362  Spectrum  Analysis  of  Blood-stains.  {^iT^mT""' 
ON  SPECTRUM  ANALYSIS  OF  BLOOD-STAINS. 
By  H.  C,  Sorby,  F.R.S.,  &c. 
The  Lancet  of  last  Saturday  (May  20th,  1871,  p.  693)  contains  an 
article  on  the  above-named  subject,  the  whole  bearing  of  which  is  to 
the  effect  that  this  method  cannot  be  relied  upon  in  such  inquiries. 
Now,  I  think  myself  entitled  to  express  a  very  decided  opinion  on 
the  subject.  I  have  for  some  years  devoted  the  greater  part  of  my 
time  to  investigations  by  means  of  the  spectrum-microscrope,  have  ex- 
amined many  hundred  different  spectra,  and  seen  those  of  the  color- 
ing matter  of  blood  and  of  the  various  compounds  derived  from  it, 
times  w^ithout  number,  and  all  that  I  can  say  is  that,  as  my  experience 
has  increased,  so  much  more  has  increased  my  confidence  in  the  rec- 
ognition of  blood  by  this  method.  Of  course,  an  inexperienced  ob- 
server could  not  be  trusted,  no  more  than  any  one  ignorant  of  chem- 
istry could  be  relied  gn  in  detecting  poisons.  I  must  be  pardoned  for 
saying  that  I  can  only  explain  the  remarks  in  the  Lancet  by  sup- 
posing that  the  writer  is  not  conversant  with  the  subject ;  for  how 
otherwise  could  he  say  that  "  no  discovery  has  yet  been  made  by 
means  of  these  (absorption)  spectra,"  when  so  much  light  has  been 
thrown  on  the  behaviour  of  blood  in  presence  of  oxygen  and  other 
gases  ;  and  when  there  have  been  discovered  in  some  of  the  lower 
animals,  other  substances  than  haemoglobin,  having  similar  proper- 
ties, and  supplying  its  place,  besides  some  hundreds  of  different  col- 
oring matters  in  animals  and  plants,  which  could  not  have  been 
studied  in  any  other  manner.  Moreover,  it  appears  to  me  that,  if  the 
writer  ever  saw  the  spectra  of  blood,  it  must  have  been  under  most 
unfavorable  circumstances  ;  he  must  have  examined  a  bad  preparation, 
with  an  unsuitable  instrument,  perhaps  out  of  focus.  I  cannot  other- 
wise understand  how  he  could  say  that  "  all  that  is  to  be  observed  is 
a  little  dimness  here  and  there  in  the  spectrum.  The  dim  spaces, 
which  are  not  sharply  bounded,  have  been  dignified  with  the  name  of 
absorption  bands."  Now,  I  would  undertake  to  show  the  w^riter  in  a 
few  miuutes,  that  the  absorption  bands  seen  in  the  spectra  of  oxidized 
haemoglobin  and  deoxidized  hsematin,  instead  of  being  a  mere  dimness, 
are  as  black  and  distinct  as  could  be  desired.  He  would  see  that 
they  are  as  well  defined  as  if  we  had  a  piece  of  a  rainbow  on  paper, 
and  marked  bands  on  it  with  the  blackest  ink.  I  willingly  admit  that, 
in  the  case  of  some  substances,  absorption  bands  are  indeed  faint,  or 
