BIOLOGY OF BACTERIA. H 



From what has been said of the properties of 

 bacteria it is possible to make a number of classifica- 

 tions; for example, there are the spore-forming and 

 non-spore-forming bacteria, the motile and non-motile, 

 fermenting and non-fermenting, acid forming and 

 alkali forming, etc. By observing these properties of 

 bacteria it is possible to identify them. 



Like all plants bacteria require food, which must Nutriment 

 be in very simple form to enable them to assimilate it. 

 Oxygen, carbon, nitrogen, hydrogen, and chemical 

 salts form their chief food. They derive the oxygen 

 from the air, although some varieties of bacteria take 

 it from substances in which the oxygen is combined 

 with other chemical elements. The bacteria that take 

 their oxygen from the air are called aerobic bacteria, 

 while those taking it from substances containing it in 

 combined form are called anaerobic bacteria. The line 

 o<f demarcation between the aerobic and the anaerobic 

 bacteria is not fixed, as sometimes bacteria thriving 

 best under aerobic conditions will, nevertheless, grow 

 in the absence of free oxygen and vice versa. These 

 are spoken of as facultative anaerobes or aerobes, as 

 the case may be. The carbon is obtained from pro- 

 teids, carbohydrates (starchy substances), or fats. 

 The hydrogen is derived for the most part from, water. 

 The nitrogen is obtained from proteids such as albumin. 

 The salts required for nutrition are sodium, potas- 

 sium, and magnesium. 



Certain conditions of environment exert a great 

 deal of influence upon the life and growth of bacteria. 



