tail has been completely absorbed and the legs have become full grown, there is no further structural change, and the metamorphosis is complete.

Development of Birds.--The white of the hen's egg is put on during the passage of the real egg (which is in the yolk or yellow portion) to the outside of the body. Before the egg is laid a shell is secreted over its surface. If the fertilized egg of a hen be broken and carefully examined, on the surface of the yolk will be found a little circular disk. This is the beginning of the growth of an _embryo_ chick. If a series of eggs taken from an incubator at periods of twenty-four hours or less apart were examined, this spot would be found at first to increase in size; later the little embryo would be found lying on the surface. Still later small blood vessels could be made out reaching into the yolk for food, the tiny heart beating as early as the second day of incubation. After about three weeks of incubation the little chick hatches; that is, breaks the shell, and emerges in almost the same form as the adult.

Development of a Mammal.--In mammals after fertilization the egg undergoes development within the body of the mother. Instead of blood vessels connecting the embryo with the yolk as in the chick, here the blood vessels are attached to an absorbing organ, known as the _placenta_. This structure sends branch-like processes into the wall of the _uterus_ (the organ which holds the embryo) and absorbs nourishment and oxygen by osmosis from the blood of the mother. After a length of time which varies in different species of mammals (from about three weeks in a guinea pig to twenty-two months in an elephant), the young animal is expelled by muscular contraction of the uterus, or is born. The young, usually, are born in a helpless condition, then nourished by milk furnished by the mother until they are able to take other food. Thus we see as we go higher in the scale of life fewer eggs formed, but those few eggs are more carefully protected and cared for by the parents. The chances of their growth into adults are much greater than in the cases when many eggs are produced.

REFERENCE BOOKS

ELEMENTARY

Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Bigelow, _Introduction to Biology_. The Macmillan Company.
Cornell _Nature Study Leaflets_. Bulletins XVI, XVII.
Davison, _Practical Zoology_, pages 185-199. American Book
Company.
Hodge, _Nature Study and Life_, Chaps. XVI, XVII. Ginn and
Company.
Sharpe, _Laboratory Manual_, pp. 195, 204-209. American Book
Company.

ADVANCED

Dickerson, _The Frog Book_. Doubleday, Page and Company.
Holmes, _The Biology of the Frog_. The Macmillan Company.
Jordan, _Fishes_. Henry Holt and Company.
Morgan, _The Development of the Frog's Egg_. The Macmillan
Company.
Needham, _General Biology_. Comstock Publishing Company.

XVII. HEREDITY, VARIATION, PLANT AND ANIMAL BREEDING

_Problems.--To determine what makes the offspring of animals or plants
tend to be like their parents._
_To determine what makes the offspring of animals and plants
differ from their parents._
_To learn about some methods of plant and animal breeding._
_(a) By selection._
_(b) By hybridizing._
_(c) By other methods._
_To learn about some methods of improving the human race._
_(a) By eugenics._
_(b) By euthenics._

SUGGESTIONS FOR LABORATORY WORK

_Laboratory exercise._--On variation and heredity among members of a
class in the schoolroom.
_Laboratory exercise._--On construction of curve of variation in
measurements from given plants or animals.
_Laboratory demonstration._--Stained egg cells (_ascaris_) to show
chromosomes.
_Laboratory demonstrations._--To illustrate the part played in plant
or animal breeding by
(_a_) selection.
(_b_) hybridizing.
(_c_) budding and grafting.
_Laboratory demonstration._--From charts to illustrate how human
characteristics may be inherited.

HEREDITY AND EUGENICS

Heredity and what it Means.--As I look over the faces of the boys in my class I notice that each boy seems to be more or less like each other boy in the class; he has a head, body, arms, and legs, and even in minor ways he resembles each of the other boys in the room. Moreover, if I should ask him I have no doubt but that he would tell me that he resembled in many respects his mother or father. Likewise if I should ask his _parents_ whom he resembled, they would say, "I can see his grandmother or his grandfather in him."

