In  this  series  of  tests,  as  also  in  those  employed  to  detect  abnor-
malities of  appreciation  of  different  degrees  of  temperature,  the  following
precautions  must  be  taken  against  error  in  the  results  obtained : —

1.  The  nature  of  the  tests  to  be  employed  must  be  clearly  explained
to  the  patient,  as  well  as  the  importance  of  accuracy  in  his  decision  re-
specting the  sensations  perceived.  This  insures  his  intelligent  coopera-
tion, and  makes  the  patient  more  earnest  in  his  endeavors  to  answer
correctl3\


Fig.  63. — Beard's  Piesmeter. — This  instrument  consists  of  a  spring  in  a  tube  that  resists  press-
ure made  upon  the  piston.  A  scale  indicates  the  amount  of  pressure  uiion  the  spring.  It
is  employed  to  determine  the  degree  of  sensitiveness  to  pressure  in  different  parts  of  the
body  The  forehead,  tongue,  and  cheek  are  the  most  sensitive  to  pressure;  the  least  so  are
the  backs  of  the  thighs  and  legs.
2.  It  is  preferable  that  the  patient  he  blindfolded,  in  order  to  avoid
any  information  respecting  the  tests  used  reaching  him  by  sight.
3.  To  malce  the  patient  keenly  alert  to  avoid  errors  of  statement,  it
is  well  to  employ  blank  experiments  from  time  to  time.  Thus,  when  the
skin  has  not  been  touched  with  any  instrument  or  foreign  substance,  it
is  well  to  ask  "where  the  object  is  now  felt,"  "how  many  points  are  now
in  contact  with  the  skin,"  etc.
