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ANTHRAX.                            357

of Davaine's conclusions and actual proof of the matter
rested with Pasteur and Koch, who, observing that the
bacilli bore spores, cultivated them successfully outside
the body, and then produced the disease by the inocula-
tion of pure cultures.

The anthrax bacilli (Fig. 101) are large rods with a

FIG. 101.—Bacillus anthracis: colony three days old upon a gelatin plate; ad-
hesive preparation; x 1000 (Frankel and Pfeiffer).

rectangular form, caused by the very slight rounding of
the corners. They measure 5-20 // in length and are
from i IJL to 1.25 p- in breadth. The pronounced tendency
is toward the formation of long threads, in which, how-
ever, the individuals can generally be made out; at times
isolated rods occur. In the threads the bacilli seem en-
larged a little at the ends, and give somewhat the appear-
ance of a bamboo cane. The formation of spores is pro-
lific : each spore has a distinct oval shape, is transparent,
and does not alter the contour of the bacillus in which it
occurs. Spores are generally formed in the presence of
oxygen upon the surfaces of the culture-media. When a
spore is placed under favorable conditions for its devel-
opment and is carefully watched, it may be observed to
increase in length a trifle, then to undergo a rupture at