The effects produced by the inhalation of the vapour of sulphuric ether, present a superficial resemblance to those produced by exposure to carbonic acid; but they are more closely analogous to the effects of inhaling nitrous oxide; and they may be compared and contrasted with those of opium and alcoholic liquors. But the patient is neither in the state of asphyxia, nor is he narcotised, nor drunk. The effects produced are peculiar, and deserve a name of their own. To give you a distinct idea of the ordinary phenomena of etherisation, I will cite three or four instances from a report on this subject by Dr Heyfelder, Knight, professor of medicine, and director of the surgical clinic at Erlangen. Dr Heyfelder himself, a strong and healthy man, after inhaling the vapour of ether for a minute, experienced an agreeable warmth in his whole person; after the second minute, he felt a disposition to cough, and diminution of ordinary sensibility. Then an impression supervened that some great change was about to take place within him. At the expiration of the third minute, he _lost sensibility and consciousness_. In this state he remained two minutes. The pulse was unaffected. Upon coming to himself, he felt a general sense of exhaustion, with weakness of the back and knees. For the remainder of the day he walked unsteadily, and his mind was confused. A. T., aged thirty-six, a tall strong servant-maid, after inhaling for seventeen minutes, became unconscious, and appeared not to feel a trifling wound with a surgical needle. In a minute consciousness returned. She laughed immoderately, spoke of an agreeable feeling of warmth, and said she had had pleasant dreams. The pulse was slower, the breathing deeper, during the inhalation. The same person upon inhaling, on another occasion, with a better apparatus, became insensible after two minutes. The eyes appeared red and suffused; a carious tooth was then extracted, which caused her to moan slightly. On returning to herself she complained of giddiness, but said she had experienced none but agreeable feelings. She had no idea that the tooth had been extracted. K. A., aged twenty-nine, upon beginning the inhalation, showed signs of excitement, but in nine minutes lay relaxed like a corpse. A tooth was extracted. Two minutes afterwards she awoke, moaning and disturbed. She stated that she _had not felt the extraction of the tooth, but she had heard it_.