1. A mixture of serum and its anti-serum has the property of fixing or deviating complement and thus interfering with haemolysis. In this there is a close analogy to the fixation of complements by cellreceptors in association with immune-bodies.
2. A large number of different complements may be fixed by the same combination of serum and anti-serum: some complements however may not be fixed.
3. The amount of homologous serum necessary to produce a distinct deviation of complement is extremely small—·000,01 c.c. and even less: as a rule it is many times less than the amount necessary to give a visible precipitate with the anti-serum.
4. When a precipitate forms, the deviating substance is present in the precipitate and may be so exclusively: precipitation is however not essential, as the deviation phenomenon may be given by an anti-serum without the formation of a precipitate.
5. The precipitin and deviation tests give results which are in great part in accord as regards specificity.
6. For any given amount of anti-serum there is an optimum amount of homologous serum which gives maximum deviation of complement: above as well as below the optimum the deviation diminishes.
7. The deviation phenomenon produces an effect similar to an “anti-complement” action and the views generally held with regard to anti-complements require revision. It is however still left an open question whether true anti-complements exist.