INNERVATION OF THE RESPIRATORY MOVEMENTS. 703 



is obtained most readily (Dixon and Brodie) by irritation of the 

 nasal mucous membrane, and it seems probable that in bronchial 

 or spasmodic asthma these fibers are also stimulated reflexly. 

 The normal conditions under which the constrictors and dilators 

 are brought into play can scarcely be stated. Irritating vapors or 

 even CO 2 lead to a bronchoconstriction and this reflex, as stated on 

 p. 693, may be regarded as protective. When a constriction of the 

 bronchial musculature exists it may be abolished by the paralyzing 

 action of atropin, or temporarily by injections of extracts of 

 lobelia or by the anesthetic effect of inhalations of chloroform or 

 ether. Nicotin also causes a dilatation. 



