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.