The experiments which follow were conducted at two different packing
establishments in one of the larger packing centers of the country.
The officials at each of these establishments showed great interest in
the experiments and were most courteous and obliging in supplying the
necessary materials.
The first question to be decided was whether the bacillus isolated from
sour hams was actually capable of causing ham souring. The bacillus in
question had, when cultivated on the egg-pork medium, given rise to a
sour odor similar to that obtained from sour hams, but this was not
regarded as proof positive that the organism was the actual cause of
souring in hams. The proper way to decide this point seemed to be to
inoculate hams with the bacillus and then subject these hams to the
regular method of cure and see whether they became sour, just as the
pathogenic properties of a disease-producing organism are determined by
the inoculation of experiment animals. The first two experiments which
follow were designed to decide this point.
It was regarded as important to conduct similar experiments at two
different establishments, in order to determine whether the same
results would be obtained under the somewhat different conditions
imposed by different methods of cure. The two experiments which follow
were carried out, therefore, at different establishments.
_Experiment I._
In carrying out this experiment four tierces of hams were “put down”
or “packed”—that is, placed in cure. Two of the tierces were given the
fancy or mild cure and two the regular or stronger cure. The hams in
two of the tierces, one mild and one regular cure, were injected with
a culture suspension of the bacillus; the other two tierces were not
injected with culture and were put down to serve as checks on the
cure. Hams weighing from 12 to 14 pounds were used for the mild cure,
while for the regular cure hams weighing from 14 to 16 pounds were
used. This was in accordance with the general rule which prevails in
packing houses, the lighter hams being subjected to the mild cure and
the heavier hams to the regular cure. The only difference between the
mild and the regular cure in this experiment lay in the pumping. The
hams which were given the mild cure were pumped in the shank only,
while those given the regular cure were pumped in the body as well as
in the shank.
All of the hams had received the usual 48-hour chill. They were all
pumped with the same pumping pickle and cured in the same curing
pickle, and were in cure for the same length of time. The pumping and
curing pickles used were the regular pumping and curing pickles of the
establishment at which the experiment was carried out, and the hams
were cured in accordance with the fancy and regular cures as practiced
at this establishment.
The hams were packed in new tierces which had been thoroughly scalded
with boiling water. The tierces were held in a curing room which was
kept at an average temperature of from 34° to 36° F., the temperature
occasionally going as high as 38° and 40° F., but never above 40°
F. The hams were left in cure for about 70 days, which is a little
longer than the usual cure. The tierces were rolled three times during
the cure. At the end of the cure the hams in all four tierces were
carefully tested by an expert meat inspector, who knew nothing of the
treatment which the hams had received.
The hams in two of the tierces were inoculated with a culture
suspension prepared as follows: Ten tubes of egg-pork medium, each
tube containing approximately 10 cubic centimeters of the medium,
were inoculated with the bacillus and held at room temperature (20°
to 25° C.) for six days. The cultures were then filtered through
sterile gauze into a large sterile flask; this was done in order to
remove the particles of meat, which might otherwise have clogged the
syringes used in inoculating the hams. In transferring the contents
of the culture tubes to the filter the tubes were washed out with
sterile physiological salt solution (0.6 per cent sodium chlorid),
and the meat particles on the filter were afterwards washed with the
salt solution, a sufficient quantity of the latter being used to bring
the total volume of filtrate to 400 cubic centimeters. A microscopic
preparation from the filtrate showed the organisms in large numbers,
with an occasional rod showing a large terminal spore. This suspension
was used for the injection of 40 hams, each ham being given 10 cubic
centimeters, or the equivalent of 2.5 cubic centimeters of the original
culture. The hams were injected with the culture suspension by means of
a sterile syringe carrying a long 5-inch needle. The needle was thrust
well into the body of the ham at a point near the upper end of the
middle bone or femur, the latter being used as a guide in inserting
the needle and the injection being made into the tissues just behind
and a little to one side of the upper end of the femur.
