DISINFECTANTS— STANDARDIZATION 9 



Paracresol and metacresol have much more germi- 

 cidal power than orthocresol, and the amount of each 

 present in the coal-tar disinfectants may vary mark- 

 edly in different lots. Therefore it is necessary to 

 determine the percentage of each, in each lot, by frac- 

 tional distillation. 



Several methods have been advanced for the testing 

 of the germicidal value of disinfectants, and lately 

 much work has been done toward standardizing such 

 methods. 



The methods of the Lancet commission and Rideal- 

 Walker, and that of Anderson and McClintic of the 

 United States Public Health Service, have all been em- 

 ployed. The Anderson-McClintic method is a modifica- 

 tion of the Rideal- Walker method to eliminate some of 

 the variations which may be obtained in the use of that 

 test. 



In all such tests the great difficulty lies in finding a 

 procedure by which the exact value of the disinfectants 

 may be determined, and a proper relative standard se- 

 cured in the laboratory. 



It must be borne in mind that such a test, no matter 

 how painstakingly and elaborately worked out, is at the 

 best but a laboratory test, and is only an indication of 

 the relative possibilities of the disinfectants under the 

 varying conditions met with in practice. 



However, it may be said safely that the Anderson- 

 ]\IcClintic method gives a basis for successful testing of 

 disinfectants and at the least will enable us to standard- 

 ize their action toward the typhoid organism, relative 

 to the action of phenol under the same conditions. 



In using the Anderson-lMcClintie method it is most 

 essential that the exact recommendations of the authors 

 be carried out to the minutest detail. Lack of attention 

 to the different factors concerned in the examination 



