1. Hyperoemia, - Ancemia

Congestion of the brain is a very common appearance; and it is generally associated with a corresponding degree of congestion of the pia mater.

Its anatomical characters are - first, injection of the cerebral vessels, and the appearance of an unusual number of bloody points on the cut surface of the brain. The gray substance, when but slightly congested, exhibits some shades of red, and in young persons, and especially in the child, it presents distinctly a bright-red color. In intense congestions, the fibrous substance loses its clear whiteness, and, in children particularly, acquires a grayish-red, and in some very rare cases a red hue. The brain is swollen; but its increase in size is distinguished from that enlargement which occurs in hypertrophy of the brain (p. 283), by the turgid condition which has evidently given rise to it. Bouillaud has called attention also to a firmer consistence of the brain, as occurring in congestion; it is, however, by no means a constant, and still less an essential appearance.

Hyperemia of the brain takes place in the course, or follows as a consequence, of very various acute and chronic diseases. It is sometimes active, sometimes passive; and it may be mechanical. Occasionally it arises from none of these causes, but comes on independently; and then it may be transitory or persistent, or may recur and become habitual. Congestions of the last kind occur especially in childhood and at the period of puberty. Hyperemia is an important condition when it is produced and kept up by structural disease, as may readily be observed in all new formations in the brain and cavity of the cranium, and especially in highly vascular turgid structures, like cancer of the brain. Those congestions, also, which result from the existence of a vacuum in cases of atrophy of the brain, and which were referred to at page 287, are of considerable importance.

Among the consequences of hyperemia, slight and repeated congestions may be mentioned as leading, especially in childhood, to hypertrophy of the brain. Another frequent and a fatal consequence of it is oedema of the brain, which may be acute or chronic, according to circumstances, and attended with an effusion of serum into the ventricles. Moreover, there is no question that hyperaemia proves fatal in cases known as vascular apoplexy. Such a result is met with in the course of many acute diseases, which give rise to local congestions. Diseases of the brain itself, especially hypertrophy, and different new formations within the cranium, the pressure of which displaces the organ, often produce sudden death by the congestion to which they give rise; and, lastly, diseases of the lungs, the heart, and the great vessels, which obstruct the circulation, and especially those which prevent the free current of venous blood towards the heart, are frequently terminated by mechanical congestions.

It is a question of much importance, whether the frequent cases of sudden and unexpected death in previously healthy persons, in which the only or the principal post-mortem appearance is a certain amount of congestion, are produced by this congestion, and are to be considered as cases of palsy of the brain from hyperaemia, whether in fact such congestions are sufficient to cause death or not.

a. In answer to this question, I may remark, that, in a certain number of the cases referred to, this congestion is the only morbid appearance in the body, and has reached a degree which, in the present state of our knowledge, justifies the conclusion that the brain has been paralyzed by it. But the number of such cases is comparatively very trifling.

b. In a considerable number of cases, again, moderate congestion of the brain is found associated with hyperaemia of the lungs. It is scarcely possible to say which of these conditions was the primary, and which the secondary, whether they did not spring both together from the same source, and which of them actually produced death. But as it is quite common for congestion of the lungs to be the only morbid appearance in cases of sudden death, and as it is decidedly the more marked appearance when cerebral hyperaemia is present also; we may, in determining the mode in which death has taken place in these cases, conclude that the congestion of the brain is usually of secondary importance.

e. Besides cases of these two kinds, there is still a number of others in which all that is discovered upon examining the body is so slight a congestion of the brain, that it would not be thought of, if any other morbid appearance presented itself. The mode of death in most cases, and especially of sudden death, is still too little understood to allow us to say positively whether these congestions are the efficient cause of it, or are merely accidental phenomena, and dependent on the agony: but perhaps we may say that there is an individual tendency of the brain to palsy (Lähmungsfahigkeit), just as there is an individual liability to death (Sterbensf ähigkeit), and so incline rather to the former opinion that in certain persons such congestions may prove fatal.

Persons of what is called an apoplectic habit, are far less subject to congestions of the brain, and particularly to vascular apoplexy, than those of an opposite conformation, and than children.

Anoemia of the brain is a highly important condition, and one very dangerous to life. It is usually a local part of the general bloodless-ness produced by hemorrhage, or by the consumption of the blood which takes place in the course of acute and chronic diseases. A very remarkable instance of anaemia is that which arises from the contraction or obliteration of the vessels, which convey blood to the brain: it is affected by deposition on their inner walls, and may occur at any part of their trunks, or at their orifices in the arch of the aorta. (See Anomalies in the Calibre of Arteries, vol. iv.) It is a very important condition also when it results from hypertrophy, swelling, compression, or displacement of the brain in cases of sanguineous apoplexy, inflammation, yellow softening, or new formations.