286 THE VITAMINS 



(further) test period of 8 weeks the same limited allowance of vita- 

 min-A-containing food. Autopsies at the end of this test period showed 

 infections established in 75 per cent of the animals which in early life 

 had received the first diet and in only 25 per cent of those which had 

 during the same early period received the diet with the larger pro- 

 portion of milk. Taking account of the relative lengths of the rat and 

 the human life cycle, and of the similarity of nutrition in the two 

 species, this may perhaps serve as an indication of the differences of 

 incidence of infection to be expected among children of around 10 

 and 12 years, resulting from differences in the way they were fed 

 before they were 3 years old. 



In terms of the chief chemical factors involved, the better diet here 

 used was richer not only in vitamin A but also in vitamin G, in calcium, 

 and in certain of the nutritionally important amino acids. It is hoped 

 that experiments now in progress may more fully differentiate the roles 

 of these several chemical factors. 



While the laboratory experiments referred to in the foregoing dis- 

 cussion of the relation of vitamin A to nutrition and health have been 

 made chiefly upon rats, this is only because of the well-established 

 general usefulness of these experimental animals. Other species, vary- 

 ing as widely as the fowl, the rabbit, the dog, the pig, and the monkey, 

 have shown analogous susceptibiHties to vitamin A deficiency (Guerrero 

 and Concepcion, 1920; Nelson and Lamb, 1920; Steenbock, Nelson and 

 Hart, 1921; Lamb and Evvard, 1922; Tilden and Miller, 1930). 



The response of monkeys to vitamin A deficiency has recently been 

 studied by Tilden and Miller (1930) who while reporting that "the 

 period of survival of monkeys on a diet deficient in vitamin A was 

 shorter than was expected," nevertheless found evidence that, in this 

 species as in others, storage of vitamin A in the body may be a factor 

 of much nutritional importance. Regarding autopsy findings, they 

 report that "the epithelial metaplasia described first by Wohlbach and 

 Howe and later by Goldblatt and Benischek as characteristic of de- 

 ficiency of vitamin A was found in one or another tissue of 9 of the 

 11 animals on the A-deficient diet, and was entirely absent in the 

 controls." 



The animals subjected to shortage of vitamin A also showed a 

 high incidence of intestinal disease. The widespread weakening of the 

 body tissues which results from shortage of vitamin A is thus shown 

 to be true of the monkey as well as of the other species which have 

 been studied, while the importance of taking a broad view of vitamin-A- 

 deficiency instead of concentrating attention upon the eye symptoms is 



