126 LIFE IN THE SEA [CH. 



their cells. This process it will be seen is analogous 

 to the assimilation of carbon dioxide by the green 

 plant and the storage of starch or sugar in the cells. 

 The sulphur is then oxidised to produce energy, and 

 ultimately forms sulphuric acid, when it cannot be 

 oxidised further. The sulphur bacteria are, like the 

 nitrifying bacteria and the green plant, prototrophic 

 in their mode of nutrition, and can form proteid from 

 inorganic materials, but they can accomplish this in 

 the absence of chlorophyll and sunlight. 



Thus we have accounted for the degradation pro- 

 ducts of the animal body whether these result from 

 the waste during life or the decomposition after 

 death. The nitrogen finally becomes nitric acid, the 

 hydrogen water, the carbon carbonic acid, the sulphur 

 sulphuric acid, and the phosphorus phosphoric acid. 

 The trace of iron also present in the body becomes 

 altered by the action of the iron bacteria to ferric 

 oxide. Plant tissues may also undergo decomposition 

 in such a way as to form masses of nearly pure 

 carbon, as in the formation of coal and anthracite, 

 and there is now evidence that even this amorphous 

 carbon may be attacked by certain bacteria which 

 can oxidise it to carbonic acid with the production of 

 heat. Thus all the products of destructive metabolism 

 (katabolism) tend to pass into the state of fully 

 oxidised compounds so that they can no longer be 

 made use of by the animal as sources of energy. 



