28 BACTERIOLOGY. 



by the pure parasitic forms find expression in disease 

 processes and not infrequently complete death. 



The role played in nature by the saprophytic bacteria 

 is a very important one. Through their presence the 

 highly complicated tissues of dead animals and vegeta- 

 bles 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 de- 

 mands 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 0) 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 micro- 

 scopic living particles, all life upon the surface of the 

 earth would undoubtedly cease. Deprive higher vegeta- 

 tion of the carbon and nitrogen supplied to it as a result 

 of bacterial activity, 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 



