ANTISEPTIC AND GERMICIDAL POWER 153 



With suitable modifications this method can be used to 

 obtain the carbolic acid coefficients for other organisms for 

 example, B. pestis, Sp. cholerae. 



It will be noticed that details are given in regard to 

 apparently trivial matters. Experience has shown that to 

 obtain identical and concordant results these small points must 

 be very carefully attended to and followed. 



The Rideal-Walker method has been very extensively used. 

 It has the great merit of introducing a regular basis of com- 

 parison with a standard germicide, while, on the other hand, it 

 suggests a scientific accuracy which is scarcely warranted. 



Lancet method. 



Considerable modifications in the Rideal-Walker method have 

 been recommended by the Commissioners appointed by the 

 Lancet to investigate the question of the Standardization of 

 Disinfectants 1 . The modifications and differences they used are 

 briefly as follows : 



B. colt communis was used as the test organism, a 24 hours' 

 growth at 37 C. in fresh meat broth being employed. All dis- 

 infectant dilutions were made up with distilled water. The 

 dilutions were placed in special glass pots instead of test tubes, 

 those actually used being 2\ inches high and f inch in diameter. 

 Instead of ordinary platinum loops being used for seeding, 

 specially constructed platinum spoons were used so that more 

 fluid could be conveyed. The spoons used took up 0*08 c.c. of 

 water. It is stated to be important that the spoons should be 

 withdrawn from the solution at the same speed. Lactose bile- 

 salt broth was used for the secondary culture tubes. Samples 

 were removed at intervals of 2\ minutes from each pot up to 

 15 minutes, and then after 15, 20, 25, and 30 minutes. All the 

 tests were done between 62 and 67 F. 



The carbolic acid coefficient was deduced as follows : " The 

 figure representing the percentage strength of the weakest lethal 

 dilution of the carbolic acid control was divided by the figure 

 representing the percentage strength of the weakest lethal 

 dilution of the disinfectant being tested. This was done both 



1 Lancet, 1909, November 13, 20, and 27. 



