120 THE PATHOGENIC MICROCOCCI. 



Immunization. The inoculation of animals with attenuated 

 cultures grown at 42 C. for twenty-four hours seems to protect 

 the animal from the after-infection of virulent cultures. An 

 infusion made of the tissues of immunized animals seems to 

 have a protective influence when injected simultaneously or 

 shortly before virulent cultures in susceptible animals. 



Pathogenesis. Mice and rabbits are very susceptible to 

 the action of the Microcoecus pneumonice, guinea-pigs much 

 less so. When injected subcutaneously into mice and rabbits, 

 it produces a general septica3mia, with considerable swelling 

 at the place of injection and the formation of a fibrinous mem- 

 brane. The spleen is enlarged, and the bacteria may be found 

 in all the internal organs and in the blood, but no specific 

 pneumonia is developed. When intrathoracic injections are 

 made in the lung substance, it produces a marked lobar 

 pneumonia with considerable fibrinous exudate, and also 

 symptoms of general infection. Injected in the dog intra- 

 thoracically, it may produce marked croupous pneumonia, 

 the animal generally recovering in two or three weeks after 

 presenting all the different stages of the disease. 



II. Streptococcus Mucosus. 



An apparently normal inhabitant of the mouth, occurring 

 usually in pairs, with a regular well-defined capsule and re- 

 sembling the pneumococcus, though not having its typical 

 lancet shape. 



Hiss has shown that sera immune to Streptococcus mucosus 

 will cause agglutination of pneumococci even in high dilu- 

 tion, thus showing the close relationship, if not identity, be- 

 tween them. 



III. Pneumococcus of Friedlaender (Bacillus Pneumonias 

 of Fluegge) (Bacillus Mucosus Capsulatus). 



The organism was discovered and described by Friedlaender 

 in 1883, and believed by him to belong to the class of cocci, 

 but recognized afterward as a bacillus. It is found : a. in a 



