Dehydrocholic acid was incubated with S. gelaticus 1164 in a synthetic medium containing this bile acid as the sole source of carbon. The following compounds were isolated: 7α-hydroxy-3, 12-dioxo-Δ⁴-cholenic acid, 7α-hydroxy-3, 12-dioxo-Δ⁴-bisnorcholenic acid, and an acid with m.p. >330°. A possible pathway for the microbiological degradation of bile acids in the intestine was discussed.

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Streptomyces gelaticus 1164, cultured in a synthetic medium containing lithocholic acid as the sole source of carbon, degraded this bile acid to an acid with m.p. 255-258° (decomp.). It was presumed that the constitution of the newly isolated acid might be tentatively designated as x-hydroxy-3-oxo-Δ⁴-etienic acid. A possible pathway for the formation of this acid from lithocholic acid was proposed.

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(1) The hemidiaphragm technique has been critically examined as a quantitative assay for small amounts of insulin with particular purpose of applying it to the determination of the insulin activity of plasma. It was found that, over the range of insulin concentration 0.01-10.0 milliunits per ml there was a linear regression between the extraglucose uptake of the hemidiaphragms and log-concentration of insulin added to the incubation medium. The slope of this regression line was 0.751 and the standard deviation of the points about the standard regression line was 0.212. The index of precision was 0.270.
(2) The extraglucose uptake by the isolated rat diaphragm in various dilutions of plasma was determined, but occasionally, the values calculated from the responses to two-fold dilutions were found to be low, while those to twenty-fold and two hundred-fold dilutions were always identical with each other. These results showed that, though the effect of the inhibiting substances was still conspicuous in the two-fold dilution, it disappeared without the loss of insulin-like activity in dilutions greater than twenty-fold. It was concluded that over twenty-fold dilutions of plasma should be used for the assay of the insulin activity in plasma.
(3) By this technique the insulin activity of plasma taken from normal and alloxanized dog was determined. The insulin activity of plasma was found to be 0.27±0.11 mu per ml in normal fasted dogs, 2.30±0.41 mu per ml in dogs 4 hours after the injection of alloxan, and 0.00 mu per ml 48 hours later.

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