The details of the experiment were as follows:
_Tierce No. 1 (fancy cure)._—This tierce contained 20 hams
weighing from 12 to 14 pounds each. These hams were pumped in
the shank only. Immediately after pumping they were injected
with 10 cubic centimeters each of the liquid culture or
suspension described above. After injection the hams were
immediately packed in the tierce, which was then headed up,
filled with the regular curing pickle, and placed in cure.
Result: When tested at the end of the cure all of the hams
in this tierce save one were found to be sour. In 10 of them
the souring was very marked throughout the body of the ham
and extended into the shank as well. In six the souring was
very marked in the body of the ham, but did not extend into
the shank. In three there was slight but well-marked souring
in the body of the ham with no souring in the shank, and one
remained sweet. The probable explanation of the variation in
the degree and the extent of the souring will be discussed
later. The bone marrow of the femur or middle bone was tested
in all of the hams and found to be sour in 18. In one of the
hams which showed only slight souring in the body the souring
did not extend through to the bone marrow, and in the ham which
remained sweet the bone marrow was also sweet. The fact that
one ham in this tierce remained sweet was in all likelihood
due to an oversight in making the inoculations. In making the
inoculations the hams were spread out in a row on a table by a
packing-house assistant, who removed the hams as soon as they
were inoculated and placed them in tierces; and it is more than
probable that the assistant removed one of the hams before it
was inoculated in the interval when the writer was busy filling
the syringe for the next inoculation.
_Tierce No. 2 (fancy cure)._—This tierce contained 20 hams of
the same average weight as the preceding. They were pumped in
the shank only, but were not injected with culture, being put
down to serve as checks on the hams in tierce No. 1. These
hams, therefore, were subjected to exactly the same cure and
were held under exactly the same conditions as those in tierce
No. 1, the only difference being that the hams in this tierce
were not injected with culture.
Result: When tested at the end of the cure all of the hams in
this tierce were found to be perfectly sound and sweet, showing
that the curing in this instance was properly carried out and
that the souring of the hams in tierce No. 1 was undoubtedly
due to the injections of culture which they received.
_Tierce No. 3 (regular cure)._—This tierce contained 20 hams
weighing from 14 to 16 pounds each. These hams were pumped in
the shank and also in the body. Immediately after pumping they
were each injected in the same manner as those in tierce No. 1
with 10 cubic centimeters of culture. The hams were then packed
in tierce and placed in cure.
Result: At the end of the cure 9 of the hams were found to be
sour, while 11 remained sweet. Of the 9 hams which became sour,
1 showed very pronounced souring in the body and in the shank
as well, 3 showed very pronounced souring in the body, 1 showed
pronounced souring in the body, and 4 slight souring in the
body. The bone marrow of the femur was tested in all of the
sour hams and was found to be sour in 7. In 2 of the sour hams
which showed slight souring in the body the souring noted in
the meat had not extended through to the bone marrow.
_Tierce No. 4 (regular cure)._—This tierce contained 20 hams
of the same average weight as those in tierce No. 3, and, like
the latter, were pumped in both shank and body, but were not
injected with culture. This tierce was put down to serve as
a check on tierce No. 3 and was held under exactly the same
conditions, the only difference being that these hams were not
injected with culture.
Result: At the end of the cure the hams were carefully tested
and all were found to be perfectly sound and sweet.
_Results of Experiment I._
───────┬────────┬─────────┬────────┬─────────────
No. of │ Number │ Average │ Cure. │ How pumped.
