VITAMIN A 245 



of a leuco-form of the vitamin as suggested by Steenbock (1919) to 

 cover the exceptions to the association of pigment and vitamin was 

 thought by Palmer to be unHkely in view of the fact that the only leuco- 

 forms of carotinoids so far produced are oxidation products and that 

 oxidation destroys the efficiency of the fat-soluble vitamin. 



Later, however, Steenbock and his associates published further evi- 

 dence of a tendency toward greater richness in vitamin A in association 

 with higher carotene or Hpochrome pigmentation. Thus Steenbock, 

 Sell and Buell (1921) pointed out that "with the diversification of 

 metabolic processes which obtain in the plant and animal kingdom, it 

 was to be expected that sooner or later the fat-soluble vitamin would 

 be found to be present in a menstruum entirely free from pigments of 

 the carotinoid type. To run across such an instance, appears to have 

 been the good fortune of Palmer and Kempster (1919) who demon- 

 strated that pork liver, rich in the vitamin, contained no pigments of 

 the aforementioned character." . . . "Nevertheless, as far as studies 

 in this domain have been pursued, both in regard to distribution of 

 vitamin and pigment and in regard to their physical and chemical 

 properties, there is left no doubt but that chemically and physiologically 

 they are related." These authors then gave experimental results of their 

 own showing high vitamin A value with very low pigmentation in 

 cod-liver oil, and further noted that "The fat-soluble vitamin content of 

 butterfat does not run closely parallel to the yellow pigment; yet in 

 general, due to determination by their content in the feed, butters highly 

 pigmented are rich in the vitamin ; butters low in pigment should be 

 looked upon with suspicion. In beef fats the relations are somewhat 

 similar ; those most pigmented are also generally richest in their fat- 

 soluble vitamin content." 



In the next paper of the series. Steenbock, Sell and Boutwell (1921) 

 recorded feeding experiments with six varieties of peas showing that 

 "those of a green color, also carrying considerable yellow pigment, were 

 far richer in their fat-soluble vitamin content than yellow peas which 

 contained much less yellow pigment." 



In 1927 Willimott and Moore reported that vitamin A is not identi- 

 cal with purified xanthophyll. 



Quinn, Eurtis and Milner (1927) demonstrated the relationship of 

 greenness to high vitamin A content in plant tissues other than leaves, 

 string beans and green peppers being found of high vitamin A value. 

 More recently, Crist and Dye have shown both with head and leaf 

 lettuce (Dye, Medlock and Crist, 1927) and with bleached and green 

 asparagus (Crist and Dye, 1929) a positive correlation between the 



