260 



Value of Antiseptics 



tabulation will make clear the details of a test (Table 17 from 

 Anderson and McClintic's paper). 



TABLE 17 

 Name "A." 



Temperature of medication 2oC. 



Culture used. B. typhosus, 24-hour extract broth-filtered. 

 Proportions of culture and disinfectant, o.i cc. X 5 cc. 



To calculate the phenol coefficient, the figure representing the 

 degree of dilution of the weakest strength of the disinfectant that 

 kills within 2^ minutes is divided by the figure representing the 

 degree of dilution of the weakest strength of the phenol control 

 that kills in the same time. The same is done for the weakest 

 strength that kills in 15 minutes. The mean of the two is the 

 coefficient. The coefficient of any disinfectant may, for practi- 

 cal purposes, be defined as the figure that represents the ratio of 

 the germicidal power of the disinfectant to the germicidal power of 

 the phenol, both having been tested under the same conditions. 



As many disinfectants and germicides are greatly modified through 

 precipitation, combination or other transformation in the presence 

 of organic matter, in all of those whose coefficient is considerably 

 more than i, it is wise to perform a second series of tests in which 

 the disinfectant is tested, and the control tests made in the presence 

 of organic matter and the coefficient calculated accordingly. It is 

 usually found that under these conditions the coefficient falls. In 

 a general way, those disinfectants are most valuable for general 

 employment, whose coefficients are highest in the presence of 

 organic matter in the test solutions. 



The difference in the details of the test given and the new test to 

 be made are as follows: 



i. The test dilutions are made 20 per cent, stronger to allow for 

 the dilution made by the addition of the solution of organic matter. 



