How Diesease Germs Are Spread
( Originally Published 1917 )
Where Disease Germs Come From.—The kinds of germs that cause disease do not come like wild animals from the forest or crawl out of the earth, nor are they created in decaying organic matter, as some people believe. To be afraid of the air that blows in through the windows, or of the good rich earth children dig in in the garden, is very foolish. Disease germs do not come from the great world of nature, but from people. They are microbes that have be-come especially fitted to live in the human body or in the bodies of some of the other higher animals. The body is the only place, as a rule, where they can grow and increase in numbers, because there only do they find the high temperature, rich food, and other conditions which they need. We may get disease germs into our bodies directly from water, milk, food, or some object; but we can always be sure that the germs came first from some other person or animal.
The germs of a particular disease must come, moreover, from a person or an animal already infected with that particular kind of microbe. Typhoid germs always come from other typhoid germs, diphtheria germs from other diphtheria germs, just as oak trees come from acorns. On the seacoast of Massachusetts there are acres and acres of pasture covered with a beautiful yellow flower called the broom plant. It is said to have spread from a few plants sent from England over a hundred years ago. So it is when some new disease, such as a plague or cholera, is introduced sir into a country. It may spread like wildfire; but it can only spread as the broom did, by the living seed being carried from place to place.
Human Carriers of Disease.—It is not only people known to be sick who may spread the germs of disease. When a person is once in bed, he can be cared for, and the danger of distributing his germs is lessened. Many diseases, however, are most catching in the early stages, before any one realizes that any-thing serious is the matter. Measles, which is a dangerous disease and often fatal to young children, is most catching at the beginning, when the child who has it shows almost no signs of illness, except that he appears to have a cold in the head. Such a child may continue to go to school and mingle with other children, and may infect many of them with measles.
In some cases, as in diphtheria and typhoid fever, the germs may continue living and growing in the bodies of people who have entirely recovered from the disease. Sometimes they even grow in the bodies of persons who have never had diphtheria or typhoid at all. Such persons are, for some reason, able to resist the germs, but may spread them to others who are not so fortunate. These well people in whose bodies disease germs are growing are called carriers. An outbreak of over three hundred cases of typhoid in New York City was caused by a milkman, a typhoid carrier, who had had typhoid in Michigan forty-six years before and had beencultivating the germs in his body ever since.
There was a famous typhoid carrier known as "Typhoid Mary," who was found by the New York City Board of Health to have caused twenty-six cases of typhoid fever in different families where she had been employed as a cook. She was kept in restraint for a time by the Board of Health, and was then released, upon her promise not to act as a cook again. In '914 a typhoid epidemic occurred in a hospital in New York City, and when it was investigated, Typhoid Mary was found to be the cause of it. She had broken her word, gone into the hospital as a cook, and had again infected food with her typhoid germs.
The studies of bacteriologists show that among people who seem to be quite well, two or three out of a hundred may be carriers of diphtheria germs, and two or three out of a thousand may be carriers of typhoid germs. The disease germs in some carriers are weak and not readily able to cause disease; in other cases they may be strong and vigorous.
What Happens to Disease Germs outside the Body.—Disease germs, as we have learned, are parasites especially suited for living in the bodies of human beings. In gaining this power, which the ordinary microbe does not have, they have lost the power of getting an honest living in the world outside. While most microbes grow and increase in numbers in dirty water, in the earth, or in decaying matter, disease germs die out in such places, for lack of the special foods and the other conditions which they need.
Fig. 89 shows how the number of typhoid germs decreases in a bottle of water which is allowed to stand quietly for several weeks. Much the same thing happens to all disease germs outside the body,—that is, they cease to multiply and gradually die out,—although in milk disease germs may sometimes actually increase.
Germs do not die off at once outside the body. They may survive for a time in drinking water, on the fingers, on the edges of drinking cups, on towels, and on other things that have been soiled. Their numbers are always growing less, however (except in milk), and the stories of disease caused by toys or books put away for months or years are not generally believed to-day. The diseases supposed to be obtained from such sources were probably caught from some unsuspected carrier in the street car or on the play-ground.
In order that communicable disease may spread, the germs, while still alive and active, must be carried quickly from one person to another. There are three principal ways in which disease germs are thus carried: by personal contact, by food and drink, and by insects. These three ways may be easily remembered by three catchwords, the three F's of sanitation: Fingers, Food, and Flies.
How Germs are Spread by Contact: The most important of all the ways in which disease germs are spread, is by what we call contact. The catchword "Fingers" stands not. only for the fingers themselves, but for all the ways in which germs may be spread by touching things. It is not necessary for people even to see each other in order to come in contact in this sense. The word contact is. used to cover direct infection, such as occurs when one person coughs or sneezes into another's face, and also more roundabout transfer, such as occurs if germs on an infected towel are transferred to another person's hands and later to his mouth.
How Germs are Spread by Food.—The second important way in which disease germs are spread from person to person is by means of articles of food and drink. A supply of water or milk may carry disease germs to hundreds of people at once, all over a whole city. Some of the most dreadful epidemics have been caused in this way.
Foods which are eaten raw are most likely to be at fault. Thorough cooking destroys disease germs; and most cooked foods are dangerous only when they have become infected after cooking. Among raw foods, many are safe because they are peeled before eating. Of all foods, the most dangerous are water and milk, because they are easily polluted, because they are drunk promptly before the disease germs have a chance to die out, and because they are usually not cooked.
How Germs are Spread by Insects. The third common way in which disease germs are spread is by means of insects. The catchword is "Flies," because flies are perhaps the most important insect carriers of disease in the United States. By picking up infected material on their legs and bodies and carrying it to food, they may distribute many microbes.
In warm countries, where there is a great deal of insect life, the danger of insect-borne disease is greatest; and in the tropics such diseases as yellow fever, which is spread by the bite of a certain mosquito, are very prevalent.
Diseases Caught from Animals.—A few diseases may be caught from animals, although, as a rule, the germs that affect animals cannot attack human beings. It is an unclean habit, however, to kiss animals or to allow them to lick one's face, because of the dirt with which they may hive been in contact. After fondling a cat or a dog, one should wash the hands with special care before eating.
The most serious disease which may be caught from animals is rabies (ra bi ez), which is contracted from the bite of a dog suffering from this infection. He is called a "mad" ,dog because a dog with rabies rushes about, biting the people and animals he meets. Whenever there are cases of rabies in the vicinity, all dogs should be muzzled, so that they may not infect people or each other.
QUESTIONS FOR DISCUSSION AND REVIEW
1. How do disease germs differ from the germs in decaying trees and leaves, and in the rich earth?
2. Where do disease germs come from?
3. In the preceding chapter, we spoke of the first epidemic of measles in the Faroe Islands. How must that epidemic have started?
4. What do we mean by a human carrier of disease? Is it necessary that a disease carrier should ever have had the disease himself?
5. The germ carrier, Typhoid Mary, could not help her unfortunate condition. Do you think that it was right, however, for her to continue to do a kind of work which endangered the lives of others?
6. Why do disease germs die after they have been outside the body for some time? If they die in this way, how are diseases spread?
7. What are the three F's of sanitation? Explain "Fingers."
8. Suggest several ways in which germs may be spread by food.
9. Why should milk and water receive special care?
10. A man made the remark that the feeling against flies was growing to such an extent that the day was not far distant when flies in a house would be regarded as a disgrace to the household. What do you think about it? Was his opinion warranted?
11. Do you consider a kitchen full of flies clean? Is there danger in one fly?
12. Why does the Board of Health sometimes require that all dogs should be muzzled?