CHAP, ii.] RESPIRATION. 631 



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

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

 followed 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 distri- 

 buted 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 vibra- 

 tions. 



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. 



