[77] We should be often exposed to commit great mistakes, if we always judged by this rule. The sensation is a very uncertain means of determining the organ that is primarily affected; this can be proved by numerous examples, we shall cite one only which relates to the brain. Nausea and vomiting are often, as is well known, among the first symptoms of cerebral affections; should we from this believe that the seat of the disease is in the stomach? Undoubtedly not: now, in syncope produced by a strong affection of the mind, there is no reason to suppose that the heart is affected before the brain, since the intellectual phenomena have necessarily preceded the sensation of joy or of sorrow which has produced the syncope. But to say that the brain was primarily affected, is not saying that its action ceased before that of the heart; and every thing, on the contrary, leads to the belief that the loss of the senses is a consequence of the suspension of the circulation.
[78] The syncope is produced in this case, from the sudden change in the circulation of the brain. But this change varies according to the seat of the effusion. If it be in the peritoneal cavity, the pressure that it makes interrupts the circulation in all the organs contained in the abdomen; the descending aorta is found compressed, and the blood, forced back towards the superior parts, accumulates in the sinuses and vessels of the brain. If the fluid be evacuated by puncture, the equilibrium is re-established in the different parts of the vascular system, the blood enters vessels which were before closed to it, it abandons in part those of the brain, and it is this sudden change in the circulation of the organ which produces syncope. If, on the contrary, the effusion be formed between the two layers of the arachnoides, and we can, as in spina bifida, evacuate the fluid by puncture, the vessels of the brain are immediately relieved of the pressure to which they had been subjected, and the blood, which before was forced back, towards the inferior parts, is driven forcibly into them; the change is, as must be perceived, the reverse of the preceding; but the result is the same, and syncope is produced in this case as in the other.