SPECIAL EXAMINATIONS 379 



The threads were then removed and carefully washed in 

 sterile water to discharge the disinfectant. They were 

 then laid on gelatin and incubated, and the result 

 was noted. This method is faulty, in that it is difficult 

 to remove the disinfectant, some of which clinging to the 

 bacteria inhibits growth. The Rideal-Walker method 

 may be applied here to determine germicidal strength 

 without comparison with carbolic acid. 



The results are stated in terms of strength used, time 

 exposed, and bacterium killed : thus carbolic acid is 

 bactericidal to anthrax spores at ordinary temperatures 

 in 1-20 dilution in four to forty-five days ; at 4OC., in 

 three hours. 



To Sp. cholerae at ordinary temperatures, 1-200 is 

 fatal in five minutes, and 1-300 is fatal in two to 

 twenty-four hours. 



To B. typhosus at ordinary temperatures, 1-50 is fatal 

 in five minutes. 



To staphylococci and streptococci at ordinary tempera- 

 tures, 1-60 is fatal in five minutes. 



Corrosive sublimate is fatal to anthrax spores in 

 1-2000 in twenty-six hours. 



To anthrax and typhoid bacilli and Sp. cholerae, in 

 1-2000 in five minutes. 



To staphylococci and streptoccoci, 1-10,000 to 1-2000 

 in five minutes. 



These tests supply useful data, but cannot be taken as 

 applying to the action of the same disinfectants, when 

 mixed with the body fluids. 



Rideal-Walker Test. In this test carbolic acid is 

 taken as the standard disinfectant, and the results of tests 

 of other disinfectants are expressed in terms of their power, 

 compared to the standard, of inhibiting growth of the same 

 organism in the same time. This is called the " carbolic 

 acid coefficient " of the particular disinfectant. 



PROCESS. A series of accurate dilutions of pure carbolic 

 acid and of the disinfectant are prepared in sterile distilled 

 water. A twenty-four hours' culture at 37 C. in Lemco 

 broth (reaction + i'5) of B. typhosus is used as the test 

 organism. A standard size of platinum loop is used to 

 make the subcultures. The disinfectant solutions are 



