Chapter II: Part 2

───────┬────────┬─────────┬────────┬─────────────
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.

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.

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.

PROBABLE METHOD BY WHICH HAM-SOURING BACILLUS ENTERS HAMS.

Regarding the question of the probable method by which the ham-souring bacillus enters hams, there were three possibilities to be taken into consideration: (1) That the bacillus is present in the flesh of hogs at the time of slaughter, (2) that the bacillus gains entrance through the pickling fluids, (3) that the bacillus is introduced into the bodies of the hams in the handling or manipulation which the hams undergo in preparation for, or during, the process of curing.

POSSIBILITY OF INFECTION PRIOR TO SLAUGHTER.

In order to throw some light upon this point, a number of fresh hams—that is, hams which had been chilled but not pumped or subjected to any other manipulation—were examined bacteriologically, but in no case could the anaerobic bacillus which was isolated from sour hams be detected in any of them. The fact that in certain of the smaller packing establishments which cure their hams without pumping the percentage of souring is extremely low would also seem to negative this possibility, for if the bacillus which causes souring were present in the hams at the time of slaughter, sour hams would be as frequent at such establishments as at those establishments which make a practice of pumping. Furthermore, a laboratory study, biological and chemical, of the bacillus isolated from sour hams shows that this organism belongs to the class of putrefactive bacteria, and while such bacteria may be present in the intestines of healthy animals, as, for example, the bacillus of Bienstock (_Bacillus putrificus_), these bacteria do not invade the organs and tissues of the body until after the death of the animal, and the packing-house practice of rapidly eviscerating the hogs immediately after slaughter would certainly preclude this possibility.

POSSIBLE INFECTION FROM PICKLING FLUIDS.

With regard to the second possibility, that the bacillus finds its way into the hams in the curing pickles, it was determined by laboratory experiment that the addition of 3 per cent of sodium chlorid or 3 per cent of potassium nitrate to laboratory media completely inhibits the growth of the bacillus. As the pickling solutions always contain considerably more than these percentages of sodium chlorid and potassium nitrate, it would be impossible for the bacillus to multiply in the pickles. Additional laboratory experiments demonstrated, however, that the bacillus or its spores may remain alive in the curing pickles for at least thirty days, and it seemed possible that the curing pickles might become contaminated at times with the bacilli, and that the bacilli, although incapable of multiplying in the pickles, might find their way into the bodies of the hams in the pickling fluids. In order to throw some light upon this point, the following experiment was carried out:

EXPERIMENT TO SHOW WHETHER INFECTION TAKES PLACE FROM THE CURING PICKLE.

In this experiment two tierces were put down, each containing 20 hams. The hams weighed from 14 to 16 pounds and had received the usual 48-hour chilling. The pickling solutions employed were the regular curing pickles of the establishment at which the experiment was carried out. The curing pickle in one tierce was inoculated with 400 cubic centimeters of a culture suspension of the bacillus, prepared in the same manner as that used for the injection of the hams in tierce 2 in Experiment II. A microscopic preparation made from a small drop of the culture suspension before adding it to the pickle showed the bacilli in large numbers, and in the 400 cubic centimeters of the suspension there were millions of the bacteria. The curing pickle in the other tierce was left untreated, the hams in this tierce serving as a check. The tierces used in this experiment, as in all of the experiments, were thoroughly cleaned with boiling water before the hams were placed in them. The experiment was conducted in a pickling room which was held at 33° to 36° F., and the tierces were rolled three times during the cure. The details of the experiment are as follows:

_Tierce 1._—Contained 20 hams, half of which were pumped in
both body and shank and half in the shank only. As soon as they
were pumped the hams were packed in the tierce. Sufficient
curing pickle to fill the tierce was then measured out in a
clean barrel and to it was added the culture suspension. The
culture was thoroughly mixed with the pickle and the latter was
then run into the tierce containing the hams.

Result: When tested at the end of the cure, two of the hams
which had been pumped in the shank only showed slight souring
in the body. The rest of the hams were sweet.

