During the last week in which I breathed it uniformly, I imagined that I had increased sensibility of touch: my fingers were pained by any thing rough, and the tooth edge produced from slighter causes than usual. I was certainly more irritable, and felt more acutely from trifling circumstances. My bodily strength was rather diminished than increased. At the end of July, I left off my habitual course of respiration; but I continued occasionally to breathe the gas, either for the sake of enjoyment, or with a view of ascertaining its operation under particular circumstances. In one instance, when I had head-ache from indigestion, it was immediately removed by the effects of a large dose of gas; though it afterwards returned, but with much less violence. In a second instance, a slighter degree of head-ache was wholly removed by two doses of gas. The power of the immediate operation of the gas in removing intense physical pain, I had a very good opportunity of ascertaining. In cutting one of the unlucky teeth called dentes sapientiæ, I experienced an extensive inflammation of the gum, accompanied with great pain, which equally destroyed the power of repose, and of consistent action. On the day when the inflammation was most troublesome, I breathed three large doses of nitrous oxide. The pain always diminished after the first four or five inspirations; the thrilling came on as usual, and uneasiness was for a few minutes, swallowed up in pleasure. As the former state of mind however returned, the state of organ returned with it; and I once imagined that the pain was more severe after the experiment than before. In August, I made many experiments with a view of ascertaining whether any analogy existed between the sensible effects of the different gases which are sooner or later fatal to life when respired, and those of nitrous oxide. I respired four quarts of Hydrogene[208] nearly pure produced from zinc and muriatic acid, for near a minute, my lungs being previously exhausted and my nostrils carefully closed. The first six or seven inspirations produced no sensations whatever; in half a minute, I perceived a disagreeable oppression of the chest, which obliged me to respire very quickly; this oppression gradually increased, till at last the pain of suffocation compelled me to leave off breathing. I felt no giddiness during or after the experiment; my pulse was rendered feebler and quicker; and a by-stander informed me that towards the last, my cheeks became purple. [208] Pure hydrogene has been often respired by different Philosophers, particularly by Scheele, Fontana, and the adventurous and unfortunate Rosier. In a second experiment, when the hydrogene was procured from iron and diluted sulphuric acid, I was unable to respire it for so long as three quarters of a minute; a transient giddiness and muscular debility were produced, the pulse was rendered very feeble, and the pain of suffocation was greater than before.