INNERVATION OF THE RESPIRATORY MOVEMENTS. 647 



that is, a condition of maintained activity of the constrictor fibers 

 may be set up by the action of a number of drugs, such as muscarin, 

 pilocarpin. and physostigmin, which in this case, as in so many 

 other instances of autonomic fibers, are supposed to stimulate the 

 endings of the fibers in the lungs. Their effect is removed by the 

 action of atropin. These fibers are stimulated also during the ex- 

 citatory stages of asphyxia. Reflex stimulation of the constrictors 

 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. 638, 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. 



