VITAMIN A 247 



green cabbage leaves was potent in restoring growth in rats in doses 

 of 0.003 milligram per day. The non-saponifiable material obtained from 

 green cabbage leaves was more abundant, more unsaturated and many 

 times richer in vitamin A than the similar product from white cabbage 

 leaves. 



Duliere, Morton and Drummond concluded in 1929: "We are in- 

 clined to accept as the most plausible explanation of the discrepancy 

 between our results and those of the investigators who have obtained 

 a growth-promoting action with carotin, that their preparations were 

 contaminated with a trace of exceedingly potent growth-promoting 

 factor which need not necessarily be different from the classical vitamin 

 A. . . . The activity of carotin decreases enormously with purification 

 . . . the growth-promoting action of liver oils is not due to carotin ; the 

 results further indicate that the classical vitamin A must be a colourless 

 substance. Its intrinsic potency must be very much higher than that of 

 any sample of carotin or dihydro-a-crocetin for which data have so far 

 been published. . . . 



"Whilst in our view it is undesirable prematurely to assume the 

 existence of a plurality of vitamins A, it must not be forgotten that 

 the identity of the growth-promoting principle in vegetable matter with 

 that present in liver oils has never been satisfactorily demonstrated. 

 The investigation of growth promotion from the points of view of liver 

 fats and vegetable extracts may well be parallel rather than converging 

 lines of study." 



The question of these divergent results being attributable to tech- 

 nique in the biological tests was discussed by several investigators. 

 Moore and Hume had each noted that the investigators obtaining nega- 

 tive results used basal diets which contained no fat, whereas those 

 obtaining positive results used basal diets containing fat. Upon investi- 

 gating the matter Hume and Smedley-MacLean (1930) satisfied them- 

 selves, however, that the differences could not be attributed to the 

 presence or absence of fat in the basal diet but more probably to the 

 nature of the solvent in which the carotene is administered. Carotene 

 appears fairly stable when dissolved in natural oils, but loses color 

 rapidly when in contact with oleic acid or ethyl oleate, the solvent used 

 by Drummond. Hume and Smedley-MacLean believed that this rapid 

 oxidation of the highly unsaturated carotene in ethyl oleate was a 

 plausible explanation for the negative results of Duliere, Morton and 

 Drummond. 



Drummond, Ahmad, and Morton (1930) later confirmed the con- 

 clusions of Hume and Smedley-MacLean concerning the destruction of 



