deals with human heredity, and only the fools will be rash enough to try to beat nature. But that's a century or two ahead yet.

Modern genetical knowledge began with Gregor Mendel, the abbot of the monastery at Brünn, in Moravia. Mendel's experiments were made with flowers in the garden of the monastery. He chose the sweet pea, because its flowers fertilize themselves and can easily be guarded against the pollen of near-by plants, so that he could make sure of the parentage of every plant in every generation. He made experiments in inbreeding and crossbreeding for eight years, and kept an accurate record of every individual plant-its own characteristics and the characteristics of every one of its

in England, France, and America. Then Professor T. H. Morgan, of Columbia University, made the most extensive experiments in heredity that have ever been carried out. He used for this purpose the pomace fly, or banana fly, because "it has many well-defined characters that can be observed under the microscope and it lives successfully upon a bit of banana in a milk bottle plugged with cotton. Every ten or eleven days a pair produces two to three hundred descendants that in turn are ready to produce similar families of their own, so that the investigator who begins with them needs to be an expert bookkeeper in order to record his results. In Professor Morgan's laboratory over ten million of these animals have passed in review under the micro

descendants. When he analyzed these records, he found that they followed a rule of heredity that could be expressed by a simple formula, which he published in 1865. We shall return to this formula later.

MENDEL AND HIS SUCCESSORS

MENDEL'S contact with the scien

tific world was through Karl Nägeli, of the University of Vienna, and to him he sent his results in pea culture. Nägeli failed to see their importance, and Mendel's work was buried until 1900, or sixteen years after his death. In that year, three botanists, working independently in Germany, Austria, and Holland, published their results from experiments similar to those of Mendel and all giving the same formula. Mendel's work was then resurrected and he was given proper credit for his pioneer labors in this field. A little later, the same formula was proved to apply to animals by biologists

scope, while pedigrees of over three hundred generations have been obtained and recorded."

The foregoing quotation is from Herbert E. Walter's "Genetics," a college textbook that is commended to readers who may wish a detailed review of the vast field of experimental results that has been covered by hundreds of investigators in the last quarter of a century.

Two other great pioneers in the study of heredity should be mentioned. The late Sir Francis Galton first applied to the subject the statistical method, that is to say, the accumulation of a vast number of facts bearing upon a particular phase of the matter and the analysis of these facts in terms of their mathematical proportions. By applying this method to the related sciences of genetics and anthropology, Galton created the modern science of eugenics, or heredity of man. And August Weismann, between 1880 and 1890,

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used the method of pure logic. Starting with what was known about the structure and growth of plants and animals, he reasoned out by logic what should be the mechanism for perpetuating structure and growth. From Weismann we first derived, by logic, what is now. generally accepted by scientists as being inevitably implied in the results of their actual experiments, namely the idea of a continuing stream of life, which he called the germ-plasm.

What is the germ-plasm?

Its nature can be suggested by a somewhat poetical analogy. Imagine that the old Greek legend of Prometheus were true, and that he really stole fire from the home of the gods and brought it to earth for the use of man. Suppose, further, that the gods had then set a sleepless watch over their fire, so that men might never again steal a brand from it. And suppose that men could not make fire by any means except lighting from some descendant fire of that original brand. If all that were true, even to this day it would be the custom, when a young man left his father's house to make a home of his own, to hand him a torch which he would carry to his own hearth to kindle the fire that should warm him and his children.

THE RESEMBLANCE TO PROMETHEUS

N OUR analogy, that continually replenished, never-dying fire is the germplasm. Weismann conceived the idea that every plant and every animal carries within itself, distinct from the cells that build the body, a small group of cells that carry on the fire of life itself. To carry our analogy further, we may liken this germ-plasm, these life cells, to the handful of glowing coals which remained when Prometheus's torch burned out. These coals have not the power to flame themselves, but they continue to burn and they have power to put flame into fresh torches, which in turn burn to coals having like limitations and like power. Practicing biologists have found by experiment that Weismann's conception fits in with all the ascertained facts of

bodily structure, bodily growth, and bodily perpetuation of life. Every plant and every animal is made up of body cells that are different in one important respect (to be noticed later) from the life cells. These body cells multiply themselves by the simple process of doubling in size and dividing themselves in two, each cell thereby becoming two cells. This process starts from the meeting of two life cells, which unite and form the one body cell which then proceeds to divide into two cells which divide into four cells and so on, until the plant or animal is complete. But, instantly this process starts, a few of the dividing cells are made containers of the elements of future life; and these lifecontaining cells do not divide but are stored away in the body till they, in turn, are called upon to join with other life cells in starting anew the endless process.

Life that is transmitted by means of these coals (life cells) is all life that is transmitted by "seeds." Most plants and most animals, including man, are perpetuated by "seeds" in the sense here meant. And, as the essence of the "seed" is the chromosomes, it is proper to give another and more literal definition of "germ-plasm," by saying that the chromosomes are the germ-plasm.

