284 THE VITAMINS 



after development of pronounced xerophthalmia symptoms, were much 

 less resistant than normal controls to infection by ingestion of a strain 

 of paratyphoid bacilli, the experiment was repeated with subcutaneous 

 injections of the bacilli instead of inoculation by mouth with like results. 

 Further investigation along these lines will be awaited with interest. 



Morgan and Osburn (1925) found that lack of vitamin A altered 

 the quantitative relations of the nitrogen compounds of the urine, at 

 least as regards allantoin, in explanation of which: "It is suggested 

 that in the absence of vitamin A the animal organism fails to produce 

 purine -containing compounds from the ordinary sources, perhaps argi- 

 nine and histidine, but continues to utilize over again such portions of 

 discarded purine-ring-containing substances as are ordinarily excreted 

 in the form of allantoin. The portions of these compounds which are 

 oxidized only to uric acid are apparently no longer usable and continue 

 to be excreted in proportion to the amount of destruction of cellular 

 material in vitamin-A deficient as in normal animals." 



Cramer's suggestion that vitamin A may play both a structural and 

 a humoral role in the body, is in a general sense confirmed by the 

 accumulation of evidence that this vitamin increases resistance to in- 

 fection (not necessarily through the ordinary immunological reactions) 

 and by the fact that actual feeding experiments with tissues of animals 

 of accurately known nutritional history have shown that the richness 

 of the food in this substance may significantly influence the concentra- 

 tion of vitamin A in lung tissue, as well as the amount of the vitamin 

 stored in the liver (Sherman and Boynton, 1925). This direct evidence 

 from the feeding of the tissues as sole sources of vitamin A by quanti- 

 tative methods such as have been described earlier in this chapter, 

 leaves no room for doubt that it is chiefly the body's store of vitamin 

 A which determines the length of the survival period upon a diet good 

 in other respects but devoid of this essential factor. 



Sherman and Cammack (1926) made further use of the method 

 of measuring the survival period upon vitamin-A-free diet as a means 

 of quantitative study of the storage of vitamin A in the body, particu- 

 larly with reference to the problem of the times and conditions of feed- 

 ing which may be expected to induce maximum storage of this vitamin 

 by animals of different ages. All of the experimental animals were 

 albino rats of the same stock and of accurately known age, pedigree, 

 and nutritional history, taken from families which had been fed a 

 mixture of one-third whole milk powder and two-thirds ground whole 

 wheat with table salt in the proportion of 2 per cent of the weight of 

 the wheat, the whole so ground and mixed as to ensure the consumption 



