Brucella-agglutinating antibodies from selected bovine blood serums and milk samples did not fix complement, and after treatment with 2-mercaptoethanol they lost agglutinating power. After infection of calves with Brucella abortus, strain 19, agglutinins for Brucella that were inactivated by mercaptoethanol appeared earlier than those stable to mercaptoethanol. Under the conditions of these experiments, the appearance and development of complement-fixing capacity coincided closely with the mercaptoethanol stability of the agglutinins for Brucella.

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Summary A substance in guinea pig serum, lytic for sheep red cells, is composed of two fractions, one heat stable and removed by zymosan, and one heat labile which is destroyed in 9 minutes at 56°C. Untreated serum or the combined fractions cause hemolysis of dilute suspensions of sheep erythrocytes. The lysin is inactive against sheep cells at 4° C but is activated by increased temperatures up to 37° C. The activity of the lysin is enhanced after storage at −24° C for 6 days; it decreases with elevation of pH, becoming negligible at pH 7.8 under the conditions studied. The characteristics of the lytic substance are distinguished from complement, the C′3 component of complement and sensitizing “natural” antibody.