118 CLINICAL DIAGNOSTICS. 



brain, which innervates the expiratory muscles and recurrent 



nerve, inducing the reflex spasm called cough. 



In exceptional cases cough can emanate from ter- 

 minals of the vagus nerve lying outside of the respiratory appara- 

 tus, as, for instance, from the external auditory meatus [ear], 

 nose, or abdominal organs. According to Albrecht cough^ can 

 occur from abscess in the liver. These are, however, exceptional 

 cases. Cough from the stomach has never been ob- 

 served in the horse. There is a possibility that cough may have 

 its origin in the brain. These exceptions are worthy of note and 

 should be considered in those cases of cough the cause of which 

 cannot be found to lie in the respiratory apparatus. 



Cough occurs: 



1. If foreign bodies are inhaled: smoke, dust (dusty 

 food), acrid gases (ammonia, sulphurous acid, chlorine, etc.). 



2. If cold air is inhaled, especially if the respiratory 

 tract is inflamed: catarrhs of the trachea and bronchi, pleuritis, 

 traumatic injuries to the pleura (traumatic gastro-diaphragm- 

 itis of the ox). 



3. If mucus, exudate or foreign bodies (food) and para- 

 sites are present in the air passages : Gastrus larvae in the 

 larynx, Syngamus trachealis in the wind pipe, Strongyli in the 

 bronchi. 



In no case can cough originate when the sensory ter- 

 minals of the vagus nerve are no longer 

 susceptible to irritation. In severe phlegmonous 

 diseases of the mucous membrane, cough is absent. The cough 

 center in the brain must also be in normal condition. It is 

 disturbed when great mental depression 

 exists. Therefore, when appreciable irritations (rales) are 

 present, unaccompanied by cough, the prognosis is an unfavor- 

 able one. 



The character of the cough. The character of the 

 cough varies with the species of animal. Healthy horses have 

 a strong, vigorous, loud, full-toned cough; cattle a sharper 

 defined, softer, toneless, prolonged cough, the glottis being 

 held open. The appearance of cough in animals is always ab- 

 normal; its character depends upon the disease which causes 



