Chapter III: Part 3

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.

The cultures developed a disagreeable, somewhat putrefactive odor, but did not give the characteristic sour-ham odor obtained from the egg-pork cultures.

The organism was also grown on anaerobic agar plates by Zinsser’s method, which is said to give absolutely anaerobic conditions. The colonies on agar have a cottony or woolly appearance at first, and spread slowly, with slightly irregular margins.

In glucose-pork-agar to which azolitmin was added the azolitmin in the lower portion of deep stab cultures was completely decolorized in five days at room temperature (20° to 25° C).

In glucose-pork-agar containing neutral red the red color in the lower portion of the tube was changed to yellow with the development of fluorescence.

_Neutral gelatin._—Tubes of ordinary neutral gelatin without the addition of glucose were inoculated and held at ice-box temperature (8° to 10° C). At five days a delicate white growth appeared along the line of stab in the lower portion of the tube. At seven days the growth showed fine radial striæ, presenting an arborescent or tree-like appearance, and extended halfway from the line of stab to the walls of the test tube. At two weeks the growth had caused a delicate clouding of the medium in the lower portion of the tube. At three weeks the gelatin in the lower portion of the tube had become liquefied and the growth had settled to the bottom as a white precipitate.

In gelatin containing glucose, gas bubbles are formed in the depth of the medium through the splitting up of the glucose, and the characteristic arborescent growth is obscured.

_Glucose-pork-bouillon._—This medium was prepared from pork instead of beef and contained 1 per cent of glucose. The best results were obtained when the reaction of the medium was neutral or slightly alkaline.

Culture tubes, which had been previously boiled to expel the contained air and then inoculated, were held in a Novy jar, in an atmosphere of hydrogen at a temperature of 20° to 25° C. At three days the tubes showed well-marked clouding. At one week the growth appeared as a heavy, white, flocculent, cottony precipitate in the bottom of the tubes with a slight flocculent precipitate above. When the culture was removed from the jar and shaken, the heavy, flocculent precipitate at the bottom of the tube broke up without much difficulty, giving rise to a heavy uniform clouding with some small floating masses, which soon settled to the bottom. On shaking the tube some evolution of gas in the form of very fine bubbles was noticed.

In Smith fermentation tubes containing neutral glucose-pork-bouillon the closed arm of the tube shows well-marked clouding with gas formation at three days at room temperature (20° to 25° C). The growth has a tufted, cottony appearance, and there are many filaments and threads. The growth settles to the bottom of the closed arm as a cottony, white precipitate (see Pl. IV). The organism splits the glucose vigorously, and at 10 days the tubes show from 40 to 50 per cent of gas. The bouillon in the open arm of the tube remains unclouded. The maximum gas production at room temperature is reached in from 10 to 14 days, by which time the growth in the closed arm has completely settled into the bend of the tube, leaving the bouillon in the closed arm clear. The gas formula, as determined by Smith’s method, was H/CO₂ = 5/1. The reaction of the bouillon becomes acid to phenolphthalein.

The organism will grow on ordinary neutral bouillon without the addition of glucose, and in Smith tubes containing this medium a small amount of gas was formed, due to the splitting of the muscle sugar.

The bacillus also grows in a sugar-free broth—that is, a broth free from muscle sugar—and from cultures grown in this medium a well-marked indol test was obtained.

_Litmus-milk._—The organism was grown in litmus-milk in Smith fermentation tubes at 20° to 25° C. At seven days the litmus in the lower portion of the closed arm had assumed a brownish-buff color. At two weeks the litmus in the closed arm had been reduced to a brownish-buff color except at the top of the tube, where a pale, bluish tinge remained, and the litmus in the open arm showed very slight reddening as compared with a check tube. At three weeks the litmus in the closed arm was entirely reduced to a light, brownish-buff color, and the litmus in the open arm showed a slight but distinct reddening as compared with the check. The reddening of the litmus in the open arm was evidently due to the transfusion of acids formed by the growth of the bacillus in the closed arm. After several weeks the milk is slowly peptonized, probably as a result of enzyme action.

MORPHOLOGY.

