512 MODIFIED KESPIKATORY 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 distributed to the meatus externus. Stimula- 

 tion of other nerves also, such as those of the skin by a draught 

 of cold air, may develop a cough. 



In sneezing the movement is the same, in so far that it con- 

 sists 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 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 

 spasmodic expirations, the glottis being freely open during the 

 whole time, and the vocal cords being thrown into character- 

 istic 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. 



