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a glass of water, just before drinking it, will be sufficient to ensure the destruction of typhoid bacilli present in the water is not well founded. Exact experiments show that the bacillus of typhoid fever is killed, in five hours' time, by a solution containing one-half of one per cent. of citric acid. But the time element must not be overlooked. However, the experimental evidence supports the view that the typhoid bacillus or the cholera spirillum would not retain their vitality very long in a strong lemonade, containing one per cent. or more of citric acid. The addition of sulphurous acid to water is still more effective, especially as regards the cholera germ, which is very sensitive to the action of acids. The addition of this acid to drinking-water during the prevalence of cholera has been recommended and practised, apparently with good results. It has been shown by carefully conducted experiments that one part in five hundred will destroy the cholera spirillum in the course of a few hours.

The caustic alkalies all have considerable germicidal value. Potash soap containing an excess of alkali will destroy the typhoid bacillus in six-per-cent. solution within thirty minutes; and the scrubbing of floors, articles of furniture, etc., with such a solution, especially when used hot, is a most reliable method of disinfection. Solutions of potash-common lye

or of soda are extremely valuable for certain purposes in domestic sanitation, and scientific researches fully justify the cleansing methods with these agents which have long been popular with good housewives. A hot solution of caustic soda or potash in the proportion of one part to two hundred of water will quickly destroy the germs of cholera, of typhoid fever, of diphtheria, or of glanders.

Caustic lime is also an excellent disinfectant and has the advantage of being comparatively cheap. For this reason it is one of the best agents for the disinfection of masses of filth in vaults or cesspools and upon the surface of the ground. Milk of lime, made by slaking fresh quicklime with water and mixing the resulting hydrate of lime with eight parts of water may be used for this purpose and also for the disinfection of liquid excreta in the sick-room. Lime wash applied to surfaces is a reliable disinfectant, as has been proved by experiment, thus giving scientific confirmation of the value of a method which has gained popular favour as a result of experience-that is, of the sanitary value of whitewash freely and frequently applied to outbuildings, cellar walls, etc.

Various coal-tar products have been proved to be valuable germicides, and on account of their comparative cheapness have been largely used in practical disinfection. Among these the most useful are

carbolic acid, creolin, cresol, and lysol. A five-per-cent. solution of either of these may be used for the disinfection of the liquid discharges of patients with cholera, cholera infantum, dysentery, or typhoid fever; also for the expectoration of those suffering from pulmonary tuberculosis, pneumonia, diphtheria, influenza, scarlet fever, measles, or whooping-cough. It must be remembered, however, that time is an element in the accomplishment of disinfection, and after adding the disinfecting solution to the material to be disinfected an interval of an hour or more should be allowed before the contents of the vessel are thrown

into a vault or sewer. A two-per-cent. solution of one of the above mentioned disinfectants may be used for washing floors, articles of furniture, leather, etc. Such a solution may also be used for the disinfection of pocket-handkerchiefs, bed-linen, underclothing, and other articles which require disinfection before sending them to the laundry. The articles to be disinfected should be completely immersed in the disinfecting solution, contained in a suitable receptacle, and left for at least an hour before removal from the sick-room or its immediate vicinity.

Chlorinated lime ("chloride of lime," "bleaching powder") is a valuable disinfectant and also a prompt deodoriser. It may be used for the disinfection of excreta in the sick-room, in open pits, etc., and for

infected sputa. A solution containing six ounces of good bleaching powder to the gallon of water will be suitable for ordinary use. By exposure to the air the chloride of lime rapidly deteriorates in quality. It should therefore be kept in air-tight receptacles, and only so much of the disinfecting solution made as is required for immediate use. Owing to its bleaching properties and injurious action upon fabrics of all kinds the chlorinated-lime solution is seldom used for the disinfection of bed-linen and articles of clothing, but it may be employed for washing floors and other woodwork.

Many of the metallic salts have decided germicidal value, and some of them have been largely used in practical disinfection. Among these the bichloride of mercury, or "corrosive sublimate," has a prominent place. In very dilute solutions this salt is fatal to all known disease germs, and in the proportion of 1:500 it will destroy the spores of pathogenic bacteria (anthrax, tetanus). For ordinary use a standard solution of one part in one thousand parts of water may be used. This will be suitable for washing surfaces and for the disinfection of bed- and body-linen. But owing to the fact that the bichloride of mercury combines with albuminous substances, and is thus rendered practically inert, this salt is not a reliable disinfectant for excreta or expectorated matters. The

very poisonous nature of this salt must be constantly kept in mind by those who make use of it for disinfecting purposes. The solution is colourless, and a fatal dose might easily be mistaken for water. To avoid such accident it is customary to colour the solution with indigo or an anilin dye.

Sulphate of copper has been used to some extent, especially in France, for the same purposes as the salt last mentioned (corrosive sublimate). Its germicidal value is considerably less, but in solutions containing from two or five per cent. it is reliable for the destruction of pathogenic bacteria not containing spores. Like the bichloride of mercury its germicidal action is neutralised to a considerable extent by the presence of albuminous material. It is therefore not to be selected for the disinfection of sputa and excreta.

With reference to the various proprietary disinfectants which are in the market and largely used, I would say that many of them are deodorants of more or less value and are entirely unreliable for the destruction of disease germs. Others contain germicidal agents of value; but, as a rule, they are not economical in use, as compared with heat, carbolic acid, formaldehyd, and other disinfectants of established value referred to in the present volume.

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