THE ACTION OF SOME DENITRIFYING BACTERIA. 155 



tion of nitrite from the nitrate takes place with considerable slow- 

 ness. 



A point that has not yet been considered is the origin of the nitrate 

 supply in the sea. Nitrates are absorbed by diatoms and the phyto- 

 plankton in general, and are presumably built up into complex nitro- 

 genous compounds within the plant. If these compounds, on the 

 death of the plant, are broken up and the Nitrogen again rendered 

 available for use in the form of nitrates, a series of reactions must be 

 gone through which may well be performed by bacterial agency, and 

 this also applies to the waste nitrogenous products of animal meta- 

 bolism. In addition, it has been shown that nitrates are actually 

 destroyed by the denitrifying bacteria, which would thus tend to 

 keep the nitrate concentration down to the level necessary for their 

 own existence, and would come into competition for this essential with 

 other forms of plant life. If the bacteria are successful in decom- 

 posing nitrates to the extent of entirely removing the Nitrogen from 

 all chemical combination, as seems probable from the experiments in 

 cultures, it follows that there must be some source of nitrates in order 

 that the concentration in the sea may remain constant. The existence 

 of nitrifying bacteria, which are capable of oxydizing the Nitrogen of 

 the air to form nitrates, and are symbiotic with some of the Algte 

 found round the shores of the North Sea, has already been demon- 

 strated, and it seems possible that forms having a similar nitrifying 

 action remain to be discovered in the open sea. 



As they at present stand, the observations noted in this paper can 

 at most be considered as offering a slight indication of the part played 

 by certain bacteria in the metabolism of the sea. 



To obtain a real insight into the question, it would be necessary to 

 make extensive bacterial and chemical investigations in tropical, tem- 

 perate, and Arctic seas, and more especially to make a study of the 

 bacterial flora at different depths at some spot where considerable 

 depth, unaffected by currents, could be obtained. The probability that 

 bacterial growth plays an important part in causing the precipitation 

 of certain bottom deposits in coastal waters, and conceivably also in 

 the deep sea, is a subject that appears well worthy of furtlier investi- 

 gation. 



