RETINAL PHOTOPIGMENTS 



121 



was found to reduce the time of visual purple regeneration 

 in the dog and rabbit. Kuhne (1879) cited the parallelism 

 between the time needed for regeneration of visual purple 

 in the frog and the length of time in which dark adaptation 

 is first accomplished as evidence of a relationship between 

 the two. 



559 



542 530 519 509 



459 



-yu./J.. 



Fig. 82. Showing the similarity between the curve representing the rate of 

 bleaching of visual purple by light of different wave lengths and the luminosity 

 curve of twilight vision. (From Starling, Human Physiology, 7th Edition. 

 Lea & Febiger, Philadelphia.) 



Garten (1907) suggested that it was not the epithehal 

 pigment that was concerned with the generation of visual 

 purple, but the basal part of the pigment cell itself. This 

 was obvious from the fact that visual purple was found to 

 occur in the pigment-free portions of the retina in many 

 animals and in the eyes of albirios. 



When a dark-adapted retina is exposed to light, its rose 

 color quickly fades to a yellowish or orange color and finally 

 to white. If it is again placed in the dark, it will regenerate 

 its original pink or rose color. On this matter there have 

 been differences of opinion, for some observers claimed that 

 the pigment will regenerate only if the retina is accompanied 



