Laurie Andersen, age 12, of Missoula, Mont., for her question:

WHAT DOES BLOOD PLASMA DO?

Blood plasma is the straw colored liquid part of the blood that carries dissolved food materials to all parts of the body. It is the part that remains after the red and white blood cells are removed.

Plasma also picks up waste materials, produced by the body cells, and carries them to the organs that remove wastes from the body. In addition, plasma also carries secretions from certain glands in the body.

Plasma contains water, salts, proteins and other materials.

One of the most important proteins found in plasma is fibrinogen. This substance keeps you from bleeding to death by making clots that seal off the wound.

Another important plasma protein is called globulin. This protein carries disease fighting substances known as antibodies that destroy germs in the body.

And a third vital protein in plasma is called albumin. This substance helps to keep the blood volume and blood pressure normal.

It was found in the 1930s that plasma could be separated from whole blood. Plasma is obtained by separating out the blood cells in a machine called a centrifuge. The liquid plasma can be kept for much longer than whole blood. It can also be frozen or dried and, in these forms, be kept indefinitely.

Plasma is used for transfusions when whole blood is not needed or cannot be obtained. It is also used to restore blood volume lost during severe bleeding.

Plasma has saved the lives of millions of wounded soldiers and persons injured in accidents. Plasma is also often used during operations to combat the condition known as shock.

In certain diseases, the body is literally starved for certain proteins. Scientists have learned to produce such substances from plasma and other materials.

Scientists have been trying to find a safe substitute for plasma, but those found so far are not very effective.

It was in 1969, just 20 years ago, that scientists both in England and at New York City's Rockefeller University found the chemical structure of gamma globulin. This was a very important advance in the study of immunity.

Most antibodies are concentrated in the portion of the globulin protein called gamma globulin. Doctors use gamma globulin to help prevent infectious jaundice, measles and other diseases.

Containers are used to freeze a plasma and alcohol mixture at minus 70 degrees.