_Tierce 2._—Contained 20 hams which were pumped in the same
manner as those in tierce 1. The curing pickle was the same as
that used for tierce 1, but without the addition of culture.
This tierce was put down as a check on tierce 1, the hams
being cured under exactly the same conditions, but without the
addition of culture to the curing pickle.

Result: One of the hams which was pumped in the shank only
developed slight souring in the body. The remainder of the hams
were sweet.

Comparing tierce 1, which contained the inoculated pickle, with tierce 2, the check tierce which contained uninoculated pickle, we find there was practically no difference in the final result. In tierce 1 two of the hams developed slight souring, while in tierce 2 one of the hams became slightly sour. All of these hams had been pumped in the shank only. The fact that one of the hams in the check tierce developed slight souring was undoubtedly due to bacterial contamination in pumping or in the handling which the hams underwent prior to pickling, and the slight souring of the two hams in tierce 1 must also be attributed to the same cause or causes, for had the souring in these last hams resulted from the penetration of the bacteria from the pickling solution a higher percentage should have become sour. Furthermore, if the souring of the two hams in tierce 1 had resulted from the penetration of the bacteria from the curing pickle, the souring should have been general throughout the bodies of these hams, whereas the souring was only evident around the bone and was slight in degree.

From this experiment the conclusion would seem justified that the bacillus which causes ham souring does not usually find its way into the bodies of the hams from the curing pickle, although it would be going too far, perhaps, to say that infection never takes place from the curing pickle. The experiment, however, indicates clearly that the curing pickles are certainly not the main channel through which the hams become infected. In referring to the curing pickles, it should be understood that we refer here to the pickling solutions in which the hams are immersed, and not to the pumping pickles. The possibility of infection through the pumping pickle will be discussed later.

POSSIBLE INFECTION THROUGH MANIPULATION OR HANDLING.

There are at least three possible ways in which hams may become infected from the handling which they receive in preparation for, or during the process of curing, viz: From the thermometers used in taking the inside temperatures of the hams, from the pumping needles, and from the billhooks used in lifting the hams.

INFECTION FROM HAM THERMOMETERS.

The packing-house method of taking the temperatures of hams by means of a pointed, metal-capped thermometer which is thrust deep into the bodies of the hams has already been referred to, but deserves to be described somewhat more in detail, as it will be at once apparent that this manipulation furnishes a ready means whereby hams may become infected with putrefactive bacteria. The construction of a ham thermometer is shown in figure 4.

FIG. 4.—Diagrammatic views showing construction of ham
thermometer. A, front view, showing open space between metal
point and mercury bulb, which becomes filled with particles of
meat, grease, and dirt; B, side view.]

The instrument consists of a glass thermometer inclosed in a metal case, the front portions of the case being cut away so as to expose the scale above and the mercury bulb below. As was explained before, the thermometer is thrust deep into the body of the ham so that the pointed end containing the mercury bulb rests beside or a little behind the upper portion of the femur, the bone being used as a guide in introducing the thermometer.

Ham temperatures are taken at three stages in the preparation for cure—(1) on the hanging floor, just before the hams go to the chill rooms, in order to determine the amount of heat lost prior to chilling; (2) on leaving the chill rooms, in order to determine the thoroughness of the chill; (3) on the packing floor, just before the hams are placed in pickle, as a further check on the thoroughness of the chilling.

In taking the temperatures of hams which have been chilled—and most of the temperatures are taken subsequent to chilling—it is customary for the packing-house attendant who has this matter in charge to warm the thermometer by holding the pointed or bulb end in his hand, so as to force the mercury column up to about 60° F., or well above the temperature of hams. The thermometer is then thrust into the ham and allowed to remain for several minutes, by which time the mercury column will have fallen to the temperature of the ham. The thermometer is then slowly withdrawn so as to expose the top of the mercury column, and an accurate reading is thus obtained of the inside temperature of the ham. The thermometer is warmed by the hand before each ham is tested, and this undoubtedly insures more accurate readings than would result were the thermometer removed from one ham and plunged immediately into another, but the procedure is open to certain objections, for the open space between the metal point of the thermometer and the mercury bulb soon becomes filled with particles of meat and with grease and dirt from the attendant’s hands, and it is at once apparent that a thermometer in this condition would furnish a ready means whereby extraneous matter might be introduced into the bodies of the hams. In other words, a contaminated thermometer would furnish an excellent means whereby hams could be inoculated with putrefactive bacteria.

