118 DISEASES OF THE HOG. 



men in the pig; but is not often noticed until after 

 death. 



Causes: Emphysema is often the result of over 

 exertion as when a pig is pursued by a dog or man 

 the increased amount of air taken in overfills the 

 air cells, which distends them to such a degree that 

 they may rupture and thus allow the air to extrav- 

 asate into the lung tissue, or the air cells do not 

 contract to their natural size. It is also the result 

 of lung disease. 



Symptoms: Slight emphysema cannot be de- 

 tected in the pig until after death, but when so 

 considerable as to produce observable effects it is 

 always attended with dyspnea (difficult breathing), 

 which is very distressing to the pig and is often 

 associated with thumps, or rather it is often mis- 

 taken for thumps. Pigs often die suddenly from 

 emphysema. Cough is sometimes present; during 

 severe paroxysms there may be an expectoration of 

 a clear fluid or it may be frothy; the animal will 

 stand during the intervals of the paroxysms with 

 its mouth open and turning its head to one side 

 'with the nose pointed upwards. In post mortems 

 that have been made of animals that died 

 of emphysema we find that the lungs do 

 not collapse on opening the chest, but 

 sometimes on the contrary expand, as if 

 previously compressed by the ribs and dia- 

 phragm. This is the result of the inelastic or rigid 

 condition of the membrane which forms the air 

 cells. In consequence of this rigidity they do not 

 contract upon the aiv which they contain and there- 