tierce.│of hams.│ weight │ │
│ │ of hams.│ │
│ │ │ │
───────┼────────┼─────────┼────────┼─────────────
│ │_Pounds._│ │
1 │ 20 │ 12-14 │ Fancy │Shank only
│ │ │ │
│ │ │ │
2 │ 20 │ 12-14 │ do │ do
│ │ │ │
│ │ │ │
3 │ 20 │ 14-16 │Regular │Shank and body
│ │ │ │
│ │ │ │
4 │ 20 │ 14-16 │ do │ do
│ │ │ │
───────┴────────┴─────────┴────────┴─────────────
───────┬─────────────────┬─────────────────────────
│ │ Condition at end
│ │ of cure
│ ├───────────┬─────────────
No. of │ Treatment │ Number of │Percentage of
tierce.│ │ sour hams │ sour hams
───────┼─────────────────┼───────────┼─────────────
1 │Each ham injected│ 19 │ 95
│with 10 c.c. of │ │
│culture. │ │
│ │ │
2 │Not injected with│ 0 │ 0
│culture; check on│ │
│tierce 1. │ │
│ │ │
3 │Each ham injected│ 9 │ 45
│with 10 c.c. of │ │
│culture. │ │
│ │ │
4 │Not injected with│ 0 │ 0
│culture; check on│ │
│tierce 3. │ │
───────┴─────────────────┴───────────┴─────────────
Three hams from each tierce were selected for bacteriological and
histological examination. From tierces 1 and 3, which contained the
injected hams, three of the most pronounced “sours” were selected from
each tierce. In examining the hams bacteriologically the following
method was adopted: The hams were sectioned near the center of the body
and the larger or butt end turned up so as to expose the cut surface. A
cross section of a ham thus cut is shown in figure 3.
Cultures were taken at the points indicated by the numbers and from the
exposed bone marrow of the femur by first searing the surface, and then
taking out plugs of the meat or marrow by means of sterile instruments.
The plugs of meat or marrow were dropped into tubes containing egg-pork
medium and pushed to the bottom of the tubes by means of a sterile
platinum wire. In the cultures made from the sour hams from tierces 1
and 3, which were injected with culture, the bacillus with which these
hams were injected was found in practically every culture, although it
was sometimes absent in the cultures taken at points near the skinned
surfaces of the hams (i. e., at points 1, 4, and 5 in fig. 3). In the
cultures taken from the meat, the bacillus was not always present in
pure culture, but this is not to be wondered at when we remember that
the pickling fluids often contain large numbers of bacteria of various
kinds, and these, of course, find their way into the hams in the
pickling fluids. Especially is this true of the hams which are pumped
in the body, where bacteria are actually pumped into the bodies of the
hams in the pumping pickle. In the case of hams which are not pumped in
the body, the pickle bacteria do not appear to penetrate the body of
the ham to any great depth.
In figure 3 the plus signs after the figures represent the distribution
of the sour-ham bacillus in one of the hams from tierce 1, and this
may be taken as a typical example of the other sour hams which were
examined in this experiment. It should be explained that the shaded
areas are not intended to represent the actual limits of souring, but
simply the areas in which the sour odor was most pronounced and from
which it could be readily obtained with the trier. In comparing the
regular and mild cure hams, it was found that the areas of souring as
defined with the trier were more restricted in the regular cure hams,
and this was undoubtedly due to the additional pumping which these hams
received, whereby the growth of the bacillus was partially inhibited.
[Illustration:
FIG. 3.—Cross section through body of artificially soured ham,
showing sour areas and points at which cultures were taken.
Darker shading indicates sour area in hams pumped in body and
shank; light shading indicates sour area in hams pumped in
shank only; figures indicate points at which cultures were
taken; plus signs indicate presence of bacillus; minus sign
indicates absence of bacillus; X indicates point of inoculation.]
