STANDARDIZATION OF DISINFECTANTS 233 



it is desirable to know what are the most efficient and cheapest 

 disinfectants for general use. It is suggested that such a method 

 of rating be in terms of comparison with phenol. 



U. S. Public Health Service Phenol CoEFnciENT 



The following is a detailed description of the method for 

 determining the comparative (phenol) germ (bacteria) destroy- 

 ing power of disinfectants as given by John F. Anderson and 

 Thomas B. McClintic of the Hygienic Laboratory. In order 

 that the results by different workers may be uniform the details 

 must be followed out exactly. 



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 accordance with the standard methods adopted 

 by the American Public Health Association for water analysis. 

 Ten cc. 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 24 hr. broth culture in 

 extract broth of the B. typhosus is used. Before beginning a 

 test the culture should be carried over every 24 hr. on at least 

 3 successive days. For carrying over the culture one loop- 

 ful of a 4 mm. 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 culture and 

 dilutions of the disinfectant are brought to this temperature be- 

 fore beginning the test. 



