THE METABOLISM OF VITAMINS 345 



assistance in the chemical isolation of this vitamin, probably on account of 

 the fact that other material, especially organic bases, are also carried along 

 with the active substance. In any attempt at the isolation of this vitamin, 

 proper consideration should be given to the possible injurious effect of 

 alkali and heat. 



Fat-soluble Vitamin (Fat-soluble A). This dietary factor was first 

 discovered in butter (McCollum and Davis (a), 1913 ; Osborne and Mendel 

 (c), 1913), and is usually found in association with certain food fats in 

 which it is very readily soluble. It can be extracted from dried spinach or 

 clover by ether (Osborne and Mendel(r), 1920). In water it is only solu- 

 ble to a very limited degree. McCollum (1917) has estimated, for in- 

 stance, that in milk one-half of the substance present is dissolved in the milk 

 fat, which indicates that the solubility in fat is approximately 30 times 

 greater than that in water. Osborne and Mendel (h) (q) (1915, 1920) 

 observed that butter fat treated with live steam for 2y 2 hours had not lost 

 any of its fat-soluble vitamin. More recently Steenbock, Boutwell and 

 Kent (1918) claimed, however, that the substance is slowly destroyed at 

 40 to 60 C., and that complete destruction takes place after 4 hours' 

 exposure to 100 C. These observations were confirmed by Drummond 

 (e) (1919), who worked with butter and whale oil. The fat-soluble vita- 

 min in plant tissues is not destroyed by autoclaving for three hours at 15 

 pounds pressure (Steenbock and Gross (&), 1920). The destructive process 

 is evidently a reaction of slow velocity, but of suificient magnitude to be 

 considered from the practical point of view of the deterioration of this 

 factor in food. 



Saponification of butter fat with alcoholic sodium hydroxid does not 

 destroy the fat-soluble vitamin (McCollum and Davis(c), 1914), whereas 

 saponification in the presence of water leads to complete destruction 

 (Drummond(/), 1919). In the commercial "hardening" of certain oils by 

 means of hydrogen, the physiological activity originally present in the 

 oil is lost, this being principally due to the high temperature used in 

 this process (Drummond, 1919). This vitamin is also destroyed when 

 butter is exposed for 8 hours to ultraviolet rays (Zilva, 1919). There is a 

 complete lack of knowledge regarding the chemical composition of this 

 substance, although recently Steenbock (1919, 1920) has called attention 

 to the possible identity of this substance with a yellow pigment, carotin, a 

 view which, however, is not shared by Palmer (1919). 



Antiscorbutic Vitamin (C Factor). This vitamin is soluble in water 

 and alcohol (Harden and Zilva(fc), 1918; Hess and Unger(&), 1918) and 

 is easily dialysable through parchment (Hoist and Frohlich(fc), 1912) and 

 porcelain filters (Harden and Zilva(rf), 1918). The substance loses i 

 physiological activity on drying, sometimes even at low temperature and 

 more readily at 100 C. (Givens and Cohen, 1918; Givens and McClug- 

 gage(6), 1919). From the experiments of Delf (1918) it appears that the 



