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The glycerol is quantitatively oxidized to formaldehyde by periodic acid, using a five minute oxidation period to minimize oxidation of glucose. The iodate and periodate are reduced to iodide by a large excess of sodium arsenite and the formaldehyde then determined directly in the oxidation mixture, by the color reaction with chromotropic acid. The precision of the method is about ± 2% in the range 2 to 8 p.p.m. of glycerol. The error due to glucose, in quantity equal to the glycerol, is only 2.5 to 5.0% and can be easily corrected for when the glucose content of the solution is known. One worker can analyze 40 to 60 samples per day.

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The optimal growth pH and conditions necessary to give a full manifestation of the effect of reductants upon the growth of Campylobacter ,fetus were investigated using static cultivation. The multiplication of cells was limited to a narrow range of added reductants. Thioglycollate supplemented without heating produced heavy growth in combinations of 0.05% at pH 6.80 or 0.1% at pH 6.60, and 0.2% at pH 7.00 or 7.20. Although the stimulating effect depended upon the time between the addition of the supplement and inoculation, two prominent peaks in the growth curve always appeared with both alkaline and acidic pH ranges of the medium. Autoclaving the medium with some SH compounds brought about this growth only at around pH 6.50. Consequently there was a uniform decrease in the initial pH. L-Cysteine and ascorbic acid also gave similar effects. Glucose remarkably prevented the growth promotion due to SH compounds. Optimal initial reduction potential for growth in a semisolid medium was considered to be-0.05 to-0.08 volt at an initial pH of 6.60. SH compounds supplemented without heating brought about a marked longevity of the culture in comparison with a culture in an autoclaved medium of the same composition. For the growth of C. fetus in semisolid medium, it was important to avoid decreasing the growth-promoting activity of some of the supplemented SH compounds by not heating but adding the supplement aseptically. Also a rigid regulation of the pH, the concentration of the added reductants, and the time of inoculation into the fresh medium were important.

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