DRUGS ACTING ON THE RESPIRATORY ORGANS 51 



Uses of Drugs Allaying Spasm and Cough. 



Coughing is a reflex act following irritation of sensory 

 nei-ve endings in any part of the respiratory tract (usually 

 of afferent vagal branches), in the pharynx, pleura, ears, teeth, 

 stomach and liver. Sensory impulses conveyed to the 

 reflex centre for coughing, — near the respiratory centre in the 

 medulla, — are there transformed into motor impulses and 

 result in coughing. Drugs may stop coughing by acting 

 locally to relieve congestion and irritation (demulcents) or 

 they may exert a topical sedative action on the nerve end- 

 ings. They also act systemically by quieting the reflex centre 

 for coughing, or the sensory or motor nerve endings ; also 

 by abating congestion in promoting secretion (expectorants), 

 or in influencing the circulation. 



Cough may be beneficial when it assists the expulsion 

 of exudation, but is not so when it is constant and ineffective, 

 as in congestion of the trachea, bronchial mucous mem- 

 branes, lungs or pleura ; in pulmonary consolidation ; and 

 in coughs originating outside of the respiratory tract. We 

 should try to arrest coughing by agents removing the cause 

 (congestion or irritation), such as counter-irritants, expector- 

 ants, local applications (sprays, inhalations) and heart 

 stimulants; but if these are inefficient and coughing is 

 immoderate, we may resort to the use of sedative agents. 

 Some preparation of opium is most frequently employed to 

 stop coughing, but should be avoided if cyanosis exists, 

 since inspiratory and expulsive efforts are weakened by th^ 

 drug. Belladonna, on the other hand, stimulates the respi- 

 ratory centres and arrests cough by depressing both the 

 afferent and efferent vagal terminations in the lungs, while — 

 like opium — lessening secretion. These drugs are often 



