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LToI. 7:: @-carbon of serine underwent approximately the same dilution.The methyl group of the thymine, isolated in experiment 1, had an activity of 7360 c . p m 3 and 0.0126 atom D. This would indicate a dilution of 43 for the carbon and 57 for the D.A contribution of D to the methyl groups from the ar position of serine (via a-deuterioglycine6), which would significantly change these ratios, is unlikely, since glycine is a poor source of methyl group^,^*^ and the a-hydrogen atoms of glycine' and (1) This method was conceived prior to 1946 as an alternative to the approach of Johnson, Jones and Schneider (ref. 2); see also the M.S. thesis of W. P. Schneider, University of Wisconsin, 1946. A similar approach has been suggested independently by

Commercial purified protein derivatives (PPD), old tuberculin (OT), the bacillary extract, and the culture filtrate of Mycobacterium tuberculosis H37Ra were submitted to Sephadex G-25 and diethylaminoethyl (DEAE)-cellulose chromatography. The ability of the fractions obtained to elicit delayed dermal hypersensitivity in M. tuberculosis H37Ra-infected guinea pigs was studied. Skin tests with Sephadex fractions in M. tuberculosis H37Ra-infected guinea pigs showed that the tuberculin activity was localized in the first fraction. All other Sephadex fractions were nonessential and nonspecifically irritating. Fractions from chromatography of Sephadex G-25 fraction 1 on DEAE-cellulose columns showed that all but the first were able to elicit delayed hypersensitivity reactions. There was a variability in the capacity to elicit the tuberculin reaction according to the fraction injected and the stage of tuberculous infection in guinea pigs. Compared to the others, the seven lots of commercial PPD were variable in composition and content. They contained both essential and nonessential materials for the tuberculin reaction. Sephadex fraction 1 would appear to be a better tuberculin as it excludes nonessential nonspecifically irritating elements and contains the complement able to elicit the tuberculin reaction. Its methodological simplicity would be economically advantageous.

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