200 HAND-BOOK OF PHYSIOLOGY. 



there is no escape of their contents, and air simply enters the lungs. In 

 the second, or expiratory part of the act of sighing, there is also pressure 

 made 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 cf 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 sud- 

 denly and spasmodically; and the air, therefore, suddenly rushing through 

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

 the peculiar sound. 



Coughing. 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 abdominal 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 passage. 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 outstreaming current of air. 



Now it is evident on reference to the diagram (Fig. 161), that pressure 

 exercised by the abdominal muscles in the act of coughing, acts as for- 

 cibly 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. 



Sneezing. The same remarks that apply to coughing, are almost 

 exactly applicable to the act of sneezing; but in this instance the blast 

 of air, on escaping from the lungs, is directed, by an instinctive con- 

 traction of the pillars of the fauces and descent of the soft palate, chiefly 

 through the nose, and any offending matter is thence expelled. 



Speaking. In speaking, there is a voluntary expulsion of air through 

 the glottis by means of the expiratory muscles; and the vocal cords are 

 put, by the muscles of the larynx, in a proper position and state of tension 

 for vibrating as the air passes over them, and thus producing sound. The 

 sound is moulded into words by the tongue, teeth, lips, etc. the vocal 

 cords producing the sound only, and having nothing to do with articu- 

 lation. 