The organism is a large bacillus having an average size of 4 to 8 μ in length by 0.5 to 0.7 μ in thickness, but there are many longer forms measuring from 10 to 20 μ in length. It develops in long, irregular chains or filaments, which at times show a slightly spiral form.

FIG. 5.—Ham-souring bacillus (_Bacillus putrefaciens_) grown
on egg-pork medium, showing tendency to form chains. Partly
developed and fully developed spores are shown at ends of rods;
also free spores. (Pen-and-ink drawing made with camera lucida
from preparation stained by Gram’s method. × 640.)]

The individual organisms show at times a widely open, slightly spiral form, which was more apparent in hanging-drop preparations made from bouillon cultures, where the organisms had been comparatively undisturbed. This appearance was also noted at times in the stained sections of soured muscular tissue, where the organisms were stained in place. The organism possesses no motility. It stains with the ordinary aniline dyes and by Gram’s method.

SPORE FORMATION.

The organism develops large, terminal spores, which are at first oval, but when fully developed are perfectly round and measure from 1.5 to 2 μ in diameter.

Spores develop rapidly in the egg-pork medium at 20° to 25° C., fully developed spores being noted in from five to seven days. At ice-box temperature (8° to 10° C.) partly developed spores were noted in the egg-pork medium at 10 days and fully developed spores at 2 weeks.

Occasional spores were noted in old agar and gelatin cultures, but abundant spore formation was seen only in the egg-pork medium. No spores were noted in bouillon cultures, even at 10 weeks.

RESISTANCE TO HEAT AND CHEMICAL AGENTS.

In its vegetative form the bacillus is killed at 55° C. in 10 minutes. The spores survive a temperature of 80° C. for 20 minutes, but are killed at 100° C. in 10 minutes.

When sodium chlorid and potassium nitrate were added to glucose-pork broth in varying amounts, it was found that 3 per cent of sodium chlorid or 3 per cent of potassium nitrate was sufficient to inhibit completely the growth of the bacillus at room temperature (20° to 25° C.).

While the growth of the bacillus was inhibited by sodium chlorid and potassium nitrate as just stated, it was found that very much stronger solutions of the two salts failed to destroy the bacillus. Thus it was found that the bacillus or its spores retained their vitality after an exposure of 30 days in a solution containing 23 per cent of sodium chlorid and 6 per cent of potassium nitrate.

GAS PRODUCTION.

The organism splits glucose, but not lactose or saccharose. That it possesses the power of splitting muscle sugar was shown by the formation of gas in Smith fermentation tubes containing ordinary neutral bouillon without the addition of any sugar.

The formation of gas in glucose bouillon varies considerably with the reaction of the medium. The largest amount of gas was formed when the broth was neutral or slightly alkaline. When the reaction of the broth was distinctly acid or distinctly alkaline the amount of gas was diminished. The gas which is formed in bouillon cultures consists chiefly of hydrogen and carbon dioxide. In order to collect a sufficient amount of the gas for analysis, two large fermentation tubes capable of holding 150 cubic centimeters each were constructed. These tubes were filled with pork-bouillon and inoculated with the bacillus. After 20 days at room temperature (20° to 25° C.) the gas was collected and the carbon dioxide and hydrogen determined, with the following result:

Cubic centimeters.
Total amount of gas collected 37.7
Carbon dioxide, by absorption with NaOH 6.2
Hydrogen, by difference 31.5

This analysis gives an approximate gas formula of H/CO₂ = 5/1, which agrees with the gas formula as determined in the small fermentation tubes by Smith’s method.

In hams which had undergone spontaneous souring and in hams which had been artificially soured by inoculation, hydrogen-sulphid was often noted when the sour portions of the meat were tested with lead-acetate paper, but no distinct odor of the gas could be obtained. Hydrogen sulphid was also noted in egg-pork cultures of the bacillus.

ACID PRODUCTION.

In glucose-bouillon, butyric and lactic acids are formed and the reaction of the medium becomes distinctly acid. Butyric and lactic acids were also noted in the egg-pork cultures.

