Inasmuch as more than 10 per cent of all deaths are due to bacterial or to various infectious diseases, it is of considerable interest to study the various means by which these germ diseases may be prevented. In this chapter it is proposed to discuss the different ways in which the active agents concerned in the spread of disease may be captured and put to death. It has already been pointed out that infectious diseases can be acquired only by the introduction of the specific germs into the human body, either through the mouth or lungs or through some skin abrasion. Further than this, it is quite as definitely known that the vitality of the germ after leaving a diseased person depends primarily upon its condition at the time of leaving the body and afterwards upon the environment which that germ finds outside of the affected person, while waiting for a chance to make its next human resting place.

It is evident, therefore, that if during the interval which elapses between the time when the germs leave a sick person and the time when they enter another person some method could be found by which these germs could be killed, the progress of the disease would be effectually stopped.

This, in the most general sense, is what is meant by disinfection. It is a determined effort to destroy the carriers of disease while temporarily absent from the human body which is their natural home. This process of killing bacteria, however, is not so simple a matter as it might at first seem. They are, unfortunately, such minute beings that they cannot be seen, so that the warfare is waged against an invisible enemy, not, however, to be despised on that account. The methods of warfare must be uncertain, since the exact location of the enemy cannot be known, and it is manifestly impossible to disinfect the universe. What is done is to fix upon the location or surroundings where the original patient was confined, and, assuming that the germs, if any, which have escaped ready for further infection are somewhere near, to poison the air and the wall and floor of the room in question so that happily the germs may be killed.

Disinfecting agents.

The various agents used to destroy those germs which are carriers of disease may be divided into two groups, namely, heat in its various forms, and chemicals. Literally, the word "disinfection" means "doing away with infection," so that to disinfect a room is to do away with the infection present in the room. It has, however, come to have a more general meaning than this and is commonly used instead of the word "destroy," so that a disinfecting solution is the same thing as a destroying solution, applied, of course, to bacteria.

It has already been explained that by far the majority of bacteria are useful if not essential to human life, and one of the difficulties in employing disinfecting or destroying solutions is that they put an end at the same time to both useless and useful bacteria. As an example, the fermentation processes in the human intestines are accompanied if not produced by certain kinds of bacteria, although on occasion these harmless or useful bacteria may develop into most obnoxious germs, producing unpleasant fermentation. It might be easy enough for a doctor to make a patient swallow some antiseptic solution, like carbolic acid or corrosive sublimate or nitrate of silver, for the purpose of getting rid of certain undesirable bacteria in the intestines, but it does not need a doctor to know that for a patient to swallow such active poisons as these would not merely kill the harmful bacteria and the good ones as well, but probably the patient himself.

Antiseptics.

There is another word often used in connection with bacteria, namely, "antiseptic," and the common significance of this word applies to a substance which interferes with or retards the growth of bacteria without actually destroying them. Doctors, for instance, use antiseptic instead of disinfecting solutions on wounds, not because they do not wish to kill the pus-forming bacteria, but because the antiseptic solution will prevent their growth and not be, as a disinfecting solution, harmful to the cells which he is trying to repair. It would be folly, for example, to inject a strong 50 per cent solution of carbolic acid into a wound on the arm produced by a saw, because all the energy of the vital forces at the seat of the wound are needed for repairs, and there is none to spare for so active a detergent as carbolic acid. An antiseptic, on the other hand, is mild enough so that it does not act on the tissue at all, but merely prevents any undesirable growth of bacteria.

Deodorizers.

There are substances used, perhaps not so much around country houses as around city houses and in water-closets, which are neither disinfectants nor antiseptic, but act as deodorizers only. Such a substance, for example, may be thrown into the kitchen sink, not at all for the purpose of killing bacteria, but for disguising the smell from the cesspool into which the sink-wastes discharge. It has no disinfecting properties and is good for nothing unless the material is so scented as to be agreeable on that score. One of the frauds perpetrated on the public is the preparation and sale of the various appliances designed and regulated to produce a perpetual smell and claimed on that account to be either disinfecting or antiseptic agents. The smell is worth nothing.

