ANTISEPTIC AND GERMICIDAL POWER 157 



Modifications for special organisms. 



The action of antiseptics upon certain special organisms 

 cannot be tested by the above methods. As a good illustration 

 of this the determination of the germicidal action upon tubercle 

 bacilli may be mentioned. The distinction between tubercle 

 bacilli in a moist state and when dried must always be kept in 

 mind. It is well known that tubercle bacilli can be dried without 

 causing their death, and in such a condition are highly resistant, 

 particularly when enveloped in dried expectoration. 



The fresh sputum should be spread upon slips of wood or 

 other substance, arid dried in a desiccator over sulphuric acid. 

 Only completely dried slips should be used. The slips are 

 soaked in different strengths of the germicidal solution under 

 examination for a definite time (e.g., three hours). The slips are 

 then washed in sterile water, and the dried expectoration scraped 

 off, made into an emulsion with sterile water, and injected into 

 a series of guinea-pigs by the method described in Chapter VI. 

 If tuberculosis develops it is obvious that all the tubercle bacilli 

 were not killed. By using an appropriate series of dilutions the 

 correct lethal strength for the tubercle bacillus, under the con- 

 ditions of the experiment, can be ascertained. 



If the test organism produces spores, it must be incubated 

 first under optimum conditions for spore formation, and cultures 

 used which contain large numbers of spores. 



Chemical analysis. 



It is very desirable that chemical analyses of disinfectants 

 should be made as well as bacteriological determinations. From 

 an estimation of the tar acids and other constituents data of 

 value as regards the probable efficiency of the disinfectant, and 

 more particularly as to its probable efficiency in the presence of 

 organic matter, can be obtained. 



To Test the Action of Volatile Disinfectants. 



Broth cultures of different organisms may be used. For 

 hygienic purposes B. typhosus, B. diphtheriae, and B. anthracis 

 are convenient. 



