DISINFECTION 403 



water destroys the bacilli of glanders and anthrax in ten 

 seconds, and the spores of the latter in ten minutes. As 

 anthrax spores are the most difficult organisms to destroy, 

 we may accept the fact that a solution of mercuric chloride 

 is the most powerful disinfectant known. 



It has certain disadvantages in being highly poisonous 

 and most destructive of metal work, and these two con- 

 siderations greatly limit its use, especially where large 

 surfaces are concerned. Further, by its coagulative effect 

 on albumin a protecting surface is formed which prevents 

 the disinfectant penetrating, so that in the case of an 

 albuminous substance, like phthisical sputum, it is said 

 that even in the strength of 1 to 500 it is ineffective, owing 

 to the coating formed around the bacilli. A solution 1 

 to 1000, well mixed with the sputum, has been found to 

 be a disinfectant after being in contact not less than twelve 

 hours. 



If mercuric chloride be employed in bulk it should be 

 •coloured to prevent accident, as the solution is quite colour- 

 less. It is usual to add aniline blue to it as a precautionary 

 measure. 



Carbolic Acid. — This held undisputed sway as a disinfec- 

 tant until the discovery of mercuric chloride, and it is still 

 a disinfectant of the utmost utility and value. The chief 

 thing in employing carbolic acid is to use it strong enough, 

 only a certain amount is soluble in water ; a saturated solu- 

 tion of the pure crystals gives a solution containing 8 '6 per 

 «ent. of phenol, but the impure acid sold for disinfecting 

 purposes is by no means so soluble ; this is owing to the 

 tar oils it contains, and it is believed that these latter are 

 without any disinfecting properties. A saturated solution 

 •of ordinary impure carbolic acid only yields 3"5 per cent, of 

 phenol, which is less than is necessary for the destruction 

 of the spores of resisting microbes. This point should be 

 borne in mind in dealing with anthrax or tuberculosis. 



Carbolic disinfecting powders prepared with lime are of 

 no value. Calvert's and Macdougall's are both without 

 lime as a basis, and are satisfactory. 



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