ORGANISM AND MECHANISM 137 



it fails all along the line in thoroughness of description, 

 and that it does not give us the kind of answer that as 

 biologists we want. No student of science could have any- 

 thing but delight in learning that the contraction of a muscle, 

 or a reflex action, or the movements of an Amoeba had been 

 satisfactorily described in terms of chemistry and physics. 

 But it has not been done as yet in the case of any single 

 vital activity. Diffusion plays its part in the interchange of 

 gases in the lungs, but the lining epithelium of the air-sacs be- 

 haves, Dr. J. S. Haldane tells us, in a way which modifies 

 diffusion processes, and that elusive modification keeps us 

 alive. In the second place, the mechanistic description, even . 

 if it attained to the completeness of a ledger of all the chem- 

 ical and physical processes in a piece of behaviour, would 

 not thereby give us a natural history description of the 

 behaviour. We need historical or genetic concepts. So we 

 do not propose to sum up the ways of a starfish as those 

 of a physico-chemical machine. 



(d) The distinctively biological position admits that phys- 

 ical and chemical formulae, concepts, or ' categories ' are 

 applicable to organisms, but argues that they are inadequate, 

 notably, for instance, because life is always in a sense his- 

 tory. But has not the line of physiological progress been 

 mechanistic? The answer is that it is part of the method 

 of science to l abstract ', and that it has been of great service 

 to corner off and analyse physical and chemical operations 

 which occur in organisms. But the success that has attended 

 the study of the chemistry of the blood or the study of the 

 optics of the eye, does not prove that the physico-chemical 

 description of a living creature is or can be adequate. 



(e) A thoroughly sound criticism is, that the concepts of 

 physics and chemistry are not stationary but in process of 



