of arachnitis, though it is by no means a necessary accompaniment. The brain, in these cases of simple meningitis offers no appreciable derangement of structure, though the symptoms during life may have shown very manifestly that its functions were involved. The formation of pus in the course of arachnitis is not an occurrence of frequency, but it is necessary to bear in mind that it is a pathological fact. A remarkable instance of this occurred under our observation recently, at St. Mary's Hospital, in a young woman in whom sudden and unexpected coma supervened, and terminated, after thirty-six hours, in death. She had previously suffered from otorrhoea; but on her admission gave no evidence of cephalic disease, nor was any direct connection traced after death between the affection of the ear and the meningitis which was found to have caused her death. Here two yellow patches were discovered on each parietal surface of the brain, owing to an accumulation of pus spread out under the meninges; the microscopic examination of the fluid satisfactorily demonstrated the characters of pus.

Cases of meningitis are now and then met with, in which the arachnoid appears perfectly transparent and normal, while there is vascularity of the pia mater with subarachnoid effusion. We should here be inclined to assume an idiopathic affection of the pia mater, and it cannot be denied that the evidence in favor of primary and independent disease in that membrane, is stronger than any arguments adducible in favor of the same disposition in the arachnoid. We cannot blind ourselves to the fact that the latter differs much in its behavior from the serous membranes of the thorax and abdomen, in the rarity of inflammatory effusion occurring within what we must term the sac of the arachnoid, if we continue to look upon it in the same light as a serous membrane. It is highly desirable that anatomists should settle its normal relations, in order that the deviations occurring in morbid processes may receive the correct and proper estimation. Thus, with regard to the effusion occurring within the ventricles of the brain, which are commonly taught to possess an arachnoideal lining, it evidently offers many relations different from the arachnoideal effusions occurring on the surface of the brain; nor is it quite intelligible why the secretion into the cavity of the ventricles should so rarely be found to communicate with the superficial arachnoideal space. Kölliker, whose profound knowledge of anatomy and physiology renders him an authority in the matter, says: "Those who state that the arachnoid lines the ventricles of the brain, and the processes of the pia mater contained in them, suppose a thing that is impossible, viz., that the arachnoid passes through the pia mater, and invests the surface of the plexuses, which is actually an internal one."

If we examine the inflamed pia mater under the microscope, we shall find the smaller vessels studded with exudation matter, in the shape of minute oily-looking vesicles; we have seen it as in the adjoining drawing, so bounded by the outline of the vessel, that it seemed to lie within its coats; there is no à priori reason why it should not be formed in the vessels. We also see numerous so-called inflammation corpuscles,

1 Mikroskopische Anatomie von Dr. A. Kölliker, 1850, vol. ii. p. 501.

which would appear rather to be a peculiar aggregation of the exudation matter than distinct formations; they are sometimes possessed of a delicate envelop, at others they are devoid of it; they may be appro

Fig. 117.

Meningeal vessels invested and surrounded by exudation matter, and glomeruli or exudation corpuscles, from a young man, aged 34, who died in consequence of injury to the head, followed by meningitis; magn. 270 di.

priately compared to a mulberry-they generally, also, offer a brownish tint. We owe the knowledge of these corpuscles to Professors Gluge

Further specimens of the microscopic appearances of the vessels in meningitis.

and Bennett; the former was the first to show their connection with inflammation generally, the latter drew attention to their presence in inflammatory affections of the brain and its membranes.

Much confusion has arisen from the misapplication of the term hydrocephalus, as it has been used to designate a variety of diseases, simply on account of their resembling one another in a comparatively

accidental feature; and we would, therefore, follow in the steps of those authors who limit the term to the dropsical effusion of serous fluid within the cranium, unaccompanied by marked symptoms of inflammatory action during life. We have already seen that an accumulation of serum beneath the arachnoid, or within the ventricles, is a common feature in both acute and chronic meningitis; and though an affection of serious import, we have abundant evidence of the value of therapeutic proceeding in arresting and completely removing the disease and all its effects. Not so with what is commonly called chronic hydrocephalus, or what ought exclusively to receive the name of hydrocephalus, while certain forms of meningitis should designate the disease acute hydrocephalus; nothing is more liable to mislead the student, or to perpetuate error, than a want of precision in our nomenclature. We must never forget that the effusion of serum is only a product of morbid action; and that inflammation, mechanical obstruction, anæmia, blood-poisoning, scrofulous cachexia, diseased conditions essentially differing from one another, may each of them give rise to a secretion of fluid into serous cavities. It is erroneous, and likely to lead to the most injurious practice, if we apply a name to a symptom, by which it becomes identified with the most opposite diseases.

