114 



the most distressful symptoms, and at length an ut- 

 ter inability to continue respiration ; and Mr Davy 

 tells us, that, after a voluntary exhaustion of his 

 lungs, he could respire the nitrous oxide with accu- 

 racy, when stooping, for about half a minute, but, 

 even then, strong sensations were produced, with 

 fulness about the head rather alarming : that if 

 the respiration extended to three-fourths of a mi- 

 nute, he could not rely on the accuracy of any ex- 

 periment ; and that the determination of blood to 

 the head became, in- less than a minute, so great, as 

 often to deprive him of voluntary power over the 

 muscles of his mouth *. But respiration is a func- 

 tion carried on by the exertion of muscular powers, 

 in a great degree obedient to the will (87.) ; and 

 the quantity of residual air in the lungs in preterna- 

 tural respiration, will, at all times, be much influen- 

 ced by the manner in which the will exerts itself, 

 and the degree in which the muscles are able to act. 

 When, therefore, the power of the will over the mus- 

 cles is in any degree diminished, or is wholly lost, or 

 the muscles themselves are much weakened, a pro- 

 portional derangement will take place in the respira- 

 tory function ; and as, in the natural condition of 

 the body, expiration is subsequent to inspiration, 

 the ability to inspire will last longer than the ability 

 to expire : consequently, the cessation of the process 

 is brought about by a failure in the expiratory 

 powers. But if the expiratory powers are unable to 

 expel the air from the lungs, it must remain in. 



Researches, p. 392. 



