OCCURRENCE 



4. OCCURRENCE OF VITAMIN B12 



Comparatively few assays have yet been reported of the vitamin 

 B12 content of natural materials and, in view of the divergent views as 

 to the specificity of both microbiological methods and animal assays, 

 such results as have been published should perhaps be accepted with 

 reserve until confirmed. 



Using a rat growth method, Lewis et al.^ found desiccated sheep 

 rumen contents, beef liver and kidney, chicken liver, condensed fish 

 solubles and dried streptomycin slop to be the richest sources of 

 vitamin B^g ; these contained between 35 and 50 /xg. per 100 g. Herring 

 stickwater and desiccated pig adrenals contained about 15 /zg. per 

 100 g. ; beef and mutton about 5 ; veal about 4 ; horsemeat, 7-5 ; 

 pork, I to 3 ; casein, milk powder and cheese, 2 to 3 ; and egg yolk 

 2-8 /xg. per 100 g. Plant materials showed no measurable activity. 



Extracts prepared by digestion with pancreatin in the case of 

 animal products and \\ith pancreatin plus takadiastase in the case of 

 plant materials gave the following values when assayed with L. 

 leichmannii ; ^ liver extract, 39 ; fish meal and condensed fish solubles, 

 9 to 10 ; crude casein, 10 ; meat scraps, 4 ; alfalfa leaf meal, 4 ; 

 soya bean meal and yellow corn, i ; dried brewers' yeast, o-8 ; and 

 wheat, 07 yig. per 100 g. 



Pig liver gave active extracts only in summer and autumn, whereas 

 calf liver showed no such seasonal variation.^ There appeared to be 

 no correlation between the microbiological response and the clinical 

 potency of liver extracts,^ though this, of course, may well be due to 

 the extreme inaccuracy of the method used to assess clinical potency ; 

 ten different liver extracts on sale in the U.S.A. gave values ranging 

 from 0-087 to 2-17 jLig. per U.S. P. unit of anti-pernicious anaemia 

 activity, although i /xg. of the pure vitamin had approximately i 

 U.S. P. unit of activity. The vitamin B^g potency of a number of 

 liver extracts tested in this country ranged from 0-2 to 22 /xg. per ml.* 



The liver, heart, small intestine and femoral muscles of vitamin 

 Bi2-depleted rats contained no vitamin B^g, whereas the kidney 

 retained a substantial quantity.^ Extracts active in pernicious 

 anaemia were obtained from human livers, from the livers of twenty- 

 six species of mammals and three species of fish, whereas inactive 

 extracts were obtained from the livers of sea-lion, reptiles and am- 

 phibia.^ A satisfactory extract was prepared from whale liver. ^ 



References to Section 4 



1. U, J. Lewis, U. D. Register, H. T. Thompson and C. A. Elvehjem, 



Proc. Soc. Exp. Biol. Med., 1949, 72, 479 ; i949, 70, 167. 



2. H. T. Peeler, H. Yacowitz and L. C. Norris, ibid., 515. 