It will be noticed that the sour-ham bacillus was present in cultures
taken at points outside the shaded areas, indicating that the organism
had extended generally throughout the bodies of the hams. As the
hams were inoculated at a point just to one side of and a little
behind the femur (i. e., at the point X in the figure), the presence
of the bacillus generally throughout the hams would indicate a very
extensive multiplication of the original bacilli with which the hams
were injected. In view of the fact that the bacillus in question is
nonmotile, the spread of the bacilli throughout the hams must result
simply from subdivision and growth by extension, and in spreading
throughout the hams the bacilli appear to follow along the connective
tissue bands which afford paths of least resistance. In the cultures
made from the bone marrow the bacillus was recovered in pure culture
from each of the hams examined, and it is probable that the bacillus
finds its way into the bone marrow from the meat by following along the
small arteries which pass through the bone. The fact that the bacillus
was found in pure culture (i. e., uncontaminated) in the cultures
made from the bone marrow is explained probably by its capacity for
growth by extension, and also by the fact that the pickling solutions
probably do not reach the bone marrow until late in the curing and
then only to a limited extent. The bacteria which ordinarily occur in
pickling fluids are not strict anaerobes and are not placed under the
most suitable conditions for growth when they reach the interior of
the ham, for it seems probable that in the interior of hams which are
totally submerged in pickling fluids the amount of available oxygen
must be extremely small. The ordinary pickle bacteria, therefore, would
not multiply as rapidly in the interior of the hams and would not find
their way into the bone marrow as soon as would a strictly anaerobic
organism.
Pure cultures of the sour-ham bacillus, recovered from the meat and
bone marrow of the injected hams, were compared with cultures of the
original bacillus used for inoculating the hams, and were found to be
identical. Furthermore, the bacillus with which the hams were injected
was recovered from the injected hams at points far removed from the
original point of injection, showing that the organism had multiplied
and extended throughout the bodies of the hams and that it was clearly
responsible for the souring which the hams had undergone.
Sound hams from tierces 2 and 4 were examined bacteriologically in the
same manner as the injected hams, and some of the cultures showed the
ordinary pickle bacteria, but in not a single instance did egg-pork
cultures yield a sour odor, and in no case could the sour-ham bacillus
be demonstrated in any of these hams.
Microscopic sections and teased preparations of the muscle fibers in
salt solution were prepared from several of the sour hams in this
experiment, and these preparations showed the same histological changes
and the same distribution of bacilli as noted in the natural sours.
In Plate III, figures 1 and 2, sections are shown of artificially
soured hams, that is, hams which were artificially soured by injections
of culture; and if these figures be compared with the sections made
from hams which had undergone spontaneous souring (see Pl. II, figs. 1
and 2) the similarity in the form and distribution of the bacilli will
be at once apparent.
[Illustration:
BUL. 132, BUREAU OF ANIMAL INDUSTRY, U. S. DEPT. OF AGRICULTURE.
PLATE III.
FIG. 1.—SECTION THROUGH MUSCULAR TISSUE OF ARTIFICIALLY SOURED
HAM, SHOWING DISTRIBUTION OF BACILLI BETWEEN THE MUSCLE FIBERS,
WHICH ARE SHOWN IN CROSS SECTION. THE DARK LINES AND MASSES
BETWEEN THE MUSCLE FIBERS REPRESENT CLUMPS OF BACILLI.
(Pen-and-ink drawing made with camera lucida from section stained by
the Gram-Weigert method to show bacteria. × 85.)]
FIG. 2.—SECTION THROUGH MUSCULAR TISSUE OF ARTIFICIALLY SOURED
HAM, SHOWING INDIVIDUAL BACILLI BETWEEN THE MUSCLE FIBERS,
WHICH ARE CUT LONGITUDINALLY.
(Pen-and-ink drawing made with camera lucida from section stained by
the Gram-Weigert method to show bacteria. × 320.)]
_Summary and discussion of Experiment I._—Comparing tierces 1 and 2,
where the hams were pumped in the shank only, the only difference being
that the hams in tierce 1 were inoculated with culture while those in
tierce 2 were not, we find that in tierce 1 nineteen out of twenty, or
95 per cent, of the hams became sour, whereas in tierce 2 all of the
hams remained sweet. In view of the fact that these tierces were held
under exactly the same conditions, we must conclude that the souring
of the hams in tierce 1 was due to the injection of culture which they
received.
