THE PHENOL COEFFICIENT AS A MEASURE OF THE PRACTICAL VALUE OF DISINFECTANTS'

The phenol coefficient test has been employed for determining the germicidal efficiency of disinfectants for over thirty years, since Rideal and Walker developed their original method in 1903. The Hygienic Laboratory Method (1921) is a modification of the Rideal-Walker Method, and the Food and Drug Administration test (1931) is a combination of the best features of both. The phenol coefficient technique as employed today does not differ fundamentally from the original test as described by Rideal and Walker, and, in one form or another, it is being used as a means of testing disinfectants in every civilized country in the world. For approximately twenty years the United States Department of Agriculture has used the phenol coefficient test in the regulation of disinfectants in this country, and it is still the most satisfactory method available for this purpose. In addition to being a satis-factory index of the germicidal value of phenol-like disinfectants, the phenol coefficient is used as a basis for determining the dilu-tions which may safely be employed in practice. This dilution is calculated by multiplying the phenol coefficient by twenty, which will give a germicidal efficiency equal to 5 per cent carbolic acid. Since, in this country, 5 per cent carbolic acid is accepted as the standard of excellence for general disinfection, phenol-like com-pounds must be recommended for general use in dilutions equal to 5 per cent phenol in germicidal efficiency. This method of 1 Read before the twenty-second annual meeting of the National Associatio