VITAMINS — HOPKINS 271 



recently, however, a further complication has come to light in this 

 connection. Preparations of " Bo " as hitherto employed would seem 

 to contain two active factors, one promoting growth without being 

 concerned with skin conditions, and a second to which the " anti- 

 pellagra " influence is due. The latter is now under intensiA^e study, 

 but its chemical nature is yet unknown. The former, like vitamin 

 A, is related, as shown by the researches of R. Kuhn and P. Karrer, 

 to a group of naturally occurring pigments, but in this case to the 

 flavines. The vitamin is in fact identical with a flavine which is 

 present in milk. 



Vitamin C. — While the prevention and curative influence of foods 

 containing this, the antiscorbutic vitamin, has been so long known, 

 it remained for quite recent research to establish its existence as a 

 definite chemical substance, to produce it pure, and to determine its 

 exact chemical nature. It is present in most fresh foods but often 

 only in very small amounts. It is present in greatest concentration 

 in fruits and green vegetables, but in amounts varying greatly from 

 species to species. Cereal foods contain none. It is characteristi- 

 cally less stable than the other laiown vitamins, being destroyed 

 when foods are long kept, dried, or heated ; the influence of oxygen 

 being a potent factor in its destruction. This instability accounts 

 for many chapters in the long history of scurvy and its incidence. 

 Much labor has been spent during recent years in determining 

 quantitatively its distribution in foods and in endeavor to isolate it. 

 Success in the latter aim was reached by A. Szent-Gyorgyi 3 years 

 ago. Its constitution has been fully worked out by W. N. Haworth 

 and his colleagues, revealing the interesting fact that the physio- 

 logically potent substance is related to the simple carbohydrates, 

 being a derivative of the hexose sugar gulose. The vitamin is now 

 to be known as " ascorbic acid.'* 



Vitamin D. — This, the antirachitic vitamin, is generally associated 

 with vitamin A in animal fats, and, with the latter, is present in 

 exceptionally large amount in fish liver oils. Studies in the etiology 

 of rickets have proved that this disease can be prevented or cured, 

 on one hand by an adequate supply of this vitamin in the food, and, 

 on the other, by adequate exposure of the body to sunlight. A sat- 

 isfactory explanation of this remarkable relation arrived with the 

 proof that ultraviolet irradiation converts an inactive precursor into 

 the vitamin itself, and that the former is present in the tissues. Dur- 

 ing the year 1929, owing in particular to the work of Rosenheim and 

 Webster, and that of Hess and Windaus, it was made clear that the 

 substance which on irradiation is activated is ergosterol, which in 

 small amounts is present in most living tissues. As it is therefore 

 present in many natural foods, the antirachitic value of these is 



