VITAMIN A 277 



arose from a deficiency of vitamin A in their food (Blunt and Wang, 

 1921); and McCollum, Simmonds and Parsons (1921) have attrib- 

 uted "night blindness," an eye trouble of frequent occurrence in 

 Northern regions, to the use of diets poor in this vitamin. Appleton 

 (1921), on the other hand, appears to doubt the dietary origin of 

 night blindness. More recently Fridericia and Holm (1925) have 

 studied the relation between malnutrition and night blindness by means 

 of observations upon regeneration of visual purple, bleached by action 

 of light upon the eyes of rats on normal diet or on diet deficient in 

 vitamin A or in vitamin B. They summarize their work in part as 

 follows : 



"Rats starved for A-vitamin and corresponding control rats re- 

 ceiving an adequate diet were examined as to the amount of visual 

 purple in their retinae and their faculty of regenerating the color of 

 the bleached visual purple. 



"No influence of starving for A-vitamin on the amount of visual 

 purple in the retinae of rats kept in darkness has been found. 



"When the visual purple of the retinae has been completely 

 bleached by exposure of the rats to light, the regeneration of the purple 

 is delayed in rats starved for vitamin A as compared with control rats 

 receiving an adequate diet. . . . The abnormality in rats starved for 

 A-vitamin as to the regeneration of the bleached visual purple occurs 

 earlier than pronounced symptoms of xerophthalmia. 



"The abnormality in the regeneration of the bleached visual purple 

 has not been found in rats starved for B-vitamin. In human beings a 

 relation between xerophthalmia and a kind of night blindness, often 

 preceding the xerophthalmia, has been suggested by several authors. 

 This kind of night blindness is by some authors thought dependent 

 on a deficiency in the diet of A-vitamin, by others on the exposure of 

 the eyes to intense light. If this kind of night blindness depends on 

 a defect in the function of the visual purple, identical to that observed 

 in rats starved for A-vitamin, both views contain part of the truth." 



Holm (1925) reported experiments in which he found that hemeral- 

 opia develops as the joint effect of shortage of vitamin A and much 

 exposure of the eyes to light. "... the hemeralopia appears very early 

 during the avitaminosis, as is also seen in man." 



The observations of Bloch referred to above, as well as some later 

 investigations by the same author, were republished in English (Bloch, 

 1921) under the auspices of the British Committee on Accessory Food 

 Factors, on account of their unusual interest when considered in con- 

 junction with the experimental production of the disease in rats by 



