612 PHYSIOLOGY CHAP. 



partial ; there is only a dulness of hearing that gradually diminishes 

 till nothing remains 1 >ut the more or less marked signs of psychical 

 deafness. 



These results confute Munk's theory of cortical deafness. 



We experimented almost entirely upon dogs, Schafer and 

 Sanger-Brown (1888) on monkeys. In h've macaques they 

 removed or destroyed the upper temporal convolution on both 

 sides, and in one they completely removed both temporal lobes. 

 The last operation for a time produced a state approximating to 

 idiocy, but hearing was not abolished in any of the animals, 

 perhaps not even diminished, since the inconstancy of reaction to 

 sounds may be interpreted as a sign of simple psychical deafness. 



These results agree with our own observations on the dog, and 

 obviously strengthen the theory that the seat of auditory per- 

 ception is not confined to the cortex of the temporal lobe, but 

 spreads to the adjacent regions as well. 



That the focal area of auditory perception lies in the upper 

 temporal convolution seems probable from the results of electrical 

 stimulation, and from Flechsig's observations as to the time at 

 which the myelination of its fibres takes place (Fig. 300), and 

 from v. Monakow's anatomical observations. The cortex of the 

 temporal lobe, and particularly that of the first convolution, 

 according to v. Monakow, is in direct communication with the 

 internal geniculate body, which in its turn is related to the 

 posterior quadrigeminal 1 todies, and these are connected with 

 the cochlear nerve by the lateral lemniscus and certain fibres of 

 the formatio reticularis. 



The results of clinical and anatorno -pathological observations 

 on the auditory sphere of the human brain are interesting. 

 Generally speaking, they are definitely in favour of the theory 

 which we brought forward with Seppilli in 1885. 



A fact which seems to be of special importance, because it is 

 at variance with Munk's cortical deafness, is the absence in 

 medical literature of any description of cases of deafness or marked 

 loss of hearing in one or both ears when the autopsy shows 

 clearly and conclusively that there was a destructive lesion, 

 exclusively localised to the cortex. Clinical observation brings 

 out a no less important positive fact that lesions of the cortex 

 of the temporal lobes produce a curious mental disorder during 

 life, characterised by the fact that the patients, while perfectly 

 aware of the least sound or noise, are incapable of understanding 

 the significance of the words they hear. Wernicke (1874) first 

 described this condition, which he termed sensory aphasia, because 

 he took it to be an affection of the paths of auditory speech. 

 Kussmaul (1876) after a more profound analysis regarded it as an 

 incomplete form of psychical deafness, and called it word deafness, 

 which finds its complement in the word blindness above described. 



