238 THE VITAMINS 



liver oil concentrates in amounts so minute that direct attempts at its 

 isolation by ordinary chemical methods are of little use. They were 

 unsuccessful in separating by fractional distillation at pressures of about 

 0.01-2 mm. the vitamin A present in the unsaponifiable matter of 

 certain liver oils. The unsaponifiable fractions of cod-liver oil and sheep- 

 liver oil tend to decompose on distillation in high vacuum, and are not 

 readily reduced by hydrogen in the presence of platinum or palladium 

 catalysts. The unsaponifiable fraction of shark-liver oil can be distilled 

 with little destruction of the vitamin A, owing, it is thought, to the small 

 proportion, or absence, of the complex alcohols and hydrocarbons of 

 the terpene series. From 90 to 95 per cent of the unsaponifiable fraction 

 of these latter oils consists of selachyl, batyl, chimyl and oleyl alcohols, 

 with small amounts of cholesterol and squalene. Probably less than 1 

 per cent of the non-saponifiable matter of shark oil with vitamin activity 

 comparable to that of good cod-liver oil, is vitamin A. 



Clenshaw and Smedley-MacLean (1929) worked extensively with 

 plant materials (unsaponifiable matters of spinach leaves and green 

 cabbage) and discussed carotene (carotin) and some other substances 

 as possibly related to vitamin A. 



Color Reactions and Spectrographic Studies. — Drummond and Wat- 

 son (1922a) suggested that the striking purple color of the sulfuric acid 

 reaction of liver oils might be due to vitamin A or some related sub- 

 stance, since there seemed to be a parallelism between the intensity of 

 the color reaction given by an oil and its vitamin A value. 



Later Rosenheim and Drummond (1925) developed the same idea 

 more fully in connection with the arsenic trichloride reaction. When this 

 reagent is mixed with a liver oil a color series follows, which is first 

 blue, then turns purplish, and gradually fades. This reaction was found 

 to be about 20-fold more sensitive than the sulfuric acid test, and was 

 given with progressively greater intensity (or at progressively greater 

 dilution) by all materials tested at the time, in which a concentration of 

 vitamin A had been effected. The highly potent fraction obtained upon 

 the removal of cholesterol from the unsaponifiable matter of cod-liver 

 oil was found to give this reaction at a dilution of 1 : 2,000,000. The 

 chromogenic factor also responded as does vitamin A to steam distilla- 

 tion and oxidation, which adds weight to the suggestion of intimate 

 relationship. 



Over 30 oils and fats were tested as to growth-promoting property 

 and reaction with arsenic trichloride, with results that showed a general 

 parallelism. Furthermore, irradiated cholesterol, although strongly anti- 

 rachitic, did not show the arsenic chloride test. 



