VITAMIN A 253 



House, Nelson and Haber (1929) also found a lesser amount of 

 vitamin A in green "mature" tomatoes than in the fully ripened fruit ; 

 but the same quantity was finally developed whether they were allowed 

 to ripen on the vines, at 22° to 25° C. in the laboratory, or by treatment 

 with an ethylene air mixture (1 : 800). Jones and Nelson (1930), how- 

 ever, consider vine-ripened tomatoes to be richer in vitamin A than 

 green, air-ripened, or ethylene-ripened tomatoes. 



Measurement o£ Vitamin A Values 



The starting point of our knowledge on this subject was the dis- 

 covery by McCollum and Davis (1913) that rats could not be nourished 

 satisfactorily upon certain food mixtures of which lard was the sole 

 fat; but the use of butterfat sufficed to make the food mixture adequate. 

 Further experiments showed that, with the samples used, no more than 

 5 per cent of butterfat need be contained in the food mixture to make 

 it adequate in this respect, whereas even 28 per cent of lard did not 

 suffice. Evidently, then, butterfat is rich in this nutritive essential (vita- 

 min A) and lard either lacks it entirely or contains so little as to show 

 no evidence of its presence in such experiments. 



Through the work of Osborne and Mendel and of McCollum and 

 his associates it was shown that egg fat, cod-liver oil, and the fat of 

 pigs' kidney resembled butter in serving as efficient sources of vitamin 

 A while cottonseed oil, olive oil, almond oil and other commercial vege- 

 table fats seemed, like lard, to lack it. The skeletal muscles (ordinary 

 meats) seemed to contain but very little vitamin A; heart muscle, 

 somewhat more, but not so much as liver or kidney. As shown by 

 Osborne and Mendel (1915a) beef fat, while not so rich as butter, 

 yet contains this vitamin in significant amounts. Daniels and Loughlin 

 (1920) and Drummond, Golding, Zilva and Coward (1920) have pub- 

 lished experimental evidence from which they conclude that lard and 

 probably some other commercial forms of fat previously regarded as 

 devoid of vitamin A are not wholly so, the vitamin value of lard (as 

 probably also that of beef fat and butter) depending largely upon the 

 food of the animal. 



That vitamin A may be stored to an important extent in the body 

 is indicated not only by the results of feeding body fats and glandular 

 organs as sole sources of this vitamin in the diet, but also by the fact 

 that when growing animals previously well fed are placed upon diets 

 certainly deficient in vitamin A and often apparently devoid of it, they 

 usually continue to grow for some time, often doubling their body 

 weights before signs of nutritive deficiency appear. See the accompany- 



