The  term  "  epilepsy  "  is  applied  to  a  disease  in  which  there  are  convul-
sions of  a  certain  type,  or  sudden  loss  or  impairment  of  consciousness,  but
in  which  the  convulsions  are  not  directly  due  to  active  organic  brain  disease,
to  reflex  irritation,  or  to  abnormal  blood  states,  and  in  which  the  loss  of
consciousness  is  not  due  to   primary  failure  of  the  heart's  action.     In  most
cases  the  change  in  the  brain  that  causes  the  convulsions  is  not  visible  to  the
naked  eye,  and  hence  the  condition  is  often  termed  "  idiopathic  epilepsy."
There  are  cases,  however,  in  which  similar  convulsions  occur  as  the^result  of
old  brain  disease,  such  as  a  spot  of  softening  which  has  long  ceased  to  cause
active  irritation.     These  cases  may  resemble  epilepsy  in  their  course,  and
sometimes  in  their  symptoms,  but  they  commonly  succeed  a  distinct  attack
of  hemiplegia.     Hence  they  are  often  termed  "  post-hemiplegic  epilepsy,"
and  are  described  in  a  separate  section.
The  convulsions  in  epilepsy  may  consist  of  tonic  or  of  clonic  spasm,  or,
commonly,  of  both,  but  the  attitude  of  movement  which  results  always
differs  from  that  which  occurs  in  voluntary  movement.  On  the  other  hand,
in  the  convulsions  of  hysteria,  the  muscular  spasm  is  so  arranged  as  to
resemble  that  which  may  result  from  a  voluntary  action.
