It is easy to prove that the movement of the blood is necessary to the life of the brain. Expose the brain of an animal in part, and tie the carotids. In such case the cerebral movement will be sometimes weakened, and then the animal will be stupified, at other times the vertebral arteries will exactly supply the place of the carotids, and then there will be nothing deranged in the principal functions of the brain; for there is always a relation existing between the alternate rise and fall of the cerebral mass, and the energy of life which it displays.[58] In general, the obliteration of the carotids is never suddenly mortal. Animals will live without them, at least for a certain time. I have kept dogs in this state for several days and have afterwards made use of them for other experiments: two however died in the course of six hours, after the application of the ligatures. After having made the above experiments which go very far to the establishment of the principle which I am labouring to prove, let a piece of the cranium be taken from another animal and tie the vertebral and carotid arteries. The movement of the brain will then be entirely interrupted and the animal immediately die. The impulse, which proceeds then from the influx of the blood into the brain, is a condition essential to the functions of this organ, but other proofs may be adduced, for the establishment of the truth of this assertion. 1st. There are a number of compressions, which can only act by preventing the brain from being duly affected by such impulse. A collection of pus, or blood, will often put a stop to all the functions, which relate to the perception, memory, and voluntary motions of the individual. Let such compression be removed and his sensibility will immediately re-appear. In such case, it is manifest that the brain was not disorganized, but only compressed, and in a state incapable of being excited by the heart.[59] I do not think it necessary on this subject to cite cases. All authors, who have treated of wounds of the head, are full of them. I shall content myself with remarking, that the same effect may be artificially produced in our experiments upon animals, and that accordingly as the brain is compressed or free, the creature will be insensible, or the contrary. According to the degree of the compression, will be the degree of the stupor.