34 The Lung Plague of Cattle. 



tant parts of the body of a sound beast rarely determines 

 the characteristic lesions in the lungs, in place of which 

 it induces in the seat of inoculation an exudation, less 

 abundant, as might be expected from the greater density 

 and resistance of the integument, but which can, like the 

 morbid lung products, be inoculated on sound animals 

 ■with protective effect. It seems probable that the poison 

 is multiplied in both cases, but that the special loose and 

 susceptible texture of the lung renders its production in- 

 comparably more abundant, as the -continuous ingress 

 and egress of air through the diseased organ renders it 

 immeasurably more infecting. 



Hoio Long is a Diseased Animal Infecting ? 



Proof is wanting as to the infecting nature of the dis- 

 ease during the incubation stage. If negative evidence 

 were of any value in a case of this kind it would be easy 

 to adduce cases in which the removal of an animal as 

 soon as it showed symptons of the plague had apparently 

 saved the rest of the herd. In other cases the malady 

 has been eradicated from a herd by careful watching and 

 the prompt removal of every animal as soon as sickness 

 appeared. The period of greatest virulence is that at 

 which the fever runs highest and when the lung is being 

 loaded with the morbid exudation. 



But it must not be inferred that with the subsidence of 

 the fever the danger is removed. It is a matter of every 

 day observation that animals which have passed through 

 the fever, that are now thriving well or giving a free sup- 

 ply of milk, and to ordinary observers would appear in 

 perfect health, retain the power of transmitting the dis- 

 ease to others. This may continue for three, six, nine, 

 twelve or according to some even fifteen months after all 

 signs of acute illness have disappeared. This is easily 

 explained : The tendency of the disease is to interrupt 

 the circulation in the most severely affected parts of the 

 lung ; this accordingly dies, and the exudation immedi- 



