VITAMIN A-DEFICIENCY AND THE RETINA 157 



diet were not uniform histologically. In one case the retina 

 appeared practically normal in the periphery, and the 

 fundus exhibited what seemed to be newly formed rod outer 

 segments. They appeared as short, slender protoplasmic 

 processes without any sign of fracture at the junction of 

 the inner and outer segments — a condition characteristic 

 of degenerating rods. In two cases the periphery of the 

 retina showed broken and abnormally stained rods and in 

 the fundus the condition was more severe. In some parts 

 of the fundus, the rods and most of the outer nuclear layer 

 were lacking completely. 



The retinae of two animals kept on a recovery diet for 

 10 days appeared quite normal in the periphery. All of the 

 layers in the fundus were normal except the visual cell 

 layer. Here the rods, like those of the 5-day recovery 

 animals, appeared to have newly regenerated outer segments. 

 (Figure 106). 



The retinae of animals kept on a vitamin A-deficient diet 

 during suckling and then weaned on an adequate diet 

 (group 3) showed no signs of A-deficiency. The retinae were 

 normal in every respect. 



The results of Miss Johnson's studies have shown, in 

 general, that with mild vitamin A-deficiency the retina 

 exhibits abnormal staining and friability of the outer seg- 

 ments at the periphery, and more or less complete degenera- 

 tion of the rod outer limbs in the fundus. These findings are 

 in general agreement with those of Tansley (1933a, 1936) upon 

 rats suffering from more severe A-deficiency. The retinae 

 of rats suffering from severe A-deficiency were found by 

 Miss Johnson to show more marked degeneration which was 

 progressive, involving in succession the rod outer segments, 

 the inner segments, the external limiting membrane, the 

 outer nuclear layer, the epithelial pigment layer, the outer 

 molecular layer, and the inner nuclear layer. No definite 

 sign of degeneration was found in the inner molecular layer, 

 the ganglion cell layer, and the nerve fiber layer. 



Although there were some indications that degenerated 



