BIOLOGY 



from abundant experience that such is actually 

 the case. 



What may be the nature of the so-called 

 Mendelian factors which modify the development 

 of an organism in so many respects we do not 

 know, but we may fairly suspect them to be 

 chemical in their mode of action. We know that 

 almost infinitesimal quantities of certain chemical 

 substances may produce profound effects upon 

 the living organism. The embryos of the fish 

 Fundulus react towards the presence of magnesium 

 chloride by developing a single eye in the middle 

 of the head instead of one on each side. The 

 mechanism of the process is as yet entirely un- 

 known, but it is a perfectly definite reaction to a 

 perfectly definite chemical stimulation. 



We are here brought face to face again with 

 our Biochemistry, and in this connection I should 

 like to give one more illustration of the close inter- 

 dependence of the different branches of our sub- 

 ject. The problem of the inheritance or non- 

 inheritance of somatogenic or so-called acquired 

 characters has long been one of the burning 

 questions of Biology. It has given rise to endless 

 scholastic argument and interminable hair-splitting, 

 the one school occupying itself in producing ' con- 

 clusive ' evidence and the other in demolishing it. 

 The difficulty in devising and carrying out really 

 critical experiments has so far proved almost 



139 



