Blood has long been thought to have properties related to health and well-being. The early Egyptians bathed in it to restore health and energy; some Romans rushed to the sides of dying gladiators to drink their blood.
In contrast, physicians of the Middle Ages applied leeches to their patients to draw off bad blood, which was thought to be the cause of their illness. After 1628, when William Harvey discovered how blood circulated through the human body, it became possible to consider the idea of blood replacement.
In 1664 the French physician Jean Denys transfused a patient with lamb's blood. Subsequently, there were successful transfusions in France and England, but also deaths, as doctors did not know that animal blood was incompatible with human blood. As a result the practice fell into disrepute.
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In the early nineteenth century the English physician James Blundell established that successful transfusions could be made only from one human to another but it was not until 1901 when the Austrian Karl Landsteiner discovered the existence of various blood groups that blood compatibility could be determined. He showed that each person has one off our possible groups, called A, B, AB and 0, and that, after the first transfusion of blood from an incompatible blood group, the recipient destroyed the cells of the donor's blood owing to the production of an antigen-antibody reaction.
Subsequently, many other blood groups have been discovered, but the A, B, 0 and Rh positive and negative groups remain the most important and the only ones necessary for routine cross-matching of blood for transfusions.
The difference between the A, B, 0 and Rh groups is that, although both are genetically determined (that is, a child can only have certain blood groups depending on those of his parents) the A, B, and 0 antigen and anti A, Band 0 antibodies occur naturally in the blood, so that a reaction to mismatched blood is possible with the first blood transfusion. With the Rh groups, the antibody is formed in people with Rh negative only after contact with the Rh antigen, so that reactions occur only with subsequent contacts. The most common situation in which this may occur is when an Rh negative woman has a husband who is Rh positive and conceives an Rh positive child.
If the child's blood comes into contact with the mother's while the child is in the uterus, there is no problem with the first pregnancy, but if she had other Rh positive babies she would then have a supply of Rh antibodies, which would be in a position to destroy the red blood cells of the baby she is carrying. In this case, exchange transfusions can be given while the baby is yet unborn.
Apart from the discovery of blood groups, there were other problems to be solved. It was discovered during the Franco Prussian War (1870) that, with transfusions, the blood used often became clotted.
This difficulty was overcome in 1914 by the addition of 0.2 per cent sodium citrate to each bottle of blood.
In 1935 the continuous drip method of transfusion was introduced, enabling the amount of blood to be regulated and obviating the danger of overloading the recipient's heart and circulatory system. By World War II the components of blood, red cells and plasma, were isolated and it became possible to use them separately and store them more effectively.
Another advance brought about by the necessities of war was the development of a blood plasma substitute so that blood volume could quickly be built up in bleeding soldiers when there was insufficient blood available for transfusions of whole blood.
Today all the apparatus used for blood transfusions is disposable, which again cuts down the risk of infection. Blood is donated by healthy people and stored in a blood bank. When required, bottles of the appropriate blood group are sent to the hospital for a particular patient and small amounts from each bottle are crossmatched with a sample of the patient's own blood to ensure that the blood will mix without being broken down.
In Australia and the United Kingdom blood banks depend solely on voluntary, unpaid donors for the supply of blood available for transfusion.
However, in the United States donors are paid for each bottle they supply.