684 TEMPERATURE AND LATENT PERIOD 



VII. 



The analysis with which we have been occupied, though it accounts 

 for the data in a simple way, is not the only one possible. Even in 

 the terms of the hypothesis of photoreception which has been adopted 

 ior Mya, there is at least one other explanation, just as plausible but 

 not as simple, which deserves to be mentioned. Without entering into 

 details, I wish to present this alternative analysis in its barest outhnes. 



The reaction of the latent period, L ^ T, is catalyzed by the 

 precursor material freshly formed during the sensitization period. 

 Organic catalysts are enzymes, and enzymes are notoriously ther- 

 molabile. Since the velocity of the latent period reaction is a linear 

 function of the concentration of catalytic precursor (Hecht, 1919, b), 

 the deviations of the latent period at higher temperatures may be 

 considered as due to the destruction of some of this catalytic agent. 

 The velocity of the latent period reaction becomes slower because 

 of the decrease of catalyst. The time required to form a definite 

 amount of T to produce a response is, therefore, lengthened beyond 

 that required on the basis of the Arrhenius equation (3). Assuming 

 that the destruction of the precursor catalyst follows the usual 

 course of such spontaneous decompositions, it is possible to estimate 

 quantitatively its velocity constant, and to express the entire process 

 diagrammatically. 



The actual mathematical considerations, however, are rather 

 involved. The destruction of the precursor material must be esti- 

 mated not only during the latent period after its production, but 

 during the sensitization period while it is still being produced. The 

 simpler analysis has, therefore, been given in detail because it fits 

 the facts just as well. Certain deductions from the two explanations 

 are, however, different for the two cases, and further experimentation 

 will show which is more probably correct. 



SUMMARY. 



1. The effect of temperature on the reaction time of Mya to light 

 is mainly confined to the latent period. The sensitization period, 

 representing a photochemical process, is changed comparatively 

 little. 



