 After having been assistant to Adolph Kussmaul, Ludwig Traube and Ernst Viktor von Leyden in Berlin, he settled in the German capital, becoming a lecturer at the university in 1877.He was a nephew of Traube, the third volume of whose ""Gesammelte Beiträge zur Pathologic und Physiologic"" he published in 1878.Fraenkel received the title of professor in 1884, and became director of the medical department of the Am Urbanplatz Hospital, Berlin.