52 PRINCIPLES OF PHYSIOLOGY 



regulate form in living mechanisms, but 

 physiological considerations cannot be ex- 

 cluded. How are we to explain the forces 

 in operation in producing the cleavages and 

 movements that are apparent ? How can we 

 account for the nutrition of the chromatin, 

 said to be the fundamental basis of heredity, 

 by which it multiplies itself ? Is there, as 

 some suppose, an inner world of molecular 

 movement in the chromatin, by which, influ- 

 enced by nutrition and by a kind of struggle for 

 existence and survival of the fittest, new com- 

 binations of chromatin-particles are effected so 

 as ultimately to produce individuals different 

 in some ways from their parents, or are the 

 phenomena only under the laws of chance like 

 the results of the rattle of the dice box ? 

 These are all profound questions lying at the 

 very basis of physiology. 



24. Not many years ago it was not uncom- 

 mon for physiologists to think of the repro- 

 ductive elements, ova and spermatozoa, as 

 practically structureless, and to regard them 

 as being composed simply of granular, jelly-like 

 matter. Since then, owing to the improve- 



