402 PA THOGENIC BA CTERIA.
The granular appearance becomes continuously more
marked, and usually a central or peripheric nucleus,
completely opaque, is seen. In time the entire colony
becomes opaque, but does not liquefy gelatin.
Stroke-cultures on obliquely solidified gelatin exhibit
brilliant, opaque, little drops similar to drops of milk.
In bouillon it develops slowly, without either pellicle
The culture upon agar-agar is said to be characteristic.
If grown at 37° C., the peculiar appearances of the
colonies do not develop; but if the culture is kept at 20°-
22° C, the colonies appear rounded, whitish, opaque, and
prominent, like drops of milk. This appearance of the
colonies shows well if the cultures are kept for the first
twelve to sixteen hours at 37° C., and afterward at room-
temperature, when the colonies will show a flat central
nucleus, transparent and bluish, surrounded by a promi-
nent and opaque zone, the whole resembling a drop of
sealing-wax. Sanarelli refers to this appearance as con-
stituting the diagnostic feature of Bacillus icteroides. It
•can be obtained in twenty-four hours.
The growth upon potato corresponds to the classic
description of that of the bacillus of typhoid fever.
The bacillus is a facultative anaerobe. It cannot be
colored by Gram's stain. It slowly ferments lactose,
more actively ferments glucose and saccharose, but is not
capable of coagulating milk. It strongly resists drying,
dies in water at 60° C., and is killed in seven hours by the
solar rays. It can live for considerable time in sea-water.
The bacterium is pathogenic for the majority of the
domestic animals. All mammals seem more or less
sensitive to the pathogenic action of the bacillus; birds
are often immune. Guinea-pigs are invariably killed by
either intraperitoneal or subcutaneous injection of o. I
c.cm. White mice are killed in five days; guinea-pigs
in eight to twelve days; rabbits in four to five days.
The morbid changes present include splenic tumor, hy-
pertrophy of the thymus, and adenitis. In the rabbit