The discoveries of Priestley about 1767 led up to the plan of administering gases and vapours of definite composition by inhalation through the lungs, and directly he had demonstrated the existence of “vital air,” or oxygen, the properties of this body were tested in the hope of great results in the art of medicine. Priestley’s experiments concerning the inhalation of oxygen were in time followed by those of Beddoes, who recommended the inhalation of oxygen, hydrogen and other gases in the treatment of disease. It seemed only natural that experiments with other gases and vapours by inhalation should follow. Pearson, of Birmingham, administered ether in this way in 1795 for the relief of consumption, and ten years afterwards Warren, of Boscombe, employed ethereal inhalation to relieve the sufferings attending the later stages of phthisis. Priestley’s discoveries of the method of liberating and collecting gases, and his demonstrations that certain gases could be absorbed and compressed in water, led to the introduction of aërated waters--carbonic acid gas being the first to be employed. [Illustration: JOSEPH PRIESTLEY] In the course of time, nitrous oxide, which had been discovered by Priestley in 1776, was compressed in water, and came into general use as a medicinal agent. [Sidenote: Anæsthetic properties of nitrous oxide] In 1798, a Medical Pneumatic Institution was established at Bristol by the exertions of Beddoes and others, and Humphry Davy was appointed superintendent. It was here that he commenced and carried on his notable researches on nitrous oxide. In one of his experiments he constructed a box or chamber in which he inhaled the gas in measured quantities. One day, in the year 1799, when suffering from toothache or inflammation of the gums, he resorted to the inhalation of the gas, and discovered to his great delight that it relieved the pain, which led him to the conclusion he expresses in the following words in “Researches Chemical and Philosophical,” 1800: “As nitrous oxide in its extensive operation seems capable of destroying physical pain, it may probably be used with advantage during surgical operations in which no great effusion of blood takes place.” [Illustration: SIR HUMPHRY DAVY] [Sidenote: Faraday points out similarity in the effects of nitrous oxide and sulphuric ether]