340 



INTENSITY AND PHOTORECEPTION 



five animals. From Fig. 1 it is clear that the duration of the latent 

 period varies inversely with the intensity of the stimulating light. 



This conclusion is precisely what is to be expected from previous 

 work. It indicates definitely enough that the velocity of the latent 

 period reaction is controlled by the products of decomposition of the 

 photochemical reaction. The data are, however, not to be dismissed 

 with a merely qualitative treatment. A closer analysis brings to 

 light a situation of the utmost significance for an understanding of 

 the mechanism of photoreception. 



I 



I 



C^ 6.0 





/ooo 



2000 



3000 



Intent I tu — /yefer-Cand/es 



Fig. 2. Relation between the intensity at constant exposure and the velocity 

 of the latent period reaction. The velocity as given by the ordinates is ten times 

 the reciprocal of the latent period. 



III. 



The reciprocal of the latent period is a direct measure of the velocity 

 of the reaction L—^T which determines the duration of the latent 

 period. Fig. 2 gives the connection between the intensity and the 

 velocity of the latent period reaction. For convenience the velocity 

 is represented as ten times the reciprocal of the latent period. This 

 makes no difference in the theoretical deductions, because it merely 

 changes the units in which the velocity is given. From the figure it 



