VITAMIN A 259 



store of vitamin A were eliminated by means of a preliminary period. 

 As a ration for the stock colony from which experimental animals are 

 to be drawn, a diet consisting of two-thirds ground whole wheat and 

 one-third whole milk powder with sodium chloride added to the mix- 

 ture in the proportion of two per cent of the weight of the wheat has 

 been extensively used with fairly satisfactory results.* This diet is not 

 recommended as an optimal food either for growth or for reproduction. 

 It has long been known that the addition of suitable fresh foods, e.g. 5 

 grams of raw lean beef per adult rat per day, often results in somewhat 

 more rapid growth and earlier and more abundant breeding. Osborne 

 and Mendel (1926) have shown that more rapid growth can also be 

 obtained with certain other dry food mixtures. The diet here described 

 contains, however, ample vitamin A to permit successful reproduction 

 and lactation, with the production of young possessing at 28 days of 

 age a moderate bodily store of vitamin A. This breeding diet also con- 

 tains sufficient of the antirachitic factor not only to prevent the de- 

 velopment of rickets at any time of the year in animals kept on the 

 stock diet and living in a laboratory lighted through glass, but also to 

 endow their young by 28 days of age with considerable antirachitic 

 reserves. Steenbock and Nelson (1923), Drummond, Coward and 

 Handy (1925) and Chick (1926) found that the young reared on their 

 stock diets have larger bodily reserves of vitamin A than of vitamin D ; 

 but we find that 28-day old animals reared by mothers on the ration 

 here described have greater bodily reserves of vitamin D than of vita- 

 min A, relative to their needs when transferred to our fat-soluble- 

 vitamin- free diet. In laboratories using animals thus reared, and em- 

 ploying a low rate of growth during the test period, quantitative studies 

 conducted before the differentiation of vitamins A and D were prob- 

 ably not invalidated by shortage of vitamin D. (Sherman and Hessler, 

 1927; Sherman and Burtis, 1928a; Sherman and Stiebeling, 1929.) 

 However, we recognize that the vitamin D content of whole milk 

 powder, the source of this vitamin for our breeding colony, and in- 

 directly for any bodily reserves in their young, may be variable, and 

 hence, subsequent to Steenbock's demonstration that vitamin D is 

 necessary for growth, we have recommended and employed measures 

 to provide vitamin D liberally in all vitamin A experiments. It is well 

 to conduct all quantitative determinations of vitamins under conditions 

 which amply provide all known nutritional essentials except the one 

 under investigation. 



* Practically the same diet may be conveniently stated in percentage form as follows: 

 Finely ground whole wheat, 66 per cent; whole milk powder, 33 per cent; sodium chloride, 

 1 per cent. 



