RESPIRATION 221 



Some Special Respiratory Acts. 



The mechanism of sneezing" and of coughing have 

 already been described. Of the latter it need only be 

 said further, that although primarily protective in its 

 nature, and designed to bring about the expulsion of 

 irritating bodies from the upper air passages, it may 

 also be excited by peripheral stimuli in various parts of 

 the body. Thus, irritation of the gastric branches of the 

 vagus is said to produce a * stomach ' cough, and of its 

 auricular branch an * ear ' cough. In persons who are 

 unduly sensitive to cold, a hard dry cough may be 

 excited by getting into bed between cold sheets, or when 

 exposed to a draught. 



Curiously enough, irritation of the interior of the 

 trachea does not seem to excite cough. Perhaps that is 

 why a tracheotomy-tube can be worn so comfortably. 

 The bronchi appear to be less sensitive than the larynx, 

 but more so than the trachea. Foreign bodies in them 

 sometimes excite cough, sometimes not. The same is 

 true of the lung substance. Disease of it does not 

 necessarily lead to coughing. Coughing may also be 

 excited by irritation of the pleura ; hence the cough of 

 pleurisy and the paroxysm of coughing which often 

 comes on in aspirating the chest. Even a ' uterine ' 

 cough has been described, although its real existence is 

 somewhat doubtful. When such peripheral irritations 

 exist, the cough which they excite is useless, and its sup- 

 pression by opium justifiable. 



Sighing" is a deep inspiration intended to make up 

 for a temporary depression or a cessation of breathing. 



