PARASITES AND SAPROPHYTES. 23 



brought about ia the tissues of their host by the pure 

 parasitic forms, find expression in disease processes and 

 not unfrequently 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 and ammonia, in which form they may be taken up 

 and appropriated as nutrition by the more highly organ- 

 ized members of the vegetable kingdom. It is to this 

 ultimate production of carbonic acid, ammonia, and water 

 by the bacteria, as end-products in the processes of de- 

 composition and fermentation of the dead animal and 

 vegetable tissues, that the demands of growing vegeta- 

 tion for these compounds can be 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 the bacteria, and as the production of these 

 simpler compounds (COj, NHg, H^O) by the animal 

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

 phyll plants, the importance of the part played by the 

 bacteria in making up this deficit cannot be overestimated. 

 Were it not for the activity of these microscopic living 

 particles, all life upon the surface of the earth would 

 certainly cease. Deprive higher vegetation of the car- 

 bon and nitrogen supplied to it as a result of bacterial 

 activity, and its development comes rapidly to an end. 

 E,ob the animal kingdom of the food-stuff's supplied to 

 it by the vegetable world, and life is no longer possible. 



It is plain, therefore, that the saprophytes, which re- 

 present by far the large majority of all bacteria, must be 



