146 



VERTEBRATE PHOTORECEPTORS 



This confirmed the work of Haig, Hecht, and Patek (1938) 

 who found more extensive changes in rod than in cone 

 function in the dark-adaptation of patients with cirrhosis 

 of the liver. Wald, Jeghers, and Arminio (1938) studying 



I 



H 



be 



10 15 20 25 



Time in Dark - Minutes 



30 



35 



Fig. 102. Curves showing dark-adaptation measurements of a human sub- 

 ject made at various times during the course of a diet practically free from 

 vitamin A. The filled and unfilled circles keep the different sets of measure- 

 ments apart and are smoothed by dotted and continuous lines respectively, 

 cf. figure 101. (From Hecht and Mandelbaum, 1939, J. A. M. A., vol. 112.) 



human dietary night blindness claimed that with a deficient 

 diet, within 25 days, the rod thresholds had risen about 

 50 times as compared with 5 times for the cones. 



The subjects studied by Hecht and Mandelbaum (op. cit.), 

 deprived of dietary vitamin A, responded by a steady rise 

 of both cone and rod thresholds, which became apparent 

 almost from the first day after removal of vitamin A from 

 the diet. After about two weeks' deprivation they showed 

 thresholds above any values normally found in the popula- 

 tion of normal individuals, and their thresholds continued 

 to rise so long as the vitamin A deprivation was maintained 

 (Figure 103). The return to a normal diet (with or without 

 supplementary vitamin A) resulted in an initial small drop 



