Ip6 MEDICAL BACTERIOLOGY 



TABLE 17 

 Name, "A." 



Temperature of medication, 2oC. 



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

 Proportion of culture and disinfectant, o.i cc. + 5 cc. 



B. The Determination of the Coefficient with the Addition of Organic Matter 



'It may be well to briefly discuss here the meaning or significance of the term 

 "phenol coefficient/' particularly when it is determined in the presence of 

 organic matter. In general terms the coefficient of a disinfectant may, for 

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

 germicidal power of the disinfectant to the germicidal power of carbolic acid, 

 both having been tested under the same conditions. 



Although the germicidal power of carbolic acid is taken as the unit of com- 

 parison, it is influenced to a certain extent by conditions, particularly the addi- 

 tion of organic matter, or, in other words, it is not a constant unit. This has 

 to be borne in mind when making a comparison of the relative values of the 

 phenol coefficients of a disinfectant determined with and without the addition 

 of organic matter, respectively. It will readily be seen, for instance, that if the 

 germicidal powers of a disinfectant and of carbolic acid were proportionately 

 reduced by the addition of organic matter the coefficient of the disinfectant 

 would remain unchanged, regardless of whether or not organic matter was used. 

 However, the germicidal power of carbolic acid, like the other pure phenols, is, 

 as compared with most other disinfectants, only slightly affected by the addition 

 of organic matter, and therefore serves as a fairly accurate means of estimating, 

 in the presence of organic matter, the germicidal values of disinfectants in 

 general. 



The method of determining the coefficient of disinfectants, with the addition 

 or organic matter, is identical in many respects with the method in which no 



