1. By strengthening the body through hygienic living so that it offers greater resistance to the invasions of germs.

2. By living as far as possible under conditions that are unfavorable to germ life.

3. By understanding the agencies through which disease germs are spread from person to person.

*Conditions Favorable and Unfavorable for Germs.*-Conditions favorable for germ life are supplied by animal and vegetable matter, moisture, and a moderate degree of warmth. Hence disease germs may be kept alive in damp cellars and places of filth. Even living rooms that are poorly lighted or ventilated may harbor them. Water may, if it contain a small per cent of organic matter, support such dangerous germs as those of typhoid fever.

Fresh air, sunlight, dryness, cleanliness, and a high temperature, on the other hand, are destructive of germs. The germs in impure water, as already noted (page 165), are destroyed by boiling.

*How Germs are Spread.*-Some of the more common methods by which the germs of disease are spread, and by so doing find new victims, are as follows:

1. _By Means of Foods._-Foods, on account of the locality in which they are produced or the method of gathering or of handling-them, may become contaminated with germs, which are then transported with the foods to the consumer.

2. _By Means of Dust._-Material containing germs, _e.g._, discharges from the throat and lungs, will on drying form dust. This is lifted with other fine particles by the air and may be carried quite a distance. The dust from public halls and other places where people congregate is the kind most likely to contain disease germs. Dust should be breathed as little as possible and only through the nostrils. Where one is compelled, as in sweeping, to breathe dust-laden air for some time, he should inhale through a moistened sponge, or cloth, tied in front of the nostrils.

3. _By Means of Domestic Pets and Different Kinds of Household Vermin._-Germs sticking to the bodies of small animals are carried about and may be easily communicated to people. By this means, rats, mice, bedbugs, etc., where such exist, are frequently the means of spreading disease; and particularly dangerous, on this account, is the common house fly. Feeding as it does on filth of all kinds, it is easy for it to transfer the bacteria that may stick to its body to the food which is supplied to the table. The proper screening of houses and the destruction of material in which flies may develop, such as the refuse from stables, are necessary precautions.

Germs are spread also by the clothing of people, by railroad and steamship lines, by the mails, and by the natural elements. In fact, any kind of carrier, in or upon which germs can live, may serve as a means of spreading those of certain kinds.

*Public Sanitation.*-The general conditions under which germs may thrive and some of the means by which they are scattered, emphasize the practical value of measures which have for their purpose the making of one's surroundings more wholesome and hygienic. Such measures may be directed both toward one's immediate surroundings-the home-and toward the neighborhood, town, or city in which one lives. The hygienic conditions of primary importance in every city or town are as follows:

1. An adequate public supply of pure water.

2. An efficient system of underground pipes for the removal of sewage.

3. An efficient system for removing from the streets and alleys everything of the nature of waste.

4. Prevention, by enforcement of ordinances, of spitting upon sidewalks and the floors of public halls and conveyances.

5. A hospital or sanitarium in which people can be cared for when sick with infectious diseases.

In the larger cities other hygienic measures demand attention, such as provisions for parks and playgrounds, the proper housing of the poor of the city, and the suppression of the smoke and dust nuisances. Crowded together as people are in the cities, the welfare of each individual depends in a large measure upon the welfare of all. Hence the problems of public sanitation are matters in which all are vitally concerned.

*Sanitary Conditions of the Home.*-The home, being the feeding and resting place for the entire family, is the most important factor in one's physical, as well as moral, environment. For this reason there is no place where careful attention to hygienic requirements will yield better results. Much of the danger from germs may be prevented by inst.i.tuting and maintaining proper sanitary conditions in and about the home.

One of the first requisites of the home is a suitable location for the house. The house should be built upon ground that is well drained, and if natural drainage be lacking, artificial drainage must be supplied. It should not be situated nearer than a quarter of a mile to any marsh or swamp and, if so near as that, it ought to be on the side from which the wind usually blows. A stone foundation should be provided, and at least eighteen inches of ventilated air s.p.a.ce should be left between the ground and the floor. Ample provisions must be made for pure air and sunlight in all the rooms. The cellar, if one is desired, needs to be constructed with special care. It should be perfectly dry and provided with windows for light and ventilation. Adequate means must also be provided, by sewage pipes and other methods, for the disposal of all waste. Where drainage pipes are provided, care must be taken to prevent the entrance of sewer gas into the house and also the pa.s.sage of material from these pipes into the water supply. The placing and connecting of sewer pipes should, of course, be under the direction of a plumber.

*The Water Supply.*-Since water readily takes up and holds the impurities with which it comes in contact, it should be exposed as little as possible in the process of collecting. Where cistern water is used, care must be taken to prevent filth from the roof (Fig. 168), water pipes, or soil from getting into the reservoir. Water should be collected from the roof only after it has rained long enough for the roof and pipes to have been thoroughly cleaned. The cistern should have no leaks (Fig. 169), and the top should be tightly closed to prevent the entrance of small animals and rubbish.

[Fig. 168]

Fig. 168-*Contamination of cistern water* by birds nesting in the gutter trough.

Shallow wells are to be condemned, as a rule, because of the likelihood of surface drainage (Fig. 169), and water from springs should, for the same reason, be used with caution. Deep wells that are kept clean usually may be relied on to furnish water free from organic impurities, but such water often holds in solution so much of mineral impurities as to render it unfit for drinking. The presence in water of any considerable quant.i.ty of the compounds of iron or calcium makes it objectionable for regular use.

[Fig. 169]

Fig. 169-*Sources of contamination of cistern and well water.*

Ill.u.s.tration shows liability of contamination from surface drainage and from entrance of filth at top.

