BACTERIA IN CROUPOUS PNEUMONIA. 403 
cultures examined under the microscope, by using a small diaphragm 
it may be seen to surround the cocci as a scarcely visible halo. 
This micrococcus stains readily with the aniline colors; and also 
by Gram’s method, which constitutes an important character for dis- 
tinguishing it from Friedlander’s bacillus. 
Biological Characters.—Grows in the presence of oxygen— 
aérobic—but is also a facultative anaérobic. Like other micro- 
cocci, it has no spontaneous movements. It grows in a variety of 
culture media when they have a slightly alkaline reaction, but will 
not develop in a medium which contains the slightest trace of free 
acid. Nor will it grow at the ordinary room temperature. Scanty 
development may occur at a temperature of 22° to 24° C., buta 
temperature of 35° to 87° C. is most favorable for its growth, which 
is very rapid in a suitable liquidmedium. In aninfusion made from 
the flesh of a chicken or a rabbit it multiplies, in the incubating 
oven, with remarkable rapidity ; at the end of six to twelve hours 
after inoculation the previously transparent fluid will be found to 
present a slight cloudiness and to be filled throughout with the cocci 
in pairs and short chains. It does not produce a milky opacity in 
liquid media, like the pus cocci, for example, but the fluid becomes 
slightly clouded ; multiplication ceases at the end of about forty- 
eight hours or less, and the liquid medium again becomes transpa- 
rent as a result of the subsidence of the cocci to the bottom of the 
receptacle. 
It may be cultivated in flesh-peptone-gelatin, containing fifteen 
per cent of gelatin, at a temperature of 24° C., or in liquefied gela- 
tin (ten per cent) in the incubating oven. 
In gelatin (fifteen ‘per cent) stab cultures 
small white colonies develop all along the 
line of puncture, and in gelatin plates 
small, spherical, slightly granular, whitish 
colonies are formed: the gelatin ts not 
liquefied. In agar plates extremely mi- 
nute colonies are developed in the course 
of forty-eight hours, which resemble little, 
transparent drops of fluid, and under the RSE: 
microscope some of these are observed to yng, 94 —gingle colony of Micro- 
have a compact, finely granular central coccus pneumonie croupose upon 
portion surrounded by a paler, transparent, ee ae 
finely granular marginal zone. Upon the 
surface of nutrient agar or coagulated blood serum development 
occurs in the form of minute, transparent, jelly-like drops, which 
form a thin layer along the line of inoculation in ‘‘ streak cultures” ; 
and in agar stick cultures the growth along the line of puncture is 
