Effect of Different Temperatures on the Medusa Cassiopea. 39 



The characteristic maxima, at an optimum temperature, exhibited 

 by curves A and B (fig. 5) require a word of comment. Maxima occur in 

 all temperature curves of vital processes. A maximum is also exhibited 

 by temperature curves of enzyme action. In fact the curves for enzyme 

 action as given in Cohen 's Physical Chemistry x are very similar to curves 

 A and B. There is the same falling off in calculated (if Q 10 were a constant) 

 velocity, ihe higher the temperature until a maximum is reached. 



Different enzymes exhibit maxima at different temperatures. Most 

 of these are rather high, much higher than the maximum for nerve- 

 conduction, which lies at about 33 C. The same ferment obtained 

 from different sources may exhibit different maxima. For instance, 

 the indigo enzyme obtained from Indigofera heptostacha has a maximum 

 at 61 C. ; from Polygonurn tinctorium, 53 C.; from Phajus grandiflorus, 

 42; and from Saccharomyces sphcericus, 44. Cohen explains this as 

 meaning that the optimum depends on the medium containing the 

 ferment. If we may assume that conditions in the nerve are such as 

 to give a very low optimum, then we may say that the propagation of 

 the nerve impulse is not only dependent on the velocity of a chemical 

 reaction, but that the reaction is further accelerated by the presence of an 

 enzyme. Thus the characteristic difference in the form of curve from 

 that of a simple chemical reaction. 



The maximum for enzyme actions is generally interpreted as the 

 point beyond which the enzyme begins to undergo decomposition with 

 consequent falling off in the reaction velocity, even though the temper- 

 ature is continually increased. 2 Taylor 3 regards all reactions as having 

 an optimum temperature at which the velocity is a maximum, only in 

 enzyme action this temperature is low. Blackman points out that in a 

 process proceeding at a certain rate (e.g., a reaction) and dependent on 

 several factors, any one of the factors may become a limiting factor for 

 the process in question. 



Whatever the explanation may be, it is interesting to find that 

 nerve conduction exhibits a falling off in rate with rise of temperature 

 to a definite maximum, similar to that for enzyme action and for other 

 life processes. 



A literature list of the effect of temperature on vital processes inter- 

 preted with respect to van't Hoff's coefficient (Q 10 ) is given by Loeb, 

 Robertson, Maxwell, and Burnett in Science, N. S., 28, p. 647, 1908. 

 References to literature on this subject are also given in Cohen's Physical 

 Chemistry, translated by Fischer, New York, 1903, pp. 50-67. 



Cases of vital processes exhibiting chemical temperature-coefficients 

 have been collected by Kan;tz, A., in Zeit. fur Elektrochemie, 13, p. 707, 

 1907, and Snyder, C. D., in Am. Jour. Physiol., 22, p. 309, 1908. The 

 reader is referred to the above four papers for the literature on this 

 subject. 



1 Translated by Fischer, p. 56. 



2 For a discussion pf the meaning of an optimum temperature, see Black- 

 man, Annals of Botany, 19, p. 281, 1905, and Am. Nat., 42, p. 659, 1908. Also 

 Bayliss, Nature of Enzyme Action, in Monographs on Biochemistry, p. 52, 1908. 



3 Taylor on Fermentation in Univ. of Cal. Pub. Pathology I. 