This wonderful force which causes the likeness of the child to its parents and to _their_ parents we call _heredity_. Heredity causes the plants as well as animals to be like their parents. If we trace the workings of heredity in our own individual case, we will probably find that we are molded like our ancestors not only in physical characteristics but in mental qualities as well. The ability to play the piano or to paint is probably as much a case of inheritance as the color of our eyes or the shape of our nose. We are a complex of physical and mental characters, received in part from all our ancestors.

Variation.--But I notice another thing; no boy in the class before me is _exactly_ like any other boy, even twins having minute differences. In this wonderful mold of nature each one of us tends to be slightly different from his or her parents. Each plant, each animal, varies to a greater or lesser degree from its immediate ancestors and may vary to a very great degree. This factor in the lives of plants and animals is called _variation_. Heredity and variation are the cornerstones on which all the work in the improvement of plants and animals, including man himself, are built.

The Bearers of Heredity.--We have seen that somewhere in every living cell is a structure known as a nucleus. In this nucleus, which is a part of the living matter of the cell, are certain very minute structures always present, known as _chromosomes_. These chromosomes (so called because they take up color when stained) are believed to be the structures which contain the _determiners_ of the qualities which may be passed from parent plant to offspring or from animal to animal; in other words, the qualities that are inheritable (see page 252).

The Germ Cells.--But it has been found that certain cells of the body, the egg and the sperm cells, before uniting contain only half as many chromosomes as do the body cells. In preparing for the process of fertilization, half of these elements have been eliminated, so that when the egg and sperm cell are united they will have the full number of chromosomes that the other cells have.

If the chromosomes carry the determiners of the characters which are inheritable, then it is easy to see that a fertilized egg must contain an equal number of chromosomes from the bodies of each parent. Consequently characteristics from each parent are handed down to the new individual. This seems to be the way in which nature succeeds in obtaining variation, by providing cell material from two different individuals.

Offspring are Part of their Ancestors.--We can see that if you or I receive characteristics from our parents and they received characteristics from their parents, then we too must have some of the characteristics of the grandparents, and it is a matter of common knowledge that each of us does have some trait or lineament which can be traced back to our grandfather or grandmother. Indeed, as far back as we are able to go, ancestors have added something.

Charles Darwin and Natural Selection.--The great Englishman Charles Darwin was one of the first scientists to realize how this great force of heredity applied to the development or evolution of plants and animals. He knew that although animals and plants were like their ancestors, they also tended to vary. In nature, the variations which best fitted a plant or animal for life in its own environment were the ones which were handed down because those having variations which were not fitted for life in that particular environment would die. Thus nature seized upon favorable variations and after a time, as the descendants of each of these individuals also tended to vary, a new species of plant or animal, fitted for the place it had to live in, would be gradually evolved.

Mutations.--Recently a new method of variation has been discovered by a Dutch naturalist, named Hugo de Vries. He found that new species of plants and animals arise suddenly by "mutations" or steps. This means that new species instead of arising from very slight variations, continuing during long periods of years (as Darwin believed), might arise very suddenly as a very great variation which would at once breed true. It is easily seen that such a condition would be of immense value to breeders, as new plants or animals quite unlike their parents might thus be formed and perpetuated. It will be one of the future problems of plant and animal breeders to isolate and breed "mutants," as such organisms are called.

Artificial Selection.--Darwin reasoned that if nature seized upon favorable variants, then man, by selecting the variations he wanted, could form new varieties of plants or animals much more quickly than nature. And so to-day plant or animal breeders _select_ the forms having the characters they wish to perpetuate and breed them together. This method used by plant and animal breeders is known as _selection_.

