The researches of Dr. JAI. Bennett,of Edin burgh, are among the most important contribu tions to the morbid anatomy of the brain of late years. I think he has clearly established that the great characteristic of inflammatory soften ing is the presence of exudation corpuscles about the minute vessels, and among the ele ments of the softened cerebral tissue. This is in in the vast majority of instances accompanied with discoloration, which sometimes is due solely to the dark colour of the exudation cor puscles themselves. When these corpuscles are not present, and especially when the soft ened portion of brain is free from colour, then we must regard the lesion as non-inflammatory, the result of imperfect nutrition, or as produced by physical causes coming into operation shortly before • or after death. As the same process of softening which involves the cerebral structure often extends to the minute vessels, small extra vasations, constituting the capillary apoplexy of Cruveilhier, frequently occur where no indica tions of inflammation exist ; in such instances the softening, although non-inflammatory', may be of a yellow colour from the effused colouring matter of the blood.
I cannot agree with Dr. Bennett in regarding svhite softenings as generally post mortem, and the result of maceration in serum. The soften ing of very thin parts, such as the fornix and septum lucidum, 710 &Uhl, is frequently of this character. But I have seen many instances of white softening of other parts of the brain which were not exposed to the physical condi tions calculated to produce such a change of consistence.
Inflammatory softening occurs most fre quently in parts which are near the great vascu lar surface of the pia mater ; the convolutions and the white matter of the centrum ovale, the corpus striatum, and the optic thalamus are the most common situations of this lesion. In thirty-three cases collected by Durand-Fardel the softening was situated in the convolutions in thirty-one, and in nine of them the convolutions were the sole seat of softening. The following table svill illustrate the statement above made ; it represents the results of fifty-three c-ases col lected from different sources.
Convolutions and white substance 22 Convolutions alone 6 White substance alone 5 Corpus striatum and optic thalamus 6 Corpus striatum alone 11 Optic thalamus alone 4 Pons Varolii . • .. . 3 Crus cerebri 1 Corpus callosum 1 Wails of the ventricles, septuna........— Fornix Cerebellum • Suppuration.—From what has been stated in the previous paragraphs it is Plain that the most important sign of inflammation of the brain is red softening. Infiltration of pus is rare. Dr. Bennett states that in no single instance of numerous examinations made by him could softening be traced to the presence or infiltration of pus. This is a direct refutation of Lalle
mand's assertion that this form of softening owes its colour to the infiltration of pus. Pus, how ever, is sometimes collected into a cavity in the biain, forming an abscess. An excavation of greater or less size is formed in the substance of the brain, and this is lined by a yellowish mem braniform layer, which resembles either lymph in an expanded form, or the purulent matter itself in a less liquid form, compressed into the form of a membrane by the accumulated liquid.
Pus in the brain is of slow formation, and has often become collected in considerable quantity before it betokens its presence by any symptoms. Sometimes we have the opportu nity of examining it before it has acquired the yellow Colour and oily consistence of laudable pus. In this stage it may be mistaken for some malignant formation ; it is whitish, semi-solid, and sometimes mixed with strealcs of blood. Its true nature may be recognized by microta scopical examination, which discloses the cha racteristic pus globules with little or no liquor puris, and by mixing some of it with liquor potassm, when it becomes converted into a viscid material resembling white of egg.
Pus in the brain is frequently of a green colour, and very commonly exhales an ex tremely fetid odour.
The cerebral matter around the purulent col lection is either somewhat indumted or it is in an cedematous state, or in one of inflammatory softening. When in this latter state the ab scess is not so defined ; the softened cerebral matter around it is broken up and mingled with pus; this, however, is rare.
An abscess of the brain rnay open upon the exterior and so evacuate its contents. This may occur either into the nose through the cribriform plate, or into the tympanic cavity or the external auditory meatus. It is sometimes difficult to determine whether inflammatory dis ease had arisen in the ear, extending to the bmin and exciting the formation of abscess, or whether the abscess already forrned in the brain had not burst into the ear. A cerebral abscess may empty itself into either of the ventricles.
Abscesses are most commonly found in one of the cerebral hemispheres, or in the cerebel lum ; they are very rarely met with in other parts of the bmin. Sometimes collections of pus form upon the surface of the brain between the pia mater and the grey matter of the cere bral convolutions. And pus or puriform mat ter is frequently found betvveen the arachnoid and pia meter, where there has been inflamma tion of either or of both those membranes. This is most common in children.