THE PRECIPITATION OF CALCIUM CARBONATE IN THE SEA. 483 



The most important work on the distribution of marine bacteria is 

 that of Fischer (8) in 1886, 1889, and 1893, but he does not enter into 

 the chemical activities of the species found, so that the observations 

 do not throw much direct light on problems of the metabolism of the 

 sea. The variations in the number of bacteria found in different 

 surface samples from positions in mid-ocean are somewhat surprising 

 and difficult to account for. Deeper samples were taken by means of 

 a water-bottle made of brass, but in view of the now well-known 

 bactericidal action of metals, and of copper in particular, I do not 

 consider that any great value can be attached to these observations. 

 With the exception of Fischer's work, little seems to have been pub- 

 lished on the general distribution of marine bacteria. 



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 

 decomposed 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 decompos- 

 ing 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 absorbing and combining with 

 the free Nitrogen of the air and eventually giving rise to Nitrates, has 

 been shown by Keding (10) and Keutner (11), but these have so far 

 only been found on the bottom close to shore, or apparently living in 

 symbiosis with algae or plankton organisms. Similarly, Thomsen (16) 

 has demonstrated the presence on the bottom of inshore waters of 

 bacteria which are capable of forming Nitrites from Ammonium salts, 

 and others which can convert Nitrites into Nitrates. It would seem 

 possible that similar bacteria having a nitrifying action remain to be 

 discovered in the open sea. 



The precipitation of Calcium carbonate in the sea by bacterial 

 agency is apparently a line of investigation that has not previously 

 been suggested or followed. Both Baur (1) and Gran (9) made use of 



