1911 Encyclopædia Britannica/Zymotic Diseases
ZYMOTIC DISEASES (Gr. ζύμη, ferment), a term in medicine, formerly applied to the class of acute infectious maladies. As originally employed by Dr W. Farr, of the British Registrar General's department, the term included the diseases which were "epidemic, endemic and contagious," and were regarded as owing their origin to the presence of a morbific principle in the system, acting in a manner analogous to, although not identical with, the process of fermentation. A large number of diseases were accordingly included under this designation. The term, however, came to be restricted in medical nomenclature to the chief fevers and contagious diseases (e.g. typhus and typhoid fevers, smallpox, scarlet fever, measles, erysipelas, cholera, whooping-cough, diphtheria, &c.). The science of bacteriology has replaced the old fermentation theory, and the term has practically dropped out of use.