Immunity And How We Can Control It
( Originally Published 1917 )
Natural and Artificial Immunity.—Vital resistance, or the natural power of the body to fight against invading microbes, varies greatly with different people. A high or a low degree of vital resistance sometimes runs in certain families. It was probably this fact that led people to think that tuberculosis could be inherited. A germ disease cannot, properly speaking, be inherited, although the germ can be passed from parent to child; but a low vital resistance against disease can be inherited.
Besides this sort of general vital resistance, there is a very special kind of vital resistance, or immunity, which follows an attack of a particular disease. Every such at-tack, as we have learned, is a real battle between the disease germ and the human body. As soon as the germ enters, the tissues begin to form substances to fight against it, and the white blood cells set out to destroy it. When a person re-covers, it is because the white cells and the substances formed to kill the disease germs have prevailed. Sometimes the body retains the power of killing this particular kind of germ, or destroying its poison, for some time after recovery, and after certain diseases it retains this power for life.
In several diseases, thanks to the brilliant discoveries of physicians and bacteriologists, it is possible to make people immune beforehand, or to help them recover after the disease has set in. This is accomplished by the use of certain substances called vaccines (vak' sins) and antitoxic sera (singular, W rum). These vaccines and sera produce an artificial immunity in the body, similar to the immunity that follows recovery from an attack of communicable disease.
Vaccination against Smallpox.—The earliest, and one of the most important, vaccines ever discovered is that used for protection against smallpox. Smallpox used to be one of the most terrible of all diseases until in 1798 Edward Jenner, an English physician, discovered this method of preventing it. Jenner was a country doctor in a dairy farm district. It had been noticed that the cows in this region suffered from a very mild disease, somewhat like smallpox, called cow pox. Little swellings, like blisters, are found on the skin of cows that have this disease. Jenner discovered that the lymph from these swellings, if rubbed into scratches in the human skin, had the wonderful power of giving a person immunity against smallpox. It has been said that this discovery of Jenner's was the greatest single practical benefit ever bestowed by one man upon the human race.
As soon as vaccination was generally introduced, the dreaded epidemics of smallpox ceased, and this disease now exists only so far as vaccination is neglected. During the eight years before the American army entered Havana, there were 3132 deaths from smallpox in the city; during the next eight years, when vaccination was enforced, there were seven.
Vaccination has conquered smallpox so successfully that people have almost forgotten what a terrible disease it was, and some of them have grown careless about vaccination. Then, too, there are others who object to being vaccinated for fear some infection may get into the wound. All vaccine used in the United States is now tested as to its purity by the national government, and there is no danger from its use, provided that the place where the vaccine is rubbed into the arm or leg is kept clean and free from dirt germs. The protective effect of vaccination wears off after a time. Every child should therefore be vaccinated when about a year old, and again at about the seventh year.
Pasteur's Work on Vaccines.-For a long time Jenner's vaccine was the only substance of its kind known. No one had any idea that the principle he had discovered could be applied to other diseases as well. It was Pasteur who laid the foundation for the many other treatments of the kind which we have to-day.
While Pasteur was studying a disease of fowls called chicken cholera, he was away from the laboratory for a time, and some of his cultures of the germs dried up. He found that these germs, though still alive, were so weakened that they could no longer cause disease. Fowls treated with these weak germs, however, were found afterward to be immune against fresh, powerful cultures. Here was a great and promising discovery; and Pasteur at once began to study whether he could produce vaccines for other diseases in the same way.
He succeeded at last in doing this with a disease of cattle called anthrax, and on a famous day in 1881 he demonstrated to a great company of doubting farmers and doctors that he could successfully protect cattle against anthrax by treatment with his vaccine, which consisted of a culture of anthrax germs that had been weakened by heating. By this discovery he has saved millions of animals, since that time, from suffering and death. Above all, he established the fact that weakened disease germs (or in some cases the dead disease germs) can stimulate the tissues of the human body and the white cells in the blood so that they can fight successfully against that particular kind of germ, just as an actual attack of the disease would do.