Patented disinfectants.

The poison of the disinfectant or antiseptic, whether it be in liquid or in gas form, is the essence of the material, and since the value of disinfectants is based on the crude raw materials which any one can buy, it is clearly unnecessary to buy expensive patented solutions for disinfectants when ordinary lime or carbolic acid are equally as good and can be had at much lower prices.

A disinfecting solution, to be successful in its action, must be reasonably proportioned in volume to the amount of material to be disinfected, whether this be a liquid or clothing or the air of a room. It is the height of absurdity, for instance, to pretend to disinfect the air of a large room by burning a tablespoonful of sulfur on a shovel in the center of a room without even taking the trouble to close the door. It is absurd to attempt to disinfect the bed linen in a single pailful of hot water, since even if the water was hot at the beginning, it would be so reduced in temperature by the first piece that went in that its efficacy would be lost for everything else. It is equally absurd that a liquid from a bottle, no matter how much advertised, can effectually disinfect a room, either by a gentle sprinkling of the liquid on the walls and floor or by a more thorough spraying of the air with an atomizer containing the liquid.

Disinfecting gases.

Two gases are available for use in disinfection, and these are valuable particularly in killing germs left in a room after a patient suffering from an infectious disease has been removed. The diseases referred to in the following chapters are all of this nature, and one of these two gases ought to be used in every case; otherwise the room may continue to harbor germs of the disease for months or years with the possibility of infecting a future tenant at a time when his vitality was such as to make him an easy prey. Nor must the contents of the room be overlooked.

The writer was recently told of a large family where one child had scarlet fever, recovering in September. The sick room was thoroughly disinfected, but the careful housewife, fearing damage to her blankets, had taken them to the attic before disinfection began. In the cold weather of February these blankets were brought down, and in six days the two children sleeping under them had contracted the disease.

Sulfur as a disinfectant.

When sulfur is burned, a gas is formed known as sulfurous acid, and until the last few years, it was the most common of all disinfecting agencies. The writer well remembers that when about to visit a city in South America infested with yellow fever, he was seriously advised to fill the inside of his shoes with sulfur as a precaution against the disease. He might as well have worn a red ribbon on his hat so far as any protection went, but it illustrates the confidence formerly shown in sulfur as a disinfectant.

It is now known that in the dry, powdered state, sulfur is of no value unless, perhaps, the germs be smothered with the sulfur flour. When burned, however, the gas given off has a certain disinfecting property, although this is limited. It has almost no power of penetrating into curtains, blankets, and upholstered furniture, although the penetration is decidedly increased if these objects are moistened either by steam or by water vapor. The proper amount of sulfur to be burned for any room is at the rate of 3 pounds per 1000 cubic feet of air space in the room. Thus, if a room be 12 feet by 15 feet and 8 feet high, containing 1440 cubic feet, it would be necessary to burn 144/100 of 3 pounds, or 4-1/3 pounds.

Before undertaking to disinfect a room with sulfur, it should be made thoroughly air-tight, and this must be done carefully, not merely by closing the larger and obvious openings, like doors and windows, but by pasting strips of paper over every crack which might allow air to escape. Thus the four edges of the window sash must be pasted up, and a strip must close the crack between the two sashes. All the doors but the one reserved for exit should be pasted up from the inside, and finally this last door pasted up on the outside. If the floor has settled away from the base-board, the cracks thus made must be pasted up. In short, the room must be made absolutely air-tight. The room should be left thus closed for at least twenty-four hours, and since there is some danger from fire, a proper provision should be made for the burning sulfur. This can be done by placing an old milk pan (a most convenient object in which to burn the sulfur) on a couple of bricks, which may be set inside a wash tub with perhaps three or four inches of water in the tub. The most convenient way of ignition is to moisten the sulfur with a little alcohol which can be readily set on fire.

