VITAMIN Bi2 (ERYTHROTIN) 



had a marked lipotropic effect when injected into rats fed a high fat 

 diet 22 and, finally, the administration of vitamin B^g to rats preceding 

 acute carbon tetracliloride intoxication prevented liver injury. ^^ 



Stimulation of the growth of rats and chicks maintained on puri- 

 fied diets has been used for the assay of vitamin B^g with conflicting 

 results (page 535). With the diets used, the response was presumably 

 not always due solely to the vitamin B^g present. 



Relation between Vitamin B12 and Folic Acid 



As already pointed out (page 499), pteroylglutamic acid and 

 vitamin B^g are not biologically equivalent. Thus, the administration 

 of vitamin B^g to folic acid-deficient chicks increased the growth rate 

 without any effect on feathering, whereas pteroylglutamic acid im- 

 proved feathering but had no effect on growth.-^ The so-called 

 vitamins B^q and B^ deficiencies (page 614) are probably deficiencies of 

 vitamin B^g and folic acid respectively. Again, pteroylglutamic acid 

 failed to increase the sub-optimal growth rate of rats fed a purified diet 

 plus sulphasuxidine, but cured the leucocytopenia, whereas a liver 

 extract produced good growth. ^^ The effect of vitamin B12 on the 

 growth of chicks was enhanced by ascorbic acid, and the amount of 

 folic acid stored in the liver was higher when vitamin B^^, and ascorbic 

 acid were given together than with vitamin B^g alone. ^^ Both pteroyl- 

 glutamic acid and vitamin B^g were essential for pigs,^'^ but vitamin 

 B12 alone was not so effective as a concentrate of the animal protein 

 factor, suggesting that the latter may contain another substance 

 besides vitamin Big-^® Whereas the addition of pteroylglutamic acid 

 to a diet deficient in both folic acid and vitamin B12 reduced the 

 amount of D-amino acid oxidase present in the livers of chickens, the 

 addition of vitamin B^g increased it ; ^^ other enzymes were not affected. 



Relation of Vitamin B12 to Thymine 



Thymine has a haemopoietic action in tropical sprue similar to that 

 produced by pteroylglutamic acid (page 514), though the clinical 

 response was less dramatic.^° It also brings about a response in 

 nutritional macrocytic anaemia and pernicious anaemia, but several 

 thousand parts of thymine were required to produce the same response 

 as one part of pteroylglutamic acid, and several thousand parts of 

 pteroylglutamic acid to produce the same response as one part of 

 vitamin B^g.^^ Thymine also produced reticulocytosis in splenec- 

 tomised rabbits. ^^ Thymidine, however, failed to produce a reticulo- 

 cyte response in a patient with pernicious anaemia,^^ so that care 

 should be taken to eliminate thymidine in assaying vitamin B12 

 preparations microbiologically (page 534). 



540 



