198 Natural Theology. 



atmosphere, it seems to have no direct relation to 

 animal life. It has mechanical relations to them, 

 and the wing of the bird and of every flying thing 

 has been fashioned with reference to it. For if the 

 nitrogen were gone, the weight of the atmosphere 

 would be so changed that very few, if any, of the 

 winged animals could sustain themselves in it. But 

 chemically considered, nitrogen is an inert body 

 mingled with oxygen, the life-sustaining element, to 

 moderate its force by dilution. But, why it may be 

 asked, could not the oxygen alone suffice, since that 

 alone takes an active part in sustaining life ? Cer- 

 tain it is, that organic substances, as they are now 

 constituted, could not exist in pure oxygen. It 

 would prove too stimulating for animal life, and 

 combustion would be terrific beyond description. 



We may therefore properly say, that the chemical 

 relations of organic beings have been adjusted with 

 reference to the amount of nitrogen in the air, 

 although it exerts no direct chemical action upon 

 them ; for both of the disastrous consequences just 

 mentioned as resulting from an atmosphere of 

 pure oxygen, would follow simply from the quantity 

 of oxygen breathed, or that would come in contact 

 with the flame in a given time. 



When the oxygen is diluted with four times 

 its quantity of this inert gas, its strong chemical 

 power still remains, but only one-fifth as much can 

 be brought into action in a given time on a given 

 space, as there would be were the atmosphere pure 

 oxygen. 



