SUPPURA TION. 199

Martin is the formation of crystals in fresh cultures.
Crystal-formation in cultures of other bacteria usually
takes place in old, partially dried agar-agar cultures. The
bacillus pyocyaneus, however, produces crystals in a few
days upon fresh media. In my experience freshly iso-
lated bacilli manifest this capability more markedly than
those which have been for some time part of the labo-
ratory stock of cultures, and subject to frequent trans-
plantation.1

Upon potato a luxuriant greenish or brownish, smeary
layer is produced. Milk is coagulated and peptonized.

This bacillus is highly pathogenic for laboratory ani-
mals. About i c.cm. of a fresh bouillon culture, if in-
jected into the subcutaneous tissue of a guinea-pig or a
*rabbit, causes a rapid edema, a suppurative inflammation,
and death in a short time (twenty-four hours). Some-
times the animal lives for a week or more, then dies.
There is a marked hemorrhagic subcutaneous edema at
the seat of inoculation. The bacilli can be found in the
blood and in most of the tissues.

When the dose is too small to prove fatal, suppuration
occurs in many cases.

When sterilized cultures are injected, the same results
follow, a relatively larger quantity, of course, being re-
quired.

Intraperitoneal injections cause suppurative peritonitis.

The organism has been found in the human being in the
pus in cases of middle-ear disease (often in pure culture),
panophthalmia, bronchopneumonia, inflammations of the
nasal fossae, meningitis, etc. Escaping from such local
lesions into the blood it sometimes causes nephritis.

It may, however, be stated that ordinarily the bacillus
is harmless for human beings, the above-mentioned ex-
amples of pathogenic activity being marked exceptions.

It is interesting to observe, in passing, that this path-
ogeny can be set aside by the immunity which develops
after a few inoculations with sterilized cultures. These

1 See Centralbl.f. Bakt., xxi., April 6, 1897, p. 473.