wliicli  combines  with  it  under  some  partial  pressures  of  that
gas,  but  gives  it  up  under  lower.
Blood  plasma  or,  what  comes  to  the  same  thing,  fresh
serum,  exposed  to  the  air,  takes  up  no  more  oxygen  than  so
much  water:  about  0.56  volumes  of  the  gas  for  every  100  of
the  liquid,  at  a  temperature  of  30°  0.  At  the  temperature
of  the  Body  the  volume  absorbed  would  be  still  less.  This
quantity  obeys  Dalton's  law.
If  fresh  whipped  blood  be  employed,  the  -quantity  of  oxy-
gen taken  up  is  much  greater;  this  extra  quantity  must  be
taken  up  by  the  red  corpuscles  (in  possessing  which  whipped
blood  alone  differs  from  blood  serum)  and  it  does  not  obey
Dalton's  law.  If  the  partial  pressure  of  oxygen  on  the  sur-
face of  the  whipped  blood  be  doubled,  only  as  much  more
oxygen  will  be  taken  up  as  corresponds  to  that  dissolved  in
the  serum ;  and  if  the  partial  pressure  of  oxygen  on  its  sur-
face be  reduced  to  one  half,  only  a  very  small  amount  of
oxygen  (one  half  of  that  dissolved  by  the  serum)  will  be  given
off.  All  the  much  larger  quantity  taken  up  by  the  red  corpus-
cles will  be  unafEected  and  must  therefore  be  chemically  com-
bined with  something  in  them.  Since  90  per  cent  of  their
dry  weight  is  haemoglobin,  and  this  body  when  prepared
pure  is  found  capable  of  combining  with  oxygen,  there  is
no  doubt  that  it  is  the  haemoglobin  in  the  circulating  blood
which  carries  around  most  of  its  oxygen.  The  red  corpuscles
are  so  many  little  packages  in  which  oxygen  is  stowed  away.
