RETINAL PHOTOPIGMENTS 



139 



Fig. 99 (Left). Frog, dark-adapted at room temperature, dark-adapted 

 one hour at 0°C, light-adapted one hour at 0°C, then allowed to come back 

 to room temperature in the light for two hours. The retina shows sparsity of 

 droplets and almost maximal migration of the epithelial pigment. 



Fig. 100 (Right). Frog, light-adapted at room temperature, then at 0°C 

 for one hour, and then dark-adapted for one hour at 0°C. The retina shows 

 sparsity of droplets and maximal migration of epithelial pigment. 



B, 5R: and Figures 97, 98, cf. Figure 92). If, after treat- 

 ment as indicated above, the frogs were allowed to come to 

 room temperature in the light (Experiment 5L, Table 4) the 

 eye in section exhibited conditions typical of hght-adaptation 

 at room temperature, viz., fully expanded epithelial pigment 

 and a sparsity of droplets. The results are shown in Table 4 

 (Experiment 5L) and in Figure 99. The failure of the epi- 

 thelial pigment to contract in the dark at 0°C is in line with 

 the former observations of Herzog (1905), Arey (1916a), 

 and Detwiler and Lewis (1926) which showed that at low 

 temperatures, in the dark, the epithelial pigment tends to 

 migrate as it does in the light. 



The converse of the above conditions is illustrated by 

 Experiment 7 (Table 4). Here the frog was first light- 

 adapted at room temperature, then brought to 0°C in the 

 light for one hour, and then placed in darkness at 0°. Eyes 

 so treated exhibited conditions more characteristic of light- 

 than of dark-adaptation. The droplets were sparse and 



