230 THE VITAMINS 



flicting results came in papers published simultaneously by Hopkins 

 (1920a), by Drummond and Coward (1920b), and by Zilva (1920a), 

 all of which presented evidence that the destruction of vitamin A takes 

 place rapidly at high temperatures when oxygen or an oxidizing agent 

 is present, but not otherwise. 



The method adopted by Hopkins was to feed young rats of the same 

 age, weight, and sex, a ration free from vitamin A to which was added 

 15 per cent of filtered butter. The butter fed to half of the animals in 

 each group had been heated in the autoclave for different lengths of 

 time, while that fed to the other half had undergone heating at the 

 same temperature but with aeration. In all of these experiments growth 

 was normal on the unaerated fat ; but on the aerated fat growth ceased 

 and in 60 per cent of the cases xerophthalmia developed. As judged 

 from the growth curves, 4 hours' exposure to a temperature of 120° C. 

 in the absence of air did not appreciably affect the vitamin content of 

 butter, at least when fed at 15 per cent of the food intake; 12 hours' 

 exposure under the same conditions involved slight destruction, aeration 

 at 120° C. for 4 hours destroyed the greater part, and for 12 hours 

 practically all of the vitamin ; aeration at 80° C. brought about quite 

 rapid destruction ; and exposure to air at ordinary temperatures for a 

 week, almost complete destruction. Of significance in this report was the 

 fact that identical figures were obtained for the iodine value of the fatty 

 acids of the butter before and after heating for 4 hours in a stream of 

 air at 120° C. 



The plan adopted by Drummond and Coward (1920b) differed from 

 that of Hopkins in that the butter fat was fed in small amounts (0.2 

 gram) as a supplement to the daily vitamin A-free basal ration to rats 

 whose growth had been completely inhibited by this ration. The tem- 

 peratures and times of aeration were : exposure to a current of live 

 steam for 6 hours, and heating at 96° C. for 15 hours, at 50° C. for 6 

 hours, and at 37° C. for 3 weeks with and without exposure to air. The 

 results of these studies also indicated that destruction of vitamin A 

 takes place rapidly at high temperatures and to a considerable extent at 

 temperatures as low as Z7° C. in the presence but not in the absence 

 of air. 



The confirmatory work of Zilva (1920a) published at the same time 

 resulted from an earlier observation that the vitamin A value of 

 butter fat is lost or lowered by exposure to ultra-violet rays (Zilva, 

 1919). In a further study to determine whether this was due to the 

 action of the rays or to ozone produced by the mercury quartz lamp, 

 cod-liver oil was exposed in thin layers to the action of ultra-violet 



