68 OUTLINES OF BACTEEIOLOGY 



A solution commonly used for the cultivation of the nitrate-bacteria 

 is one composed of the following : 



Sodium nitrate, - 1 gram. 



Sodium carbonate, 1 



Potassium hydrogen phosphate, - 0*5 ,, 



Common salt, O5 



Ferrous sulphate, 0'4 ,, 



Magnesium sulphate, - 0-3 ,, 



Water, 1000 c.c. 



The carbon for the building of the bacterial cell is thus derived 

 entirely from the inorganic sodium carbonate (Na 2 C0 3 ) and from the 

 carbon dioxide of the atmosphere. The same applies to the nitrite - 

 bacteria which change ammonium compounds, formed by the putre- 

 faction of organic remains, into nitrites. The composition of the 

 solution commonly used in the cultivation of nitrite-bacteria is the 

 following : 



Ammonium sulphate, 2 grams. 



Magnesium sulphate, - 0*5 ,, 



Potassium hydrogen phosphate, - 1-0 



Common salt, - 2*0 ,, 



Ferrous sulphate, 0*4 



Distilled water, - 1000 c.c. 



In this case the carbon necessary for the construction of the body of 

 the cell is derived entirely from the carbon dioxide of the atmosphere. 

 The nitrite- and nitrate-bacteria thus resemble the higher green 

 plants, which also get their carbon dioxide from the atmosphere, but 

 there is this difference : the higher green plants require the green 

 colouring matter, chlorophyll, and also the energy of the sun's rays, 

 before they can accomplish the assimilation of carbon dioxide, whereas 

 these bacteria can do this without their aid. 



It has been claimed that another class of microbes, the purple- 

 bacteria, obtain their carbon supply in the same way as green plants. 

 These possess a colouring matter called purpurin, which has been 

 stated to play the same rdle as the chlorophyll of green plants. If 

 this be true, they obtain energy in two ways. First, they obtain it 

 by assimilation, whereby more complicated compounds have been 

 elaborated from the carbon dioxide of the atmosphere, for these 

 compounds, when broken down again, will supply energy. Secondly, 

 they obtain it in virtue of the fact that they are also sulphur-bacteria, 



