ON EPIDEMICS AMONGST MICE. 301 



colonies corresponded to the quantity of bacilli found in the 

 expressed preparations. In those cases where no bacilli could be 

 discovered with the microscope a few typical colonies were only 

 developed exceptionally by cultivation. 



The mode of increase of the bacilli was as follows : — On 

 gelatine -tubes kept in the temperature of the room hardly 

 anything was to be seen with the naked eye after twenty-four 

 hours. But with the lens small colourless particles were already 

 discernible. After forty-eight hours the colonies became visible 

 as round, greyish white or bluish-hyaline bodies, about as large 

 as a pin's head. During the next few days the colonies enlarged, 

 if they were wide apart, till they formed patches from 3 — 4 mm. 

 in breadth. They then generally lost their rounded shape, and 

 formed zigzag protuberances with rough edges. Then the gelatine 

 began to get somewhat turbid. Slight alterations in the com- 

 position of the gelatine (as happens with each new preparation) 

 influenced the appearance of the colonies. In one preparation 

 the colonies were always round and rather thick, and consequently 

 but slightly transparent, and whiter. In another the condition 

 already described appeared more like that of typhus-bacilli. The 

 individual bacilli in this cultivation were of unequal length. 

 Among the more numerous were short forms, with lively motions; 

 others long and thread-like, sluggish, or even motionless. They 

 were readily coloured by the aniline dyes employed, and best 

 with the alkaline solution of methyline-blue, which I have 

 elsewhere recommended. 



In plate-cultivations {plattenkulturen), the deep-seated colonies 

 appeared round, at first hyaline-grey and slightly granulated, after- 

 wards yellowish brown, and strongly granulated. The colonies 

 nearer the surface were strongly granulated, and delicately fur- 

 rowed, like colonies of the typhus-bacillus, but not so prominent. 



On "Agar-Agar," a greyish white and little-characteristic 

 coating was formed. On blood-serum, and especially on sweetened 

 peptonized bouillon, mixed with blood-serum, as I have elsewhere 

 recommended, a transparent coating appeared. Distilled water 

 soon became turbid. The formation of spores was not observed 

 in any nutritive fluid, not even when heated. 



They grew upon potatoes in a very characteristic manner. 

 They formed a whitish and not very thick coating, and the 

 adjacent substance of the potato showed a dirty greyish blue 



