662 MODIFIED RESPIRATORY MOVEMENTS. [BOOK n. 



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 movement is the same, in so far that it consists 

 of a deep inspiration followed by a sudden and forcible expiration. 

 But the mouth, instead of being widely open as in coughing, is 

 partly, or at first even wholly closed, and the buccal cavity with 

 the pharynx is so disposed that the blast of air in being driven out 

 through the mouth produces the characteristic sound. If the 

 obstruction, the sudden removal of which initiates the expiratory 

 blast, is caused by closure of the glottis, and this is not clear, 

 the glottis is so disposed as not to give rise to a vocal sound as 

 is the case in coughing. Though the movement is accompanied 

 by secretion from the nasal passages, the outgoing blast appears 

 not to pass through the nose, being cut off from that passage by 

 elevation and pressing back of the soft palate. The afferent im- 

 pulses 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. 



