REPRODUCTION 21 



come surrounded by a thick wall and assume the structure 

 and character of spores ; these are designated arthro- 

 spores. The spores of bacteria are capable of resisting ad- 

 verse conditions which would instantly destroy the vitality 

 of the organisms in an active vegetative state. Some of 

 them can withstand boiling in water for an hour, and 

 are not damaged by chemical solutions which would kill 

 off all growing bacterial cells. They are also able to 

 retain their power of germination for many years in a 



I 



FIG. ii. i. Spore formation in a bacillus. 



2. Chain of bacilli with spore in each cell ; isolated spores below. 

 3 and 4. Forms of Clostridium cells with spores. 

 5. Drumstick -shaped cells with spores. 



dry state. When placed under favourable conditions of 

 temperature, and provided with a suitable moist nutrient 

 material and a proper air supply, the spores germinate. 

 They absorb water, enlarge and become less refractive. 

 In the anthrax bacillus the whole spore becomes gradually 

 transformed into a new elongated bacterium or bacillus, 

 the thin spore membrane is absorbed in the surrounding 

 liquid, and the protoplasm gradually assumes the form 

 of an actively-growing vegetative rod. In Bs. mega- 

 therium^ after the spore has absorbed a certain amount 

 of water its cell wall opens at one end and the proto- 

 plasmic contents escape and grow into a typical rod- 



