Another lesson, which has been taught in the history of many other discoveries, is clear in this--the lesson that great truths may be very near us and yet be not discerned. Of course, the way to the discovery of anæsthetics was much more difficult than it now seems. It was very difficult to produce complete insensibility with nitrous oxide till it could be given undiluted and unmixed; this required much better apparatus than Davy or Wells had; and it was hardly possible to make such apparatus till india-rubber manufactures were improved. It was very difficult to believe that profound and long insensibility could be safe, or that the appearances of impending death were altogether fallacious. Bold as Davy was, bold even to recklessness in his experiments on himself, he would not have ventured to produce deliberately in any one a state so like a final suffocation as we now look at unmoved. It was a boldness not of knowledge that first made light of such signs of dying, and found that what looked like a sleep of death was as safe as the beginning of a night's rest. Still, with all fair allowance for these and other difficulties, we cannot but see and wonder that for more than forty years of the nineteenth century a great truth lay unobserved, though it was covered with only so thin a veil that a careful physiological research must have discovered it. The discovery ought to have been made by following the suggestion of Davy. The book in which he wrote that "nitrous oxide--capable of destroying physical pain--may probably be used with advantage during surgical operations," was widely read, and it would be hard to name a man of science more widely known and talked of than he was. Within two years of the publication of his _Researches_ he was appointed to a professorship in the Royal Institution; and in the next year he was a favourite in the fashionable as well as in the scientific world; and all his life through he was intimately associated with those among whom all the various motives for desiring to find some means "capable of destroying physical pain" would be most strongly felt. Curiosity, the love of truth, the love of marvels, the desire of ease, self-interest, benevolence,--all were alert in the minds of men and women who knew and trusted whatever Davy said or wrote, but not one mind was earnestly directed to the rare promise which his words contained. His own mind was turned with its full force to other studies; the interest in surgery which he may have felt during his apprenticeship at Bodmin was lost in his devotion to poetry, philosophy, and natural science, and there is no evidence that he urged others to undertake the study which he left. Even his biographers, his brother, Dr. John Davy, and his intimate friend, Dr. Paris, both of whom were very capable physicians and men of active intellect, say nothing of his suggestion of the use of nitrous oxide. It was overlooked and