SUMMARY: The strain of 4228 studied differed from those previously used for the assay of vitamin B in that it required this vitamin for rapid growth in the absence of added thiamine. The rate, rather than the ultimate extent, of growth of the organism is proportional to the concentration of vitamin B, and the size of the inoculum and its physiological age, the duration and temperature of incubation and the degree of aeration, must be strictly controlled. Non-phosphorylated forms of the vitamin only are utilized, and natural materials are acid-extracted before assay. The organism responds a little less well to pyridoxamine than it, does to pyridoxal and pyridoxine. A linear response curve is obtained over a range of pyridoxine concentrations (0·2 to 2 x 10 ) when incubation is in static culture at 37° (24 hr.) in a basal medium slightly modified from those previously used.


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