METHODS 109 



How far can such differentiation go ? We have already 

 said that habit has limits. Ought we to think that each cell 

 of a body comes to a point of differentiation where it is 

 capable of but one function exclusively the function 

 (A x Bj), for example ? Or ought we, on the contrary, to 

 believe that differentiation is limited to the development, 

 in each cell, of certain organs rather than others which 

 still exist there, although now of little importance ? This 

 is a disputed question. 



The chicken comes from an egg which has neither muscles, 

 nor nerves, nor bones ; but we have an idea that functional 

 assimilation develops differently for each tissue certain 

 peculiarities, all of which existed in the egg. In other 

 words, the egg is somewhat muscle, somewhat nerve, some- 

 what bone ; the question is to know whether muscle, nerve, 

 bone are also somewhat egg, that is, whether, along with the 

 organ corresponding to their special function, they contain 

 rudiments of organs corresponding to the functions of other 

 tissues. 



However this may be, the law of functional assimilation, 

 from the start, prevents us from being astonished at one 

 thing, namely, that in so complicated a mechanism as 

 man each tissue should be exactly adapted to the needs of the 

 place it occupies. The law of functional assimilation has 

 been established for cases in which exterior circumstances 

 B are reduced to transportable colloid elements and this 

 limits us here to the functions of protoplasmic mechanism. 

 But it is easier for us, after what we have learned, to extend 

 this general law to functions of the mechanism as a whole. 



