OCCURRENCE OF THE VITAMINS A 685 



(dog, guinea pig), small intestine (rabbit), large intestine (cat), stomach 

 (guinea pig, cat), heart (guinea pig), spleen (rabbit, guinea pig), pancreas 

 (rabbit), ovaries (rabbit), thyroid gland (rabbit), and adrenal (gopher). 

 Further studies in this field to determine the relationship between vitamin 

 A content and function are obviously most desirable. 



Another site for the storage of vitamin A, in addition to the liver, may be 

 the depot fat. Such storage depends upon the species as well as upon the 

 vitamin A intake. Certain mammals such as cattle, sheep, and pigs do not 

 contain vitamin A in these fat depots; on the other hand, the depot fats of 

 the dog may contain as much vitamin A as the liver, or even more.^^-^*' 

 In some cases, the intestinal fats of fishes may contain 60-70% of the total 

 vitamin A.^^ An average value of 32.3 I.U. per gram of storage fat has 

 been reported in the general body fat of the chicken, although, after sup- 

 plementation with massive doses of vitamin A, this value was increased 

 about 8-fold (222.6 I.U.).i«2 



(6) Vitamin A and Carotene in Milk 



One of the principal natural sources in which vitamin A is found is but- 

 ter fat. Vitamin A is present in this product not only as such but also in 

 the form of the provitamin A, /3-carotene. In a recent nation-wide survey^"^ 

 on the role of butter as a source of vitamin A in the diet of the people of the 

 United States, it was found that the vitamin A content of summer butter 

 approximated 15,000 International Units per pound, or 33 units per gram. 

 In the case of winter butter, the total vitamin A averaged about 50% of the 

 summer level (7500 I.U. per pound or 16.5 I.U. per gram), when the herds 

 were fed on U. S. No. 2 field-cured alfalfa hay or average quality corn sil- 

 age; when an excellent quality of alfalfa silage was used, the summer levels 

 of vitamin A were largely maintained. 



A number of factors other than season can influence the total amount of 

 vitamin A in milk, as well as the proportion of carotene and vitamin A. 

 One of the most important of these is the breed of the cow. It is well 

 known that, in the case of the Holstein cow, the carotene level is relatively 

 lower than in the Guernsey breed; on the other hand, the amount of pre- 

 formed vitamin A in the former case may be higher, so that the total vita- 

 min A may approximate the same values in the two species. The total 

 vitamin A and the carotene fraction are dependent upon the feed, being 

 highest when the consumption of carotene-rich green grass is abundant, and 

 lower in the winter when only dry feed is available. The vitamin A in milk 



"« H. J. Deuel, Jr., M. C. Hrubetz, F. H. Mattson, M. G. Morehouse, and A. Richard- 

 son, J. Nutrition, 26, 673-685 (1943). 



1" U. S. Dept. Agr., Misc. Bull., No. 636, 1-47 (1937). 



