The  Reflexes  in  the  Spinal  Animal

With  reasonable  attention,  however,  the  dog  makes  a  wonderful  re-
covery. After  an  interval  of  two  weeks  the  hind  limbs,  although  com-
pletely paralyzed  so  far  as  voluntary  movement  is  concerned,  begin  to
show  considerable  signs  of  improvement.  The  first  reflexes  to  return
are  those  concerned  with  the  deeper  structures,  such  as  the  vascular
reflexes,  thus  bringing  the  skin  back  to  its  normal  temperature  and
condition.  The  reflexes  of  micturition  and  defecation  also  soon  return,
so  that  the  animal  no  longer  suffers  from  the  continuous  discharge  of
urine  and  feces.  About  the  same  time  the  knee-jerk  becomes  elicitable.
This  reflex  is  obtained  by  tapping  the  tendon  which  connects  the  patella
with  the  tibia,  the  response  being  a  smart  contraction  of  the  extensor
muscles  of  the  knee  joint.  The  flexion  reflex  also  begins  to  reappear.
This  is  elicited  by  applying  a  pinprick  or  other  hurtful  stimulus  to
the  skin  of  a  lower  extremity,  and  when  fully  developed  consists  in  a
flexion  of  the  knee  and  hip  joints.  The  evident  object  of  this  move-
ment is  that  the  stimulated  parts  may  be  removed  from  the  source  of
stimulation,  and  it  is  plain  that  all  stimuli  that  produce  the  flexion
reflex  are  such  as  would  cause  in  the  intact  animal  a  sensation  of  pain.
