178 ESSENTIALS OF BACTERIOLOGY 



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. Gelatin 

 not liquefied. Easily destroyed by sunlight and drying. Very 

 resistant to cold. 



Growth. Best at 37 C. 



Gelatin. At 22 C., in twenty-four hours, white, point-like 

 colonies on the plates, with broad and flat surface, turning gray 

 and then brown. 



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

 and fluorescent. 



Bou'llon. Granular precipitate, with clear fluid above. 



AgLr and Blood-serum. Glass-like colonies like drops of dew 

 at first, then growing larger with iridescent edges. 



Potato. At 37 C. small white mass. 



No gas-jormation in glucose media. 



Staining readily with all basic dyes. 



Pathogenesis. After subcutaneous injection in rats death fol- 

 lows in forty to sixty hours, with symptoms of severe toxemia 

 and convulsions. The point of infection shows a local edema 

 and inflammation of the lymphatics. All the organs congested 

 and surrounded by a bloody exudate. The characteristic bacilli 

 in all the tissues and secretions. Nearly all the domestic 

 animals are susceptible. Mosquitoes and pigeons, however, 

 are immune flies are not; fleas are a very important element 

 in the transmission, and the rat-flea may communicate the 

 disease to the rat from man or from the rat to man. Animals 

 protected from the flea may live near infected animals without 



