16 THE NEW PHYSIOLOGY. 



tions and therefore purely artificial. The difficulty 

 remains of reconciling the fundamental conceptions of 

 biology with those of physics and chemistry. This is, 

 however, a matter of which the discussion must be 

 handed over to philosophy, which has many similar 

 matters to deal with. If it is a fundamental axiom 

 that an organism actively asserts or maintains a specific 

 structure and specific activities, it is clear that nutrition 

 itself is only a constant process of reproduction : for 

 the material of the organism is constantly changing. 

 Not only is there constant molecular change, but the 

 living cells are constantly being cast off and reproduced. 

 It is only a step from this to the reproduction of lost 

 parts which occurs so readily among lower organisms ; 

 and a not much greater step to the development of a 

 complete organism from a single one of the constituent 

 cells of an embryo in its early stages. In all these facts 

 we have simply manifestations of the fundamental 

 characters of the living organism. The reproduction of 

 the parent organism from a single one of its constituent 

 cells separated from the body seems to me only another 

 such manifestation. Heredity, or, as it is sometimes 

 metaphorically expressed, organic memory, is for bio- 

 logy an axiom and not a problem. The problem is 

 why death occurs, what it really is, and why only 

 certain parts of the body are capable of reproducing 

 the whole. These questions carry us, at least in part, 

 beyond the present boundary lines of biology. They 

 involve those ultimate questions which, as has just 

 been pointed out, it is the province of philosophy to 

 deal with. 



To turn to another set of questions, the distinctively 