In order to determine whether hams actually become inoculated in this manner, the following experiment was carried out:

EXPERIMENT TO SHOW WHETHER HAMS BECOME INFECTED FROM HAM THERMOMETERS.

This experiment was designed to show (1) whether the usual packing-house method of taking ham temperatures was apt to induce souring in the hams thus tested, and (2) whether souring would result in hams which were tested with a thermometer purposely contaminated with the bacillus isolated from sour hams.

The experiment was carried out as follows: Thirty hog carcasses were selected as they entered the hanging floor from the killing floor. They had been cleaned, eviscerated, and split, and were of the same average weight and of sufficient size to yield hams weighing from 12 to 14 pounds. They were divided into three lots of 10 each and were allowed to remain on the hanging floor for two hours, after which they were given the usual 48-hour chilling.

_Lot 1._—The hams in this lot were tested with an ordinary ham
thermometer as they entered the hanging floor, as they left the
hanging floor, and as they left the coolers. The thermometer
used was borrowed from one of the plant attendants and was used
in the condition in which it was received from him; that is, it
was not cleaned or disinfected prior to use.

_Lot 2._—The hams in this lot were tested as they entered the
hanging floor with a thermometer which had been previously
cleaned and disinfected and then dipped in a culture suspension
of the meat-souring bacillus which was isolated from sour
hams. The thermometer was dipped in the culture suspension
before each ham was tested. No further temperatures were taken
of these hams. The thermometer was carefully cleaned and
disinfected before it was returned to the attendant from whom
it was borrowed.

_Lot 3._—The hams in this lot were not tested at all, and were
intended as checks on the cure.

The three lots of carcasses were carefully tagged and were chilled in a special cooler to themselves. Upon leaving the cooler the hams were cut from the carcasses and trimmed. The three lots of hams were then cured in separate tierces. All of the hams were subjected to exactly the same cure.

The pickles used were the regular pumping and regular curing pickles of the establishment at which the experiment was carried out.

The hams in lot 3 were pumped first and those in lot 1 were pumped next. The needle was then removed and a fresh, clean needle was used for lot 2. This was done in order to prevent the possibility of carrying over bacteria from one lot of hams to another on the pumping needle. The tierces were thoroughly cleaned with boiling water before being used. The curing was carried out in a pickling cellar which was held at 33° to 36° F., the temperature never rising above the latter figure. The tierces were rolled three times during the curing. The details and results were as follows:

_Tierce 1._—Contained 20 hams, half of which were pumped in
both body and shank and half in the shank only. These hams were
taken from the carcasses in lot 1 and had been tested several
times with a ham thermometer, as already described.

Result: At the end of the cure it was found that of the 10 hams
which were pumped in the shank, 5 showed well-marked souring in
the body, while of the 10 hams which were pumped in both body
and shank, 2 showed slight souring in the body.

_Tierce 2._—Contained 20 hams, which were pumped in the same
manner as those in tierce 1. These hams were taken from the
carcasses in lot 2 and had been tested once with a thermometer
which was dipped in a culture suspension of the bacillus
isolated from sour hams.

Result: The 10 hams which were pumped in the shank only all
became sour. When they were tried out at the end of the cure,
they showed pronounced souring throughout the entire body and
were classed as “stinkers” by the meat inspector who examined
them. The souring extended through to the bone marrow of the
femur in all of these hams. Of the 10 hams which were pumped in
both body and shank, 7 showed well-marked souring in the body,
but not as pronounced as in those pumped in the shank only; in
five of these hams the souring extended through to the bone
marrow of the femur, while in 2 the bone marrow remained sweet.

