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have been discussed from several points of view by Eigenmann, Davenport, Jennings, Conklin, and others. References to these articles may be found in the bibliography at the end of this article. Obviously, any experimental work which demonstrates the effects or lack of effects of the environment on the germ plasm of animals will have a direct bearing on this subject. It is with this idea in mind that the following material is reviewed.

It is quite obvious that the developing chick in the egg is not much influenced by the activities of the mother hen except as regards temperature, moisture, and mechanical disturbances. of the egg. In other words, a good incubator will hatch out the same kind of chicks and will hatch them about as well as their own mother. We must not forget, however, that the egg cells (yolks) as they develop in the ovary may be influenced by the body of the female parent before they are laid or the sperm cells in the male may be influenced. Among the mammals, the developing young are separated from the female parent but not so completely as are the chicks in the egg. Three questions arise in our mind immediately. Are the eggs and developing young more influenced by the parent or less than those of the bird? Do external factors influence the germ cells before fertilization? If so, do the same stimuli affect different animals in different ways? While recent researches have not given by any means a complete answer to these questions, some progress has been made and many interesting experiments have been recorded.

In 1897 Heape showed that when the fertilized egg of a rabbit of one variety (for example, a long-haired albino) was removed from the oviduct of the mother before it had become attached to the uterine wall, and was transferred to the oviduct of a rabbit of a different variety (for example, a Belgian hare which is neither white nor long-haired), the transferred egg became attached in its new position and passed through all the stages of gestation. Young rabbits produced in this way were both longhaired and albinos like the mother of the eggs, not like the rabbit which bore the young (Castle and Phillips). This experiment shows very clearly that the body of the parent has little if any effect on the developing young. It does not indicate, however, that the eggs may not be influenced by a foster mother if they grow up and mature in the body of the foster mother. This case may be tested by transplanting the ovary from one individual to another and allowing the egg to go through the stages of

development previous to fertilization within the foster mother. Castle and Phillips have made many ovary transplantations from one young female guinea pig to another. These foster mothers were then mated to males whose color and ancestry were known. In three cases the foster mothers raised young. In one case an ovary from a black female had been placed in a white guinea pig which was then mated to a white male. White offspring would be expected because white by white always produces white. However, the six young were all black. The eggs from the black female had not been influenced so far as could be detected. These and other experiments make it seem unlikely that the body cells or normal bodily processes leave any effects on the germ cells.

Eggs developing in the ovary or sperm cells developing in the testis if not influenced by the parents' make-up are not likely to be influenced by the ordinary changes in the environment from which they are protected by the body of the parent. Some changes of the environment, however, do penetrate the tissues of the ovary or testis and may cause changes directly in the germ cells.

Two interesting series of experiments in which alcohol vapor was administered to fowls and guinea pigs did not yield exactly similar results. According to Stockard, offspring from guinea pigs, which had been made to inhale alcohol for long periods before mating, were much less vigorous and showed among them many more abnormal young than the untreated stock. These abnormal young appeared during the three or four generations subsequent to the treatment, the individuals showing abnormal nervous systems, sense organs (especially the eyes), and in a few cases abnormal legs. Analysis of his results indicates that sperm cells are more easily affected by alcohol than egg cells, and it seems likely also that the sons of alcoholized mothers are more affected than the daughters, while the daughters of alcoholized fathers are more injured than the sons. The per cent of deformed offspring from inbred descendants of alcoholized stock sometimes ran as high as fifteen per cent, while the descendants of normal stock showed no deformities.

If we assume that alcohol has the same effect on man and guinea pigs we would have data to delight the most ardent prohibitionist, but before making the comparison it may be well to note two more researches. In a long and carefully executed experiment with fowls which were made to inhale

alcohol, methyl alcohol, or ether, Pearl has found that from birds, one or both of which had been treated, fewer fertile eggs were obtained, but of these eggs which were fertile fewer died during development than in the untreated stock. The offspring of treated parents showed a higher average body weight than the offspring of the untreated. They were a selected, superior set of offspring, the weaker eggs and sperms having been eliminated by the treatment. The treated and untreated animals produced about the same proportion of abnormal chicks (treated, 1 to 234, untreated 16 to 1,527). This indicates that surviving eggs and sperms were not injured so far as could be detected, though it is possible that a more severe treatment would have produced some injury. Guinea pigs are apparently much more likely to be injured by alcohol than fowls.

Elderton and Pearson, who made a careful statistical study of alcoholic parents and children, found that "the general health of the children of alcoholic parents appears on the whole slightly better than the health of the children of sober parents. There are fewer delicate children, and in a most marked way cases of tuberculosis and epilepsy are less frequent than among the children of sober parents. The source of this relation may be sought in two directions. The physically strongest in the community have probably the greatest capacity and taste for alcohol. Further, the higher death rate of the children of alcoholic parents probably leaves the fitter to survive" (p. 31). "To sum up then, no marked relation has been found between the intelligence, physique, or disease of the offspring and parental alcoholism in any of the categories investigated. On the whole the balance turns as often in favor of the alcoholic as of the nonalcoholic parentage" (p. 32).

