In the amplest sense of the term, Disinfectants embrace all agencies which are available for the destruction or prevention of offensive or noxious effluvia, and other influences injurious to health, whether solid, liquid, or aeriform, which have their origin in animal or vegetable decomposition. This subject belongs properly to Hygiene; but it is, in many points, so closely connected with Materia Medica and Therapeutics, that, in a treatise on these branches of medical science, it cannot, in the existing state of knowledge, be wholly overlooked, without leaving the work more or less imperfect. I propose, therefore, to introduce, in the present revision, a general view of disinfectants, with some detail upon points more peculiarly interesting to our special science, but without any pretense to an exhausting consideration of the subject.

In the beginning, we are met by the existence of a striking difference in the character of disinfectant agencies, which ranks them in two great divisions, having nothing in common except the properties essential to the class. in examining the various influences which it is the office of the disinfectants to counteract, we find a set of them dependent on the agency of living and organized microscopic bodies, cryptogamous or animalcular, capable of rapid multiplication, which are either themselves directly noxious to health, or give rise, as a result of their reproduction and growth, to numerous noxious or offensive agents. Now disinfectants may act either on the non-vital agents through a mechanical or chemical influence, or upon these living bodies by destroying their vitality or suspending their action, and thus preventing their noxious operation. Upon this basis, I propose to divide them into two categories, one purely physical in their action, the other operating through their influence on the organized beings referred to. To the former I limit the term disinfectant as employed in this work; the latter, for reasons to be given hereafter, I propose to treat of under the name, for want of a better, of antizymotics. The latter clearly belong to the parasiticides, and will be treated of as a sub-class under that heading. The former will be considered under the present head of disinfectants. There are, however, several substances, and those among the most important, which act in both methods; that is, they destroy effluvia by a chemical agency, and the living source of them through a dynamic influence. Of these I shall treat fully under the parasiticides; alluding to them, however, as chemical agents in their proper place among the disinfectants.

Mode of Operation

Disinfectants may operate either by preventing the development of noxious or offensive agents, or by destroying them when produced. As the agents are the result of the decomposition of organic substances, whatever prevents decomposition may prove disinfectant. There are three influences essential to putrefaction, and other noxious or offensive change, in dead organic matter. These are water, air through its oxygen, and temperature within a certain range. Organic substances when perfectly dry, entirely deprived of oxygen, or exposed to a very high heat as that of boiling, or severe cold as that of freezing, cannot undergo injurious decomposition. Hence the exclusion of air and moisture, and exposure to a boiling or freezing temperature, act powerfully as protective disinfectants. Again, when the noxious or offensive agent is already in existence, it may by chemical change be rendered quite harmless, and completely deodorized. This is effected by oxidizing or deoxidizing the offending body, or by neutralizing it through combination; and there are various disinfectants which operate in these methods. In considering the several articles, it may be observed that almost all of them have been treated of in other parts of this work, in consequence of their possession of other powers, and will require little to be said of them in this place.

The disinfectant agent may be solid, liquid, or gaseous; but those which are in themselves aeriform, or, if liquid or solid, are volatile, that is disposed to rise in vapour, as iodine among the solids, and bromine among the liquids, are usually most efficient as deodorizers, because odorous substances are generally in the state of effluvia in the air. Yet it is not true that solids and non-volatile liquids cannot be made to act efficiently on such effluvia. Thus, charcoal will absorb odorous substances from the air; and a liquid deodorizer, by being sprinkled in the contaminated atmosphere, will often act with great energy. I have frequently rendered the air of apartments, which were exceedingly offensive with putrid exhalations, perfectly sweet by sprinkling a very weak solution of permanganate of potassa through them with the hand; and, if liquids are thus distributed, in the form of spray, by means of the atomizer, they will scarcely be less efficacious than volatile substances.