Morbid Changes of the Labyrinth.— These have affected either the whole labyrinth or only parts of it. The so called entire absence of the labyrinth plays an important part among the former class, partly on account of its comparative frequency, and partly on ac count of its origin.. The majority of authors have hitherto regarded the ab sence of the labyrinth as the result of ar rested development. I have, however, in several of my works proved that par tial or complete absence of the labyrinth, or of parts of it, may be, and probably most frequently is, caused by the de posit of osseous tissue in the labyrinth ine cavity, which becomes thus more or less completely filled up, under which process the normal outlines may disap pear entirely. Such a formation of osseous tissue is without doubt the re sult of a previous inflammatory process; that is, of an otitis intima. I have also pointed out that it is impossible to dis tinguish between fcetal and post-fcetal morbid changes by post-mortem exami nation, unless accompanied by exhaust ive and reliable information as to the cause and date of the affection. From the following it will bc evident that the deposit of osseous tissue in the cavity of the labyrinth is one of the most frequent labyrinthine anomalies found upon post mortem examination of deaf-mutes, the osseous mass sometimes filling the whole cavity, while sometimes only a section exhibits a parietal deposit which has merely caused a diminution of the cavity in question. The most extensive forma tions of osseous tissue in the labyrinth are apparently the result of a post-natal otitis intim. It is interesting to ob serve that various investigators have dis covered such osseous deposit sometimes on the one side only, sometimes on both, some having also found osseous tissue on the one side, and deposits of chalk or fibrous tissue—which may also, as is well known, be tbe result of inflammatory processes—on the other side, while both the latter deposits have also been fre quently found in the labyrinths of deaf mutes when there was no formation of osseous tissue on either side. Inflam matory and also degenerative processes may leave other products behind them, which may appear in like manner in other parts of the body. I would not, however, imply that the partial or total absence of the labyrinth may not be the result of arrested development, which, on the other hand, may be due to feetal in flammatory processes. Still, it is often difficult to find proofs that such has been the origin of the abnormalities in indi vidual cases. A case observed by Michel is, however, of this nature, as the petrous bone was entirely deformed, and it seems as if we might be justified in expecting important malformations of the laby rinth to be reflected in the shape and ap pearance of the petrous bone. In many cases the inflammatory process in the labyrinth causing its partial or complete destruction was secondary to an inflam mation of the middle ear. According to the reports of several post-mortem ex aminations, the inflammation of the mid dle ear was due to acute infectious dis eases, in particular scarlet fever and measles. In conformity with the above, it will be seen that in dissections, in which the complete or partial absence of the labyrinth was discovered, toler ably well-marked changes were found in the middle ear, consisting, in great part, in the remains of inflammatory processes; and this was true of many of the cases which will be mentioned further on as examples of circumscribed deposit of osseous substance in the labyrinth. On the other hand, the absence of inflam matory processes in the middle ear, or the traces of such, and in other cases the histories of the cases seem to indicate that the labyrinthine inflammation is not of necessity propagated from the middle ear, but that it frequently originates in the membranes of the brain. This is especially probable in all cases where meningitis is with certainty stated to be the cause of deafness. There is, perhaps, a third kind of labyrinthine inflamma tion,—viz., primary inflammation,— which has been especially defended by Voltolini and called after him otitis intima of Voltolini. The existence of this affection cannot be proved or dis proved by arguments drawn from the material here under discussion.
As far as the seat of the labyrinthine changes in deaf-mutes is concerned, the vestibule (with the exception of its aqueduct) is the part of the labyrinth which has been least frequently found to be the seat of morbid changes. The reason is that the vestibule is, compara tively speaking, seldom found to be abnormally changed on post-mortem examination of deaf-born deaf-mutes, anomalies in the two other principal sec tions of the labyrinth being twice as frequent in these cases. It is also re
markable that in no hitherto-published post-mortem examination of a deaf-mute with acquired or congenital deafness, or where the orizin of the deafness is not stated, has the vestibule been the only section of the labyrinth which has been the seat of abnormalities, the other sec tions being also changed when this has been the case with the vestibule.
The semicircular canals are decidedly the portion of the labyrinth which is most frequently the seat of pathological changes; these are, indeed, so frequent here, that more than one-half of the dissections have yielded positive re sults. Indubitable cases of congenital malformations have been observed by several investigators, but it is question able whether such abnormalities as the union of the two canals into one, short ening or lengthening of the canals, etc., are to be regarded as of vital importance. In not less than one-fifth of all the dis sections yielding positive result the semi circular canals were the only part of the labyrinth which exhibited morbid changes. In the majority of cases in which the semicircular canals have been the seat of abnormalities they, or a part of them, have been filled up by osseous tissues, or must have been supposed to have been so; for instance, in the naany eases where the reports simply mention "absence" of these canals. The poste rior canal has been most frequently at tacked, either above or together with the superior, but principally together with both the superior and the external. There is no reason to presume the fre quent occurrence of abnormalities of the semicircular canals to be a frequent cause of deaf-mutism, but only a conspicuous proof of the frequency with which laby rinthine inflammations are a cause of that anomaly. The abnormalities dis covered in the semicircular canals point also in another direction when it is re membered that it is an approved fact that disturbances of the equilibrium are very common among deaf-mutes. In this respect post-mortem clinical observations of deaf-mutes speak strongly in favor of the theory of the influence of the semi circular canals on the equilibrium of the body: a theory which has lately found much support in Ewald's work.
Morbid changes of the cochlea are somewhat more frequent than those of the vestibule, and are very equally di vided between congenital and acquired cases of deaf-mutism. In several cases the cochlea was the only part of the labyrinth which was the seat of morbid changes; in the great majority of cases, however, other parts of the inner ear have been abnormal, the semicircular canals having been at the same time es pecially frequently the seat of anomalies. The raore or less entire filling up by osseous or calcareous masses is the anom aly most common to the cochlea, and under this heading may doubtless be in cluded all cases in which the cochlea is reported to be entirely absent, or in which only one or two cavities remained. Abnormalities of this nature are men tioned in about one-eighth of all hith erto-published post-mortem examina tions.
Morbid Ch,anges of the Auditory Nerve. —It is a fact that, although atrophy and degeneration of the auditory nerve, or a part of it, are frequent in deaf-mutes, they are far from being always present, as believed by many, since Hyrtl put forward that supposition, based upon post-mortem examinations performed by him. As it is to be supposed that the auditory nerve of the majority of cleaf-mutes examined post-mortem has been out of function some time, with out there being found any atrophy or degeneration in it or its branches, it would seem that this nerve is 'not par ticularly disposed to become atrophied or degenerated from inactivity. The correctness of this hypothesis is con firmed by morbid anatomical examina tions hitherto published of persons who have become deaf at a more advanced age, which examinations all point in the same direction. The cases of atrophy or degeneration of the auditory nerve which have been found by post-mortem exam inations of deaf-mutes, seem, therefore, as a rule, to be due to some other cause, and we are obliged to regard them as the result of either centripetal atrophy or degeneration subsequent to labyrinthine destructive processes, or as the expres sion of a centrifugal change arising from primary disease of the central nervous system.