A series of Smith fermentation tubes containing 10 c. c. each of glucose-pork broth medium was inoculated with the bacillus and held at room temperature (20° to 25° C.). These cultures were titrated against [N/40]NaOH, with phenolphthalein as an indicator at intervals of two days up to nineteen days, and then at two-week intervals up to sixty-one days. Three of the cultures were titrated each time so as to give a fair average of the acidity of the cultures, and an uninoculated check tube was also titrated each time to see if there was any change in the reaction of the medium. The results of the titrations are shown in the following table:

_Acidity determinations in glucose-pork broth cultures._

──────────────┬───────┬───────┬───────┬────────┬───────┬───────────
Age of culture│Culture│Culture│Culture│Average.│Medium.│Acidity of
(days). │ A. │ B. │ C. │ │ │ culture.
──────────────┼───────┼───────┼───────┼────────┼───────┼───────────
│ │ │ │ │ │_Per cent._
2 │ 0.038 │ 0.030 │ 0.040 │ 0.036 │ 0.009 │ 0.027
4 │ .105 │ .100 │ .102 │ .102 │ .009 │ .093
6 │ .106 │ .110 │ .109 │ .108 │ .009 │ .099
8 │ .124 │ .115 │ .117 │ .119 │ .009 │ .110
10 │ .128 │ .130 │ .126 │ .128 │ .009 │ .119
12 │ .129 │ .120 │ .129 │ .126 │ .009 │ .117
19 │ .126 │ .125 │ .125 │ .125 │ .009 │ .116
33 │ .125 │ .123 │ .125 │ .124 │ .009 │ .115
47 │ .122 │ .120 │ .121 │ .121 │ .009 │ .112
61 │ .121 │ .116 │ .119 │ .118 │ .009 │ .109
──────────────┴───────┴───────┴───────┴────────┴───────┴───────────

From the above table it will be seen that the maximum acidity was reached at ten days, after which there was a gradual reduction in the acidity, due probably to the formation of ammonia compounds.

PATHOGENIC PROPERTIES.

Rabbits, guinea pigs, and white mice were inoculated and fed with cultures of the bacillus without effect, from which it would appear that the bacillus possesses no pathogenic or disease-producing properties.

NATURE OF THE BACILLUS.

The bacillus is essentially a saprogenic bacterium with zymogenic properties. A preliminary study of the chemical changes which take place in sour hams shows that these changes are of a putrefactive nature. Hams which had undergone spontaneous souring were compared with hams which had been artificially soured by inoculation, and the chemical changes were found to be identical. A chemical study was also made of the changes taking place in egg-pork cultures of the bacillus at different stages of growth, and these changes were found to be of a putrefactive nature and similar in character to the changes which occur in sour hams. Among the putrefactive products formed by the growth of the bacillus in the egg-pork medium were indol, skatol, volatile fatty acids, skatol-carbonic acid, and hydrogen sulphid.[4]

[4] The tests for the putrefactive products formed by the growth of the bacillus in the egg-pork medium were made by P. Castleman, of the Biochemic Division, who also determined the percentage composition of the gas formed by the growth of the bacillus in the glucose-pork-bouillon medium.

BUL. 132, BUREAU OF ANIMAL INDUSTRY, U. S. DEPT. OF AGRICULTURE.
PLATE IV.

GLUCOSE BOUILLON CULTURE IN SMITH FERMENTATION TUBE AT FOUR
DAYS. CULTURE GROWN AT ROOM TEMPERATURE (20° TO 25° C.). GROWTH
CONFINED ENTIRELY TO CLOSED ARM, WITH GAS COLLECTING AT TOP.]

A more extended study is now being carried on in the Biochemic Division of the chemical changes which take place in hams during the process of souring, together with a further study of the chemical changes which result from the growth of the bacillus in the egg-pork medium. The results of this investigation will be given in a later paper.

The bacillus described in this paper belongs to the class of putrefactive anaerobes, which are widely distributed in nature in dust, soil, and excrementitious matters. This group of bacteria contains both pathogenic and nonpathogenic forms. The former have received considerable attention, but the latter have never been thoroughly cleared up. The bacillus isolated from sour hams belongs in the latter category, being possessed of no pathogenic or disease-producing properties. It occurs in the dust and dirt of the packing house and finds its way into the hams in the various manipulations to which the hams are subjected.

