CH. XIl] THE CIRCULATION OF NITROGEN 287 



too would die out. There would be a continual resolution of the 

 organic substance of the animal body into carbon dioxide, water, 

 and inorganic nitrogen salts, but these substances could no longer 

 be utilised. For a time bacterial life would find all the conditions 

 of well-being. Putrefactive micro-organisms would flourish on the 

 dead bodies of the animals that had died of starvation; and then the 

 nitrifying bacteria would attack the decomposition products of the 

 putrefying proteids. But this process of nitrification would tend 

 towards the final disappearance of all trace of organic nitrogenous 

 substance, and since the bacteria require these, or the less highly 

 oxidised nitrogen compounds, as sources of energy, they too would 

 cease to find their conditions of life and would also cease to exist. 

 Even those micro-organisms which are able to reduce nitrous and 

 nitric acids to free nitrogen require some carbon compound, other 

 than carbon dioxide, as a source of food ; and since all such substance 

 would gradually become oxidised to the latter compound, the 

 nitrifying bacteria too would apparently suffer extinction. So far 

 as we can see the complete disappearance of plant life from such a 

 sea-area would result in its utter sterility. 



If, in an enclosed sea-area, the addition of nitrogenous and 

 carbonaceous drainage from the land was suddenly to cease plant 

 and animal life would nevertheless continue indefinitely. For such 

 an area of water would be self-supporting, the animals feeding 

 ultimately upon the plants, and the plants utilising as food-stuffs 

 the excretory products of the animals. Possibly there would be 

 denitrifying bacteria present in this sea-area, and one might 

 conclude that the effect of the activity of these organisms would 

 be gradually to reduce the amount of available nitrogen compounds 

 present in the water, by reducing the inorganic forms of these to 

 free nitrogen, which would be given off to the atmosphere. But, 

 supposing that no addition of nitrites, nitrates or ammonia salts 

 occurs, then it is probable that a struggle for existence, that is for 

 these food salts, would arise between the protophyta and denitrify- 

 ing organisms, and the effect of the latter would be minimised. 

 From what we know of the conditions of life in the sea, it appears 

 reasonable to suppose that nitrogen-fixing bacteria would also be 

 present. These would fix free nitrogen from the solution of the 

 latter gas in the water, combining the element with oxygen so 



