404 YETEEINARY HYGIENE 



In the use of carbolic acid, as with sublimate, a suffi- 

 ciency must be added ; for instance, if a fluid is being dis- 

 infected it is no use to add a 5 per cent, solution to it and 

 expect disinfection. The fluid to be disinfected must contain 

 5 per cent, of the acid in order that destruction may occur. 



The difficulty in obtaining a sufficiently high percentage 

 of impure carbolic acid in solution, may be got over by the 

 use of cresol or lysol, both of which mix with water in any 

 proportion ; it is said that a 2 per cent, solution of the 

 latter is equal to 5 per cent, of carbolic acid. 



Izal is a disinfectant well spoken of, and experimentally 

 has yielded very good results. It mixes readily with water 

 forming an emulsion. In a 10 per cent, solution Notter* 

 found it destroyed the spores of anthrax in twenty minutes, 

 while the rods were destroyed after five minutes' exposure 

 to a 0'5 per cent, solution : it further has the advantage of 

 being non-poisonous. It is considered that exposure to a 

 1 per cent, solution for fifteen minutes will be sufficient for 

 all ordinary eases of infectious disease. 



No dependence can be placed on the disinfecting pro- 

 perties of either zinc chloride, or iron sulphate ; a solution 

 of the former was at one time in great request. 



Caustic lime is largely used as a disinfectant for stables 

 and cow-houses ; in the caustic state it may be of some use, 

 but as whitewash plastered on indiscriminately, it is simply 

 covering up the pathogenic matter. Limewash is not 

 without its utility in its proper place, as will be indicated 

 later, but it is not a disinfectant in the sense in which we 

 have been considering this question. Whitewash, which 

 is limewash minus its caustic action, is utterly useless. 



Disinfection by Heat. — The practical application of heat 

 as a disinfectant is somewhat different to that employed in 

 human hygiene. In the latter chambers are constructed 

 for dry heat, moist heat, or for sterilizing by steam, but 

 these are adopted for the reason that people are loathe to 

 part with their dresses, furs, underclothing, feathers, bed- 

 ding, blankets, etc., so that some method, not always satis- 

 * ' Theory and Practice of Hygiene,' Notter and Firth. 



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