The composition of blood

Blood is made up of minute elements or cells suspended in a pale yellow fluid, the plasma. The cells are so small that a drop of blood contains about 250,000,000 red corpuscles, 400,000 white corpuscles and 15,000,000 platelets.

Red corpuscles carry oxygen from the lungs to every part of the body so that the tissues may breathe. They are manufactured in red bone marrow.

White corpuscles form part of the body's defence system and will normally increase in number to attack and destroy any germs which invade the body.

Platelets take part in the clotting of blood and so help to stop bleeding when blood vessels are cut or damaged.

Plasma acts mainly as a carrier, transporting the corpuscles and platelets to all parts of the body, as well as foodstuffs and waste products. It is a valuable transfusion fluid and has the advantage that it can be stored without refrigeration for several months without deterioration. If suitably prepared, plasma can be given safely to patients of any of the four blood groups. It is the fluid portion of blood which has been rendered incoaguable and from which corpuscles have been removed.

Serum, the fluid separated from blood which has been allowed to clot, can be used in the same way as plasma. It is more easily filtered than plasma and has similar keeping properties.

Plasma and serum are usually dried and in this form they keep for very long periods of time. They are prepared for use by adding sterile distilled water or salt and glucose solution.

The ABO Blood Groups

The four main blood groups became known as a result of Landsteiner's research in the early part of the twentieth century and can briefly be described as follows:

These group-substances (A and B) can be identified by their reactions with the two antibodies (anti-A and anti-B) which exist in the liquid part (plasma) of the blood.