Abstract
Summary. In the normal sera of bulls, rams and sows, antibodies agglutinating not only homologous but also heterologous spermatozoa were determined. In the normal sera of some rabbits, only feeble antibodies against boar spermatozoa were present. The sera of bulls and rams also contained spermagglutinins against their own spermatozoa. The absorption of normal sera with homologous spermatozoa suppressed the formation of reactions against homologous and heterologous germ cells. The heterologous spermatozoa only absorbed agglutinins against the spermatozoa of their own species. Antibodies obtained by immunizing rabbits with bull and ram spermatozoa not only agglutinated homologous spermatozoa, but also produced cross-reactions with germ cells of other species. Immune antibodies against boar spermatozoa agglutinated only homologous spermatozoa. Immune antibodies produced by immunizing rabbits with seminal plasma from a bull agglutinated not only bull but also ram spermatozoa. Antibodies against the seminal plasma of a boar agglutinated only boar spermatozoa. The results of the absorption of immune sera with homologous and heterologous spermatozoa were similar to those obtained with normal sera. Absorption with seminal plasma diminished the titres of antibodies, especially against heterologous spermatozoa.