THE REVIVAL OF ORGANISMS PRESUMABLY KILLED BY PHENOL

In evaluating disinfectants and antiseptics, it is important to know the speed with which they kill various organisms in vitro or, in the case of water-soluble products, the dilution which kills the organisms in a specified time. After a number of different techniques had been proposed, Ruehle and Brewer (1931) of the United States Department of Agriculture published a method for testing antiseptics and disinfectants which is generally known as the F.D.A. Phenol Coefficient Method and is recognised as an official method by the Association of Official Agricultural Chemists (1940). The end point of the test is the dilution of the product which kills the organism in ten minutes but not in five. This same end point is determined for phenol as a standard. The sole criterion for establishing the death'of the organism is its failure to grow under optimum conditions. If the organism fails to grow when transferred or retransferred to a suitable medium, it is presumed to have been dead at the time of transfer. Since there'is no positive or absolute method of ascertaining whether an organ-ism is dead, appreciable errors can occur in determining the killing dilution, an