DRUGS WHICH ACT ON THE LUNGS 469 



The lining membrane of the air - passages contains mucous glands 

 which secrete a liland fluid for lubricating and moistening the surface, 

 and is further clothed with fine hair-like processes (cilia), which, waving 

 gently, like a field of corn in the wind, carry any superfluous secretion 

 to be exj^ectorated along the bronchial tubes towards the larynx, whence 

 it passes out by the nose. 



The structure of the lungs facilitates the exchange of gases in the 

 process of respiration, and this is largely regulated by the movements of 

 the heart; upon its force and frequency tlie amount of work thrown upon 

 the lungs will depend. A proper understanding of the subject is essential 

 to the treatment of pulmonary diseases upon any rational basis. The 

 confusion which exists in the minds of horse-owners and others as to con- 

 gestion and inflammation of these organs arises from want of knowledge 

 of the distribution of blood from tlie ditferent sides of the heart, and its 

 destination. Circulation of blood in the lungs is quickened by any agent 

 which stimulates the heart. Remedies having this effect are referred to 

 under the head of stimulants, as alcohol, ammonia, strophanthus, digitalis, 

 essential oils, &c. 



A stimulating effect upon the air-jiassages and the membranes which 

 line them is produced by warm food and copious draughts of fluid. Some 

 alkaline preparations, as acetate of ammonia, and other drugs, derived both 

 from the vegetable and mineral kingdoms, have the eff"ect of increasing 

 the amount of secretion poured out from the respiratory surfaces when 

 congestion has induced undue dryness. 



Among the remedies that thus increase the amount of material in the 

 air - tubes may be mentioned iodide of jjotassium, i^jecacuanha, squills, 

 ■camphoi', tui'pentine, benzoin, balsams of Tolu and Peru, stramonium, &c. 



Notwithstanding the disadvantage our equine patients possess of being 

 unable to expectorate in the ordinary sense of the term, they yet derive 

 great benefit from the class of remedies known in human practice as ex- 

 pectorants. The dryness of the membranes in cases of bronchitis may by 

 their judicious administration be relieved, and the sujjcrfluous mucus got 

 rid oft" by way of the nostrils. 



By reducing the force and frequency of the heart's action, the circula- 

 tion of blood in the lungs may be reduced in speed as well as volume, and 

 for this purpose aconite is often prescribed. Counter-irritants, as mustard 

 plasters, turpentine, and ammonia liniments, by withdrawing blood from 

 the pulmonary vessels to contiguous structures, relieve the overloaded 

 lungs, and aid in restoring the circulation to its normal condition. 



In some chronic forms of disease, as in the bronchial catarrh of old 

 horses, it may be desirable to reduce the activity of the glands and 



