CHAPTER I. 



Definition of bacteria — Their place in nature — Differences between 

 parasites and saprophytes — Nutrition of bacteria — Products of bac- 

 teria — Their relation to oxygen — Influence of temperature upon 

 their growth. 



Because of their capacity for developing in infusions, 

 their property of spore-formation, their resistance to 

 drying, their power of independent motion, and the 

 absence of chlorophyll from their tissues, bacteria (more 

 properly bacteriacese or schizomycetes) were regarded by 

 the older writers as infusoria. In the modern concep- 

 tion, however, this classification is untenable, and the 

 bacteria, by virtue of their distinguishing peculiarities, 

 are now treated as a group by themselves that may 

 briefly be defined as comprising microscopic unicellular, 

 vegetable organisms that multiply by the process of 

 transverse division. 



Inasmuch as bacteria are not possessed of chloro- 

 phyll,^ their metabolic processes are fundamentally dif- 

 ferent from those of the higher plants in which it is 

 present. They cannot, as in the case of the green 

 plants, obtain carbon and nitrogen from such simple 

 bodies as carbon dioxide and ammonia, but are forced 

 to secure these essential elements from organic matter 

 as such. This power to decompose and assimilate 



' Chlorophyll is the green coloring-matter possessed by the higher 

 plants by means of which they are enabled in the presence of sunlight 

 to decompose carbonic acid (CO2) and ammonia (NH3) into their ele- 

 mentary constituents. 



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