182 



SUPPURATION. 



It grows fairly well on all the ordinary culture-media 

 except potato ; but its growth is somewhat retarded by the 

 formic acid which the organism produces in the course of its 

 development. It is desirable for this reason to have a slightly 

 alkaline medium. Like the meningococcus, it must be trans- 

 planted frequently in order to preserve its vitality. It is 

 extremely sensitive to antiseptics and disinfectants. 



A mixture consisting of one-third ascitic or pleuritic fluid 

 and two-thirds bouillon is the best culture-medium. When 



FIG. 78. 



Pneumococcus from bouillon culture, resembling streptococcus. (Park.) 



inoculated into this medium and then placed on ice, the pneu- 

 mococcus will retain its vitality as well as its virulence for 

 months. Milk is coagulated rapidly. The high temperature 

 required for the growth of this organism makes it necessary 

 to use a greater percentage of gelatin culture-medium ; 15 or 

 20 per cent, will not melt at a temperature of 24 C. When 

 plated in this medium very minute round and finely granular 

 white specks appear. On agar-agar plates the colonies are so 

 transparent as to be scarcely perceptible. They are granu- 

 lated and have a dark central portion. 



In the gelatin tube culture little whitish colonies form along 



