30 BACTERIOLOGY FOR NURSES 



free oxygen, called obligatory anaerobes; and (3) the 

 facultative anaerobes, which may exist with or with- 

 out oxygen. 



The obligatory anaerobes derive the small amount 

 of oxygen necessary to them from the oxygen com- 

 pounds of the material in which they are growing. 



Food. Bacteria obtain their food from many 

 diverse substances, organic compounds of all kinds 

 serving them. Nitrogenous substances especially 

 are quickly attacked by many species, as may be 

 witnessed in the rapid decomposition of meats. 



Carbon, nitrogen, and water are essential for the 

 growth of both bacteria and the higher plants, but 

 in the case of the latter both carbon and nitrogen 

 must be resolved into simpler forms before absorption 

 can take place ; while bacteria obtain these elements 

 as already prepared in complex organic material, 

 either animal or vegetable. 



Bacteria differ greatly in their food requirements, 

 some species thriving best upon a concentrated form 

 of nourishment, and others requiring only a limited 

 amount of protein substances. 



The greater number of bacteria belong to the class 

 known as saprophytes, which find their food in dead 

 organic matter and cannot exist in living tissues; 

 parasites, on the contrary, as the name indicates, 



