ABNORMALITIES OF THE EYE.—Al though we find several notices of abnor malities of the eyes of deaf-mutcs, it is often difficult to decide whether these are accidental phenomena or connected etiologically with deaf-mutism. Among the abnormalities of the latter category may be mentioned retinitis pigmentosa, various malformations of the eye; atrophy of the bulb caused by panoph tbalmia, a result of the same acute dis ease as caused the deafness; finally syph ilitic interstital keratitis.
Diagnosis. — Although dcaf-mutism from a theoretical point of view is not a very distinctly-defined condition, still the majority of cases are easily recog nized. The question whether a person is a deaf-mute or not must, according to what has been laid down in the fore going pages, be principally decided by examinations as to the function of the auditory nerve. If this is entirely sus pended, or so reduced that speech can not be heard, and if the history of the case proves that this condition dates from birth or infancy, then the subject must be regarded as a deaf-mute. We are also justified in applying this term, as has already been pointed out, even where there exists some power of speech either acquired by special means of instruction or where the deaf-mutism has appeared at a more advanced age, retained to a greater or less extent. The circumstance that the pathological condition called deaf-mutism is based upon a symptom, the extent of which cannot be measured with any degree of certainty, but which, nevertheless, is decisive, naturally causes arbitrary decisions in some cases, which decisions generally depend upon purely practical considerations. In other words, there are persons as to whom it is difficult to say with certainty whether they are deaf-mutes or not. Such are persons who can hear the human voice to a certain extent, and who consequently learn to articulate by the aid of special methods of education, or such as have lost the power of hearing so late that they have retained the power of speech, although their voice is always somewhat peculiar. Such persons are, however, but few in number, and consequently the difficulty in diagnosing deaf-mutism mentioned here is of very slight practical impor tance.
Of much greater importance are the difficulties which present themselves when the person in question is an infant.
It must, however, be pointed out that the term "deaf-mute" is incorrect when applied to children under a year old, as no children can speak at that age. It would seem, indeed, that great caution must be observed in drawing the con clusion that deaf-mutism will rrecessarily be the result of even total deafness ob- I served during the first year of infancy, since, according to the experience of many etiologists there are some children who are linable to react, or who react very slowly, to sounds during the first year of infancy, but whose hearing, nev ertheless, when older, is perfectly normal. In any case it is extremely difficult to arrive at any decided opinion whether an infant possesses the power of hearing or not, and especially as to what degree of hearing it possesses, and, as a rule, the younger the child, the greater is this dif ficulty. The reason is, doubtless, that the sound-conducting apparatus of in fants is not complete at birth. The ex ternal meatus and the tympanic cavities are transformed after birth from cavities filled with cellular tissue to pneumatic cavities. It was formerly supposed that infants did not react to sound, but it has been proved that this is not the case, even with newborn infants, and infants can also perceive musical notes. Even in the second half of the first year of childhood it is, however, very difficult to decide whether the power of hearing ex ists or not. No great confidence can be attached to the statements of a child's friends as to its having heard certain sounds; as the vibrations of the air caused by certain sources of sound may produce effects upon the sensory nerve which may be mistaken for the result of vibrations of air acting upon the auditory nerve. It is, therefore, of the greatest impor tance, in experimenting with the hearing of infants, to make use of such sources of sound, or to make use of them in such a manner, that only the vibrations of sound produced can be perceived. Loud dinner-bells are suitable for this pur pose; the so-called watchman's whistle, Galton's whistle, clapping of hands, and the firing of small pistols, which the child should not be allowed to see. If the child reacts to these sounds it will blink its eyes or exhibit either joy or fear.