274 THE CIRCULATION OF NITROGEN [PART III 



the incredibly great mass that is present in the atmosphere. But 

 when we think of the almost infinite numbers of plants and 

 animals that have existed on the earth since life first began, it is 

 evident that the total quantity of nitrogen which has been 

 contained in their tissues must have been inconceivably great. 

 But there is no accumulation of this element in the crust of the 

 earth, and the composition of the atmosphere has been much the 

 same since very remote times. Therefore the nitrogen w^hich is 

 now present in the bodies of living plants and animals must have 

 been transmitted from organism to organism throughout biological 

 time. 



Minute portions of organic matter receive their legacies of life, 

 and growing, take up nitrogen, and the other constituents of their 

 bodies, from the media in which they live. Having lived its 

 allotted time the organism dies, and its constituent elements 

 return to the dust. Or perhaps it may be devoured by another 

 organism and then part of its substance becomes rebuilt up into 

 that of the animal which has consumed it. And yet again this 

 animal may be the prey of others. Thus there is a transmigration of 

 the atoms of the material bodies of organisms through long series 

 of animate and inanimate forms. But while there is an ultimate 

 Nirvana in the transmigrations of souls, the atoms of nitrogen are 

 bound on the wheel of change, and ceaselessly pass through living 

 and non-living phases. Imperious Caesar dead and turned to clay 

 does not at once fill a crevice in a wall, or stop a bunghole, but 

 may have a place in the architecture of humbler creatures. Per- 

 haps only after many transmutations through living organisms 

 may the nitrogen and carbon of the organism reassume the 

 inorganic phase. But sometime or other, they return to the 

 earth or become dispersed in the sea or air. Dante, in his vision, 

 saw the souls of sinners impelled by a furious wind, and it may be 

 that the material atoms, the substrata of the souls, are carried far 

 and wide in the currents of the atmosphere. 



Even the substance of the body of the individual animal has 

 but a transitory existence when compared with the normal span of 

 life of the organism. The circulation of nitrogen and carbon takes 

 place in this manner : certain food-stuffs, proteids, fats and carbo- 

 hydrates are ingested and are broken down in the alimentary canal 



