A CENTURY OF CHEMISTRY. 123 



trites, or ammonia ; these compounds are used in the 

 elaboration of complex nitrogenous bodies such as 

 proteids. These proteids produced by the plant form 

 the food of animals and become part of their vital 

 capital. As the animals live there is a continual dis- 

 ruption of the complex nitrogenous substances and 

 the formation of less complex nitrogenous waste 

 products. This also takes place in plants, but there 

 is this difference, that while the plant retains its 

 nitrogenous waste, the animal gets rid of it in the 

 form of urea, uric acid, urates, and the like. These 

 waste products rapidly decompose after they have 

 been excreted, and ammonia is formed available 

 once more to enter upon the cycle. 



If the animal or plant die, the agency of putre- 

 factive bacteria brings about decomposition, and the 

 disruption of the nitrogenous materials yields am- 

 monia, nitrates, and the like, which may be again 

 utilised. The availability of nitrogenous material 

 is not thereby affected. On the other hand, as Bunge 

 forcibly points out,* the burning of wood, the crema- 

 tion of an animal, the explosion of gunpowder, in- 

 volve a liberation of nitrogen from its fixed or com- 

 pound form, and a consequent diminution of the 

 available supplies. 



" It would appear, therefore, that there is a con- 

 tinuous degradation of nitrogen to the elementary 

 condition a very serious matter if the nitrogen so 

 degraded is finally removed from the sphere of action 

 of organised beings. Are there, then, any other 

 agencies at work to restore the balance, and enable 

 this apparently useless gas to return within the 

 arena of physiological activity ? " f 



* Bunge, op. cit., p. 21. 



t F. W. Stoddart, " The Circulation of Nitrogen in Na- 

 ture," Proc. Bristol Nat. Soc.. IX. (1899), pp. 57-74. 



