Since the 18th of May, I have very often breathed nitrous oxide. In the first experiments when pure, its effects were generally similar to those just described. Lately I have seldom experienced vivid sensations. The pleasure produced by it is slight and tranquil, I rarely feel sublime emotions or increased muscular power. J. W. TOBIN. _October, 1799._ II. _Detail of_ MR. WM. CLAYFIELD. The first time that I breathed the nitrous oxide, it produced feelings analogous to those of intoxication. I was for some time unconscious of existence, but at no period of the experiment experienced agreeable sensations, a momentary nausea followed it; but unconnected with languor or head-ache. After this I several times respired the gas, but on account of the fulness in the head and apparent throbbing of the arteries in the brain,[222] always desisted to breathe before the full effects were produced. In two experiments however, when by powerful voluntary efforts I succeeded in breathing a large quantity of gas for some minutes, I had highly pleasurable thrillings in the extremities, and such increase of muscular power, as to be obliged to exert my limbs with violence. After these experiments, no languor or depression followed. WILLIAM CLAYFIELD. [222] In some of these experiments, hearing was rendered more acute. III. _Letter from_ DR. KINGLAKE. In compliance with your desire, I will endeavour to give you a faithful detail of the effects produced on my sensations by the inhalation of nitrous oxide. My first inspiration of it was limited to four quarts, diluted with an equal quantity of atmospheric air. After a few inspirations, a sense of additional freedom and power (call it energy if you please) agreeably pervaded the region of the lungs; this was quickly succeeded by an almost delirious but highly pleasurable sensation in the brain, which was soon diffused over the whole frame, imparting to the muscular power at once an encreased disposition and tone for action; but the mental effect of the excitement was such as to absorb in a sort of intoxicating placidity, and delight, volition, or rather the power of voluntary motion. These effects were in a greater or less degree protracted during about five minutes, when the former state returned, with the difference however of feeling more cheerful and alert, for several hours after. It seemed also to have had the further effect of reviving rheumatic irritations in the shoulder and knee-joints, which had not been previously felt for many months. No perceptible change was induced in the pulse either at or subsequent to the time of inhaling the gas.