Man And The Microbe
( Originally Published 1917 )
The Art of Sanitation.—So far, we have, for the most part, been studying about the body itself and the way to use it so as to keep it in good health. Some diseases come, however, not primarily from any careless use of the body or any natural weakness in it, but from some cause entirely outside, as when one has "caught" measles or scarlet fever or some other disease. The work of guarding against these diseases that come from outside, keeping water and food pure, and preventing the spread of communicable diseases from one person to another, is called sanitation.
A great deal has been learned by scientific men in their laboratories about the working of the body itself, but the most remarkable discoveries have been made in this field of sanitation—discoveries that have given us protection against many dread diseases and have saved millions of human lives.
Communicable Diseases.—The diseases with which sanitation deals are those known as communicable diseases. Diphtheria, scarlet fever, measles, and whooping cough are all sicknesses of this kind; so is tuberculosis; so is a common cold. All of them are alike in certain particulars.
These diseases begin in a very characteristic way. A child may get up in the morning seeming perfectly well. After a while he begins to feel dull and heavy and does not want to work or play. Then he has a headache, perhaps, and grows hot and feverish. He says he is sick, and goes home to bed. The doctor is sent for. What has happened to change a healthy child into a sick one in a few hours?
Communicable diseases stop almost as mysteriously as they begin, after a regular course of a few days or weeks. The sick person gets worse for a certain length of time and then (if he does not die) he begins to get better and finally recovers. After recovery, he is fairly certain not to have that particular disease again for a while, and in the case of some diseases he will never have another attack.
The most striking thing, however, about diseases of this kind is the fact which gives them their name, "communicable,"—the fact that they are communicated or spread from one person to another. When measles was introduced for the first time into the Faroe Islands, over 6000 of the 7782 inhabitants suffered from it. What is it that causes a particular disease to spread thus from one person to an-other, striking down each one in turn almost as fire spreads through a heap of papers?
The Discoveries of Pasteur.—It was Louis Pasteur (pas tur'), the great French scientist (1822-1895), who first found the answer to these questions. In the year 1865 there was great trouble in the districts in the south of France, where many of the people followed a curious industry, the raising of silkworms. Silk is obtained from the cocoon spun by a caterpillar, and the silkworm cultivators must constantly feed and care for these caterpillars up to the time when they spin their precious web. At the period of which we are speaking, there was something wrong with the silk-worms. Instead of spinning their cocoons, they stopped eating the fresh green leaves that were brought to them, turned dark-colored, dropped to the ground, and died.
The loss of the silk crop was very serious to the people who made their living in this way, and Louis Pasteur was called on to help the silk growers. He was busy with his scientific studies and did not wish to leave the work in which he was obtaining brilliant results; he protested that
he had never even seen a silkworm. Those who knew Pasteur's keenness and patience insist d, however, that he was the man to solve the mystery, and his patriotism finally yielded to this call for help from one of the great industries of his country. He went to the silkworm district. He discovered in the bodies of the sick worms tiny living organisms that he could just barely see with his microscope. He succeeded at last, after several years of study, in showing that these little organisms were the cause of all the trouble, and he taught the silk growers how to select healthy worms and keep them free from the disease.
Microbes and Disease.—This discovery, as is often the case, led to other discoveries of far greater importance. Pasteur was soon able to show that not only this disease of silkworms, but also diseases of chickens and cattle, and finally of men, were caused in the same way. To-day, thanks to the work of Pasteur and of his followers, Koch in Germany, Lister in England, and many more, we know that all the communicable diseases are caused by microbes or germs, tiny living plants or animals. It is these living microbes which are spread from one person to another. In the body of, each new victim they grow and multiply, very much as a mold grows in jelly, and poison the tissues by the sub- stances they form, as the mold may turn the jelly musty.
All through the course of the disease, there is a struggle between the invading microbes and the tissues of the body, and when a person gets well it is because the body tissues have at last conquered the microbes.
Parasites.—When any plant or an mal lives in the body of some other plant or animal and at i s expense, we call it a parasite. This was the name the ancient Greeks gave to any one who lived in the house of a rich m. n and ate at his table without doing anything for him in ret rn. The mistletoe is a plant which grows as a parasite . a tree, sending its suckers down into the wood and sucking out its food from the tree itself. The tapeworm, whic sometimes gets into the intestines and lives on the food the e before it can be absorbed, so that the person affected almost dies of starvation, is a parasite. The flea, which lives on he blood it sucks out of its victim, is a parasite. But disease microbes are the most dangerous parasites of all.
Activities of Microbes.—The word microbe means simply a little living thing; and there are a great many different kinds of microbes which play an important part in the world.
