CHAP. XIL] RESPIRATION. 141 



diaphragm ; the glottis suddenly closes and cuts off the column 

 of air just entering , which, striking upon the closed glottis, 

 gives rise to the characteristic sound. 



In sobbing, a series of convulsive inspirations follow each 

 other slowly, the glottis is closed, so that little or no air enters 

 the chest. 



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 

 forcible and sudden expiration, in the midst of which the glottis 

 suddenly opens, and thus a blast of air is driven through the 

 upper respiratory passages. 



In sneezing, the general movement is the same, except that 

 the opening from the pharynx into the mouth is closed by the 

 contraction of the pillars of the throat and the descent of the soft 

 palate, so that the force of the blast is driven entirely through 

 the nose. 



Laughing consists essentially in an inspiration, followed by a 

 whole series of short spasmodic expirations, the glottis being 

 freely open during the whole time, and the vocal cords being 

 thrown into characteristic vibrations. 



In crying, the respiratory movements are the same as in 

 laughing ; the rhythm and the accompanying facial expressions 

 are, however, different, though laughing and crying often be- 

 come indistinguishable. 