The bacillus described in this paper does not seem to correspond with any forms heretofore described. It differs from Klei bacillus (_Bacillus fœdans_) in the following important particulars: (1) It forms large terminal spores, whereas Klein’s bacillus formed no spores; (2) it will grow at a temperature of 34° F., while Klei bacillus did not grow below 50° F.; (3) it produces an acid reaction in culture media, while Klei bacillus gave a distinctly alkaline reaction; (4) it will grow on the ordinary nutrient media—gelatin, agar, and broth—without the addition of glucose, while Klein’s bacillus did not; (5) it peptonizes the casein in milk, whereas Klein’s bacillus had no action on milk; (6) it liquefies gelatin more rapidly, causing complete liquefaction after three weeks at 8° to 10° C., whereas Klein’s bacillus caused only partial liquefaction after eight weeks at 20° C.; (7) it can be conveyed from turbid broth cultures to new culture material by means of the platinum loop, whereas Klein’s bacillus could not be thus conveyed.

For the bacillus described in the present paper the following name is proposed: _Bacillus putrefaciens_.

PREVENTION OF HAM SOURING.

As it has been shown that souring in hams results from the growth of a bacterium which is introduced into the bodies of the hams in the various manipulations which the hams undergo, the only way to eliminate souring in hams, as they are cured in the larger packing establishments, would be to cure the hams under aseptic or sterile conditions, which would, of course, be a physical impossibility.

While it will probably be impossible, therefore, to eliminate souring entirely under the methods of ham curing which are at present employed in the larger packing establishments, much can undoubtedly be done toward reducing the percentage of sours. In the matter of taking ham temperatures, for instance, if the thermometers used were thoroughly cleaned and disinfected and the surfaces of the hams seared at the point where the thermometer is introduced, infection from this source could be entirely prevented; or it might be possible so to regulate the temperature of the chill rooms that the taking of ham temperatures could be discontinued.

The elimination of the souring that results from the introduction of foreign matter on the pumping needles could be effected in two ways only, (1) by not pumping the hams at all, or (2) by pumping them under sterile or aseptic conditions. As has been stated before, some of the smaller packing establishments cure their hams without pumping, and in these establishments the percentage of sours runs very low. When hams are cured without pumping, however, the period of curing has to be materially lengthened in order to give the curing pickles sufficient time to penetrate thoroughly, and this is what the larger plants wish to avoid because of the greater space and greater number of vats which would be necessitated. The object of pumping in the larger plants, where the number of hams handled daily runs into the thousands, is to hasten the cure and thus prevent the accumulation of a great number of hams at one time. It is doubtful, therefore, whether the larger packing houses could conveniently discontinue pumping.

To pump the hams under aseptic conditions would necessitate a technique far too elaborate for routine use in the packing house; in fact, anything like complete asepsis would be out of the question. Certain measures might be adopted, however, that would tend to prevent the possible introduction of ham-souring bacilli in the process of pumping. It would undoubtedly be safer, for instance, to boil the pumping pickle before use, and the chances of carrying in contaminated foreign matter on the pumping needles could be lessened by sterilizing the pumps and needles with boiling water and by frequently dipping the needles, while in use, in boiling water. If the hams were sprayed with clean water just prior to pumping, there would be less likelihood of carrying in foreign matter on the needles. The danger of introducing contaminated foreign matter on the needles might be further obviated by searing the surfaces of the hams at the points where the needles are introduced; but such a procedure would be hardly practicable in the larger packing houses, where the great number of hams cured necessitates rapid handling.

While the danger of possible contamination in pumping, through the introduction of contaminated foreign matter on the pumping needles, can not well be avoided, this danger is partly counterbalanced by the inhibitory action of the pumping pickle, which is strikingly shown in the experiments which have been described. In these experiments, 100 hams received large doses of the ham-souring bacillus, half of these hams being subjected to the mild cure and half to the regular cure, with the following result: In the case of the mild-cure hams, which were pumped in the shank only, the percentage of sours was practically 100 per cent, every ham with possibly one exception becoming sour; whereas in the regular-cure hams, which were pumped in both body and shank, only 58 per cent of the hams became sour. In other words, the additional pumping which the regular-cure hams received served to prevent souring in 42 per cent of these hams. In these experiments the number of bacteria introduced into the hams was very great, thousands and even millions of the bacilli being introduced into each ham, whereas in the routine of the packing house it is not likely that more than a few of the bacilli are ever introduced at one time on the thermometers and pumping needles. In view of these results it is safe to say that in the larger packing houses, where pumping seems to be necessary, the number of sours could be reduced fully 50 per cent if all hams were pumped in the body as well as in the shank.

