THE RESPIRATORY SYSTEM 95 



Etiology. Obstructed outflow of blood from the 

 vena cava, with engorgement, is the principal cause of 

 hydrothorax. Chronic disease of the cardiac valves and 

 chronic pneumonia are the most common causes of 

 obstruction of the outflow of venous blood from the 

 vena cava. Tumors, abscesses, and malformed thorax 

 may also be responsible for the causation of pneumo- 

 thorax. 



Lesions. Accumulation of varying quantities of a 

 pale yellow fluid in the thorax is the characteristic lesion, 

 and in addition the primary lesions in the heart or lung 

 are usually evident. The accumulated fluid will com- 

 press the lung. 



Symptoms, It is not possible in the beginning to 

 detect any particular symptoms. Those produced by 

 the accumulated fluid are frequently so overshadowed 

 by the primary condition that it is not possible to clini- 

 cally diagnose hydrothorax until the advanced stages. 

 There will be difficult respiration, and if the thoracic 

 wall is not too thick a splashing sound may be noted 

 synchronous with the heartbeat. An exploratory punc- 

 ture with a small hypodermic needle will usually result in 

 the discharge of serous fluid. 



Treatment. Temporary relief may be obtained by 

 withdrawing the fluid from the cavity, but permanent 

 results cannot be expected until the primary causative 

 factor has been removed or overcome. 



Hemothorax 



Hemothorax is a condition of the escape and accumu- 

 lation of blood in the thoracic cavity. It is not a recog- 

 nized clinical entity, particularly in relation to swine, 

 yet it does occur, and is sometimes observed by inspectors 

 of meat-food products. 



Etiology. This condition is observed in swine that 

 have been transported to market, and the affected swine 

 at the time of autopsy show evidence of having been 

 injured, probably while in transit. The injury may be 

 a puncture, wound, or a contusion. 



