METABOLISM OF THE B VITAMINS 341 



which may be well utilized by normal persons, but are apparently un- 

 available to patients with pernicious anemia, although folic acid itself 

 is effective. In this instance there is some reason to believe that "vitamin 

 B 12 " functions in the enzyme which hydrolyzes vitamin B c conjugate to 

 folic acid. 9 A variety of other disturbances which involve the gastro- 

 intestinal tract have similarly been shown to produce B vitamin de- 

 ficiencies, and may involve drastically reduced abilities to liberate bound 

 forms of the B vitamins. Among healthy persons, the differences may not 

 be so manifest, but they undoubtedly do exist and may markedly pre- 

 dispose certain individuals and groups to avitaminoses. The factors 

 influencing intestinal liberation of the B vitamins are at least as manifold 

 as those affecting the digestive process in the broader sense. They lack 

 experimental elucidation at present, but may be surmised generally on 

 the basis of our overall knowledge of gastrointestinal digestion. Because 

 of the lack of data, a more extended consideration of these factors is 

 not now possible. 



Mention has previously been made of the unavailability of the B 

 vitamins in live yeast (p. 291) , and this must be considered in the broader 

 sense as a digestive limitation. It seems equally certain that other cellular 

 forms that are not disrupted during digestion may similarly withhold 

 their vitamins, so that cellular disintegration is a critical factor in the 

 digestive process. While the cells of most food material are apparently 

 not as resistant to fracture as are yeast cells, further investigation of 

 this point is merited. The possibility of irreversible adsorption of the B 

 vitamins upon other nutritional components in the intestine seems also 

 worthy of consideration in this regard. Fuller's earth adsorbates of rice 

 polishing extract were early used as a thiamine standard, but it has been 

 subsequently shown that only about half of the thiamine present could 

 be eluted in the animal digestive tract. 10 Similar adsorbents are now 

 broadly used as medicants, and undoubtedly they similarly limit the 

 available thiamine in some cases. Cellulose may exert a similar effect, 

 although the evidence now available seems to disprove this belief. 11 



The free vitamin may in some instances be converted by the digestive 

 process to an even more active form, although this is not apparently a 

 general process. Phosphorylation and bacterial conversion to functional 

 forms probably account for the cases in which this is so, although it is 

 by no means certain that other vital changes in vitamin structure do not 

 occur in the intestinal tract of some species. The conversion of the higher 

 homologues of folic acid to folic acid in the animal digestive tract must, 

 moreover, be considered as one example of an increase in vitamin activity 

 in the light of our present understanding of this group of substances. In 

 addition, it is probable that many other such apparent effects are actually 



