In the retrospect from the vantage ground of half a century of sanitary progress we recognize that during the third quarter of the last century the people of England were waging a successful war on domestic uncleanliness as a contributory, if not the sole cause of epidemic diseases. The health officer of England insisted that domestic filth was the actual cause of many of the low forms of disease, and named them accordingly, “filth diseases.” This official act of the highest health authority of that country led to the practice of cleanliness in the home and its surroundings. Filth in every form was removed as the necessary remedial Filth
Diseases measure against these diseases, with the result that not only were foreign pestilences prevented, but the whole brood of domestic diseases was greatly reduced in number, and the severity of cases that did occur was greatly diminished in virulence.

But during the fourth quarter of the last century186 the question arose among scientists, “Why is filth—that is, decomposing matter—the prolific cause of disease?” The answer came from the famous Pasteur of Paris, and Lister of Edinburgh. “Filth is dangerous, because it is filled with germ life. The mere removal of filth from one locality to another does not render it harmless, except to those who are no longer in personal contact with it.” So-called filth was indeed harmless if the germs it contained were killed.

The whole scheme of sanitation was at once changed: agents that would kill germs were eagerly sought by many scientists, and germicides were found in abundance. Cremation was most effectful, and was available in the destruction of masses of The Scheme of
Sanitation Changed filth; but there was a phase of the question that required other methods.

Lister announced that these disease-producing germs entered wounds and prevented healing, and that a germicide was required which would kill the germ in the wound and would not injure the living, healthy tissue. Further investigations showed that these dangerous germs were not confined to dust heaps, but existed in the unclean recesses of the human body.

187 Sternberg startled the world with the announcement that an unclean human mouth contained germs of the most poisonous character.

An eminent German surgeon declared that germs of a dangerous character existed in the folds of the skin of the palms of the hand which no amount of washing with soap and water could remove, and could be destroyed only by some agent directly applied.

Sanitation of the body as well as of the dust heap now became the paramount question and especially did this apply to the practice of surgery.

How infection affects the body was the supreme mystery that the scientists of the past strove in vain to penetrate. By no devices of their laboratories could they detect the agents that caused the epidemic. There was only one satisfactory explanation The Mystery
of Infection of the origin and spread of the devastating plagues, which seemed to fall from the heavens on the people, and that was that epidemics were “a visitation of God” on account of the sins of the people. Of course, the only preventive and curative measure available and effectual was “repentance, prayer, and humiliation.”

It is a cause of devout thankfulness that while these things were hidden from the “wise and188 prudent” of former times, they have in these latter days been revealed unto “babes.” No event in human history would have more greatly taxed the credulity of the most learned and experienced physician of half a century ago than the prophecy that in the early years of the twentieth century school children would be taught by simple and easily understood object lessons how to prevent and how to cure consumption, the Asiatic cholera, yellow fever, and other epidemics that have devastated cities, destroyed armies, and swept from the earth whole tribes of primitive people.

But that prophecy has been literally fulfilled. During the last summer there has been a traveling object lesson that visited the different sections of the State of New York and taught the people, especially the children, all the essential facts as to the nature of the infection of tuberculosis, its effects on the body, and the methods of prevention and cure.

As infective diseases cause the vast majority of cases of severe and crippling affections and of deaths in every community, the value of a knowledge of the nature of infection and how it affects the body, by the people of all How Infection
Works ranks, ages, and conditions, cannot be estimated in its influence on the future of the human race. Already we learn that within the period referred to the sickness and death-rates of communities189 where the people have been most thoroughly instructed as to the nature of infective diseases, and how they affect the body, have greatly diminished, and the average human life has been markedly lengthened. Indeed, it now seems possible to restore the patriarchal age when a man may live to be “an hundred and twenty years old ... his eye ... not dim, nor his natural force abated.”

To understand how infection affects the body involves an inquiry as to the nature of infection, its mode of entrance into the body, and its operation on its organs and tissues. The terms “infection” and “contagion” are often used as synonymous; but a strict definition according to the medical significance of each limits the former to “the transmission of disease by actual contact of the diseased part with a healthy absorbent or abraded surface,” and the latter to “transmission through the atmosphere by floating germs.” But in the final analysis the cause of disease in both infection and contagion is so similar in its action that the medical profession has adopted the term “communicable disease” in all cases where the disease is communicated from one person to another by means of a germ, whatever may be its method of attack on the body. The common characteristic of “communicable diseases” is their germ origin.

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What is this communicable germ or agent? A bacterium—a little stick, staff—so called from the rodlike shape it assumes in the process of growth. The individual bacterium (plural, bacteria) is an organism representing a low form of vegetable What the
Germ Is life; resembles mold; in size the smallest living thing that can be seen with the microscope; in masses forming the films floating on foul fluids or covering decomposing animal or vegetable matter. It consists of a single cell, and its mode of increase when placed under proper conditions of growth is by division of the cell body; the two cells formed out of the first being divided into four before complete separation has taken place; the four dividing into eight, the eight into sixteen, the sixteen into thirty-two, and so on indefinitely.

