6 BACTERIOLOGY FOR NURSES 



the nineteenth century the familiar processes of 

 putrefaction and fermentation were not understood, 

 and that the causes of infectious diseases were 

 equally obscure, shows what an important change 

 took place in man's conception of the living world 

 around him, when Pasteur and Koch founded 

 bacteriology. 



The part played by bacteria in the causation of 

 disease may be regarded as of surpassing importance, 

 but the work done by them in other directions 

 exerts a mighty influence upon the welfare of man- 

 kind. Bacteria not only act as scavengers in de- 

 stroying dead organic material, but they also change 

 the form of important chemical elements, such as 

 nitrogen and carbon, into substances which are 

 available for the nutrition of the higher plants, 

 thus proving themselves as important in construc- 

 tive as in destructive processes. 



