THE VISUAL PIGMENTS 



The proportions of vitamin A^ and Ag in fish-eye tissues and 

 Hvers. The results are expressed in 'colour equivalents' of the 

 Carr-Price test: the extinction at 618 m/u due to vitamin A^ com- 

 pared with the extinction at 696 m/Li due to vitamin Ag. Each 

 pair of values is scaled to 100. (Wald, 1939a.) 



* Pigmented epithelium included. 



Presumably these operate through specific enzyme systems which 

 govern the conversion of dietary carotenoids, ultimately of plant 

 origin, into the vitamins A.* 



WALD (1941) found that the visual pigment solutions obtained 

 from euryhaline fish had density spectra intermediate between those 

 of rhodopsin and porphyropsin. In Fig. 2.5 the density spectra of 



36 



