300 THE BIOCHEMISTRY OF B VITAMINS 



this technique and in those methods where drugs are involved, which may 

 likewise modify other factors influencing the requirement. In many cases, 

 moreover, cecectomy merely serves to shift the area of bacterial synthe- 

 sis to another portion of the intestinal tract. 



Some idea of the extent of bacterial synthesis in humans may be 

 gained from the excellent study of Denko et al., 52 in which the urinary 

 and fecal excretion of eight B vitamins was measured over a period of 

 time in seven individuals on controlled and analyzed diets. They found 

 that the urinary and fecal folic acid averaged 5.5 times the intake, 

 p-aminobenzoic acid 2.3 times, biotin 3.8 times, and pantothenic acid 1.1 

 times. Riboflavin was slightly less than the intake, and thiamine, niacin, 

 and vitamin B 6 considerably less. In this latter regard, however, certain 

 known metabolic products of vitamin B G , niacin, thiamine and riboflavin 

 were not measured ; hence it is likely that the excretion of these vitamins, 

 too, may exceed the intake. 



It was also found in this same study that the fecal excretion of ribo- 

 flavin and p-aminobenzoic acid was 1.5 times the urinary excretion; fecal 

 thiamine and niacin were double the urinary excretion; fecal biotin was 

 four times as much; and fecal folic acid 75 times as much. Only about 

 60 per cent of the pantothenic acid and pyridoxine appeared in the urine, 

 however. It would thus appear that in these well nourished individuals, 

 bacterial synthesis of the B vitamins may well exceed the normal intake. 



Most nearly approaching the ideal from the scientific standpoint would 

 be the study of the B vitamin requirements of bacteriologically sterile 

 animals. While it has been possible to obtain such animals for over fifty 

 years by aseptic delivery on Cesarean section, it has been only in recent 

 years that the techniques have been so improved as to be practical by 

 the efforts of Glimmer 189 and Reyniers. 190 Reyniers et al. have been able 

 to obtain and raise to maturity a variety of "germ-free" animals in this 

 fashion; and the study of the nutritional requirements of these animals 

 promises to be one of the great advances in the science of nutrition in the 

 years ahead. Unfortunately even in this case, however, the animals must 

 be considered as very different from their symbiotic "cousins," and results 

 so obtained will be viewed with caution because of this fact. Life as it 

 exists is a highly symbiotic process, and the knowledge that is so obtained 

 with germ-free animals will not apply with certainty to animals living 

 in natural surroundings. No one of the approaches mentioned can be 

 expected to supply the desired information ; but over an extended period, 

 the synthesis of data obtained by the various techniques will result in an 

 increase in knowledge regarding the functioning of intestinal symbionts. 



