VITAMIN A 231 



light in an atmosphere of carbon dioxide gas for 16 hours, at the end 

 of which time it was found to have lost none of its growth-promoting 

 activity. On exposure for from 6 to 10 hours to a current of ozone in 

 a bottle impervious to light, it became so inactivated that large doses 

 failed to promote growth in rats on a diet otherwise deficient in vitamin 

 A, showing that ozone destroys or inactivates the vitamin A, a finding 

 in complete agreement with the observations noted above, the action 

 of ozone being more drastic and therefore more rapid than aeration. 



Accepting these findings as conclusive, the discrepancies in earlier 

 conclusions concerning the stability of vitamin A are readily understood. 

 In cases where stability was reported as in the exposure of butterfat to 

 live steam, the conditions of the experiment gave an approximately air- 

 free medium, while in such experiments as the removal of vitamin A 

 from butterfat by repeated shaking with hot water, in the presence of 

 air, the destructive action was probably one of oxidation. It should be 

 noted, however, that in all the experimental work reviewed above, 

 animal fats, sometimes referred to as the secondary source of vitamin 

 A, have been used. 



Steenbock and Boutwell (1920a) determined the stability of the 

 fat-soluble vitamin in plant materials by means of feeding experiments 

 in which the vitamin-containing material was dried at room temperature, 

 soaked in water, autoclaved for 3 hours at approximately 15 pounds 

 pressure, and again air-dried before being incorporated into the ration. 

 This treatment appeared to cause no noticeable destruction of the fat- 

 soluble vitamin of yellow maize, chard, carrots, sweet potatoes, and 

 Hubbard squash. The results, in growth of rats, obtained with dried 

 alfalfa were not so favorable, although this was fed at a level at least 

 twice as high as is usually necessary for normal growth. The rats on 

 this diet after a normal growth for 3 or 4 weeks declined and died, some 

 showing signs of xerophthalmia. While at this time the efifect of heat 

 rather than possible destruction by oxidation through exposure to air in 

 the drying process was the one chiefly considered, the authors called 

 attention to the fact that the alfalfa meal used was a commercial product, 

 the history of which was not known, and that possibly while the fat- 

 soluble vitamin was not destroyed by the heat treatment itself, it was 

 made more susceptible to destruction — possibly by liberation from com- 

 binations — by the agents operative in the aging process. 



That vitamin A as it exists in plant tissues is not in a form to be as 

 easily acted upon by oxidation as it is in animal fats is further indicated 

 from the ability to prepare highly potent materials by extraction of air- 

 dried vegetables as illustrated by work of Osborne and Mendel (1920c), 



