Precipitin Test

1. Precipitin Test

2. What is the Precipitin Test? • The precipitin test is used after a unknown sample has been identified as blood to determine whether the blood sample originated from a human or an animal • It uses antiserum normally derived from rabbits that have been injected with the blood of an known animal to determine the species of origin of a questioned blood stain

3. History of the Precipitin Test Paul Uhlenhuth, a German biologist, discovered that if he had injected protein from an egg of a chicken into a rabbit, andlater mixed the serum from the rabbit with the egg white, the egg proteins would separate from the liquid to form a cloudly like substance called precipitin (an antibody)

4. How it works • When animals (rabbits) are injected with blood of a human, antibodies form and react with the human blood to ‘neutralize’ it’s presence • The antibodies can then be recovered by ‘bleeding’ (drawing blood from the animal) and isolate the blood serum that contains antibodies that react with human antigens • The blood is then placed inside a small test tube. The human blood gives a precipitin band with the sensitized rabbit serum (Picture showing the process is on the next slide)

6. Advantages • Readily applicable to comparison of antibodies • Provides opportunity to isolate antigenic constituents

7. Disadvantages • Does not detect all antibodies known to occur • Not as sensitive as other test for detection

8. On August 15, 1974, a man named John Doe was hunting in the woods when he mistakenly shot a person thinking it was a deer. As inveatigators examined the crime scene, they discovered that John Doe had tried to get away with murdering a man. He tried to cover up the crime scene by hising the body and placing deer blood next to the corpse. The investigator had forensic scientist use the precipitin test with the blood sample found at the scene. Results from the forensic scientist showed that the test could not detect all of the antibodies in the serum. The case remained unsolved.

10. Case of Norrh Mohammad(1925) • John Keen, Robert Fletcher, William Dayer and John McCormack were accused of the assault and murder of Norrh Mohammed in Port Dundas. • “in Port Dundas, Glasgow, late on Saturday night when, in an outbreak of vicious hooliganism, Norrh Mohammed (27) was stabbed to death in a struggle with a gang of men. Mohammed who made a living by hawing drapery goods was approached by three men, who asked him to show them some jumpers and blouses. When Mohammed refused to do so he was beaten and stabbed.” • John Keen was charged with murder and sentence to death.

13. In his report Glaister concluded that:Group I: Contained seven productions, consisting of clothing worn by the deceased Norrh Mohammed that stains 1 to 6 were that of mammalian blood, and that they originated from the wound found by dissections of the body of the deceased. No stains were found on production 7 (pair of socks). Group II: Four productions comprising Group II, clothing worn by John Keen, that stains found on (1) Jacket, (2) Vest, and (4) right boot were stains of blood, but that found on the trousers was not. The stain on the toe-cap of the right boot was proved to be composed of human blood. Group III: Three productions forming Group III, as consisting of clothing worn by John McCormick that the stains found upon both legs of the trousers were stains of blood, and from the special test employed, that these stains were composed of human blood (no stains were found on the boots or the jacket). Group IV: The stains found on the dagger and sheath were composed of mammalian blood.

14. Review Questions • What is the precipitin test? • What two animals did Paul Uhlenhuth use to discover precipitin? • What are some examples of animals whos antiserum is commercially available with rabbits? • What are two advantages? • What are two disadvantages?

15. References • Textbook • http://www.trutv.com/library/crime/criminal_mind/forensics/serology/3.html