40 The Significance of Chemical Molecules 



processes of life of that very substratum. The former 

 processes are purely physical or chemical ; in a word, they 

 are aplasmatic processes ; the latter ones we must designate 

 as plasmatic; that is, as taking place in the molecules of 

 the living protoplasm itself. The former belong to phy- 

 siological chemistry and physics, the latter form the 

 proper subject of physiology. But toward an under- 

 standing of the latter we have taken only the first steps. 



It is neither by general considerations, nor on an ex- 

 perimental basis, that we can penetrate, at the present 

 moment, into the relations between the qualities of the 

 chemical molecules of the protoplasm and the phenomena 

 of heredity. It can therefore be only a matter of try- 

 ing, by means of hypotheses, to get an insight into these 

 relations. 



It is evident that we are justified in making such an 

 attempt. This right is very generally acknowledged, for 

 several prominent investigators have published their 

 views on this subject. Some have even made their hy- 

 potheses accessible to the critical consideration of others 

 by working out logically the consequences arising there- 

 from. And certainly, no one can doubt for a moment that 

 these hypotheses, much as they differ at present, have 

 aroused scientific interest in these questions. 



The directions which these hypotheses take can, I be- 

 lieve, be summarized under three heads. Some authors 

 go directly back to the chemical composition of proto- 

 plasm and seek to derive the life-processes from it. 

 Others again assume that the chemical molecules are com- 

 bined into larger, but still invisibly small organic units, 

 and regard these units as the real bearers of heredity. 

 Some of them imagine that these units always represent 

 the whole specific character, and that therefore the in- 



