The terms immune and immunity were

The terms immune and immunity were used for many decades to denote the fact that certain individuals who recovered from a particular disease would not again contract the same disease and that immunity could be actively induced by introducing the infectious agent, usually in altered form, into the host.2. His work and the subsequent findings of Pasteur proved the reliability of immunization procedures and the main underlying principle: the need for using altered agents, i.e., agents the virulence of which has been attenuated by various means such as passage through unnatural hosts, aging, or killing by chemical or physical means.3. Serology (the study of serum) deals with the specific reactions of antigens and antibodies and is a more restrictive term than immunology. It has been defined as the study of diagnostic and experimental procedures connected with immunology, involving serum reactions.4. It should be kept in mind that prior vaccination may be responsible for the presence of antibodies. Serologic diagnosis is of little aid in rapid or early diagnosis, since significant antibody response, with some exceptions, is not produced until the infection has persisted at least 7-10 days.