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 [Footnote: Yves Delage, _L'Heredite_
(Paris, 1895), pp. 806-812.] 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 l'oeuf de recevoir la modification reversible c'est
qu'etant constitue autrement que les cellules differenciees de l'organisme
il est influence autrement qu'elles par les memes causes perturbatrices.
Mais est-il impossible que malgre la difference de constitution
physico-chimiques il soit influence de la meme facon?'

The author's meaning would probably have been better expressed if he had
written 'ce qui parait empecher.' 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 the development of the body from the ovum Is not an influence
at all but a direct conversion by cell-division and differentiation of the