I.] THE HISTORY OF THE COMMA-BACILLUS, u 



only causes a liquefaction of the gelatine, but also a speedy 

 evaporation of the liquid formed. We already know a 

 number of other kinds of bacteria which, in quite the same 

 manner, gradually liquefy the gelatine in test-tubes, starting 

 from the point of inoculation. But in these cases there is 

 never such a cavity, nor this bubble-like hollow space. 1 I 

 must further mention that the liquefaction of the gelatine, 

 starting from a single isolated colony (the best way of 

 observing it is in a layer of gelatine, which is spread out on 

 the glass plate), never spreads very wide. The diameter of 

 the liquefied district of a colony may be estimated at one 

 millimetre. 2 Other kinds of bacteria can liquefy the gelatine 

 to a much greater extent, so that a colony attains a size of 

 one centimetre in diameter, and more. In the cultivations 

 of comma-bacilli made in test-tubes, the liquefaction of the 

 gelatine extends by degrees and very slowly, starting from 

 the point of inoculation ; and continues in such a manner 

 that, after about a week, the whole contents of the tube 

 have become liquid. Unimportant as all these qualities 

 seem in themselves, special weight is to be laid on them, 

 because they serve to distinguish comma-bacilli from other 

 kinds of bacteria. 



" Comma-bacilli can also be cultivated on Ceylon moss 

 (Agar-agar), to which meat-broth and peptone are added. 

 This agar-agar jelly is not liquefied by the comma-bacilli. 

 They can also be raised on boiled potatoes a fact which 

 is very important for certain questions. They grow on 

 potatoes exactly like the bacilli of glanders. The cultiva- 

 tions of comma-bacilli, when grown on potatoes, look like 

 those of glanders-bacilli, but are not coloured so intensely 

 brown, rather a light greyish-brown. 



1 As will be shown later, this is not correct. 



2 This also is not correct. 



