222 RESBIEATIOH. 



on the abdominal viscera in the opposite direction, by the 

 elastic or muscular recoil of the abdominal walls ; but the 

 pressure is relieved by the escape of air through the open 

 glottis, and the relaxed diaphragm is pushed up again into 

 its original position. The sphincters of the stomach, 

 rectum, and bladder act as before. 



Hiccough resembles sighing in that it is an inspiratory 

 act, but the inspiration is sudden instead of gradual, from 

 the diaphragm acting suddenly and spasmodically ; and the 

 air, therefore, suddenly rushing through the unprepared 

 rima glottidis, causes vibration of the vocal cords, and the 

 peculiar sound. 



In the act of coughing, there is most often first an in- 

 spiration, and this is followed by an expiration ; but when 

 the lungs have been filled by the preliminary inspiration, 

 instead of the air being easily let out again through 

 the glottis, the latter is momentarily closed by the 

 approximation of the vocal cords ; and then the abdo- 

 minal muscles, strongly acting, push up the viscera 

 against the diaphragm, and thus make pressure on the 

 air in the lungs until its tension is sufficient to burst 

 open noisily the vocal cords which oppose its outward pas- 

 sage. In this way a considerable force is exercised, and 

 mucus or any other matter that may need expulsion from 

 the lungs or trachea is quickly and sharply expelled by 

 the out-streaming current of air. 



Now it is evident on reference to the diagram (fig. 65 ), 

 that pressure exercised by the abdominal muscles in the 

 act of coughing, acts as forcibly on the abdominal viscera 

 as on the lungs, inasmuch as the viscera form the medium 

 by which the upward pressure on the diaphragm is made, 

 and of necessity there is quite as great a tendency to the 

 expulsion of their contents as of the air in the lungs. 

 The instinctive and, if necessary, voluntarily increased 

 contraction of the sphincters, however, prevents any 

 escape at the openings guarded by them, and the pres- 



