Page:Popular Science Monthly Volume 45.djvu/197

Rh would have a similar effect. These agencies may he regarded as the opposites of nutrition—i, e., as constituting part of the "inequalities of nutrition" that affect the germ and cause it to vary. Variations in the germ-plasm are necessarily quantitative, more or less, according as nutrition is abundant or deficient, and all qualitative differences must be due to the external influences affecting certain constituents more strongly than the rest. How, then, does this differ from pure Lamarckism?

When we say that an organ is strengthened by use, there is obviously an ellipsis. What we mean is that exercise increases nutrition and nutrition strengthens the organ. We may be even more explicit and say that exercise causes increased circulation to the part exercised, causing more tissue to be deposited, thus enlarging and strengthening the organ. Lamarck, of course, understood all this, but did not think it necessary to explain these elementary principles. It is the same with the influence of climate and of the environment in general. All these agencies produce variation by affecting nutrition. If defective nutrition can affect the germ-plasm, why can not abundant nutrition affect it? How does the germ get its nutrition except in the same way that all the other cells of the body get theirs, through the food supply? Is the germ "immortal" in the sense that, like spirit, it can subsist indefinitely upon nothing? If it depends upon sustenance from the body, it must receive its nutrition from the body, and the quantity and quality of that nutrition will vary as those of the body vary. That they do vary he admits, and makes this the very fons et origo of hereditary variation.

But it does not seem possible to Prof. Weismann that a specific variation of some organ or part of the body can influence the reproductive products in precisely the same way so as to perpetuate that variation in the progeny. That we can not understand this may be freely admitted. It is the essence of the mystery of heredity. We know that like produces like. If we abandon that principle, there will be no stopping short of the opposite one, that like produces unlike. It is the same in principle to say that horses may produce cattle as to say that robust horses may produce feeble ones, although the robust ones may have acquired their robustness, not formerly possessed, through proper food, care, and treatment. And there is still no difference in the principle if, instead of robustness, the character be some specific one, such as a "racking" gait, which might be acquired during the life of a single individual. Such qualities are often transmitted. So, too, are the colors of flowers, which can be changed by adding certain ingredients to the soil, as are also certain artificially enforced habits in plants, such as are engendered by "layering," etc. But these are characters only feebly impressed and can not be expected