ASPECTS OF AN OLD AGRICULTURAL QUESTION. 257 



form capable of forcing free nitrogen into the synthesis 

 of organic compounds in some such way as is hinted at, 

 though we are quite unable to explain the machinery which 

 effects this. The probability is that nascent hydrogen 

 combines with the free nitrogen and ammonia is formed. 



In our astonishment at any such processes as these, we 

 must not lose sight of the truth that when a living cell 

 respires, and oxidises large quantities of carbo-hydrate in 

 the process, the respiration is not a mere direct oxidation of 

 these combustible substances, but is a complex physiologi- 

 cal process where the energy obtained from the destruction 

 of the carbo-hydrate is unlocked in the living protoplasm 

 and applied in ways which it is true we cannot yet trace, 

 but which we are sure are rhythmical and effective in their 

 action beyond our present powers of imitation. 



Where a "nitrifying" bacterium oxidises ammonium- 

 carbonate to nitrite and nitrate, energy is available, and can 

 be employed in doing work in the cell, e.g., forcing other 

 parts of the ammonium-carbonate into the synthesis of 

 organic compounds, and if we are astonished at this usage 

 of ammonium-carbonate, what shall we say to the corre- 

 sponding oxidation of sulphur or sulphuretted hydrogen by 

 the sulphur bacteria, or of compounds of iron by the bac- 

 teria of ferruginous waters ? Nevertheless Winogradsky's 

 work has rendered it extremely probable that many such 

 cases will yet be discovered to exist. 



As Pfeffer (18) has pointed out very clearly, these cases 

 do not render the bacteria in question any more indepen- 

 dent of solar energy than the green plant itself; for the 

 oxygen necessary is in the last case derived from the 

 chlorophyll activity of these plants, and the reduction of 

 nitrates to ammonia is sooner or later referable to the 

 action of living green plants. 



After all, therefore, the actions of these "nitrifying" 

 and " de-nitrifying " organisms are just as dependent on 

 the process of synthesis of carbo-hydrates by the green 

 plant, as are the actions of ordinary saprophytes and para- 

 sites, and herbivorous and therefore carnivorous animals. 



While, then, the investigation of the numerous organisms 



