Hyperemia and Anamia.—An organ so largely supplied with blood as the brain, is liable to variations in the amount of that sup ply under various circumstances. It is unne cessary to recapitulate here the arguments already adduced to show that the opinions of those who maintain that the quantity of blood in the brain cannot vary, is erroneous. Indeed it is much to be wondered at how persons accustomed to inspect the brain post mortem could have adopted such a doctrine.
In the greatest degree of 14perwmia of the brain, all the vessels of the organ are full ; the veins which lie between the convolu tions are full; the vessels of the pia water are fully injected. Often there are diffused extra vasations through the areolm of this membrane, causing a red blotch over more or less of the surface of the brain. The grey. matter of the convolutions is extremely dark in colour, and if a small portion of it be examined under the microscope the minute vessels which abound in it are found distended with blood. On the sur face of a section of the white matter numerous bloody points are found, being the orifices of vessels cut across. These points are sometimes very large; sometimes they are surrounded by sinall extravasations of blood, proceeding from the rupture of some small vessel. In this state of the brain the vessels of the choroid plexus Ind of the velum interpositum are very full, md also those of the dura meter.
Cerebral hyperxmia is geuemlly caused by some obstruction to the free return of the blood to the right side of the heart. IIence we see it always after death by asphyxia. and very com monly in cases of disease of the heart. When the breathing has been seriously impeded just before death, there will always be considerable hypermmia of the bmin. Hence in judging of the nature of a cerebral hyperremia, the anato mist may be materially assisted in coming to a, correct conclusion if he can ascertain the cause of death and the symptoms immediately pre ceding it; a fact which clearly denotes how little is the value of mere dissection of morbid parts, unassociated with some knowledge of the symptoms manifested during life.
In the bodies of persons dead of epilepsy, during or immediately after the epileptic fit, there is always cerebral hyperxmia. In these cases the hypermmia is due to the retardation and obstruction of the venous circulation, occa sioned by the convulsive struggles of the pa tient and the resulting impediment to respira tion. It may be caused, likewise, by au in
creased attraction of blood to the organ taking place at the moment of the occurrence of the fit. For the same reason, whenever death is ushered in by convulsions, the brain will be found in a state of congestion, the amount of which will vary with the quantity of blood in the body. Whatever may be the condition of the brain prior to the epileptic paroxysm, it is always in a rnore or less congested state during and immediately after it. The too prevalent notion that cerebral congestion is the cause of the epileptic paroxysm has but little foundation, while there is abundant evidence to prove that the epileptic paroxysrn may give rise to cerebral congestion. It is well known that animals bled to death die in convulsions ; and many cases of puerperal convulsions are clearly caused by excessive loss of blood resulting from parturition.
Hyperwmia of tile brain is frequently found after death from depressing and exhausting maladies, typhus fever, &c., all diseases of the low typhoid type, and in cases of general paralysis. The powers by which the circulation is carried on in the vessels are greatly depressed, and the blood accumulates in them, especially in the veins.
I know of no means of distinguishing active front passive hypermmia excepting probably that the capillaries may be more injected in the former and the veins more filled in the latter. To enable the anatomist to make a correct dis tiuction, the detail of symptoms during life must be called to his assistance.
Antesnia.—This condition, the opposite to that last considered, is very cornmon. It is frequently met with in children, and in such cases is accompanied with more or less of serous fluid, either in the subarachnoid space or within the ventricles. The brain of the ill nourished strumous child is generally an atomic brain.
Anwmia of the brain occurs when death has been caused, whether quickly or gradually, by the loss of blood. It is also preseut when the hmt, oppressed by some disease affecting its own structure, fails to propel the blood with its proper force to the brain. The delirium which comes on in rheumatic fever, when pericarditis or endocarditis commences, is indicative of an atimmic state of the brain; and in some in stances in which I have had the opportunity of examining the brain, when the patient died in this delirium, I have found marked and obvious anmmia of this organ.