INTRODUCTION 



HISTORICAL SURVEY OF THEORIES OR SUGGESTIONS 

 OF CHEMICAL INFLUENCE IN HEREDITY 



WEISMANN, strongly as he denied the possibility of 

 the transmission of somatic modifications, admitted 

 the possibility or even the fact of the simultaneous 

 modification of soma and germ by external conditions 

 such as temperature. Yves Delage l in 1895, in 

 discussing this question, pointed out how changes 

 affecting the soma would produce an effect on the 

 ovum (and presumably in a similar way on the sperm). 

 He writes : 



' Ce qui empeche 1'ceuf de recevoir la modification 

 reversible c'est qu'etant constitue autrement que les 

 cellules differenciees de I'organisme il est influence 

 autrement qu'elles par les memes causes pertur- 

 batrices. Mais est-il impossible que malgre la 

 difference de constitution physico-chimiques il soit 

 influence de la meme fagon ? ' 



The author's meaning would probably have been 

 better expressed if he had written ' ce qui parait 

 empecher. 5 By ' modification reversible ' he means 

 a change in the ovum which will produce in the next 

 generation a somatic modification similar to that by 

 which it was produced. It seems natural to think 

 of the influence of the ovum on the body and of the 

 body on the ovum as of similar kind but in opposite 

 directions, but it must be remembered always that 



1 Yves Delage, VHeredite (Paris, 1895), pp. 806-812. 



xi 



