A MORE COMPLETE DESCRIPTION OF BACTERIUM TRUTTyE. 
413 
to ii depth of about 2 cm. in seventeen days, fading gradually into the pale agar. 
The surface growth takes on a brownish color. 
Agar plate surface colonies are round, slightly convex, the outline well defined. 
Microscopically they are granular, and when more than two days old the deep colo- 
nies and the surface colonies near the center become grumose. The edge of young- 
colonies is slightly erose, but usually becomes entire or rarely broadly undulate. 
Well -developed colonies are translucent and yellowish under the microscope by 
transmitted light. Plates of about 400 colonies have, after two days, surface colonies 
about 0.58 mm. in diameter; after five days 0.85 mm., and then increase but little. 
Plates of 200 colonies have 0.54 mm. surface colonies in one day; and plates of 
about 25 colonies have 0.83 mm. surface colonies in two days, and after about one 
week these reach 3 mm. and cease to increase. Plates crowded with colonies are 
tinged with the brown color on the second day. 
Gelatine: In +1.5 gelatine there is probably a very slight multiplication, the 
line of puncture showing a slight growth like a nonliquefying organism. No visible 
surface growth occurs and no evident liquefaction. In +0.5 gelatine abundant 
growth and liquefaction take place. The latter at first is either crateriform or 
funnelform, but may finally become stratiform, reaching the walls of the tube and 
extending down horizontally. Occasionally the lower end of the stab liquefies faster 
than the portions above it and produces a terminal sac of liquefaction. Gelatine 
plate cultures liquefy rapidly. 
Blood serum: Blood serum is liquefied; a streak culture on solid serum results 
in a visible growth in eighteen hours. On the second day evident liquefaction has 
occurred, a shallow groove without sharply defined edges having formed, the growth 
sedimented on the bottom and collected at the foot of the slant with the liquefied 
serum. After three or four days there is a marked brown color, and the slanted 
portion of the serum is rapidly liquefying. After about eleven days the growth 
becomes slow and the color very dark brown, much darker than in old agar cultures. 
Potato: On ordinary acid potato no growth occurs. On potato boiled in a 
known quantity of distilled water, which is then titrated and neutralized to phenol- 
phthalein and the potato boiled in it again, there is a very slight growth. It becomes 
visible on the third day and appears as a faint and scanty growth of white, which is 
not elevated above the surface of the potato. It does not increase after four or five 
days and never produces color. 
Milk: It grows abundantly in milk and does not cause coagulation. The reac- 
tion is unchanged or becomes slightly acid. The milk is peptonized and becomes 
fairly clear in from one to two weeks, and pepton may be detected in the liquid. 
Dunham’s pepton solution: The growth resembles that in bouillon, but proceeds 
more slowly. The characteristic pigment begins to be evident after about three 
weeks. The cultures tested gave the nitroso-indol reaction on account of indol 
present in the pepton. The organism does not produce indol. In Dunham’s pepton 
solution containing rosolic acid a deepening of the pink color after about two weeks 
indicates the production of alkali. 
Temperature relations . — The exact optimum was not determined, but it is not far 
from the room temperature, or 20° C. In the refrigerator at a temperature between 
3° and 6° C. no visible growth occurs, but the organism is not in jured; 31° C. inhibits 
