CHAPTER III 



THE RELATION OF BACTERIA TO ENVIRONMENT, AND THEIR 

 CLASSIFICATION 



NUTRITION OF BACTERIA 



LIKE all protoplasmic bodies, bacteria consist of carbon, oxygen, 

 hydrogen, and nitrogen, to which are added inorganic salts and vary- 

 ing quantities of phosphorus and sulphur. In order that bacteria 

 may develop and multiply, therefore, they must be supplied with 

 these substances in proper quantity and in forms suitable for assimi- 

 lation. To formulate definite laws based on chemical structure as to 

 the compounds suitable, and those unsuitable for use by the bacteria, 

 is obviously impossible owing to the great metabolic variations exist- 

 ing within the bacterial kingdom, and notable attempts to do so, 

 such as those by Loew, 1 have not successfully withstood critical 

 inquiry. So unlike are the food requirements of bacteria that a basis 

 for identification even among closely related species may often be 

 found in differences in metabolism of carbohydrates, and the sugges- 

 tion has frequently been made that with further knowledge of food 

 requirements would come a more logical classification of microor- 

 ganisms than any at present available. 2 



Carbon. The carbon necessary for bacterial nourishment or anab- 

 olism may be obtained either directly from proteins, carbohydrates, 

 and fats, or from the simpler derivatives of these substances. Thus, 

 the amino-acids, ketons, and organic acids, like tartaric, citric, and 

 acetic acids, glycerin, and even some of the alcohols, may furnish 

 carbon in a form suitable for bacterial assimilation. A limited num- 

 ber of bacterial species, furthermore, notably the nitrobacteria of 

 Winogradsky, are capable of obtaining their required carbon from 

 atmospheric C0 2 , and possibly from other simple carbon compounds 

 added to culture media. 3 



1 Loew, Cent, f . Bakt., I, xii, 1892. 

 -Doryland, Jour, of Bacter., 1, 1916, 135. 

 'Hunts, Compt. rend, de Tacad. des sciences, t. iii. 



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