252 GRAZING CATTLE DISEASES 



into prominence in this country owing to its frequent 

 recurrence among live cattle imported from Canada and the 

 United States of America, and on account of its having been 

 repeatedly mistaken for pleuro-pneumonia. The difference 

 in the post-mortem appearances and in the actual seats of the 

 two diseases makes it extremely unlikely for any one versed 

 in morbid anatomy to mistake the one for the other. In 

 pleuro-pneumonia contagiosa the true seat of the disease is 

 not in the bronchial tubes, although the smaller of these 

 become gorged, as already stated. 



Broncho-pneumonia is not a " specific " disease like pleuro- 

 pneumonia contagiosa, but one which originates spontaneously 

 when animals are exposed to cold and wet, 1 especially after 

 being heated, as cattle are during transit by rail and sea. 

 It may fitly be compared with influenza in the human 

 species, not of the epidemic type, but of the old and familiar 

 form of a severe cold. It is termed "cornstalk disease" in 

 America, because it appears in autumn, when the cornstalks 

 are past their best and beginning to decay. The true seat 

 of the disease in broncho-pneumonia is the air-passages, 

 large and small. Although the lung-parenchyma, through 

 which the multitudinous ramifications of the air-tubes pass, 

 naturally becomes congested, it is not subject to such changes 

 as are found in a case of pleuro-pneumonia contagiosa. It 

 is very different with the bronchial tubes, more especially 

 the smaller of them. The desquamation, or, in common 

 language, peeling off, of the columnar cells forming the 

 epithelial lining of the air-passages indicates the seat of the 

 disease. As the alteration of structure does not extend to 

 the blood-vessels, nature may in time repair the injury, if 

 death be not induced at the acute stage of the disorder. 



Not only is the fibrinous exudation of pleuro-pneumonia 

 absent in the air-passages, but pus and degraded epithelial 

 debris take its place, and are expelled from the lungs by 

 the act of coughing in a manner corresponding to expectora- 

 tion in a human being. The differences described are 



1 See a treatise by Dr Frank S. Billings on " Cornstalk Disease," in 

 which the cause is attributed to a micro-organism which is found on the 

 leaves of maize ; but as the organism is probably one of the commonest 

 kind, there is not sufficient proof that it is actually the cause of the 

 injury. 