Selective Planting.--_By selective planting we mean choosing the best plants and planting the seed from these plants with a view of improving the yield._ In doing this we must not necessarily select the most perfect fruits or grains, but must select seeds from the _best plants_. A wheat plant should be selected not from its yield alone, but from its ability to stand disease and other unfavorable conditions. In 1862 a Mr. Fultz, of Pennsylvania, found three heads of beardless or bald wheat while passing through a large field of bearded wheat. These were probably _mutants_ which had lost the chaff surrounding the kernel. Mr. Fultz picked them out, sowed them by themselves, and produced a quantity of wheat now known favorably all over the world as the Fultz wheat. In selecting wheat, for example, we might breed for a number of different characters, such as more starch, or more protein in the grain, a larger yield per acre, ability to stand cold or drought or to resist plant disease. Each of these characters would have to be sought for separately and could only be obtained after long and careful breeding. The work of Mendel (see page 257) when applied to plant breeding will greatly shorten the time required to produce better plants of a given kind. By careful seed selection, some Western farmers have increased their wheat production by 25 per cent. This, if kept up all over the United States, would mean over $100,000,000 a year in the pockets of the farmers.

Hybridizing.--We have already seen that pollen from one flower may be carried to another of the same species, thus producing seeds. If pollen from one plant be placed on the pistil of another of an _allied_ species or variety, fertilization _may_ take place and new plants be eventually produced from the seeds. This process is known as _hybridizing_, and the plants produced by this process known as _hybrids_.

Hybrids are extremely variable, rarely breed from seeds, and often are apparently quite unlike either parent plant. They must be grown for several years, and all plants that do not resemble the desired variety must be killed off, if we expect to produce a hybrid that will breed more plants like itself. Luther Burbank, the great hybridizer of California, destroys tens of thousands of plants in order to get one or two with the characters which he wishes to preserve. Thus he is yearly adding to the wealth of this country by producing new plants or fruits of commercial value. A number of years ago he succeeded in growing a new variety of potato, which has already enriched the farmers of this country about $20,000,000. One of his varieties of black walnut trees, a very valuable hard wood, grows ten to twelve times as rapidly as ordinary black walnuts. With lumber yearly increasing in price, a quick growing tree becomes a very valuable commercial product. Among his famous hybrids are the plumcot, a cross between an apricot and a plum, his numerous varieties of berries and his splendid "Climax" plum, the result of a cross between a bitter Chinese plum and an edible Japanese plum. But none of Burbank's products grow from seeds; they are all produced _asexually_, from hybrids by some of the processes described in the next paragraph.

The Department of Agriculture and its Methods.--The Department of Agriculture is also doing splendid work in producing new varieties of oranges and lemons, of grain and various garden vegetables. The greatest possibilities have been shown by department workers to be open to the farmer or fruit grower through hybridizing, and by budding, grafting, or slipping.

_Budding._--If a given tree, for example, produces a kind of fruit which is of excellent quality, it is possible sometimes to attach parts of the tree to another strong tree of the same species that may not bear good fruit. This is done by _budding_. A T-shaped incision is cut in the bark; a bud from the tree bearing the desired fruit is placed in the cut and bound in place. When a shoot from the embedded bud grows out the following spring, it is found to have all the characters of the tree from which it was taken.

Grafting.--Of much the same nature is grafting. Here, however, a small portion of the stem of the closely allied tree is fastened into the trunk of the growing tree in such a manner that the two cut layers just under the bark will coincide. This will allow of the passage of food into the grafted part and insure the ultimate growth of the twig. Grafting and budding are of considerable economic value to the fruit grower, as it enables him to produce at will, trees bearing choice varieties of fruit.[34]

Footnote 34: For full directions for budding and grafting,
see Goff and Mayne, _First Principles of Agriculture_, Chap.
XIX, Mayne and Hatch, _High School Agriculture_, pp.
159-165, or Hodge, _Nature Study and Life_, pages 169-179.

