Animal research earlier this century showed that it was possible to remove toxic metabolites from the blood using special membranes, and return the blood to the body. The first practical demonstration of this process, known as continuous dialysis of blood was by John Abel 1 in 1914, using anaesthetised rabbits and dogs and dialysis membranes made from treated parchment. After 2-3 hours of dialysis, the animals made complete recoveries. Although the intention was to develop a way to measure the blood concentration of substances such as hormones, Abel highlighted the potential of his process as an 'artificial kidney'.
Blood clotting is a potential problem when blood flow is disturbed in any way.
Abel prevented coagulation using an anticoagulant extracted from leeches, hirudin. However, it was expensive, difficult to extract and early preparations were very impure. They caused severe heart and lung problems and allergic reactions, and were thus unsuitable for human use. The discovery of heparin, an anticoagulant occurring naturally in mammals, was thus a significant step. In 1925, George Haas 3 produced it in larger quantities and showed that it worked well during animal studies of dialysis.