CHAPTER XVIII.

DISINFECTION.

ASIDE from the prophylactic measures already spoken of, there are other measures in common use to limit the spreading of the infectious diseases. These measures are employed to destroy the specific bacteria and other infective agents outside the body. These measures are commonly included under the broad term disinfection. To disinfect is to render non-infective, and a disinfectant is, therefore, any agent that is capable of destroying infective materials or of rendering them inert. Chemical substances which in certain definite proportions kill bacteria in fluids, and when present in smaller amounts prevent their multiplication, are disinfectants. When present in the larger amounts they act as germicides—that is, they kill the bacteria; while in the smaller amounts they are simply disinfectants, because they render the bacteria. incapable of multiplication. The term disinfectant is also sometimes applied to substances which destroy bad odors. This is, however, an improper use of the term disinfectant. These substances which destroy bad odors are deodorants, and may or may not be disinfectants. Substances which retard or prevent the growth of bacteria are usually spoken of as antiseptics, because they prevent the growth of the septic bacteria as well as others. These antiseptic substances, in larger amounts, generally are germicides.

A reliable disinfecting agent is, therefore, one that is germicidal in its action. A good disinfectant should, however, be as free as possible from poisonous action upon those who use it, and, at the same time, it should not be destructive to the articles to be disinfected.

The latter quality is a most important one from the fact that a number of very useful disinfecting agents have an injurious or even destructive action upon the articles to be disinfected. For this reason dry heat is not applicable to the disinfection of fabrics, because the degree of heat required to disinfect thoroughly would be sufficient to char them. Articles of clothing containing blood or other stains should not be disinfected by means of hot water or steam, because these agents fix the stains so that they remain permanent. Many of the other disinfecting agents have a corrosive action upon metals, and are, therefore, not adapted for the disinfection of metallic articles. Consequently it is necessary to select that disinfecting agent which is least likely to prove objectionable. Fortunately we have a rather wide range of substances and agencies to select from according to the nature of the articles to be disinfected.

The disinfecting agent should be cheap, in order to lessen the expense as much as possible. Here again it is possible to select, for certain purposes, agents that are comparatively cheap and yet quite efficient. Under other circumstances it is not possible to avail ourselves of the cheapest agents, because they are not suitable for other reasons. For instance, milk of lime is a most excellent disinfectant for rough work, but it would not be applicable under all conditions.

All our present knowledge of the value and efficiency of the different disinfecting agents is based upon laboratory experiments, and it is only since the evolution of modern bacteriology and the perfection of bacteriologic methods that it was possible to give intelligent direction to our efforts toward the limitation and eradication of disease by such means.

Disinfectants in Common Use.-The disinfectants in common use are of two classes, heat and chemical substances. Heat may be employed as a disinfectant in several different ways-as dry heat, 150° to 175° C., for one to two hours; or as moist heat, as steam or boiling

water. The principal chemical disinfectants are formaldehyd gas and solution, mercuric chlorid solution, carbolic acid solution, trikresol, chlorid of lime and caustic lime, sulphur dioxid, zinc chlorid, and copper sulphate. Fire is also a most efficient disinfectant, but is applicable only for substances that are not combustible, or for combustible substances that are of little or no value. Sunlight is also an efficient disinfectant. This agent is constantly acting and, no doubt, removes most of the detrimental agents on surfaces exposed to the sun. Most bacteria grow best in the dark. Many species fail to grow at all in diffuse daylight, while direct sunlight is injurious to all species.

Disinfection on Large Scale.-Disinfection on a large scale, for infected clothing and bedding, is usually accomplished by means of steam under pressure. A special form of apparatus is required for this purpose (see Fig. 58). A special building should be constructed. for a municipal disinfecting plant. The disinfecting chamber should be so arranged that the infected clothing is brought into one room, where it is introduced into the disinfecting chamber. After it has been disinfected, it is taken out of the chamber from the other side of a partition wall and stored in a room that has no connection with the first room except through the disinfecting chamber. The doors of the disinfecting chamber should be so arranged that only one can be opened at a time, so as to prevent infectious materials from being carried over into the room containing the disinfected clothing. The attendants handling the infected clothing should not come in contact with those who handle the disinfected clothing. The disinfected clothing should never be returned in the same conveyance used for the collection of infected clothing.

The disinfecting power of steam is dependent upon the extent of the pressure to which it is subjected, the greater the pressure the higher its disinfecting power, because the temperature of the steam increases

with the increased pressure. The steam given off from boiling water in an open vessel has the same temperature as that of the water-100° C. At one additional atmosphere pressure we obtain a temperature of 121.5° C.; at two atmospheres, 135° C.; at three atmospheres, 145° C.; at four atmospheres, 153.3° C.; and at five atmospheres, 160° C. A pressure of one atmosphere

is equal to 1 kilogram per square centimeter of surface. Spores are not destroyed when heated to the temperature of boiling water, but at a pressure of two to three additional atmospheres disinfection by steam kills spores almost immediately. All pathogenic bacteria in the vegetative stage are killed when heated to from 65° to 75° C., so that the temperature of boiling water is sufficient to kill a large number of the different species of pathogenic bacteria-the non-spore-bearing forms. When

infected clothing and bedding are to be disinfected by means of steam, it is necessary to use steam under pressure to cause the heat to penetrate into the interior of the bundles to be disinfected.

Formaldehyd.-Of the different chemical disinfectants, formaldehyd is now considered the most efficient, and is in general use for the purpose of room disinfection. The disinfectant action of formaldehyd was discovered in 1886 by O. Loew. The formaldehyd gas, as generally employed for purposes of disinfection, has no great penetrating powers, and it cannot, therefore, be relied upon for the disinfection of bundles of clothing and bedding. For the disinfection of such articles the gas must be applied under pressure by means of a vacuum chamber. This disinfectant is most commonly used for the disinfection of rooms in which there have been cases of infectious diseases. It is entirely harmless for all classes of household goods. Upon the removal of the patient the room is closed as tightly as possible, and all cracks are closed by means of gummed paper; all the bedding and clothing are spread out, the drawers, doors of cupboards, and closets are opened, and the gas is introduced through the keyhole of the door. The gas is generated in a special apparatus outside the room, either from an aqueous solution of the gas by the application of heat, by the oxida tion of wood alcohol, or by the volatilization of paraform by means of heat.

Generation of Formaldehyd Gas.-An excellent form of formaldehyd gas regenerator is that manufactured by Lentz & Sons, of Philadelphia (Fig. 59), which consists of a stout copper retort of about 2 liters (4 pints) capacity, with funnel filling tube and level indicator, a stopper of special construction, and inclined brass outlet tube of large bore, connected by means of a flexible tube with another and smaller brass tube, which is inserted through the keyhole of the room to be disinfected.

The solution in the retort is heated by means of a special form of "Primus" lamp, D, which burns kero