The origins and effects of testosterone have been recognized throughout the history of humankind. Hunter performed testicular transplantation experiments in 1767 while studying tissue transplantation techniques, and almost a century later Berthold linked the physiological and behavioral changes of castration to a substance secreted by the testes. Brown-Sequard gave birth to the field of organotherapy in 1889 when he announced that his auto-injection of testicular extracts resulted in rejuvenated physical and mental abilities. Steinach and Niehans expanded upon Brown-Sequard's work with rejuvenation treatments involving vasoligation, tissue grafts and cellular injections. In 1935 David et al isolated the critical ingredient in organotherapeutic treatments, testosterone. The effects of the powerful hormone testosterone continue to inspire research and controversy 65 years later.