The intimate relation subsisting between the pia mater and the brain, and the frequent coexistence of disease in the latter with that of the former, render the affections of the pia mater those of the greatest importance. In accordance with what has been said of the arachnoid, and in opposition to the general relations of subserous tissue to serous membranes, the most important processes that occur in this situation, viz., those attended with exudation, greatly preponderate in the tissue of the pia mater.

1. Diseases Of Texture

1. Congestion And Its Consequences: - Hemorrhage

There is no question that congestion of the pia mater (commonly called congestion of the membranes, or inner membranes of the brain) is a very frequent occurrence; and we have already (p. 252) arrived at the same conclusion from our observations on the arachnoid. Yet, on the whole, if we except the "post-mortem" congestion of the pia mater covering the posterior lobes of the cerebrum, any considerable degree of congestion is far less commonly met with in the dead subject than is usually supposed; and there is, perhaps, no respect in which moderation in estimating appearances needs so much to be impressed upon the unpractised observer as in regard to the quantity of blood contained in the vessels of the pia mater: as a general rule, a very moderate injection of these vessels is erroneously looked upon as congestion.

The marked congestions which are met with in the brain and its membranes in very delicate children form an exception to this rule. Much interest attaches to these instances, from their being associated with more or less striking general plethora in children who are usually emaciated.

The congestions are, in general, active, or mechanical, i. e. resulting from disease of the heart, or obstruction in the lungs: sometimes they are passive. They are generally combined with a corresponding degree of congestion of the brain; and sometimes they destroy life, either of themselves, as vascular apoplexy, or by causing an effusion of serum into the tissue of the pia mater and substance of the brain.

The terminations and consequences of congestions vary according to the frequency and the duration of their cause. They consist of thickening and condensation (increase of volume) of the pia mater and arachnoid, of permanent infiltration of the former, and a varicose condition of its vessels. Such a state of the inner membranes is well marked after the congestions which are produced by continued and forced exertion of the mind, or by repeated intoxication, especially with alcoholic drinks. Congestions from the latter cause leave behind them an extremely varicose state of the vessels.

The (mechanical) congestions, infiltrations, and thickenings which the pia mater suffers when atrophy of the brain has formed a vacuum within the skull, also require particular notice in this place.

Spontaneous hemorrhages into the tissue of the pia mater (apoplexy of the vascular coat), though they rarely take place in adults, are frequently met with in new-born children and in the delicate period of childhood. In the latter, the part which mostly suffers from hemorrhage is the pia mater at the base of the brain. Cases of this kind must be distinguished from those in which the pia mater is infiltrated with the blood that escapes from an apoplectic spot, whether peripheral or deeply seated. Except in some rare instances, in which a large vessel, or an aneurism of one of the large arteries is ruptured, the source of the bleeding is the fine vessels of the pia mater. Hemorrhages which result from the skull being shattered, or otherwise injured, are mostly accompanied with bruising and hemorrhage on the surface of the brain.