SELIG HECHT 



659 



For the experiments, animals were used which had been in the 

 dark for some time,— more than long enough for them to have become 

 thoroughly dark-adapted (Hecht, 1919, a). Observations were made 

 by the dim light of a ruby lamp to which the animals are practically 

 insensitive. The reaction time to Hghts of different intensities 

 and for different exposure periods was determined for twenty-two 

 individuals. 



I 



I 



O. OS o./o 



0./5 

 Seconds 



0-2O 



Fig. 1. Individual determinations of the reaction time of four animals for 

 different exposure periods. The points read to the nearest tenth of a second. 

 The curve joins the averages for the different exposures. 



All the experiments agree in showing that for a given intensity 

 the reaction time varies inversely with the exposure, for exposure 

 periods shorter than the sensitization period. Exposures for intervals 

 greater than the sensitization period make no change in the duration 

 of the reaction time. The sensitization period may thus be defined 



