INTRODUCTION xiii 



for their removal causes increase in the blood of the 

 exciting substances urea and uric acid. 



The effects of disuse are similar to those of mutila- 

 tions and of use vice versa. Delage, as seen above, 

 does not consider that increase or decrease of par- 

 ticular muscles can be inherited, but only the 

 muscular system in general. If, however, in con- 

 sequence of the disuse of a group of muscles there 

 was a general diminution of the inherited muscular 

 system, the special group would remain diminished 

 while the rest were developed by use in the in- 

 dividual : there would thus be a special heredity 

 produced indirectly. With regard to general con- 

 ditions of life, Delage states that there are only 

 two of which we know anything — namely, climate 

 and alimentation — and he merely suggests that tem- 

 perature and food act at the same time on the cells 

 of the body and on the similar substances in the egg. 



H. M. Vernon {Variation in Animals and Plants, 

 1903, pp. 351 seq,) cites instances of the cumulative 

 effects of changed conditions of life, and points out 

 that they are not really instances of the inheritance 

 of acquired characters, but merely of the germ- 

 plasm and the body tissues being simultaneously 

 affected. He then asks, Through what agency is 

 the environment enabled to act on the germ-plasm ? 

 And answers that the only conceivable one is a 

 chemical influence through products of metabolism 

 and specific internal secretions. He cites several 

 cases of specific internal secretions, making one 

 statement in particular which seems unintelligible, 

 viz. that extirpation of the total kidney substance of 

 a dog leads not to a diminished secretion of urine 

 but to a largely increased secretion accompanied by 

 a rapid wasting away which soon ends fatally. 