Whether we look upon the arachnoid as a serous membrane or not, and whether or not we continue to consider the lining of the ventricles as a prolongation of the external arachnoid, there is no doubt of the close resemblance between the structure of the latter, with this difference, that while the superficial arachnoid overlays the pia mater, the lining of the ventricles is in direct opposition with the gray matter of the brain. In examining the pathology of the brain, we shall have occasion again to allude to the ventricles, but it seems advisable to advert to some changes which occur in them at this part of our inquiry. Here, as in the superficial arachnoid, we see no traces of active congestion, even where we have the undoubted evidence of inflammatory action. Hemorrhage into the ventricles is invariably the result of injury to or disease of the brain, and the effusion of blood into them is stated by Dr. Bright to be the most rapidly fatal of any kind of apoplexy. It has already been mentioned that in meningitis it is common to find an increase in the ordinary amount of secretion of the ventricular fluid; but while this may be measured by drachms, the fluid accumulating in hydrocephalus reaches to several pints, and is commonly the result of defective action, not so much in the membrane as in the cerebral and general circulation. Though we fail to find a congested state of the vessels in the ventricular lining membrane, it often presents an indurated, thickened, and granular condition, indicative of previous inflammation. The septum lucidum, and the commissura mollis, are generally involved in the morbid processes occurring in the ventricles the former is more particularly liable to suffer in chronic hydrocephalus from distension; and yielding to the mechanical pressure, it becomes perforated, and allows of free communication between the two cavities. The granulations of the arachnoid occasionally become prominent, and even pediculated; at other times the inflammatory product is rather of an adhesive character, and the opposite sides of the

ventricles, especially the corpora striata, may then become agglutinated to one another.

It must be considered as one of the great goals which this and future generations of scientific inquirers have to pursue, in how far these and similar changes in the membranous or parenchymatous structures are to be attributed to dyscrasic conditions. The combined modes of research represented by the microscope and the test tube, must assist in solving many of the problems that yet puzzle the physician; and if there are various cachectic conditions differing essentially in their character, of which we have no doubt, we must hope to succeed eventually in demonstrating them more palpably than has yet been done, both in the living and the dead subject. That the rheumatic and gouty diathesis should produce their definite lesions within the cranium, as well as externally, can scarcely be denied; but we do not possess sufficiently satisfactory evidence. Purpuric spots are occasionally seen on the arachnoid, indicating a scorbutic crasis; but none of the crases have hitherto been shown to have such decided traces within the cranium as the scrofulous or tubercular. The frequency of meningitis in childhood is in a great measure due to this fact; and to it we may also in a measure attribute the great prevailing fatality, owing to the misconceptions that the term inflammation gave rise to; and which, therefore, seemed to necessitate antiphlogistic treatment of as active a character as if we had to deal with sthenic inflammation.

TUBERCULAR MENINGITIS.

The deposit of tubercle on the pia mater of the brain occurs in the shape of small miliary granules, resembling the Pacchionian bodies in

Deposit of tubercular matter in the Sylvian fissure of the brain of a child, aged 19 months, who died ten days from the first appearance of head symptoms, which were treated antiphlogistically. The white circular spots represent the tubercles, which were surrounded by highly congested blood vessels. The white deposit examined by the microscope showed granular matter and granular corpuscles varying in size.

appearance, but differing from them both in their site and in their microscopic relations. They are not seen on the free surface of the arach

noid; and, in fact, seem in no way connected with this membrane; a point which establishes a marked difference between it and the serous membranes of the thorax and the abdomen. They are found most frequently deeply within the Sylvian fissure, in the convolutions of the brain, and at the base; they are of the size of pins' heads, and appear in the form of gray granulations, imbedded among a vascular network; they are very rarely found upon the cerebellum. A careful examination is necessary, to prevent their being overlooked; but in a therapeutic point of view, it is most important that their presence should be duly appreciated, and that they should be taken as an indication of a state of the blood, requiring a different line of treatment from what ought to be adopted in meningitis, unconnected with the pathological condition of the fluids that tubercle implies. It is only by the aid of the microscope that we have been able positively to determine the real nature of these granulations, for they closely resemble a mere puckering of the membrane; seen under a power of three or four hundred diameters, their elements resolve themselves into the corpuscles peculiar to tubercle, possessing a faint outline, with granular contents, and surrounded by granular matter. The tubercular corpuscles must not be confounded with epithelium, which may be seen under the same field, and which is to be distinguished by the nuclei it contains, within which, again, one or two nucleoli are visible.

This form of meningitis is generally met with in connection with or secondary to tuberculosis of other organs; though we see it occasionally in the idiopathic form, as in the instance from which our delineation was taken, where no tubercular deposit was found in any of the viscera beside the brain. In the former case, the tubercular deposit may take place so insidiously as to offer no marked inflammatory symptoms during life; and it is only on the dissecting-table that the physician becomes aware of the cerebral disease. It must, therefore, be borne in mind that scrofulous children have a tendency to become afflicted in this manner; and it is an additional reason for watching them with care, and avoiding such debilitating measures as would be likely to encourage the dyscrasia. It is not our province to enter into the consideration of nosological or therapeutic inquiries, but we cannot avoid remarking that the frequency of tubercular deposit in the pia mater in children is a strong argument against those powerful depleting measures which inflammatory symptoms presenting themselves in the head of a young subject, are generally calculated to provoke.

HYDROCEPHALUS.

The irritation of the tubercular deposit is very liable to induce the secretion of serum, either beneath the arachnoid membrane, or in the cavities of the brain, and this leads us to the consideration of that formidable disease of childhood, hydrocephalus.

The etymology of the term indicates the main feature that characterizes the morbid condition, and, provided its application be limited to the class under consideration, it is not likely to mislead the practitioner, as