Pathogenic Bacteria

TYPHOID FEVER. 373

and thoroughly dissolved by a few minutes' boiling. The
medium is then titrated to determine its reaction, phenol-
phthalein being used as the indicator, and enough HC1 or
NaOH added to bring it to the desired reaction—i. e. a re-
action indicating i. 5 per cent, of normal acid. To the clear
medium add one or two eggs, well beaten in 25 c.cm. of
water; boil for forty-five minutes, and filter through a
thin filter of absorbent cotton. Add the glucose after
cleaning.

The medium is used in tubes, in which it is planted by
the. ordinary puncture. The typhoid bacillus alone, of
many of the allied forms studied, has the power of cloud-
ing this medium uniformly without showing streaks or
gas-bubbles.

The second medium is used for plating. It contains
10 grams of agar, 25 grams of gelatin, 5 grams of beef-
extract, 5 grams of sodium chlorid, and 10 grams of glu-
cose. The method of preparation is the same as for the
tube-medium, care always being taken to add the gela-
tin after the agar is thoroughly melted, so as not to alter
this ingredient by prolonged exposure to high tempera-
ture. This preparation should never contain less than 2
per cent, of normal acid. Of all the organisms with
which Hiss experimented, the Bacillus typhosus alone
displayed the power of producing thread-forming colonies
upon this medium.

The colonies of the typhoid bacillus when deep in the
medium appear small, generally spherical, with a rough,
irregular outline, and by transmitted light are of a vitreous
greenish or yellowish-green color. The most character-
istic feature consists of well-defined filamentous out-
growths, ranging from a single thread to a complete
fringe about the colony. The young colonies are, at
times, composed solely of threads. The fringing threads
generally grow out nearly at right angles to the periphery
of the colony.

The colonies of the colon bacillus are, on the average,
larger than those of the typhoid bacillus; they are spher-