IMPORTANCE OF COUGH IN A CLINICAL SENSE. 
551 
cough ; but when the irritability of the sensory nerves is de¬ 
stroyed as by infiltration of the subinucosa, cough of necessity 
is absent. T^he impossibility to produce cough when the sen- 
soriuin is depressed is always a bad omen. The forcible expira¬ 
tion, that is cough, is followed by a more or less rapid entrance 
of air into the air-passages. This gives rise to a slightly wheez- 
ing inspiratory sound, especially marked in angina laryngea and 
confirmed roarers. In the earliest stages of a laryngitis acuta 
this wheezing inspiratory sound is often the only diagnostic 
symptom, barring a slight rise of temperature. 
Animals have no motive to cough and for this reason cough 
must be a valuable agent from a diagnostic standpoint. But 
we must remember that cough is under the influence of the will 
of the animal to a certain extent. We often see the horse make 
desperate attempts to modify the intensity of the cough. He 
will stretch the neck, move the lips as if mumbling, shake the 
head, paw and finally an evasive cough makes its appearance. 
Of the various mucous membranes which when irritated 
would cause the animal to cough, the one of the larynx ranks 
foremost next that of the bronchi and finally that of the trachea, 
while the alveolar parenchyma has no nerves which might in¬ 
duce cough. The mucosa of the trachea will permit, when in a 
normal state and when diseased, a great deal of insult before 
cough is produced. For instance, swabbing it during an aryte- 
nectomy gives negative results with regard to cough. Artificial 
cough produced by pressing with the fingers upon the region of 
the arytenoids or superior extremity of the trachea will as a rule 
cause the animal to cough from one to four times in succession. 
To induce the animal to cough quite some compression is re¬ 
quired, while cough following slight pressure upon these parts 
is suggestive of an irritative state. 
Of the many acute and chronic diseases of the respiratory 
tract accompanied by cough, the following are of special inter- 
Hlt from a clinical standpoint: 
1. Pharyngo-laryngeal lesions. 
2 . Acute and chronic laryngitis. 
