RELATIONS OF INSPIRATION AND EXPIRATION. 393 



with inspiration, it is found that this act maintains about the 

 same intensity from its commencement to its termination ; 

 there is then a very brief interval, when expiration follows, 

 which has its maximum of intensity at the commencement 

 of the act, and gradually dies away. 1 Between the acts of ex- 

 pi^ation and inspiration is an interval, somewhat longer than 

 that which occurs after inspiration. 



The duration of expiration is generally somewhat greater 

 than that of inspiration, though they may be nearly, or in 

 some instances quite, equal. 



After from iive to eight ordinary respiratory acts, one 

 generally occurs which is rather more profound than the rest, 

 and by which the air in the lungs is more effectually changed. 

 The temporary arrest of the acts of respiration in all violent 

 muscular efforts, in straining, in parturition, etc., is familiar 

 to all. 



Ordinarily respiration is not accompanied by any sound 

 which can be heard without applying the ear directly, or by 

 the intervention of a stethoscope, to the respiratory organs ; 

 excepting when the mouth is closed, and breathing is carried 

 on exclusively through the nasal passages, when a soft, 

 breezy murmur accompanies both acts. If the mouth be 

 sufficiently opened to admit the free passage of air, no sound 

 is to be heard in health. In sleep, the respirations are un- 

 usually profound ; .and if the mouth be closed, the sound is 

 rather more intense than usual. 



Snoring, a peculiar sound, more or less marked, which 

 sometimes accompanies the respiratory acts during sleep, oc- 

 curs when the air passes through both the mouth and the 

 nose. It is more marked in inspiration, sometimes accom- 

 panying both acts, and sometimes not heard in expiration. 

 It is not necessary to describe the characters of a sound so 



1 Iu listening to the respiratory murmur over the substance of the lungs, the 

 expiratory follows the inspiratory sound without an interval (see p. 395). The 

 interval between the acts of inspiration and expiration is only appreciated as the 

 air passes in and out at the mouth. 



