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nitrate or nitrite at all there, in solution, reflects the activity 

 either in situ , or on land, of other groups, not only the nitrogen- 

 fixers just mentioned, but of the putrefactive "bacteria, and of the 

 so-called nitrifiers. A.nd until the complex protaids and carbo- 

 hydrates from the bodies of dead animals are reduced to simple com- 

 pounds, they are usable only by animals, by fungi and by bacteria, 

 not by the photosynthet ic plants. Great amounts of nitrogen, it is 

 true, in combinations directly usable by plants, are contributed to 

 the sea by the discharges of river water that carry with them the 

 drainage from the land; also fro.m air. But a greater potential 

 source is the decomposition of the carcasses of marine animals and 

 plants. Bacteria of decay seem to be as ubiquitous in the sea as 

 they are on the land; witness the rapidity with which carcasses rot 

 in the water at moderately high temperatures. And not only can they 

 usually bs isolated from decaying fish, out certain of them are 

 normal intestinal inhabitants of Haddock, no doubt of other species. 

 But how do temperature, darkness, pressure and the supply of avail- 

 able oxygen affect the activities of this putrefactive group in the 

 deeps? 



This question is important in oceanic economy because the 

 rapidity with which decomposition takes place (one of the two 

 factors that in the end control the fertility of the sea) controls 

 that state in which organic detritus reaches the sea floor in its 

 descent from the upp^r layers, to maintain the reserve supoly of 

 dissolved phosphates, etc. , in the abyssal water. 



A very important question in connection with the r6"le of the 

 nitrifiers is to what extent marine plants can use the ammonia 

 compounds to which the putrefactive bacteria reduce the complex 

 animal and vegetable proteins, and the ammonia which the sea absorbs 

 from the atmosphere and from atmospheric electric discharges. What 

 evidence has yet bien obtained suggests thst sea weeds (differing in 

 this respect from land plants) ca.nnot, as a group, utilize ammonia 

 salts directly, but only after the latter have been altered to 

 nitrates or to nitrites, Thie alteration is the task of the nitrate 

 and nitrite bacteria. It has been proven that this nitrigying o-poup 

 does exist in the sea i,e. that the ammonia salts formed there in_ 

 _situ and received from the air, are actually a potential source of 

 plant food locally. We have here both the indirect evidence that 

 when the store of nitrates in the water is exhausted by rich growth 

 of plnnts, it shortly becomes renewed when the latter die out, with 

 experimental knowledge of the chemical reactions that this group of 

 bacteria affect in sea wat<=r under controlled conditions in the labor- 

 atory, and the direct evidence that members of this group have been 

 discovered free in the sea water as well as in bottom deposits from 

 many localities over a considerable ransre of depth. However, empiric 

 knowledge of the seal-- on which they actuallv oo-rate in the sea is 

 still practically nil . 



■A'e can safely interpr^^t their responses (in rate of multiplica- 

 tion and efficient action) to variations in temperature, lir^ht, 

 ozygen and state of the ammonia and other ore-anic compounds "pres.^^nt , 

 by analogy with their activities on land? Or do they" follow differ- 

 ent laws in the sea? 'JVhat is their relative role in deep and in 

 shoal water, under the conditions actually existent? These questions 

 (about which different views are held) must be answered, before we 

 can assess the relative importance of different depth zones in the 

 ocean as sources for the renewal of nitrates and nitrites. What 



