124 LIFE IN THE SEA [CH. 



after death by the decomposition of the substance of 

 its body: that is, they are carbonic acid, water, 

 ammonia with traces of sulphuretted hydrogen and 

 phosphoretted hydrogen. The nitrogen which was in 

 the proteid is not however completely degraded for 

 it can be oxidised and can still yield energy. But 

 we do not find ammonia in nature except where it is 

 being produced, as in the emanations from volcanoes, 

 or in decomposing matter, such as farmyard manure, 

 for example. It is never stored in nature, and the 

 only natural nitrogen compounds are nitrates, chiefly 

 Chili saltpetre (sodium nitrate). The conversion of 

 ammonia to nitric acid is a process of oxidation and 

 it is accomplished by the agency of bacteria. 



These nitrifying bacteria introduce us to another 

 mode of nutrition of extraordinary interest. They 

 exist wherever there is plenty of oxygen and ammonia. 

 There are various species the same apparently in all 

 parts of the world and sea where they have been 

 investigated. One species oxidises ammonia (NH 3 ) 

 to nitrous acid (KN"0 2 ) and another species further 

 oxidises the latter compound to nitric acid (HN0 3 ). 

 They do not require organic matter as a source of 

 food, and are indeed inhibited by the presence of 

 such; and like green plants they can form proteid 

 and carbohydrate from simple inorganic compounds 

 of nitrogen, and from carbonic acid and water. But 

 a green plant can only do this in the presence of 



