_Rozier_ and _Sir Humphrey Davy_ conclude from their experiments that carbonic acid kills by exciting a spasmodic action, in which the epiglottis is closed, and the entrance of this fluid into the lungs altogether prevented. _Dr. Babington_ appears to entertain a different opinion, (see “a case of exposure to the vapour of burning charcoal,” Medico-Chirurg. Trans. vol. 1, p. 83,) and asks how we shall explain the fact, that the loss of irritability in the muscles of animals which have been destroyed by immersion in noxious airs, is comparatively greater than in such as are hanged or drowned, unless we suppose that the carbonic acid exerts a deleterious influence on the nervous and muscular systems? The farther consideration of this subject will be more properly entertained under the head of poisons. Footnote 49: Comparative anatomy would furnish us with a variety of beautiful arguments, if it were necessary, to support these views. The bird whose muscular exertion is so great during its flight, is provided with a more than ordinary extent of pulmonary apparatus; and amongst insects we find that many of the _coleopterous_ species disclose avenues of air, in the act of flying, which, in their quiet state, are closed by the cases of their wings, thus procuring for themselves a larger supply of oxygen, at a period when from their exertions they most require it. Flat fish who, having no swimming bladder, remain at the bottom, and possess but little velocity, have gills that are quite concealed, while those who encounter a rude and boisterous stream, as trout, perch, or salmon, have them widely expanded. For further observations upon this subject, the author begs to refer to his paper in the 10th vol. of the Linnean Transactions, entitled “On the Physiology of the Egg,” by _J. A. Paris, M. D._ &c. Footnote 50: