136 RESPIRATION 



autonomic fibers in the lungs, and their effect may be removed 

 by atropine. Bronchoconstriction can be excited by stimulating 

 the nasal mucous membrane, particularly a small area well 

 back on the nasal septum. Cauterization of a corresponding 

 area in man is said to give permanent relief in cases of spasmodic 

 asthma which is associated with spasm of the bronchial muscles. 

 These fibers are also stimulated during the excitatory stages 

 of asphyxia. 



There are a number of involuntary and voluntary special 

 respiratory acts, largely reflex, which result from modifications 

 of inspiration and expiration. 



Sighing. This results from a prolonged inspiration, the 

 air passing noiselessly through the larynx and being expelled 

 rather suddenly. 



Hiccough. The inspiration is sudden, and terminated by 

 closure of the glottis. 



Cough. This results from a deep inspiration followed by 

 a forced and sudden expiration, during which the glottis is 

 closed momentarily by the spasmodic action of the vocal 

 cords. 



Sneezing. In this case after a deep inspiration the air is 

 directed through the nasal passages by a sudden and forced 

 expiration. 



Speaking. In this case there is a voluntary expiration, 

 and the vocal cords being rendered tense by their muscles 

 vibrate as the air passes over them, producing sound. 



Singing. This varies from speaking only in the differing 

 tension and position of the vocal cords and the consequently 

 different sounds produced. 



Sniffing. This results from rapid repeated but incomplete 

 nasal inspirations. 



Sobbing. This consists of a series of convulsive inspirations, 

 during which the glottis is more or less closed. 



Laughing. This results from a series of short and rapid 

 expirations. 



Yawning. This is an act of inspiration more or less involun- 

 tary, accompanied by a stretching of various facial muscles. 



Sucking. This is caused chiefly by the depressor muscles 

 of the os hyoides, which, by drawing down and back the floor 

 of the mouth, produce's a partial vacuum in it. 