Some plants and some animals, however, can be otherwise perpetuated. We can cause a new begonia plant (of the variety Gloire de Lorraine) to rise from the soil by planting only a fragment of one leaf torn from another begonia. What happens here is that the process of division and multiplication of body cells goes on uninterruptedly and perpetually. The new plant is not a new plant: it is simply a branch of the old plant that keeps on growing even when detached from the main stem. In this case of the begonia, there is no heredity involved, because there is no succession of generations. The begonia of to-day is not the grandchild of the begonia of ten years ago; it is the same plant. There is only one begonia plant of this variety in the world; the piece of it in our garden is a piece of the original plant.

Numerous lower orders of animals,

such as jelly-fish, live this same immortal, continuous life of a multiple-division.

But men, the beasts of the field, the fish of the sea, the fowls of the airthese are flashes of flame from an inexhaustible Roman candle, or, better, from a sky-rocket that explodes, sending out a shower of flaming meteors which in turn explode sending out further showers of flaming meteors, and so on, world without end.

Having thus, we hope, burned into the mind this distinction between life cells and body cells, let us proceed with sober science.

Life cells and body cells are alike in one respect, namely, they are made up chiefly of a fluid, in which is a nucleus of more solid matter called chromosomes— the "strings of beads" mentioned earlier in this article.

But life cells and body cells are unlike in one most important respect, namely, that life cells have only half as many chromosomes as the body cells.

(Parenthetically at this point it may be well to explain that scientists have seen the structure of these cells with their eyes, through microscopes. They have counted the number of chromosomes [the strings of beads] from actual observation in the two kinds of cells. They have not seen the individual beads; but their existence, location, and function have been determined by Professor Morgan, for example, with the experiments he has tried with his ten million banana flies-precisely as no scientist has ever seen electricity or a watt or a volt, but nevertheless knows they exist and how they work by reason of many years of experiments with millions of electric lights, dynamos, generators, telephones, and radio sets. In other words, if you see something work but cannot "see the wheels go round," and if you then imagine the arrangement of the hidden wheels, and if you then think of something entirely new that such an arrangement on wheels ought also to be able to do, and upon experiment find that such an arrangement works as you thought it would, you may be pretty sure that your idea was correct.)

Life cells, to repeat, have been observed by human eyes to have only half the number of chromosomes that body cells have. Therefore, when two life cells meet and unite, becoming one body cell for the purpose of starting a new individual (by the process of repeated division), that one new cell starts life with one complete set of chromosomes, one half from the one life cell and the other half from the other life cell. And that one new cell is the whole new individual. All that happens to it thenceforward is that it grows by division of itself. Nothing new is added to it. Nothing is taken from it. It is as if you could get a thin piece of rubber so endlessly elastic that if you fastened it over the end of a penny whistle you could inflate it with your breath until it were the size of a Zeppelin airship. When it got that big, it would still be the same piece of rubber, and the air inside would still be your breath. As Herbert Walter so simply but so dramatically says: "This single cell is the actual bridge of continuity between any parental and filial generation. Moreover, it is the only bridge."

In other words, every essential characteristic that is to mark the mature adult has got to be present in that single cell when it starts growing, by division of itself, to make that adult. There must be present in that single cell actual physical objects that decree how its multiplying divisions shall arrange themselves to form the completed physical structure of man or beast or flower.

THE UTILITY OF EUGENICS

HIS discovery, of this single-cell

bridge between parents and child, is probably the most stupendously important discovery yet made by man. The discoveries of Archimedes made mechanical engineering a science. The discoveries of Copernicus and Newton made navigation a science. The discoveries of Franklin and Faraday made electrical engineering a science. But the discovery of the single-cell bridge between human generations has made possible a science of human heredity, by which man can already control many aspects of future

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human life and may reasonably hope eventually to learn how to build a human race free from crime, free from poverty, free from idiocy and imbecility and feeble-mindedness, a race of stronger and wiser men, of more beautiful and wiser women, and of happier and more promising children.

This discovery has settled one age-old controversy. It has settled the question of the relative importance of the gift of inheritance a child receives from the mother and of the gift of inheritance he receives from his father. Biologists now know that these two gifts are of exactly the same importance-that is to say, the mother and the father each contribute exactly half the quantity of that gift. But (fortunately in some cases and unfortunately in others) one parent may contribute a half of better quality than the other. Mendel's Law states the mathematical proportions in which the children of such parents may be expected to inherit the better or worse qualities, and the mathematical proportions in which these qualities may reappear in later generations than the first. Mendel was the first man to discover that the "wheels do go round." In other words, he was the first to prove that there were uniform results in human heredity. Until that was proven, there was no reason to suppose that there was a hidden mechanism that produced those results. Later investigators have found the machine and have identified many of its wheels. But Mendel's fame as a pioneer is secure. Unless, indeed, we ought to credit equally the author of the ancient legend of Prometheus, who must have had at least a glimmering of the human significance of his story. Poets usually precede scientists in just this way. They see the great coincidences of nature long before the scientists do. They call attention to them in such alluring terms that men of the patient explorer type enter the field which the poet saw from afar, and by long search unearth the actual diamond whose gleam caught the distant poet's eye. The poet is excited by the gleam because he believes it to be