Comparing tierces 3 and 4, where the hams were pumped in both shank and
body, the hams in tierce 3 being injected with culture while those in
tierce 4 were not, we find that in tierce 3 nine out of twenty, or 45
per cent, of the hams became sour, whereas in tierce 4 all of the hams
remained sweet. As the conditions of cure were the same for all four
tierces, we must again conclude that the souring of the hams in tierce
3 was directly attributable to the injections of culture which they
received.
If now we compare tierces 1 and 3, the two tierces which were injected
with culture, we find that in the case of tierce 1, where the hams were
pumped in the shank only, 95 per cent became sour; whereas in the case
of tierce 3, where the hams were pumped in both shank and body, only
45 per cent became sour. In other words, the percentage of souring in
those hams which were pumped in the body as well as in the shank was 50
percent less than in those hams which were pumped in the shank only.
Inasmuch as the only difference in the treatment accorded tierces 1
and 3 lay in the additional pumping given the hams in tierce 3, we
must conclude that the marked diminution in the percentage of souring
in the case of tierce 3 was undoubtedly due to the additional pumping
which these hams received, the hams being saturated at the start with
the pumping pickle. It will be shown later that both sodium chlorid and
potassium nitrate exert an inhibitory effect upon the bacillus with
which the hams were injected, which directly bears out the foregoing
conclusion.
In tierces 2 and 4, the two check tierces which were not injected with
culture, all of the hams were sweet at the end of the cure, showing
that the conditions under which the experiment was carried out were
entirely favorable to a successful cure.
The sour odor obtained from the artificially soured hams in this
experiment was pronounced by the meat inspector who tested the hams,
and who was entirely unaware of the treatment they had received, to be
identical with the usual sour odor which characterizes hams that have
undergone spontaneous souring; in other words, there was no difference
in odor between these artificially soured hams and natural sours.
With regard to the variation in the degree and the extent of the
souring exhibited by the individual hams in the two inoculated tierces,
where some of the hams showed pronounced souring throughout the body
and shank, while others which had been injected with the same amount of
culture showed only slight souring in the body, several factors must
be considered, viz: (1) Differences in the reaction of the meat of the
individual hams which may have exerted an influence on the growth of
the bacteria with which the hams were injected. (2) Variations in the
texture of the muscle fibers and connective tissue of the individual
hams, permitting in some cases a more rapid and thorough penetration of
the pickling fluids to the interior of the hams, whereby the inhibitory
effect of the sodium chlorid and the potassium nitrate on the bacteria
would come into play earlier. (3) Variations in pumping, whereby more
of the pickling solution was forced into some of the hams than into
others. Probably all three of these factors would have to be taken into
account in explaining the variation in the degree and extent of the
souring exhibited by the injected hams.
With regard to the souring of the bone marrow, we find that of nineteen
sour hams in tierce 1 eighteen showed sour marrows, while in tierce 3
nine sour hams showed seven sour marrows. The high proportion of marrow
sours is not surprising when it is recalled that of the nineteen sour
hams in tierce 1 the meat was markedly sour in sixteen, while of the
nine sour hams in tierce 3 the meat was markedly sour in five. In the
case of the four sour hams in tierce 3 which showed slight souring in
the body, two of these showed sour marrows, while in two the marrows
were sweet. In this experiment the percentage of sour hams showing sour
marrows corresponds with the percentage of marrow-sour hams found in
the packing house, where, as has been pointed out before, a ham which
is markedly sour in the body will practically always show sour marrow,
while in hams which show only slight souring in the body the marrow is
involved in about 50 per cent of the cases.
_Experiment II._
This experiment was essentially a repetition of Experiment I, but was
carried out at a different packing establishment and under somewhat
different conditions.
Two lots of hams were injected with a culture suspension of the
bacillus at different stages of the cure, or rather at different stages
in the preparation for cure, i. e., (1) on the hanging floor, previous
to chilling, and (2) after chilling and pumping and immediately before
packing. Three tierces, each containing 20 hams, were put down. Two of
the tierces contained the hams injected with culture, while the third
tierce contained check hams which had not been treated with culture.
