THE DEEPENING OF PHYSIOLOGY. 317 



could be isolated. Therefore, it seems advisable to 

 keep to the cautious vagueness of Huxley's phrase, 

 protoplasm is the physical basis of life. 



There are three slightly different physiological 

 conceptions of protoplasm at present in the field, 

 (a) Some regard protoplasm as a substance analogous 

 to a ferment, capable of acting on less complex ma- 

 terial which is brought within its sphere of influ- 

 ence. It is the strange characteristic of a ferment, 

 like diastase or pepsin, that it can act on other sub- 

 stances without being itself essentially affected by 

 the changes it induces, and that a minute quantity 

 can continue its work with a power which seems to 

 have little direct relation to its amount.* (&) 

 Others have suggested that protoplasm is, as it were, 

 the central term in a complex series of chemical 

 changes, itself the seat of continual change, ever be- 

 ing unmade and remade.f (c) Others again have 

 suggested that there is probably no one thing that can 

 be called protoplasm, for vital function may depend 

 upon the interactions or inter-relations of several 

 complex substances, none of which could by .itself be 

 called alive. Just as the secret of a firm's success 

 may depend upon a particularly fortunate associa- 

 tion of partners, so it may be with vitality. J 



As to the chemical composition of the physical 

 basis of life, physiologists are not at present in a 

 position to make many general statements. 



"Just as very different structural constituents may 

 be distinguished in living substance, so very different 



♦ See Sir J. S. Burdon-Sanderson, Pres. Address, Section 

 D, Rep. Brit. Ass. for 1889, pp. 604-614. 



t See Sir Michael Foster, Article, Physiology. Encycl. 

 Brit. 



X See E, B. Wilson. The Cell in Development and Inherit- 

 ance, 1896, new ed., 1900. 



