GROWTH AND NUTRITION 



87 



as reported by McCollum and Davis, also by Osborne and Men- 

 del, were due to unsuspected impurities. In the first case this 

 impurity was present in the crude lactose employed, while in 

 the latter it was present in the protein-free milk. Milk then 

 contains both factors, and they may be roughly separated by re- 

 moving the fat. 



McCollum named these factors in the order in which they 

 were first brought to his attention, not in the order in which 

 they were really discovered, and the names were based on their 

 solubility. Thus the vitamin 

 in milk and egg fat was called 

 Fat-Soluble A, and the other 

 vitamin was called Water- 

 Soluble B. 



Practically all workers in 

 the field of nutrition have con- 

 curred that these two nutri- 

 tional factors, A and B, do 

 exist, though for some years 

 there were at least a few dis- 

 senters. It was also tacitly as- 

 sumed by the great majority that these two were the only un- 

 identified factors, but gradually evidence was accumulated that 

 made it certain that scurvy, also, is a deficiency disease. It has 

 long been known that the disease is dietetic in origin, that it ap- 

 pears during periods when fresh foods are not available, and 

 that it disappears when such materials are included in the diet. 



Modern experimental work, however, had to await the dis- 

 covery of an animal that is susceptible to scurvy, and that was 

 afforded by the guinea pig. Apparently this was first noted by 

 Professor Alex Hoist, 28 University of Christiana, who made a 

 careful study of guinea-pig scurvy. He showed that on a mixed 

 vegetable diet, guinea pigs can be maintained in perfect health, 

 but if all green feed is removed, so the animals must subsist on 

 grain only, they develop the disease. He also demonstrated 



Figure 54. Avian xerophthalmia, due to a 

 lack of vitamin A. Note that the eye is 

 swollen and closed. Courtesy of Prof. H. L. 

 Kempster. 



