t866 human anatomy. 



thorax, the air entering the pleural cavity ; in traumatic interlobular emphysema, or 

 pneumothorax, the chest on the affected side will be hyper-resonant, the vesicular 

 murmur will be feeble or absent, and in the latter there may be amphoric breathing 

 and — if there is a coincident effusion — metallic tinkling ; hcemoptysis, not an invaria- 

 ble symptom in either these injuries or lacerations by fractured ribs, probably because 

 they are usually on the external lung surface and remote from the larger bronchi 

 (Bennett) ; hcemothorax, indicated by percussion dulness gradually extending upward, 

 by weakness or absence of respiratory murmur, by bronchial breathing over the 

 compressed lung, and by absence of vocal fremitus. 



Penetrating wounds of the lung will have many of these signs plus the escape 

 of blood from the external wound. In the absence of haemoptysis, the possibility of a 

 wound of the costal pleura and of an intercostal or internal mammary artery 

 causing haemothorax, dyspnoea (from pressure), and hemorrhage, apparently in- 

 fluenced by respiration, should be borne in mind. Wounds of the pleura without 

 involvement of the lungs are rare, the visceral pleura being closely adherent to the 

 lung surface and the two pleural layers in close contact with each other. At the base 

 of the pleura, where a potential cavity (page 1859) — costo-phrenic sinus — exists 

 between the costal and diaphragmatic layers, a wound could penetrate both layers 

 and the diaphragm and open the abdominal cavity and involve the liver or spleen 

 (page 1788) without implicating the lung, which even in forced inspiration does not 

 descend to the bottom of this sinus. Wounds of the pleura are apt to be followed 

 by pneumothorax and by collapse of the lung, which is partly driven back towards 

 its root and the vertebral column by the atmospheric pressure from without, and 

 partly drawn there by its own elasticity even when the pressure within and without 

 is equal. In operations for empyema this collapse of the lung may take place, but 

 is infrequent because the pulmonary tissue has often already undergone considerable 

 compression, and because the atmospheric pressure is resisted by preformed pleural 

 adhesions. 



General emphysema is often associated with wounds of the lungs and pleura. It 

 may be due to {a) escape of air from a pneumothorax into the subcutaneous tissue 

 during respiratory movements, or {b) escape of air direct from injured lung- tissue 

 when pleural adhesions about the wound prevent the formation of a pneumothorax. 

 Its occasional occurrence in laceration of the lung without external wound and 

 without involvement of the pleura has been explained {vide supra). It may follow 

 a non-penetrating wound of the chest if the opening happens to be valvular, so that 

 the air drawn in during respiratory movements cannot make its exit by the same 

 channel. 



Pneuniocele — hernia of the lung — is rare as a result of thoracic wounds because 

 the elasticity of the lung-tissue and atmospheric pressure tend to cause collapse and 

 retraction of the lung rather than protrusion. When it is primary it therefore follows 

 {a) a limited and oblique wound through which air cannot freely enter the pleural 

 cavity, although the egress of the lung under the pressure of muscular effort or the 

 strain of coughing is unopposed ; or {b) a very large wound when the lung escapes 

 at the moment of injury (Bennett). Treves says that these recent herniae are most 

 common at the anterior part of the chest where the lungs are most movable, and that 

 the injuries that cause them are often associated at the time with violent respiratory 

 efforts. 



Pneumocele is more apt to follow the rare wounds that divide only the costal pleura, 

 as a wound of the lung itself tends to the production of a pneumothorax — which 

 would lead to collapse of the lung — and instantly lessens the pressure of air con- 

 tained in the lungs and trachea, one of the forces favoring protrusion. 



Diseases of the pleurae and lungs can here be very briefly summarized only with 

 reference to the anatomical factors. 



Pleurisy is at first attended by a " friction-sound" due to the roughening of the 

 opposed surfaces of the visceral and parietal pleurae by fibrinous exudate. Later it 

 may be lost by reason of (a) the temporary disappearance of the roughness, ib) 

 the formation of adhesions between the surfaces, or (r) their separation by effusion. 

 It is lost momentarily when the patient holds his breath, which will serve to differ- 

 entiate it from a pericardial friction-sound. As the costal pleura, the intercostal 



