appearance. It must be remarked that when sudden
transplantations are made from blood-serum to agar-
agar the growth resulting is meagre, but the oftener
this growth is transplanted to fresh agar-agar the more
luxuriant it becomes.
The growth in gelatin puncture-cultures is character-
ized by small spherical colonies which develop along the
entire length of the needle-track. The gelatin is not
Upon the surface of gelatin plates the colonies that
develop do not attain anything like the size of the colo-
nies upon Loffler's mixture. They appear to the naked
FIG. 79.—Bacillus diphtherias, colony twenty-four hours old upon agar-agar;
x loo (Frankel and Pfeiffer).
eye as whitish points with smooth contents and regular
though sometimes indented borders. Under the micro-
scope they appear as granular, yellowish-brown colonies
with irregular borders (Fig. 79).
When planted in bouillon the organism causes a diffuse
cloudiness at first, but, not being motile, soon settles to
the bottom in the form of a rather flocculent precipitate:
which has a tendency to cling to the sides of the glass.
Sometimes a delicate irregular mycoderma forms upon: