BACILLUS PESTIS. 177 



ficial media. On gelatin, after twenty-four or thirty-six 

 hours the colonies appear as small, sharply defined, round, 

 white masses which do not liquefy the medium. Its growth 

 in agar in the incubator is a little more rapid than in gelatin. 

 It does not cloud bouillon. Cultures in this medium show a 

 number of flocculi in the tube and a deposit at the bottom. 

 It does not cause fermentation, and it gives no indol reaction. 

 It coagulates milk. 



Vitality. The Bacillus pestis is very susceptible to the 

 action of disinfectants, 1 per cent, carbolic acid being suf- 

 ficient to kill it in one hour. 



Pathogenesis. Man, mice, rats, guinea-pigs, rabbits, cats,- 

 hogs, horses, chickens, and sparrows are very susceptible to 

 the disease. Pigeons, dogs, amphibia, and bovines appear to 

 enjoy immunity. During an epidemic of bubonic plague sus- 

 ceptible animals seem to contract the disease naturally. 



For experimentation subcutaneous inoculation with liquid 

 cultures of the bacillus is generally resorted to. The changes 

 produced are : Swelling of cedematous character at the point 

 of inoculation, and involvement of the lymphatic glands ; 

 death resulting in from twenty-four to forty-eight hours. At 

 the autopsy the local swelling is found to be due to an oedem- 

 atous condition of the part, the bloody fluid containing a 

 large number of bacilli. The neighboring lymphatic glands 

 are also greatly inflamed, and some of them are found sup- 

 purating. In their substance the pest bacilli are also found 

 in great number. There also occurs a purulent exudate in 

 the peritoneal and pleural cavities. The internal organs, liver, 

 lungs, adrenal bodies, and spleen are very much affected. 



Three forms of the disease are recognized in man : the 

 bubonic or ganglionic, the septicaemic, and the pneumonic form, 

 the most frequent of these being the bubonic, and the most 

 fatal the pneumonic. 



Infection generally takes place through an abrasion of the 



skin, but the disease may be caused by inhalation of the pest 



I'n* 



bacilli. 



The usual form of the disease presents the following symp- 

 toms : a sudden rise of temperature accompanied by great 

 12 M. B. 



