ISOLATING THE TYPHOID BACILLUS. 429 



Agar-agar 10 grammes. 



Gelatin 25 



Liebig's beef-extract 5 " 



Sodium chloride 5 " 



Glucose 10 



Water 1000 c.c. 



The reaction of this medium is equivalent to 2 per cent. 

 of normal acid to the litre i. e., an acidity that would 

 require 20 c.c. of normal sodium hydroxide solution to 

 the litre to bring it to the phenolphtalein neutral point. 

 In plates made from this medium the deep colonies of 

 bacillus typhosus are small, more or less spherical, and 

 have a rough, irregular outline. Their most character- 

 istic feature ".consists of well-defined, filamentous out- 

 growths, ranging from a single thread to a complete 

 fringe around the colony. The young colonies are at 

 times composed solely of threads." The fringing 

 threads grow almost straight out from the colonies. 

 The surface colonies are small and have usually a 

 dense centre that is surrounded by an almost trans- 

 parent zone or by a fringe of threads somewhat similar 

 to those seen about the deeper colonies. 



The deep colonies of the colon bacillus are, as a rule, 

 larger, denser, of an oval or lens-shape, and are more 

 sharply circumscribed than those of bacillus typhosus. 

 On the surface they are also larger, and, as a rule, 

 spread out as a moderately thick layer from a denser 

 centre. The younger the colonies of the typhoid bacil- 

 lus the more characteristic their appearance. They are 

 seen at their best after from 16 to 18 hours' growth at 

 37.5 C. 1 



1 The reader is referred to the original article for many important 

 details that are not included here. 



