LIFE IN THE OCEAN. 495 



Inorganic nitrogenous compounds appear in three forms in nature— 

 those of ammonia, nitrates, and nitrites. Since no plant can grow 

 unless it finds inorganic nitrogenous compounds in its neighborhood, 

 and since the life of animals depends on that of plants, it follows that 

 all the life on the globe depends absolutely upon the existence of these 

 nitrogenous compounds. It is, therefore, of the first importance to 

 follow closely the cycle of transformations of nitrogen in nature. 



We know only three sources of the three kinds of nitrogenous 

 compounds which interest us. In the first place, all living beings con- 

 tain nitrogenous substances, notably albumen, and these are in part 

 eliminated during life as residuary products (urine, etc.), and for the 

 rest are decomposed by putrefaction after death. The albuminoid sub- 

 stances are then transformed into ammonia, which in its turn fur- 

 nishes nitrites and nitrates, so that the nitrogen is brought back to a 

 form in which it can be used by plants in a new production of albu- 

 men. All the processes of putrefaction by which animal carcasses and 

 vegetable remains are transformed into carbonic acid, subterranean 

 nitrogenized waters, and other inorganic substances, are due exclu- 

 sively to certain definite bacteria. If these are not present or do not 

 meet with the conditions of life which they require, putrefaction is 

 adjourned and with it the utilization of the nitrogenous matter of dead 

 bodies by living ones. 



Nor is the decomposition of albuminoids the only process caused by 

 bacteria; they are equally necessary for the conversion of ammonia 

 into nitrous acid, and ultimately into nitric acid, and for the reverse 

 changes. A sort of bacterium called a nitrifying bacterium, or nitro- 

 bacterium, existing, it would seem, all over the globe, produces the oxi- 

 dation necessar}" to transform ammonia first into nitrous and finally into 

 nitric acid, provided there is enough oxygen at hand. The reverse 

 process of reduction is due to another kind of bacterium, called a deni- 

 trifying bacterium, which transforms nitric acid into nitrous acid, and 

 this again into ammonia, and finally sets nitrogen free. The final prod- 

 uct of this reduction consists of free nitrogen, which, mingling with 

 the air, is lost from the cycle of transformation. With one excep- 

 tion, nitrogen can not be utilized by plants to form albumen unless it 

 is in a state of combination. Thus, though the greater part of the 

 organic nitrogen returns to living organisms, a certain portion of it is 

 lost by the action of the denitrifying bacteria. The quantity of living 

 organisms would, therefore, be gradually diminished Avere there no 

 other source of combined nitrogen to make up for the loss. 



This compensation is furnished by the free nitrogen of the atmos- 

 phere, which, under certain conditions, can enter into combination 

 and become available for plants. Combinations of this kind are 

 brought about in two ways— by the action of lightning, that is, of 

 electrical discharges, and by the symbiosis, or mutual parasitism, of 

 SM lyuo 35 



