The search for the causes (etiologies) of human diseases goes back to antiquity. Hippocrates, a Greek physician of the 4th and 5th centuries bce, is credited with being the first to adopt the concept that disease is not a visitation of the gods but rather is caused by earthly influences. Scientists have since continually searched for the causes of disease and, indeed, have discovered the causes of many. In the development of a disease (pathogenesis) more is involved than merely exposure to a causative agent. A room full of people may be exposed to a sufferer from a common cold, ...(100 of 22361 words)