In view of the results obtained in the last experiment, in which it was
shown that hams may become infected from the use of ham thermometers,
it seemed not improbable that hams might also become infected from
the pumping needles, which, like the thermometers, are thrust deep
into the bodies of the hams beside the bone. In order to throw some
light upon this point, cultures were taken from the grease and dirt
that accumulate on the shields at the bases of the pumping needles,
as such material must undoubtedly be carried into the hams at times
on the needles. The ham-souring bacillus was found several times in
these cultures, and hence it is fair to infer that hams may also
become infected at times from the pumping needles, just as they become
infected from the thermometers. Bits of contaminated meat and grease
and particles of dirt carried in on the pumping needles would be forced
out into the hams by the pumping pickle, which passes out through small
openings or fenestræ in the needles, and this probably affords one
explanation as to why so many more body sours occur in the mild-cure
hams. In the mild-cure hams, which are pumped in the shank only, the
pumping needle is introduced near the femorotibial articulation, and
the shank is saturated at the start with a strong brine solution, while
the body of the ham is not. If the ham-souring bacillus were carried
into these hams on the pumping needle, the growth of the bacillus in
the shank would be inhibited by the strong brine solution with which
the shank is saturated, but there would be nothing to prevent the
bacillus from growing upward into the body of the ham, which has not
been pumped and is free from pickle. This would also explain the fact
that the souring often starts at the knee joint and extends upward into
the body of the ham. In the case of the regular cure hams, where the
ham is pumped in both body and shank, the entire ham is more or less
saturated at the start with the strong brine of the pumping pickle,
which tends to inhibit the growth of the ham-souring bacillus even
if this bacillus should find its way into these hams on the pumping
needles. It is in the mild-cure or partly pumped hams, where the body
of the ham is left unpumped, that the ham-souring bacillus finds its
best opportunity for development, and the greater proportion of the
sours that occur in the packing house are found in these hams.
As regards the possibility of infection from the pumping pickle
itself, it does not seem probable that this would often occur, for
the pumping and curing pickles are always prepared on an upper floor
of the pickling houses and are delivered to the pickle cellars in
closed pipes, so the chances for the accidental contamination of these
solutions from floating dust or dirt would not be great. Furthermore,
the strong brine of the pumping pickle would completely inhibit the
growth of the ham-souring bacillus, and the bacillus would be incapable
of multiplying, even if it found its way into the pickle. On the other
hand, laboratory experiments show that the bacillus or its spores may
remain alive for a considerable length of time in the pumping pickle,
so the possibility of infection from this source can not be overlooked.