MORPHOLOGY OF CAUSATIVE AGENTS. 



119 



the form of small, delicate colonies. Upon solidified agar 

 in slants, when only feebly alkaline, upon agar-plates and 

 upon blood-serum it develops in the form of small, finely 



Fig. 40. Diplococcus pneumonise in the blood (Frankel and Pfeiffer). 



granular colonies, resembling dewdrops. Development in 

 bouillon presents nothing characteristic. Some varieties 

 induce coagulation in milk. The cultures die with extra- 

 ordinary rapidity, usually in the course of a few days. The 

 cause of death has been attributed to the formation of lac- 

 tic acid and formic acid, which can 

 always be demonstrated in cultures 

 several days old. If the cultures 

 are neutralized with calcium carbon- 

 ate, they may retain their vitality 

 for several months. The diplo- 

 coccus of Frankel thrives best 

 upon culture-media that contain 

 considerable blood. This is added 

 to solid media in a thick layer, 

 or it is mixed in considerable 

 amounts with fluid media. The 

 diplococcus grows well in the 

 absence of oxygen and thus retains longer its vitality and 

 its virulence. 



Diplobacillus Pneumonia Friedlander. Much larger 

 than the preceding (minimum, I //), the bacterium of Fried- 



Fig. 41. Diplococcus pneu- 

 moniae: a, Cocci without cap- 

 sules ; b, single and paired 

 cocci with capsules ; c, chain- 

 form; d, colony of cocci (Zieg- 

 ler). 