_Tierce 3._—Contained 20 hams, which were pumped in the same
manner as those in the two preceding tierces. These hams were
not tested with a thermometer, and were put down as a check
on the cure. They were pumped with the same pumping pickle,
subjected to the same cure, and held under precisely the same
conditions as the hams in the two preceding tierces.

Result: When tested at the end of the cure, all of these hams
were found to be perfectly sound and sweet.

_Results of experiment to show whether hams become infected from ham
thermometers._
────────┬────────┬───────────┬──────────────┐
│ │ │ │
│ │ │ │
No. of │ Number │ Average │ How pumped. │
tierce.│ of │ weight of │ │
│ hams. │ hams. │ │
────────┼────────┼───────────┼──────────────┤
│ │ _Pounds._ │ │
│ │ │ │
│ │ │{ 10 in shank │
│ │ │{ │
1 │ 20 │ 12-14 │{ │
│ │ │{ │
│ │ │{ │
│ │ │{ │
│ │ │{ │
│ │ │{ 10 in body │
│ │ │{ and shank │
│ │ │ │
│ │ │{ 10 in shank │
2 │ 20 │ 12-14 │{ │
│ │ │{ │
│ │ │{ │
│ │ │{ │
│ │ │{ │
│ │ │{ 10 in body │
│ │ │{ and shank │
│ │ │ │
│ │ │{ 10 in shank │
3 │ 20 │ 12-14 │{ │
│ │ │{ 10 in body │
│ │ │{ and shank │
────────┴────────┴───────────┴──────────────┘

────────┬─────────────────┬──────────────────
│ │ Condition at
│ │ end of cure.
No. of │ ├───────┬──────────
tierce.│ Treatment. │Number │Percentage
│ │of sour│ of sour
│ │ hams. │ hams.
────────┼─────────────────┼───────┼──────────
│ │ │
│Tested at several│ 5 │ 50
│stages in │ │
1 │preparation for │ │
│cure with ham │ │
│thermometer which│ │
│had not been │ │
│cleaned. │ │
│ do │ 2 │ 20
│ │ │
│ │ │
│Tested once with │ 10 │ 100
2 │ham thermometer │ │
│dipped in culture│ │
│suspension of │ │
│anaerobic │ │
│bacillus isolated│ │
│from sour hams. │ │
│ do │ 7 │ 70
│ │ │
│ │ │
3 │Not tested with │ 0 │ 0
│thermometer. │ │
│ do │ 0 │ 0
────────┴─────────────────┴───────┴──────────

Several hams from each tierce were examined bacteriologically. cultures being taken from the meat near the bone and from the bone marrow of the femur.

In the sour hams from tierce 1 cultures taken from the meat near the bone showed the same anaerobic bacillus noted in other sour hams (i.e., the same bacillus which caused souring in Experiments I and II), but these cultures were contaminated with other bacteria which were probably introduced on the thermometer along with the ham-souring bacillus. None of the contaminating bacteria were capable, however, of producing a sour-meat odor when grown on the egg-pork medium. Pure cultures of the ham-souring bacillus were obtained from the bone marrow of some of these hams, showing that this bacillus had penetrated through to the bone marrow while the other bacteria had not.

From the sour hams in tierce 2 the ham-souring bacillus was recovered readily, and often in pure culture, from the hams which had been pumped in the shank only, whereas it was usually contaminated with pickle bacteria in the hams which had been pumped in both body and shank.

In the case of the sound hams in tierce 3, cultures taken from the meat near the bone and from the bone marrow of the femur were negative in the hams which had been pumped in the shank only, while cultures taken from corresponding points in the hams pumped in both body and shank showed ordinary pickle bacteria, which had evidently been introduced into the bodies of these hams in the pumping pickles. None of these hams exhibited the slightest sour odor.

_Summary of experiment._—In this experiment 20 hams (tierce 1) were tested with an ordinary ham thermometer in the usual packing-house manner. Half of these hams were subjected to the mild cure and half were given the regular cure, with the result that 50 per cent of those receiving the mild cure and 20 per cent of those receiving the regular cure became sour.

