Abstract
Abstract A standardised membrane filter technique, adapted to the counting of organisms previously exposed to disinfectants, has been compared statistically with the pour-plate method. The membrane filters were found to be as suitable as pour-plates for counting viable organisms. The filter method is superior in disinfection experiments, since any quantity of test-mixture can be filtered and the danger of bacteriostasis is excluded. In disinfection experiments with high mortality levels, a great increse in variation occurred in replicate tests. Enriched media were not found to be superior to ordinary nutrient agar for the incubation of filter discs. The Gram-positive organisms tested showed a marked decrease in viable cells after storage at room temperature in slightly acid phosphate solutions for 24 hours, whereas in neutral and slightly alkaline solutions the viable count remained constant. The Gram-negative test organisms were not significantly affected by the phosphate buffer solutions.
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