502 BACTERIOLOGY. 
granular in structure, and have a somewhat darker, 
more compact centre, surrounded by a paler marginal 
zone. With high magnification rows of cocci are seen 
sprouting from the edges. In stick cultures along the 
line of puncture minute transparent drops appear. 
Growth on Gelatin. The growth on gelatin is slow, 
if there is any development at all, owing probably to 
the low temperature—viz., 22° to 24° C.—at which the 
gelatin has to be kept. The gelatin is not liquefied. 
Growth on Blood-serum. The growth on Liffler’s 
blood-serum mixture is very similar to that on agar, 
but somewhat more vigorous, appearing on the surface 
as a delicate layer of dew-like drops. 
Growth in Bouillon. In bouillon, at the end of twelve 
to twenty-four hours in the incubator, a slight cloudi- 
ness of the liquid will be found to have been pro- 
duced, due to the development of the micrococci, 
which on microscopical examination can be seen to be 
arranged in pairs or longer and shorter chains. After 
two or three days the medium becomes again trans- 
parent, owing to the subsidence of the cocci to the 
bottom of the tube. 
Special Media. Fraenkel was the first to draw at- 
tention to the fact that this organism soon loses its 
reproductive power when grown on ordinary culture 
media, and more particularly solid media. In fluid 
media the vitality is not quite so quickly lost; but 
even here it is found advisable in practice to transplant 
fresh cultures every day. By this method, when bou- 
illon cultures are used, the vitality may be indefinitely 
prolonged; but after transplantation through several 
generations it is found that the cultures begin to lose 
in virulence, which finally disappears entirely. In order 
