SUMMARY: Discrepancies found in the use of three previously published micromethods for fermentations were traced to at least three possible sources of error: contamination of the water used for making suspensions; contamination of capillary tests from non-sterilizable Perspex plates; chemical breakdown or contamination of certain sugar solutions. To overcome these discrepancies one of the methods was modified; the other two were abandoned.

Suspension concentration is important and, measured as opacity, should not be less than the equivalent of 10 cells/ml. Sugar concentration is much less critical, and 0·1 concentrations are recommended. Dilution of the test mixture with 0·5 ml. sterile water speeds up fermentations; the addition of formalin or thiomersalate inhibits certain enzyme systems but does not hinder glucose fermentation.


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