MOTOR RESPONSES 



293 



of an exposure period and a latent period. With increase in intensity 

 of illumination, the exposure period decreases, at first rapidly, then 

 more slowly, until it becomes nearly constant; the latent period increases 

 to a maximum and then decreases, and the amount of light energy re- 

 quired during the exposure period increases from 22,970 meter-candle 

 seconds at 538 meter-candles to 54,315 meter candle seconds at 2,152 

 meter-candles, and then decreases to 13,498 meter-candle seconds at 



I Z 3 4 



TIME. IN LIGHT IN H0UR5 



Figure 105. Graphs showing rate of light-adaptation. Dark-adapted peranemas were 

 exposed to light (intensity given in the graph) for the time indicated, then subjected 

 to darkness one half hour, then exposed to 2,152 m.c, and the reaction time measured. 

 Each point on the curves represents the average reaction time for ten tests, different 

 individuals being used in each test. (After Shettles, 1937.) 



6,458 meter-candles (Fig. 106) . He concludes that "the amount of light 

 energy required to induce a shock-reaction in Peranema varies greatly 

 with the intensity of the light and that the Bunsen-Roscoe law conse- 

 quently does not hold." 



The latent period decreases from 39-68 seconds at 10° C. to 24.3 

 seconds at 30° (15.38 seconds), but the exposure period decreases from 

 27.87 to 22.97 seconds (only 5.8 seconds). This indicates that there 



