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:
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.
[2] Rettger, L. F. Studies on putrefaction. Journal of Biological
Chemistry, vol. 2, 1906.
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.