1 1 82 THE EAR. 



find any loss of perception for low tones, when in guinea-pigs the upper 

 parts of the cochlea were destroyed. He tested hearing by the doubtful 

 expedient of observing a reflex movement of the auricle when a sound 

 was heard, and he found that the animals reacted even after the peri- 

 lymph and endolymph were flowing out of the broken cochlear apex. 

 This was too rough an experiment, and does not appear to have much value. 



Hensen x has demonstrated that in the supposed auditory organ of 

 arthropods certain hairs vibrate in sympathy with certain tones, and not 

 with others. In certain Crustacea these hairs number about 468 ; the largest 

 is about '72 mm. long, and the shortest "14 mm. The hairs vibrated within 

 a range of three octaves. In Mysis, one of the hairs answered strongly 

 to d$ and d% more weakly to g, and very weakly to Gr. Its pitch was 

 between d" and d'% or the second partial of d' to d'% the third of g to 

 gift, the fourth of d to d%, and the sixth of G- to GS. Another hair 

 answered strongly to a%, more weakly to d% and AS. Its tone, therefore, 

 was about a#. 2 



There is a certain amount of clinical evidence on this question. One 

 case is on record where an individual showed during life a total want of 

 perception of high tones, while tones low in pitch were audible. The 

 necropsy showed that there was atrophy of the fibres of the nerve furnish- 

 ing the lowest whorl of the cochlea. 3 In boilermaker's deafness the 

 hearing power for high tones is particularly affected. In one such case, a 

 necropsy showed that the lowest whorl was diseased. 4 It is the general 

 opinion of aurists that in cases of partial deafness from diseases of the 

 inner ear, the loss of audibility is for the higher tones, and, as a rule, post- 

 mortem examination shows changes in the basal portion of the cochlea. 

 A case is recorded of a man, set. 52, suffering from locomotor ataxia, who 

 was deaf to the ticks of a watch and to ordinary speech. The fork (c) was 

 heard by bone conduction, while c" was inaudible. After death the left 

 ear showed the cochlear division of the nerve to be degenerated, and the 

 corresponding organ of Corti also much altered. On the right, however, 

 there still existed a large bundle of nerve fibres at the apex of the 

 cochlea, and the corresponding part of Corti's organ was intact. The 

 rest of the nerve and cochlea were degenerated, as on the left side. 5 



On the other hand, cases have been cited in which the whole cochlea 

 of one side has been exfoliated, and yet the individual was able to dis- 

 tinguish tones with that ear. These are extremely doubtful, and the 

 observation is open to the objection that the patient probably heard, by 

 bone conduction, with the sound ear. There can be no doubt that 

 exfoliation of both cochleae causes complete deafness for tones, although 

 there may still be something like a sensation of sound. 6 



I have constructed a model of the cochlea, consisting of a rectangular box, 

 with glass sides and top, which is completely filled with water. It is 

 divided horizontally by a glass partition, to represent the basilar mem- 

 brane (it is not necessary to imitate the membrane of Reissner) ; the upper 



1 Hermann's "Handbuch," 1880, Bd. iii. Th. 2, S. 107; Hensen, " Stud, ueber das 

 Gehbrorgan der Decapoden," Leipzig, 1863 ; also Ztschr. f. wissensch. Zool., Leipzig, Bd. 

 xiii. S. 398. 



2 Helmholtz, op. cit., p. 225. 



3 Moos and Steinbriigge, Ztschr. f. Ohrenh., Wiesbaden, Bd. x. S. 1. 



4 Habermann, Arch. f. Ohrenh., Wiesbaden, Bd. xiii. S. 1. 



5 Ibid. , Bd. xxxiii., S. 2 ; also Ccntralbl. f. Physiol., Leipzig u. Wien, 1892, S. 776. 



6 Gruber, Allg. Wien. med. Ztg., 1864, Bd. ix. Nos. 41, 43, 45, ; also Bezold, Ztschr./. 

 Psychol, u. Physiol, d. Sinncsorg., Hamburg u. Leipzig, 1896, Bd. xiii. 



