228 THE VITAMINS 



fresh carrots or about one half of the total solids. This sirupy extract 

 given daily in amounts equivalent to from 10 to 12 grams of fresh 

 carrots provided sufficient vitamin A to promote normal growth in rats 

 subsisting on a diet otherwise lacking this vitamin. On extracting with 

 ether the concentrated extract obtained by evaporation of the alcohol, 

 an oily residue remained which, in amounts equivalent to 25 grams of 

 fresh carrots, promoted recovery and renewed growth in rats declining 

 on a basal diet lacking in vitamin A. 



Thus, the evidence indicates that vitamin A may be removed from 

 either animal or vegetable material by extraction with alcohol. This has 

 led to the custom of subjecting materials to be used in a basal ration 

 free from vitamin A to prolonged extraction with alcohol or alcohol and 

 ether. Drummond and Coward (1920) have emphasized the necessity 

 of such extraction, stating that in their opinion "it is frequently the 

 composition of the basal dietary which is responsible for the many mis- 

 leading and contradictory statements which tend to confuse the literature 

 on the vitamins at the present time." 



The present writers concur fully in the view that careful extraction 

 of possible traces of vitamin A (preferably by hot strong alcohol) 

 should be a universal precaution in the preparation of experimental 

 rations which are designed to be devoid of this vitamin; but believe that 

 the "misleading and contradictory statements which tend to confuse the 

 literature" are due largely to the further factor of storage of vitamin A 

 in the body of the experimental animal, so that whether the vitamin 

 causing the confusion came from the food or the animal's body has not 

 always been clear. We now use experimental animals which have been 

 carefully depleted of any bodily surplus of vitamin A, and to ensure 

 freedom of food materials from this vitamin we extract them repeatedly 

 with hot strong alcohol in the manner recommended by Osborne and 

 Mendel (1921) and described in full in connection with methods for the 

 quantitative determination of vitamin A further on in this chapter. 



Stability to Heat and Oxidation. — Similar confusion has existed in 

 regard to the stability of vitamin A. In their early work McCollum and 

 Davis reported that the factor was present in the ether extract of boiled 

 eggs and Osborne and Mendel (1915a) found that butterfat treated with 

 steam for two and one half hours did not appear to have lost its growth- 

 promoting properties. The fat-soluble vitamin was generally considered 

 a thermostable substance and in experimental work on its occurrence in 

 foods but little thought was given to the possibility that the manipulation 

 involved, such as shaking of the butterfat with water, or subjecting 

 materials to prolonged drying with artificial heat, might destroy their 



