After considerable experimentation as to a suitable culture medium for the bacteriological study of sour hams, a modification of the “egg-meat mixture” used by Rettger[2] in his studies on putrefaction was found to be the most satisfactory. This medium, which consists of chopped meat and egg albumen, furnishes an excellent medium for the growth of putrefactive organisms which rapidly break down the proteids of the meat, giving rise to the characteristic odors of putrid decomposition. Rettger used chopped beef and egg albumen, but for the present work chopped pork was substituted for the beef, as affording a more suitable medium for the growth of organisms accustomed to growth in pork hams. The modified medium is prepared as follows:
[2] Rettger, L. F. Studies on putrefaction. Journal of Biological Chemistry, vol. 2, 1906.
A. One-half pound of lean pork, freed from excess of fat and sinew, is finely chopped in a meat chopper, 250 cubic centimeters of water is then added, the meat acids are neutralized with sodium carbonate, and the mixture is heated in an Arnold sterilizer for 30 minutes, with occasional stirring. It is then set away in a cold place for several hours. A small amount of fat collects at the top in the form of a fatty scum, as it is impossible to remove all of the fat from the meat before it is chopped. The fatty scum, which hardens upon standing in the cold, is now removed.
B. The whites of three eggs are mixed with 250 cubic centimeters of water. The mixture is rendered neutral to phenolphthalein by means of dilute hydrochloric acid and heated for 30 minutes in the Arnold sterilizer, with occasional stirring.
A and B are now mixed and 2.5 grams (0.5 per cent) of powdered calcium carbonate added. The mixture is next run into large sterile test tubes, or sterile flasks, and sterilized in an Arnold sterilizer on three successive days.
In addition to the egg-pork mixture described above, culture tubes of agar and bouillon prepared from pork instead of beef, with the addition of 1 per cent of glucose, were also used; but the best results were obtained with the egg-pork medium, as with this medium, the early development of sour or putrefactive odors furnished a valuable indication as to the presence of organisms capable of producing sour or putrefactive changes in meat.
METHOD OF PROCEDURE IN EXAMINING HAMS.
The hams were sectioned through the body, the femur, or “middle bone,” as it is known in packing-house parlance, being cut at a point about 1-1/2 or 2 inches below its head. A cross section of a ham thus cut is shown in figure 1. After sectioning, the hams were subjected to a microscopical, bacteriological, and chemical examination as follows:
Microscopical examination.—Bits of muscular tissue, taken from various points, were teased out in salt solution and the condition of the muscle fibers noted. Smear preparations were also made from bits of muscular tissue and from the bone marrow, and these were stained and subjected to microscopical examination. Portions of the meat were also hardened and cut into microscopic sections, which were stained and mounted for histological and bacteriological study.
Bacteriological examination.—In the bacteriological examination of sour hams, especial attention was directed to the detection of anaerobic species, as it seemed reasonable to suppose that if the changes taking place in sour hams were due to bacteria these bacteria would in all likelihood be anaerobes (i. e., organisms which develop in the absence of oxygen). This assumption was based upon the fact that, as a rule, souring begins in the interior of the ham next to the bone, and, furthermore, the hams are cured in large vats where they are completely submerged in the pickling fluids, so that any bacteria which develop within the bodies of the hams while they are in cure are probably restricted to practically anaerobic conditions.