For a better understanding of the case it is necessary to recall briefly the structure of that portion of the ear affected, namely, the drum membrane placed at the bottom of the outer canal of the ear to receive the sound waves transmitted through that passage and in turn to transmit them through the three small bones which form a chain of communication with the internal or perceptive portion of the ear; the drum membrane forming the boundary between the outer passages and the middle ear, the latter cavity communicating by means of the Eustachian tube with the upper part of the throat and being lined throughout with mucous membrane continuous with that in the latter cavity; in the middle ear this mucous membrane, very delicate and rich in blood vessels, not only lines the middle ear cavity but forms the inner coat of the drum-membrane and also covers the small bones, their articulations and attachments, one of these latter being a muscle, the tensor tympani, which by its contraction renders all the sound-transmitting apparatus more tense. It is easily appreciable that a gradual thickening of this mucous membrane would result in a progressive impairment of the sound-transmitting apparatus, with a corresponding decrease in its power of transmitting sound waves not only from without inward but from within outward. This interference would be first noticed in the transmission of such short sound waves of slight impulse as occur in instruments of high pitch or such as make up the qualitative overtones of the human voice and it was therefore at a comparatively early period in his disease that Beethoven failed to hear the distant sound of the flute, and of the shepherd singing, and to distinguish the difference in the more delicate modulations of the voices of his friends. The distress induced by exposure to loud noises is also accounted for by the fact that the comparative rigidity of the sound transmitting apparatus deprived the deeper sensitive portion of the ear of the protection normally afforded it by the elastic structure capable of taking up and dispersing the excessive impulse and by the further fact that the contraction of the tensor tympani muscle, which contraction is an almost invariable accompaniment of certain chronic diseases of the middle ear, served to still further impair the mobility of the drum-head and ossicles.