THE ACTIONS OF CERTAIN ANTISEPTICS. 145 



producer, of which the " Equifex " may be taken as a type. With 

 such a machine it is calculated that i oz. of perchloride of mer- 

 cury used in a solution of i-iooo will probably disinfect 3000 

 square feet of surface. Such a procedure has been extensively 

 used in the disinfection of plague houses, but the use of a 

 stronger solution (1-500 acidulated) is probably preferable. 



Formalin as a commercial article is a 40 per cent solution of 

 formaldehyde in water. This is a substance which of late years 

 has come much into vogue, and it is undoubtedly a valuable 

 antiseptic. A disadvantage, however, to its use is that, when 

 diluted and exposed to air, amongst other changes which it under- 

 goes it may be transformed, under little understood conditions, 

 into trioxymethylene and paraformaldehyde, these being poly- 

 mers of formaldehyde. The bactericidal values of these mix- 

 tures 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 contain- 

 ing pyogenic organisms a 10 percent 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 40 c.c. of water 

 is sufficient when vaporised to disinfect i cm., so far as non- 

 sporing organisms are concerned. It is 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. 



