[223] Dr. Mitchill (an American Chemist) has erroneously supposed its full admission to the lungs, in its concentrated state, to be incompatible with animal life, and that in a more diluted form it operates as a principal agent in the production of contagious diseases, &c. This gratuitous position is thus unqualifiedly affirmed. “If a full inspiration of gaseous oxyd be made, there will be a sudden extinction of life; and this accordingly accounts for the fact related by Russel (History of Aleppo, p. 232.) and confirmed by other observers, of many persons falling down dead suddenly, when struck with the contagion of the plague.” Vide Remarks on the Gaseous Oxyd of Azote, by Samuel Latham Mitchill, M. D. IV. _Detail of_ MR. SOUTHEY. In breathing the nitrous oxide, I could not distinguish between the first feelings it occasioned and an apprehension of which I was unable to divest myself. My first definite sensation was a dizziness, a fulness in the head, such as to induce a fear of falling. This was momentary. When I took the bag from my mouth, I immediately laughed. The laugh was involuntary but highly pleasurable, accompanied by a thrill all through me; and a tingling in my toes and fingers, a sensation perfectly new and delightful. I felt a fulness in my chest afterwards; and during the remainder of the day, imagined that my taste and hearing were more than commonly quick. Certain I am that I felt myself more than usually strong and chearful. In a second trial, by continuing the inhalation longer, I felt a thrill in my teeth; and breathing still longer the third time, became so full of strength as to be compelled to exercise my arms and feet. Now after an interval of some months, during which my health has been materially impaired, the nitrous oxide produces an effect upon me totally different. Half the quantity affects me, and its operation is more violent; a slight laughter is first induced,[224] and a desire to continue the inhalation, which is counteracted by fear from the rapidity of respiration; indeed my breath becomes so short and quick, that I have no doubt but the quantity which I formerly breathed, would now destroy me. The sensation is not painful, neither is it in the slightest degree pleasurable. ROBERT SOUTHEY. [224] In the former experiments, Mr. Southey generally respired six quarts, now he is unable to consume two. In an experiment made since this paper was drawn up, the effect was rather pleasurable. V. _Letter from_ DR. ROGET.