BACILLUS TYPHOSUS 483 



centre than at the periphery. When magnified, the colonies 

 present wrinkles or folds, which give to them, in miniature, 

 the appearance seen in relief maps (Fig. 87). These colonies 

 have sometimes the appearance of flattened pellicles of glass- 

 wool, and usually a pearl-like lustre. 



Agar-agar. — On agar-agar the colonies present nothing 

 typical. 



Stab-cultures. — In stab-cultures the growth is mostly on 

 the surface, there being only a very limited development 

 down the track made by the needle. The surface-growth 

 has the same appearance in general as that given for the 

 colonies. 



Fig. 87 



Colony of bacillus typhosus on gelatin. 



Potato. — ^The growth on potato is usually described as 

 luxuriant but invisible, making its presence evident only 

 by the production of a slight increase of moisture at the 

 inoculated point, and by a limited resistance offered to a 

 needle when it is scraped across the track of growth. While 

 this is so in many cases, yet it cannot be considered as 

 invariable, for at times this organism develops more or less 

 visibly on potato. 



Potato-gelatin. — The growth is similar to that upon 

 ordinary nutrient gelatin. 



Milk. — It does not cause coagulation when grown in 

 sterilized milk. 



