ISO ANTISEPTIC AND GERMICIDAL POWER 



The vehicle in which the bacteria are suspended. This is of 

 extreme importance and very greatly influences the result. It 

 is discussed in greater detail below. 



The nature of the bacillus to be employed as the test organism 

 will obviously depend upon the purposes for which the dis- 

 infectant is required. For general work B. typhosus is very 

 frequently employed and is a convenient organism for this 

 purpose, but care must be taken to use a strain which does not 

 show pseudo-dumping in ordinary broth. 



A number of methods has been used to estimate the ger- 

 micidal power of liquids of which the thread, garnet and various 

 drop methods may be mentioned. 



Thread method. 



In Koch's thread method silk threads are sterilized and then 

 impregnated with the organism. They are then transferred to 

 the antiseptic solution under investigation, and left in contact 

 for a given time. After thorough washing in sterile water, to 

 remove the antiseptic, the threads are sown on agar or other 

 suitable nutrient medium, which is then incubated and examined 

 for growth. 



In ascertaining germicidal power it is very important to be 

 certain that none of the germicide is carried over into the 

 cultivation solution, as a very small amount may be sufficient to 

 inhibit growth. In the thread method this danger is not fully 

 guarded against. 



Absence of growth cannot be taken as a certain indication 

 of the lethal power of the antiseptic so employed, as in practice 

 it is extremely difficult to get rid of all traces of antiseptic, 

 and a quantity sufficient to inhibit growth may be left. 



Garnet method. 



In the garnet method of Kronig and Paul (1897) garnets 

 of similar size are selected, and, after careful cleaning, are 

 dipped into a filtered watery emulsion of sporing anthrax or 

 other bacillus selected. The emulsion is allowed to dry on 

 them in a thin film. The loaded garnets are then immersed in 

 the disinfectant solutions under investigation. After definite 



