(b)  Freciuent  Micturition. — This  occurs  in  polyuria.  It  is  obvious
that  in  the  absence  of  dilatation  of  the  bladder  an  increase  in  the  quantity
of  urine  must  be  followed  by  an  increase  in  the  frequency  with  which  it  is
voided.  Hence  in  diabetes  insipidus  and  diabetes  niellitus,  in  contracted
kidneys  and  in  some  forms  of  pyelitis  the  frequency  of  urination  is  ^n'eatly
increased.  A  diabetic  who  voids  6  litres  of  urine  in  twenty-four  hours,
with  an  average  vesical  capacity  of  about  300  c.c,  would  be  obliged  to  pass
water  at  least  twenty  times  in  the  course  of  the  day — a  requirement  which
is  slightly  diminished  by  a  giadual  increase  in  the  size  of  the  bladder.  When,
on  the  other  hand,  the  bladder  has  undergone  concentric  hypertrophy  in
consequence  of  chronic  cystitis  and  its  capacity  is  greatly  diminished,  the
necessity  to  void  urine  at  short  intervals  becomes  imperative.  If  the  call
be  not  obciyed,  as  in  deep  sleep,  the  urine  may  be  involuntarily  discharged.
Frequent  micturition  is  often  due  to  psychical  causes,  among  thfm
fright  ami  excitement.  Soldiers  in  battle  and  students  awaiting  examina-
tion constitute  oft-quoted  examples.  The  urine  is  voided  at  short  inter\'al8
and  in  small  amounts  and  often  involuntarily.  It  is  also  a  common  sj-mp-
tom  in  hysteria  and  neurasthenia.
