CHAP, ii.] RESPIRATION. 383 



that the further entrance of air into the chest is prevented, while 

 the impulse of the column of air just entering, as it strikes upon 

 the closed glottis, gives rise to a well-known accompanying sound. 

 The afferent impulses of the reflex act are conveyed by the gastric 

 branches of the vagus. The closure of the glottis is carried out by 

 means of the inferior laryngeal nerve. See Voice. 



In sobbing a series of similar convulsive inspirations follow each 

 other slowly, the glottis being closed earlier than in the case of 

 hiccough, so that little or no air enters into the chest. 



Coughing consists in the first place of a deep and long-drawn 

 inspiration by which the lungs are well filled with air. This is fol- 

 lowed by a complete closure of the glottis, and then comes a 

 sudden and forcible expiration, in the midst of which the glottis 

 suddenly opens, and thus a blast of air is driven through the upper 

 respiratory passages. The afferent impulses of this reflex act are 

 in most cases, as when a foreign body is lodged in the larynx or by 

 the side of the epiglottis, conveyed by the superior laryngeal nerve ; 

 but the movement may arise from stimuli applied to other afferent 

 branches of the vagus, such as those supplying the bronchial 

 passages and stomach and the auricular branch distributed to 

 the meatus externus. Stimulation of other nerves also, such as 

 those of the skin by a draught of cold air, may develope a cough. 



In sneezing the general movement is essentially the same, 

 except that the opening from the pharynx into the mouth is 

 closed by the contraction of the anterior pillars of the fauces and 

 the descent of the soft palate, so that the force of the blast is 

 driven entirely through the nose. The afferent impulses here 

 usually come from the nasal branches of the fifth. When sneezing 

 however is produced by a bright light, the optic nerve would seem 

 to be the afferent nerve. 



Laughing consists essentially in an inspiration succeeded, not 

 by one, but by a whole series, often long continued, of short spas- 

 modic expirations, the glottis being freely open during the whole 

 time, and the vocal cords being thrown into characteristic vibrations. 



In crying, the respiratory movements are modified in the same 

 way as in laughing; the rhythm and the accompanying facial 

 expressions are however different, though laughing and crying 

 frequently become indistinguishable. 



