114 THE NATURE AND ORIGIN OF LIFE 



of the whole mechanism ; each element, situated at a fixed 

 point of the adult mechanism, can execute only one kind 

 of protoplasmic function. Muscle is muscle, nerve is nerve, 

 and we never find a muscle transforming itself into a nerve. 

 Here, then, there is no longer question of variation in the 

 nature of the mechanism of each cell, but simply of a more 

 or less considerable functioning of the cell according to a 

 model traced beforehand in each element as histologically 

 defined. In other words, a given element situated at the 

 point M of the body always does the same thing, no matter 

 what may be the function of the mechanism as a whole 

 determined in the animal by circumstances. Only, this 

 same thing which it can do it does a great deal, or little, 

 or not at all, according to the manner in which the organ 

 that the animal is at the given moment happens to be defined. 



Besides, we do not know if the elements of tissues under 

 observation here and now in an adult animal have come 

 to the absolute term of their differential evolution. We 

 said a little while ago that we never know whether to-day's 

 muscle is not still a trifle egg, that is, whether it does not 

 still contain rudiments of functions which are characteristic 

 of other tissues. If this were so, we ought to expect an 

 application of the law of functional assimilation as pre- 

 viously established by dint of acting as a muscle (by 

 muscle-ing) the muscle becomes more muscle. In any case 

 we should remember that this happens in the evolution 

 of species which, by progressive adaptations, has given to 

 each present species its own exact anatomy and histology. 



Suppose the muscle becomes more muscle by dint of 

 muscle-ing ; the case is exactly the same as with the proto- 

 plasmic elements which struggle against toxins or microbes 

 the colloid organ is created by repeated colloid functions. 



On the contrary, suppose that, in adult animals, each 



