224 THE VITAMINES 



The first statement on the stability of the active substance from 

 butter was made by Osborne and Mendel (I.e. 581). They found 

 that when steam was passed through butter for 2| hours, the 

 vitamine was unaffected. That this substance in egg-yolk is resistant 

 to heat, was shown by McCollum and Davis (596) . In this connec- 

 tion, Drummond (597) found that vitamine A from butter and other 

 sources is veiy unstable to heat, thus corroborating the statements of 

 Steenbock. Drummond also reported that oxidation does not seem 

 to play any part in the destruction of this substance. Steenbock and 

 Boutwell (598) found yellow corn and alfalfa active after heating in 

 the autoclave for three hours. Osborne and Mendel (599) found 

 butter, as such, much more stable against storage and the influence of 

 light, than the uncrystallizable part butter oil. 



All of these apparently conflicting statements may be well under- 

 stood when the new observation of Hopkins (I.e. 595 and 599a) 

 is taken note of. He found that in the destruction of vitamine A 

 oxidation, not temperature, plays the chief part. This has been 

 confirmed by Drummond and Coward (599b) and is in agreement 

 with the observation of Osborne and Mendel (600), who found butter 

 stable when steam was passed through it, but not when the butter 

 was heated in the absence of water. The stability in this case may 

 be explained by the replacement of air by steam, although even dry 

 butter could be heated at 96C. for 15 hours without noting any loss 

 of activity. 



As regards the action of physical factors, Zilva (I.e. 513) showed 

 that butter lost its activity on exposure to ultra-violet rays for 8 

 hours. The possibility of the formation of ozone was considered in 

 a later paper, and it was actually found that ozone is destructive 

 to vitamine A (600a). 



Although the destruction of vitamine A by oxidation has been well 

 explained by various statements, it is more difficult to understand 

 the destruction of fat on reducing at a temperature of 75 to 120C., 

 as carried out by Fahrion (601). For, in the first place, vitamine A, 

 according to the newer findings, is quite resistant to heat, and 

 second, the substances sensitive to oxidation are, for the most part, 

 resistant to reduction. Nevertheless, according to the findings of 

 Drummond and Coward (I.e. 592), as well as of Fahrion, the reduced 

 fats are totally inactive. Fahrion believed that vitamine A is almost 

 insoluble in fat solvents. 



