DEVELOPMENT AND COMPOSITION OF BACTERIA 11 



but, as is the case with all organisms, mathematical 

 increase never continues without check or hindrance. 



In the case of bacteria the check arises largely from 

 the products of the bacteria themselves; the organ- 

 isms in their activity upon food substances produce 

 acids and other injurious materials which check 

 further multiplication. Lack of proper food, or 

 moisture, or favorable temperature, and conflict 

 with other species of organisms, are also checks 

 upon growth and multiplication. 



Spore-formation. Following a period favorable 

 to reproduction, certain bacteria (notably bacilli) 

 enter into a stage known as spore-formation; this 

 usually occurs when food nears exhaustion, or 

 injurious substances have been formed, or unfavor- 

 able temperature conditions arise, and is character- 

 ized by the development of round or oval glisten- 

 ing bodies (spores) within the cell which are oij 

 dense compact structure and possess an extraor- 

 dinary resistance to heat (70-100 C., or 158- 

 212 F.), chemicals, and other injurious sub- 

 stances. 



A single cell produces but one spore, as a rule, 

 although there are said to be rare exceptions. 



Spore-forming bacteria are said to be in the 

 vegetative stage while growth and reproduction 