Half of the hams in each tierce were pumped in the shank, while the
other half were pumped in both body and shank. The same pumping and
curing pickles were used for all three tierces, and were the regular
pumping and regular curing pickles of the establishment at which the
experiment was carried out. The hams used were all 14 to 16 pounds
in weight and were subjected to the usual 48-hour chill with an
additional chill of 48 hours after they were cut from the carcass. They
were packed in tierces which had been thoroughly scrubbed and cleaned
with boiling water. The tierces were held in a pickling room at a
temperature of 33° to 36° F., the temperature never rising above 36°
F., and were rolled three times during the curing period. The hams were
in cure for about eighty days. At the end of the cure the hams were
carefully tested by a trained meat inspector, who knew nothing of the
treatment they had received.
The culture suspension was prepared from 20 tubes of egg-pork medium
in the same manner as that used in Experiment I, the cultures being
diluted with sufficient salt solution to give 400 cubic centimeters of
suspension. The cultures from which the suspension was prepared had
grown at room temperature for ten days. The suspension was examined
microscopically and showed large numbers of the bacilli in the form
of filaments or long chains, with many of the individual organisms
showing large terminal spores. The hams were injected with the culture
suspension in the same manner as those in Experiment I.
The details of the experiment were as follows:
_Tierce No. 1._—Contained 20 hams, each ham being injected
with 20 cubic centimeters of the suspension or the equivalent
of 10 cubic centimeters of the original culture. The hams were
injected while on the hanging floor, before they had been cut
from the carcasses and previous to chilling. The carcasses were
still quite warm—that is, had lost but little of their body
heat when the injections were made. The carcasses, which had
been carefully tagged, were then run into coolers and given the
usual 48-hour chill, after which the hams were severed from the
carcasses and given an additional 48-hour chill in accordance
with the custom of the packing house at which the experiment
was carried out. The hams were next pumped with regular pumping
pickle, 10 being pumped in both body and shank and 10 in shank
only. They were finally packed in a tierce, which was then
headed up, filled with regular curing pickle, and placed in
cure.
Result: When tested at the end of the cure it was found that
the 10 hams which were pumped in the shank only were all sour.
In each of them the souring extended throughout the entire ham,
in the shank as well as in the body, and was very pronounced,
so much so that they were characterized as “stinkers” by the
meat inspector who assisted in testing them. The bone marrow
of the femur or middle bone was sour in all of these hams. Of
the 10 hams which were pumped in both body and shank 7 showed
well-marked souring throughout the body, but the souring did
not extend into the shank. The bone marrow of the femur was
found to be sour in 6 of these hams, while in 1 the souring had
not extended through to the bone marrow.
_Tierce No. 2._—Contained 20 hams which were chilled and pumped
in exactly the same manner as those in tierce No. 1. These hams
were injected with culture after they had been chilled and
pumped, or just before they were placed in cure. The hams in
this tierce, therefore, were injected with culture four days
later than those in tierce 1. The hams were injected with a
bacterial suspension prepared in the same manner as that used
for tierce 1, except that the egg-pork cultures from which
the suspension was prepared were 7 days instead of 10 days
old. Each ham was injected with 20 cubic centimeters of the
suspension or the equivalent of 10 cubic centimeters of the
original culture. The hams were injected in the same manner as
those in tierce 1.
Result: When tested at the end of the cure, it was found that
of the 10 hams which were pumped in the shank all were sour; in
8 of these the souring was very marked throughout the body of
the ham and extended into the shank; in all of these hams the
souring had extended through to the bone marrow of the middle
bone or femur. Of the 10 hams which were pumped in both body
and shank 6 were sour in the body. These hams were classed by
the meat inspector who examined them as “light body sours,”
and in none of them did the souring extend into the shank or
through the bone into the bone marrow of the femur.
