392 THE EAR who suffer from disturbance of hearing after very small doses of quinine the trouble is probably due to an idiosyncrasy of an anaphylactic nature. Changes in the cells of the spiral ganglion have been found in quinine poisoning. Mercury and aspirin may cause neuritis of the eighth nerve. In rare cases, tobacco and alcohol, if used to excess, may cause impairment of the hearing. It is accordingly advisable to prohibit their use in cases of nerve deafness in which no other cause can be ascertained and in which excessive consumption of alcohol or tobacco is suspected or admitted. Abstinence is frequently followed by improvement in hearing. The organic arsenical drugs may have a secondary action on the eighth nerve, due to a Herxheimer reaction. The cochlear branch is affected four times as often as the vestibular branch, but both portions may be involved. In some cases the changes are not limited to the eighth nerve, but also involve other cranial nerves. Lead poisoning may give rise to nerve deafness and vertigo. Certain hair dyes contain a labyrinthine poison—paraphenylenediamene—which causes headache, vertigo, deafness and tinnitus. The symptoms clear up when the dye is stopped. The number of ototoxic antibiotics is now quite considerable. Streptomycin, particularly if given in large doses and over a prolonged period, not infre- quently causes vertigo and changes in the caloric reactions. The hearing may occasionally be affected. On the other hand, deafness occurs much more frequently when dihydrostreptomycin is administered and its use should be avoided as far as possible. The list also includes neomycin, kanamycin, vancomycin^ viomycin and ristocetin. Deafness has recently been found in subjects with renal failure treated by haemodialysis combined with the use of the antiheparinizing agent poly- brene. It may also result from the use of some diuretics. SENILE DEAFNESS (PRESBYACUSIS) In old age the hearing frequently becomes impaired to some extent. This impairment is characterized by a rise in threshold for the higher frequencies, a lowering of the upper tone limit, and the presence of loudness recruitment (patients may remark that they can no longer hear the birds whistling— while raising the voice, because of their inability to understand, will some- times elicit the response 'don't shout'). Bone conduction is shortened and Rinne's test is positive. The pathology of senile nerve deafness is said to consist of degeneration of the cochlear ganglion cells and hair cells of Corti's organ. The onset of the deafness is generally very insidious and the progress slow. A good deal of what is usually regarded as 'deafness' in old people is really due to the fact that they do not 'comprehend' what is said as well as they did in childhood, youth and middle age, i.e. there is a loss of discrimina- tion. Lack of concentration along with a slowing down of the mental processes must also be taken into account. Old people suffering from nerve deafness often talk in a loud, unpleasant tone—in marked contrast to the low, well- modulated voice of cases suffering from otosclerosis. Hearing aids are often of benefit in senile deafness, but they are frequently not tolerated. Some assistance may be obtained by placing the hand behind the auricle and holding it forward so as to collect the sound waves.