504  Alkalinity  of  the  Blood.  {AW^S££?$£' 
From  this  it  will  be  seen  that  the  alkalies  of  the  blood  have  im- 
portant physiological  functions,  and  variations  from  the  normal 
standards  must  result  when  pathological  conditions  ensue. 
It  is  very  desirable  then  that  some  simple  method  be  devised 
whereby  blood  alkalinity  may  be  speedily  and  accurately  determined  ; 
and  this  the  writer  believes  he  has  accomplished  by  the  invention 
of  an  apparatus  termed  a  hemo-alkalimeter. 
With  this  apparatus  the  alkaline  blood  is  titrated  with  acid  as 
usual,  but  chemical  indicators  to  show  the  end-reaction  are  not  em- 
ployed, their  use  having  been  found  altogether  impracticable. 
The  quantity  of  blood  used  for  such  work  must  be  minute  and  the 
quantity  of  indicator  to  be  employed  must  of  necessity  be  so  small 
that  the  end-reaction  becomes  obscured  by  the  coloring  principles 
of  the  blood,  hence  the  use  of  phenolphtalein,  methyl  orange,  litmus 
or  other  indicators  are  wholly  inadmissible. 
In  the  series  of  preliminary  experiments  made,  one  very  interest- 
ing fact  was  discovered,  and  this  was,  that  when  the  alkalies  in  the 
blood  were  neutralized  by  added  acid,  the  oxyhemoglobin  bands  of 
the  spectroscopic  field  were  first  diminished  in  thickness  until  the 
point  of  neutralization  was  reached,  when  they  disappeared  entirely. 
Here  then  was  a  "  natural  indicator"  and  this  phenomenon  was  then 
utilized  as  a  means  of  indicating  the  exact  point  of  neutrality. 
As  is  well  known,  blood  exhibits,  when  examined  spectroscopically, 
the  characteristic  absorption  bands  of  oxyhemoglobin,  unless  modi- 
fied by  the  presence  of  certain  gases  or  substances  that  change  the 
composition  of  the  blood.  Under  such  circumstances  we  may  have 
the  blood  spectrum  of  methemoglobin,  carbon  monoxide  hemoglobin, 
etc.,  but  the  presence  of  hemoglobin  will  be  still  evident  by  the 
characteristic  spectrum. 
Oxyhemoglobin  is  recognized  by  two  dense  shadows  which  appear 
in  the  highly  colored  field  of  the  spectroscope  as  parallel  absorption 
bands  between  d  and  e  of  Fraunhofer's  lines,  the  line  nearest  to  d 
being  darker,  narrower  and  more  strongly  marked,  while  that  next 
to  e  will  be  less  sharply  defined  and  broader. 
When  blood  is  titrated  with  an  acid,  and  examined  spectroscop- 
ically, the  absorption  bands  of  oxyhemoglobin  disappear  and  cannot 
be  restored  by  the  addition  of  an  alkali,  clearly  showing  that  the 
added  acid  has  neutralized  the  non-diffusible  alkali  of  the  red  blood 
corpuscles,  as  well  as  the  more  readily  neutralizable  and  diffusible 
alkali  of  the  blood  plasma. 
