Nitrogene 71,7 Oxygene 22,5 Carbonic acid 4,5 This experiment I likewise repeated four or five times, with very little difference of result, and there always seemed to be a small diminution of nitrogene. I made no corrections on account of the residual air of the lungs in these processes, because there was every reason to suppose that it was always of similar composition. _c._ Before I could ascertain whether similar changes were effected in atmospheric air, by natural inspirations as by forced ones, I was obliged to practise respiration in the mercurial airholder, by differing the conducting tube to communicate with the atmosphere till I had attained the power of breathing in it naturally, without labor or attention; I then found by a number of experiments, that I took into my lungs at every natural inspiration, about 13 cubic inches of air, and that I threw out of my lungs at every expiration,[201] rather less than this quantity; about 12¾ cubic inches. [201] The diminution of air by single inspirations, was particularly noticed by Dr. Goodwyn. The mean composition of the 13 cubic inches of air inspired, was cub. in. Nitrogene 9,5 Oxygene 3,4 Carbonic acid 0,1 That of the 12,7 of air expired Nitrogene 9,3 Oxygene 2,2 Carbonic acid 1,2 These results I gained from more than 20 experiments, so that I could not possibly entertain any doubt of this accuracy. I found, by making a person observe my respirations when I was inattentive to the process, that I made about 26 or 27 natural inspirations in a minute. So that calculating from the above estimations, it would follow, that 31,6 cubic inches of oxygene were consumed, and 5,2 inches of nitrogene lost in respiration every minute, whilst 26,6 cubic inches of carbonic acid were produced. To collect the products of a great number of natural expirations so as to ascertain whether their composition corresponded with the above accounts, I proceeded in the following manner. I fastened my lips tight on the mouth-piece of the exhausted airholder, and suffering my nostrils to remain open, inspired naturally through them, throwing the expired air through my mouth into the airholder. In many experiments, I found that in about a half a minute, I made in this way 14 or 15 expirations. The mean quantity of air collected was 171 cubic inches, and consisted of cub. in. Nitrogene 128 Oxygene 29 Carbonic acid 14 Comparing these results with the former ones, we find the mean quantities of air respired in equal terms rather less; but the proportions of carbonic acid, nitrogene and oxygene in the respired air, nearly identical.