THE LUNG PLAGUE. 37 



of pleuro-pneumonia iu these animals. Delafond made similar observa- 

 tions, bnt lias created some confnsion by including cases of tuberculosis 

 with others of pleuro-pneumonia. In 1839, a cow that had gone six 

 months in calf was killed in Fribourg, Switzerland, while suffering from 

 pleuro-pneumonia. The foetus presented signs of the malady. It is 

 common for calves to take the disease soon after birth, and I have 

 shown in a government report that the contagious cattle diseases of 

 Ireland, including pleuropneumonia, were mainly due to the active 

 trade in sucking- calves between the large towns of England and 

 Dublin. 



It has been necessary frequently to refer to animals that are suscepti- 

 ble and insusceptible to attacks of pleuro-pneumonia. This has been 

 ascribed by some to constitutional or inbred resistance or weakness. 

 It is due to what pathologists term, for want*of a better name or expla- 

 nation, idiosyncrasy. At times it appears that young animals resist 

 the disease better than old ones ; and Mr. Harvey, of Glasgow, found 

 that by communicating the disease to yearlings and two-year-olds, he 

 had fewer deaths than when he had it among his pregnant and milch 

 cows. But, as Sauberg has observed, outbreaks occur in which the 

 older animals seem to bear up better than the young ones, and it is 

 difiQcult, on present data, to establish any rule on the point. 



It may be accepted as proved that all cattle, whatever their age, 

 breed, sex, conditiou, &c., are susceptible to pleuro-pneumonia until 

 they have been once seized, and then it is rare to witness a second 

 attack. An insusceptible animal is, therefore, an animal that has once 

 had the disease, either in a mild or latent, or severe and apparent, form. 



It is, however, certain that a degree of insusceptibility may be traced 

 in animals that have never been affected, and we are quite at a loss to 

 account for this. Similar observations are made in relation to all fevers 

 affecting men and animals. A person has been known to nurse many 

 during an outbreak of yellow fever, escape and live for a year, when 

 the disease has reappeared, and the individual who has been proof 

 against the malady one year has been among the first to die from it the 

 next. 



Not a few cases have been recorded of rinderpest — and I have wit- 

 nessed a remarkable one — of a cow standing for weeks by animals that 

 died of the malady and which never showed signs of it. More strange than 

 this are two observations, one in Lyons in 1853, and the other in Vienna 

 in 1805, of dogs which could not be rendered rabid by the bites of, and 

 inoculations from, undoubtedly rabid dogs. For the tune, at all events, 

 we must rest satisfied with the pathologist's explanation that these 

 animals had' a peculiar constitutional immunity or idiosyncrasy. 



CONTAGION AND INFECTION. 



Not only have thecnies in relation to the cause or combinations of 

 causes which may lead to the development of pleuro-pneumonia been 