Cole and Bachuber have found that acetate of lead taken internally seriously affects the sperm cells of the male rabbit, causing the offspring to be weak and underweight, and causing a considerable mortality shortly after birth. In these experiments the litters were in all cases from one mother and two fathers, one of which was poisoned. The colors of the males differed so that the male parent of each young rabbit could be determined at birth. The effect of the lead on the germ cells of the males could be estimated by comparing the young and the relative number of young from each male.

Other agents which have been used with success are the light waves of very short wave length, ultra violet rays, X-rays, and

radium rays. Guyénot and also Packard have experimented with these, using the fruit fly (Drosophila). The germ cells are much more easily affected than the body cells, though in this case the germ cells seem to be either not affected at all or eliminated completely. Hereditary modifications do not seem to be caused.

The limits of a paper of this nature prevent us from reviewing the extensive literature of this subject. Part of the literature is speculative, part needs repeating or verification in some particular. For our purposes we may make certain statements in conclusion which will serve to summarize the prevailing opinions held by zoologists at the present time as to the status of this very fundamental question. First, it may be stated that no clear-cut proof exists that the bodies of animals normally have any directive or modifying influence on the germ cells or embryos which they contain. Weismann's contentions have been supported, and Lamarck's have been discarded. Second, certain external readily transmitted materials or forces do act directly on the germ cells, eliminating or injuring them in some cases. Inherited injury in this case is not usually comparable to the process known as mutation or the production of new hereditary variations, but rather to a general weakening effect. Third, it is not safe to assume that because one agent causes a certain change in the germ plasm of one animal that it will cause a similar change in another animal.

BIBLIOGRAPHY.

CASTLE AND PHILLIPS: Carnegie Inst. Publication No. 144 and Science, Nov. 28, 1913.

COLE AND BACHUBER: Proc, Soc. Exp. Biology and Medicine, Vol. XII, No. 1, Oct. 7, 1914.

CONKLIN: Science, Jan. 10, 1913, pp. 46-54.

DAVENPORT: Pop. Sci. Mon., July, 1913, Vol. 83, p. 33.

EIGENMANN: The Geographical Review, Vol. IV, No. 3, September, 1917, p. 171.

ELDERTON AND PEARSON: Eugenic Lab. Memoirs X (London), p. 1. GUYENOT: Bull. Scientifique, 7e ser., 7, XLVIII.

HEAPE: Proc. Roy. Soc., V. 48, p. 457, and V. 62, p. 178.

JENNINGS: Science, Dec. 29, 1911, p. 902.

PACKARD: Jour. Exper. Zool., Vol. 19, No. 3, October, 1915, p. 332.

PEARL: Jour. Exper. Zool., Vol. 22, No. 1, p. 125, and No. 2, p. 241. STOCKARD: American Naturalist, Vol. 50, p. 65, and p. 144.

THE FABRIC OF OUR PHYSICAL KNOWLEDGE.

By ROGERS D. RUSK,

Columbus, Ohio.

The teacher of physics in the secondary school is frequently so engrossed with a study of the details of physical phenomena that he overlooks the larger meaning of the science, its actual basis in thought and reality, and the fundamental relations of its parts. Certainly a comprehensive view of any science as a whole is as valuable and as important to the teacher as a more intimate acquaintance with its details. Such a view should make the study mean vastly more to the teacher himself, and enable him to present his subject with much more of that degree of understanding to be desired and yet so often found lacking.

Sooner or later both student and teacher of any science must look at the facts of that science as a whole, and ask themselves the question, "What is the actual basis in reality of this intricate construct called a science?" The man of the street says a thing is, or is not, so absolutely because science has proved or disproved it. In this he discloses a naive ignorance as to the significance of science and the meaning of proof, to say nothing of his utter neglect of the fact that scientific knowledge is a mental fabric more or less conditioned by the mind itself. We cannot escape the fact that science is not final, that it is far from it, in fact, and that man's true knowledge of the external world as such can be obtained through no more than five gateways to the mindthe five senses. In the real basis of a science is thus in doubt, its superstructure can be no more substantial. Certainly, the physicist should analyze the situation as fully as possible. He should understand his position as a physicist, and if the principles of psychology and philosophy can be of aid to him he should use them. Too often these subjects suggest infinite terrors to the teacher of physics instead of aiding him very greatly in the fuller criticism of his own position as they really should. If psychology and possibly philosophy are invoked rather freely in the following pages, it is only because of their fundamental connection with physics, which too often passes unnoticed.

Man's sum total of knowledge does not consist of what he knows to be absolutely and unqualifiedly true with reference to external reality, but rather it is composed of those mental constructs which are too often taken to be a complete representation of external reality.

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