Fowl antibody: IV. The estimation of haemolytic fowl complement.

The degree of haemolysis () of SRC sensitized with horse haemolysin by fowl complement was measured. A linear relation was not found between log [/(1—)] and log , the log volume of fowl complement used. Absorption of fowl C′ in the cold with packed SRC did not always result in C′ free from lysins to SRC. Estimations on two C′ sera from which SRC lysins had been removed gave a straight line with an indicator system of SRC sensitized with immune' fowl haemolysin. Linear relations over a wide range of C′ concentrations, were also obtained when the indicator system consisted of SRC sensitized with a combination of immune' and naturally occurring antibodies. The range could be extended by the addition of a small amount of heated normal fowl serum.