Bacilli Resembling the Typhoid Bacillus 683 



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

 characteristic. 



The peculiar and characteristic appearances of the colonies 

 do not develop if grown at 37 C.; but at 20 to 22 C. the 

 colonies appear rounded, whitish, opaque, and prominent, 

 like drops of milk. This appearance of 

 the colonies also shows well if the cul- 

 tures are kept for the first twelve to six- 

 teen hours at 37 C., and afterward at 

 the room temperature, when the colonies 

 will show a flat central nucleus, trans- 

 parent and bluish, surrounded by a 

 prominent and opaque zone, the whole 

 resembling a drop of sealing-wax. Sana- 

 relli refers to this appearance as consti- 

 tuting the chief diagnostic feature of 

 Bacillus icteroides. It can be observed 

 in twenty-four hours. 



Blood-serum. Upon blood-serum the 

 growth is very meager. 



Potato. The growth upon potato cor- 

 responds with that of the bacillus of 

 typhoid fever. 



Vital Resistance. It strongly resists 

 drying, but dies when exposed in cultures 

 to a temperature of 60 C. for a few 

 minutes, and is killed in seven hours by 

 the solar rays. It can live for a consider- 

 able time in sea- water. 



Metabolism. The bacillus is an op- 

 tional anaerobe. It slowly ferments dex- 

 trose, lactose, and saccharose, forming 

 gas only in dextrose solutions in which 

 there are no other sugars. It does not 

 coagulate milk. In the cultures a small 

 amount of indol is formed. 



Pathogen esis. The bacillus is patho- 

 genic for the domestic animals, all mammals seeming to be 

 more or less sensitive to it. Birds are often immune. 

 White mice are killed in five days, guinea-pigs in from eight 

 to twelve days, rabbits in from four to five days, by virulent 

 cultures. The morbid changes present include splenic tumor, 

 hypertrophy of the thymus, and adenitis. In the rabbit 



Fig. 229. Cul- 

 ture of bacillus 

 icteroides on agar 

 (Sanarelli). 



