The  local  examination  should  In  all  cases  be  followed  by  a  post-
coital one,  at  which  time  specimens  of  the  semen  deposited  by  the  male
are  removed  from  the  vagina  and  cervix  and  studied  under  the  micro-


68  STERILITY  AND  CONCEPTION

scope.  Valuable  information  is  to  be  obtained  in  this  way,  but  unless
the  technique  is  accurately  carried  out,  and  the  interpretation  made  by
an  expert,  the  result  may  be  misleading.  When  specimens  taken  from
the  seminal  pool  in  the  vagina  are  examined  under  the  microscope,  the
presence  or  absence  of  spermatozoa  can  be  easily  determined.  If  such
examinations,  made  within  one  hour  after  intercourse,  disclose  the
presence  of  spermatozoa,  a  majority  of  these  will  usually  be  found  to
have  lost  their  normal  motility,  or  to  have  it  very  greatly  inhibited.
This  is  probably  due  to  the  acidity  of  the  vagina,  which  is-  generally
supposed  to  be  inimical  to  the  life  of  the  spermatozoa,  and  the  greater
the  length  of  time  that  has  elapsed  since  intercourse,  the  fewer  will  be
the  number  of  live,  motile  individuals  found.  After  ten  hours  or  more,
live  spermatozoa  are  rarely,  if  ever,  found  in  the  vagina,  but  in  the
cervical  canal  they  live  much  longer  and  may  even  be  found  in  an
active  state  days  after  coitus.  The  exact  period  of  life  of  the  spermato-
zoa within  the  genital  tract  is  unknown.  For  all  practical  purposes  the
examinations  made  in  carrying  out  the  spermatozoa  test  may  be  con-
fined to  specimens  taken  from  the  vagina  and  cervical  canal.  If  live,
healthy  spermatozoa  are  found  in  the  cervical  canal,  it  is  unnecessary
to  search  the  uterine  cavity.
