172 ANTISEPTICS 



mixtures are thus indefinite. Formalin may be used either by 

 applying it in its liquid form or as a spray, or the gas which 

 evaporates at ordinary temperatures from the solution may be 

 utilised. To disinfect such an organic mixture as pus containing 

 pyogenic organisms, a 10 per cent, solution acting for half an 

 hour is necessary. In the case of pure cultures, a 5 per cent, 

 solution will kill the cholera organism in three minutes, anthrax 

 bacilli in a quarter of an hour,- and the spores in five hours. 

 When such organisms as pyogenic cocci, cholera spirillum, and 

 anthrax bacillus infect clothing, an exposure to the full strength 

 of formalin for two hours is necessary, and in the case of anthrax 

 spores, for twenty-four hours. Silk threads impregnated with 

 the plague bacillus were found to be sterile after two minutes' 

 exposure to formalin. 



The action of formalin vapour has been much studied, as its 

 use constitutes a cheap method of treating infected rooms, in 

 which case some spray-producing machine is employed. It is 

 stated that a mixture of 8 c.c. of formalin with 48 c.c. of water 

 is sufficient when vaporised to disinfect one cubic metre, so far 

 as non-sporing organisms are concerned. It is also stated that 



I part formalin in 10,000 of air will kill the cholera vibrio in 

 one hour, diphtheria bacillus in three hours, the staphylococcus 

 pyogenes in six hours, and anthrax spores in thirteen hours. In 

 the .case of organisms which have become dry it is probable, 

 however, that much longer exposures are necessary, but on this 

 point we have not definite information. 



Formalin gas has only a limited application ; it has little 

 effect on dry organisms, and in the case of wet organisms, in 

 order to be effective, probably must become dissolved so as to 

 give the moisture a proportion analogous to the strengths stated 

 above with regard to the vapour. 



Sulphurous Acid. This substance has long been in use, 

 largely from the cheapness with which it can be produced by 

 burning sulphur in the air. An atmosphere containing -98 per 

 cent, will kill the pyogenic cocci in two minutes if they are wet, 

 and in twenty minutes if they are dry ; and anthrax bacilli are 

 killed by thirty minutes' exposure, but to kill anthrax spores an 

 exposure of from one to two hours to an atmosphere containing 



I 1 per cent, is necessary. For a small room the burning of about 

 a pound and a half (most easily accomplished by moistening the 

 sulphur with methylated spirit) is usually considered sufficient. 

 It has been found that if bacteria are protected, e.g. when they 

 are in the middle of small bundles of clothes, no effect is 

 produced even by an atmosphere containing a large proportion 



