Hess was born in Frauenfeld as the second of three children to Clemens Hess and Gertrud Hess (née Fischer). His father encouraged him to pursue a scientific career and with him he conducted experiments in his physics laboratory. He started to study medicine in Lausanne in 1899 and then in Berlin, Kiel and Zurich. He received his medical degree from the University of Zürich in 1906 and trained as surgeon in Münsterlingen (in the same canton as his birthplace Frauenfeld) under Conrad Brunner (1859–1927). He developed a viscosimeter to measure blood viscosity and published his dissertation in 1906 titled "Zum Thema Viskosität des Blutes und Herzarbeit". In 1907, he went to the University of Zurich to study under Otto Haab to be trained as an