The origin of deafness in scarlet fever has been elucidated by clinical research, which proves that ear diseases caused by scarlet fever generally consist of inflam mation of the middle ear, with a marked tendency to destroy the mucous mem brane and osseous walls of the tympa num, and also the auditory ossicles. The inflammations of the middle ear, which are most frequently propagated through the Eustachian tubes, but which may, perhaps, appear independently, are not, as a rule, in themselves capable of caus ing a diminution of hearing in infancy so lasting and so considerable as to result in deaf-mutism, unless the labyrinth is affected. Scarlatinal deafness resulting in deaf-mutism is then, doubtless in most cases, due to a partial or entire destruc tion of the membranous contents of the labyrinth. This destruction is, in many cases, caused by the propagation of the inflammation to the internal ear either through the fenestra! (fenestr rotundis et ovalis) or through the vessels leading from the tympanum to the labyrinth. Some post-mortem examinations of deaf mutes, whose deafness was the result of scarlet fever, support the former theory, indications of an inflammation of the middle ear being found, also abnormali ties in one or both fenestra3, doubtless the result of an inflammatory process. On tbe other hand, there are various circumstances which indicate that scar latinal afketions of the labyrinth may appear independently of an inflamma tion of the middle ear, or that, if such inflammation had existed, it has been very slight. Thus, for instance, it is often found, on otoscopic examination of deaf-mutes, who have become deaf after scarlet fever, that the drum-head ex hibits but slight or no abnormalities.
Measles (morbilli). The reports relat ing to the frequency of measles as a cause of deaf-mutism vary greatly, though not so much as was the case with scarlet fever, which disease also assumes a much more prominent rank in the eti ology of deaf-mutism; the lowest rate is Wurtemburg and Baden (1.0 per cent.), the highest Meeklenburg-Schwerin (8.3 per cent.).
Among other infectious diseases which now and then cause deaf-mutism may be mentioned the different varieties of typhus (typhoid fever, exanthematic ty phus), diphtheria, small-pox, chicken pox, erysipelas, dysentery, influenza; ague, whooping-cough, mumps, inflam mation of the lungs, and rheumatic fever.
C onstitutional Diseases.—Of these may be mentioned rickets, scrofula and syph ilis. Although syphilis is represented in most statistics relating to the causes of deaf-mutism by only a fraction or not at all in modern statistics, there can be no doubt that when inherited from the parents it plays some part in deafness ac quired in infancy and resulting in deaf mutism. Inherited syphilis may, as is well known, produce a peculiar form of deafness accompanied by certain ocular affections, which, it is true, generally appears after the age of puberty, but which, however, also shows itself before that period, even as early as the age of four. The circumstance, however, that hereditary syphilitic deafness often ap pears without any other marked symp toms of syphilis, and that it is extremely difficult to discover syphilis in the par ents, especially by questions alone, ex plain why this disease is so seldom no ticed in the parents of deaf-mutes in hitherto-published statistics. It seems,
also, that acquired syphilis may cause deaf-mutism; but no investigators have, up to the present, touched upon this sub ject.
Injury (Trauma). — Although it is probable that traumatic influences, such as falls, blows on the head, etc., to which children are especially subject, are some times stated as being the cause of deaf mutism in cases of really congenital ori gin, there is no doubt that such causes may produce deafness resulting in mut ism, as car diseases of traumatic origin are not at all unknown, even among adults. Injury also is included in the causes of deaf-mutism in nearly all the more considerable statistics, the figures, however, being but small.
Morbid Anatomy.—Although a partial examination of the auditory organs of deaf-mutes during life-time is possible, still it can only embrace the peripheral parts, and there must always be a dif ficulty in deciding whether the morbid changes thus revealed are of primary or secondary importance, or, indeed, only accidental. It is, therefore, only possible to arrive at an intimate knowledge of the morbid changes causing deaf-mutism and hence, at the just comprehension of its nature, by means of post-mortem ex amination. Wre have but few reports of such examinations dating earlier than the commencement of this century, and they yield so little information that we can only surmise that the examinations have been incomplete.
Before discussing the different parts of the auditory organs in which morbid changes have been found, it must be ob served that several investigators have found no changes whatever in some of the cases examined by them; indeed, lbsen's and Mackeprang's investigations gave negative results in no less than one third of all their cases. As, however, these investigations date from a period when the microscopical examination of the labyrinth was but little developed, and as no mention is made of an exam ination of the brain or of the auditory nerve, the negative results arrived at lose considerably in importance, for it is pos sible that the parts of the auditory organ above mentioned have been the seat of undetected abnormalities.
Morbid Changes of the Middle Ear.— If we take a survey of the pathological changes of the middle ear which have been found in post-mortem examina tion of deaf-mutes, we shall find that such changes are remarkably frequent. It is only exceptionally that these have been the result of malformation; they have, in the majority of cases, owed their presence to inflammatory processes or the remains of such. These inflammatory processes have sometimes been of ca tarrhal nature, but generally suppura tive, in which cases they have been in tense and destructive. The abnormali ties 1-vhich are characteristic of the mor bid anatomy of deaf-mutism have had their seat about the two fenestrw, es pecially in and around the fenestra ro tunda, which has exhibited anomalies in not less less than one-fourth of all the dissections which yielded positive results, and has in particular been frequently closed by osseous masses. In the ma jority of cases, however, the abnormali ties of the middle ear have been accom panied by marked changes of the inner ear.