120 CLINICAL DIAGNOSTICS. 



animals, pulmonary emphysema, bronchitis, hydrothorax ; or 

 if the expiration is painful: pleurisy, pneumonia, pleurodynia. 

 The cough is s t r o n g if the elasticity of the lungs is normal 

 and no pain attends the act. 



The length of the cough is determined by the 

 force with which the pulmonary air is held repressed by the 

 closed glottis. If the pressure is great, the glottis will be 

 suddenly forced open and the cough will be short. If the 

 glottis is not completely closed (paralysis of the arytenoid 

 cartilage — roaring) or the repression of the air causes pain 

 (pleurisy), the cough is long — prolonged. 



The depth and magnitude of the cough 

 depend partly upon the force and duration of the cough im- 

 pulse. The magnitude is influenced by the quantity of ex- 

 pelled air. We speak of a deep and a shallow cough. 



The cough sound is dependent upon the force of 

 the cough impulse, the tension of the vocal cords and the spe- 

 cial condition of the surface of the mucous membrane. The 

 sound may be loud, low, clear, dull, sharp, whistling, dense, 

 hollozv, loose, moist, dry. 



The cough is moist when easily movable masses of mucus 

 are collected below the larynx ; it is dry when either no exu- 

 date is present or only small, viscid accumulations are in the 

 air passages. 



The ''return sound'' of the cough (Hus- 

 tenrueckstoss). Each cough is followed by a short, deep in- 

 spiration. If the glottis is not fully open at the moment this 

 inspiration takes place, the air rushing in causes the partially 

 stretched vocal cords to vibrate, causing a harsh, short, laryn- 

 geal stenotic sound to be emitted. It is heard in paralysis of 

 the larynx (paraplegia, hemiplegia) and in severe inflamma- 

 tory swelling. 



Expectoration. The act of coughing tends to eject 

 masses of mucus, exudate, etc., from the bronchi, trachea, and 

 larynx. Animals do not expectorate because that which 



