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 varying 

 quantities of phosphorus and sulphur. In order that bacteria may 

 develop and multiply, therefore, they must be supplied with these sub- 

 stances in proper quantity and in forms suitable for assimilation. To 

 formulate definite laws based on chemical structure as to the compounds 

 suitable, and those unsuitable for use by the bacteria, is obviously im- 

 possible owing to the great metabolic variations existing within the 

 bacterial kingdom, and notable attempts to do so, such as those by 

 Loew, 1 have not successfully withstood critical inquiry. 



Carbon. The carbon necessary for bacterial nourishment or ana- 

 bolism may be obtained either directly from proteids, carbohydrates, 

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

 amido-acids, leucin and tyrosin, 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 

 number of bacterial species, furthermore, notably the nitrobacteria of 

 Winogradsky, are capable of obtaining their required carbon from 

 atmospheric CO 2 , and possibly from other simple carbon compounds 

 added to culture media. 2 



Oxygen. Oxygen is obtained, by the large majority of bacteria, 

 directly from the atmosphere in the form of free O 2 . For many micro- 

 organisms, moreover, the presence of free oxygen is a necessary condi- 

 tion for growth. These are spoken of as the "obligatory aerobes." 

 Among the pathogenic bacteria proper, many, like the gonococcus, 

 bacillus influenzas, and bacillus pestis, show a marked preference for a 

 well-oxygenated environment. Probably there is no pathogenic micro- 



iLoew, Cent. f. Bakt., I, xii, 1892. 



2 Murtiz, Compt. rend, de 1'acad. des sciences, t. iii, 



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