When an organism has been infected with pathogenic germs to such a degree as to produce a disease, and spontaneous recovery occurs, a change has taken place, so that the specific germ which produced that disease can find no longer suitable soil for multiplication and growth, and hence its deleterious effects on the tissue-elements cease to exist. This changed condition we call immunity. Some individuals possess this immunity naturally to a marked degree, while others exhibit only a very feeble resistance to bacterial organisms. It is relative also in degree in different races. For instance, tuberculosis is comparatively rare in the Hebrew race, while in the American Indian we find great susceptibility. Immunity is never general, conferring protection against all contagious or infectious disease, but always special, according to the disease, rendering a person perfectly invulnerable to one and not to another.
Some infectious diseases differ, as diphtheria, while others,
WEAVER HB. HOW SHALL WE INDUCE IMMUNITY IN TUBERCULOSIS. JAMA. 1900;XXXV(17):1079–1080. doi:10.1001/jama.1900.24620430015001e
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