EVOLUTION IN NATURE 173 



given heritage would show any characters which 

 this environment could bring out. The modification 

 of the body would certainly subject the germinal 

 tissues to a change of environment through this 

 continued individual response of successive gen- 

 erations. We may say that any resulting change in 

 the heritage is a mutation because it is directly due 

 to conditions limited to the body, but we gain 

 little by doing so, for again we are concerned with 

 the response of living substance to the conditions 

 surrounding it, and the chain of environmental 

 relationships always involves both external and 

 internal factors. 



The possibility also exists that the effect of in- 

 dividual responses in the body is only quantitative. 

 If so, have we any reason to expect qualitative 

 changes to result.'^ Unfortunately no definite con- 

 clusion is indicated here, but quantity is difference 

 of a kind and may provide for unexpected con- 

 tingent actions. Le Dantec regards the variations 

 due to individual response in this light, and traces 

 quantitative change to a point where the complete 

 elimination of one or another xjomponent may bring 

 about a definitely qualitative result. ^^ And the 

 formation of CO and COg may depend entirely on 

 the amount of oxygen available. Indeed, the two 

 gases are quantitatively different in a sense, but 

 they are also qualitatively different in many ordi- 



25 Evolution individuelle et heredite, 1898. 