Other Methods.--Other methods of plant propagation are by means of runners, as when strawberry plants strike root from long stems that run along the ground; layering, where roots may develop on covered up branches of blackberry or raspberry plants; slips, roots developing from stems which are cut off and placed in moist sand; from tubers, as in planting potatoes; and by means of bulbs, as the tulip or hyacinth. All of the above means of propagation are asexual and are of importance in our problem of plant breeding.

The Work of Gregor Mendel.--Fifty years ago, an Austrian monk, Gregor Mendel, found in breeding garden peas that these plants passed on certain _fixed characters_, as the shape of the seed, the color of the pod when ripe, and others, and that when two pea plants of different characters were crossed, one of these characters would be likely to appear in the offspring of the second generation in the ratio of three to one. Such characters as would appear to the exclusion of others in the first crossing of the plants were called _dominant_, the ones not appearing, _recessive_ characteristics. When these seeds were again sown the ones bearing a recessive characteristic would produce only peas with this recessive characteristic, but the ones with a dominant characteristic might give rise to a pure dominant or to offspring having partly a dominant and partly a recessive character; pure dominants being to the mixed offspring in the ratio of 1 to 2. The pure dominants if bred with others like themselves would produce only pure dominants, but the cross breeds would again produce mixed offspring of three kinds in the ratio of one dominant to two cross breeds and one recessive. The feature of this work that interests us is that _unit_ characters are passed along by heredity in the germ cells _pure_, that is, unchanged, from one generation to another, and independently of each other.

Determiners of Character.--A child then resembles his parents in some definite particulars because certain _determiners_ of characters have been present in the germ cells of one of the parents. If the determiner of a certain character is _absent_ from the germ cells of both parents, it will be _absent_ in _all_ of their offspring.

These discoveries of Mendel are of the greatest importance in plant and animal breeding because they enable the breeder to isolate certain characters and by proper selection to breed varieties which have these desired characters, instead of waiting for a _chance_ union of the desired characters by nature.

Animal Breeding.--It has been pointed out that the domestication of wild animals, the horse, cattle, sheep, goats, and the dog, marked a great advance in civilization in the history of the earth's peoples. As the young of these animals came to be bred in captivity the peoples owning them would undoubtedly pick out the strongest and best of the offspring, killing off the others for food. Thus they came unconsciously to select and aid nature in producing a stronger and better stock. Later man began to recognize certain characters that he wished to have in horses, dogs, or cattle, and so by slow processes of breeding and "crossing" or hybridizing one nearly allied form with another the numerous groups of domesticated animals began to appear.

In Darwin's time animal breeding was so far advanced that he got his ideas of selection by nature in evolution from the artificial selection practiced by animal breeders. A glance at the pictures will give some idea of the changes that have taken place in the form of some animals since man began to breed them a few thousand years ago.

Some Domesticated Animals.--Our domesticated dogs are descended from a number of wolflike forms in various parts of the world. All the present races of cats, on the other hand, seem to be traced back to Egypt. Modern horses are first noted in Europe and Asia, but far older forms flourished on the earth in former geologic periods. It is interesting to note that America was the original home of the horse, although at the time of the earliest explorers the horse was unknown here, the wild horse of the Western plains having arisen from horses introduced by the Spaniards. Long ages ago, the first ancestors of the horse were probably little animals about the size of a fox. The earliest horse we have knowledge of had four toes on the fore and three toes on the hind foot. Thousands of years later we find a larger horse, the size of a sheep, with a three-toed foot. By gradual changes, caused by the tendency of the animals to vary and by the action of the surroundings upon the animal in preserving these variations, there was eventually produced our present horse, an animal with legs adapted for rapid locomotion, with feet particularly fitted for the life in open fields, and with teeth which serve well to seize and grind herbage. Knowledge of this sort was also used by Darwin to show that constant changes in the form of animals have been taking place since life began on the earth.

