DISINFECTANTS AND DISINFECTION The importance of disinfection in connection with isolation permits this subject to be considered to best advantage at this time.
Disinfection may be defined as the destruction of infective agents where ever they may be; while disinfectants are agents capable of producing disinfection. Disinfection is not neces sarily the same as sterilization, by which process we mean the certain destruction of all forms of life.
i. Disinfectants in Relation to the relation to the body disinfectants may be either internal or external.
(a) Internal disinfectants are employed chiefly as therapeutic agents, though some endeavor has been made to employ them in the sterilization of carriers. Their employment is the basis of specific therapy as applied to infection. As examples one may site the employment of mercurials and arsensicals in syphilis, of quinine in malaria, of ipecac in amoebic dysentery and ethyl-hydro-cuprein in lobar pneumonia.
(b) External disinfection is the practice in which we are at present interested. It is employed upon infective agents with out the body under the following circumstances: 1. As they leave the body in the infective secretions and excretions.
2. After they have been distributed in the environment of the patient.
3. After they have gained access to their definitive (insect) host.
2. Disinfecting Agencies may be Either Natural or Artificial. —We may perhaps best consider them according to whether their action is physical or chemical.
(a) Physical Disinjectants.—The natural agencies of disin fection are for the most part physical in character and com monly their importance is sadly ignored. Their efficiency is undoubtedly the principle reason for the salvation of most higher organisms from the ravages of the lower parasites, as witness the extraordinary numbers of these which are dis 94 charged from the infected host while so few succeed in reaching a new host. Most of these countless parasites are doomed to certain destruction by these natural agencies (see Table II, page 3o). The physical agencies include the following: z. Dessication.
2. Heat, either in the form of dry or moist heat, or complete incineration. Moist heat may be artificially employed either as boiling water, streaming steam, or steam under pressure.
3. Light: particularly sun light, and of the sun's rays the ultra-violet are those of greatest bactericidal action.
(b) Chemical Disinjectants.—Most of the artificial methods, particularly these employed in connection with medical asepsis in isolation are of this group. These are either: I. Liquids, which in turn are either: Solutions, such as bichloride of mercury, phenol, formalin, iodin, chlorin, bleach, "etc., or suspensions, such as the cresol compounds.
2. Gases, such as sulphur dioxide or formaldehyde. The employment of gaseous disinfectants is known as fumigation.
3. Manner of agencies exert their lethal action in different ways. Some of the lethal effects are known, but our knowledge of the means of their is obviously incomplete. Among these we may consider the following:
(a) Abstraction of water, i.e., dessication. This may be lethal to some organisms, or cause others to enter upon a con dition of suspended activity.
(b) Coagulation of the protein of the micro-organisms, either with or without an ionic poisoning of their protoplasm. The first is produced by the action of metallic salts, while such agen cies as phenol do not produce an ionic poisoning.
(c) Destruction by emulsoid action. The lethal effect is due to a molecular bombardment of the micro-organism by the finely suspended particles, associated with a certain amount of poisoning through absorption.
(d) Oxidation of the protoplasm, such as that produced by ozone, chlorine, or the permanganates.
4. Standardization of Disinfectants.—Accurate comparisons of the efficiency of disinfectants, particularly of their efficiency under conditions of actual employment is very difficult, due to the absence of suitable standards. Laboratory experimenta tion together with empirical experience has demonstrated the effectiveness and reliability of the disinfectants in the dilutions later named. It is when one is called upon to express an opin ion as to the use of some proprietary preparation of uncertain strength and composition, that the greatest need of such standards is felt. While some progress has been made in the comparison of the relative efficiency of these substances, the question of standarization is still far from settled. This is chiefly due to the great number of factors which influence the activity of disinfectants, the different conditions under which they must act in practical employment, and the species of infective agent upon which they may have to act. The most important ad vance in this direction was the method introduced by Rid eal and Walker, of which other recent methods such as the Hy gienic Laboratory method are modifications. In the deter mination time of action and temperature of exposure are arbitrarily taken as constants and the strength of the disin fectant solutions as the variable. Phenol has been chosen as an arbitrary standard. Cultures of B. typhosus in broth have commonly been employed as the test organism. In practice varying dilutions of the standard phenol are compared with varying dilutions of the unknown disinfectant being tested, until dilutions of the two are found which kill after the same period of exposure, usually arbitrarily taken at seven minutes. The results are expressed by dividing the lowest dilution of the unknown by the lowest dilution of phenol which killed in the same space of time. The result is called the carbolic coefficient of the unknown. A low carbolic coefficient, expressed as a number less than unity, usually means the substance possesses slight disinfecting value. On the other hand, the possession of a high coefficient does not necessarily mean a substance is suit able for practical use. Other factors must be taken into consideration.