440 



VITAMIN Bi2 



liver extract powder. The basal diet was incapable of supporting growth, 

 and very little improvement was obtained by adding cystine, but the addi- 

 tion of either methionine or homocystine enabled growth to take place. 

 The presence of liver extract in the diet used in these experiments is of 

 much significance when viewed in the light of later findings. 



It was found'^2 that rats usually lost weight when fed an amino acid 

 mixture without methionine but containing homocystine. Rice bran ex- 

 tract, 12.5 mg. daily, was the only "crude" B-complex supplement added 

 to the diet. Rice bran, like all cereal products, is low in folic acid and 



Fig. 5. Growth of chicks on a methionine-deficient diet with various supplements 

 in the presence and absence of vitamin Bio. 



vitamin B12. The addition of choline to the diet or the substitution of 

 methionine for homocystine enabled growth to take place. However, a few 

 animals on the basal diet grew slowly without added choline, and the 

 authors speculated as to the possibility of "refection" being an explanation 

 for this apparent anomaly. The involvement of vitamin-like factors in the 

 utilization of homocystine by rats was studied by Bennett and Toennies,"^ 

 who showed that crude liver extract supplied unidentified factors which 

 enabled rats to grow on a "labile-methyl-free" diet containing homocystine 

 and succinylsulfathiazole. No growth was obtained when a more refined 

 and concentrated extract was used. This latter extract was shown elsewhere 



"2 V. du Vigneaud, J. P. Chandler, A. W. Moyer, and D. M. Reppel, J. Biol. Chem. 



131, 57 (1939). 

 '" M. A. Bennett and G. Toennies, J. Biol. Chem. 163, 235 (1946). 



