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58                  PATHOGNEIC BACTERIA.

bacteria produce powerful metabolic poisons—toxins,
ptomaines, etc.—which either cause widespread destruc-
tion of the tissues immediately acted upon, or, circulating
throughout the organism, produce fever, nervous excita-
tion, and a general overthrow of the normal physiological
equilibrium. These peculiarities serve to divide the bac-
teria into

Phlogistic bacteria,

Toxic bacteria,
Septic bacteria.

The bacteria of suppuration probably act in several
ways. Their products may be of a violently chemotactic
nature, or their virulence, exerted upon the surrounding-
tissue, may destroy large numbers of the cells, whose
dead bodies may be chemotactic. When the suppura-
tion is violent the toxic product of the bacterium is itself
most probably strongly chemotactic.

The great majority of suppurations depend upon bac-
teria, but there are sterile suppurations which sometimes
follow the use of croton oil, turpentine, etc. The differ-
ence between infectious and sterile pus is marked, for
the former, containing the virulent germs, tends to invade
new tissue or distribute its disease-producers to new parts
of the body, while the latter remains local.

There are few purely toxic bacteria, the tetanus and
diphtheria bacilli serving as typical examples. By sep-
tic bacteria, I mean those whose habitual tendency is to
grow in the blood and lymph and distribute to all the
organs. Anthrax is a type of the class.

How the disease-producing bacteria effect their en-
trance into the tissues is an interesting question. The
channels naturally open to them are those leading into
the interior of the organism, and must be separately con-
sidered.

(a) The Digestive Tract.— Attention has already been
called to the facility with which the bacteria enter the
digestive tract in foods and drinks. Once their metabo-
lism is in active progress, the poisons which they produce