INFECTIOUS DISEASES OF CATTLE. 379 



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appears that the number of infected districts and of diseased animals 

 have rapidly diminished, and there is good reason to believe that if the 

 work is continued for a sufficient time it will meet with success. The 

 chief obstacle appears to be in connection with Ireland, where the con- 

 tagion is believed to be widely disseminated and where the activity of 

 the authorities is not so manifest as in England and Scotland. If the 

 contagion is allowed to linger in Ireland it is very plain that Great 

 Britain can never long remain free from it. 



The other infected European countries, though they maintain a vet- 

 erinary sanitary service, are not making satisfactory progress in eradi- 

 cating the disease. This is due partly to delays in carrying out the 

 provisions of the laws and partly to mistaken ideas as to the measures 

 which are necessary to accomplish the object. The United States was 

 the last of the countries, having old infected districts, which undertook 

 to stamp out this contagion, and, excepting Holland, it is the first to 

 reach success. 



The cause (etiology) of pleuro-pnenmonia. This is a contagious dis- 

 ease, and on the American continent, at least, it only arises by contagion 

 from a previously affected animal. It is, consequently, never seen here 

 except as the result of importing affected animals from the Old World. 

 When thoroughly stamped out it does not reappear, and if imported 

 animals continue to be properly inspected and quarantined we have 

 every reason to believe that pleuro-pneumonia will never again be seen 

 affecting the cattle of this country. 



The exact nature of the virus or contagion of lung plague has never 

 been determined. Efforts have been made by the methods now common 

 in bacteriology to cultivate and isolate the pathogenic germs, but up 

 to the present these have not been successful. Various investigators 

 have from time to time claimed the discovery of the specific germs of 

 the disease, but in every case these claims have proved to be unfounded* 

 The methods now in use for such investigations do not appear proper 

 for the discovery of these germs. They do not multiply in any of the 

 substances which are used to cultivate other disease germs, and they 

 are not revealed by the most advanced methods of microscopical 

 research. That this disease is caused by microorganisms of some kind 

 appears certain from our knowledge of the cause of other contagion* 

 diseases, and these no doubt will l>e discovered when our methods of 

 research are sufficiently advanced. 



As the specific cause of the disease is not known, we arc, of course, 

 uncertain in regard to many of the characters of the virus and of the 

 conditions necessary for it to retain its virulence when outside of the 

 animal body. Some investigators and writers arc of the opinion that 

 the disease can only be contracted by an animal coining near enough to 

 a living diseased animal to receive the contagion directly from it. They 

 hold that the contagion is expired with the air from the affected lungs, 

 and that it must l>c almost immediately inspired by another animal in 



