444 CONTAGIOUS PLEURO-PNEUMONIA 



No case has occurred in the state of New York since April 30, 1891, 

 a period of more than one year and four months. 



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

 1892, a period of six months, and no case has occurred in any other 

 portion of the United States within the past five years. 



I do therefore hereby official!}- 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 26tli day of September, 

 A.D., 1892. 



The time required for its eradication was only about five 

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

 $1,500,000. 



§ 353- 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, uten- 

 sils, 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 

 principally by the respired air. Infected cattle are reported to 

 be able to transmit it even during the period of incubation, 

 before the symptoms are apparent. The disease is particularly 

 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 infec- 

 tiousness in cases of encapsulated necrotic foci to be as long as 

 fifteen months. It is said, but the evidence is not given, that 

 the virus may be conveyed by the respired air for as great a 

 distance as forty yards or more. In exceptional cases, the 

 contagium is transmitted from the pregnant cow to the fetus. 



Pols and Nolen, in 1886, at Amsterdam, found micrococci 

 alway present in the exuded matter of the lungs. These mi- 

 crococci were about 0.9// in diameter and occurred either iso- 

 lated or in chains up to six in number. In the unstained 



