396 RESPIRATION 



us, of organic identity. It is the same in connection with the phe- 

 nomena of circulation, excretion, absorption, and other physio- 

 logical activities. I wish to claim very definitely that in dealing 

 with biological phenomena and putting her questions to Nature, 

 biology must use her own working hypothesis, and not those of the 

 physical sciences. 



The organic regulation which we find everywhere in a living 

 organism does not represent something imposed from without on 

 the processes occurring in the organism, but is simply a natural 

 expression of the reality which is present. It is Nature we are 

 studying in biology, not a special "vital force" or other super- 

 natural influence. But the biologist must be free to interpret 

 Nature in his own way; and it is Nature as Hippocrates saw her, 

 and not as Democritus saw her, that he sees and cannot help 

 seeing. Organic regulation, maintenance, and reproduction are 

 nothing but the expression of this biological Nature. 



The universal acceptance among biologists of the doctrine of 

 evolution has often been assumed to carry with it the corollary that 

 life has arisen out of inorganic conditions ; and in this way a short 

 cut has been made to the conclusion that biology must in ultimate 

 analysis be nothing but physics and chemistry. This reasoning 

 cannot be justified. Even in the simplest forms of life it is still 

 unmistakably life that we are dealing with ; and if we succeed in 

 tracing life to yet simpler forms we shall still find life, so that the 

 "inorganic conditions" into which we have traced life will ap- 

 pear to be something very different from inorganic conditions 

 as we now represent them to ourselves. 



We can see, and particularly clearly in the case of higher or- 

 ganisms, that the life of each organism is an association of the 

 lives of more elementary organisms, each of which shows its full 

 being only in the life of the whole, but is also more or less capable 

 of independent existence. It is by the separation and subsequent 

 full development of these more elementary organisms that re- 

 production is brought about. The life of a higher organism has 

 been said to be the "sum" of the lives of its constituent cells. Such 

 an expression is, however, misleading: for a cell apart from its 

 particular place in the living body, or the particular environment 

 which exists there, behaves very differently from the same cell 

 in its proper place. It thus cannot be physiologically defined apart 

 from its place in the whole organism. The organism as a whole is 

 no less real because it includes in its life the lives of individual 

 cells, and each cell, as shown very clearly in connection with the 