a reflection of a celestial light. The scientist is excited by the search because he believes the act of perpetual searching brings him nearer to God. The poet calls the gleam Beauty. The scientist calls the diamond Truth. Two business men take the diamond and cut it up and one of them sells a piece of it mounted in a platinum ring which you and I buy (if we can) to put on the finger of the lady we love, and the other sells another piece of it mounted on a steel rod which you and I buy to cut a glass to replace a broken window-pane. At this point you and I return the compliment upon our benefactors by saying the poet is a fool when he tells us he has seen another gleam, and the scientist is a blasphemer when he tells us he can bring us closer to God by showing us the road to another diamond.

HOW

NOT AN ALLEGORY

OWEVER, this article is not an allegory, so we had better get out of the company of the fools and the great men, and back into the company of the scientists. Here are some of the things in which Mendel's Law has been proved by experiment to operate: beans, barley, wheat, oats, lentils, peas, lupines, rats, chickens, potatoes, potato beetles, garlic, corn, banana flies, rabbits, guinea pigs, snails, cattle, sheep, nearly all ornamental flowering plants that propagate by seed. By statistical study of careful observations, Mendel's Law has been proved to operate just as surely on man himself. The following human characteristics are some of those now known to be hereditary: absence of pigment from the eyes (albinism), six-fingered hands and six-toed feet, color of hair, color of eyes, shape of the facial features, double cow-lick, color blindness, inability to see at dusk, musical talent, mathematical talent, inventive genius, literary talent, high temper, cheerful disposition, feeble-mindedness, epilepsy, certain types of insanity, and certain types of criminality.

In another article, Mendel's Law and some of the more recent additions to the knowledge of heredity will be more fully considered.

T

O MOST of us the era of Noah and the flood seems like the beginning of time. In fact, that era is near the beginning of recorded history, so near, in fact, that that great event in the history of the world is reported only in a fragmentary manner, even in the Book of Genesis.

Yet the joint expedition of the British Museum and the University Museum of Philadelphia have unearthed at Tell-elObeid and the site of ancient Ur of the Chaldees dated objects which antedate all but the first few chapters of the first book of the Bible, and move back the known frontiers of ancient history more than 2,000 years, to a dynasty known in Babylonian tradition as the First Ur Dynasty, the third line of kings after the flood, reigning about 4,300 B. C.

At Tell-el-Obeid, near Ur, excavators found indisputable evidences of a high order of civilization flourishing more than 6,000 years ago in a city then at the junction of the Tigris and the Euphrates, at the head of the Persian Gulf. One of the authentic pieces of evidence was a marble foundation tablet from a temple erected to the goddess Ninkhursag by King A-an-ni-pad-da, son of King Mesan-ni-pad-da, dating to about 4,300 B. C. This tablet is the oldest dated document ever found, and "it proves the historic existence of a dynasty hitherto commonly regarded as mythical, and it gives a date, if not an authorship, for a very remarkable series of art objects."

THE OLDEST ROYAL JEWEL UST as remarkable a find was a large scaraboid, fifteen millimetres long, engraved with the name of A-an-ni-padda, the king whose existence before the discovery of this oldest royal jewel and

the foundation tablet of his temple, was

wholly a mythical figure in Babylonian tradition.

"It is really a sensational find," wrote C. Leonard Woolley, the director of the expedition, "and the form of the bead will appeal strongly to Egyptologists."

In this group of objects known to be at least 6,000 years old were artificial flowers, veritable gardens of them: inlays, mosaics, and copper reliefs of bulls. They support the theory that this race of men dated far back in dim antiquity, and that only centuries of development could have carried them to a civilization which flowered at Ur, mistress of early Babylon, 2,000 years or more before the time of Abraham.

Possibly this race migrated to the flat country near the Persian Gulf from the hilly country farther north in prehistoric, pre-Biblical times. In all their cities. they built stage towers, of which one of the largest was the Tower of Babel, 300 feet high, possibly because they had been accustomed to conduct their rites of worship on the hilltops. Certainly these ancient folk observed the signs of the stars. That evidence is visible in their art, and in many places in the early books of the Bible appears the advice to send for the astrologers, the soothsayers, the Chaldeans.

The Tower at Ur dates to a prehistoric period, and when Abraham lived there, before he migrated to the Land of Canaan, it was a completed monument. Around the tower, or Ziggurat, was the enclosure sacred to the worship of the Moon God, Nannar or Sin, whose name is preserved in the name of Mount Sinai and in other names of the period. In this enclosure was the Shrine of Nannar, the shrine of Nin-Sun; the palace E-HarSag, which was built by Dungi, second