Standardization of a Complement Fixation Reaction with Chicken Serum as Complement *

In the course of experiments dealing with the specificity of certain heterologous tumqr transplants it was necessary to compare the reactivity of antisera to guinea-pig, rabbit, human, and mouse tissues with antigens of the homologous and of heterologous species. Preliminary attempts to carry out the titrations by means of the ring precipitin test failed to yield satisfactory results, due chiefly to the opalescence of the tumor antigens, the frequent occurrence of non-specific reactions, and the low titers of the antisera. As a result, the technic selected was the complement fixation reaction. However, since guinea-pig serum, the usual source of complement, could not be employed in the titrations with anti-guinea-pig sera, the use of the reaction was possible in either of two ways. One was to employ several complements; the majority of the tests could then be carried out according to the usual procedure. The other was to use the serum of a species unrelated to the experiment, which would have the advantage of giving uniformity to the resulting data. In either case, it became necessary to determine the suitability of various complements and to standardize a technic which would make possible the study planned.