BLOOD AND BLOOD STAINS

• Blood is one of the most significant & frequently encountered types of physical evidence in forensic investigation of death & violent crimes.
• Lattes crust method: The common blood groups ABO, MNS and Rh systems can be determined in a blood stain by .
• Luminol spray is used to identify blood stains which are no longer visible due to washing of crime scene.
• Kastle-Meyer test is used to identify visible blood stains.
• Haemin crystal test is a confirmatory test for blood stains.

The points that are usually required to be determined regarding stains are: 

1. nature  of stain (whether  the  stains is  blood  or not)
2. the  species  (human  or animal)  from  which  the  blood  has come  from
3. blood  group.

(A) Nature  of  stain  {whether the  stain  is  blood  or  not)

• To  determine  the  nature  of stain,  following tests  are  used :

1) Chemical  tests

• These  tests  are based  on the  peroxidase  activity  of haematin,  which  is,  derived  from  oxidation  of  haem  of haemoglobin or methemoglobin present. 
• This  enzyme,  in the  presence  of hydrogen  peroxide converts  colourless  salts  into  coloured  bases. Thus these  tests  are based  on H₂O₂ and peroxidase  enryme.

Tests are  :

1. Benzidine  test : Greenish  blue  colour.
2. Phenolphthalein  test (kastle myere test):  Deep permanganate  colour.
3. Leucomalachite  green  test :  Bluish green  or peacock  blue  colour.
4. Guaiacum  test:  Blue colour.
5. Orthotoludine test  (kohn  test) :  Blue or green  colour.
6. Amidopyrine  test:  Purple colour.

2) Microchemical  tests: These  tests  are based  on  property  of  haem  part  of hemoglobin  to  form  characteristic  coloured  crystals.

The  tests  are:

1. Teichmann’s haemin  crystal  test.(hydrogen  peroxideis not used as in others.)
2. Takayama  hemochromogen  crystal  test.
3. Luminal  spray test  :  It  is  especially useful  in old obscure  blood  stains.
4. Spetroscopy: It  is  most delicate  and  reliable  test, It  is  based on  the  principle  that  hemoglobin  and  its  derivatives  give  characteristic absorption  bands  when  viewed  through  a spectroscope.
5. Microscopy: Microscopic  examination  of  RBCs is  possible  only  in  fresh  stains.

(B) Detection of  species  {whether  the  blood  has come  from  human  or animal}

For  detection of species,  serological  (immunological)  tests  are used.  These  tests  are  :

1. Precipitin test
2. Haemaglutination  inhibition  test  (antiglobulin  consumption  test or absorption  inhibition  test).
3. Gel diffusion  test.
4. Double  diftrsion  test.
5. Precipitation  electrophoresis.
6. Latex  agglutination  test.
7. Isoenzyme  method  (enzymological  test).) Detection of blood group  of blood  stain : These  tests  are  :

l)  Immunological  (serological)  :  (i)  absorption-elution  test, (11)  absorption-inhibition  test, (ii)  mixed agglutination  test, (iv) latex  test.

2) Enzymological  methods.

3) Lalte’s  crust  method