Many years ago, it was customary to "bleed" people who were thought to be too "full-blooded." Some of the smaller veins were opened and blood was allowed to flow out. Doctors thought this would cure many diseases common to such "fullblooded" persons (often another way of saying fat people). Actually, without knowing it, many of these doctors dangerously weakened their patients. Today, bloodletting is practiced very rarely. In fact, we try to prevent the loss of blood wherever possible.
When a major blood vessel has been cut during an accident, we apply a tourniquet to stop the flow of blood. (To learn how this is done, read the article on FIRST AID.) When a person bleeds large amount, the doctor gives him someone Else's blood. This is called a blood, transfusion. In emergencies, blood transfusions may be given directly from person to person by joining their veins with a rubber tube. But usually, a pint of blood from the donor, or person giving blood, is drained into a sterilized container; from this the blood is let through a rubber tube, ending in a hollow needle, into the patient's veins. There are four different types of human blood. Persons having the same type of blood may receive transfusions from one another. Certain blood types mingle freely with other types. These are said to be compatible. Only compatible blood types can be used in transfusions. The blood in our bodies is called whole blood-that is, blood containing all the specks of matter ordinarily floating in it. For a short time, whole blood can be stored for future transfusions; the place in which it is stored is called a blood bank.
To store blood for longer periods, the specks of matter are removed, leaving the liquid portion of the blood. This is called plasma. Plasma can be kept in storage almost indefinitely. It can also be dried and shipped in powdered form, just like powdered milk. Then sterilized water is added and the plasma is ready for a transfusion. Plasma can be given in transfusion to persons of all blood types. This is especially important in times of disaster, such as war or epidemics, when many people must have emergency transfusions. Thousands of lives have been saved by transfusions of blood plasma.