Now, as it requires only thirty minutes for one cell to divide, it has been estimated that a single bacterium will in twenty-four hours increase to the number of over sixteen million five hundred thousand, and in forty-eight hours to two hundred and eighty-one million five hundred thousand. At this rate of increase, in three days there would be a mass of bacteria weighing about sixteen million pounds. As the multiplication of bacteria depends upon conditions that soon interfere with or interrupt their growth, as the want of food, their own secretions,191 and certain natural forces operating against them, these stupendous figures are useful only as an illustration of the enormous fertility of these organisms, and their destructive energy when they attack a susceptible living body.

What is the function of bacteria in the economy of nature? It would be surprising if such a menace to human life as some species of bacteria have proved themselves to be had no other place among the forces of nature than to prevent the The Function of
Bacteria too rapid increase of the human race on this earth, as our forefathers believed. It is gratifying, and quite satisfying to a revengeful spirit, to learn from the modern laboratory that the special and only function of the bacterium is to perform the duties of a universal scavenger. It is always seeking to decompose animal and vegetable matter. It lives on filth, riots in it, and dies when deprived of it. It enters the human body only in search of filth, and if it finds none it does the person no harm, and dies either from the want of food or by starvation, or escapes from the body, or secretes itself where it may safely await the creation of decomposing matter, when it will begin its life-work.

Thus, there may be and doubtless is at all192 times a great variety of bacteria of a virulent type, quiescent in our bodies only for the time that they find no decaying matter adapted to their special tastes or wants.

It is a most interesting fact, therefore, that this most deadly foe of man becomes dangerous only when the latter is harboring in his body waste or decomposing matters that are slowly poisoning him. It is in the process of digesting this material that the bacterium excretes poisons—toxins—of the most virulent nature, which are absorbed into the blood of the human victim, creating the condition popularly known as blood poisoning.

Bacteria perform a most important function in the economy of nature, viz., the conversion of decaying and dead matter into food for plants. Biologists assert that without bacteria plant life on the earth would be scanty or entirely wanting; they are the natural intermediaries between plants and animal in point of food production. They are therefore called scavengers, because they live on decomposing matter; but in the very act of digesting such waste they convert it into products essential to plant life (carbon dioxide and ammonia) and by their excretions restore to vegetation its chief supply of food.

It appears on the same authorities that bacteria not only assist materially in maintaining vegetable and animal life on this planet, but193 “in the arts and industries they are as essential to modern economic life as are the ingenious mechanical inventions of men. Many secret processes now in use in the arts and manufactures are but devices to harness these natural forces. Thus in the manufacture of linen, hemp, and sponges, in the butter, cheese, and vinegar industries, in tobacco-curing, etc., bacteria play an important r?le.”

It naturally occurs that to meet the various conditions under which decomposing matter exists in nature there is a great variety of species of bacteria, each species being adapted to a special field of operations. These species are distinguished from one Bacteria for
Every Condition another by the shapes they assume during their growth, some being rod shaped (the bacillus), others spherical (the coccus), and others spiral (the spirillum). Under one of these divisions the various species are classified.

In these latter days of popular knowledge of scientific progress, but without precise information of details, bacteria are associated in the public mind with disease, especially of the epidemic form. While this prejudice is useful in stimulating the people to adopt and enforce preventive measures against conditions that tend to promote bacterial life in their homes and in their own persons, yet it should be understood194 that comparatively few of the great number and variety of bacteria are pathogenic, or disease producing, in man.

So throughout the animal kingdom we find that few are susceptible to a common disease; or, in other words, that the same species of bacteria attack in equal force several varieties of animals.

The explanation of this peculiarity is found in the variations of the quality or intimate nature of the tissues and organs of different species of animals. The same may be said of our own bodies—the several organs vary greatly in their susceptibility to the attacks of the different kinds of bacteria; hence the latter are classified as specific and nonspecific, according as they cause specific or nonspecific disease.

The distribution of bacteria is limited only by the existence of plants and animals; that is, the existence of decomposing vegetable and animal matter. Though they are more abundant in the earth where such matter is found most abundantly, yet they abound in the air, the water, on plants, animals, and insects, on our own bodies, and in every cavity leading to the exterior. As bacteria are always searching for food, the number present is a sure indication of the degree of cleanliness of the thing, individual, or locality where they are found.

The movements of bacteria from one point to another are through the medium of some195 other mode of conveyance than their own bodies afford. Thus they are borne by the water, by vegetation, by animals of every kind, especially insects, by the air on particles of dust. The typhoid bacillus, borne in water and milk, has caused innumerable epidemics of that dreaded disease.

The tubercle bacillus is borne on the air through the medium of particles of dust, and in cities where the victims of tuberculosis scatter these germs profusely in the streets, public conveyances, churches, and places of resort, in the act of The Deadly
Tubercle Bacillus coughing, sneezing, and spitting, the dust borne on the winds is a constant and most fertile source of infection of tuberculosis. In a city like New York thousands are annually infected by the dust-borne tubercle bacilli, not only by inhaling them in the street, but even more certainly in the quiet of their homes, where the germ-bearing dust accumulates in clothing, bedding, carpets, rugs, and upholstered furniture, and is daily forced into the air of the living rooms by broom and duster.

Foul as is the air of the unventilated tenements of the poor, it has been demonstrated that the dust which saturates the furniture, carpets, rugs, and hangings of residences of............