324 BACTERIOLOGY. 



authors, be detected ; but this is by no means constant, 

 or even frequent. 



Even under the most favorable artificial conditions 

 this organism grows but slowly and frequently not at 

 all. 



When successfully grown upon the diflPerent media it 

 presents somewhat the following appearances : 



On gelatin its development is very limited and often 

 no growth at all occurs. This is probably due in part 

 to the low temperature at which gelatin cultures must 

 be kept. If development occurs, the growth appears 

 as minute whitish or blue-white points on the plates. 

 These very small colonies are round, finely granular, 

 sharply circumscribed, and slightly elevated above the 

 surface of the gelatin. They do not cause liquefaction 

 of the gelatin. 



If grown in slant- or stab-cultures, the surface-devel- 

 opment is very limited ; along the needle-track tiny 

 whitish or bluish-white granules appear. 



On nutrient agar-agar the colonies are almost trans- 

 parent, more or less glistening, and very delicate in 

 structure. On blood-serum development is more 

 marked, though still extremely feeble, appearing as 

 a cluster of isolated fine points growing closely side by 

 side. 



Growth on potato is not usually observed. 



When grown in milk it commonly causes an acid 

 reaction with coincident coagulation of the casein. 

 Some varieties, especially non-virulent ones, do not 

 coagulate milk.^ 



It is not motile. 



It grows best at a temperature of from 35° to 38° C. 



' Welch : loc. cit. 



