Thus among the elastic fluids which he tried, he found sulphuretted hydrogen, the deutoxide of azote, chlorine and ammoniacal gas eminently deleterious; for introduced in sufficient quantity into the animal economy they uniformly cause death, whilst others, such as oxygen, azote, hydrogen, carburetted hydrogen, carbonic acid, oxide of carbon, and protoxide of azote do not produce death when introduced into the lungs, except by excluding the only mixture, that can support respiration; in no other way do they occasion death, at least in a sudden manner. If however, they are thrown quickly into the blood vessels, they cause death, but it is mechanically and in the same way as atmospheric air would do it. It should also be observed that these different gases do not all act in the same way when they are introduced into the lungs; the gaseous oxide of carbon destroys animals much quicker than azote or the protoxide of azote. They die also quicker in the proto-phosphuretted hydrogen, and even in the carbonic acid gas. There are also in the action of deleterious gases certain anomalies which have not hitherto been explained. Nysten injected, at three injections, into the veins of a dog of middle size thirty centimetres of sulphuretted hydrogen. The animal after the first injection, was agitated, and made powerful inspirations; the second produced convulsive motions and the third apparent death; but the next day he was entirely well. Now a less quantity of sulphuretted hydrogen carried into the organs of respiration and mixed with five or six hundred times its volume of air, would infallibly destroy the animal. [104] The composition of some of these vapours is better known at the present day; but there are others in which our means of analysis have been unable to detect the deleterious principle; thus in the _malaria_, which has depopulated the country in the neighbourhood of Rome, our chemists have as yet only found as constant elements, those which enter into the composition of atmospheric air. [105] It appears from the experiments of M. Desormes that the contact of sulphuretted hydrogen on the skin of an animal is immediately fatal. [106] We know that fine injections pass from the branches of the pulmonary artery into the divisions of the bronchia; and that even water, when pushed into the trachea, will return, at least a small quantity of it, by the pulmonary veins and arteries. Bichat thought that the gases absorbed in the lungs must pass through the mucous membrane; but this is not the case unless absorption takes place at the time they are in the bronchia, for the mucous membrane which lines the air-tubes does not extend into each bronchial lobule.