774 A MANUAL OF BACTERIOLOGY 



every two hours with Dakin's hypochlorite solution by an arrange- 

 ment of tubes maintained in position and claims that this is the 

 most satisfactory treatment. 



The Determination of the Germicidal Power 



For determining germicidal power on sporing organisms, 

 anthrax spores are generally used ; on non-sporing organisms, 

 cultures of the B. typhosus are usually employed. 



(1) Thread method. Sterilised silk threads are impregnated 

 with sporing and non-sporing organisms, lightly dried, and then 

 exposed to the action of the antiseptic solution of a known strength 

 for a given time. After treatment the threads are thoroughly 

 washed with distilled water to remove the antiseptic, and sown 

 on the surface of agar or other suitable culture medium. If no 

 growth occurs the organisms are assumed to have been destroyed. 

 As a matter of fact, however, it is extremely difficult to get rid of 

 the last traces of the antiseptic, which may inhibit growth although 

 the organisms may yet be alive, a fallacy which caused an exag- 

 gerated value to be assigned to many substances for example, 

 corrosive sublimate. If pathogenic organisms be the subject of 

 experiment, the threads may be inoculated into a susceptible 

 animal. The author finds that in disinfection experiments with 

 anthrax spores, surface agar is a much better medium than 

 broth. 



In experiments with corrosive sublimate, by whatever method, the 

 last traces of this substance must be converted into the inert sulphide 

 by treatment with hydrogen or ammonium sulphide. 



(2) Garnet method. Small garnets the size of a pea are sterilised, 

 soaked in a suspension or a broth culture of the organism, removed 

 and dried. The garnets with the organisms attached are then 

 soaked in solutions of the disinfectant of known strengths for 

 various periods of time ; they are then removed from the solution, 

 well washed with sterile water, and finally placed in tubes of 

 broth. 



(3) Rideal-Walker or drop-method. Moor first suggested that 

 the germicidal efficiency of a disinfectant might be compared 

 with that of a standard solution of carbolic acid, which has a 

 definite composition, is stable, and can be accurately standardised, 

 and Rideal and Walker devised an ingenious and simple method 



