210 RESPIRATION. 



ing to inspire after a violent expiration, of course almost suspends 

 the circulation, by depriving the heart of blood % which is no 

 longer drawn to the heart by inspiration, and has been squeezed 

 out by expiration : a continuance in refraining to expire after a 

 deep inspiration has the same effect, but more slowly. In both 

 cases the blood is no longer drawn to the heart by inspiration, 

 and does not experience those chemical changes in the lungs 

 which are indispensable to its free passage through them; though, 

 they being, in the former, filled with air, and empty in the latter, 

 it can continue to pass through them much longer in the former. 



And this leads me to observe, that the mere suspension of re- 

 spiration impedes the circulation through the heart, by causing 

 obstruction in the lungs ; and that, consequently, inspiration, by 

 giving free passage to the blood through those organs, will acce- 

 lerate its course through the veins, independently of a vacuum ; 

 although the influence of the vacuum is shown by the effect of 

 inspiration upon the contents of tubes inserted, not into the veins, 

 but merely into the cavity of the pleura or pericardium. Whether 

 respiration is suspended after an expiration or an inspiration, the 

 effect is the same: the blood accumulates in the lungs and 

 right side of the heart, if the windpipe is tied, whether the lungs 

 be empty or full at the time of the ligature ; and therefore it is 

 not merely the mechanical condition of the lungs that produces 

 the obstruction in this case, as was once supposed, but the want 

 of chemical changes.' 



But for this consideration, the effects of the thoracic vacuum 

 on the circulation might be overrated ; and, indeed, that too high 

 an estimate has been formed of it is very certain: for, 



after expiration, as there is a supply of air in the lungs in the former case, and 

 not in the latter (in the latter I can refrain for a quarter of a minute, and in 

 the former for rather above a minute) the pulse gradually resumes its former 

 quickness; and, when the breath can be held no longer, evidently grows more 

 and more rapid and weak. The effects of refraining from expiration are the 

 same in me as of refraining from inspiration. Rapid respiration quickens the 

 pulse, by drawing the blood more frequently to the heart ; and, in my case, if 

 very deep as well as rapid, the circulation through the head becomes so violent 

 that vertigo occurs, and, between this and the rapidity of the pulse, I at length 

 cannot count the latter. 



i My own pulse, if a deep expiration is made, and inspiration refrained from, 

 becomes rapid and excessively feeble, and more and more so till I can hold out 

 no longer. 



r See Haller, 1. c. lib. vii. sect. iv. p. 253. 



