186 APPLIED PHYSIOLOGY 



these is promoted by the pulsation of the adjoining 

 artery. Secondly, a peripheral set which run in the 

 fibrous tissue between the lobules, and often into the 

 lymphatic plexus of the pleura. The flow in these is 

 kept up by the respiratory movements of the lung. 

 It will therefore be most active where these movements 

 are freest e.g., in the lower and anterior parts of the 

 lung, and most sluggish where expansion is least e.g., 

 at the apices. This helps to determine the greater 

 liability of the apices to become the seat of tuberculosis. 

 Both of these are in communication with the air cavities 

 by means of stomata, and are provided with valves, 

 so that any foreign particles which have successfully run 

 the gauntlet of the arresting mechanisms of the nose and 

 air passages are finally conveyed either to the bronchial 

 glands or pleura. 



It is in this way that disease of these parts is so often 

 set up. Tubercle bacilli, for instance, get lodged in the 

 bronchial glands, and set up there a local tuberculosis, 

 which may become the starting-point of a general infection; 

 or particles of dust pass from the alveoli to the pleura! 

 cavity, and are thence taken up into the costal pleura, 

 and may thus excite a pleurisy by purely mechanical 

 means.* A consideration of these facts still further 

 emphasizes the importance of keeping the nose and 

 other protective mechanisms of respiration in a healthy 

 condition. 



The respiratory movements favour absorption from 

 the pleural cavity, acting like a * pleural pump ' through 

 the stomata, and as these movements are more extensive 

 * Grawitz, Berlin. Ktin. Woch., 1897, xxxiv. 621. 



