RESPIRATION. 355 



short intervals, is nothing to the purpose. The neces- 

 sity that animals have for breathing, depends upon the 

 quantity of food that they take, or, which is the same 

 thing, upon the rapidity with which the matter of their 

 bodies is changed. In those animals which pass the 

 cold months in a state of torpidity, breathing and 

 feeding are nearly equally suspended, and as the animal 

 intrudes toward its state of quiescence, the breathing 

 becomes interrupted. But the greater part of chry- 

 salids are in a dormant state, and therefore they may 

 remain under the water without breathing, in the same 

 manner that a dormant marmot remains under the 

 earth. 



But though the process of breathing differs so much 

 with the two fluids breathed, that it seems contrary to 

 the usual law of nature, that the one should be changed 

 to the other, yet the result and purpose of the ope- 

 ration are the same in both cases. The result is the 

 separation of a certain quantity of oxygen. It was 

 long supposed that this oxygen was an aliment, and 

 that it was taken into the blood, and thence into the 

 structure of the animal ; but that did not agree with 

 the fact that the blood is always exhibited to the organs 

 of respiration after it has gone its circuit for the 

 nourishment and repair of the system ; and that a 

 substance in nature should be made fit for its purpose 

 only after that had been accomplished, really seems 

 contrary to the wisdom and design that pervade the 

 works of nature in operations ten-fold more complicated 

 than this, so that one cannot help being a little surprised 

 that it should ever have been entertained. It must have 

 arisen from that disposition to look at, and draw con- 