At present the usual procedure is to pump all hams, both mild and regular cure, with the same pumping pickle, the mild-cure hams being pumped in the shank only and the regular-cure hams at two additional points in the body. The experiments quoted above show that the additional pumping which the regular-cure hams receive undoubtedly tends to prevent the development of souring in these hams, and this result is unquestionably due to the inhibitory action of the salts contained in the pumping pickle, as it was found by laboratory experiment that the addition of 3 per cent of sodium chlorid to culture media is sufficient to inhibit the growth of the ham-souring bacillus. The pumping pickles consist of strong brine solutions and always contain considerably more than 3 per cent of sodium chlorid. If, therefore, the pumping of regular-cure hams were made more thorough than at present, and all of the deeper portions of the ham were thoroughly saturated with the strong brine solution, souring could be largely eliminated, if not entirely prevented, in these hams, as an unfavorable medium or soil would thus be created in which the ham-souring bacillus could not develop. The ham-souring bacillus is able to develop within the bodies of the regular-cure hams because the pumping of these hams is not always thorough and there are certain areas in the inner or deeper portions of the hams in which the tissues are not thoroughly saturated with the pumping pickle.

Under the present methods of curing, the greater proportion of the sours occur among the partly pumped or mild-cure hams. These hams are pumped in the shank only, and the growth of the ham-souring bacillus within the bodies of these hams is not interfered with until the curing pickle has penetrated from the outside. As it requires several weeks for the curing pickle to penetrate thoroughly into the deeper portions of these hams, the bacillus is thus afforded a considerable interval in which to develop before it is exposed to the inhibitory action of the pickle. If these hams could be thoroughly pumped in the body at the beginning of the cure in the same manner as the regular-cure hams, the chief loss from ham souring would be eliminated. It would not do, however, to pump these hams in the body with the same pumping pickle used in the regular cure, as the meat would be rendered too salty and the mild flavor of the ham would be lost. There is undoubtedly a demand for mild-cure hams, otherwise they would not be on the market; and the question then arises how to pump these hams and still retain a mild cure. This might be accomplished by pumping these hams with their own curing pickle, which is usually a milder pickle than that employed in the regular cure, or an even milder pumping pickle might be used. If mild-cure hams were pumped in this way, the percentage of souring in these hams could undoubtedly be greatly diminished without materially affecting the flavor of the ham.

To recapitulate briefly, the prevention of ham souring is to be sought in two ways: (1) Through greater care in handling the hams and the adoption of precautionary measures to prevent the introduction of the ham-souring bacillus into the bodies of the hams, and (2) through more thorough pumping of the deeper or inner portions of the hams, so as to create an unfavorable soil or medium in which the ham-souring bacillus can not develop even if it should gain entrance into the bodies of the hams.

From what has been said it will be apparent that ham souring can probably never be entirely eliminated from the packing house under the present methods of curing, but the adoption of precautionary measures in testing and pumping hams, together with a more thorough pumping of all hams in ways similar to those suggested, would unquestionably reduce very materially the losses from this source.

GENERAL SUMMARY AND CONCLUSIONS.

1. In this paper it has been shown that ham souring, as encountered in the wet cure where the hams are entirely submerged in pickling fluids, is due to the growth of an anaerobic bacillus within the bodies of the hams. This bacillus (_B. putrefaciens_) was found in sour hams obtained from four different packing establishments. It was isolated and grown in various laboratory media, in one of which, the egg-pork medium, it gave rise to the characteristic sour-ham odor. This bacillus was the only organism that could be isolated from sour hams that was capable of producing the characteristic sour-ham odor in the egg-pork medium.

2. When injected into the bodies of sound hams, the bacillus caused these hams to sour in the process of curing. In hams which had been inoculated with the bacillus and thus artificially soured, the bacillus was recovered in cultures taken at points far removed, relatively speaking, from the point of inoculation, indicating that the bacillus had multiplied and progressed by extension throughout the bodies of the hams.

