124 Anatomy Applied to Medicine and Surgery. 



plies the pleura as well as the diaphragm. In the next 

 stage of pleurisy, i.e., the stage of effusion, the following 

 conditions may be present : 1. The lung may be com- 

 pressed, but not to any great extent, unless the chest be at 

 least two-thirds full of fluid, since the retractility of the 

 lung prevents any decided compression, unless this amount 

 be present. In cases of extreme effusion the lung may be 

 forced into a bulk, one-third or even one-sixth, its normal 

 size. 2. The heart may be displaced. Normally the 

 heart and the mediastinum are held in position by the re- 

 traction caused by the elasticity of one lung counterbalanc- 

 ing that resulting from the elasticity of the other, and hence, 

 when one lung is, even slightly compressed, its power of 

 retraction is lessened, while the retractility of the sound 

 side draws the mediastinum and heart over towards itself. 

 This is the probable explanation of the slight displacement 

 of the heart found in the early stages of pleurisy, when 

 only a small amount of effusion is present. But, when 

 the quantity of fluid is markedly increased, then it 

 mechanically forces the heart and the mediastinum over 

 towards the sound side. 3. Displacement downwards, of 

 the liver, stomach and spleen. This occurs when the 

 amount of fluid is considerable, so that its weight, mechan- 

 ically, lowers the arch of the diaphragm, and dis- 

 places these organs downwards. 4. Disappearance of 

 the tympanitic sound in Traube's semilunar space. This 

 space is situated on the left side, is half-moon in shape, and 

 is about four inches in width; the upper limit extends 

 from the sixth costal cartilage in front, and passes in a 

 curved manner, with the concavity downwards, to the 

 tenth rib, i.e., to the anterior border of the spleen. The 

 space is bounded, inferiorly, by the lower margin of the 

 thorax. The tympanitic sound, elicited in the normal 

 state by percussion over this region, depends for its pro- 