_Tierce No. 3._—Contained 20 hams which were chilled and pumped
in the same manner as those in the two preceding tierces. These
hams were not injected with culture and were put down to serve
as checks on the cure. In other words, they were pumped with
the same pickling fluids, were subjected to exactly the same
cure, and were held under precisely the same conditions as
those in the preceding tierces, the only difference being that
the hams in this tierce were not injected with culture.
Result: When tested at the end of the cure, all of the hams in
this tierce were found to be perfectly sound and sweet.
_Results of Experiment II._
───────┬──────┬─────────┬──────────────────────
│ │ │
No. of │Number│ Average │ How pumped.
tierce.│ of │ weight │
│hams. │ of hams.│
│ │ │
───────┼──────┼─────────┼──────────────────────
│ │_Pounds._│
│ │ │{ 10 in shank
1 │ 20 │ 14-16 │{
│ │ │{
│ │ │{ 10 in body and shank
│ │ │
│ │ │{ 10 in shank
2 │ 20 │ 14-16 │{
│ │ │{
│ │ │{ 10 in body and shank
│ │ │
3 │ 20 │ 14-16 │{ 10 in shank
│ │ │{ 10 in body and shank
───────┴──────┴─────────┴───────────────────────
───────┬───────────────────────────┬───────────────────
│ │Condition at end of
No. of │ Treatment. │ cure.
tierce.│ ├————————┬——————————
│ │ Number │Percentage
│ │of sour │ of sour
│ │ hams. │ hams.
───────┼───────────────────────────┼────────┼───────────
│ │ │
│Each ham injected with 20 │ 10 │ 100
1 │c. c. of culture prior to │ │
│chilling and pumping. │ │
│ do │ 7 │ 70
│ │ │
│Each ham injected with 20 │ 10 │ 100
2 │c. c. of culture subsequent│ │
│to chilling and pumping. │ │
│ do │ 6 │ 60
│ │ │
3 │Not injected with culture. │ 0 │ 0
│ do │ 0 │ 0
───────┴───────────────────────────┴────────┴──────────
Four hams were selected from each tierce for bacteriological and
histological examination. From tierces 1 and 2, in which the hams
were injected with culture, 4 of the sourest hams were selected from
each tierce. Cultures were made from these hams in the same manner
as described under Experiment I and with the same result—that is,
the sour-ham bacillus was found throughout the bodies of the hams.
Microscopic sections were also prepared from these hams and showed the
same histological changes and the same distribution of bacilli as noted
for the hams in Experiment I.
_Summary and discussion of Experiment II._—Comparing tierces 1 and 2,
in which the hams were injected with culture, with tierce 3, where the
hams were not injected with culture, we find that in tierce 1 seventeen
hams (85 per cent) became sour and in tierce 2 sixteen hams (80 per
cent) became sour, whereas in tierce 3 all of the hams were sweet. The
fact that all of the hams in tierce 3, the check tierce, were sweet
indicates that the conditions were favorable for a successful cure; and
as all three tierces were cured under exactly the same conditions, the
only difference being that the hams in tierces 1 and 2 were injected
with culture, whereas those in tierce 3 were not injected with culture,
we must conclude that the souring of the hams in tierces 1 and 2 was
due to the injections of culture which they received.
