Coughing. 453 



of the opposing rima glottidis and drives everything in the larynx 

 and trachea (to a certain extent, too, that which is in the pharynx) 

 out into the mouth (Krehl). Foreign bodies, exudates, etc., 

 lodged below the bifurcation of the wind pipe may also at times 

 be carried out ; but there is a chance that objects in this position 

 may be driven deeper into the bronchial tubes (Krehl). Expec- 

 toration, removal of such substances from the chest (or better, 

 the lungs) is accomplished primarily by the ciliated epithelium 

 and the upward convection, by this means, of the mucous vehicle; 

 the stimulus to cough acting upon the expectorate (sputum) 

 only from the level of the bifurcation upwards. 



These defensive mechanisms may be of no efficience it the 

 harmful chemical, bacterial or mechanical agents are of such a 

 character that they paralyze and destroy the epithelial cells and 

 their ciliary action, and the phagocytes or the smooth muscles 

 of the bronchial tubes, or if the foreign bodies are held firmly 

 because of swelling of the bronchial mucous membrane, or if the 

 obstruction be tightly fixed because of its size; and may be in- 

 effective because of lesion or disease of the motor or sensory ap- 

 paratus involved in coughing movements. The retention of for- 

 eign bodies and pathological secretions may be followed by 

 asphyxia, because of the obstruction to the air passages ; or may 

 be the cause of such serious effects as gangrene of the lung, etc., 

 as the obstructing substances usually carry bacteria with them, 

 (Under normal conditions the pulmonary alveoli, the bronchial 

 tubes and trachea are sterile, because in the first place the bacteria 

 entering with the air lodge on the mucous membrane of the 

 nose and pharynx, where the current of air first strikes at an angle 

 and sweeps over the moist surface, and in the second place be- 

 cause they are carried up and out by the activity of the ciliated 

 cells.) 



The act of coughing may itself be dangerous. In conditions 

 which increase the irritability of the respirator}- mucous mem- 

 brane or of the pleura T inflammations) frequent coughing is ex- 

 cited without there being anything requiring removal in the air 

 passages. The violent expiratory force of coughing raises the 

 intra-pulmonary air pressure and may thus cause pulmonary dis- 

 tension (emphysema) : it interferes with the return flow of venous 

 blood into the thorax and heart, to the extent that the latter 

 may be practically empty, raises the arterial pressure all over 

 the body, and may cause rupture of the vessels (KrehlV The 



