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392                  PATHOGENIC BACTERIA.

Indol is formed in both bouillon and pepton solu-
tions. Phenol is not produced. Ivitmus added to the
culture-media is ultimately decolorized by the bacilli.

The presence of indol is probably best determined by
Salkowski's method. To the culture i of a 0.02
per cent, aqueous solution of potassium nitrate and a
few drops of concentrated sulphuric acid are added. If
a rose color develops, indol is present.

Nitrates are reduced to nitrites by the growth of the

Upon potato the growth is luxuriant. The bacillus
forms a yellowish-brown, glistening layer spreading from
the line of inoculation over about one-half to two-thirds
of the potato. The color shown by the potato-cultures
varies considerably, sometimes being very pale, some-
times quite brown. It cannot, therefore, be taken as a
characteristic of much importance. Sometimes the po-
tato becomes greenish in color. Sometimes the growth
on potato is almost invisible.

In milk there are rapid coagulation and acidulation,
with the evolution of much gas.

The bacillus seems to require very little nutriment. It
grows in Ilscllinsky's asparagin solution, and is frequently
found living in river and well waters.

It is qnite resistant to antiseptics and germicides, and
grows in culture-media containing from 0.1-0.2 per cent,
of carbolic acid. It lives for months upon artificial

The bacillus begins to penetrate the intestinal tissues
almost immediately after death, and is the most frequent
contaminating micro-organism met with in cultures made
at autopsy. Exactly how it penetrates the tissues is not
known. It may spread by direct continuity of tissue, or
via the "blood-vessels.

While nnder normal conditions a saprophytic bacte-
rium, the colon bacillus is far from harmless. It not
infrequently is found in the pus of abscesses remote from
the intestine, and is almost always found in suppura-