148 STERILIZATION AND DISINFECTION 
Hycientc LABORATORY PHENOL COEFFICIENT 
A. WITHOUT ORGANIC MATTER 
Having discussed the necessity for a satisfactory method of stand- 
ardizing disinfectants and the factors involved in the examination 
of disinfectants, we present below the method we* have devised. 
When this method is used for the standardization of disinfectants 
we recommend that it be referred to as the “ Hygienic Laboratory 
phenol coefficient.” 
We prefer to use the word “ phenol ’”’ instead of ‘ carbolic acid ” 
when speaking of the coefficient, especially since certain dealers adver- 
tise for sale carbolic acids which vary greatly in the proportion of 
phenol present. 
Media. Standard extract broth is used, both for the culture to be 
tested and for the subcultures made after exposure to the disinfectant. 
The broth is made from Liebig’s extract of beef and is in exact accord- 
ance with the standard methods adopted by the American Public Health 
Association, for water analysis. Ten c.c. of the broth are put into each 
test tube. This amount of broth has been found sufficient to avoid any 
antiseptic action of the disinfectant carried over. It is important that 
the reaction of the media is just +1.5. 
Organism. For the test organism a twenty-four-hour-old broth 
culture in extract broth of the B. typhosus (Hopkins) is used. Before 
beginning a test the culture should be carried over every twenty-four 
hours on at least three successive days. For carrying over the culture 
one loopful of a 4mm. platinum loop is used. 
Before being added to the disinfectant the culture is well shaken, 
filtered through sterile filter paper, and placed in the water bath in 
order that it may reach a temperature of 20° C. before being added to 
the disinfectant. 
Temperature. A standard temperature of 20° C. has been adopted 
for all experiments. This temperature is obtained by the use of a 
specially devised water bath. The cultures and dilutions of the dis- 
infectant are brought to this temperature before the beginning of the 
test. 
Proportion of Culture to Disinfectant. One-tenth c.c. of the culture 
is used, added to 5 c.c. of the disinfectant dilution. The amount of 
culture is measured with a pipette graduated in tenths of a cubic cen- 
{imeter. 
* This method is quoted from Anderson and McClintic’s original publication, 
