142 THE SOIL: ORGANIC MATTER 



Bacteria are one-celled plants which are composed of 

 cell walls of protein — not cellulose — cell contents or proto- 

 plasm and enzymes, but no nucleus. They are very much 

 like any of the simple cells in crop plants except for the 

 absence of nuclei. These bacterial cells require soluble 

 material which can diffuse through their walls and from which 

 can be built up the various components of the cell wall and 

 contents, and permit them to reproduce themselves by sub- 

 division. The cells are small, about 1 micron (0.001 mm.) in 

 diameter, or even smaller. Some bacteria are more or less 

 spherical, others are rod-shaped, perhaps two or three times 

 as long as they are wide, and some of them are spiral- 

 shaped. They consist of about 85 per cent, of water, and 

 of the dry matter some 8 per cent, is composed of inorganic 

 compounds. The rest is fat, carbohydrate, and protein 

 material largely, very much like the cell contents of any 

 plant. 



Bacteria contain no chlorophyl, hence do not make their 

 organic food by means of the energy derived from the sun's 

 rays. The energy they use in synthesizing compounds is 

 derived by oxidation of various compounds, with or without 

 the aid of free oxygen, or by intercellular decomposition, 

 which releases energy. Many bacteria, like crop plants, 

 oxidize organic compounds to carbon dioxide and water. 

 Some oxidize nitrogen, sulphur, iron, and other inorganic 

 elements (considering nitrogen an inorganic element) to 

 nitrites and nitrates, sulphuric acid, and ferric oxide. In 

 this way they derive energy. Others reduce highly oxidized 

 compounds like nitrates and sulphates, using the oxygen 

 thus derived to oxidize other compounds. And still others 

 merely decompose compounds without any oxidation, deriv- 

 ing such energy, for example, as is released when dextrose is 

 changed to lactic acid. 



The material which bacteria use as food for building pur- 

 poses is largely organic in nature, although there are some 

 bacteria which live without any organic matter— that is, 

 they use inorganic compounds entirely from which to make 

 their cell substance. The organic material that is most 

 frequently used is composed of the various carbohydrates, 