The horse, which for some reason disappeared in this country, continued to exist in Europe, and man, emerging from his early savage condition, began to make use of the animal. We know the horse was domesticated in early Biblical times, and that he soon became one of man's most valued servants. In more recent times, man has begun to change the horse by breeding for certain desired characteristics. In this manner have been established and improved the various types of horses familiar to us as draft horses, coach horses, hackneys, and the trotters.

It is needless to say that all the various domesticated animals have been tremendously changed in a similar manner since civilized man has come to live on the earth. When we realize the very great amount of money invested in domesticated animals; that there are over 60,000,000 each of sheep, cattle, and swine and over 20,000,000 horses owned in this country, then we may see how very important a part the domestic animals play in our lives.

Improvement of Man.--If the stock of domesticated animals can be improved, it is not unfair to ask if the health and vigor of the future generations of men and women on the earth might not be improved by applying to them the laws of selection. This improvement of the future race has a number of factors in which we as individuals may play a part. These are personal hygiene, selection of healthy mates, and the betterment of the environment.

Personal Hygiene.--In the first place, good health is the one greatest asset in life. We may be born with a poor bodily machine, but if we learn to recognize its defects and care for it properly, we may make it do its required work effectively. If certain muscles are poorly developed, then by proper exercise we may make them stronger. If our eyes have some defect, we can have it remedied by wearing glasses. If certain drugs or alcohol lower the efficiency of the machine, we can avoid their use. With proper _care_ a poorly developed body may be improved and do effective work.

Eugenics.--When people marry there are certain things that the individual as well as the race should demand. The most important of these is freedom from germ diseases which might be handed down to the offspring. Tuberculosis, syphilis, that dread disease which cripples and kills hundreds of thousands of innocent children, epilepsy, and feeble-mindedness are handicaps which it is not only unfair but criminal to hand down to posterity. The science of being well born is called _eugenics_.

The Jukes.--Studies have been made on a number of different families in this country, in which mental and moral defects were present in one or both of the original parents. The "Jukes" family is a notorious example. The first mother is known as "Margaret, the mother of criminals." In seventy-five years the progeny of the original generation has cost the state of New York over a million and a quarter of dollars, besides giving over to the care of prisons and asylums considerably over a hundred feeble-minded, alcoholic, immoral, or criminal persons. Another case recently studied is the "Kallikak" family.[35] This family has been traced back to the War of the Revolution, when a young soldier named Martin Kallikak seduced a feeble-minded girl. She had a feeble-minded son from whom there have been to the present time 480 descendants. Of these 33 were sexually immoral, 24 confirmed drunkards, 3 epileptics, and 143 _feeble-minded_. The man who started this terrible line of immorality and feeble-mindedness later married a normal Quaker girl. From this couple a line of 496 descendants have come, with _no_ cases of feeble-mindedness. The evidence and the moral speak for themselves!

Footnote 35: The name Kallikak is fictitious.

Parasitism and its Cost to Society.--Hundreds of families such as those described above exist to-day, spreading disease, immorality, and crime to all parts of this country. The cost to society of such families is very severe. Just as certain animals or plants become parasitic on other plants or animals, these families have become parasitic on society. They not only do harm to others by corrupting, stealing, or spreading disease, but they are actually protected and cared for by the state out of public money. Largely for them the poorhouse and the asylum exist. They take from society, but they give nothing in return. They are true parasites.

The Remedy.--If such people were lower animals, we would probably kill them off to prevent them from spreading. Humanity will not allow this, but we do have the remedy of separating the sexes in asylums or other places and in various ways preventing intermarriage and the possibilities of perpetuating such a low and degenerate race. Remedies of this sort have been tried successfully in Europe and are now meeting with success in this country.

Blood Tells.--Eugenics show us, on the other hand, in a study of the families in which are brilliant men and women, the fact that the descendants have received the _good_ inheritance from their ancestors. The following, taken from Davenport's _Heredity in Relation to Eugenics_, illustrates how one family has been famous in American History.

