144 THE NEW PHYSIOLOGY. 



in the organism there is individual variety of detail, 

 and yet perfectly definite and specific unity of plan. 

 For the formation of the crystal it is necessary that each 

 molecule of water should have the property of tending 

 to orientate itself to any other in a certain definite 

 manner. Mere central forces of attraction do not ex- 

 plain the formation of a crystal from molecules or of a 

 molecule from atoms. Similarly, in the development of 

 an organism we seem bound to assume that the germ 

 has the property of tending to orientate towards itself 

 certain surrounding molecules in the specific arrangement 

 of the fully developed organism, and that these surround- 

 ing molecules have corresponding properties. 



It may be pointed out that this is no explanation. 

 Nor is it meant to be an explanation. It is a mere 

 general statement of what appear to be the facts of 

 observation. In mechanical physics we have become 

 accustomed to think of molecules or atoms as quite 

 simple things with easily definable properties, such as 

 mass, extension, and central forces of attraction. For 

 biology, the properties which must be assumed in the 

 unit of living structure are enormously more complex, 

 and are only capable at present of statement in general 

 terms. It is solely from previous actual observation 

 that we can predict how the living structure will behave, 

 and we can only do so if the environment is about the 

 same as in the previous observation. 



Practically, therefore, we must look upon organism 

 and environment as one interconnected whole which, 

 as a matter of empirical fact, tends to maintain itself, 

 just as a crystal and its mother-liquor do, or a molecule 

 and the solution in which it has formed. From no 



