THE EFFECTS OF SERUM ON SPERMATOZOA.

A spermicidal factor was found in fresh human, bovine, rabbit, guinea pig, and rat sera. It kills the spermatozoa of its own species (except in the case of human serum) and the sperms of other species. It was unstable, thermolabile, and of large molecular size. It was present in limited quantity in the fresh serum and could be used up by a definite number of spermatozoa. It could be destroyed by sodium citrate, by Seitz filtration, by trypsin, and by snake venom. This factor was not present in tissue extracts and various plasma protein fractions. The strength or concentration of this factor varies in different individuals and in different species. This factor has several characteristics similar to those of complement.