METHODS OF DISSEMINATION 19 



The practice of taking breeding hogs to dis- 

 tant points to mate them is a fruitful source of 

 new herd infections, and in more than one instance 

 we have known the virus to be carried from one 

 farm to another as a result of neighbors exchang- 

 ing help during butchering time. Small streams 

 to which many hogs have access may also become 

 polluted and carry destruction to herds below the 

 one in which the original infection occurs. Show 

 hogs returned from fairs often contract hog chol- 

 era en route or during their contact with other 

 hogs in the show ring, only to infect the herds they 

 represent when they return home. 



Besides the regular channels of infection which 

 we have already indicated, and which severally 

 are responsible for most new outbreaks of hog 

 cholera, there are almost an infinite number of 

 casual carriers of the virus, such as crows, spar- 

 rows, buzzards, pigeons, and various predatory 

 animals. These, by feeding in infected yards or 

 on carcasses of hogs dead of cholera, may carry 

 the infection to clean territory, but the probabili- 

 ties are that in most localities the number of herds 

 thus infected is relatively small. 



In recent experiments Dr. Marion Dorset has 

 found it difficult to transmit hog cholera from 

 herd to herd by employing attendants, pigeons 

 and sparrows as agents of transmission, and in 

 our own experiments we have failed in a surpris- 