Comparing tierce 1 with tierce 2, we find that the hams in tierce 1
showed more extensive souring than did those in tierce 2, this being
especially noticeable in the case of the hams which were pumped in both
body and shank. This difference in the extent or degree of souring was
probably due to the fact that the hams in tierce 1 were injected while
they were still warm and before they had lost their animal heat, the
bacterial suspension thus having a better chance to become disseminated
through the meat. The hams in tierce 2 were injected with culture after
they had been chilled, when the tissues were more or less contracted
and the conditions less favorable for the dissemination of the
suspension throughout the meat. The hams in tierce 1 were also injected
four days earlier than those in tierce 2, and prior to pumping; and
this would explain the greater difference in the extent of the souring
in the case of the hams which were pumped in both body and shank, as in
tierce 1 the bacteria had four days in which to develop before coming
in contact with the pickling fluids, whereas in tierce 2 the bacteria
were injected after the hams were pumped with pickle and were thus
brought into immediate contact with the pickling fluids, which, as will
be shown later, have a distinct inhibitory action upon the bacillus in
question. In the case of the hams which were pumped in the shank but
not in the body there was not this difference, as in these hams the
pickling fluids must penetrate into the bodies of the hams from the
outside. As it requires some time for the pickling fluids to reach the
interior of a ham, the bacteria were thus afforded quite an interval
in which to develop before being exposed to the inhibitory action of
the pickling fluids. A chemical study of the processes involved in
ham curing has been carried out in the Biochemic Division and the
approximate rate of penetration of the curing pickle determined,
and it was found that it required about four weeks for the interior
of a 10-pound ham which had not been pumped to acquire its maximum
percentage of sodium chlorid.
To recapitulate: In this experiment 40 hams were injected with culture,
half of this number being pumped in the shank only and half in both
body and shank. Of the 20 which were pumped in the shank only, every
ham without exception, or 100 per cent, became sour. Of those which
were pumped in both body and shank, 13, or 65 per cent, became sour.
The reduction in the percentage of sours in the last lot was clearly
due to the additional pumping which these hams received.
If now we compare tierce 2 in this experiment with tierces 1 and 3 in
Experiment I—these three tierces being comparable, as they were all
injected with culture at the same stage in their preparation for cure,
that is, subsequent to chilling and pumping—we find, in the case of the
hams pumped in both body and shank, 65 per cent of sours in Experiment
II as against 45 per cent in Experiment I, and this difference is
undoubtedly due to the heavier dose of culture used in Experiment
II, where the hams were given the equivalent of 10 cubic centimeters
of egg-pork culture as against 2½ cubic centimeters in Experiment
I. In the case of the hams which were pumped in the shank but not in
the body, the percentage of sours was practically the same in the two
experiments—in Experiment I all but one of these hams became sour,
while in Experiment II all of them became sour. The degree or extent of
the souring in these last hams, however, was greater in Experiment II,
a result of the heavier injections of culture which they received.
_Summary of Experiments I and II._
Summarizing the results obtained in Experiments I and II, we find that
culture suspensions of the anaerobic bacillus isolated from sour hams
caused souring with great uniformity when injected into the bodies of
sound hams which were pumped in the shank only. In the two experiments,
40 sound hams which were pumped in the shank only were injected with
culture suspensions of the bacillus, with the result that 39, or 97.5
per cent, became sour during the process of cure; and it is quite
probable, as we have pointed out before, that one of these hams was
overlooked in making the inoculations, otherwise the entire lot would
have become sour.
The inhibitory action of the pickling fluids upon the bacillus is well
shown in the case of those hams which were pumped in both body and
shank. Out of 40 hams which were pumped in both body and shank, 22, or
55 per cent, became sour in the process of curing. Inasmuch as these
hams were cured under precisely the same conditions as the hams which
were pumped in the shank only, we must conclude that the diminution in
souring in these hams was undoubtedly due to the additional pumping
which they received, whereby the bacteria with which these hams were
injected were brought into immediate contact with the strong pumping
pickle and their development thereby inhibited.
In these two experiments it was proven beyond doubt that the anaerobic
bacillus isolated from sour hams was capable of producing souring
when introduced into the bodies of sound hams; and in view of the fact
that this bacillus was constantly present in hams which had undergone
spontaneous or natural souring, and was the only organism that could
be isolated from such hams that was capable of producing in egg-pork
cultures the characteristic sour-ham odor, the conclusion seems
justifiable that this bacillus is an undoubted cause of the ham souring
which occurs in the packing house; and the results thus far obtained
indicate that it is an important, if not the only, factor concerned in
ham souring.
Having established the etiological relation of the bacillus isolated
from sour hams with ham souring, the next point to be considered was
the manner in which this bacillus finds its way into the bodies of the
hams.