200 BESPIBATIOff. 



Respiratoi-y Rhythm. 



The acts of expansion and contraction of the chest, take 

 up, under ordinary circumstances, a nearly equal time, and 

 can scarcely be said to be separated from each other by an 

 intervening pause. 



The act of inspiring air, however, especially in women 

 and children, is a little shorter than that of expelling it, 

 and there is commonly a very slight pause between the end 

 of expiration and the beginning of the next inspiration. 

 The respiratory rhythm may be thus expressed : 



Inspiration .... 6 



Expiration . . . . 7 or 8 



A very slight pause. J 



Respiratory Movements of the Glottis. 



During the action of the muscles which directly draw 

 air into the chest, those which guard the opening through 

 which it enters are not passive. In hurried breathing the 

 instinctive dilatation of the nostrils is well seen, although 

 under ordinary conditions it may not be noticeable. The 

 opening at the upper part of the larynx, however, or rima 

 glottidis (fig. 65), is dilated at each inspiration, for the 

 more ready passage of air, and collapses somewhat at each 

 expiration, its condition, therefore, corresponding during 

 respiration with that of the walls of the chest. There is a 

 further likeness between the two acts in that, under ordi- 

 nary circumstances, the dilatation of the rima glottidis is a 

 muscular act, and its contraction chiefly an elastic recoil ; 

 although, under various conditions, to be hereafter men- 

 tioned, there may be, in the contraction of the glottis, con- 

 siderable muscular power exercised. 



