54 DISEASES OF POULTRY. 



one step beyond congestion. If a bird is affected with 

 congestion of the lungs and does not die or recover 

 within a few hours, the disease may develop into 

 pneumonia. In this disease there is not only disten- 

 tion of the bloodvessels, as with congestion, but there 

 is thrown out from these vessels a liquid which fills 

 the air-ceirs and by coagulating forms a semi-solid, 

 gelatinous substance, that excludes the air and renders 

 the lungs useless for respiration. The lung is then 

 darker in color than in health, and when pressed upon 

 gives a sensation of firmness and solidity comparable 

 with the liver; therefore, the lung in that condition is 

 said to be hepatized. 



Causation. — Two factors are believed to work to- 

 gether in the production of pneumonia. There must 

 be the conditions which produce congestion, viz., 

 refrigeration, chilling of the surface of the body, dis- 

 turbance of the general circulation from some cause, 

 inhalation of irritating vapors or plethora ; and there 

 must apparently be something else. This additional 

 factor is in many cases, at least with the larger animals 

 and man, a species of the bacteria. The same proba- 

 bly holds true with birds. 



It appears that the bacteria which change congestion 

 into inflammation are germs which under ordinary cir- 

 cumstances are harmless, and which may often be 

 found upon the surface of the mucous membrane of 

 healthy animals. Now, if there are simultaneously in 

 the same animal, germs which are sufficiently active, 

 and, also, a congestion of the lungs, there have been 

 brought together the conditions required to develop 

 pneumonia. 



Symptoms. — The symptoms are similar to those seen 

 in pulmonary congestion. The breathing is rapid 



