110 THE PATHOGENIC MICROCOCCI. 



its culture becomes very much attenuated, practically losing 

 its virulence. 



In bouillon it grows rapidly, and in twenty-four hours 

 causes a distinct cloudiness of the medium. At the end of 

 forty-eight hours its growth ceases, and in four or five days 

 the bouillon becomes clear again, the bacillary growth being 

 deposited at the bottom of the tube. In 15 per cent, gelatin 

 at 24 C. its growth is slow. The gelatin is not liquefied. 

 On blood-serum at the temperature of 37 C. it grows as clear, 

 almost transparent spots. Its growth on agar is very much 

 like that on blood-serum. It does not grow on potato. It 

 causes coagulation of milk. 



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 Microeoccus pneumonice, guinea-pigs much 

 less so. When injected subcutaneously into mice and rabbits, 

 it produces a general septicaemia, 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. Pneumococcus of Friedlaender (Bacillus Pneumoniae 

 of Fluegge). 



The organism was discovered and described by Friedlaender 

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