If a glass of milk, a jar of jelly, or a piece of meat stands for a few days in a warm place, the milk sours, the jelly turns musty, and the meat decays. In each case there is a chemical change, called fermentation or decomposition, and in each case the change is not due to the food itself but to microbes which have entered the food in some way and changed it.
Some microbes are little animals and some are little plants. The microbe that causes malaria is classed as an animal, although you would never guess it from its looks. The yeast which makes our bread rise is a plant microbe. The molds which grow on preserves are plant microbes—very familiar to housekeepers. The most important of all the microbes are those which belong to the group called bacteria.
Bacteria.—Although they are plant microbes, bacteria are very different from the plants we are accustomed to see. They are so small that 400,000,000 of them could be packed in, a grain of granulated sugar. They are simple in shape and look like tiny rods or dots, or minute sausages or cork-screws. Some of them have slender fins or flagella by which they swim about when they are in a liquid (for they are like animals in their power of movement), but they have no other parts at all, no stem, leaves, or fruit—no head, eyes, or stomach.
Bacteria grow very fast when they have plenty of food; and when one bacterium gets to a certain size, it simply splits in half, and then there are two. This may happen again and again, every twenty minutes under favorable conditions. A little arithmetic will show that a very few bacteria in a glass of milk may increase to millions and millions within ten or twelve hours. Figure it out for yourself and see.
Bacteria can live on many different kinds of food, but they must first change, or decompose, the food substance to a form which they can absorb. They bring about the changes in these sub-stances by producing chemicals called enzymes or ferments, which are much like the enzymes formed by the digestive glands in your body.
How Bacteria are Studied.—The men and women who study bacteria are called bacteriologists, and in their laboratories they cultivate all sorts of bacteria, somewhat as plants are cultivated in a garden. All you would see in such a germ garden would be rows and rows of glass test tubes partly filled with liquid, or with slanting surfaces of jelly in them. On the top of the jelly, if you looked closely, you would see a grayish smear, or perhaps a whitish paste, or a brown wrinkled mass; this smear or paste or mass would be a growth made up of millions of bacteria. The bcteriologist, when he wishes to plant bacteria in a new tube, carries a tiny bit over from the growth on the point of a fine wire. By growing bacteria in different kinds of fluid, he can study their action on proteins, sugars, and other substances, and find out what they do and how the harmful ones can be killed and the useful ones cultivated.
The bacteriologist can determine, by a simple process, how many of these tiny plants there are in water or milk or any other substance. He mixes a measured amount of milk, for instance, with a melted jelly containing food which the microbes can use. Then he lets the jelly cool and harden in a covered glass dish, and keeps it at a temperature favor-able for germ life. Each of the microbes imprisoned in the jelly begins to grow and multiply. After a day or two, little spots will appear, each spot being a colony of millions of microbes descended from the single germ planted there. By counting these colonies, we can determine how many germs there were in the milk that was mixed with the jelly.
Good and Bad Microbes.—Bacteria of some sort are found almost everywhere. There are a few floating in the air. There are some in almost all water, even the clear water we drink. There are more in dirty water, and untold numbers in the tiniest speck of earth. There are millions and millions of them in your mouth and in your intestines, and many on your skin, hair, and every part of your body. If you could see the tip of your finger with a high-power microscope, you would find bacteria clinging there.
Many kinds of bacteria are useful rather than harmful to mankind. The flavor of butter is due to bacteria which have grown in the cream from which the butter was made, and have formed pleasant-tasting compounds. Vinegar is made out of fruit juices by the action, first of yeast microbes, and then of vinegar bacteria. Bacteria destroy the dead bodies of plants and animals and other waste materials, which would make the woods and fields very unpleasant if they were not removed; and they change the waste materials into a form in which they can be used as food by plants, thus helping to make the soil fertile.
Sometimes microbes decompose things we do not want changed, like the molds which grow in jelly, or the microbes which sour milk or spoil meat. We have to take great pains to prevent these microbes from growing, by keeping food cold, or by killing the germs by heat, as in canning and preserving.
Finally, there are several kinds of microbes which grow in the human body and cause disease. It is with these disease germs that we are particularly concerned just now.
How Microbes Cause Disease.—The particular kinds of microbes that cause disease are parasites; that is, they have the special power of growing in the body and at its expense. Some microbes may multiply in the nose and throat or in the intestines without doing any harm. The disease germs, how-ever, form poisons called toxins, which are absorbed into the blood and cause the dull feeling, the headache, and other symptoms of sickness. Most disease germs do more than this. They find their way through the walls of the nose or alimentary canal, for instance, into the blood stream itself, and grow and multiply in the blood or in the organs of the body. Each kind of disease germ grows in certain special parts of the body, producing a particular kind of toxin and causing particular symptoms of disease, so that we can often tell by the kind of sickness which sort of microbe is at work.
