Part 9

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.