Fig. 1. Hayes demonstrating his “face piece and generator.” A bearded and bespectacled Rev. Dr. Samuel J. Hayes demonstrates his “process of generating and applying anaesthetics” on a female patient. The woman depicted may be his oldest daughter, Cora. (Image cropped from Gaertner F: Hayes’ process of generating and applying anaesthetics, the most improved. Dent Surg Microcosm 1893; 3: 7.)  37