350 THE CHEMISTRY OF CREATION. 



of the limbs ! This of course answers the 

 same purpose as the other arrangement, the 

 blood-vessels of the insect ramifying over these 

 air-tubes, or tracheae, as they are scientifically 

 called. The same objects are effected by 

 this arrangement as by the other, namely, the 

 oxygenization of the blood and the removal 

 of its impurities. The breathing of those 

 members of the zoological kingdom whose 

 abode is in the waters will be noticed in the 

 concluding part of this work. 



Yet while fulfilling these important duties, 

 the air has others of an opposite kind also to 

 discharge with respect to all animal bodies. The 

 whole bodily frame is in process of incessant 

 change, to a large degree, by the influence, 

 direct or indirect, of the vastly important 

 function of respiration, and by the oxidation 

 which goes on to a greater or less extent through 

 the skin all over the body. No part remains per- 

 manent. Its tissues are nourished by the blood, 

 their waste parts are carried off into the air, or 

 rejected in other ways as excrementitious, and 

 new particles take their place. In a little time 

 these again, having served their turn, become 

 effete, and are cast out of the body. Yet these 

 ceaseless changes do not affect the form of 

 organs and their peculiar characters, unless, 

 indeed, disease has been established in them. 

 Curious truth ! even the accidental impression 



