Bilateral  deafness  may  be  due  to  various  causes:  (i)  Symmetrical  disease
of  the  labyrinth,  which  is  common  ;  acute  inflammation  is  sometimes,  and
chronic  degeneration  is  often,  bilateral;  double  otitis  has  sometimes  been
mistaken  for  meningitis;  (2)  symmetrical  lesions  of  the  two  auditory
nerves,  which  are  very  rare  ;  (3)  possibly  disease  of  the  medulla  ;  (4)  a
tumor  in  the  corpora  quadrigemina,  damaging  the  crustse  of  the  crura  cere-
bri ;  (5)  symmetrical  disease  of  each  temporo-sphenoidal  lobe ;  syphilitic
gummata  caused  this  effect  in  a  case  recorded  by  Wernicke  and  Fried-
lander.
Treatment. — For  a  description  of  the  little  that  can  be  done  in  the
treatment  of  disease  of  the  labyrinth,  the  reader  is  referred  to  special  trea-
tises. The  treatment  of  disease  of  the  nerve  trunk  or  centres  is,  for  the
most  part,  that  of  the  morbid  process,  and  must  be  conducted  on  the
same  principles  as  that  of  similar  lesions  in  the  other  cranial  nerves.  In
cases  of  acute  deafness,  counter-irritation,  as  by  blisters,  is  often  of  great
service,  and  even  in  chronic  cases  may  do  some  good.  The  auditory  nerve
may  be  stimulated  by  electricity,  but  the  results  obtained  by  most  of  those
who  have  employed  this  method  have  been  slight  and  disappointing.
AUDITORY   HYPERESTHESIA.
The  term  is  applied  to  an  increased  or  perverted  action  of  the  auditory
nerve  or  centres.     While  deafness  is  much  more  frequently  due  to  diseases

*  See  a  curious  case  of  tumor  of  the  right  cerebellar  amygdala  (Wolf,  Archiv  f.  Ohren-
heilk.,  Bd.  xvi,  p.  157),  which  compressed  the  right  auditory  region,  and  is  said  to  have
caused  deafness  of  the  left  ear  and  left  facial  paralysis.  The  latter,  however,  might  have
been  due  to  a  tumor  that  existed  in  the  ascending  parietal  convolution.
