480 RESPIRATION. 



sense of suffocation which attends an interruption in the re- 

 spiratory process. Under ordinary conditions, the act of 

 breathing takes place without our knowledge; but even 

 when the air is but little vitiated, when its entrance into the 

 lungs is slightly interfered with, or when a considerable 

 portion of the pulmonary structure is involved by disease, 

 we experience a certain sense of uneasiness, and become con- 

 scious of the necessity of respiratory efforts. This gradually 

 merges into the sense of suffocation, and, if the obstruction be 

 sufficient, is followed by convulsions, insensibility, and final- 

 ly by death. 



Though we are not sensible of any want of air under or- 

 dinary conditions, it was proven by the celebrated experi- 

 ment of Robert Hooke, in 1664, that there is a \vant always 

 felt by the system ; and that if this want be effectually sup- 

 plied, no respiratory movements will take place. We have 

 often repeated the experiment demonstrating this fact. If a 

 dog be brought completely under the influence of ether, the 

 chest and abdomen opened, and artificial respiration be 

 carefully kept up by means of a bellows fixed in the trachea, 

 even after the animal has come from under the influence of 

 the anaesthetic, so as to look around and wag his tail when 

 spoken to, he will frequently cease all respiratory move- 

 ments when the air is properly supplied to the lungs. This 

 fact can be very satisfactorily observed, as the diaphragm 

 and other important respiratory muscles are denuded, and 

 exposed to view. If the artificial respiration be interrupted 

 or imperfectly performed, the animal almost immediately 

 feels the want of air, and the exposed respiratory muscles 

 are thrown into violent but ineffectual contraction. 1 



It is generally admitted, indeed, that there exists in the 



1 For full details of these experiments the reader is referred to an article by 

 the author, entitled Experimental Researches on Points connected with the Action 

 of the Heart and with Respiration (American Journal of the Medical Sciences, Oct., 

 1861). Since the publication of this paper, the experiments on respiration have 

 been frequently repeated publicly, and the conclusions verified. 



