In this way the symptoms of asphyxia are not the symptoms of syncope. In the latter the cardiac and cerebral actions are suspended at the same instant, in the former the heart survives, as in cases of strong concussion of the brain for many seconds. It follows, that in asphyxia, the different organs do not cease to act, because the heart has ceased to supply them with blood, but because it no longer supplies them with that sort of blood by which they can be stimulated. 2dly. If the trachea of an animal be stopped, and an artery opened, the colour of the blood which it emits, will gradually be changed, and at last become as black as that of venous blood. Now, notwithstanding this phenomenon, which is as apparent as it can be, the fluid for some time afterwards is thrown out full as strongly as it would be, were it red. I have seen a quantity of black blood discharged in this way, more than sufficient to kill the creature from hæmorrhage; were it not already dead, in consequence of its asphyxiated state. 3dly. In the last-mentioned experiment, it may, indeed, be alleged, that some remains of air in the air cells, might, as long as the black blood continued to flow, have communicated to it a principle of excitement; but to put it out of all doubt, that the venous blood does really pass into the aortic ventricle, unaltered in its passage from the corresponding cavity, the air may be entirely pumped out of the lungs with a syringe, by exposing the trachea, in the first place, and then adapting the instrument to the transverse section of the tube; after this, let the carotid be opened; now as soon as the red blood contained in this artery is exhausted, the black blood will succeed to it, and that, without undergoing a variety of gradations in colour; in this case also for a time, the jet will be very powerful, and only be gradually weakened; but if the black blood were not an excitant to the heart, its interruption should be immediate. 4thly. The following is another proof of the same nature. Expose the breast on one side by sawing exactly through the ribs before and behind: when this is done, the lungs on that side will collapse. Proceed to open one of the pulmonary veins; fill a syringe warmed to the temperature of the human body with venous blood, then push it into the red-blooded ventricle. Now, according to the common opinion upon the subject of asphyxia, such fluid should at least diminish in a sensible way, the movement of that cavity, notwithstanding which, in four successive experiments, I could not observe any such diminution. On the contrary, in one of them, on pushing the piston, the strokes of the heart were augmented in number.