ISOLATING THE TYPHOID BACILLUS. 429 



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 badUus 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.i 



Method of Gapaldi and. Proslcauer? As a result of 

 an elaborate series of experiments, these authors recom- 

 mend the use of two special culture-media for the dif- 

 ferentiation of the t}'phoid and colon bacilli. 



Medium No. 1 consists of: 



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

 details that are not included here. 



2 Capaldi and Proskauer : Zeitschrift fur Hygiene und Infektions- 

 krankheiten, 1896, Band xxiii. S. 452. 



