PATHOGENIC BACTERIA. 165 



Potato. Creamy pale growth, turning brown in a week. 



Pathogenesis. Dogs and rabbits, when inoculated with pure 

 cultures, are affected with symptoms exactly similar to those 

 seen in yellow-fever patients a hemorrhagic gastro-enteritis, 

 steatosis of the liver, and albuminuria. 



Two theories exist as to the etiology of yellow fever : (a) That 

 it is due to the Bacillus icteroides. The results of Sanarelli 

 have not been universally accepted, (b) That the causative 

 agent is so small as to be microscopically invisible, and that it 

 is transmitted from man to man through the bite of a mos- 

 quito, the Stegomyia fasciata, which acts as intermediate host. 

 Individuals who have allowed themselves to be bitten by in- 

 fected mosquitoes have contracted the disease, while others 

 exposed to infection in all ways but this have remained well. 



Bacillus of Bubonic Plague. (Yersin and Kitasato, 1894. ) 



Bubonic plague or pest is an extremely infectious disease 

 more or less common in China and the East, and is believed 

 to have its origin in man from rats and other rodents. It 

 spreads with great rapidity, especially among those living under 

 unsanitary conditions. 



Nearly at the same time Yersin and Kitasato, working inde- 

 pendently, discovered in the bubonic swellings and blood of 

 affected persons a distinctive bacillus which has conformed to 

 all the conditions necessary to make it the cause of the disease. 



Origin. In the tissues and all the body fluids and secretions 

 of affected individuals. 



Form. Short, thick rods with an indistinct capsule, rounded 

 ends. Growing in chains in fluid media. 



Properties. Immotile. Stains readily. No spores. Culti- 

 vated best in oxygen, but is facultative anaerobic. Stains 

 stronger at the ends, producing bipolar appearance. Gelatine 

 not liquefied. Easily destroyed by sunlight and drying. 



Growth. Best at 37 C. 



Gelatine. At 22 C., in 24 hours white, point-like colonies on 

 the plates, with broad and flat surface, turning gray and then 

 brown. 



Stab. Snow-white, spreading out an the surface to the edge, 

 and fluorescent. 



