VITAMIN A 229 



activity. In 1918, however, Steenbock, Boutwell, and Kent, in the first 

 of a series of studies on the fat-soluble vitamins, reported that vitamin A 

 was comparatively labile to heat. Melted butterfat shaken with water 

 for 12 hours became inactive as did butter aerated for 12 hours at 

 100° C. Against the possibility that the destruction was due to oxidation, 

 they cited similar results obtained when butter was shaken with car- 

 bonated water. Butter heated in jars at 100° C. in a Freas oven also lost 

 its activity as did butter kept unsalted under poor storage conditions for 

 three weeks. The authors concluded that "the failure of other investi- 

 gators to note this destructive action was undoubtedly due to the high 

 initial content of fat-soluble vitamin in the material studied. The de- 

 structive process is evidently a reaction of low velocity. With large 

 amounts of vitamin present and with heat treatment for a limited period 

 of time sufficient amounts of the vitamin remained to satisfy all the 

 requirements for normal growth in the experimental animals." 



Shortly afterward, Drummond (1919a), in an investigation of the 

 effects of hydrogenation on the vitamin content of oils, found that 

 vitamin A was destroyed in experiments with whale oil, both during the 

 hardening process involving exposure to hydrogen gas at 250° C. for 

 four hours or more, and also upon heating the oil to 100° C. or more 

 for four hours. These results were thought to demonstrate beyond any 

 doubt that the fat-soluble vitamin A in the form in which it occurs in 

 natural animal fats is much less stable to high temperatures than had 

 previously been assumed. "Such an observation necessitated a complete 

 revision of all the previous experiments to isolate and identify the factor 

 in many of which high temperatures had been employed." In a series of 

 experiments reported at the time on the effect of heat on the vitamin 

 present in certain oils, the results obtained supported the conclusions of 

 Steenbock that the vitamin was comparatively easily destroyed by heat. 

 The conclusion drawn at the time was that "the chief agent in the 

 inactivation of fat-soluble A is temperature. It must, however, be borne 

 in mind that all these speculations refer solely to the factor as present in 

 secondary sources such as the animal oils. It is quite possible that the 

 factor occurs in a different form in its primary environment in the plant 

 tissues." 



That vitamin A as it exists in animal fats is stable to heat under 

 certain conditions was shown by Osborne and Mendel (1920c) who pub- 

 lished a confirmation of their earlier work indicating that the vitamin 

 present in butter is notably stable at relatively high temperatures. 

 Butterfat treated with steam and also heated at 96° C. for 15 hours 

 retained its growrth-promoting activity. The explanation of these con- 



