224 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



the clam, Mya arenaria. Hecht found the duration of the latent period was 

 inversely related to the temperature. The average Qio was 2.5. 



INIore recently, the effect of temperature on the latent period of the 

 retinal electric response has been investigated in the grasshopper, Limulus, 

 and frog photoreceptor. The data show that latent period and temperature 

 are reciprocally related. The Qio values obtained range from 2.34 to 4.01, 

 the larger values applying to low temperature ranges. The results from 

 all animals are rather similar and may be illustrated by the data obtained 

 from the grasshopper (fig. 2). 



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LOG« INTENSITY 



Fig. 2. Curves showing the relationship between the latent period of the retinal 

 action potential and the logarithm of the intensity of illumination, and the effect of 

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

 adapted grasshoppers equilibrated to the indicated temperatures for several days. 

 The flash durations used were 0.05 and 0.01 sec. and were maintained constant in any 

 one experiment. Unit intensity represents 11,800 foot candles at the cornea. 



The effect of temperature upon the retinal action potential is in sharp 

 contrast to the temperature effect on the latent period. In the grasshopper, 

 it is possible to select intensities and short durations of stimulation such 

 that the magnitude of the response is not at all affected by temperature 

 (fig. 3). On the other hand, one can select long flash durations such that 

 the magnitude of the potential is larger, the lower the temperature. The 

 marked differences in the behavior of the latent period and the magnitude 

 of the retinal action potential to altered temperatures are predicted by a 

 kinetic model of coupling processes between the photochemical and elec- 

 trical events in photoreceptors (8, 2) . Incidentally, the kinetic model was 

 developed independently of the temperature effects just described. The 



