• PATHOGENIC BACTERIA. 30c; 



often contains great numbers of the diplococci. The virulence 

 of the organism is very variable. In the sputum of a case of 

 lobar pneumonia, early in the disease, it is likely to be virulent. 

 The virulence is best maintained by repeated inoculations into 

 mice or rabbits. 



The Micrococcus lanceolatus has been detected very fre- 

 quently in the mouths of healthy individuals. But under these 

 conditions it is not, however, pathogenic for animals in many 



Fig. 72. — Pneumococciis, showing capsule, from pleuritic fluid cf infected 

 rabbit, stained by second method of Hiss. 



instances, being found virulent in only from 15 to 20 per cent, 

 of such cases. While it is unquestionably the cause of croupous 

 or lobar pneumonia in man in most if not in all cases, there 

 are competent observers who hold that lobar pneumonia is also 

 ca"used by other bacteria. In that disease the characteristic 

 lesion consists of an inflammation of the lung, involving large 

 areas — usually one or several lobes. An exudate is poured into 

 the air-vesicles, which in the early part of the disease contains 

 red blood-cells, imparting the rusty color to the sputum. The 

 principal element in the exudate is fibrin; it also contains leuko- 