In 1667 Elizabeth Tuttle, "of strong will, and of extreme intellectual vigor, married Richard Edwards of Hartford, Conn., a man of high repute and great erudition. From their one son descended another son, Jonathan Edwards, a noted divine, and president of Princeton College. Of the descendants of Jonathan Edwards much has been written; a brief catalogue must suffice: Jonathan Edwards, Jr., president of Union College; Timothy Dwight, president of Yale; Sereno Edwards Dwight, president of Hamilton College; Theodore Dwight Woolsey, for twenty-five years president of Yale College; Sarah, wife of Tapping Reeve, founder of Litchfield Law School, herself no mean lawyer; Daniel Tyler, a general in the Civil War and founder of the iron industries of North Alabama; Timothy Dwight, second, president of Yale University from 1886 to 1898; Theodore William Dwight, founder and for thirty-three years warden of Columbia Law School; Henrietta Frances, wife of Eli Whitney, inventor of the cotton gin, who, burning the midnight oil by the side of her ingenious husband, helped him to his enduring fame; Merrill Edwards Gates, president of Amherst College; Catherine Maria Sedgwick of graceful pen; Charles Sedgwick Minot, authority on biology and embryology in the Harvard Medical School; Edith Kermit Carow, wife of Theodore Roosevelt; and Winston Churchill, the author of _Coniston_ and other well-known novels."

Of the daughters of Elizabeth Tuttle distinguished descendants also came. Robert Treat Paine, signer of the Declaration of Independence; Chief Justice of the United States Morrison R. Waite; Ulysses S. Grant and Grover Cleveland, presidents of the United States. These and many other prominent men and women can trace the characters which enabled them to occupy the positions of culture and learning they held back to Elizabeth Tuttle.

Euthenics.--Euthenics, the betterment of the environment, is another important factor in the production of a stronger race. The strongest physical characteristics may be ruined if the surroundings are unwholesome and unsanitary. The slums of a city are "at once symptom, effect, and cause of evil." A city which allows foul tenements, narrow streets, and crowded slums to exist will spend too much for police protection, for charity, and for hospitals.

Every improvement in surroundings means improvement of the chances of survival of the race. In the spring of 1913 the health department and street-cleaning department of the city of New York cooperated to bring about a "clean up" of all filth, dirt, and rubbish from the houses, streets, and vacant lots in that city. During the summer of 1913 the health department reported a smaller percentage of deaths of babies than ever before. We must draw our own conclusions. Clean streets and houses, clean milk and pure water, sanitary housing, and careful medical inspection all do their part in maintaining a low rate of illness and death, thus reacting upon the health of the citizens of the future. It will be the purpose of the following pages to show how we may best care for our own bodies and how we may better the environment in which we are placed.

REFERENCE BOOKS

ELEMENTARY

Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Bailey, _Plant Breeding_. Macmillan and Company.
Harwood, _New Creations in Plant Life_. The Macmillan
Company.
Jordan, _The Heredity of Richard Roe_. American Unitarian
Association.
Sharpe, _Laboratory Manual_, pp. 64-72, 345-347. American
Book Company.

ADVANCED

Allen, _Civics and Health_. Ginn and Company.
Coulter, Castle, East, Tower, and Davenport, _Heredity and
Eugenics_. University of Chicago Press.
Davenport, _Heredity in Relation to Eugenics_. Henry Holt
and Company.
De Vries, _Plant Breeding_. Open Court Publishing Company.
Goddard, _The Kallikak Family_. The Macmillan Company.
Kellicott, _The Social Direction of Human Evolution_.
Appleton Company.
Punnet, _Mendelism_. The Macmillan Company.
Richards, Helen M., _Euthenics, the Science of Controllable
Environment_.
Walter, _Genetics_. The Macmillan Company.

