522 VITAMIN Bi2 



nants, which actually does not appear to differ greatly from that of chicks 

 and rats when computed on the basis of body weight. It was found by 

 Becker and Smith''^ that the injection of 15 U.S.P. units of concentrated 

 liver extract was effective for sheep, and Johnson'^^ noted that calves on 

 purified diets containing inorganic cobalt showed a deficiency which was 

 alleviated bj'' vitamin B12. Hale and coworkers^^ suggested that the earlier 

 doses of vitamin B12 may have been too small. They obtained partial 

 responses in two cobalt-deficient lambs which received, respectively, 100 7 

 of vitamin B12 injected daily and 200 7 by mouth daily for 4 weeks. Even 

 better responses w^ere given by other cobalt-deficient lambs which were 

 given a mixture of B vitamins not including B12. Smith" and Marston'^^ 

 also concluded that the amounts of vitamin B12 given in their earlier studies 

 were insufficient. It was reported" that cobalt deficiency was induced in 

 lambs by feeding them a diet of low-cobalt hay, shelled corn, and milk 

 powder containing approximately 0.03 part of cobalt per million. The typi- 

 cal signs of deficiency were quickly alleviated when the lambs were injected 

 with 150 7 or more of vitamin B12 over a 2-week period. In a second experi- 

 ment, orally administered cobalt salts were compared with injections of 

 vitamin B12 and Bi2b. No significant differences were obtained among the 

 three treatments, and the lambs all responded well, gaining an average of 

 0.35 lb. daily. 



The reason for the observation that non-ruminants on cobalt-deficient 

 forage crops do not develop vitamin B12 deficiency remains unexplained. 

 Perhaps the non-ruminants have a lower requirement for vitamin B12, or 

 their intestinal synthesis or absorption of vitamin B12 is more efficient than 

 that of ruminants. The finding that B-complex vitamins other than vitamin 

 B12 alleviated cobalt deficiency in lambs^^ is also unexplained. 



E. OF HUMAN BEINGS 



FRANK H. BETHELL 



Vitamin B12 is probably the most biologically active of the known vita- 

 mins in terms of the amount required by the organism. Although B12 is an 

 essential nutrient, it appears that normal nutrition and blood cell produc- 

 tion can be maintained in almost complete absence of a dietary supply of 

 the material. In such cases, where the diet has been lacking in foods of 



7" D. E. Becker and S. E. Smith, J. Animal Set. 8, 615 (1949). 



^^ B. C. Johnson, Gordon Research Conferences, American Association for the Ad- 

 vancement of Science, 1950. 



76 W. H. Hale, A. L. Pope, P. H. Phillips, and G. J. Bohstedt, J. Animal Set. 9, 484 

 (1950). 



" S. E. Smith and B. A. Koch, /. Animal Sci. 10, 1062 (1951). 



'8 H. R. Marston, Personal communication, 1951. 



