| When a human blood stain is found at the scene of a | | | | antiserums.--The antibodies within the antiserums |
| crime, forensic scientists must ascertain the blood's | | | | form a complex with the antigens. |
| type in a procedure called blood typing. Blood typing | | | | 2. Wash the object.--This steps involves the removal |
| refers to the classification of blood based on the | | | | of any excess antiserum-containing antibodies. |
| presence of inherited antigenic substances on the | | | | 3. Elute the sample.--Eluting breaks down hydrogen |
| surfaces of red blood cells (RBC's). Agglutination, or | | | | bonds between the antigens and antibodies in the |
| clumping, of RBC's is a positive indicator if the blood is | | | | presence of heat. The free antibodies are then |
| liquid and the RBC's remain intact. | | | | washed off. |
| What if the blood is dry? What then? | | | | 4. Test the eluted antibodies against known blood |
| Most blood found at crime scenes is dry. This kind of | | | | antigens.--The antigens to which the antibodies react |
| blood is most likely going to be a stain that is clotted | | | | determine which antigens are present in the original |
| and dried, and the RBC's have been destroyed. | | | | unknown sample of blood. |
| Therefore, clumping of RBC's is highly unlikely, and | | | | By simply typing the blood found at a crime scene, |
| blood typing can not be conducted. What does the | | | | forensic scientists can narrow their list of suspects |
| CSI do? He circumvents this problem using a | | | | and completely rule out other suspects. |
| procedure that draws out the remaining antigens. | | | | The next time your watch your favorite CSI TV |
| The absorption-elution procedure is a method that | | | | program, you will be more cognizant of the |
| draws out antigens. This is a four-step process: | | | | procedures that crime lab technicians use to type, or |
| | | | classify, dried blood. |
| 1. Treat the object containing the blood stain with | | | | |