476 THIAMINE 



Theiler et al.^^ demonstrated that ruminants may be sustained on a thi- 

 amine-deficient food: the thiamine is produced by the flora of the rumen. 



Fridericia et aJ}^ found that rats that normally need the thiamine from 

 their food can produce sufficient thiamine in their intestines, if the diet 

 contains a large amount of fresh potato starch. They called this phenome- 

 non "refection." 



Under normal circumstances, however, all non-ruminant higher animals 

 depend on their diets for their supply of thiamine. Apparently no one has 

 yet undertaken the experiments to feed animals on a carbohydrate-free diet 

 to see whether those animals and also the next generation can normally live 

 a whole lifetime without thiamine. However, Dann" was able to maintain 

 rats for more than a year (about half the lifetime of a rat) on a thiamine- 

 free, carbohydrate-free synthetic diet. It is possible that the refection — the 

 production of thiamine by the microorganisms in the gut — in this case is 

 sufficient to produce enough thiamine for protein and fat metabolism. 



(6) Individual Genetic Factors. Practically all initial research on nutrient 

 requirements has been performed with large groups of animals or human 

 beings. 



Already Ancel Keys, in his carefully conducted experiments with healthy 

 volunteers who were maintained for several months under strictly con- 

 trolled conditions, observed that one "normal" person may excrete two or 

 even three times as much thiamine as another "normal" person on exactly 

 the same diet (Mickelson et al.^^). These volunteers were all "normal" 

 young men with no history, signs, or symptoms of nutritional, digestive, 

 or metabolic peculiarities. Just recently, Williams^^ has stressed the fact 

 that individual requirements may differ widely. Thus the need for thiamine 

 in man may vary from 0.5 to 1.5 mg. daily. Therefore it is possible that 

 the quantity contained in a certain nutrient, which is sufficient for the 

 average person or animal, may be too low for some individuals, depending 

 on their genetic makeup. Williams coined the term "genetotropic diseases" 

 for diseases that are caused by a genetically larger requirement of a nutri- 

 ent in a certain individual. ^^ Everyone experimenting with animals knows 

 that even in largely inbred rats individual requirements are widely different. 

 Therefore it is important to work with groups of at least eight to ten, but 

 preferably with even larger groups of animals, to obtain reliable average 



^^ A. Theiler, H. H. Green, and P. R. Viljoen, S. African Direct. Vet. Research Resp. 



pp. 3-4 (1951). 

 '^ L. S. Fridericia, P. Freudenthal, S. Gudjonsson, G. Johansen, and N. Schoubje, 



J. Hyg. 27, 70 (1928). 

 " W. J. Dann, Federation Proc. 4, 153 (1945). 



38 O. Mickelsen, W. O. Caster, and A. Keys, /. Biol. Chem. 168, 415 (1947). 

 3^ R. J. Williams, L. J. Berryand, and E. Beerstecher, Jr., Arch. Biochem. 23, 275 



(1949). 