3. The bacillus possesses no motility, and its extension throughout the bodies of the hams is a result of multiplication. In its growth it follows along the connective-tissue bands between the muscle bundles, which are composed of comparatively loose tissue and afford paths of least resistance. When it invades the muscle tissue proper, it follows along the sarcolemma sheaths between the muscle fibers. As a result of this growth the muscular tissue becomes softer and tends to break more easily.

4. The bacillus belongs to the class of putrefactive anaerobes which are widely distributed in nature in dust, soil, and excrementitious matters. The bacillus or its spores is present in the dust and dirt of packing houses and finds its way into the hams in the various manipulations to which they are subjected.

5. The bacillus or its spores may be introduced into hams on the thermometers used in testing the hams, on the pumping needles, and possibly on the billhooks used in handling the hams. It may also be carried into the hams in the pumping pickle, and may even find its way into the hams from the curing pickle, although infection through the latter channel probably does not often occur.

6. The bacillus develops in the deeper portions of the ham because of the anaerobic conditions there prevailing, and souring is most often encountered, therefore, in the deeper portions of the ham near the bone.

7. A preliminary study of the chemical changes which take place in the process of souring shows that these changes are of a putrefactive nature, and ham souring, as ordinarily encountered, is to be regarded as an incipient putrefaction. Hams which had been artificially soured by injections of culture were compared with sour hams obtained from the packing house, and the putrefactive changes were found to be identical.

8. Hams which have once become sour can never be restored to a sound condition, because of the chemical changes which result from the growth of the bacillus. In other words, the tissues of the ham undergo certain chemical changes in the process of souring, and when these changes have once taken place the tissues can never be restored to a sound condition. The repumping of slightly soured hams with a strong pumping pickle will check further souring, by inhibiting the growth of the bacillus, but will not restore to a sound condition those portions of the ham which have become sour.

9. The salts of the pickling fluids have a marked inhibitory action on the ham-souring bacillus, and sours occur less frequently in regular-cure hams.

10. In regular-cure hams the growth of the ham-souring bacillus is restricted and often completely inhibited as a result of the additional pumping which these hams receive, whereby they are more or less saturated with pickle at the beginning of the cure.

11. If the pumping of regular-cure hams were more thorough and all of the deeper portions of the ham were thoroughly saturated with the pumping pickle, souring could be largely eliminated if not entirely prevented in the hams, as an unfavorable medium or soil would thus be created, in which the ham-souring bacillus could not develop. The reason that souring does develop in regular-cure hams is because the pumping is not always thorough and there are certain areas in the deeper portions of these hams which are not saturated with the pumping pickle.

12. Under the present methods of curing, the partly pumped or mild-cure hams furnish the greater proportion of the sours, as these hams are not pumped in the body and the growth of the ham-souring bacillus within the bodies of these hams is not interfered with until the curing pickle has penetrated from the outside. As it requires several weeks for the curing pickle to penetrate thoroughly into the deeper portions of these hams, the bacillus is thus afforded a considerable interval in which to develop.

13. The percentage of souring in the mild-cure hams could be greatly reduced without materially affecting the cure by pumping these hams with their own curing pickle, which is usually a milder pickle than that employed in the regular cure; and if the pumping were thorough the number of sours in these hams could be reduced to a small figure.

14. The only way by which ham souring could be entirely eliminated from the larger packing establishments under the present methods of curing would be to handle the hams throughout under aseptic conditions, and this, for obvious reasons, would be an impossibility. The losses from ham souring may be materially reduced, however, by greater care in handling the hams and the adoption of precautionary measures designed to prevent the introduction of contaminated foreign matter into the bodies of the hams, together with more thorough methods of pumping.

ACKNOWLEDGMENTS.

In conclusion, the writer desires to express his obligations to Dr. S. E. Bennett, of the Inspection Division, inspector in charge at Chicago, for the assignment of trained meat inspectors to assist in the work, as well as for kind assistance in obtaining data and material for laboratory study, and to Dr. L. E. Day, of the Pathological Division, who kindly prepared the sections which are figured and described in the present article.