Not many years ago the main purpose of “complement” seemed to be to drill holes in sheep erythrocytes. In the classic experiment which was part of every medical student’s microbiology laboratory experience, a magic stuff called complement, somewhat mysteriously obtained from guinea pigs, was either “fixed” or not “fixed” and the sheep cells either not lysed or lysed accordingly. That was about all there was to know about complement, and all one needed to know. Today the term complement embodies a group of plasma proteins which react in a complex sequence to mediate a variety of inflammatory effects, including changes in vascular permeability, the attraction of polymorphonuclear or mononuclear leukocytes, the enhancement of phagocytosis, and damage to cell membranes and osmotic lysis such as the sheep erythrocyte suffered in the complement fixation test
