232 THE VITAMINS 



Alfalfa, clover, timothy, and spinach, freshly dried at 60° C. apparently 

 furnished, in amounts of 0.1 gram of the dried substance, as much vita- 

 min A as did 0.1 gram of butter fat ; while with tomatoes more rapid 

 growth resulted from the addition of 0.1 gram of the dried material 

 than of the same amount of butterfat. In this case, however, the rapid 

 growth is attributed partly to the richness of the tomato in vitamins 

 B and C. 



Experiments were later made by Sherman, Quinn, Day and Miller 

 (1928) to determine the relative stability of vitamin A from plant and 

 animal sources when heated under like conditions, and also to ascertain 

 the influence of such conditions as the nature of the solvent and the 

 hydrogen-ion activity (pH) of the medium upon the rate of destruction 

 or inactivation. 



In these experiments, albino rats were placed on a vitamin A-free 

 diet (described in the section on quantitative determination beyond) at 

 28 days of age and the feeding of this diet continued until the surplus 

 vitamin A stored in the animal's body was depleted, as evidenced by 

 cessation of growth and by the incipient appearance of other symptoms 

 characteristic of vitamin A deficiency. Graded portions of the test foods 

 whose relative vitamin A values were to be compared were then fed as 

 supplements to the vitamin A-free diet. All of the feeding experiments 

 were made in pairs upon litter mates of essentially the same weight, one 

 being fed one material, the other the same material but differently 

 treated or a different material similarly treated, as the case might be. 

 Those portions of the two samples which, when fed daily during an 

 8-week experimental period, gave the same small but definite gain in 

 weight, i.e., those portions which contained the same amount of vitamin 

 A, were thus determined ; and from these values the amount of destruc- 

 tion of the vitamin due to any particular treatment was calculated. 



First, a study was made of the stability of vitamin A in a plant 

 material (filtered tomato juice) when heated for 4 hours at 100° C. 

 under anaerobic or aerobic conditions. 



For the study of the stability of the vitamin in the absence of oxygen 

 the juice was placed in a 1 -liter flask provided with a rubber stopper 

 through which passed a reflux condenser with its open end protected 

 from the air by a water seal, and nitrogen, freed from oxygen by pass- 

 ing through alkaline pyrogallol and then over 12 inches of red-hot 

 copper gauze, was bubbled through the liquid for 2 hours. At the end of 

 this 2-hour period, half of the juice was withdrawn through a properly 

 arranged delivery tube to an evacuated bottle and the remainder heated 

 on a steam bath for 4 hours at 97° C. ± 2°. Nitrogen was permitted to 



