THE STORY OF GERM LIFE. 



inous substance, which forms what is called a 

 capsule (Fig. 10). This capsule may connect them 

 and serve as a cement, to prevent the separate 

 elements of a chain from falling apart (Fig. 10 c). 



Sometimes such 

 a gelatinous se- 

 cretion will unite 

 great masses of 

 bacteria into 

 clusters, which 

 may float on the 

 surface of the 

 liquid in which 

 they grow or 

 may sink to the 

 bottom. Such 

 masses are called 

 zooglcea, and their 

 general appear- 

 ance serves as 

 one of the char- 

 acters for distin- 

 guishing differ- 

 ent species of 

 FIG. ii. Various types of bacteria "colo- bacteria (Fig. IO, 

 nies " formed when growing in nutrient a and A). When 

 gelatine. Each different type of colony orowino-in cnliH 

 is produced by a different species of Sowing in SOlld 



bacterium. media, such as a 



nutritious liquid 



made stiff with gelatine, the different species have 

 different methods of spreading from their central 

 point of origin. A single bacterium in the midst 

 of such a stiffened mass will feed upon it and pro- 

 duce descendants rapidly; but these descendants, 

 not being able to move through the gelatine, will 

 remain clustered together in a mass, which the 