XVIII. THE HUMAN MACHINE AND ITS NEEDS

_Problem.--To obtain a general understanding of the parts and uses of the bodily machine._

LABORATORY SUGGESTIONS

_Demonstration._--Review to show that the human body is a
complex of cells.
_Laboratory demonstration_ by means of (_a_) human skeleton
and (_b_) manikin to show the position and gross structure
of the chief organs of man.

Man and his Environment.--In the last chapter we saw that one factor in the improvement of man lies in giving him better surroundings. It will be the purpose of the following chapters to show how man is fitted to live in the environment in which he is placed. He comes in contact with air, light, water, soil, food, and shelter which make his somewhat artificial environment; he must adapt himself to get the best he can out of this environment.

The Needs of Living Things.--We have already found that the primary needs of plants and animals are the same. They both need food, they both need to digest their food and to have it circulate in a fluid form to the cells where it will be used. They both need oxygen so as to release the energy locked up in their food. And they both need to reproduce so that their kind may be continued on the earth. What is true of plants and other animals is true of man.

The Needs of Simple and Complex Animals the Same.--The simplest animal, a single cell, has the same needs as the most complex. The _cell_ paramoecium feeds, digests, oxidizes its food, and releases energy. The _cells_ of the human body built up into tissues have the same needs and perform the same functions as the paramoecium. It is the _cells_ of the body working together in groups as tissues and organs that make the complicated actions of man possible. Division of labor has arisen because of the complex needs and work of the organism.

The Human Body a Machine.--In all animals, and the human animal is no exception, the body has been likened to a machine in that it turns over the _latent_ or potential energy stored up in food into _kinetic_ energy (mechanical work and heat), which is manifested when we perform work. One great difference exists between an engine and the human body. The engine uses fuel unlike the substance out of which it is made. The human body, on the other hand, uses for fuel the same substances out of which it is formed; it may, indeed, use part of its own substance for food. It must as well do more than purely mechanical work. The human organism must be so delicately adjusted to its surroundings that it will react in a ready manner to stimuli from without; it must be able to utilize its fuel (food) in the most economical manner; it must be fitted with machinery for transforming the energy received from food into various kinds of work; it must properly provide the machine with oxygen so that the fuel will be oxidized, and the products of oxidation must be carried away, as well as other waste materials which might harm the effectiveness of the machine. Most important of all, the human machine must be able to repair itself.

In order to understand better this complicated machine, the human body, let us briefly examine the structure of its parts and thus get a better idea of the interrelation of these parts and of their functions.

The Skin.--Covering the body is a protective structure called the skin. Covered on the outside with dead cells, yet it is provided with delicate sense organs, which give us perception of touch, taste, smell, pressure, and temperature. It also aids in getting wastes out of the body by means of its sweat glands and plays an important part in equalizing the temperature of the body.

Bones and Muscles.--The body is built around a framework of bones. These bones, which are bound together by tough _ligaments_, fall naturally into two great groups, the bones of the body proper, vertebral column, ribs, breast bone, and skull, which form the _axial_ skeleton, and the appendages, two sets of bones which form the framework of the arms and legs, which with the bones which attach them to the axial skeleton form the _appendicular_ skeleton.

To the bones are attached the muscles of the body. Movement is accomplished by contraction of muscles, which are attached so as to cause the bones to act as levers. Bones also protect the nervous system and other delicate organs. They also help to give form and rigidity to the body.

Hygiene of Muscles and Bones.--Young people especially need to know how to prevent certain defects which are largely the result of bad habits of posture. Standing erect is an example of a good habit, round shoulders a bad habit of this sort. The habit of a wrong position of bones and muscles once formed is very hard to correct. This can best be done by certain corrective exercises at home or in the gymnasium.

Round shoulders is most common among people whose occupation causes them to stoop. Drawing, writing, and a wrong position when at one's desk are among the causes. Exercises which strengthen the back muscles and cause the head to be kept erect are helpful in forming the habit of erect carriage.