Since clothes of every sort are more effectually acted upon when moist, they should be sprinkled with a hand atomizer just as the sulfur is lighted, and this should always be done in the case of any stuffed furniture or hangings. Anything that can be removed should be taken out and sterilized by steam, since live steam is the only disinfecting agent which will penetrate such things as mattresses, pillows, and rolled-up bundles of every sort, and with these last even steam is not certain. It is far safer to send a mattress to the cleaner to be steamed than to try to sterilize such bulky objects at home. It requires about twenty-four hours with the room tightly closed to generate enough gas so that the bacteria which may have found their way onto the walls or floor or ceiling or into the air of a room will be surely killed. After that time the room can be opened and then the usual household cleansing processes carried out as an additional safeguard. It is a wise measure in the case of infectious diseases, even after a room has been fumigated with sulfurous gas, to wipe off the woodwork and the walls, if their construction allows it, with a solution of carbolic acid, since in this way the germs which have accumulated on the woodwork will certainly be killed.

Formaldehyde disinfectant.

Formaldehyde is the other gas which is commonly used for disinfecting the air of a room. It is most readily produced by buying solidified formaldehyde and then decomposing it by the action of heat. Formaldehyde candles, as they are called, may be purchased at almost any drug store, and while special forms of generating stoves may be found in the open market, an ordinary heating apparatus of almost any sort will answer the purpose of decomposing the solid formaldehyde. About 20 ounces of the formalin should be used for each 1000 cubic feet of space. With this agent, however, as with sulfur, the penetrating power of the gas is not very great, and such things as mattresses and clothing should be sent to a steam sterilizer rather than be trusted solely to the power of the formaldehyde.

In using this gas, the same care about pasting up cracks and crevices in the room should be followed as already prescribed for the use of sulfur, and, as with sulfur, a reasonable precaution against fire should be taken by placing the apparatus in a tub of water or in a large pan of sand where accidents cannot happen. The room should be kept closed for at least twelve hours, and then should be thoroughly aired, and if the room is to be used again soon, the disagreeable odor may be removed by the free use of ammonia, either sprinkling it around in the room or by placing about saucers of ammonia.

Liquid disinfectants.

More common than gases and most readily suggested as disinfectants are certain liquids which have been proved both by laboratory experimentation and by actual experience to have the power of killing bacteria when brought into contact with them. Those liquids which have commended themselves particularly have additional advantages in not destroying fabrics, metals, or tissue with which they are brought in contact and in being purchasable at moderate prices.

There is little choice between a number of such liquids, and the number of modifications or combinations which are made and bottled and sold under some fancy name is legion. But the label, the name, and the additional price add nothing to the value of the basic chemical from which they are all compounded, and except for their convenience, they have little to recommend them.

Carbolic acid as disinfectant.

Carbolic acid is one of the most useful of these liquids, and in its various forms appears in almost all disinfectants. It may be obtained from the drug store in two forms, either as a crystal or as a concentrated solution.

A 2 per cent solution, that is, one pint of carbolic acid to six gallons of water, is the proper strength for all such uses as wiping off wooden surfaces, furniture, floors, etc. A stronger (5 per cent) solution is used when it is intended to destroy organic matter containing large quantities of germs. This is practically a saturated solution, so that if a bottle be partly filled with the crystals of carbolic acid and then completely filled with water, the water will absorb enough of the carbolic acid to make a 5 per cent solution, and the water may be poured on and off as long as the crystals remain. This 5 per cent solution is the proper strength to receive sputum from tuberculous patients, material ejected from the stomach in diphtheria, and fecal matter from typhoid and cholera patients. This strong solution should not be used on the living human body, since it is powerful enough to eat directly into the flesh, and being a violent poison, it should be kept out of the way of the household and carefully labeled to avoid accidents.

