PATHOGENIC BACTERIA. 



2m 



artificial media. When virulent, it is pathogenic for mice and 

 rabbits; less so for guinea-pigs. In these animals it is likely 

 to lead to fatal septicemia in twenty-four to forty-eight hours 

 when introduced subcutaneously or into the peritoneum or 

 when liquid cultures are injected intravenously. The blood 

 often contains great numbers of the diplococci. The viru- 

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

 case of lobar pneumonia, early in the disease, it is hkely to be 

 virulent. The virulence is best maintained by repeated inocula- 

 tions into mice or rabbits. 



f.-f; ... 







Fig. 67. — Pneumococcus, Showing Capsule, prom Pleuritic Fluid of 

 Infected Rabbit, Stained by Second Method of Hiss. (X iooo.) 



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 

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

 of such cases. It is the specific cause of croupous or lobar 

 pneumonia in man. 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 



