WEISMANN'S CONCESSIONS. 183 



would have a similar effect. These agencies may be 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 quantita- 

 tive, more or less, according as nutrition is abundant or deficient, 

 and all qualitative differences must be due to the external in- 

 fluences 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 en- 

 larging and strengthening the organ. Lamarck, of course, under- 

 stood all this, but did not think it necessary to explain these ele- 

 mentary 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 sub- 

 sist 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/ons 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 re- 

 productive 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 pro- 

 duce 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 prin- 

 ciple 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 cer- 

 tain 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 



