Part 6

FIG. 2.—SECTION THROUGH MUSCULAR TISSUE OF HAM WHICH HAS UNDERGONE NATURAL OR SPONTANEOUS SOURING, SHOWING INDIVIDUAL BACILLI BETWEEN THE MUSCLE FIBERS, WHICH ARE CUT SOMEWHAT OBLIQUELY. NUCLEI HAVE LOST SHARP OUTLINE AND CROSS STRIATION IS INDISTINCT.

(Pen-and-ink drawing made with camera lucida from section stained by the Gram-Weigert method to show bacteria. × 320.)]

In the sour areas near the bone the muscular tissue was distinctly softer; that is, it broke and cut more readily than the surrounding tissues. This was usually quite noticeable in cutting out plugs of the meat for making cultures. In a ham which shows pronounced souring the muscular tissues in the worst affected areas may become quite soft and even slightly gelatinous.

The sour areas, when tested with litmus paper, frequently showed a slight but distinct alkaline reaction. When aqueous extracts of the sour meat, however, were titrated with phenolphthalein they were found to be acid.

HISTOLOGICAL CHANGES IN SOUR HAMS.

In preparations made by teasing out bits of the meat in physiological salt solution, the cross striation of the muscle fibers from the sour areas was found to be much less distinct than in similar preparations taken from sound portions of the meat or from sound hams. At times it was found that the muscle fibers in the sour areas had completely lost their cross striæ, but the longitudinal striation could still be made out. In cases where the souring was pronounced there was sometimes complete loss of both longitudinal and cross striation; in these cases the muscle fibers appeared to have undergone slight swelling and the protoplasm exhibited a finely granular appearance.

In stained sections of the sour meat another striking change was noticed in the disintegration of the nuclei of the muscle fibers, which are at times completely broken up, appearing as bluish granular masses in sections stained with hematoxylin and eosin. (Compare figs. 1 and 2 of Pl. I.)

In sections stained by the Gram-Weigert method to show the presence of bacteria, a large Gram-staining bacillus was noted between the muscle fibers in the connective-tissue elements of the muscle. In some of the sections these bacilli were present in great numbers, sometimes in densely packed clumps or masses, while in other sections, or in other portions of the same section, they were only sparsely distributed between the muscle fibers. Where the bacteria were more numerous the histological changes in the muscle fibers, especially the breaking down of the nuclei, were more noticeable. The intermuscular connective tissue had apparently furnished paths of least resistance along which the organism followed. In Plate II, figures 1 and 2, the bacteria are shown between the muscle fibers under low and high power magnifications.

In Plate II, figure 1, under the low-power magnification, the bacteria appear as dark clumps or bands between the muscle bundles. Under the high power they are shown following along the sarcolemma sheaths between the muscle fibers.

CHEMICAL ANALYSES OF SOUR AND SOUND HAMS.

In order to determine whether there was any difference in regard to the penetration of the pickling fluids in the sour hams as compared with sound hams, a series of four sour hams were subjected to a chemical examination in comparison with four sound hams. All were sweet-pickle hams and were obtained from the same packing establishment. They were all of the same cure and the same approximate age (i. e., length of cure) and the same approximate weight.

In taking samples for chemical analysis, the following procedure was adopted: A section about 2½ inches wide was cut from the center of the body. The two ends of this section were then trimmed off along the lines L-M and N-O, as shown in figure 2. Beginning at the skinned surface, four slices, A, B, C, and D, were then made, as indicated by the dotted lines. Slice B contained the bone in each instance. Slice D was practically all fat. Each slice was ground separately in a meat chopper and the sample thoroughly mixed before taking out portions for analysis.

As all of the hams examined were mild-cure hams, that is, had been pumped in the shank only, the pickling fluids in order to reach the bodies of these hams had to penetrate chiefly from the skinned surface of the ham, as little if any penetration takes place through the thick skin of the ham.

The analyses shown in the following tables therefore indicate the degree of penetration of the pickling fluids.

These analyses were made by Mr. R. R. Henley, of the Biochemic Division, Bureau of Animal Industry.

