VITAMIN A-DEFICIENCY AND THE RETINA 153 



epithelial layer than in normal eyes. Not only did the rods 

 stain abnormally, but many had lost their outer segments 

 (Figure 107, A, cf. Figure 104). The degenerative outer seg- 

 ments appeared finely granular, staining very faintly or 

 not at all. Other variations from the normal were found in 

 this (fundus) region. The rod inner segments were swollen 

 and presented a glassy, hyaline appearance. The external 

 limiting membrane was found to become wavy and irregular, 

 and in the central portion where visual cell degeneration was 

 most marked (Figure 107, B) it had disappeared completely. 

 The nuclei of the outer nuclear layer exhibited an edematous 

 appearance and were pushed apart, so that their characteristic 

 orderly arrangement was lost. The other layers of the retina 

 showed no abnormality. 



In group 2 (vide supra) eight of the twelve animals which 

 showed symptoms of extreme vitamin A-deficiency pre- 

 sented similar histological features of the retina. The pe- 

 ripheral portion of some retinas showed more degenerative 

 changes than those in group 1. The outer segments were 

 found to be very friable, most of them being broken at the 

 junction of the inner and outer segments. In the fundus of 

 all these retinae and in the periphery of two, the rods had 

 disintegrated completely, leaving only pink-staining frag- 

 ments of what appeared to be the remains of the inner seg- 

 ments (Figure 108). The external limiting membrane 

 became lost to view and the outer nuclear layer exhibited 

 definite signs of degenerative changes. The outermost rows 

 of nuclei appeared to have undergone karyorrhexis. Instead 

 of the usual 6 to 9 rows of nuclei, there were only 3 to 5 rows. 

 The nuclei appeared pyknotic and the coarse, heavily 

 stained chromatin granules became clumped so as to give 

 to the nuclei a definite crenated appearance. 



In some of the retinae, the degenerative changes towards 

 the fundus were more extreme. In these cases the visual 

 cells, the external limiting membrane, most of the outer 

 nuclear layer, and part of the outer molecular layer had 

 disappeared completely (cf. regions A and B, Figure 109). 



