108 THE NEW PHYSIOLOGY. 



germ-material " germ-plasma," as if it were a liquid 

 similar to the blood-plasma, and capable of having 

 similar liquid added to or subtracted from it without 

 alteration of its properties. 



To speak quite plainly, this theory is completely self- 

 contradictory. A plasma is a liquid containing various 

 kinds of molecules in simple solution, and possibly also 

 aggregates of molecules in suspension. In such a liquid 

 the molecules and aggregates are free to move about, 

 and are in constant and rapid motion. Fixed and 

 definite structure does not exist. For a mechanistic 

 explanation of heredity a most definite structure of 

 inconceivable complexity must be postulated — no mere 

 plasma ; and the difficulty of conceiving how this 

 structure reproduces itself remains just as before. 

 Weismann only shifted the difficulty from one place to 

 leave it without the slightest simplification at another. 

 On denying the influence of changes in the somatic cells 

 on the germ-material, the necessity arises of making 

 the structure of the germ-material so much more 

 complex, to account for the fact that both parent 

 and offspring develop similar new characteristics in 

 similar new environments. Whether we regard the 

 germ as very simple or as very complex, the problem 

 remains equally insoluble from a mechanistic standpoint ; 

 but if the germ-material is supposed at one and the 

 same time to be an extremely complex and definite 

 structure, and a simple " plasma," the supposition 

 makes sheer nonsense. 



Physiologists who have seriously considered the 

 problem of heredity, and yet adhere to the orthodox 

 mechanistic opinions, are, I think, for the most part 