*Hygienic Housekeeping.*-However carefully a house has been constructed from a sanitary standpoint, the constant care of an intelligent housekeeper is required to keep it a healthful place in which to live.

Daily cleaning and airing of all living rooms are necessary, while such places as the kitchen, the cellar, and the closets need extra thoughtfulness and, at times, hard work. Moreover, the problem is not all indoors. The immediate premises must be kept clean and sightly, and all decaying vegetable and animal matter should be removed. Home sanitation consists, not of one, but of many, problems, all more or less complex.

None of these can be slighted or turned over to a novice.

*Destruction of Infectious Material.*-At times the housekeeping has to be directed especially toward hygienic requirements, such an occasion being the sickness of one of the inmates with some contagious disease. Unless special precautions are taken, the disease will spread to other members of the household and may reach people in the neighborhood. Not only must great care be exercised that nothing used in connection with the sick shall serve as a carrier of disease, but germs pa.s.sing from the patient should, as far as possible, be actually destroyed. All discharges from the body likely to contain bacteria, should be burned or treated with disinfectants and buried deeply at a remote distance from the water supply to the house.

After recovery all clothing, bedding, and furniture used in connection with the sick should be disinfected or burned. The room also in which the sick was cared for should be thoroughly disinfected and cleaned; in some instances the woodwork ought to be repainted and the walls repapered or calcimined. The purpose is, of course, to destroy all germs and prevent, by this means, a recurrence of the disease.

*Fumigation.*-To destroy germs in the air or adhering to the walls of rooms, furniture, clothing, etc., fumigation is employed. This is accomplished by saturating the air of rooms with some vapor or gas which will destroy the germs. Fumigation is quite generally employed in the general cleaning after the patient leaves his room. This, to be effective, must be thorough. Formaldehyde is considered the best disinfectant for this purpose, and it should be evaporated with heat in the proportion of one half pint of the 40 per cent solution to 1000 cu. ft. of s.p.a.ce. Since formaldehyde is inflammable and easily boils over, it has to be evaporated with care. It should be boiled in a tall vessel (a tin or copper vessel which holds about four times the quant.i.ty to be evaporated) over a quick fire, the room being tightly closed (openings around windows and doors plugged with cotton or cloth). After three or four hours the room may be opened and thoroughly aired. Since formaldehyde is most disagreeable to breathe, one should not attempt to occupy the room until it is free from the gas. This will require a day or more of thorough ventilation.

*Facts Relating to the Spread of Certain Diseases.*-The problem of preventing disease in general often resolves itself into the problem of preventing the spread of some particular disease. It is then of vital importance to know the special method by which the germs of this disease leave the body of the patient and are conveyed to the bodies of others.

Some of these methods are novel in the extreme, and are not at all in accord with prevailing notions. Particularly is this true of that disease known as

*Malaria, or Malarial Fever.*-This disease, so common in warm climates and also prevalent to a large extent in the temperate zones, is due to animal germs (protozoa), which attack and destroy the red corpuscles of the blood. These germs, it is found, pa.s.s from malarial patients to others through the agency of a variety of mosquitoes known as _Anopheles_. In sucking the blood of a malarial patient, the mosquito first infects her own body.(131) In the body of the mosquito the germs undergo an essential stage of their development, after which they are injected beneath the skin of whomsoever the mosquito feeds upon. For the spreading of malaria, then, two conditions are necessary: first, there must be people who have the disease; and second, there must be in the neighborhood the special variety of mosquito that spreads the disease. If either condition be lacking, the disease is not spread. The malarial mosquito (_Anopheles_) may be distinguished from the harmless variety (_Culex_) by the position which it a.s.sumes in resting, as shown in Fig. 170.

[Fig. 170]

Fig. 170-*Mosquitoes* in resting position. (From Howard's _Mosquitoes_.) On left the malarial mosquito (_Anopheles_); on the right the harmless mosquito (_Culex_).

*Remedies against Mosquitoes.*-The natural method of preventing the spread of malaria is, of course, the destruction of mosquitoes. This is accomplished by draining pools of water where they are likely to breed, and by covering pools of water that cannot be drained with crude petroleum or kerosene. The kerosene, by destroying the larvae, prevents the development of the young. In communities where such measures have been diligently carried out, the mosquito pest has been practically eliminated.

Other methods are also under investigation, such as the stocking of shallow bodies of water with varieties of fish that feed upon the mosquito larvae.

[Fig. 171]

Fig. 171-*Stegomyia*, the yellow-fever mosquito (after Howard).

*Yellow Fever.*-This scourge of the tropics is, like malaria, caused by animal germs. It is also propagated in the same manner as malaria, but by a different variety of mosquito (_Stegomyia_, Fig. 171). The stamping out of yellow fever in Havana, the Panama Ca.n.a.l Zone, and other places, through the destruction of this variety of mosquito, affords ample proof of the correctness of the "mosquito theory."

[Fig. 172]

Fig. 172-*Consumption germs* from the spit of one having the disease.

Highly magnified and stained. (Huber's _Consumption and Civilization_.)

*Consumption*, or tuberculosis of the lungs, spoken of as the "white plague," was among the first diseases shown to be due to bacteria.

Consumption is now recognized as an infectious disease, though not so readily communicated as some other diseases. Several methods are recognized by which the germs are pa.s.sed from the sick to the well, the most important being as follows:

1. By personal contact of the sick with the well, especially in kissing.

2. By the sputum, or spit, which, if allowed to dry, is blown about as dust and breathed into the lungs(132) (Fig. 172).