The  destruction  of  haemoglobin  proceeded  rapidly  at  37°  C., 
usually  half  to  three-quarters  disappearing  in  the  course  of  two  hours. 
At  31°  C.  one-fifth  lo  two-fifths  of  the  haemoglobin  was  destroyed 
m  the  same  period  of  time,  and  at  25°  C.  less  than  one-tenth.  When 
a  comparison  of  these  amounts  with  the  specific  gravity  and  reaction 
of  the  urine  is  made  (Table  25),  it  is  seen  that  with  the  higher  specific 
gravity  (i’026)  obtaining  in  Experiment  I  the  rate  of  destruction  was 
most  rapid,  with  the  lower  specific  gravity  of  Experiments  2  and  3 
(ro20  and  ro22)  was  less  rapid,  while  in  Experiment  4  in  which 
the  urine  had  a  specific  gravity  of  roi5,  haemoglobin  was  destroyed 
with  considerable  slowness.  In  the  last  case  another  factor  was 
perhaps  operating  to  retard  the  action  of  the  urine  upon  haemoglobin, 
namely,  its  alkaline  reaction  ;  for  alkaline  urine  was  found  to  be  slow 
111  its  action  upon  red  cells,  even  when  its  specific  gravity  exceeded 
r020.  The  variations  met  with  in  different  experiments  seem, 
however,  to  be  m  part  attributable  to  the  diurnal  variations  in  the 
red  blood  cells  already  encountered  in  experiments  made  with  quinine 
(Tables  16  and  17).  The  breaking  up  of  haemoglobin  in  the  urine  is 
not  due  to  the  presence  in  the  latter  of  a  thermolabile  ferment,  for 
previous  boiling  does  not  alter  the  rate  at  which  destruction  proceeds. 
In  red  cells,  whose  haemoglobin  has  been  largely  destroyed, 
methaemoglobin  is  found,  on  laking,  to  be  present.  The  amount  of 
this  substance  is  very  small  relatively  to  the  unaltered  haemoglobin, 
until  the  destruction  exceeds  85  per  cent.,  when  its  presence  is 
generally  readily  recognisable,  though  it  is  still  found  in  much  smaller 
amount  than  oxyhaemoglobin. 
It  will  be  seen  from  Table  26  that  haemoglobin  did  not  find  its 
way  into  the  urine  until  the  destruction  of  haemoglobin  within  the 
red  cells  had  reached  or  exceeded  75  per  cent.  At  about  this  point 
haemoglobin  began  to  escape,  and  when  the  percentage  of  destruction 
exceeded  go  per  cent.,  the  percentage  of  haemoglobin  in  the  urine 
was  sometimes  5  per  cent,  of  the  amount  originally  present  in  the 
red  blood  cells,  in  one  case  reaching  as  much  as  10  per  cent.  Thus, 
although  haemolysis  did  not  occur  in  amount  sufficient  to  produce 
after  centrifugalisation  a  red  coloration  of  the  urine,  nevertheless 
as  destruction  of  haemoglobin  approached  completion  a  slight  degree 
of  haemolysis  took  place,  causing  oxyhtiemogiobin  bands  to  make 
their  appearance. 
