Virchow was instrumental in introducing into Germany an epidemiology based on the study of multiple factors – sociological as well as bacteriological. In the above report on the reappearance of typhus in Berlin and East Prussia, he showed the connection between famine conditions and typhus outbreaks and strongly emphasized the social element in the generation of typhus. Digital facsimile from Google Books at this link. English translation, as On famine fever and some of the other cognate forms of typhus. A lecture for the benefit of the sufferers in East-Prussia. London: Williams and Norgate, 1868. Digital facsimile of the English translation from wellcomelibrary.org at this link.