XIII. REQUIREMENTS 513 



fiizyinr. St>nH' of tlie results arc .sliow n in 'J able XXI . Ihc aiitli(jrs .suggested 

 that vitamin Bjo aids in the transfer of pantothenic acid from the Hver for 

 use elsewhere in the body of the chick. Similar experimental results were 

 reported by Yacowitz and coworkers,^' who also noted that the free panto- 

 thenic acid content of breast muscle tissue was not affected by dietary 

 vitamin Brj while the free pantothenate content of liver tissue was decreased 

 as compared with the content of the livers of chicks receiving no dietary 

 vitamin Bjo. The pantothenic acid requirement of chicks for growth ap- 

 peared to be increased somewhat when the vitamin B12 supply was inade- 

 c[uate. 



B. OF RATS 



THOMAS H. JUKES and WILLIAM L. WILLIAMS 



For maii}'^ years, "synthetic" diets have been used for nutritional studies 

 with rats. These diets have commonly contained a purified carbohydrate, 

 such as starch, sucrose, glucose, or dextrin, together with casein as a source 

 of protein. The casein of commerce is generally washed with dilute salt 

 solution or treated alternately with alkali and acid to remove B-complex 

 vitamins, or it may be extracted with a fat solvent to remove vitamin A. 

 Yeast and wheat germ were often added in former years, but as the B- 

 complex vitamins became available in synthetic form, it has been quite 

 customary to replace the yeast and wheat germ with synthetic vitamin 

 mixtures. It is possible to obtain reproduction in rats on diets of this type,^" 

 but breeding diets commonly used for the production of experimental rats 

 are prepared with crude natural foods and are frequently supplemented 

 with such materials as raw liver and fresh milk. This practice reflects the 

 awareness that the nutritional re(iuirements for reproduction in rats are 

 more exacting than the needs for growth. 



A series of investigations, particularly those of Coward, Mapson, Gary, 

 Hartman, and their coworkers,^""^'' have led to the realization that casein 

 contains an essential vitamin component which is not readily removed by 

 washing with water and which is not present in yeast, cereal grains, or 

 vegetable protein concentrates. This substance is now known to be vitamin 



29 H. Yacowitz, L. C. Norris, and G. F. Heuser, ./. Biol. ('hem. 192, 141 (1951). 



'" T. H. Jukes, Proc. Soc. Exptl. Biol. Med. 45, 625 (1940). 



3' K. H. Coward, K. M. Key, and B. G. K. Morgan, Biochcm. ./. 23, 695 (1929). 



'2 K. H. Coward, K. M. Key, F. J. Dyer, and li. G. E. Morgan, Biochem. J. 24, 1952 



(1930); 25, 551 (1931). 

 " K. H. Coward, F. J. Dyer, R. A. Morton, and J. H. Gaddum, Biochem. J. 25, 1102 



(1931). 

 " L. W. Mapson, Biochem. J. 26, 970 (1932). 

 " L. W. Mapson, Biochem J. 27, 1061 (1933). 

 36 A. M. Hartman, L. P. Dryden, and C. A. Gary, J. Biol. Chem. 140, liv (1941). 



