THE RESPIRATORY SYSTEM 85 



air contained in the air cells being absorbed and per- 

 mitting them to collapse. 



Lesions. The affected lung tissue collapses and does 

 not crepitate. It is red or reddish-brown in color, feels 

 dry, is tough, and sinks in water. If the condition is 

 of long standing, the affected area becomes darker in 

 color and is designated cornification. In some instances 

 the atelectic areas become spleen-like, due to the develop- 

 ment of fibrous tissues, and this is termed splenization. 



Atelectasis diminishes the breathing capacity, which 

 is the only symptom characterizing the condition. Small 

 areas of the lung will not produce visible symptoms. 

 This condition is usually associated with other disease 

 processes, the symptoms of which mask those of atelec- 

 tasis. 



Atelectasis occurs in the lung of swine as a result of 

 swine plague, hog cholera, bronchitis, pneumonia, and 

 pleurisy, as well as of other less important diseases. 



Emphysema 



Pulmonary emphysema has been observed in swine 

 but is not of common occurrence. It is due to con- 

 ditions that favor the inflation of the lung with excessive 

 quantities of air. Bronchopneumonia is occasionally 

 associated with emphysema. The affected areas are 

 soft, spongy, anemic, and project beyond the surface of 

 the lung. 



Edema 



Pulmonary edema is not common in swine kept under 

 ordinary conditions, but it is often found in those that 

 are hyperimmunized for the production of anti-hog- 

 cholera serum. Those having experience as serum pro- 

 ducers occasionally have a swine die of pulmonary 

 edema at the time or immediately after the intravenous 

 injection of quantities of virulent blood. 



In comparison to their size, swine have a relatively 

 small lung. The virulent blood that is used in hyper- 

 immunizing is defibrinated but contains both the red and 



