46 STUDY AND IDENTIFICATION OF BACTERIA. 



The Pneumococcus of Fraenkel. This is by far the most com- 

 mon cause of pneumonia, whether it be of the croupous, catarrhal or 

 septic type. It is also frequently found in meningitis, empyema, 

 endocarditis and otitis media. It should not be confused with the 

 pneumobacillus of Friedlander, which, although possessing a capsule 

 like the pneumococcus, differs from it by being Gram negative, being a 

 bacillus and having large viscid colonies. The pneumococcus is the 

 cause of more than 80% of the cases of pneumonia. It does not grow 

 below 20 C. and is best cultivated on blood-serum, or blood-streaked 



. 



*% , 



.; * - 







FIG. 13. Pneumococcus, showing capsule, from pleuritic fluid of infected 

 rabbit, stained by second method of Hiss. (Williams.) 



agar. On plain agar it grows as a very small dew-drop-like colony, 

 which is slightly grayish by reflected light. It is smaller and more 

 transparent than a streptococcus colony. In sputum or other patholog- 

 ical material it is best recognized by the presence of a capsule inclosed 

 in which are two lance-shaped cocci with their bases apposed. In arti- 

 ficial culture we rarely get the capsule. It also sometimes grows in 

 short chains like a streptococcus. The best medium for differentiating 

 is the serum of a young rabbit, in this it grows as a diplococcus, while 

 streptococci show chains. The best method of isolating it in pure 



