_d._ In many experiments made in the mercurial airholder on the capacity of my lungs under different circumstances, I found that I threw out of my lungs by a full forced expiration at temperatures from 58° to 62° cub. cub. in. in. After a full voluntary inspiration, from 189 to 191 After a natural inspiration, from 78 to 79 After a natural expiration, from 67 to 68 So that making the corrections for temperature, it would appear, that my lungs in a state of voluntary inspiration, contained about 254 cubic inches; in a state of natural inspiration about 135; in a state of natural expiration, about 118; and in a state of forced expiration 41.[197] [197] This capacity is most probably below the medium, my chest is narrow, measuring in circumference, but 29 inches, and my neck rather long and slender. As the exhausted capacity as well as impleted capacity of the internal organs of respiration must be different in different individuals, according as the forms and size of their thorax, fauces, and bronchia are different, it would be almost useless to endeavour to ascertain a standard capacity. It is however probable, that a ratio exists between the quantities of air inspired in the natural and forced inspiration, those expired in the natural and forced expiration, and the whole capacity of the lungs. If this ratio were ascertained, a single experiment on the natural inspiration and expiration of common air, would enable us to ascertain the quantity of residual gas in the lungs of any individual after a compleat forced expiration.[198] [198] Dr. Goodwyn in his excellent work on the connexion of life with respiration, has detailed some experiments on the capacity of the lungs after natural expiration. He makes the medium capacity about 109 cubic inches, which agrees very well with my estimation.—page 27. V. _Additional observations and experiments on the Respiration of Nitrous Oxide._ _a._ Having thus ascertained the capacity of my lungs, and the composition of the residual gas of expiration, I proceeded to reason concerning the experiments in section III, on the respiration of nitrous oxide. In Exp. I. nearly 100 cubic inches of nitrous oxide, making the corrections on account of the common air, were respired for half a minute. In this time, they were reduced to 62 cubic inches, which consisted of 3,2 carbonic acid, 29 nitrous oxide, 4,1 oxygene, and 25,7 nitrogene.