1. In this paper it has been shown that ham souring, as encountered in
the wet cure where the hams are entirely submerged in pickling fluids,
is due to the growth of an anaerobic bacillus within the bodies of the
hams. This bacillus (_B. putrefaciens_) was found in sour hams obtained
from four different packing establishments. It was isolated and grown
in various laboratory media, in one of which, the egg-pork medium, it
gave rise to the characteristic sour-ham odor. This bacillus was the
only organism that could be isolated from sour hams that was capable of
producing the characteristic sour-ham odor in the egg-pork medium.
2. When injected into the bodies of sound hams, the bacillus caused
these hams to sour in the process of curing. In hams which had been
inoculated with the bacillus and thus artificially soured, the bacillus
was recovered in cultures taken at points far removed, relatively
speaking, from the point of inoculation, indicating that the bacillus
had multiplied and progressed by extension throughout the bodies of the
hams.
3. The bacillus possesses no motility, and its extension throughout
the bodies of the hams is a result of multiplication. In its growth it
follows along the connective-tissue bands between the muscle bundles,
which are composed of comparatively loose tissue and afford paths of
least resistance. When it invades the muscle tissue proper, it follows
along the sarcolemma sheaths between the muscle fibers. As a result of
this growth the muscular tissue becomes softer and tends to break more
easily.
4. The bacillus belongs to the class of putrefactive anaerobes which
are widely distributed in nature in dust, soil, and excrementitious
matters. The bacillus or its spores is present in the dust and dirt
of packing houses and finds its way into the hams in the various
manipulations to which they are subjected.
5. The bacillus or its spores may be introduced into hams on the
thermometers used in testing the hams, on the pumping needles, and
possibly on the billhooks used in handling the hams. It may also be
carried into the hams in the pumping pickle, and may even find its way
into the hams from the curing pickle, although infection through the
latter channel probably does not often occur.
6. The bacillus develops in the deeper portions of the ham because of
the anaerobic conditions there prevailing, and souring is most often
encountered, therefore, in the deeper portions of the ham near the
bone.
7. A preliminary study of the chemical changes which take place in
the process of souring shows that these changes are of a putrefactive
nature, and ham souring, as ordinarily encountered, is to be regarded
as an incipient putrefaction. Hams which had been artificially soured
by injections of culture were compared with sour hams obtained from the
packing house, and the putrefactive changes were found to be identical.
8. Hams which have once become sour can never be restored to a sound
condition, because of the chemical changes which result from the growth
of the bacillus. In other words, the tissues of the ham undergo certain
chemical changes in the process of souring, and when these changes
have once taken place the tissues can never be restored to a sound
condition. The repumping of slightly soured hams with a strong pumping
pickle will check further souring, by inhibiting the growth of the
bacillus, but will not restore to a sound condition those portions of
the ham which have become sour.
9. The salts of the pickling fluids have a marked inhibitory action
on the ham-souring bacillus, and sours occur less frequently in
regular-cure hams.
10. In regular-cure hams the growth of the ham-souring bacillus is
restricted and often completely inhibited as a result of the additional
pumping which these hams receive, whereby they are more or less
saturated with pickle at the beginning of the cure.
11. If the pumping of regular-cure hams were more thorough and all
of the deeper portions of the ham were thoroughly saturated with the
pumping pickle, souring could be largely eliminated if not entirely
prevented in the hams, as an unfavorable medium or soil would thus
be created, in which the ham-souring bacillus could not develop. The
reason that souring does develop in regular-cure hams is because the
pumping is not always thorough and there are certain areas in the
deeper portions of these hams which are not saturated with the pumping
pickle.
12. Under the present methods of curing, the partly pumped or mild-cure
hams furnish the greater proportion of the sours, as these hams are not
pumped in the body and the growth of the ham-souring bacillus within
the bodies of these hams is not interfered with until the curing pickle
has penetrated from the outside. As it requires several weeks for the
curing pickle to penetrate thoroughly into the deeper portions of these
hams, the bacillus is thus afforded a considerable interval in which to
develop.
13. The percentage of souring in the mild-cure hams could be greatly
reduced without materially affecting the cure by pumping these hams
with their own curing pickle, which is usually a milder pickle than
that employed in the regular cure; and if the pumping were thorough
the number of sours in these hams could be reduced to a small figure.
14. The only way by which ham souring could be entirely eliminated from
the larger packing establishments under the present methods of curing
would be to handle the hams throughout under aseptic conditions, and
this, for obvious reasons, would be an impossibility. The losses from
ham souring may be materially reduced, however, by greater care in
handling the hams and the adoption of precautionary measures designed
to prevent the introduction of contaminated foreign matter into the
bodies of the hams, together with more thorough methods of pumping.