Hickman was the first to prove that the pain of surgical operations could be abolished by the inhalation of a gas. He rendered animals unconscious, first through partial asphyxiation by the exclusion of air, then by inhalation of carbon dioxide. He amputated limbs without pain and with good surgical results. His work, the first in the field of surgical anesthesia, was received with apathy, and no use was made of it. His “Letter” was reissued in the Hickman centenary volume, published by the Wellcome Historical Medical Museum, London, 1930.