SUMMARY: The speed of development of narrow zones of opacity due to massed growth of leptospira a few millimetres below the surface in cultures in soft agar, a phenomenon first fully described by Dinger (1932), has been used as a criterion of the nutritional value of media for certain pathogenic leptospira. In applying this test to assess the value of the addition of peptone to a basal medium of 10% (v/v) rabbit serum in diluted meat extract, the impression was formed that peptones contained substances which promoted growth and others which were inhibitory. Witte's peptone was the most constantly favourable of those which were tested. Tryptic digest broth (Hartley's) gave results at least as good. Inhibitory effects with peptone may develop on autoclaving, especially at high pH values, or on leaving sterilized solutions to stand for considerable periods at room temperature. The value of haemoglobin (as laked blood) may depend on its catalase content since Czeka-lowski, McLeod & Rodican (1953) showed that leptospira did not produce this enzyme. The range of pH suitable for the development of cultures is narrow with pH 7.6 as optimum; but the leptospira are more tolerant to divergences on the alkaline side in the media at the time of inoculation.


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