Of these the most important is probably cleanliness. To remove entirely from the sphere of injurious operation all the decomposing organic substances which serve as the source of noxious or offensive effluvia, is the most effectual method of disinfection. Hence the importance of full ventilation of all inhabited buildings; so as to substitute pure air from without, for that of the apartments as fast as it becomes contaminated, whether by animal exhalations or excretions, or by the decomposition of organic substances. in prisons, hospitals, barracks, ships, and wherever living beings are crowded together, this is of the utmost importance for the preservation of health; and great numbers of human beings perish annually in large cities from the want of this simple precaution.

Ventilation may be greatly aided by the free use of water, whether upon the person, clothing, or in dwellings; care being taken in the latter case to obviate, by suitable precautions, the injurious effects of too much moisture in the air. On the large scale, for the preservation of health in cities, a due employment of water in cleansing the streets, and proper arrangements for carrying, by means of sewerage, the constantly accumulating filth to a safe distance from human habitation or resort, are now universally acknowledged to be of the highest importance.

These methods of cleanliness must be aided by collecting together and carting away the solid matters not removed by washing; and the best method of appropriating them is for the promotion of vegetation in gardening and agriculture; so that, from instruments of disease and death, they can be converted into the means of supporting life. Even to isolated dwellings in the country the same rules apply; and serious disease may often be prevented, in such places, by sedulously removing all offal, decaying vegetables, and filth of all kinds from the house to the compost, where, by a due admixture of lime, it may without danger to health be converted into valuable manure.

Other mechanical disinfectants are substances or agencies which prevent the access of air to bodies liable to decomposition by exposure to the influence of oxygen. Thus, meats, vegetables, etc. may be prevented from undergoing decomposition by being enclosed in air-tight receptacles; care having been previously taken to expel the air as far as possible; and, when admissible, to apply a sufficient heat to destroy organic germs, which are the fruitful source of putrefaction, and all kinds of fermentation.

The Class of medicines which I have denominated Protectives (see page 848) may operate as preventive disinfectants, simply by excluding atmospheric oxygen from contact with inflamed and ulcerated surfaces.

Under the same head may be ranked absorbent substances, such preeminently as charcoal, which act by absorbing noxious gases and vapours, and retaining them within their own tissue. These substances require only a brief notice. Though there are many possessing more or less of the absorbent power, the number is very small which have enough of it to be of practical utility on this score; and charcoal and lime are perhaps all that demand special notice.

Charcoal has already been treated of under the absorbents (page 886). it will here be sufficient to say a few words on this particular application of it. As a deodorizer, it should either be freshly made, or have been well kept, excluded from air and moisture. it should be used in the form of coarse powder, and may be exposed in pans, or be mixed with the substance to be disinfected, as with the contents of the close-stool, or in privies. it may also be applied in cataplasms to ulcerated and gangrenous surfaces. in France, it is sometimes employed in the form of charred charpie for the dressing of offensive ulcers. it is highly probable that charcoal does more than merely absorb the noxious gases. Brought as they are, within its pores, in a concentrated state, into contact with atmospheric oxygen similarly condensed, it is reasonable to presume that they undergo chemical changes which actually destroy their nature. Charcoal is said to absorb 15 or 20 times its own volume of the noxious and fetid gases. (Squibb, Medical Record, May 15, 1866.) Dr. T. Herbert Barker states, as the result of his experiments with charcoal, that, though possessed of limited deodorizing power, it is relatively much inferior to some other substances as an antiseptic. He found that animal intestines, surrounded with powdered charcoal, renewed every day for four days, underwent putrefaction, and at the end of the time mentioned were very offensive. The experiment was made in June. (Am. J. of Med. Sci., July, 1867, p. 164.)

Lime requires notice here only on account of its absorbent properties. For this purpose it should be in the unslaked state, and should not have been long exposed to the air. in this condition it has a very strong affinity for water, with about an equal weight of which it unites to form a perfectly dry hydrate, crumbling at the same time into the condition of a soft white powder. Now, if exposed to the air before having become thus hydrated or slaked, it rapidly though gradually absorbs the atmospheric moisture; and an idea may be formed of its efficiency, in this respect, from the fact that it is thus able to abstract from the air about sixteen hundred times its volume of watery vapour. But most of the atmospheric impurities which injuriously affect the system have an affinity for moisture, and, being held in solution, or, as in the instance of organic germs, in close connection with the aqueous vapour of the air, are absorbed by the lime along with it. Lime, therefore, employed in its dry caustic condition, is an excellent disinfectant. it may be distributed in shallow vessels in apartments requiring disinfection, and thrown into the ordinary receptacles of filth, or decomposing organic matters of all kinds. Dr. Squibb strongly recommends a mixture of lime and charcoal,, in the proportion of two parts of the former to one of the latter, to be ground into coarse powder, and used for disinfecting purposes. (Med.

Record, May 15, i860, p. 125.) Besides its absorbent property, lime has other powers which greatly add to its efficiency as a disinfectant, and which, strictly, would rank it in one of the following categories. it has a strong affinity for carbonic acid, and for many of the products of organic decomposition, especially those of an acid, oleaginous, or sulphurous character, with which it combines to form solid and inodorous compounds. Besides, by its alkaline causticity it destroys organized tissue, and thus deprives of vitality the organic germs which maintain the putrefactive and fermentative processes, and are often so noxious in their results. Spread in the form of white-wash over the walls of apartments, it tends greatly, in the recent state, before it has become perfectly dry and impenetrable, to preserve them sweet and wholesome when exposed to infecting agencies, or to render them so if already infected. it is worth recollection, however, that chlorine should not be used at the same time, as it reacts with lime to form the chloride of calcium, which is a highly deliquescent salt, and would therefore have a tendency to keep the air unwholesomely damp.

Besides the two absorbents just described, two or three others merit, perhaps, a brief notice. Sulphate of lime and dry argillaceous earth have a considerable power of absorbing noxious and offensive effluvia, and, though little used by themselves, have been found serviceable as vehicles of other more powerful disinfectants. Thus, coal-tar is conveniently incorporated with either of these excipients, and the same may be said of carbolic acid. The former of these mixtures constitutes the noted French disinfecting powder of MM. Gome and Demeaux; the latter, McDou-gall's powder and the Ridgewood disinfectant. (Report of Dr. Elisha Harris, of New York; B. and F. Medico-chir. Rev., Oct. 1864, p. 537.)