GEORGE F. REDDISH 



PHENOL 



305 



If the reading is as follows: 



350-^90 = 3-89 

 Coefficient is 3.8 



DISINFECTANT 



Dilution 



1-30 



1-35 



1-40 



1-45 



S Min. 



+ 

 + 



10 Min. 



+ 

 + 



15 Min. 



+ 



PHENOL 



then estimate the dilution of the disinfectant killing in 10 but not in 5 minutes as 1-37.5 

 and the phenol as 1-95 (37.5-^-95 = 0.395 or 0.4) giving a coefficient of 0.4. 



In the method just described the figure obtained is named the "B. typhosus phenol 

 coefficient." When any other organism is used, the coefficient could then be named 

 after the organism employed. The coefficient so named will be of service in making 

 specifications for any soluble disinfectant; it is far easier to name a certain figure than 

 it is to enter into a cumbersome, minute description of what is desired, as would be the 

 case if all coefficients were entirely abolished. 



M. AUREUS 



When M. aureus is substituted for B. typhosus some changes in the dilutions of the 

 phenol control are found necessary. The same medium and general technique have been 

 found to be satisfactory, but the organism is much more resistant to phenol. At 20° 

 C. it should survive a 1-70 dilution of phenol for ten minutes, and may or may not 

 be resistant to a 1-60 dilution for five minutes. In routine work both dilutions may 

 be used as controls, and the results obtained are used in calculating the M. aureus 

 phenol coefficients. Thus in the following example the figure used as divisor would 

 be 65. 



