Part 11

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.

In view of the results obtained in the last experiment, in which it was shown that hams may become infected from the use of ham thermometers, it seemed not improbable that hams might also become infected from the pumping needles, which, like the thermometers, are thrust deep into the bodies of the hams beside the bone. In order to throw some light upon this point, cultures were taken from the grease and dirt that accumulate on the shields at the bases of the pumping needles, as such material must undoubtedly be carried into the hams at times on the needles. The ham-souring bacillus was found several times in these cultures, and hence it is fair to infer that hams may also become infected at times from the pumping needles, just as they become infected from the thermometers. Bits of contaminated meat and grease and particles of dirt carried in on the pumping needles would be forced out into the hams by the pumping pickle, which passes out through small openings or fenestræ in the needles, and this probably affords one explanation as to why so many more body sours occur in the mild-cure hams. In the mild-cure hams, which are pumped in the shank only, the pumping needle is introduced near the femorotibial articulation, and the shank is saturated at the start with a strong brine solution, while the body of the ham is not. If the ham-souring bacillus were carried into these hams on the pumping needle, the growth of the bacillus in the shank would be inhibited by the strong brine solution with which the shank is saturated, but there would be nothing to prevent the bacillus from growing upward into the body of the ham, which has not been pumped and is free from pickle. This would also explain the fact that the souring often starts at the knee joint and extends upward into the body of the ham. In the case of the regular cure hams, where the ham is pumped in both body and shank, the entire ham is more or less saturated at the start with the strong brine of the pumping pickle, which tends to inhibit the growth of the ham-souring bacillus even if this bacillus should find its way into these hams on the pumping needles. It is in the mild-cure or partly pumped hams, where the body of the ham is left unpumped, that the ham-souring bacillus finds its best opportunity for development, and the greater proportion of the sours that occur in the packing house are found in these hams.

As regards the possibility of infection from the pumping pickle itself, it does not seem probable that this would often occur, for the pumping and curing pickles are always prepared on an upper floor of the pickling houses and are delivered to the pickle cellars in closed pipes, so the chances for the accidental contamination of these solutions from floating dust or dirt would not be great. Furthermore, the strong brine of the pumping pickle would completely inhibit the growth of the ham-souring bacillus, and the bacillus would be incapable of multiplying, even if it found its way into the pickle. On the other hand, laboratory experiments show that the bacillus or its spores may remain alive for a considerable length of time in the pumping pickle, so the possibility of infection from this source can not be overlooked.

INFECTION FROM BILLHOOKS.

After the hams are cut from the carcasses they are handled entirely by means of billhooks. In handling the hams the hooks are inserted beneath the skin of the shank at a point just above the tibio-femoral articulation. The hooks should be inserted in the connective tissue beneath the skin and should not penetrate the muscular tissue to any depth. When the hams lie in the right position, with the butt or large portion away from and the shank toward the operator, it is an easy matter to pick them up in the proper manner; but when they lie at different angles and are being rapidly handled it is almost impossible to prevent the hook from penetrating the muscular tissues, and if the hook should penetrate to the bone it might carry in foreign matter contaminated with the meat-souring bacillus. It is not probable that many hams become contaminated in this way, as the men who handle the hams are very skillful in manipulating their hooks; but the possibility that hams may become contaminated in this manner should not be entirely overlooked.

BIOLOGICAL AND MORPHOLOGICAL CHARACTERISTICS OF THE HAM-SOURING BACILLUS.

CONDITIONS FAVORABLE TO GROWTH.

The most favorable medium for the growth of the organism was found to be the modified egg-meat mixture of Rettger, which has been previously described. In this medium the organism develops rapidly at a temperature of 20° to 25° C., giving rise to the characteristic sour-meat odor. Like the bacillus described by Klein, it also grows readily on pork-agar and pork-bouillon containing glucose, but differs from Klein’s bacillus in that it will grow, though less luxuriantly, on ordinary nutrient media—agar, gelatin, and bouillon—without the addition of glucose.

The optimum temperature for growth is 20° to 25° C. The organism does not grow at incubator temperature (37.5° C.). At ice-box temperature (8° to 10° C.) it develops readily, although the growth is less rapid than at 20° to 25° C. That the organism will develop at even lower temperatures was shown in the inoculation experiments with hams, where it developed and multiplied extensively in the bodies of the hams at the temperature of the pickling cellars, which are held usually at 34° to 36° F. (1° to 2° C.).

The organism develops best in a neutral or slightly alkaline medium.

GROWTH ON DIFFERENT CULTURE MEDIA.

Growth on egg-pork medium.—At a temperature of 20° to 25° C. the cultures show a slight but distinct sour odor in from two to three days. This odor, as before stated, closely resembles the odor of a sour ham. Egg-pork cultures from three to five days old were given to a trained meat inspector, who knew nothing whatever as to the contents of the tubes, and he was asked to describe the odor; he described it as that of a sour ham.

At one week the albumins of the medium are gelatinized or partly coagulated and the odor is more pronounced. At ten days the albumins are completely coagulated except at the surface, where there is no apparent growth; the odor is more putrefactive in nature, and the reaction of the medium is slightly acid. At three weeks the coagulated albumin splits up into fragments and appears to undergo a slow digestion, gas bubbles form in the lower portion of the culture, and the odor becomes distinctly putrefactive in character. The slow digestion of the albumin is probably due to a proteolytic enzyme elaborated by the bacillus.

At the end of a week a dark zone usually appears at the surface of the coagulated albumin and gradually darkens until it becomes almost black. This zone is probably due to a pigment elaborated by the bacillus.

At ice-box temperature (8° to 10° C.) the same changes and the same odor were noted, but were somewhat slower in developing.

Glucose-pork-agar.—This medium was prepared from pork in the same manner as beef-agar, and contained 1 per cent of glucose. The organism grows readily on this medium and may be conveniently cultivated in deep stab cultures. The medium was always thoroughly boiled and then rapidly cooled in order to expel the inclosed air. The growth of the organism was found to vary considerably with the reaction.

When the reaction was +1.5, deep stab cultures at three days (20° to 25° C.) showed a well-marked arborescent growth, appearing as delicate filaments extending outward from the line of stab. The growth stopped within one-fourth or one-half inch of the surface of the agar on account of the presence of oxygen in the upper part of the culture medium. As the growth extended toward the walls of the test tube the agar became clouded, and there were sometimes gas bubbles in the depth of the agar, but the gas formation was not extensive.

When the reaction of the agar is neutral or slightly alkaline, extensive gas formation occurs and the agar is often much broken up.