What is the difference between negative and positive blood types? ADA LAM About 400 antigens - substances which stimulate the production of antibodies - have been discovered in human blood. However, only a handful of them are of real importance: those classified under the AOB and rhesus systems. In 1900, Austrian pathologist Karl Landsteiner discovered that red blood cells from one person will clump together when they come in contact with blood from certain other people. From this, he worked out that there must be different blood groups, which he called A, B, AB and O.
In 1940, working together with A S Wiener, he discovered that an injection of blood from a rhesus monkey into a rabbit stimulated the production of antibodies. When human blood was tested with the rabbit blood, the red blood cells from 85 per cent of the humans tested clumped together. The researchers found that 85 per cent of white people (a higher percentage for blacks and Asians) had the same factor in their blood as rhesus monkeys - which came to be called the rhesus positive factor, or Rh positive. The roughly 15 per cent of people who lacked the rhesus factor were classified as having Rh negative blood.
In general, having Rh positive or Rh negative blood is only important during blood transfusions and pregnancy. If an Rh negative person was given Rh positive blood, the person would produce antibodies to destroy the Rh positive blood. If sufficient Rh positive blood was transfused into an Rh negative person, the immune system's attack on the transfused blood could prove fatal.
With an Rh negative mother and Rh positive father, it is possible that the foetus would be Rh positive. Foetal blood cells pass through the placenta into the mother's blood stream, and the mother produces anti-Rh antibodies.
In the first pregnancy this is not a problem since the production of antibodies in not high enough to harm the foetus. However, in a subsequent pregnancy these antibodies could be numerous enough to result in a still birth. To prevent this, after the birth of an Rh positive baby, the Rh negative mother is giv en an injection of antibodies which destroy Rh positive red blood cells from the baby. Thus during her next pregnancy the mother will produce few, if any, antibodies to destroy foetal Rh positive blood cells.
When was the Smithsonian Institution set up? The Smithsonian Institution in Washington, DC, was founded in 1846 under the terms of the will of James Smithson of London.