The most characteristic lesion is a fibrinous or purulent exudation in the meshes of the pia mater. American physicians described it as early as 1806 in such terms as these: "The dura mater and pia mater in several places adhered together and to the substance of the brain; ... between the dura mater and the pia mater was a fluid resembling pus" (Danielson and Mann). In 1810, Bartlett and Wilson found "an extravasation of lymph on the surface of the brain;" and in the same year Jackson and his colleagues, after describing the congestion and serous effusion found within the cranium "in those who perished within twelve hours of the first invasion," state that the arachnoid and pia mater present an effusion between them of "coagulated lymph or semi-purulent lymph" both on the convexity and at the base of the brain. These descriptions correspond in all respects with those of Mathey relating to the epidemic at Geneva in 1805, for he says: "The meningeal blood-vessels were strongly injected. A jelly-like exudation tinged with blood covered the surface of the brain; ... on its lower surface and in the ventricles a yellowish puriform matter was found." Such lesions have been described by a long line of observers—by Wilson in 1813, Gamage in 1818, Ames and Sargent in 1848; by Squire, Upham, and a host of others since 1860 in the United States, and by Tourdes, Gilchrist, Ferrus, Wilks, Gordon, Banks, Gaskoin, Niemeyer, Burdon-Sanderson, and many more in Europe.
It is evident, therefore, that in a certain number of fatal cases only sanguineous congestion of the membranes of the brain and spinal cord are found, and in certain others—constituting, it may be added, nine-tenths of the whole number—evidences exist of cerebro-spinal meningitis. Hence the natural conclusion is that the congestive lesions represent the first stage of a process which if prolonged and perfected occasions the lesions peculiar to inflammation. For the development of the latter two factors would seem to be essential—not only a fibrinous condition of the blood, but also sufficient time for exudation to occur. But when we come to study the actual results of examinations post-mortem, it is found that the duration of the attack does not determine absolutely the nature of the lesions. On the one hand, in a case which terminated fatally after a week's illness there was found reddish serum between the arachnoid and the pia mater and in the lateral ventricles, with intense injection of the pia mater of the base, medulla oblongata, and upper part of the spinal cord, but no exudation of lymph.49 And, on the other hand, numerous cases have been published in which, although death occurred within twenty-four hours from the onset of the attack, coagulated lymph and also pus were found upon the brain and spinal marrow. For example, during the winter of 1861-62, in the army, that then lay near Washington, D.C., a soldier was attacked with a chill, severe fever, and headache, followed by opisthotonos and repeated convulsions before his death, which occurred in about twenty-four hours. No eruption or discoloration of the skin is mentioned in the history. On examination there was found beneath the arachnoid a thin layer of lymph and abundant exudation over the posterior lobes of the cerebrum, and also at the base of the brain and on the medulla oblongata.50 In a case reported by Gordon51 the entire duration of the illness was under five hours, and after death the cerebral arachnoid was more or less opaque, and in some spots had a layer of very thin purulent matter beneath it. And, again, not only may the symptoms belonging to blood-dissolution be consistent with a certain prolongation of life, but also with decidedly inflammatory tissue-changes. Thus, in another case of Gordon's the duration of the illness was at least six days, and the patient presented all the characteristic symptoms of the disease, including "a most wonderful and uniform curve of the spine and head backward," "spots black as ink," "bullæ which rapidly became opaque and dusky," "herpetic eruption, etc." After death the body had a very frightful appearance. It was still prominently arched forward. It was of a dusky blue color, with a copious eruption of black spots of various sizes, and one or two of them were gangrenous.... When the theca vertebralis was opened purulent matter flowed out, and a purulent effusion was found in patches on the brain. The cerebral arachnoid was all opaque, the lateral ventricles were filled with serum, and the blood in all the cavities was very fluid and dark colored. From all that precedes, therefore, it must be inferred that the nature of the lesions in this disease depends not on the type alone, nor on the duration merely, of the attack—that a very brief course is compatible with marked inflammatory lesions, and a prolonged one with profound alterations in the condition of the blood. In other words, it seems that there must be something besides the appreciable lesions that influences, if it does not determine, the issue of an attack of this affection. While bringing forward prominently this proposition, and the facts on which it rests, we have no intention of under-estimating the relative significance of the two most conspicuous types of the disease, the purely inflammatory and the adynamic, or calling in question the fact that the evolution of the former is most usually comparatively slow and regular, and of the latter rapid and irregular. In the one, when death takes place early, congestive changes are found, and when later these have merged into exudative lesions; in the other or adynamic cases congestion and liquid transudation prevail, and the results of complete inflammation are seldom seen. When the disease has been very much prolonged the exudation becomes tough, adherent, and shrivelled.