Carbolic acid has no value at all in the way of disinfecting the air, although fifty years ago surgeons were accustomed to use a spray of carbolic acid around the operating table before an operation in order to destroy any germs of the air lingering in the vicinity. It is equally futile to pour carbolic acid into sewers or to stand it around on the mantelpiece for the purpose of disinfecting a room. Nor are sheets wet in carbolic acid and hung over doorways and at the end of passages anything more than a remnant of medievalism.

Coal-tar products.

There are certain preparations made from coal-tar which, either alone or combined with carbolic acid, have very strong disinfecting properties and which are the bases of most of the patented disinfecting solutions now sold. They are commonly called cresols or creosols and a 4 per cent solution of any of the three ordinary forms will destroy bacteria in a few hours. They are commonly used for receiving organic excretions of sick persons in the same way as carbolic acid is used, and have about three times the power of carbolic acid to destroy bacteria.

They have one great advantage besides the strength mentioned, in that they are not materially affected or interfered with by the presence of albuminous material. Carbolic acid in the presence of albuminous material, like sputum, for instance, has the strength of the disinfectant partly used up in combining with this albuminous material so that the strength remaining for disinfection is weakened, and the result is not as satisfactory as it would otherwise be. The coal-tar products, on the other hand, are not so interfered with, and the solution acts in full strength upon the bacteria.

Mercury for disinfectant.

Corrosive sublimate, or bichloride of mercury, is one of the most active poisons known and is as effective in dealing with the microscopic organisms known as bacteria as it is in dealing with the larger animals for which it has been used for years past,—the destruction of bed-bugs.

For general cleaning purposes, such as scrubbing woodwork, floors, and walls, it should be used in strength of about 1 part to 3000 parts of water. This means that for 1 ounce of corrosive sublimate 3000 ounces of water or 25 gallons must be taken. This solution is very active in its effect on all metal, so that it must be kept in brassware or earthenware, and when mixed with the material which it is intended to disinfect, it must be kept from tin or iron. This solution is also affected by albuminous material, although this may be counteracted by the addition of salt. It is a good plan, therefore, to add to the solution salt at the rate of about 4 teaspoonfuls to each gallon of solution. On account of the very poisonous action of this solution great care must be taken to keep it away from children, and it has been suggested that it is desirable to add some coloring matter to the liquid, since without this it may be mistaken for clear water.

Lime for disinfecting.

Chloride of lime is one of the most useful as well as one of the cheapest disinfectants available. It costs about $25 a ton, although by the pound this wholesale price would not be obtained. It is effective in a 1 per cent solution, that is, 1 pound of chloride of lime to 100 pounds or 12 gallons of water. To be effective, the solution must be well stirred into the organic matter to be disinfected, since it is the chloride rather than the lime which is the disinfecting agent. Saucers or soup plates of chloride of lime standing around the room have no effect upon the germs in the air and on the floor and are of no more value than sulfur, or roses for that matter. Chloride of lime is commonly known as bleaching powder, and its effects on clothes or on any substance which can be eroded is well known. It is, therefore, not a suitable material for disinfecting towels, because the action is on the towel as well as on the bacteria, differing in this respect from mercury, which does not hurt the fiber of clothes.

Milk of lime is produced by slaking ordinary building lime until a fine white powder is obtained, about an equal quantity of water to the amount of lime to be slaked being necessary. When the powder has formed and steam has ceased to be given off, then about four gallons of water should be added to each gallon of the powder and the mixture well stirred. This will probably always leave some lime in the bottom of the vessel, since limewater is a saturated solution, and these proportions furnish more lime than is necessary. If not too thin, it is a good whitewash and is a most important agent when used as a whitewash in disinfecting walls and ceilings of such rooms as hospitals and cellars and other places where have been contagious diseases. Milk of lime is an admirable disinfectant in the sick room and generally in houses where infectious diseases have been. It may be poured down drains, into water-closets and privies, and used liberally in all places where bacteria may be supposed to thrive. It must come into intimate contact, however, with the bacteria, and merely sprinkling a little lime dry around the borders of a gutter or drain is of no value. The writer saw, not long ago, a chicken yard where the inspector of a health department had undertaken to secure disinfection by a generous sprinkling of white lime powder around the yard. Such a procedure, however, is not effective, but in a drain the dry powder might be of value because it would later become effective when washed in solution into the drain. Ordinarily, the dry powder is to be avoided.

