436	PA THOGENIC BA CTERIA.
six days the islands are still more compact and solidified.
If the vessel be disturbed, the islands fall like snow and
are deposited at the bottom.
Upon gelatin plates at 22° C. the colonies may be ob-
served in twenty-four hours by the naked eye. They are
pure white or yellowish-white, spherical in the deep gela-
tin, fiat upon the surface, and are about the size of a
pin's head. The gelatin is not liquefied. The borders
of the colonies are, upon microscopic examination, found
to be sharply defined and to become more granular as
their age increases. The superficial colonies occasionally
are surrounded by a fine, semi-transparent zone.
In gelatin puncture-cultures the development is scant.
The medium is not liquefied (?); the growth takes place
in the form of a fine duct, little points being seen on the
surface and in the line of puncture.
Upon agar-agar—glycerin agar-agar is best—the bacilli
grow freely, the colonies being whitish in color, with a
bluish tint by reflected light. Under the microscope
they appear moist, with rounded, uneven edges. The
small colonies are said to resemble little tufts of glass-
wool; the larger ones have large round centers. Micro-
scopic examination of the bacilli grown upon agar-agar
reveals the presence of long chains resembling strepto-
cocci.
Klein1 states that the colonies develop quite readily
upon gelatin made from beef-bouillon (not infusion),
appearing in twenty-four hours, at 20° C., as small, gray,
irregularly rounded dots. Magnification shows the col-
onies to be serrated at the edges and made up of short,
oval, sometimes double bacilli. Some colonies contrast
markedly with their neighbors in that they are large,
round, or oval, and consist of longer or shorter, straight
or looped threads of bacilli. The appearance was much
like that of the young colonies of the Proteus vulgaris.
At first Klein regarded these as contaminations, but later
' he was led to believe that their occurrence was character-
1 Centralbl.f. Bakt. u. Parasitenk., xxi., Nos. 24 and 25, July 10, 1897.