V. J. WULFF 



225 



model assumes two coupling processes between the photochemical and 

 electrical events: an electrochemical process and a timing process which 

 determines when the potential change becomes manifest. 



The electrochemical model is defined by the equation dc/clt = 

 bl — k (c — Ci). The positive term controls the formation of an electro- 

 chemical substance, C, and the negative term controls the breakdown or 

 disappearance of this substance. The first term is directliy linked to the 

 photochemical event and may be assumed to be temperature insensitive; 

 the second term is a decay process and may be assumed to be temperature 



TEMPERATURE 

 DEGREES CENT 

 10 



LOG 



10 



-3 -2 



FLASH DURATION 



Fig. 3. Curves showing the relationship between the magnitude of the retinal action 

 potential and the logarithm of the duration of illumination, and the effect of tem- 

 perature on this relation. The data were obtained from the eyes of intact dark-adapted 

 grasshoppers equilibrated to the indicated temperatures for several days, and at two 

 levels of illumination. Unit intensity represents 11,800 foot candles at the cornea. 



labile. When stimulating with short light flashes, the first term largely 

 controls the equilibrium concentration of the material, C (11). The model 

 predicts, therefore, that temperature should not appreciably affect the 

 magnitude of the retinal action potential obtained in response to short 

 light flashes. In the grasshopper this is indeed so, and in the case of Limulus 

 and frog photoreceptors the effect of temperature is small, Qio's from 1.0 

 to 1.3. On the other hand, for longer exposures the decay process contrib- 

 utes more and more to the equilibrium concentration of the electrochemical 

 substance; here temperature should have an effect, but the effect should 

 be inverse, i.e. lowering the temperature should slow the decay process, 

 thus increasing the equilibrium concentration of the electrochemical sub- 



