| Whenever the presence of blood is confirmed at the | | | | testing blood samples to find out whether they are |
| scene of a crime, the medical examiner (ME) must | | | | from humans. |
| ascertain whether the blood is really from a human | | | | If a substance containing antiserum interacts with a |
| being and not from a wolf or a bear. After he makes | | | | blood sample containing the antigen, a chemical |
| that determination, he can then conduct subsequent | | | | reaction occurs. The reaction makes an |
| testing to determine the person to whom the blood | | | | antigen-antibody complex that forms a precipitate. |
| belongs. | | | | The effect is a visible precipitation line falling out |
| The tests used for determining which species that | | | | where the two reagents, the antiserum and antigen, |
| blood belongs to are called antigen-antibody reactions. | | | | meet. |
| These are the same tests used for determining blood | | | | Put in other ways, if an antibody against the human |
| type in an individual. The main difference is that an | | | | blood antigen comes into contact with a substance |
| antiserum has to be created so that it reacts with | | | | containing human blood, the reaction produces a |
| antigens that are unique to humans. Antiserum refers | | | | visible line of precipitation, or solid substance between |
| to a substance that has antibodies that interact with | | | | the two solutions. If there is no chemical reaction |
| a specific antigen. An antigen is a molecule that | | | | that produces a precipitate, then the ME can |
| generates an immune response. Therefore, a specific | | | | conclude that the blood is not human. |
| antibody that interacts with a human antigen is | | | | The modern day forensics laboratory contains various |
| created so that the resulting reaction will determine | | | | antiserums of common animal bloods. Sheep, cow, |
| the blood's origin whether it is human or not. | | | | deer, wolf, and cat antiserums are commercially |
| A human antiserum is made by injecting human | | | | available. Using these antiserums, a criminalist can |
| antigen such as human blood into laboratory rat or | | | | determine what species shed the blood. |
| any other animal and then allowing enough time for | | | | The next time you watch your favorite CSI program, |
| the animal to make enough antibodies specific for the | | | | you will be better cognizant of the chemicals used in |
| human blood antigen. The animal's blood now | | | | the crime lab to determine if a blood stain they find is |
| containing high quantities of antihuman antibodies is | | | | really human. |
| harvested. The antiserum is now isolated for use in | | | | |