VITAMIN A-DEFICIENCY AND THE RETINA 151 



to rod disfunction, the only references to structural changes 

 in the retina prior to the work of Johnson (1939) appear to 

 be those of Tansley (1933g, 1936). 



Tansley (1933a) showed that under conditions of mild 

 vitamin A-deficiency, in rats, the outer segments of the rods 

 fail to take on the characteristic dark stain with phospho- 

 tungstic acid-hematoxylin. She observed also a degenera- 

 tive change taking place at the junction of the inner and 

 outer segments. In cases with severe vitamin A-deficiency 

 she found a disappearance of the outer segments of the 

 rods and an ^unhealthy' appearance of the whole retina. 

 Tansley (1936) studied the development of the retina of 

 rats suckling on A-deficient mothers, and on an A-deficient 

 diet after weaning. The eyes of 59 young rats were examined 

 at ages ranging from 3 to 61 days. The retina w^as found to 

 have undergone normal development during the first 12 

 days post partem, at the end of which time the outer seg- 

 ments of the rods normally appear. After this period the 

 outer segments tended to show retarded growth, but they 

 never failed to develop. Of 23 rats killed between 12 and 

 21 days, 12 show^ed almost normal development of the retina, 

 although only 4 had perfectly healthy outer limbs. Visual 

 purple which normally is present at about 12 days, was not 

 found in these A-deficient rats until 21 days of age and then 

 only in amounts far below the normal. In some cases no 

 visual purple was formed. In young rats which did not 

 receive cod-liver oil (7 cases), those which were killed 

 between 44 and 58 days of age showed typical symptoms 

 of vitamin A-deficiency, viz., poorly staining outer segments 

 and thinning at the junction of the outer and inner segments. 

 Dosing with cod-liver oil for 3 days was sufficient to restore 

 the staining reactions, but even 6 days' treatment was insuffi- 

 cient to repair the damage to the structure of the outer 

 segments. Tansley 's results show^ that the first effects of 

 vitamin A-deficiency on young rats is either a delay or 

 complete failure of visual purple formation, and that this is 

 followed by structural damage to the rods. 



