Disinfectants, substances used to counteract or destroy noxious odors and exhalations, or whatever may produce infection. The term is also made to embrace substances used to prevent decay of organic bodies. (See Antiseptics, and Embalming.) In the present article disinfectants will bo considered as agents for deodorizing and fumigating. As the causes of infection exist in the atmosphere, and are spread over wide districts, disinfectants properly include whatever is used to purify the air, and the term may even be applied to the means employed to prevent the formation of noxious miasmata, as to a proper system of drainage, the destruction by fire of vegetable matter exposed to decay, the thorough ventilation of buildings, the provisions for abundant supplies of pure air and light, and the free use of clear water for washing away unclean matters. No more powerful disinfectant exists than the fresh wind, which stirs up the infectious vapors, dilutes them with pure air, and sweeps them away. Violent winds, as hurricanes, are observed to arrest the progress of disease; efficient ventilation has in many hospitals mitigated it to a wonderful extent. The light and warmth of the sun have also an extraordinary influence in promoting health and vigor, and destroying some of the causes of injurious exhalations.

Other agents are abundantly provided by nature which man may employ to remove infectious matters. They may be swept away by running water, or their gaseous emanations be absorbed by the earth in which they are buried. Exposure to heat may change their properties, or cause their elements to enter into new and harmless combinations; or by a freezing temperature decomposition may be arrested, and the formation of noisome gases prevented. Peat bogs present their antiseptic qualities as means of accomplishing the same end, and the astringent extracts of the bark of trees, such as are employed in tanning, possess the qualities of disinfectants. - In the selection and preparation of these agents, none is found more effi-cient than that which imitates the great natural disinfectant, a strong current of heated air. The method of artificially applying it to the removal of noxious effluvia from clothes and articles of merchandise has been patented in Great Britain; the articles are exposed in large chambers to rapid currents of air, heated from 200° to 250° F., the infectious matters being decomposed by the heat, or swept off in the hot blasts. Earth and porous bodies generally are employed to absorb injurious vapors; none possess this property in so remarkable a degree as charcoal.

De Saussure found that a single volume of this substance, prepared from boxwood, absorbed 90 volumes of ammonia; of sulphuretted hydrogen it took up 55 times its own bulk; of carbonic acid, 35 times; of carbonic oxide, 9.42; of oxygen, 9.25; of nitrogen, 7.50; and of hydrogen, 1.75. Bodies of animals have been buried in charcoal powder, which, while it did not prevent decay, still arrested all escape of disagreeable odors. The gases it retained indicated that it exerts an influence in causing the decomposition of the exhalations, and the combination of their elements to form new compounds with the oxygen of the air. Chlorine, which has for many years been in use in hospitals and other places exposed to noxious exhalations, acts as a powerful disinfectant by producing a chemical change in the injurious compounds, and also by arresting decay. It is generated by the decomposition of hydrochloric acid, which is effected by adding to it some black oxide of manganese. The chloride of lime, as it is commonly known, is the usual medium for distributing it, the gas being freely evolved on the exposure of the salt to the air.

It is set free by the presence of any acid fumes, and as carbonic acid is evolved in the decomposition of organic matters, the noxious effluvia themselves provide one of the agents for their own disinfection. Vinegar or dilute sulphuric acid, however, added to the chlorinated lime, causes a more rapid evolution of the disinfecting gas. In consequence of the acrid nature of the vapor, it should be used for fumigating rooms only when these are not occupied by invalids; and the same may be said of the disinfecting solutions, as the hypochlorite of soda, of which chlorine is the active agent. The more powerful fumes of nitrous acid, which possess the highest disinfectant qualities, are liable to the same objection; yet so important is their application regarded that Dr. Carmichael Smyth, who first proposed their use, received therefor from the British government the sum of £5,000. The unwholesome sulphuretted hydrogen is decomposed by these fumes, as it is by chlorine, the sulphur being set free and the hydrogen uniting with the disinfectants.

In combination with some of the metals, chlorine has been much used as a disinfectant, especially with zinc, in the aqueous solution of the chloride of the metal, which is known as the disinfecting fluid of Sir William Burnett. Its use is somewhat objectionable, from its poisonous qualities. The same compound is advantageously applied to arresting dry rot in timber. Chloride of manganese is an efficient salt of similar properties, and, being the refuse of chloric manufacture, may be cheaply procured. Chloride of aluminum, under the popular name of chloralum, has recently come into use. The action of iodine is similar to that of chlorine, and more powerful. Its application is simple. The solid substance, exposed to the air in a plate, will disengage at ordinary temperatures sufficient vapor to exert a chemical action on deleterious organic compounds. Nitrate of lead has been recommended for its disinfectant properties, particularly in the solution known as Ledoyen's disinfecting fluid. It corrects the fetid odors of sulphuretted hydrogen and sulphuret of ammonium by decomposing those compounds, but it has no antiseptic properties, and is objectionable on account of its cost and poisonous nature.

Sulphate of iron, which is used for the cleansing of sewers, drains, and soil pipes, depends for its efficacy upon a similar action, and upon its deoxidizing power. The permanganate of potassa is, under certain circumstances, an excellent disinfectant and deodorizer, readily parting with its abundant oxygen; but it is not volatile, and cannot be brought into efficient contact with large quantities of air, so that its action in purifying the atmosphere is insignificant. For washing dirty and decomposing surfaces, and for the disinfection of fluids, as bilge water, it has been found very effective. Sulphurous acid, including the sulphites and hyposulphites, which easily disengage it, is an exceedingly active substance in several ways; it is a deoxidizer, and has besides the power of destroying life in the lower organisms. Sulphurous acid may be generated by burning sulphur in the apartment to be disinfected, care being taken to remove anything which might be bleached by its action. It has been found, however, that although 1/4 of 1 per cent. of sulphurous acid in the atmosphere is sufficient to prevent the action of yeast as a ferment, yet 1/4 to 1/2 of 1 per cent. is not enough to destroy colors.

It cannot be conveniently used in inhabited rooms, on account of its irritant properties; although some physicians who have used it consider that its power of producing bronchial irritation has been exaggerated, and that patients may become well accustomed to it. The sulphites and hyposulphites may be used for the deodorization of stables and manure heaps; for this purpose they have the advantage of adding to the fertilizing value of the substances acted upon, by retaining the phosphoric acid and ammonia. These salts have been used as medicines for the purpose of destroying a hypothetical ferment in the blood. Carbolic acid and creosote are disinfectants which have been much used of late. They prevent putrefaction by killing the microscopic organisms that accompany this process. They have, however, but little power in preventing the action of emulsine on amygdaline, or diastase on saliva or starch; from which it may be inferred that the estimate of their action upon other fermentations has been somewhat exaggerated.

Carbolic acid may be employed by. vaporizing it from a hot plate or brick, by scattering a spray of its solution through the air and upon the walls, by placing open dishes filled with the acid or with carbolate of lime in localities to be disinfected, or by using dilute solutions to wash floors, etc. Its use in the surgical wards of hospitals has been said to diminish the mortality from infectious diseases, such as erysipelas and pyemia. Dr. Sansom has shown that in order to purify the atmosphere properly, and prevent the development of fungi, bacteria, and vibriones, and hypothetically of disease germs, it is necessary that the disinfectants should be volatile, as in the case of iodine and sulphurous and carbolic acids. The others, however, may be used to prevent or arrest the development of injurious gases from decomposing solids and fluids, or to neutralize them when formed.