The Antigens and Toxins of Pasteurella multocida 4 Bacterial Toxins Extracellular or Free Endotoxins 18 MATERIALS Sources of Chemicals and Biochemicals Source of Animals Equipment METHODS Bacteriological Methods Isolation of the Immunogenic and Toxic Complex 27 Chemical Methods Physical Methods 35 Biological Methods 45 Serological Methods 49 RESULTS 51 Isolation Procedures 52 Biological and Serological Studies of the 40,000 rpm Preparations 55 Chemical Analysis of the Toxic and Immunogenic 40-P Preparations 69 Isoelectric Focusing Experiments with the 40-P Preparations 83 iii Page Fractionation by Gel Filtration Chromatography The Results of Biological Studies of the Gel Filtration Fractions Particle Size Determination of the Gel Filtration Fraction S-II Estimation of the Particle Weight of the Sepharose 2B Fraction S-II Electrophoretic Studies on the Sepharose 2B Fraction S-II DISCUSSION OF RESULTS 161 Comparison of These Results with Other P. multocida Studies 174 SUMMARY 179 LITERATURE CITED 183 ACKNOWLEDGEMENTS 195 P. multocida. Both encapsulated, virulent and nonencapsulated, avirulent forms of P. multocida have been described by Heddleston (1962) and both forms of the organisms have been found to be highly immunogenic in chickens when used as killed bacterins. The substance characterized in this investigation was isolated from saline extracts of the avirulent nonencapsulated P. multocida strain P-1059 Gray. Since this organism did not have a capsule, it was felt it would be easier to isolate and characterize the immunogenic substance. The P-1059 strain (originally a turkey isolate) has been described by Heddleston and co-workers (1962, 1966) and is considered to represent the most prevalent P. multocida immunogenic type found in field cases of fowl cholera.