Henry Head’s first self-experiment in sensory physiology is well known. On April 25, 1903 a small portion of his left radial nerve was excised and the lateral antebrachial cutaneous nerve sectioned. Over the next 4.5 years, the resultant sensory loss and recovery were tested in exquisite detail by his collaborator, WHR Rivers. The results of this self-experiment were published in a 127 page article in Brain in 1908. This article devotes less than 4 pages to a lesser known self-experiment by Head, who allowed Rivers to test the sensation of his penis with the same degree of detail devoted to their study of Head’s left hand. They were drawn to study the glans penis as an area of the body having only “protopathic” or primitive characteristics in contrast to the more refined “epicritic” sensation, reflecting what they believed were anatomically separate sensory systems. Using a variety of modalities, including cotton wool, tactile hairs, interrupted current, heat and cold, Head and Rivers studied different part of Head’s penis for their unique sensibilities. Temperature was studied using drinking glasses: with Head’s eyes closed, “the foreskin was drawn back, and the penis allowed to hang downwards.” Rivers dipped Head’s penis into glasses of different water temperatures “… until the surface of the water covered the glans but did not touch the foreskin.” In support of their dualistic sensory systems, the glans demonstrated primarily protopathic but not epicritic qualities: it was sensitive to cold but not heat, insensitive to cutaneous tactile sensation, and sensitive to pressure and pain with the latter “more unpleasant than over normal parts.” Head’s curiosity about sensation led him to undergo sectioning of a branch of his radial nerve, and to subject to testing the sensation of his penis, the latter being his “lesser known” self-experiment.