CHAPTER III 



GENERAL BIOLOGY, INCLUDING THE 



CHEMICAL CHANGES WROUGHT 



BY BACTERIA 



Bacteria. The bacteria with which the physician is 

 chiefly concerned as disease-producing, are but a very 

 small number when compared with the multitude of 

 species in nature. The lay mind is apt to consider any 

 germ as noxious, but instead of this it can be said that 

 without the activity of many saprophytes, life on the 

 earth would soon be extinct. Animals require organic 

 material for their nourishment, but their cells do not 

 possess the power to put together (synthesize) the 

 elementary constituents necessary for their complex 

 cell composition. Bacteria have the power both of 

 breaking down and building up; that is, they may 

 reduce some compounds to their elements or build 

 up elements into more complex substances. 



The products of their breaking down and building 

 up are utilized by plants and are presented to animals 

 as food in such a form that the animals can use them 

 for their cell needs. It is not the purpose of this book 

 to dwell upon this abstract matter of general biology, 

 but the principles of the activities of non-pathogenic 

 bacteria can well be seen in those inhabiting the 

 intestines. 



It may be possible for a human being to live without 

 3 



