132 GERMINATION 



And now let us consider some " faults " which commonly 

 occur in the apparatus. 



Conditions essential to the efficient working of the installa- 

 tion are that the drum of the external and the tones of the 

 middle ear are free to vibrate, that the penlymph and 

 endolymph are in normal quantity, that the organ of Corti 

 is uninjured and that the line wire — the cochlear nerve at 

 least — is adequately electrified. 



Four '* faults " which should be capable of repair are 

 liable to occur, i.e. : 



1. The drum of the external ear may be thickened, 

 or overlaid by inflamed tissue — due, for instance, 

 to rheumatoid arthritis — or by wax ; 



2. The bones of the middle ear may be clogged by 

 catarrh or by inspissated mucus, so that they are 

 not free to vibrate ; 



3. The Auditory nerves may be faulty, or 



4. There may be a general deficiency of nerve-force, 

 resulting in deficient neuro-electrification of the 

 auditory nerves (purely nervous deafness). 



In each case the sound waves do not reach the brain 

 unimpaired because : 



1. They are partly or wholly stopped, or rendered 



" woolly " by the drum ; 



2. If responded to by the drum they fail to set fully 

 in motion the clogged bones of the middle ear ; 



3. The faulty line wire fails to carry them fully, or at 

 all, to the brain, or, 



4. The neuro-electrification of the line wire is too 

 feeble to transmit them without loss, if at all. 



When one of these faults occurs the system should be 

 galvanometrically tested and the nature and locality of the 

 fault ascertained. There is no difficulty about it. It is 

 just an ordinary everyday test, except that battery power 

 is not employed. 



If the drum of the external ear is thickened, or the passage 

 to it swollen by rheumatoid arthritis or by other causes 

 contributory to local pyrexia it will 5deld a rapid excursion 



