322 1- H. HYMAN AND A. \V. BELLAMY. 



with rise of temperature, those in which it does not alter with 

 change of temperature, and those in which it increases with rise 

 of temperature, so that the chain cools in giving rise to a current. 

 The concentration cells belong to the third class. In concentration 

 chains, also, the increase in electric energy with rise of temperature 

 is proportional to the absolute temperature. It appears that the 

 bioelectric currents possess these properties, so far as tested i.e., 

 the potential difference increases with rise of temperature and the 

 increase is approximately proportional to the rise ; further in at 

 least one case, that of the electric organ of the torpedo (Bernstein 

 and Tschermak, '06), the circuit cools during the discharge, al- 

 though only a few thousandths of a degree. 5 



The concentration-cell theory can be included in the metabolic 

 rate theory advanced in this paper. For differences in metabolic 

 rate lead to differences in the concentration of ions, which thus 

 become the sources of potential differences. This view was pre- 

 sented above (p. 315). That the electromotive force is propor- 

 tional to the absolute temperature need not greatly concern us, 

 since this is also not infrequently the case where chemical reactions 

 are obviously involved (cf. Bayliss, '15, pp. 42-43). 6 



The membrane-depolarization theory is closely related to the 

 concentration-cell theory, in that its adherents suppose the concen- 

 tration differences to arise through the presence of semipermeable 

 membranes in living organisms. This matter is discussed by 

 Bernstein ('02, '12), Cremer ('06), Briinings ('03), R. S. Lillie 

 ('ii, '13), and others. The chief tenets of this theory are: that 

 the cell membranes are semipermeable membranes, which are per- 

 meable only to certain ions, chiefly, in the opinion of most authors, 

 positively charged ions ; that the cations pass through the mem- 



5 If the production of electromotive energy in organisms is an endothermic 

 reaction, as Bernstein maintains, this may account for the lack of heat 

 production in a stimulated nerve. 



6 It is rather amusing to note that whereas on p. 42 Bayliss severely 

 criticises the idea that the temperature coefficient furnishes reliable infor- 

 mation concerning the chemical or physical nature of a biological process 

 and mentions some cases where chemical reactions are obviously involved 

 in which the velocity is a linear function of temperature, on p. 644 he rejects 

 the possibility that the bioelectrc currents are due to chemical reactions on 

 the grounds that the electromotive force is proportional to the absolute tem- 

 perature. 



