28 BA CTEEIOL OGY. 



pure parasitic forms find expression in disease-processes 

 and not infrequently in complete death. 



The role played in nature by the saprophy tic bacteria is 

 a very important one. Through their functional activities 

 the highly complicated tissues of dead animals and vege- 

 tables are resolved into the simpler compounds, carbonic 

 acid, water, and ammonia, in which form they may be 

 taken up and appropriated as nutrition by the more 

 highly organized members of the vegetable kingdom. 

 It is through this ultimate production of carbonic acid, 

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

 the processes of decomposition and fermentation of the 

 dead animal and vegetable tissues, that the demands of 

 growing vegetation for these compounds are supplied. 



The chlorophyll plants do not possess the power of 

 obtaining their carbon and nitrogen from such highly 

 organized and complicated substances as serve for the 

 nutrition of bacteria, and as the production of these 

 simpler compounds (CO 2 , NH 3 , H 2 O) by the animal 

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

 rophyll plants, the importance of the part played by 

 bacteria in making up this deficit cannot be overesti- 

 mated. Were it not for the activity of these microscopic 

 living particles, all life upon the surface of the earth 

 would cease. Deprive higher vegetation of the carbon 

 and nitrogen supplied to it as a result of bacterial ac- 

 tivity, and its development comes rapidly to an end; rob 

 the animal kingdom of the food-stuffs supplied to it by 

 the vegetable world, and life is no longer possible. 



It is plain, therefore, that the saprophytes, which 

 represent the large majority of all bacteria, must be 

 looked upon by us in the light of benefactors, without 

 which existence would be impossible. 



