324 CLINICAL APPLIED ANATOMY. 



products prevents absorption, and in exceptional cases the effu- 

 sion may exercise pressure on the lymphatic trunks. Aspiration 

 of the fluid facilitates absorption by relieving pressure on the 

 lymphatics and rendering more free the respiratory movements. 



Pleural effusions are naturally limited by the boundaries of 

 the pleural sacs. The costo-diaphragmatic reflections of the 

 pleural sacs are decidedly lower than the lower edges of the 

 lungs. The pleural reflection is about two inches below the 

 border of the lung in the nipple line, nearly four inches below it 

 in the mid-axilla, and about an inch and a half below it in the 

 line of the lower angle of the scapula. The left pleural sinus 

 overlies the stomach, and a change from resonance to dulness in 

 this area is very characteristic of the presence of fluid in the 

 pleural sac. The resonant gastric area is known as Traube's 

 semilunar space. The boundaries of this space are, the lower 

 border of the left lung above, the sloping lower edge of the left 

 lobe of the liver to the right, the left costal margin below, and 

 the anterior border of the spleen to the left. The space is 

 crossed midway between its upper and lower borders by the costo- 

 diaphragmatic reflection of the left pleural sac, consequently 

 fluid in the sac will encroach on the area of gastric resonance 

 much more than a solid lung does. 



The lowest part of the pleural sac lies in the mid-lateral line 

 of the body. It corresponds to the tenth rib or intercostal space, 

 and can be readily found by drawing a horizontal line round the 

 trunk at the level of the lower part of the first lumbar spine. 

 This is the part of the pleura in which fluid can be early found, 

 and from which it is late to disappear. (See also page 409.) 



When effusion occurs into the pleural sac, the negative pres- 

 sure in the sac is diminished and the mediastinum, being flexible, 

 very soon undergoes a suction displacement to the opposite side. 

 The heart lies in the mediastinum, and is displaced with it, 

 affording an index of its displacement. At the same time the 

 lung will become retracted towards its fixed point, which is its 

 root. In most cases of pleural effusion the manometer still 

 shows a negative pressure to exist within the thorax on the 



