INHIBITORY MEANS. 



653 



Koch has tested the inhibitory action of various poisons Experiments 

 on non- spore -bearing anthrax bacilli. The results were 

 obtained by tilling small vessels with 10 com. of blood 

 serum or of peptonised meat infusion (1 per cent, peptone, 

 ^ per cent, meat extract and water), and then adding the 

 disinfecting substances. A number of these vessels, and 

 among them some without any disinfecting substances, 

 were placed side by side under a bell-jar in the presence 

 of moisture. A silk thread, impregnated with anthrax 

 spores, was then placed in each vessel ; in the control 

 vessels growths of long anthrax threads were always pre- 

 sent after twenty-four hours, and presented a very charac- 

 teristic appearance, and one not easily mistaken. In a 

 similar manner the other vessels were examined under the 

 microscope in the course of the next few days, and thus 

 absence of growth or the appearance of threads indicated 

 the activity or inactivity of the disinfecting means. (In 

 the case of other species of bacteria nutrient gelatine is 

 often preferable for these experiments, the chemical 

 substance to be tested, and also a small quantity of the 

 bacteria, being added to it, and then the liquefied jelly 

 poured out on glass plates.) The following are the most 

 important figures obtained by Koch : 



Distinct hindering of Complete cessa- 

 growth tion of growth 



Occurred when the concentration reached 



300,000 

 33,000 



10,000 



8,000 



1,000 



1,700 

 800 



