cases  may,  at  times,  show  a  condition  in  which  an  occasional  beat
through  at  a  much  higher  level  than  that  at  which  all  the  beats  can
be  detected.  Often  this  is  due  to  the  action  of  respiration.  This  should  be
noted  in  the  estimation  thus:  High  pressure,  occasional  beat  at  170;  all
other  beats  at  155.    Diastolic  level  with  increasing  pressure.    Where  the


116


MEDICAL  DIAGNOSIS


diastolic  level  is  hard  to  obtain,  it  is  of  help  to  get  the  greatest  oecillation
with  increasing  as  well  as  with  decreaung  pressure."

The  modification  of  the  Riva-Rocci  sphygmomanometer  by  Beall  and
Mason  is  portable  and  compact.  The  manometer  tube  is  in  two  sections,
connected  by  a  rubber  cuff,  and  the  scale  is  hinged  at  195  mm.
Janeway's'  studies  show  that  the  upper  limit  of  normal  blood-pressure
in  young  adults  is  about  145  mm.  and  the  lower  limit  about  80  mm.  In
the  great  majority  of  young  males  the  upper  limit  is  100  mm.  to  130  mm.
In  females  it  is  about  10  mm.  lower.  In  infants  the  pressures  are  lower;
after  fifty  they  are  higher.  Blood-pressures  above  160  or  180  mm.  are
almost  always  associated  with  disease.  Janeway  places  normal  diastolic
pressure  at  25  to  40  mm.  below  systolic  pressure  in  the  same  individual,
that  is  to  say,  between  65  and  1 10  mm.     In  the  aged  a  difference  of  50

mm.  is  common.  A  dif-
ference of  less  than  20
mm,  between  the  systo-
lic and  diastolic  pressure
indicates  an  abnormally
small  pulse;  a  difference
of  more  than  50  mm.  an
abnormally  large  pulse.
Pacbon's  Sphyg-
mometrlc  Oscillometer.
— This  instrument,  con-
structed on  the  aneroid
principle,  is  much  more
convenient  and  sensitive
and  fully  as  accurate  as
the  mercurial  devices.
