'Natural' erythrocyte agglutinins in the serum of the Australian freshwater catfish, Tandanus tandanus Mitchell. II. Serum fractionation studies.

Normal serum samples from the Australian freshwater catfish possessing ABH-specific haemagglutinating activity, were fractionated using the techniques of gel filtration, ion-exchange chromatography, zone electrophoresis and isoelectric focusing in free solution. The successful isolation of the agglutinins is described and some of the difficulties involved in purifying and studying such natural' vertebrate agglutinins are discussed. Reasons against the automatic classification of poikilothermic natural' agglutinins as antibodies are advanced.