156 



ESSENTIALS OF BACTERIOLOGY. 



Bouillon. Granular precipitate, with clear fluid above. 



Agar 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 formation in glucose media. 



Staining readily with all basic dyes. 



Pathogenesis. After subcutaneous injection in rats death fol- 

 lows in 40 to 60 hours, with symptoms of severe toxaemia and 

 convulsions. The point of infection shows a local oedema 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 



FIG. 89. 



Bacillus of bubonic plague (Yersin). 



are susceptible. Mosquitoes and pigeons, however, are im- 

 mune; flies are not. 



Products. A toxin has been obtained and immunity has been 

 effected; the serum of immune animals has protective prop- 

 erties. The serum likewise shows agglutinating powers, as with 

 typhoid and cholera serums. 



Habitat. Not found in water, but most likely spreads from the 

 soil in damp and darkened areas. Rats become affected first, 



