Diseases  outside  the  nervous  system  which  have  been  mistaken  for  infant-
ile paralysis  are  chiefly  those  in  which  local  pain  interferes  with  the  move-
ment of  the  limbs,  and  the  child  is  young.  I  have  known,  for  instance,
the  mistake  to  be  made  in  the  case  of  hip-joint  disease,  necrosis  of  the  femur,
and  the  affection  termed  "  scorbutic  rickets,"  in  which  there  is  enlargement
of  the  shafts  of  the  long  bones,  extreme  pain  on  movement,  and  spongy
gums.  In  all  these  cases,  a  careful  examination  will  show  that  movemeat  is
interfered  with  only  by  the  pain ;  there  is  no  actual  paralysis,  and  there  is
no  interference  with  reflex  action.  The  preservation  of  the  myotatic  irrita-
bility is  often  of  considerable  assistance  in  these  cases.  It  is  common,  for
instance,  for  the  extension  of  the  knee  to  be  interfered  with,  but  the  pres-
ervation of  the  knee  jerk  at  once  proves  that  atrophic  paralysis  is  not  the
cause  of  the  defect.
