Mery had long since observed, that, in opening the abdomen of a dog, and puncturing the vena cava above the origin of the emulgents, as the vein become emptied of blood, it filled with air, which went to the right ventricle. Haller also observed that air entered into the veins of frogs and other cold-blooded animals in consequence of a wound of some large vessel. He has shown that it was from this source that was derived that which Redi, Caldesi, and Morgagni saw circulating in the vessels of these animals, since it is not observed, when the necessary precautions are taken to prevent its introduction. Nysten has made a great number of experiments upon the injection of elastic fluids into the veins, and the results which he has obtained accord perfectly with those which we have observed. He is not satisfied with injecting atmospheric air, he has introduced in the same way a great number of other gases. He has remarked, that among the gases not deleterious he can introduce, without causing death, a much greater quantity if these gases are easily dissolved in the blood. We cannot follow him in the detail of these experiments; we shall only relate a result relative to the colouring of the blood in the lungs. He has observed, that by injecting air into the vein, so slow as not to produce the death of the animal, the colouring of the arterial blood is rendered imperfect. He is satisfied, he says, that it is not owing to the embarrassment of the lungs. The injection of oxygen does not alter this colouring. The injection of azote completely prevents it; that of the oxide of carbon does not produce any change in it. I give these results from his work; I have not had occasion to verify them myself. [67] When air is introduced into the vena portæ, there is not only no ill effect at the moment of injection, but there usually follows no apparent effect on the animal. It is not the same when air is injected into the veins of the general system, with so much care as not to produce instantaneous death by the dilatation of the heart. The effects do not then appear till a long time after the injection; but they are wholly different from the primary effects which we have described. These consecutive symptoms from the entrance of air into the veins are, as Nysten has remarked, the result of an obstruction of the lungs produced by the accumulation of air in the last divisions of the pulmonary artery. The embarrassment in respiration often appears at the end of half a day, it becomes greater and greater, the bronchiæ are filled with a viscid fluid; and the animal usually dies on the third or fourth day. On examination of the body, no air is found in the heart or the vessels; but the lungs, instead of being pink-coloured, are greyish, tinged with brown, and loaded with frothy blood and mucus.