[The origination of preventive medicine in the process of reforming of practical medicine in XVII-XIX centuries: report three. The development and implementation of the new approach in investigating the epidemics and its role in the reformation of hygiene is discussed].

The present report considers the ideas of T. Sydenham regarding the causes and essence of epidemics and their role in origin of new methodological approach to studying epidemics. The corresponding issues of health maintenance and disease prevention are also discussed.