METABOLISM OF THE B VITAMINS 359 



with C 13 , 95.7 per cent of the original concentration of C 13 is recovered as 

 F 2 . 143 Tracer work with C 14 indicates, however, that both nicotinic acid 

 and its amide are to some extent decarboxylated, 144 although the products 

 are as yet unknown. F 2 is distinguished in urine by its formation of a 

 bluish white fluorescent compound when examined under ultraviolet 

 light in the presence of alkali and butanol, 137, 138 and its part in nicotinic 

 acid metabolism has been realized only during the past few years. It 

 does not promote growth in Lactobacillus arabinosus (which can utilize 

 both nicotinamide and nicotinuric acid) nor in Leuconostoc mesenteroides 

 (which cannot utilize low levels of nicotinamide or any levels of nico- 

 tinuric acid, but requires free niacin). 139 Liver slices in vitro, but not 

 kidney or muscle tissue, convert nicotinamide to F 2 , and in vivo studies 

 have shown that the intact liver is capable of performing this methylation 

 at a rapid rate, whereas the intact kidney is not. 140 The liver is thus be- 

 lieved to be the sole site of F 2 formation; and F 2 formation from nicotina- 

 mide has been shown to be a valuable test of hepatic function, employing 

 as the test dose a physiological compound within physiological levels, as 

 contrasted with the usual tests employing substances foreign to the ani- 

 mal body. 141, 142 The reaction has been of some value in the study of 

 transmethylation in healthy persons, and it appears that in studies with 

 rat liver slices, the methylation is frequently enhanced by methionine. 140 

 Bearing upon the nature of the methylation process, as well as the utiliza- 

 tion of F 2 as a nicotinamide source, is the demonstration that the incor- 

 poration of 2 per cent of F 2 into the Griffith and Wade fatty liver diet of 

 four rats for three months resulted in liver fats of 24.5, 8.2, 10.6 and 

 23.5 per cent, as compared to rats on the unsupplemented diet with liver 

 fats of 36.1, 39.1, 39.7 and 34.7 per cent. It would thus appear that the 

 methyl group of F 2 is available for choline formation (p. 353) , 145 



As a corollary of this latter study, 146 it was found that 1 per cent F 2 

 in the diets of four rats on this diet produced after three months an 

 average daily excretion of 11.8 fig per day of nicotinamide, as compared 

 with 4.5 fig per day in four controls on this diet. While these data have 

 been criticized on the basis of the smallness of the groups and the pos- 

 sibility of nicotinamide contamination in the large amounts of F 2 em- 

 ployed, general metabolic considerations would make it seem likely that 

 F 2 was at least to some extent available as a nicotinamide source. Tests 

 have to date strongly indicated that F 2 is ineffective in the treatment of 

 pellagra 146 and blacktongue, 147 although in the latter case seriously con- 

 flicting reports do exist. 148, 149 



That F 2 is derived rather directly from nicotinamide is shown by the 

 facts (1) that nicotinamide is more effective than nicotinic acid in pro- 

 ducing urinary F 2 , 150 (2) that oral doses of equivalent amounts of nico- 



