THE DESTRUCTION OF BACTERIA 79 



tus, and peppermint. Omeltschenko * believes that the employment of 

 these oils in emulsions is illogical, inasmuch as their bactericidal powers 

 depend upon their vaporization. He classifies the oils in decreasing 

 order of their efficiency as follows: Oil of cinnamon, prunol ; oil of thyme, 

 oil of peppermint, oil of camphor, and eucalyptol. 



Methods of Testing the Efficiency of Disinfectants. The efficiency of 

 any given disinfectant depends, as we have seen, upon a number of 

 factors, any one of which, if variable, may lead to considerable differences 

 in the end result. Thus, as far as the bacteria themselves are concerned, 

 it is necessary to remember that not only do separate species differ in 

 their resistance to disinfectants, but that different strains within the 

 same species may show such variations as well. This fact largely ac- 

 counts for the widely varying reports made by different investigators 

 as to the resistance of anthrax spores, and depends possibly upon tem- 

 porary or permanent biological differences produced in bacteria by the 

 conditions of their previous environment. 



The numbers of bacteria exposed to the disinfectant, furthermore, 

 is a factor which should be kept constant in comparative tests. The 

 medium, moreover, in which bacteria are brought into contact with the 

 disinfectant is a matter of great importance, inasmuch as either by 

 entering into chemical combination with the disinfectant it may detract 

 from its concentration or by coagulation it may form a purely mechanical 

 protection for the microorganism. Thus bacteria which may be de- 

 stroyed in distilled water or salt-solution emulsion with comparative 

 ease, may evince an apparently higher resistance if acted upon in 

 the presence of blood serum, mucus, or other albuminous substances. 

 Temperature influences bactericidal processes in that most chemical 

 disinfectants are more actively bactericidal at higher than at lower 

 temperatures, a fact due most likely to the favorable influence of tem- 

 perature upon all chemical reactions. 2 As far as merely inhibitory or 

 antiseptic values are concerned, however, the temperature least favor- 

 able for the reaction of the antiseptic is that which represents the opti- 

 mum growth temperature for the microorganism in question and the 

 inhibitory effects of any substance are less marked at this point than at 

 temperatures above or below it. 



The important influence exerted by the solvent in which the 



Omeltschenko, Cent. f. Bakt., I, ix, 1891. 



* v. Behring, " Bekaempf. der Infektions-Krankh., Infektion u. Desinfection," 

 Leipzig, 1894. 



7 



