VITAMIN A-DEFICIENCY AND THP: RETINA 149 



in groups 1 and 2. Seven subjects showing similar degrees 

 of response were distributed in all three groups. Three 

 subjects who showed no immediate effects of the diet were 

 all in group 2, which received adequate supplements of other 

 vitamins. The data which these authors obtained suggest 

 that such individuals who fail to respond for long periods 

 of time may have an exceptional storage of vitamin A in 

 the tissues which they eventually exhaust. It thus appears 

 that storage capacity for vitamin A has no relation to 

 amounts recently ingested. Steininger, Roberts, and Brenner 

 (1939) found it to depend more on individual capacity and 

 on long term history. This was supported by the observa- 

 tions of Wald and Steven (op. cit.), who gave their subjects 

 a short period of high vitamin A dosage, and yet ol^tained 

 widely different individual effects wdth a subsequent deficient 

 diet. 



Not only do the experiments show marked variations in 

 the time required for raising the visual thresholds in sul^jects 

 on a vitamin A-deficient diet, but the recovery time also 

 has l)een found to vary greatly. Clinical cases of night 

 blindness have been reported as cured within 24 hours by 

 single oral administration of a large quantity of vitamin A 

 (Aykro3^d, 1930; Lewis and Haig, 1940) and by intramuscular 

 injections of vitamin A concentrates (Edmund and Clem- 

 mesen, 1936). Wald, Jeghers, and Arminio (1938), and Wald 

 and Steven (1939) reported recovery to normal visual thresh- 

 olds within minutes after ingestion of moderate concentra- 

 tions of vitamin A or of carotene. Hecht and Mandelbaum 

 (1939) obtained only slight effects with two subjects whose 

 thresholds had risen 1 and 2 log units above normal, when 

 oral doses of vitamin A concentrates containing 100,000 units 

 w^ere given. McDonald and Adler (1939) were unable to 

 lower the visual threshold with single large doses, nor were 

 Steffens, Bair, and Sheard (1939). Hecht and Mandelbaum 

 (1940), w^ho administered single doses of oleum percomorphum 

 or of a concentrate containing a high value of vitamin A, 

 obtained disappointing results. Whereas single large doses 