Soap as an antiseptic.

No better antiseptic exists than ordinary soap, not altogether because of the properties of the soap, but because of the action of the soap combined with hot water. Washing soda, dissolved in water and used for boiling clothes which have become polluted, adds to the disinfecting power of the hot water the disinfecting properties of the soap, and the result is most effective. Ammonia has not the same value as the soda or potash soap, although it has the power of destroying bacteria in the course of a few hours.

It may not be out of place to emphasize the value of soap, not particularly in times of epidemic or contagious disease, but as a continual safeguard against infection. A large proportion of the contagious diseases are probably the result of infected fingers or hands coming in contact with the mouth and leaving there the germs of infection. One of the first things a surgeon learns, in order to avoid any possible infection of wounds or of openings which he makes for an operation, is to thoroughly wash his hands in order to remove therefrom all possible germs. He scrubs his hands, particularly his finger nails, with soap and water and then bathes them in a solution of bichloride of mercury before touching the patient in any place where infection might occur. The difficulty, even with this great care, of freeing their hands from bacteria has been found to be so great that, in late years, surgeons have preferred to use, during operations, thin rubber gloves which can be boiled before using and can be soaked in a stronger antiseptic than the hands could bear.

It is extraordinary, from the standpoint of self-infection, to see how men can be so careless as to sit down to dinner, after having worked in places where their hands have come in contact with all sorts of organic filth, without stopping to wash those hands even in cold water. It is certainly providential that disease germs are as uncommon as they are, for with the careless habits of most people in putting their hands to their mouths, the death-rate from infectious diseases would be much higher than it is except for the fact that most of the germs thus introduced into the mouth are not disease-producing.

Disinfecting by heat.

Better than any chemical agent known to be a destroyer of bacteria is heat in one form or another. This may be steam or hot water or dry heat. If a high enough temperature is maintained for a sufficient length of time, the action is absolutely destructive to all germs. Fire does, of course, destroy bacteria along with whatever material the bacteria are concealed in, but such a disinfectant is of little value for ordinary purposes, since the object of disinfection is to destroy bacteria without destroying the surface on which they are lodged. In some old buildings, where consumption or smallpox, for example, has become permanent, it may be that the surest way of killing all the bacteria is to burn up the house.

Dry heat.

Unfortunately, even a moderate heat cannot always be applied. One's hands, for example, can neither be heated in an oven to the necessary temperature for destroying bacteria in their pores, nor can they be immersed in boiling water or steam for a sufficient time to secure thorough disinfection. Therefore, with the body, chemical means for disinfection must be employed. Also when it is desired to disinfect a liquid, such as beef broth, in which the experimenter desires to grow some particular species to the exclusion of all others, dry heat is inapplicable because it would evaporate the liquid, nor is chemical disinfection possible because of its antiseptic effect on the bacteria to be cultivated. Moist heat, therefore, must be used. When dry heat is used, it is usually for the disinfection of glassware or earthenware or metallic objects, the quality of which will not be affected by the necessary temperature, namely, 150 degrees Centigrade, or about 300 degrees Fahrenheit. This temperature must be maintained for at least an hour, and it is not certain even then to penetrate in full power to the middle of blankets or comfortables. Except for glassware to be used in a laboratory, dry heat, such as would be obtained by a kitchen oven, is not to be recommended.

Boiling water.

