414 CLINICAL BACTERIOLOGY. 



of true chemic reaction, but one of solution manifestations, 

 similar to those better-known processes, of which, for in- 

 stance, we have long had knowledge in a whole series of 

 stains. 



The distinction between the two classes of disinfectants 

 is of significance also for practical purposes. It thus be- 

 comes clear why, on addition of other substances for 

 instance, acids the action of the one class (chemic disin- 

 fectants) is usually lessened, while that of the other for 

 instance phenol is increased, whereas addition of alcohol 

 has the reverse effect. An explanation is afforded also for 

 the practically significant phenomenon that the disinfection 

 of organic or albuminous nutrient media (such as feces, 

 sputum, etc.) is- effected more readily with the second class 

 of agents than with the first. 



In order to determine the activity of a disinfecting agent, 

 according to Koch's procedure highly resistant bacteria 

 anthrax-spores that have been dried upon short pieces of 

 sterile silk thread are most commonly employed as test- 

 objects are introduced into a solution of the agent and 

 from time to time it is noted in specimens that are removed 

 and transferred to nutrient medium whether the bacteria 

 have already been destroyed or not. Geppert has called 

 attention to a possible source of error attending this mode 

 of procedure. With the silk thread not alone the spores 

 are transferred to the new nutrient medium, but always, 

 even when the thread is rinsed with water after removal, 

 also a certain amount of the disinfecting agent. This 

 diffuses from the silk into the nutrient medium, and renders 

 it unsuitable for the culture of the bacteria. Growth, there- 

 fore, may readily fail to take place, although all of the bac- 

 teria may not be destroyed. 



Koch has himself studied the' inhibition of growth in 

 culture-media to which antiseptics were added in varying 

 amount, and in which then silk threads with anthrax-spores 

 were introduced. He found 



DISTINCT RETARDATION COMPLETE CESSATION 



OF GROWTH OF GROWTH 



ON ADDITION OF 



Mercuric chlorid in the strength of I : 1,600,000 I : 300,000 



Thymol " I : 80,000 



Oil of turpentine " 1:75,000 



Potassium-soap " I : 5000 I : looo 



