Respectfully,

A. D. Melvin,
Chief of Bureau.

Hon.James Wilson,
Secretary of Agriculture.

CONTENTS.

Page.
Introductory[7]
Method of curing hams[8]
Definition of souring[10]
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.
Plate[I]. Fig. 1.—Section of muscular tissue from sound ham, showing musclefibers cut longitudinally; nuclei sharply defined and cross striationdistinct. Fig. 2.—Section of muscular tissue from sour ham,showing muscle fibers cut longitudinally; nuclei undergoing disintegration and cross striation indistinct16
[II]. Fig. 1.—Section through muscular tissue of ham which has undergonenatural or spontaneous souring, showing distribution ofbacilli between the muscle fibers, which are cut obliquely.Fig.2.—Section through muscular tissue of ham which has undergonenatural or spontaneous souring, showing individual bacilli betweenthe muscle fibers, which are cut somewhat obliquely18
[III]. Fig. 1.— Section through muscular tissue of artificially soured ham, showingdistribution of bacilli between the muscle fibers, which are shownin cross section. Fig. 2.—Section through muscular tissue ofartificially soured ham, showing individual bacilli between themuscle fibers, which are cut longitudinally26
[IV]. Glucose bouillon culture in Smith fermentation tube at four days48
TEXT FIGURES.
Fig.[1]. Cross section through body of ham, with sour areas indicated by shadingand dotted lines11
[2]. Cross section through body of ham to show method of sampling forchemical analysis18
[3]. Cross section through body of artificially soured ham, showing sourareas and points at which cultures were taken25
[4]. Diagrammatic views showing construction of ham thermometer36
[5]. Ham-souring bacillus (Bacillus putrefaciens), grown on egg-pork medium46

A BACTERIOLOGICAL STUDY OF HAM SOURING.