In this paper Professor Tschisch sets forth his conception of pain as a form of death. Pain, he points out, does not depend on the intensity of the stimulus; a Paquelin cautery at a white heat causes much less pain than at a lower temperature. The really significant fact is that those chemical substances which produce pain kill living tissues. Pain is bound up with the existence of nerves, and appears before the tissue is killed; so it is that it arises under comparatively weak stimulation, while strong stimulation produces death. “Those chemical substances which excite no pain cannot kill any living tissue. Every chemical agent which changes living tissue into dead arouses pain.” Thus it is that excitations like strong light, loud sounds, repulsive smells, cause no pain; while heat, cold, mechanical and electrical stimuli, poisons, arouse pain. It is true that some poisons cause no pain; such poisons, however, do not act directly on living tissue; those which act directly on living tissue, like corrosive sublimate, produce pain. Pain is thus the first reaction of the organism to stimuli which kill living tissue; it is the guardian of the organism, the messenger which brings warning of approaching danger; it announces that death has already begun to appear.