DISINFECTION 397 



obstinate. The disinfecting agent for the one is unsuitable 

 for the other, so that some selection is necessary in the 

 matter, and this selection is based on experimental enquiry. 



In judging of the value of a disinfectant experimentally, 

 it is usual to select the most resistant organism known, 

 viz. anthrax rods with and without spores, and expose 

 them to the action of the substance, determining from time 

 to time by inoculations on a susceptible animal whether the 

 organism is dead or not. In this way a deal of exact 

 knowledge has been obtained, and the fallacy of using 

 certain popular disinfectants has been exposed. 



Experiments conducted on these lines have demonstrated 

 what strength of disinfectant should be employed, and for 

 how long its action should continue ; in other words, the 

 subject has been reduced to a degree of exactitude quite 

 unknown a decade ago. 



The strength of a disinfectant is a most important point ; 

 sufficient may be added to a diseased fluid or substance to 

 control or prevent the growth of the organism, and yet 

 insufficient to kill it. Disinfection that does not kill is of 

 no use. 



Again, it is sometimes believed that where disease poisons 

 are associated with organic matter in a state of putrefaction, 

 or emitting foul smelling gases, the mere destruction of 

 the latter ensure the death of the former. But this is 

 not so, a deodorizer is by no means necessarily a disin- 

 fectant. 



The most perfect disinfectant is of no use in unskilled 

 hands, for disinfection to be effective must be complete and 

 thorough. It is no use disinfecting the walls of a stable 

 and leaving the mangers untouched, nor of thoroughly 

 doing the stable and omitting to destroy the bedding ; while 

 disinfecting the mangers within and neglecting to do the 

 outside can only lead to disappointment. Disinfection to 

 be thorough must be carried out under expert supervision, 

 by one who knows where danger lurks, where to look for 

 it, and brings that skilled and special knowledge to bear 

 which can only be obtained by an intimate acquaintance 



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