When supplementary thiamin (Vitamin B1) is ingested or injected, the amount which appears in the urine during the succeeding twenty-four hours usually increases, but the total additional excretion always falls short of the supplement, even when the vitamin is injected and there can be no question of incomplete absorption. We have sought information on this unaccounted-for moiety by synthesizing thiamin from sulfur which contains the radioactive isotope S35 (designated as B1*) and by following, after injection of the B1*, the excretion of the radiosulfur (S*) in the urine and feces and the excretion of total free B1 in the urine.
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Borsook et al. (1940) studied this question.