As blood is a life-saving fluid, it is often required for transfusions during operations and accidents. Without knowing its group it cannot be donated or received. The blood groups fall into four categories. They are A, B, AB, and O. If a man belongs to group A, it means that on his RBC, there is a special compound, which mazy be designated as ‘A’. If a person belongs to group B, it means that on his RBC, there is a different compound called ‘B’; a person of AB group has both these compounds; and a person of O group does not have any of these compounds. O group is universal donor, while AB group is universal receiver.
Besides these types, more than 85% of the people can be Rh positive and 15% Rh negative. Before blood transfusion Rh factor is also testd. Rh factor is also a compound on RBC which was first seen on the RBC of Rhesus monkey. If this compound is present in man, the person is Rh positive, and if this is absent, he or she is Rh negative.
You can feel pumping of blood through the heart in certain places of the body. The blood vessels in the wrist are the most convenient. Take your left wrist in your right hand and press gently like a doctor. You will feel pulsations with your right thumb. Count the number of pulsations per minute while resting. Again count the number after brisk exercise or after running for a few minutes. Observe the time take to restore the original pulse rate. The pulse rate may double in an excited state.