Published online by Cambridge University Press: 15 May 2009
This communication contains a record of a series of experiments undertaken primarily to elucidate tbe action of complement and its fractions on a Tropin-B. typhosus system as estimated by the phagocytic index. Haemolytic experiments were also undertaken with the combined object of testing the activity of the complement-fractions and of investigating by the use of another system, certain points which arose in the course of the phagocytosis experiments. The haemolytic experiments are recorded in Part II of this communication. The term “ Tropin ” employed throughout the paper to designate the antibody in an inactivated immune serum which, in the absence of complement, is able to effect sensitisation of micro-organisms for phagocytosis, has been adopted solely for the sake of convenience and entirely without prejudice to the conception we have formed of its relation to the immune opsonin so-called, or to the general antigen-antibody reaction which, under certain conditions of experiment, involves the fixation of complement.