232 THE THEORIES OF EVOLUTION 



will be deprived of the source from which it received 

 that substance. This substance will not be found in 

 the sexual product or only in very small quantities. 

 When the ovum develops, the organs characterised by 

 that special substance will only appear in a degener- 

 ated condition. 



The same holds true of modifications resulting from 

 use or disuse of organs or from hereditary after- 

 effects of diseases which affect the cell plasm for a 

 greater or smaller length of time. This is the way 

 immunity, for instance, can be transmitted to the 

 offspring. Vaccines affect certain chemical elements 

 of the organic cells and the related substances in the 

 ovum which will impart to the future organism the 

 same character of immunity. 



Certain characters are acquired under the influence 

 of life conditions, nutrition being one of the fore- 

 most factors. Our explanation of the mechanism of 

 transmission can be easily applied to nutrition, for 

 the influence of diet on the composition of the blood 

 is incontestable. Through the medium of the blood, 

 food stuffs act upon the sexual cells and upon the sub- 

 stances they contain and which will, afterwards, re- 

 appear in the cells of the future organism. This 

 accounts, if not for the influence of soma cells upon 

 germ cells, at least for the simultaneous and correla- 

 tive influence of certain external factors upon soma 

 and germ cells. 



