350 MANUAL OF PHYSIOLOGY. 



so that rapidly repeated blasts of air pass through the upper air 

 passages and mouth, which is generally held open. 



Sneezing is caused by a stimulus applied to the nose or eyes, 

 the impulses being carried to the respiratory centre by the nasal 

 and other branches of the fifth nerve. It consists of a deep in- 

 spiration and closure of the glottis, followed by a single explo- 

 sive expiration and sudden opening of the glottis and posterior 

 nares. 



Sneezing is a purely reflex act, it being impossible to produce 

 it voluntarily, except by the stimulation of the nasal mucous 

 membrane with some irritating substance. 



Laughing consists in a full inspiration, followed by a long 

 series of very short, rapid expiratory efforts. The facial mus- 

 cles are at the same time thrown into a characteristic set of 

 movements. 



Crying is made up of a series of short sudden expirations, 

 accompanied with peculiar facial contortions, and commonly 

 following or associated with the following : 



Sobbing, which consists of a rapid series of convulsive inspira- 

 tory efforts, causing but little air to enter the chest, and followed 

 by one long expiration. 



Sighing is a long, slow inspiration, quickly followed by a cor- 

 responding expiration. 



Yawning is a very long, deep inspiration, completely filling 

 the chest. It is accompanied by a peculiar depression of the 

 lower jaw, wide open mouth, facial movements, and commonly 

 stretching of the limbs. 



Hiccough is a sudden in^piratory spasm, chiefly of the dia- 

 phragm, the entrance of the air being suddenly checked by the 

 sudden closure of the glottis. 





