ETIOLOGY 293 



No case of this disease has occurred in the state of Illinois since 

 December 29, iSSy, a period of more than four years and eight months. 



No case has occurred in the state of Pennsylvania since September 

 29, 188S, a period of four years within a few days. 



No case has occurred in the state of Maryland since September 18, 

 1S89, a period of three years. 



No case has occurred in the state of New York since April 30, 1S91, 

 a period of more than one year and four months. 



No case has occurred in the state of New Jersey since March 25, 1S92, 

 a period of six months, and no case has occurred in any other portion of 

 the United States within the past five vears. 



I do therefore hereby officially declare that the United States is free 

 from the disease known as contagious pleuro-pneumonia. 



J. M. RUSK, Secretary. 



Done at the city of Washington, D. C, this 26th day of September, 

 A.D., 1892. 



The time required for its eradication was only about five 

 years and the total expenditure was btit a little in excess of 

 $1,500,000. 



§221. Etiology. The specific cause of contagious pleuro- 

 pneumonia has not been fully demonstrated. The infection 

 may be introduced either by diseased cattle, or, less commonly, 

 by bearers such as cattle dealers, attendants, utensils, fodder, 

 dogs, etc. The sheds in cattle markets are very dangerous 

 centers for the dissemination of the disease. All cattle are not 

 equally susceptible. It is generally supposed that about one 

 animal in four is immune. The virus is spread principallj' by the 

 respired air. Infected cattle are reported to be able to trans- 

 mit it even during the period of incubation, before the symp- 

 toms are apparent. The disease is particulary infectious when 

 it is at its height and the animal remains capable of transmitting 

 the disease for eight or ten weeks or even longer, after the 

 infection, especially when necrotic foci remain in the lungs. 

 Walley estimates the duration of infectiousness in cases of 

 encapsuled necrotic foci to be as long as fifteen months. It is 

 said, but the evidence is not given, that the virus may be con- 

 veved by the respired air for as great a distance as forty yards 

 or more. In exceptional ca.ses, the contagium is transmitted 

 from the pregnant cow to the fetus. 



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