402 PATHOGENIC BACTERIA. 



The granular appearance becomes continuously more 

 marked, and usually a central or peripheric nucleus, 

 completely opaque, is seen. In time the entire colony 

 becomes opaque, but does not liquefy gelatin. 



Stroke-cultures on obliquely solidified gelatin exhibit 

 brilliant, opaque, little drops similar to drops of milk. 



In bouillon it develops slowly, without either pellicle 

 or flocculi. 



The culture upon agar-agar is said to be characteristic. 



If grown at 37 C., the peculiar appearances of the 

 colonies do not develop; but if the culture is kept at 20- 

 22 C., the colonies appear rounded, whitish, opaque, and 

 prominent, like drops of milk. This appearance of the 

 colonies shows well if the cultures are kept for the first 

 twelve to sixteen hours at 37 C., and afterward at room- 

 temperature, when the colonies will show a flat central 

 nucleus, transparent and bluish, surrounded by a promi- 

 nent and opaque zone, the whole resembling a drop of 

 sealing-wax. Sanarelli refers to this appearance as con- 

 stituting the diagnostic feature of Bacillus icteroides. It 

 can be obtained in twenty-four hours. 



The growth upon potato corresponds to the classic 

 description of that of the bacillus of typhoid fever. 



The bacillus is a facultative anaerobe. It cannot be 

 colored by Gram's stain. It slowly ferments lactose, 

 more actively ferments glucose and saccharose, but is not 

 capable of coagulating milk. It strongly resists drying, 

 dies in water at 60 C., and is killed in seven hours by the 

 solar rays. It can live for considerable time in sea-water. 



The bacterium is pathogenic for the majority of the 

 domestic animals. All mammals seem more or less 

 sensitive to the pathogenic action of the bacillus; birds 

 are often immune. Guinea-pigs are invariably killed by 

 either intraperitoneal or subcutaneous injection of o. i 

 c.t'in. White mice are killed in five days; guinea-pigs 

 in eight to twelve days; rabbits in four to five days. 

 The morbid changes present include splenic tumor, hy- 

 pertrophy of the thymus, and adenitis. In the rabbit 



