ANTISEPTICS AND DISINFECTANTS. 



101 



These different methods give results which cannot be directly 

 compared one with another, for to obtain corresponding results we 

 must have identical conditions. 



Test by Inoculation into Susceptible Animals. In testing the 

 action of disinfectants upon anthrax spores and other infectious dis- 

 ease germs, we may inoculate the microorganisms, after exposure to 

 the disinfectant, into a susceptible animal. This method was adopted 

 by the writer in a series of experiments in 1881, but he has not since 

 employed it, for reasons set forth in his paper giving an account of 

 these experiments. 



"First. The test organism maybe modified as regards repro- 

 ductive activity without being killed; and in this case a modified form 

 of disease may result from the inoculation, of so mild a character as 

 to escape observation. Second. An animal which has suffered this 

 modified form of the disease enjoys protection, more or less perfect, 

 from future attacks, and if used for a subsequent experiment may, 

 by its immunity from the effects of the pathogenic test organism, 

 give rise to the mistaken assumption that this had been destroyed 

 by the action of the germicidal agent to which it had been sub- 

 jected.'' 1 



In experiments to determine the value of an agent as a disinfec- 

 tant, no matter by what method, the following conditions, which in- 

 fluence the result, should be kept in view : 



(a) The difference in vital resisting power of different species 

 of bacteria. As a rule, the pathogenic species have rather less re- 

 sisting power than the common saprophytes, and the micrococci 

 have greater resisting power than many of the bacilli. The differ- 

 ence in the vital resisting power of some of the best known patho- 

 genic species is shown in the following table, which we have made 

 up from determinations made by Boer cultures in bouillon twenty- 

 four hours old ; time of exposure, two hours. 



(b) The presence or absence of spores. The reproductive ele- 

 ments known as spores have a far greater resisting power to chemi- 

 cal agents, as well as to heat, than have the vegetative cells. In 



1 Quoted from article on " Germicides and Disinfectants," in " Bacteria," p. 212. 

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