COUGHING; SNEEZING; VOMITING. 233 



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 pressure is 

 effective at one part only, namely, the rima glottidis. 



The same remarks that apply to coughing, are almost 

 exactly applicable to the act of sneezing ; but in this in- 

 stance the blast of air, on escaping from the lungs, is 

 directed by an instinctive contraction of the pillars of the 

 fauces and descent of the soft palate, chiefly through the 

 nose, and any offending matter is thence expelled. 



In the act of vomiting, as in coughing, there is first an 

 inspiration; the glottis is then closed, and immediately 

 afterwards the abdominal muscles strongly act ; but here 