Vaccination against Typhoid Fever.—One of the most successful of the vaccines discovered in recent years is that used to protect against typhoid fever. Its effects in con-trolling this disease in the American army have been most remarkable (see Fig. 117). In 1913 there was not a single death from typhoid fever among the United States troops. Vaccines against typhoid, cholera, and other diseases were used with striking success in the European armies in 1914 and succeeding years.
The Treatment of Diphtheria by Antitoxin..—Vaccines, as we have seen, are weakened or dead germs which stimulate the body tissues to form substances that will destroy the particular germ used, or its poisons. Vaccines are generally used beforehand as preventives of any future attack of disease.
Another way of controlling immunity is by the use of antitoxic sera, or antitoxins, as they are often called, of which diphtheria antitoxin is the best example. Diphtheria antitoxin is made by introducing into the body of a horse the poison, or toxin, formed by the diphtheria germ. The toxin acts somewhat like a vaccine and stimulates the tissues of the horse to form an antitoxin, a substance which destroys this particular toxin. Then some of the blood of the horse is drawn off, the clear part or serum is separated and purified, and this serum (containing the antitoxin formed by the tissues of the horse) can be put into the body of a person suffering from diphtheria, to destroy the poisons of the germ.
Diphtheria antitoxin was introduced into the United States by the New York City Department of Health. in 1894, and it has reduced the death rate from diphtheria in that city from 155 deaths for every hundred thousand of the population to 24. The antitoxin is of comparatively little use when the disease has gone on for a long while and the body has become severely poisoned; but if it is used as soon as the disease begins, it is a practically certain cure.
When a case of diphtheria occurs in a family or in a school, the children and grown people who have been exposed to infection and are likely to come down with the disease, may be given doses of antitoxin to head it off.
Keeping up the General Vital Resistance.—It must be remembered that, aside from the special immunity which follows an attack of a particular disease, or treatment with a vaccine or serum, there is a considerable vital resistance against most diseases that goes with a general condition of good health. All the things that hygienic living demands—such as good food, fresh air, exercise, and rest—help to build up vital resistance.
Alcohol and Vital Resistance.—Alcohol and other poisons lower vital resistance and make the body a more ready prey to disease germs.
Observers who have studied the effect of alcohol on the power of animals to form immune substances in the blood, report that it reduces this power. As a matter of practical experience, physicians find that in fighting against such a disease as typhoid fever, where the struggle is a long and severe one, the person who has used alcohol to any considerable extent is heavily handicapped.
The importance of the part played by vital resistance varies a great deal in different diseases. In smallpox, for instance, there is almost no natural vital resistance. Every one who has not had smallpox already, or has not been protected by vaccination, will take this disease if the germ enters his body. In pneumonia, on the other hand, many people may have the germs in their noses or throats without having pneumonia—provided they are strong and well. Just as soon as the general vital resistance is lowered, the pneumonia germ is likely to grow and produce disease. In such a case as this, the effect of indulgence in alcoholic drinks is particularly serious; the danger of pneumonia in a person poisoned by alcohol is well recognized by all physicians.
QUESTIONS FOR DISCUSSION AND REVIEW
1. How does the body fight disease?
2. Can vital resistance be inherited? What would be meant if any one said, " Catching cold seems to run in a family? "
3. What is immunity? When you have a disease, what change takes place within your body, to make you immune?
4. Can you ever be made immune without having a disease? How? Which is better—to become immune before you are ex-posed to a disease or after you have had it?
5. What diseases do you know of, from which you can be made immune without having the diseases?
6. What does vaccination do to the body? Why does the law almost everywhere require that a child must be vaccinated against smallpox before he can enter the public schools?
7. How may all danger in vaccination be avoided?
8. Who discovered the power of vaccination against small-pox? Who found that the theory could be applied to diseases other than smallpox? How was each discovery made?
9. What is the difference between a vaccine and an antitoxic serum?
10. How is diphtheria antitoxin made? When is it used? Is the antitoxin of any use when diphtheria is well started?
11. What has the use of diphtheria antitoxin accomplished in New York City? What has typhoid vaccine accomplished in the United States army?
12. How does the power of vital resistance vary in different diseases?
13. How does hygienic living lessen the chances of catching a communicable disease?