PNEUMONIA. 355

occurs. Such a pneumonia may be caused by the tubercle
bacillus alone, but more often it is aided by accompany-
ing staphylococci, streptococci, tetragenococci, pneumo-
cocci, pneumobacilli, and other organisms apt to be pres-
ent iu a lung in which tuberculosis is in progress and
ulceration and cavity-formation are advanced.

4. Mixed Pneumonias.—It frequently happens that
pneumonia occurs in the course of, or shortly after the
convalescence from, influenza. In these cases a mixed
infection is present, and there is no diiBculty in deter-
mining that both the influenza bacillus and the pneumo-
coccus are present. Again, sometimes the pneumococci
and staphylococci operate simultaneously, and produce
a purulent pneumonia with abscesses as the conspicuous
feature. As almost any combination of the described
bacteria is possible in the lungs, and as these combi-
nations will all produce varying inflammatory conditions,
it must be left for the student to imagine what the par-
ticular characters of each may be.

Among these mixed pneumonias may be mentioned
those called by Klemperer and Levy " complicating
pneumonias," occurring in the course of typhoid, etc.