268 THE VITAMINS 



Plant products as primary sources of vitamin A will here be con- 

 sidered first. These may be grouped under green and other vegetables, 

 fruits, cereals, nuts, and plant fats and oils. 



Green leaves and other green vegetables are important sources of 

 vitamin A. A rating of them in order of their content of this factor 

 must necessarily be more or less tentative: the following estimates are 

 made with the realization that they do not represent fixed values but 

 with the belief that they indicate approximate relative values more 

 nearly than do the conventional signs previously used. 



Escarole, a green leafy vegetable with a vitamin A content of 

 around 200 units per gram is the richest green vegetable which we 

 have seen reported. Next is spinach which contains about 60 units 

 per gram. Indications based on experiments made on the dried product 

 are that the leaves of alfalfa, chard, clover, and cowpeas may contain 

 amounts fairly comparable with spinach. One sample of dried alfalfa 

 cured in the dark contained approximately 100 units per gram. Quan- 

 titative studies of vitamin- A values of hays are reported to be in 

 progress. Vegetables (among others) reported to contain from 1 to 

 10 units per gram are artichoke, green string beans, brussels sprouts, 

 celery leaves, lettuce, green peas, and red and green peppers. Successive 

 tests in one laboratory indicated that green string beans may vary from 

 4 to 10 units per gram (Quinn, Burtis and Milner, 1927). Bleached 

 celery leaves were found to contain only about one-fourth as much 

 vitamin A as green leaves. No significant difference has been reported 

 between canned and fresh samples of green peas and spinach. One 

 unit per gram or less has been reported in headed cabbage, cauliflower, 

 cucumber, and eggplant. Old cabbage, sauerkraut and white leaves 

 seem to contain significantly lesser amounts of the vitamin than do the 

 fresh green leaves of cabbage. The rind of the cucumber has in one 

 instance been reported richer than the fleshy tissue. Bleached celery 

 stems did not show detectable quantities of vitamin A. Green outer 

 leaves of lettuce are reported to be 30-fold richer in vitamin A than 

 the white inner leaves from the same heads (Kramer, Boehm and 

 Williams, 1929). McLaughlin (1929) reports the small leaves of New 

 Zealand spinach to be especially rich in vitamin A. 



Carrots, which are reported to vary from 25 to 70 units per gram 

 are conspicuously the richest in vitamin A of vegetables other than 

 green tissues which have thus far been reported. Next are found the 

 yellow tissues of pumpkin, sweet potatoes, yellow yautia (a Porto 

 Rican root vegetable) and green dried peas which contain from 4 to 

 10 units per gram. While the indication is that yellow squash contains 



