554 SENSORY EQUILIBRIUM AND DARK ADAPTATION 



in the dark. After such a rest, the experiment was repeated at a 

 lower temperature. This means that both the exposure to the in- 

 tense light and the dark adaptation were conducted at the lower 

 temperature. After some hours of rest the experiment was again 

 repeated at a still lower temperature. 



Mya is a particularly good animal for such purposes because the 

 continuous water current from its siphons goes through the body and 

 serves to stir the water. The animal is thus maintained at the tem- 

 perature of the water. Reliance was, however, not placed upon 

 this, and the usual precautions were taken for maintaining an approxi- 

 mately constant temperature throughout an experiment. 



The results obtained with five animals are shown in Fig. 2. Each 

 point represents an individual reading of the reaction time of the ani- 

 mal indicated. The data as plotted serve, therefore, to show the 

 experimental error as well as the regularities observed. In order 

 to point out the trend of the data of Fig. 2, I have drawn as solid 

 lines the course of a reaction of the second order at the three tem- 

 peratures indicated. The velocity coefiicients (k) are 0.095 at 

 11.5°C., 0.182 at 16.2°C., and 0.228 at 21.9°C. In making the 

 calculations according to the equation 



1 X 



at a—x 



it should be remembered here also that the latent period is to be 

 subtracted from the reaction time to get the sensitization period. 

 The latent period varies with the temperature (Hecht, 1919) . For this 

 group of animals and at the temperatures indicated above, the latent 

 periods are, respectively, 2.02, 1.57, and 1.31 seconds. How well 

 the theoretical curve corresponds with the observed individual read- 

 ings is clear from the figure. Table IV in addition gives a com- 

 parison between the calculated and the average observed values of the 

 reaction time. 



The data show the two corollaries of the hypothesis to be cor- 

 rect. Taking the value of a-x at t ^ o we get the sensitization 

 period for the last moment of sensory equilibrium at the three tem- 

 peratures. These are 5.38 seconds at 11.5°, 3.43 seconds at 16.2°, 

 and 1.79 seconds at 21.9°. They therefore show a decided increase 



