368 THE BIOCHEMISTR Y OF B VITAMINS 



more complete than most similar studies. Those interested in specific 

 aspects of the excretion problem may readily find a vast current literature 

 dealing with the individual vitamins: thiamine, 188-196 riboflavin, 197 " 204 

 niacin, 205 - 211 pantothenic acid, 212 " 213 biotin, 214 ' 215 folic acid, 216-218 vita- 

 min B 6 , 219 p-aminobenzoic acid and inositol, 220 and the antipernicious 

 anemia factor. 221 Problems dealing with obstetrics and pediatrics are 

 similarly well covered in the current literature, 188 - 199 - 20 °- 207 > 210 > 222 and 

 ready access to the vast earlier literature on the topic may be gained 

 through these references. Unfortunately, there is not at present sufficient 

 information to draw any conclusion as to the variations in levels among 

 various species, however. 



Fecal and Dermal Excretion. As shown in Tables 29 and 30, except 

 for pantothenic acid and pyridoxine, fecal excretion of the B vitamins far 

 exceeds urinary excretion, but there is little information to indicate what 

 part of the fecal excretion represents dietary intake and what part in- 

 testinal synthesis. Undoubtedly the greater part of the fecal vitamin 

 content is of bacterial origin, since the combined fecal and urinary ex- 

 cretion of biotin, pantothenic acid, PABA, and folic acid exceeds the 

 intake, and since the remainder of the B vitamins have other major 

 products of metabolism which were not considered in this study. More- 

 over, the consideration of dermal excretion was not made in assessing these 

 data. Furthermore, there is no apparent correlation between the com- 

 bined urinary and fecal excretion and the dietary intake. 



It seems quite certain that fecal thiamine is almost entirely in the form 

 of cocarboxylase, in contrast with urinary thiamine. 194 Little is known 

 of the precise form of the other vitamins in the feces, although from 60 

 to 100 per cent of the fecal B vitamin content is said to be "water-sol- 

 uble." 27 Similarly, little is known as to the precise forms of the B vita- 

 mins excreted in sweat. Vitamin concentrations in sweat appear to be 

 quite similar to those in urine, and it is consequently generally felt that 

 under normal environmental conditions the dermal excretion is negligible 

 by comparison with urinary excretion. Pantothenic acid normally occurs 

 in sweat in concentrations of about 3.8 fig per cent, 212 and the fact that 

 this level cannot be increased by higher dosage with pantothenic acid 

 suggests that the excretory ability of the skin is more limited than that 

 of the kidney. Inositol and PABA occur in sweat in concentrations of 

 about 21. fig per cent and 0.24 fxg per cent, respectively. 220 



Recent studies on urinary and dermal excretion of- pyridoxine and its 

 derivatives are of interest in that they strongly suggest that sweat con- 

 tains metabolites of B vitamins quite similar to those in urine. Table 31, 

 taken from Johnson, Hamilton and Mitchell's paper, 223 indicates that 

 sweat normally contains pyridoxal, pyridoxamine and 4-pyridoxic acid. 



