DEFINITION OF BACTERIA 33 



The life-processes of bacteria are so rapid, complex, and 

 energetic that they result in the most profound alterations 

 in the structure and composition of the materials in and 

 upon which they are developing. 



Disintegrations and decompositions result from the acti- 

 vities of the saprophytic bacteria; while the changes brought 

 about in the tissues of their living host by the purely 'parasitic 

 forms find expression in disease-processes not infrequently 

 leading to complete death. 



Their Place in Nature. — ^The role played in nature by 

 the saprophytes is a very important one. Through their 

 functional activities the highly complicated tissues of dead 

 animals and vegetables are resolved into the simpler com- 

 pounds, carbonic acid, water, and ammonia, in which form 

 they may be taken up and appropriated as nourishment by 

 the more highly organized members of the vegetable king- 

 dom. It is through this ultimate production of carbonic 

 acid, ammonia, and water by bacteria, as end-products in 

 the processes of decomposition and fermentation of dead 

 animal and vegetable tissues, that the demands of growing 

 vegetation for these compounds are supplied. 



The more highly organized chlorophyl plants do not 

 possess the power of obtaining their carbon and nitrogen 

 from such complicated organic substances as serve for the 

 nutrition of bacteria, and as the production of the simpler 

 compounds, carbon dioxide and ammonia, by the animal 

 world is not sufficient to meet the demands of the chloro- 

 phyl plants, the importance of the part played by bacteria 

 in making up this deficit is obvious and cannot be overesti- 

 mated. Were it not for the activity of these microscopic 

 living creatures all life upon the surface of the earth would 

 cease. Deprive higher vegetation of the carbon and nitrogen 

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