320 THE VITAMINS 



the fat-soluble organic factor (bred from parents who, in addition to 

 the normal diet, received cod-liver oil breeding paste) grading the 

 content of that factor in their diet results in only the slightest gradation 

 of the percentage of calcium in the bones. Even in some of these well- 

 bred rats, on diets deficient in the organic factor, very slight osteo- 

 malacia or rickets may develop." 



Further evidence of storage of vitamin D was offered by Goldblatt 

 and Soames (1923a) who found that "if rats are kept on a diet deficient 

 in vitamins A and D until they have ceased gaining weight for about 

 four weeks their livers, fed to other rats, do not possess growth- 

 promoting properties; but if, after complete cessation of growth, rats 

 are irradiated for a few weeks by means of a mercury-vapor quartz 

 lamp, their livers acquire the property of stimulating for a short time 

 the gain in weight of rats that have ceased growing on a diet deficient 

 in the fat-soluble vitamin" — implying, of course, that it was vitamin D 

 and not vitamin A which was here the growth-limiting factor. This was 

 confirmed by Steenbock and Black (1924) who showed that liver from 

 irradiated rats was growth-promoting for those whose growth was 

 inhibited for lack of antirachitic vitamin, while liver from non-irradiated 

 rats was not. The same was found true for lung and muscle tissue. In 

 this work Steenbock and his coworkers used his "synthetic" diet con- 

 taining an adequate salt mixture with or without the addition of a 

 small amount of dried alfalfa to provide vitamin A. This basal diet 

 consists of purified casein 18, salts No. 40 4, yeast 8, agar 2, dextrin 

 68 parts. The addition of the alfalfa (0.3 gram per 100 grams ration) 

 postpones for about two weeks the xerophthalmia and infections of the 

 respiratory tract which otherwise occur within 5 to 7 weeks after the 

 animals have been put on the diet at an initial age of 21 to 25 days, and 

 weight of 35 to 60 grams. 



The fact that smaller amounts of vitamin D are detectable by the 

 use of diets having a good salt mixture was indicated by the early work 

 of McCollum, Simmonds, Shipley and Park (1922c) when they found 

 that "3 per cent butterfat is ample for providing the animals with 

 sufficient fat-soluble A and any other organic substance exerting a 

 special effect on the bones when the content of calcium is raised to 

 approximately half the optimal. The provision of nearly seven times 

 this amount does not exert much protection to the animals against the 

 specific detrimental effect of lack of calcium when the content of the 

 diet in this element is from one-fifteenth to one-fifth or sixth the optimal 

 amount." These findings emphasize the importance of considering the 

 pre-experimental bodily store of vitamin D in animals used in studies on 



