PRACTICAL STERILIZATION AND DISINFECTION 151 



and McClintic, formerly of the above laboratory, the strength 

 of the dilution of the disinfectant to be tested which kills a 

 culture of Eherthella typhi in two and a half minutes is 

 divided by the strength of the dilution of carbolic acid 

 which does the same; and the dilution which kills in fif- 

 teen minutes is likewise divided by the corresponding dilution 

 of carbolic acid. The two ratios thus obtained are aver- 

 aged and the result is the " phenol coefficient." For example, 



2)10.60 

 Average =5.30 =" phenol coefficient." 



Standard conditions of temperature, age of culture, medium 

 reaction, etc., and of making the dilutions and transfers are 

 insisted on. Details may be found in the Journal of Infec- 

 tiovs Diseases, 1911, 8, page 1. 



This is probably as good a method as any for arriving at 

 the relative strengths of disinfectants, and in the hands of 

 any given worker concordant results in comparative tests 

 can usually be attained. Experience has shown that the 

 results obtained by different workers with the same disin- 

 fectant may be decidedly at variance. This is to be expected 

 from a knowledge of the factors affecting the action of 

 disinfectants above stated, and from the known specific 

 action of certain disinfectants on certain organisms (com- 

 pare anilin dyes, page 148). 



It seems that the only sure way to test the action of such 

 a substance is to try it out in the way it is to be used. It is 

 scarcely wise to adopt the "phenol coefficient" method as a 

 legal standard method, as some states have done. 



PRACTICAL STERILIZATION AND DISINFECTION. 



The methods for sterilizing in the laboratory have been 

 discussed and will be referred to again in the next chapter. 



