238 RELATION OF RESPIRATION WITH THE NERVES 



Emily. Such constant exertions must necessarily be 

 attended by a great expenditure of power, and therefore 

 a corresponding activity of those organs, whose function 

 it is to purify and renovate the fluid from which it is sup- 

 plied, is also required. 



Dr. B. In reptiles also, we find a condition of the 

 muscular powers in perfect keeping with their feeble and 

 inactive respiration. Their motions are slow and un- 

 frequent, and there is a constitutional sluggishness and 

 indolence. For several months in every year, they shut 

 themselves up in holes and dark places, and remain in a 

 state of torpidity, in which motion and sense are utterly 

 suspended. 



In fishes, there are relations between the quantity of 

 respiration and that of muscular motion, no less uniform 

 and striking. They consume but little air, and they 

 have but little muscular power. 



Emily. I thought that they were remarkable in this 

 respect. Their motions are certainly very rapid ; and 

 salmon are said to ascend falls thirty feet high. 



Dr. B. True, indeed, and the darting of a salmon 

 or trout in the water is often compared to an arrow, but 

 such rapid motions cannot be continued longer than a 

 few minutes. Their powers are soon expended, and 

 not receiving a proportional supply from the respiratory 

 organs, their exertions are necessarily short. 



The relations between the respiratory function and 

 the nervous system, are just as strict and invariable. In 

 cold-blooded animals, whose respiration is almost an 

 accessary circumstance merely, the external senses are 

 deficient in acuteness, and the mental faculties are lim- 

 ited and dull. The nervous system derives its energy 

 from the blood, and it will always be proportional to the 

 degree of renovation which this fluid receives from the 

 action of the respiratory organs. In the reptiles, the 

 nervous energy, weak as it is, is sufficient for their pur- 

 pose. Strong sensations, and acute sensibility were not 

 wanted by animals whose muscular power needs but lit- 

 tle reanimation, because little is expended. 



