108 GENERAL THERAPEUTICS FOR VETERINARIANS 



Action. — To understand the action of expectorants, it must be 

 remembered that the body is provided with certain protective 

 arrangements by which it is possible for foreign bodies entering 

 the air passages to be removed without the assistance of medi- 

 cines. These physiological expectorants are cough, the outward- 

 directed movement of the cilia of the epithelial cells and, some- 

 times, sneezing. As a result of catarrhal swelling of the mucous 

 membrane or the deposit of thick, viscid mucus and masses of 

 exudate, the activity of the ciliated epithelium is reduced or sup- 

 pressed. The same effect is produced when the cilia are involved 

 by excessive catarrhal desquamation, inflammatory infiltration 

 or ulceration, and also when they are paralyzed by the products 

 resulting from the decomposition of the retained bronchial con- 

 tents (fatty acids). Cough, also an important natural healing 

 force, is sometimes suppressed or abolished by general bodily 

 weakness or by paralytic conditions of the sensory nerves of the 

 mucous membrane (necrosis of the lungs, severe laryngitis). 

 Cough and the movement of the cilia can both be artificially 

 stimulated by certain expectorant drugs. These, however, are 

 not the only methods of action of expectorants; there are several 

 others. In general, the methods of action of the expectorants are 

 as follows: 



1. Stimulation of the ciliated epithelium. The principal reme- 

 dies are ammonium chloride and other ammoniacal preparations : 

 ammonium carbonate, ammonia water and aromatic spirit of 

 ammonia. Most of the stimulant expectorants also increase the 

 activity of the cilia. 



2. Stimulant (cough-producing) expectorants. These stimu- 

 late either the peripheral sensory nerves of the mucous membrane 

 or the respiratory centre. They include tar, creosote, turpentine 

 oil, camphor, benzoin, balsam of Peru, emetine, ipecac, senega and 

 quillaja. Turpentine oil at the same time decreases the secretions 

 of the respiratory mucous membrane and suppresses the abnormal 

 secretion of mucus. 



3. Increase of the gland secretions dissolves mucus and 

 thereby assists expectoration. Gland secretions are increased by 



