244 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1941 



or because it was destroyed as in the case of winter cabbage, the 

 inner leaves of lettuce, and the bleached stems of asparagus and celery 

 have practically no vitamin-A value. 



In general, roots and tubers may be accepted as low in vitamin-A 

 value with the exception of carrots and sweet potatoes, as noted above. 

 Seeds, including nuts, cereal grains, and legumes (peas and beans), 

 are on the whole low in, or totally devoid of, vitamin-A value unless 

 they have some green or yellow color as peas and yellow corn. 



Vegetable oils contain little or no vitamin A. 



Among the foods of animal origin, eggs and milk are important 

 sources. The hen and the cow do not convert all of the carotene 

 obtained from their feed into vitamin A, and eggs and milk contain 

 both vitamin A and carotene. In both cases the proportion of vita- 

 min A is much higher than that of carotene. The ratio between the 

 quantities of these two substances in milk from different breeds of 

 cows may be significantly different, some breeds, for instance, con- 

 sistently giving milk which contains a higher proportion of carotene 

 than others. Since vitamin A is soluble in fat and only slightly, if at 

 all, soluble in water, the vitamin-A value of the egg is in the yolk 

 and that of milk is in the cream. Butter is an important source of 

 vitamin A, and other milk products, such as cheese, contain it in 

 proportion to the quantity of milk fat present. 



Eggs and milk show wide variations in vitamin-A values. The 

 total quantities of both vitamin A and carotene in eggs and milk are 

 influenced by the quantities present in the feed of the respective ani- 

 mals producing these foods. During the summer months, when 

 green feed is available, milk and eggs may show radically higher 

 values than during other months of the year, although present-day 

 feeding practices, by the use of feeds of high vitamin-A value 

 throughout the year, tend to eliminate seasonal variation. 



In contrast to its precursors, the carotenoids, vitamin A has very 

 little color. Inasmuch as milk and eggs contain both carotene and 

 vitamin A, color is of little value in judging their vitamin-A po- 

 tency. This is especially true of eggs. If the hen derived vitamin-A 

 value from green feed or products rich in carotene, the yolk of the 

 eggs will be deep yellow in color and will have a high vitamin-A 

 value. If the hen did not have access to green feed or other highly 

 colored food, but was given feed containing cod-liver oil, which 

 contains vitamin A but not carotene, then the yolk of the eggs will 

 be very light in color and still will be rich in vitamin A. 



Meats vary considerably in their vitamin-A value since much 

 more of this factor is stored by some tissues than by others. Liver, 

 especially, retains large amounts of it when there is an abundance of 

 the vitamin in the diet, which makes it a rich food-source but from 

 the standpoint of cost it can hardly be considered an important one. 



