SUBCLINICAL VITAMIN DEFICIENCY. IV. PLASMA THIAMIN1

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Abstract
The yeast-stimulating activity of plasma was detd. by the yeast-fermentatioa method and recorded in terms of thiamin equivalence. The yeast-stimulating activity due to thiamin in the plasma was destroyed by sulfite cleavage and the residual yeast-stimulating activity detd. The "true" plasma thiamin was then calculated by subtracting the activity due to residual yeast-stimulating substances from the total yeast-stimulating activity of the plasma. It was found that the yeast-stimulating materials in plasma, thiamin, and others, were freely diffusible at pH''s 5 to 7, from which it was concluded that they were probably free to exchange in vivo with similar materials in the general extracellular fluids. The yeast-stimulating activity of plasma varied with the level of thiamin nutrition, with the level of thiamin excretion, and with the "true" plasma thiamin conc. "True" plasma thiamin values of the order of 3 to 10 millimicrograms/ml. of plasma were found in a small group of detns. on plasma from individuals subsisting on a normal diet. It was concluded that measurements of the yeast-stimulating activity of plasma could be used as indices of thiamin nutrition. However, since some variation in activity, due to materials other than thiamin, was observed, calculation of "true" plasma thiamin appeared preferable, particularly in plasma of low thiamin content.