Ecker and his co-workers1 of the Institute of Pathology, Western Reserve University, report the fractionation of human serum complement into four essential components. Originally Bordet, Ehrlich and others assumed that "complement" or "alexin" is a single chemical entity, a panimmunizing enzyme that requires specific antibodies for its lytic action. This concept was soon challenged by Ferrata,2 who showed that if guinea pig serum was separated into a globulin and albumin fraction neither fraction contained complement but that the original complement titer could be restored by combining the two fractions. Complement thus became an albumin-globulin complex, the terms "end piece" and "mid piece" being applied to the -two fractions, so that complement was still conceived to be a single chemical entity.
In 1914 Coca3 suggested that there was a third essential factor in guinea pig complement, which could be specifically absorbed on yeast or on insoluble yeast carbohydrate
HUMAN SERUM COMPLEMENT. JAMA. 1944;124(3):163. doi:10.1001/jama.1944.02850030031012
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