134 



THE VITAMINS 



serve as carriers of the vitamin, even though the concentrations of the 

 vitamin vary widely. When growth is thus restricted the response by 

 gain in weight to small additions of vitamin is quite deHcate and the 

 bodily vigor of the animal is sufficiently maintained that the physiologi- 

 cal variation does not vitiate average results. Average curves of growth 

 at different levels of feeding are shown in Fig. 6. 



In the Bourquin experiments summarized in Fig. 6, the vitamin 

 G was fed in the form of milk which contains all the known vitamins 

 and appears to be relatively rich in both or all of the heat-stable factors 

 of the vitamin-B complex (i.e., of the other factors mentioned at the 



10 20 30 ^ so 60 



r/ME IN DAYS 



Fig. 6. — Average growth curves of rats receiving different amounts of vitamin 

 G. The lowest curve shows the gradual loss of weight on the Bourquin basal diet 

 alone; the others, the effects of feeding x amount per day of vitamin G in the 

 form of milk, and 2, 4, and 8 times this amount. (Courtesy of Dr. Anne 

 Bourquin.) 



end of this chapter as well as of vitamin G — Gi, Bo itself). This fact, 

 together with the use of test animals whose previous diet had given 

 them opportunity to gain good bodily stores of the newer factors, 

 helped to permit the steady gains shown in these curves. Where either 

 of these two conditions is less favorable, there is apt to be a flattening 

 of the curves. This is more fully discussed elsewhere in this chapter. 



Numerous data not yet published indicate that if test animals of a 

 less satisfactory nutritional history are employed, particularly when 

 fractions of food products rather than the natural materials are being 

 tested for their vitamin G values, quantitative estimations of the vita- 

 min content should be based on experiments terminated after 4 or 5 



