On  account  of  the  difficulty  in  securing  intelligent  cooperation  in  the
application  of  this  method,  particularly  Avith  children,  others  have  been
devised.  One  of  the  simplest  is  that  of  Fridericia,  which  is  a  modifica
tion  of  the  Haldane-Priestley  method,  the  apparatus  for  which  is  shown
in  the  figure  (Fig.  125),  and  the  manipulation  of  which  is  outlined  in
the  legend.  Another  is  to  take  a  mixed  sample  of  the  very  last  portion
of  several  normal  expirations.  On  account  of  the  extended  use  which  is
being  made  of  measurements  of  alveolar  air  composition,  both  in  lab-


*In  place  of  the  gas-sampling  tube  it  is  much  more  convenient  and  equally  accurate  to  employ  one
of  the  modern  ground  glass  piston  syringes  (L,uer).  The  piston  should,  of  course,  be  well  smeared
with  a  good  mineral  grease.
THE    CONTROL   OF    THE   RESPIRATION


341


Fig.  125. — Fridericia's  apparatus  for  measuring  the  CO™  in  alveolar  air.  The  person  expires
forcibly  through  the  tube  with  the  stopcocks  as  in  I.  A  is  closed  and  the  tube  placed  in  water  to
cool  the  air,  after  which  B  is  turned  as  in  II.  The  entrapped  column  of  air  equals  100  c.c.  A
solution  of  caustic  alkali  is  now  sucked  into  C  with  stopcocks  as  in  II.  B  is  then  turned  as  in
I  but  with  A  still  closed,  and  the  alkali  solution  allowed  to  enter  b,  after  which  B  is  turned  off,
the  excess  of  alkali  solution  in  C  allowed  to  run  out  and  the  burette  shaken.  The  burette  is
then  submersed  up  to  a  in  a  cylinder  of  water,  with  B  as  in  III.  After  allowing  for  cooling,
the  level  at  which  the  water  stands  gives  the  per  cent  of  CO».
