THE BACTERIA 275 



where they pass into a resting condition. At this stage 

 the cells remain connected together in long filaments, 

 and their outer cell -walls become very gelatinous. This 

 is called the zoogloca condition, and is easily recognised 

 by the gelatinous iridescent film which the colonies of 

 the organism form on the surface. 



Lastly, when the food in the liquid is getting ex- 

 hausted, the spores begin to form. This takes place 

 after locomotion has ceased and the Bacillus has entered 

 the filamentous condition (see Fig. 109, A). The spores 

 in this species and in a very large group of allied Bacteria, 

 are endospores, one spore being produced in the interior 

 of each cell. A new wall appears round a portion of 

 the contents, in which a nucleus is said to be included. 

 The young spore absorbs the remaining protoplasm, 

 and it becomes elliptical in form, and increases suffi- 

 ciently in bulk for its walls to touch those of the mother- 

 cell. In the mean time it has completely used up the sur- 

 rounding protoplasm, and now lies within a mere empty 

 membrane. The endospore itself acquires a comparatively 

 thick cell-wall, and is extraordinarily tenacious of life. 

 These spores can bear being completely dried up without 

 injury ; they are little affected by poisons, and survive a 

 very high temperature, withstanding even an hour's 

 boiling in the case of the hay Bacillus. Hence spore- 

 forming Bacteria are extremely difficult to extirpate, so 

 that in order to make sure of effectually " sterilising " any 

 substance (i.e. destroying any living things which it con- 

 tains) it is often necessary to expose it to a temperature 

 considerably above the boiling-point of water, or, if that be 

 impracticable, at least to continue boiling for some hours. 



The spores germinate when brought into a suitable 

 food-solution. The outer-membrane splits across, and 



