1 78 ANTISEPTICS 



in water by 1-500,000. Plague bacilli are killed by one to two 

 minutes' exposure to 1-3000. Generally speaking, it may be said 

 that a 1-2000 solution must be used for the practically instan- 

 taneous killing of vegetative organisms. 



Perchloride of mercury is one of the substances which has 

 been used for disinfecting rooms by distribution from a spray 

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

 such a machine it is calculated that 1 oz. of perchloride of 

 mercury used in a solution of 1-1000 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 

 undergoes it may be transformed, under little understood 

 conditions, into trioxymethylene and paraformaldehyde, these 

 being polymers of formaldehyde. The bactericidal values of 

 these mixtures are 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 

 1 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 cass of organisms which have become dry it is probable, 



