Lab notes on complement fixation experiments

These notes document Heidelberger's experiments on complement fixation during a critical period of research through which Heidelberger showed that complement, until then a poorly understood component of antibodies, consisted of a group of specific chemical substances, most likely protein. At the time, the term referred to the heat-sensitive factors in serum that trigger cytolysis, the dissolution of antibody-coated cells. Today, complement is understood as a functionally related system of at least twenty different serum proteins that play a key enzymatic role not just in cytolysis, but in other immune responses, including phagocytosis, the engulfing of foreign matter by immune cells, and anaphylaxis, a form of hypersensitivity reaction to a specific antigen with often life-threatening consequences. Heidelberger described the methods and results of these experiments in two articles on complement published in 1941.