1. This brings us to Blood
Blood by far is the most common bodily fluid left at a crime scene and it’s the most useful because it opens up many avenues of investigation for the forensics team to travel down.

2. Understanding Blood Blood is a mixture of many components.
The liquid portion of blood is the plasma. It contains proteins, enzymes, clotting factors, electrolytes and various cells.
Serum is the yellowish liquid leftover after the blood clots.
Blood cells come in three types:
Leucocytes or white blood cells (WBC)
Erythrocytes or red blood cells (RBC)
Platelets or tiny cells involved in blood clotting.

3. The Discovery of Blood Groups
Experiments with blood transfusions, the transfer of blood or blood components into a person's blood stream, have been carried out for hundreds of years. Many patients have died and it was not until 1901, when the Austrian Karl Landsteiner discovered human blood groups, that blood transfusions became safer.

4. ABO blood grouping system
According to the ABO blood typing system there are four different kinds of blood types: A, B, AB or O (null).
Do you know what type you are???

5. What makes you the type that you are?
Antigens – Antibodies
What makes you the type that you are?
Blood group A
If you belong to the blood group A, you have A antigens on the surface of your red blood cells and B antibodies in your blood plasma.

6. Blood group B
If you belong to the blood group B, you have B antigens on the surface of your red blood cells and A antibodies in your blood plasma.  

7. What do you think blood type
???
What do you think blood type
AB looks like?
Type O?

8. Blood Type AB
Blood Type O

9. What about this Rh stuff?
Think of the + and – of a blood type as another antigen found on the surface of a RBC. If you are positive (Ex: A+) you have the extra protein. If you are negative, you do not have the extra protein.

10. Transfusions
A transfusion is often shown as a bag of blood hanging next to a hospital bed with a tube going into a patient.
The key thing to note is that consider that only the RBC are being transfused; not the plasma. If you remember this key point all will be well.

11. Fill in the chart with the appropriate terms:
Blood Group
Antigens
Antibodies
Can give
blood to
Can receive blood from AB A B O

12. So, are you ready to play the blood typing game?

14. OK…so what does this have to do with forensic science?
First, if you find blood at a crime scene you can eliminate someone from being a suspect with a quick blood typing test (DNA fingerprinting is so expensive and takes weeks to complete). It may not pinpoint someone specific but it is useful.