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 

 aerobic but is also a facultative anaerobic. 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., but a 

 temperature of 35 to 37 C. is most favorable for its growth, which 

 is very rapid in a suitable liquid medium. In an infusion 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 is 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 

 microscope some of these are observed to FIG. 94 



have a Compact, finely granular Central coccus pneumonias crouposae upon 



portion surrounded by a paler, transparent, XFSSSSSSSiS* ' 



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 



icro- 