At the place where the microbes are growing, there is al-most always inflammation, or a reddening and heating of the part, due to the dilation of the fine blood vessels; and there is often local swelling and pain as well. Headache, fever, weakness, and disturbance of the bowels are common general symptoms of a bacterial invasion.
How the Body Fights the Microbes. After the microbes have been at work for a while, and the body feels the effect of their poisons, one of the most wonderful of its powers, vital resistance begins to show itself. The body attempts to defend itself against the invading germs.
This fight against the microbes is carried on, in large part, by the colorless cells of the blood, the white corpuscles, to which reference was made in Chapter X. These white corpuscles are scavenger or soldier cells, which attack microbes in the blood, swallow them, and digest them by means of enzymes.
In the blood itself, too, special chemicals appear, which tend to kill the disease microbes and also to destroy the poisons they have formed. Throughout the course of the disease, this struggle is going on between the invading microbes and the body. If the patient gets well, it is because the microbes have been beaten.
After recovery, the blood for some time keeps the power of destroying that special kind of microbe and its poisons. This is why the person who has recovered from an attack of a communicable disease is immune from that particular disease for a longer or shorter time.
The Common Cold as a Type of Communicable Disease. The next time you have a cold in the head, think about these things you have learned, so that you may understand just what is going on.
There are three or four kinds of germs that cause colds. Whenever any one "catches cold," it is because some of these germs have entered his nose or throat and begun to grow there.
A cold often begins just after one has been chilled, or has had wet feet, or has become overtired. The healthy body can defend itself against the germs of a cold, and such germs may be present in the nose or throat for a long time without causing any trouble. But after a chill, the body is weakened so that the microbes begin to grow and the real cold develops.
When the sneezing or coughing starts and the nose begins to run, it is because the germs are growing in the nose and throat and poisoning and irritating the delicate membranes. Some of the poisons have meanwhile been absorbed into the blood and are causing the sick feeling and the fever.
The best thing to do for a cold is to stay quietly in bed for a day. Rest helps the body to fight off the disease and destroy the poison of the germs. When one recovers from a cold, this process has been successfully accomplished, and for a little while afterward (only a little while in the case of the common cold—much longer in many diseases), the body is able to defend itself against germs of the same kind.
Too often, however, a person has meanwhile passed on the germs of his cold to other people, and by the time he has recovered they are going through the discomfort and danger-for danger may sometimes follow even from a common cold.
It is important that people should learn more about the way in which disease germs spread. They may then know how to avoid real dangers, and they may also save them-selves from worrying needlessly about things that some people fear without good reason.
QUESTIONS FOR DISCUSSION AND REVIEW
1. What is the difference between hygiene and sanitation?
2. What is a communicable disease? Name some common communicable diseases. Which have you had?
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3. Describe some of the general symptoms of a communicable disease.
4. Who first discovered how communicable diseases pass from one person to another? How did the discovery happen to be made?
5. Do you know of any diseases which are carried from one plant to another or from one animal to another?
6. What is a microbe? What changes do microbes cause in different kinds of food?
7. What is a parasite? Give examples not in the text. Do we ever call people parasites nowadays?
8. What are bacteria? How do they grow? How fast do they multiply under favorable conditions? What do you mean by "favorable conditions"?
9. How do bacteria change food so that they can absorb it? Give examples of similar work done in our bodies in the process of normal digestion.
10. How do bacteriologists study the characteristics of different bacteria?
11. What work is done by some of the "good" microbes?
12. In what ways are all disease microbes alike? How do they differ?
13. What weapons do bacteria use in attacking the body? What is the defending army of the body? How does this army fight? How does it destroy its enemies?
14. Is the body always successful in its fight? How does the length of the fight vary?
15. What is meant by vital resistance? What effect do hygienic habits have upon it? What habits can you name which tend to lower vital resistance?
16. What is immunity? Does it always last through life?
17. One boy has a very slight cold. Another "catches" a cold from him. Is the second boy's cold sure to be as slight as the first, or may it develop into a more serious cold?
18. After thinking about the last question, do you believe that for the sake of other people we are bound to avoid having colds, as far as possible? Explain.
19. A man said, "I was all run-down and I caught a cold." What did he mean?
20. A woman said, "When I am very tired and run-down, I do not dare to ride in crowded street cars." What did she mean?
21. What is the danger in leaving a soiled handkerchief about when you have a cold? What is the danger in sneezing, with-out putting a handkerchief to the mouth?
22. When one has a cold, why is it wise (1) to rest in bed, (2) to eat lightly of simple food, (3) to keep the intestines clear, (4) to have plenty of fresh air, (5) to drink plenty of fresh water, (6) to keep the body warm?