VITAMIN A 235 



oils that had been inactivated by treatment with sulfur dioxide and 

 oxygen were unsuccessful. 



Attempts to Isolate Vitamin A and Determine Its Chemical Nature. 

 — It was early found that vitamin A belongs to the unsaponifiable 

 fraction of natural fats rather than to the triglycerides themselves. The 

 unsaponifiable matter consists chiefly of unsaturated monatomic alcohols 

 of high molecular weight which are solid at ordinary temperatures and 

 are therefore called "sterols." The best known members of the sterol 

 group are cholesterol and phytosterol occurring in animal and vegetable 

 fats respectively. Animal fats have served as the starting point in most 

 of the attempts to isolate vitamin A so that references to its properties 

 are often in terms which suggest comparison or contrast with cholesterol. 

 In 1924, Drummond reported the first results of his studies in this field, 

 which showed that vitamin A could be separated from cholesterol and 

 could be distilled in superheated steam without losing its vitaminic 

 activity. He succeeded in effecting a 1,000- fold concentration of the 

 vitamin A of cod-liver oil. Description of his actual procedure is omitted 

 here as the method in its more fully developed form is outlined below 

 in discussing the work of Drummond, Channon and Coward (1925). 

 The purified material which Drummond described in 1924 appeared to 

 consist chiefly of an unsaturated sterol. Similar results were reported 

 from Japan in the following year (Takahashi, Nakamiya, Kawakami 

 and Kitasato, 1925). Takahashi et al. believed their preparation to con- 

 sist essentially of vitamin A in a practically isolated condition. This they 

 described as showing the properties of a sterol and proposed to designate 

 as "biosterol" or "biosterin." 



A critical discussion of this work together with additional experi- 

 mental evidence from their own investigations has been offered by 

 Drummond, Channon and Coward (1925), who believe that the "bio- 

 sterin" or "biosterol" of the Japanese investigators cannot be regarded 

 as a pure substance nor as approximating closely to an actual isolation 

 of vitamin A. Drummond, Channon and Coward here reported work of 

 their own in which they effected essentially the same concentration of 

 the active substance as did Takahashi et al., but with a resulting product 

 which they describe as being still a mixture. 



The methods and results of Drummond and his coworkers may be 

 briefly outlined as follows : Cod-liver oil is poured slowly with vigorous 

 stirring into a hot solution of potassium hydroxide in alcohol, the 

 mixture boiled for about 30 minutes (the alkali being present in an 

 excess of about 10 per cent over the amount theoretically necessary for 

 saponification of the oil), then cooled, diluted with 10 volumes of water 



