Health protection did not attain a scientific basis, in fact, until the germ theory of disease was worked out and accepted. This theory, which is simple enough in its elementary principles, completely reconstructed the ideas of the human race concerning the causes and methods of preventing bodily ailments. It provided a complete explanation for many things which had been looked upon as utter mysteries. The wonder is that the world spent so many centuries in discovering it. Even in the days of the Roman Empire intelligent men suspected that there was some connection between filth and pestilence; but just what this connection was they never were able to trace out satisfactorily, nor did anyone manage to do it for more than fifteen hundred years after them.[[253]] How long it has sometimes taken the world to move from one step in knowledge to the next!
Explanation of this theory.
The Causes of Disease and Infection.—The germ theory of disease may be concisely stated in this way: Innumerable small organisms (known as microbes, bacteria, bacilli, or germs) exist in the air, and in or upon nearly all substances. These organisms or germs are so small that they are invisible to the eye unless a powerful microscope is used. They are so small that thousands of them can assemble on the head of a pin or in the smallest drop of water. |Harmless bacteria.| Most of them are harmless; and some of them render useful service. Without the aid of these little organisms we could not make cheese or vinegar. On the other hand nearly all organic decay, of whatever sort, is caused by the action of bacteria. When apples rot, or milk grows sour, or butter becomes rancid, it is all due to bacterial action. Bacteria multiply with extraordinary rapidity wherever the temperature and other conditions are favorable; most species increase by division, that is, one micro-organism divides itself into two, these two into four, and so on by geometrical progression. As successive divisions often take place within a few hours it is easy to see how a very few germs today may number millions tomorrow. Under the microscope most of the different species can be identified, for they assume varying shapes and display a variety of characteristics.
Harmful bacteria.
But although most of these diminutive organisms are harmless, many of them are what scientists call pathogenic germs, in other words, they are a menace to health when they gain access to the human body. The human body, in fact, is the most favorable environment for these disease-bearing bacilli, and most of them can live but a short time outside of it. Access may be gained in various ways, but principally through the food and drink we consume, or through the bites of germ-carrying insects. The bacteria, when they gain lodgment in the tissues of the body, often multiply with great rapidity, creating poisonous substances, and thus increase the normal bodily temperature—a condition which we speak of as fever. When the body is strong and vigorous, it can sometimes overcome and throw off the effects of this bacterial action, for the human blood, under normal conditions, possesses powers of resistance to pathogenic germs; but when people are frail or exhausted, this power of resistance is greatly diminished and the bacilli are enabled to gain the upper hand.
Water-Borne Diseases—Typhoid Fever.—One way in which pathogenic bacilli gain access to the human body and produce disease may be illustrated by the case of typhoid fever. Fifty years ago this disease was one of the most common in all countries; today it has been almost entirely eradicated in civilized lands. Both armies in the Civil War lost thousands of men through its ravages, but in the American army during the World War there were only a few cases. Accurate knowledge of the way in which typhoid is transmitted has given mankind an almost complete mastery over this scourge of many centuries.
The causes of typhoid and the remedies.
Typhoid is caused by a germ which is most commonly found in polluted water, but sometimes makes its way into milk through the use of water in washing cans and utensils. It does not come from bad ventilation, sewer gas, ash piles, or exposure to cold, as some people imagine. The typhoid bacilli, being taken into the stomach with water, milk, or any other contaminated nourishment, find their way into the intestines and cause inflammation there, thus producing a fevered condition. If the sewage from hospitals and homes where there are typhoid patients is not carefully guarded, it gets into lakes, rivers, or wells, polluting them and spreading the disease. The elimination of typhoid is, therefore, very largely a problem of protecting the water supply against contact with human sewage. This is one reason why progressive communities are giving so much attention and spending so much money upon modern methods of sewage disposal and upon the rigorous protection of their public water supplies. An epidemic of typhoid is always the outcome of somebody’s ignorance or neglect. It has been suggested, with a good deal of force, that for every such epidemic somebody ought to be put in jail.
Insect-Borne Diseases.—Another way in which disease-bearing bacilli obtain access to the human blood is through the bites of insects. |The scourge of yellow fever.| Fifty years ago yellow fever was the great scourge of all tropical countries. When the French built a railway across the Isthmus of Panama in 1885 it is said that the work cost one life for every tie in the road, so great were the ravages of yellow fever among the laborers. But the United States, twenty-odd years later, succeeded in digging a canal across the Isthmus without the loss of a single life from this disease. Under Spanish rule, Cuba was never free from yellow fever; the island has been free from it since the Americans cleaned it up.
The war upon insects.