As the meningeal tuberculosis is usually merely a part of a general dis tribution of " tubercle" over the body, the gray granulation is found also in other organs and serous membranes, and has been noticed by Cohnheim on the vascular tunic of the retina.
The vessels of the pia mater are engorged, and the membrane is cloudy and often adheres closely to the surface of the brain, so that when torn away it brings with it small particles of the cerebral substance. More or less copious yellowish or greenish jelly-like exudation is found in the meshes of the subarachnoid tissue, often running in streaks along the course of the vessels. It is usually confined to the base of the brain.
An almost invariable feature in these cases is the ventricular effusion. This is so constant a phenomenon that it used to be looked upon as con stituting the essence of the disease (hence the name of " acute hydroceph alus," by which the affection was formerly distinguished). The quantity is often very considerable. It may distend the ventricles, flatten the con volutions, and even cause rupture of the septum lucidum. In appearance it is clear, or turbid with suspended flocculent particles, or tinged with blood. The cerebral substance around the ventricles is softened. The softening is attributed by some writers to the effects of mere imbibition and maceration. Others ascribe it to inflammation. Dr. Bastian is inclined to the opinion that it is often the result of degenerative changes set up by the anasarcous condition of the central brain tissue ; and tkat both the ventricular effusion and the softening result from the pressure of the blood in the overloaded veins and capillaries, and in some cases, perhaps, from actual thrombosis in the veins of Galen.
Besides this softening of the central parts of the brain, the cortical substance is inflamed as well as the pia meter which invests it, and some times spots of softening with capillary have been seen in the substance of the corpora striate and the optic thalami. As a rule the brain substance is pale and bloodless, and the greater the ventricular effusion the whiter and softer the cerebral tissue becomes.
The above morbid appearances are singularly constant in cases of tubercular meningitis. The granulations, the exuded lymph, the vascular engorgement, the superficial encephalitis, the ventricular effusion, and the softening of the ventricular walls are almost invariably to be dis covered when death has occurred from this disease. In addition, signs of
more or less general tuberculosis are also present. These in infants are usually well marked, and almost all the other organs and serous membranes may be sprinkled over with the gray granulation. In older children, how ever, the meningitis occurs before nutrition has been appreciably impaired, and is perhaps itself the earliest indication of the diathesis. In such eases the other organs may be healthy, and the granulations scattered over the pia meter may be the only morbid formation to be discovered in the body. Usually, however, signs of the cachexia are perceptible in other organs, and sometimes the granulations are so equally and generally distributed that we cannot but wonder at the little interference the constitutional and local states had exercised upon the general health of the patient.
Symptoms.—The onset of the illness is almost always preceded by a pro dromal period of variable duration. This is to be expected in every malady where disease of special organs is dependent upon a general diathetic state. In all forms of tubercular disease it is a rule which is rarely infringed that local symptoms are preceded by phenomena indicating the general disorder of nutrition induced by the constitutional cachexia.
The premonitory symptoms vary in severity, partly according to the age of the child, partly according to the previous state of his health, and partly according to the intensity of the diathetic influence to which he is subject. In young babies, in whom the disease invariably occurs at the end of an attack of general tuberculosis, the head symptoms are preceded by others indicative of the disease from which he has been suffering. In older children, especially in those in whom the diathetic tendency is com paratively feeble, the prodromal period may be short and the symptoms trifling. Therefore in different cases we may find marked variety in the duration and severity of the symptoms which immediately precede the outbreak of the disease.