Classification of sour hams and location of sour areas 10 Method of detecting sour hams 12 Theories in regard to ham souring 12 Previous experimental work to determine cause of ham souring 13 The present experiments 14 Media employed 14 Method of procedure in examining hams 15 Results of examination of sour and sound hams 16 Histological changes in sour hams 17 Chemical analyses of sour and sound hams 18 Bacteriological examination of sour and sound hams 20 Inoculation experiments with hams 21 Probable method by which ham-souring bacillus enters hams 33 Possibility of infection prior to slaughter 33 Possible infection from pickling fluids 34 Experiment to show whether infection takes place from the curing pickle 34 Possible infection through manipulation or handling 35 Infection from ham thermometers 35 Experiment to show whether hams become infected from ham thermometers 37 Infection from pumping needles 41 Infection from billhooks 42 Biological and morphological characteristics of the ham-souring bacillus 43 Conditions favorable to growth 43 Growth on different culture media 43 Morphology 46 Spore formation 46 Resistance to heat and chemical agents 47 Gas production 47 Acid production 48 Pathogenic properties 48 Nature of the bacillus 48 Prevention of ham souring 50 General summary and conclusions 53 Acknowledgments 55 ILLUSTRATIONS. PLATES. Page.