SELIG HECHT 



549 



the reaction time at frequent intervals, it is possible to follow the 

 progress of the acquisition of sensitivity. 



The details of an experiment are as follows. An animal is exposed 

 to an intensity of about 3,000 meter candles. At the end of an 

 hour the light is turned off and the animal left in complete darkness 

 except for the presence of a ruby light. After definite intervals the 

 response of the animal to a hght of 225 meter candles is determined 

 by recording the reaction time. 



% 

 I 



I 



2.0 



/.5 







/O 



20 30 



77/7)6 7d dar/r - 



^o 



^o 

 •/^/nufe3 



Fig. 1. The course of dark adaptation. Each point is the average of six 

 determinations of the reaction time. The curve represents the progress of a 

 chemical reaction of the second order with a velocity coefficient of ^ = 0.245. 



Preliminary experiments showed that the animals became sensitive 

 to the weak light in less than 5 minutes. From then on the reac- 

 tion time became progressively shorter until it reached a constant 

 minimum in about 45 minutes. Six experiments were therefore 

 made on as many animals, under conditions of exposure, temperature, 

 etc., as similar as possible. The data are given in Fig. 1. Each 

 point represents the average of six determinations. It is apparent 