49 Davis, Richmond Med. Jour., June, 1872, p. 709.
50 Frothingham, Amer. Med. Times, Apr., 1864, p. 207.
51 Dublin Quart. Jour., May, 1867, p. 409.
The brain-tissue has generally been found softer than natural, and, although in some cases this diminished consistence might be attributed to post-mortem changes, yet on the whole it must be associated with the inflammatory lesions of the meninges. As a rule, it is greater the longer the attack has lasted, and is by no means equally diffused, but is more marked where the meningeal alterations are greatest. Ames found softening in nine out of eleven cases, and chiefly in the cortical substance, but also in the fornix and septum lucidum; and Chauffard states that in protracted cases "the interior surface of the ventricles, the fornix, and septum lucidum, were reduced to a pultaceous and creamy consistence." But it is by no means true that softening is met with in all cases of long duration.
The lesions of the spinal marrow and its membranes correspond with those of the brain. The dura mater is often very dark, its blood-vessels engorged, its arachnoid cavity distended with serum more or less bloody, turbid, or purulent. Two ounces of pus have been removed from it through a puncture. Fibrinous and purulent exudation fills the meshes of the pia mater, and is usually most abundant in the cervical and dorsal portions, and generally upon the posterior rather than upon the anterior surface of the organ; but sometimes large accumulations of lymph and pus are found at the lower end of the cord. Gordon52 relates of a case that "when an opening was made into the lower part of the theca vertebralis purulent matter flowed out, and the entire surface of the pia mater was covered with a coating of thin purulent matter, which, like a thin layer of butter, remained adherent to it." Occasionally the cavity of the spinal arachnoid contains blood. Softening of the spinal cord has been often noticed. Chauffard states that in some cases of particularly long duration it was reduced to a mere pulp, and he adds, "in the place of portions of the spinal marrow, completely destroyed, was found only a yellowish liquid, or the empty membranes fell into contact where it was wanting." Similar disorganization has been described by Ames, Klebs, and others. Fronmüller reports the case of a girl aged fourteen years in whom the central canal of the spinal cord was distended with pure pus.
52 Dublin Quart. Jour., xliii. 414.
The lesions of the internal auditory apparatus consist of softening in the fourth ventricle and of the root of the auditory nerve, yet such lesions are said to have been found even when no defect of hearing had existed. In other cases in which deafness did occur the lesions consisted of inflammatory changes in the cavity of the tympanum and suppuration of the labyrinth. They probably arose from an extension of inflammation from the pia mater along the trunk of the auditory nerve (Von Ziemssen). In like manner, the inflammatory and destructive changes in the eye which have been elsewhere described arise from an analogous cause affecting the optic nerves.
It is unnecessary to dwell upon the condition in which other organs are found after death from epidemic meningitis. In cases that present a typhoid type, and even in such as are rapidly fatal with ecchymotic discoloration of the skin, the various organs present no distinctive tissue-change, but only such engorgement as is common to all diseases of a similar type. It deserves to be particularly mentioned that in this affection the spleen is not enlarged, as it always is in a greater or less degree in diseases whose primary stage involves an altered condition of the blood. This fact becomes all the more important in view of the remarkable contrast which the constitution of the blood presents in epidemic meningitis and in various typhous affections.