Whatever be the manner in which the pulmonary functions are interrupted, it is always the interruption of the chemical changes, which troubles the functions of the brain.[91] What I have said upon this point with respect to the heart, is exactly applicable to the cerebral mass: I shall not repeat it. It remains to shew by experiment, and the observation of diseases, that when the chemical functions of the lungs are put a stop to, it is the black blood which interrupts the action of the brain and that of the nervous system. In the first place let us examine our experiments. I first began by transfusing into the brain of an animal, the arterial blood of another, that this essay might serve as a point of comparison for others. Open one of the carotids of a dog; tie the extremity towards the brain, and fasten a tube to that which is next the heart; then open the carotid of another dog, tie the extremity of the vessel next the heart, and fix the other end of the tube into that which is next the brain; then let the assistant, who meanwhile should have had his fingers upon the artery of the first dog underneath the tube, remove his compression, and the carotid of the second dog will be seen beating under the impulse of the blood injected from the heart of the first. This operation fatigues but little the animal which receives the blood, particularly if one of the veins be previously opened, to prevent too great a fulness of the vessels. It will live very well afterwards. This experiment has been often repeated, and always with the same results. After this experiment, I opened the carotid, and the jugular vein of another dog, and after tying the extremity of the carotid next the heart, received the blood of the jugular into a warm syringe, and injected it into the brain. The creature appeared immediately to be agitated, breathed quickly, and seemed to be in a state of suffocation, similar to that of asphyxia. Its animal life became entirely extinct; the heart, however, continued to beat, and the circulation to go on for half an hour afterwards; at the end of which time the organic life was terminated also. This dog was of a middle size, and about six ounces of blood were injected with a gentle impulse, for fear of that being attributed to the shock, which ought to have been the result of the nature and composition of the fluid. I repeated this experiment upon three dogs the same day, and afterwards at different times upon others; the result was invariable, not only as to the asphyxia of the animal, but even as to the concomitant appearances.