Analyses of sour hams. ───┬────────────┬──────┬───────────┬─────────── No.│Description.│Slice.│ NaCl. │ KNO₃. ───┼────────────┼──────┼───────────┼─────────── │ │ │Per cent.│Per cent. 1 │Sour body │ A │ 6.18 │ 0.175 │ │ B │ 4.83 │ .224 │ │ C │ 3.65 │ .299 │ │ D │ 1.03 │ .074 │ │ │ │ 2 │ do │ A │ 5.34 │ .174 │ │ B │ 3.70 │ .150 │ │ C │ 2.79 │ .174 │ │ D │ 1.12 │ .012 │ │ │ │ 3 │ do │ A │ 5.04 │ .125 │ │ B │ 4.08 │ .149 │ │ C │ 2.72 │ .099 │ │ D │ 1.19 │ .048 │ │ │ │ 4 │ do │ A │ 7.78 │ .250 │ │ B │ 5.31 │ .100 │ │ C │ 4.76 │ .200 │ │ D │ 1.96 │ .048 ───┴────────────┴──────┴───────────┴───────────

Analyses of sound hams. ───┬────────────┬──────┬───────────┬─────────── No.│Description.│Slice.│ NaCl. │ KNO₃. ───┼────────────┼──────┼───────────┼─────────── │ │ │Per cent.│Per cent. 1 │Sound │ A │ 5.80 │ 0.211 │ │ B │ 4.83 │ .188 │ │ C │ 3.86 │ .221 │ │ D │ 1.33 │ .063 │ │ │ │ 2 │ do │ A │ 4.94 │ .197 │ │ B │ 4.08 │ .149 │ │ C │ 3.05 │ .223 │ │ D │ 1.56 │ .059 │ │ │ │ 3 │ do │ A │ 5.92 │ .173 │ │ B │ 4.29 │ .099 │ │ C │ 4.12 │ .139 │ │ D │ 2.32 │ .049 │ │ │ │ 4 │ do │ A │ 5.53 │ .119 │ │ B │ 4.89 │ .079 │ │ C │ 4.32 │ .099 │ │ D │ 2.19 │ .041 ───┴────────────┴──────┴───────────┴───────────

Taking an average of the four slices in each ham so as to get an average for the entire ham, and comparing the sour hams with the sound hams, we have the following comparison:

NaCl. KNO₃. Average for 4 sour hams (entire ham) per cent. 3.84 0.143 Average for 4 sound hams (entire ham) do 3.93 .131

These figures show practically no difference between the sour and the sound hams as regards the sodium chlorid and potassium nitrate content of the entire ham.

If, now, we compare the bone slices—and these afford really a better basis for comparison, as in sour-body hams the souring is always more pronounced around the bone—we have the following figures:

NaCl. KNO₃. Average for 4 sour hams (bone slice) per cent. 4.48 0.155 Average for 4 sound hams (bone slice) do 4.52 0.129

Here, again, we find no essential difference between the sour and the sound hams, and we must conclude from these analyses that souring does not depend upon or result from a lack of penetration of the pickling fluids.

It seems probable that in mild-cure hams, which are pumped in the shank only, the souring begins in the upper portion of the shank and extends upward along the bone into the body of the ham, and that it takes place before the pickling fluid has penetrated to the interior of the ham. When the pickling fluid reaches the interior of the ham it tends to inhibit the souring, which, as will be shown later, is due to the development of bacteria within the bodies of the hams. The growth of the bacteria, however, within the bodies of the hams and the histological changes in the muscle fibers do not seem to interfere with the penetration of the pickling fluids.

BACTERIOLOGICAL EXAMINATION OF SOUR AND SOUND HAMS.

In all of the sour hams which were examined bacteriologically a large anaerobic bacillus was found to be constantly present. From several of the hams this bacillus was obtained in pure culture; that is, it was the only organism present in cultures made from the sour meat and from the bone marrow of the femur. Such cultures, when held at room temperature, gave, at three days, a sour-meat odor exactly resembling that obtained from sour hams.

In many of the sour hams other bacteria were found in association with the anaerobic bacillus noted above. These other bacteria, however, were not constant, being sometimes present and sometimes absent. Among the other bacteria noted in the sour hams, the following forms occurred most frequently:

1. A nonmotile, gram-positive bacillus, measuring from 1.5 to 4 microns in length by 0.5 micron in breadth, sometimes in chains and filaments.