XIII. REQUIREMENTS 515 



was fed in diet A (containing 5% of yeast protein) to X-deficient rats, 

 growth rates were 54% and 25% of normal, respectively. Coagulated egg 

 albumin gave growth similar to that obtained with casein C, and with 

 60% of casein C the rats generalh^ died within 2 weeks. On diet A with 

 25% of lactose and 20% of casein C growth was 3G% of normal. When a 

 few milligrams of certain commercial li\'er extracts were fed daily with diet 

 A to sex-litter mates of the above rats, growth was normal or approximately 

 normal except with 60% casein (85% normal). A few micrograms of a 

 crude concentrate of X, fed separately, gave normal growth when tested 

 with the 20 % casein diet. The active factor in liver extracts was water- 

 soluble, dialj^zable, and precipitable with ammonium sulfate. 



Further characteristics of the deficiency were described in a popular 

 article by Gary and Hartman.^^ Increasing the protein in the basal ration, 

 adding casein, egg albumin, or yeast, or feeding soybean meal or linseed oil 

 meal in place of carbohydrates did not improve growth ; in fact, the addition 

 of soN^bean meal, linseed meal, or yeast actually depressed growth. In 

 contrast, certain preparations of the growth-promoting nutrient concen- 

 trated from liver brought about optimum growth in daily doses of 20 7 

 and were active in daily doses of 2 7. Furthermore, a supplement of liver 

 extract enabled normal growth to take place in the rats fed diets containing 

 additional amounts of soybean meal, linseed meal, and yeast. These im- 

 portant observations showed that these various high protein diets were 

 not in themselves deleterious, for the unidentified factor enabled normal 

 growth to take place Avhen a high level of protein was fed. 



^^itamin B12 was found to increase the rate of growth on all levels of 

 protein under the same conditions as liver extract,^* and a maximally effec- 

 tive dosage level of vitamin B12 produced practically the same effect as doses 

 of liver extract which had been found to be maximally effective for male 

 rats. The results are illustrated in Table XXII. Vitamin B12 also prevented 

 the kidney hypertrophy which occurred on the basal diet. 



The effect of all-vegetable diets on rats was studied by Zucker 

 and Zucker,^^ who described a deficiency which was prevented by liver or 

 crude casein but not by yeast. Cottonseed meal was used at high levels in 

 the basal diets. In the year following, they reported that fish solubles and a 

 concentrate prepared from cow manure by H. R. Bird's group were both 

 active and suggested that this indicated a similarity between the deficien- 

 cies occurring in rats and chicks. *° A number of interesting explorations of 

 the natural distribution of the factor were made by the Zuckers, who found 



"C. A. Gary and A. M. Hartman, Yearbook of Agr. 194S-1947, U. S. Dept. Agr. 



p. 779 (1947). 

 38 A. M. Hartman, L. P. Dryden, and C. A. Gary, Arch. Biochcm. 23, 165 (1949). 

 33 L. M. Zucker and T. F. Zucker, Abslr. 111th Meeting, Am. Chem. Sac. p. 45B (1947). 

 ^0 T. F. Zucker and L. M. Zucker, Vitamins and Hormones 8, 1 (1950). 



