SELIG HECHT 553 



Effect of Temperature. 



1 . The significance of an hypothesis is materially strengthened by 

 the testing of certain corollaries that follow from its acceptance. 

 One such prediction was investigated in the case of Ciona with re- 

 sults that amply justified the application of the hypothesis. The 

 greater definiteness of the reaction system in the case of Mya made 

 possible the investigation of other phases of the hypothesis. 



It is well known that the rate of photochemical reactions is com- 

 paratively uninfluenced by a change in the temperature (Redfield 

 and Bright, 1919). Therefore the decomposition of photosensitive 

 material, S -^ P -\- A, should proceed practically independent of the 

 temperature. The reverse reaction, however, P -\- A —^ S, being an 

 ordinary bimolecular reaction and independent of the presence of 

 light, should be decidedly influenced by the temperature. 



Two things obviously follow from these conceptions. The first 

 is that the amount of precursor substances present at the ''station- 

 ary state" for a given intensity will vary inversely with the tem- 

 perature. The rate of formation of precursor substances being prac- 

 tically the same at all temperatures, the amount of precursor sub- 

 stances present will depend solely on the rate of their recombination. 

 Therefore at low temperatures there will be more precursor in the 

 system than at high temperatures. Since the sensitization period 

 at any moment measures the amount of precursor substances present 

 in the system, the sensitization period for a sensory equilibrium at a 

 given intensity will vary inversely with the temperature. 



The second corollary concerns the rate of dark adaptation. This is 

 determined entirely by the reaction A -\- P -^ S. With the complete 

 exclusion of light, this reaction should proceed faster at higher tem- 

 peratures and slower at lower temperatures. The curve of dark 

 adaptation as given in Fig. 1 should therefore show changes with 

 temperature of the kind usually associated with chemical reactions. 



2. Both of these points were investigated, and the experiments 

 verified the assumptions unequivocally. The procedure was essen- 

 tially the one previously described for the experiments on dark 

 adaptation. After determining the rate of dark adaptation at room 

 temperature on an animal, it was kept undisturbed for several hours 



