having  a  specific  action  on  a  certain  part  of  the  nerve  centres,  is  more  prob-
able, since  the  facts  of  toxicology  show  a  large  number  of  chemical  sub-
stances have  an  action  limited  in  a  remarkable  way  to  certain  parts  of  the
nervous  system.*

Occasionally  chorea  is  accompanied  by  such  severe  general  symptoms  as
to  suggest  the  influence  of  a  very  intense  blood  disturbance.  The  concur-
rence of  rheumatic  hyperpyrexia  may  be  regarded  as  a  complication,  but  it
is  a  very  significant  one.  In  the  case  mentioned  already,  as  fatal  by  ulcer-
ative endocarditis,  the  symptoms  of  this  coincided  in  onset  with  those  of
the  chorea.  In  another  recorded  case  the  symptoms  of  chorea  in  a  child  of
seven  were  quickly  followed  by  those  of  an  intense  blood  disease,  which
was  quickly  fatal. f

We  must  not,  however,  regard  the  blood  change  as  the  exclusive,  or  even
the  dominant  element  in  the  causation  of  chorea.  Important  facts  already
considered  demonstrate  the  influence  of  functional  development  as  a  pre-
.  disposition  and  of  functional  disturbance  as  an  excitant  of  the  disease.  No
theory  is  complete  that  does  not  take  cognizance  of  all  three  factors.  The
ascertained  facts  of  etiology  seem  to  show  that  the  part  played  by  the  three
influences  varies  in  different  cases.  Always,  probably,  the  functional  pre-
disposition is  essential ;  it  may  in  some  instances  attain  such  an  intensity
that  the  disease  occurs  without  other  causes ;  in  other  cases  the  change  in
the  blood,  or  the  influence  of  emotion,  or  both,  are  combined  with  the  pre-
disposition in  various  degrees.
