Immunity

Collier's New Encyclopedia (1921)

in medicine the name given to a condition of the living body in which it is safe from the attacks of particular infectious germs, or certan poisons. Although the phenomena of immunity occur in cases of several vegetable and animal poisons (ricin, and snake venom for instances) not associated with disease, and are, hence, not strictly limited to the infectious diseases, they are of chief prophylactic and therapeutic interest in connection with the where yellow fever abounds, certain ingroup of maladies. In a region dividuals remain healthy, while their neighbors fall victims to the fever. These persons are spoken of as im- Their immunity may be due to munes. a natural insusceptibility, or may have com a preceding attack of yelresulted from low fever. One attack of many of the infectious diseases confers immunity from any further attacks by the same germ. This fact, long ago noted by the medical practitioner (and utilized for the prevention of smallpox in China several hundred years ago), is now being applied in prevention and curative work in the case of many common infectious diseases-typhoid fever, chol cholera, plague, etc. The imcerebrospinal meningitis, is, munity conferred upon person by an attack of disease is called active; that resulting from an artificial treatment or sera, passive. The with vaccines remedies used in producing artificial immunity are called vaccines, antitoxins and toxins. Vaccines usually consist of living or dead bacteria or their poisons (toxins); sometimes the living organisms are weakened or attenuated by heat, growth on special culture media, passage through other animals, etc., before use in the human body. The injection of vaccines, in small, frequently repeated doses, stimulates the normal protective agencies of the body. If the special disease germs, for which the vaccine is intended, are present in the body, in other words if the man already has the disease, the vaccine serves as an aid to the regular body forces, in raising a defensive army. If the disease is not present, the vaccine builds up a condition of immunity, so that an attack by the germ, if it occurs at a later period, can be warded off. Vaccines have been more successful as preventives than as cures. The immunity produced may be permanent and lasting or merely temporary, a few weeks or months. Antitoxins are substances which act as antidotes to the toxins produced by disease germs. They are commonly manufactured by repeatedly injecting in an animal (horse, goat, dog, etc.), with increasingly virulent doses of the organism or its poisons against an antitoxin is desired. The which animal's blood finally becomes highly resistant to this particular organism, and it can withstand without harm many times the dose of germs fatal to a similar animal not so artificially immunize immunized . A portion of the blood of the immunized animal is drawn, and the serum obtained from this constitutes the essential elements of the commercial antitoxin.