Boiling water, on the other hand, is the most effective and penetrating disinfecting agent available. One has only to expose an object to boiling water for five minutes to absolutely kill all disease-bearing bacteria contained, and since bed linen, clothes, blankets, and such articles as are naturally used in a sick room have to be washed after a patient's recovery, it requires but very little additional trouble to subject the soiled articles to that temperature of the water which will secure disinfection at the same time. But the water must be boiling. The mere fact that it was once boiling water gives it, half an hour later, no disinfecting properties, and complete disinfection can be secured only by actually boiling the garments or articles for at least five minutes. The apparatus necessary therefore—and no better piece of disinfecting apparatus can be secured anywhere—is a good old-fashioned wash boiler. The action is more certain, that is, more penetrating, if a little washing soda is added to the water at the rate of a tablespoonful of soda to a gallon of water. This solution is admirable for washing dishes, spoons, knives, forks, and other eating utensils used by sick persons. It is always a mistake to wash dishes from the sick room in the same vessel with other dishes. They should not only be washed separately, but they should be washed in boiling water, and preferably in a soap solution as just described.

Steam.

For some purposes, steam is better even than hot water; its effect on cotton and woolen garments is not so disastrous. A comfortable or blanket, for instance, may be subjected to steam without losing its elastic quality, and for small garments, an ordinary steamer, such as is used for puddings, answers admirably. Cities use steam sterilizers because of the greater convenience in furnishing steam to a large tank as compared with filling and emptying a tank with water and then providing sufficient heat to boil that water. The exposure to steam should last from half an hour to an hour, depending on whether the objects to be disinfected are small, open, and loose, or large, compact, and dense. Some articles, like bales of rugs, rolls of wool, and large bundles of cloth, cannot be sterilized at the center by ordinary steam, and while it is not likely that infection at the centers of such tightly rolled bundles has occurred if exposure took place while rolled up, yet it is certain that the disinfection does not reach these centers. In the case of such bundles as rugs from infected countries, where any single rug may become the medium of infection, it is requisite to thoroughly sterilize all parts of the bundle. For this purpose, it is necessary not merely to expose the articles to live steam, but to have the live steam under pressure so that it is forced into the inside of the packages by an excess of external pressure. This is probably not available in an ordinary house, where boiling must continue to be the method of disinfection.

Drying, light, and soil.

Before leaving this chapter, three agencies for disinfection may be pointed out, not perhaps to be depended on, but in order that the kindly provisions of nature may be appreciated. All germs removed from the body, which is their natural home, and exposed to the air are subject to drying and thus are killed. Unfortunately, this does not become true except after long periods of time, nor is it equally true with all germs, but it is certainly one of the methods by which the evil effects of disease germs may be lessened. The germ of consumption lasts as long as any germ, and yet this, when dried in the street, loses its vitality after about a week. Similarly, the typhoid fever germs, unless kept in a moist condition, dry up and die in a few days. With the drying, however, comes the danger that in the process they may be lifted by the wind and carried in the air to the mouths or nostrils of well persons, so that it is not wise to depend solely on this method of disinfection.

Sunlight is more positive than the wind, and the exposure to direct sunlight of a bottle filled with disease germs will kill them all in two or three hours. The surface layers of a pond never have as many bacteria in them as the lower layers, partly on account of the sedimentation, but largely because they are killed by the direct action of sunlight. The bacillus of consumption and bacillus of diphtheria are both killed in an hour or so by direct sunlight. This is one reason why living rooms should have sunny exposure and why, on the other hand, disease thrives in dark tenements.

The soil is the third natural method of disinfection, not because the soil itself destroys bacteria, but because in the soil are to be found millions of non-harmful germs and these germs are hostile to the disease-producing germs, so that they destroy their virulence. It is on this principle that the wastes from typhoid fever patients are buried in the garden, the presumption being that the bacteria there present will destroy the typhoid fever germs before they can escape and do any harm. While this action undoubtedly exists, it is not positive enough to depend upon, and disinfection by the use of chemicals should always be practiced.