The circumstances which affect the amount of blood in the vessels are the mode of douh and the position in which the head has been laid after death. Death by asphyxia, whether rapid or gradual, favours the accumulation of blood in the vessels of the brain. Convulsions preceding death likewise cause turgescence of these vessels. Any impediment to the circula tion through the heart has the same effect, but to the greatest degree when the impediment is much felt on the right side of the heart.
The position of the head after death affects the vascular fulness by favouring the accumula tion of blood in the most dependent parts. From this circumstance and from the custom of placing bodies on the back, we always find the posterior lobes of the cerebral hemispheres and the cerebellum most filled with blood, and it is OT/ this account that the straight and other posterior sinuses of the dura mater are always filled with blood.
The quantity of fluid around the brain and spinal cord is least in the young and greatest in the old : it is influenced by the bulk of the brain or spinal cord, sometimes disappearing entirely when the brain is so large as to fill the cranial cavity ; it is inversely as the quantity of blood, and therefore is considerable in cases of anmmic brain, unless the bulk of the organ have increased from some other cause. Slow deaths from chronic disease favour the accu mulation of this fluid by diminishing the supply of blood to the brain. In phthisis and other lingering maladies there is almost always a con sidemble amount of subarachnoid fluid. The practitioner should bear in mind that the ab sence of subarachnoid fluid is always abnormal, and is in general due to an enlargement of the brain from hyperxmia or from sorne other cau Softening of the nervous matter rnay pseudo-rnorbid. The spinal cord softens v
soon after death ; but if examined wit twenty-four hours it exhibits more density th the brain. With the advance of decompositi the cord becomes extremely soft and al diffluent. In the brain the pseudo-m softening is colourless, and may be r mistaken for disease. That the brain i prone to imbibe fluids is shown by Dr. son's experiments. The brains of shee allowed to remain for a certain num hours in a given quantity of water, whi rapidly absorbed. The weight of the was increased proportionally to the quanti water which had been imbibed, and the most exposed to the fluid were found in cued state. In one instance the brain prived of its rnembranes on one side, hours after death it was immersed in a mi composed of equal parts of ox-bile and wa It weighed three ounces, seven drams, and fo grains when prepared for experiment. A remaining in the mixture thirty-six hours weighed eight ounces and one dram.° Th experiments show that the brain readily imbibes fluid, and that parts in the vicinity of and bathed in fluid may present a pseudo-morbid softening from such imbibition. The fact, thus ascertained, serves to account for the more frequent occurrence of softening in the fornix and septum lucidum than in other parts of the brain. It is obvious that pseudo morbid softening of this kind vvould occur only in parts within the ventricle or in the cerebral substance forming their walls, or on the surface of the brain itself, and that it is less likely to be limited to one side than the morbid softening. Now and then, however, in cases of general anasarca, where the blood is in a very watery condition and much fluid is effused, the brain exhibits a softened state from the imbibition of this fluid.