A second lot of 20 hams (tierce 2) were tested with a thermometer which had been purposely contaminated with a culture suspension of the ham-souring bacillus. These hams were cured in the same manner as the first lot, with the result that all of those receiving the mild cure and 70 per cent of those receiving the regular cure became sour.

A third lot of 20 hams (tierce 3) which had not been tested at all were cured in the same manner as the two preceding lots, as a check on the cure. All of these hams were sweet at the end of the cure.

Inasmuch as the three lots of hams were cured under precisely the same conditions and were handled in the same manner prior to pickling, the only difference being that the hams in tierces 1 and 2 were tested with the ham thermometer while those in tierce 3 were not, we must conclude that the souring of the hams in tierces 1 and 2 resulted from the testing which these hams received. In the case of tierce 1 the hams became infected from a thermometer which, in the ordinary routine use of the packing house, had become accidentally contaminated with the ham-souring bacillus. In the case of tierce 2 the hams became infected from a thermometer which had been artificially contaminated with the bacillus. The high percentage of sours in this last lot is due to the fact that these hams were heavily infected with the ham-souring bacillus, for owing to the construction of the ham thermometer many thousands of the bacilli were unquestionably introduced into each ham on the point of the thermometer. In the ordinary routine of ham testing, where hams become infected from foreign matter introduced on the thermometer, the percentage of souring, as shown in tierce 1, would be less, for it is not to be supposed that ham thermometers are always contaminated with the ham-souring bacillus, but that they only become so at times, and that probably only a few of the bacilli are then introduced.

This experiment, we think, proves conclusively (1) that the ham-souring bacillus may be introduced into the bodies of hams on the thermometers used in testing the hams, and (2) that the packing-house method of taking ham temperatures by means of a thermometer which is thrust deep into the bodies of the hams may cause souring in the hams thus tested.

As a further proof that hams may become contaminated in this manner, a series of cultures were made from scrapings taken from ham thermometers. The scrapings consisted of the accumulations of bits of meat, grease, and dirt that collect on the thermometers, and were taken from the thermometers while the latter were in ordinary routine use in the packing house. In a series of six cultures which were made from such scrapings at different times, the same bacillus which was isolated from sour hams and shown to cause meat souring was found three times. In other words, the ham-souring bacillus was present in 50 per cent of the cultures made from thermometer scrapings, and many hams undoubtedly become infected from the thermometers. Souring would be almost certain to result in mild-cure hams if these hams were tested with a thermometer which had become accidentally contaminated with the ham-souring bacillus, as the bacillus would have time to develop within the bodies of the hams before being inhibited by the curing pickle, which penetrates slowly into the bodies of these hams. In the case of regular cure hams—that is, hams which are pumped in both body and shank—souring would be much less apt to occur after the use of a contaminated thermometer, as these hams are more or less saturated with a strong pumping pickle at the beginning of the cure, which would tend to inhibit the growth of any bacteria that might be introduced on the thermometers.

The fact that souring may result in hams from the use of a contaminated thermometer would explain the occurrence of several sours in one vat, for in testing hams just before they go into cure several hams are usually tested in succession, and these would in all likelihood go into the same vat. Supposing the thermometer to have been contaminated with the ham-souring bacillus at the time these hams were tested, this would explain a fact which has been often noted, namely, the occurrence of several sours in one vat while other vats containing the same run of hams show no sours.

If souring resulted in all of the hams which are subjected to a thermometer test in the daily routine of the packing house, this manipulation alone might account for nearly all of the sours which occur, but the experiment which has been just described shows that all of these hams do not become sour. In tierce 1, where each ham was subjected to three thermometer tests at different times, souring resulted in 35 percent (this includes both mild and regular cure) of the hams thus tested, and in actual practice the percentage of sours in hams which have been subjected to the thermometer test would probably be somewhat less. Quite a large percentage of sour hams are thus left unaccounted for by the thermometer test, and we believe that these are chiefly the result of contamination carried in on the pumping needles or in the pumping pickles.

INFECTION FROM PUMPING NEEDLES.