PREVENTION OF PLEUKO-PNEUMONIA. 169 



the blood, travels to its own particular seat, and there, in its 

 ravages, produces all the acknowledged signs. Thus, for instan^^e, 

 the special poison or virus of rabies produces rabies ; that of 

 glanders, gives rise to glanders ; and the same law prevails with 

 respect to small-pox, farcy, cow-pox, and others which are known 

 as contagious, and are propagated only by means of the morbid 

 products of the disease. It does not, however, appear that 

 pleuro-pneumonia spreads itself by these means so much as by 

 and through the medium of the atmosphere, the poisonous pro- 

 ducts being evolved from diseased animals and carried by the 

 air in an invisible and imponderable form, constituting the 

 process known as infection. All the experiments hitherto made 

 distinctly show that the introduction of blood, serum, &c., of 

 diseased animals to healthy ones gives rise to a septic or putrid 

 blood-poisoning, and in this particular, pleuro-pneumonia. 

 resembles other diseases, as strangles in the horse, and some of 

 the various forms of anthrax fevers — the original disease never 

 being produced by inoculation. 



Dr Willems laid some stress on the preservative influence of 

 the inoculation, and gives instances of annuals remaining alive 

 and well although they continued to be located with diseased 

 and dying cattle ; while in his own town of Hasselt, where no 

 less than 2000 animals are fed, during the extreme prevalence of 

 the pest in 1852, the cattle of several of the large distillers entirely 

 escaped on which no inoculation had been performed. This has 

 been the oft-repeated experience of those who have since given 

 the matter consideration, and the only plea that can be advanced 

 in support of the theory is that of the so-called " virus " acting 

 as a derivative, or more simply, just as a blister or seton, b}^ 

 diverting the course of the ailment ; and the last portion, like- 

 wise unexplained to the present moment, is the uncertainty of 

 the time over which the prophylactic influence spreads, a question 

 which is rendered more and more profound \)j the conflicting 

 evidence which is being daily produced. Inoculated animals 

 have resisted the disease up to various periods. We have 

 witnessed attacks of veritable pleuro-pneumonia within ten days 

 after the operation, and also at difterent times up to a year or 

 thereabouts, and at the same time herds of cattle, contiguous or 

 at a distance, have exhibited exactly the same phenomena 

 although no inoculation had been 2:)ractised, and some have 

 remained free altogether. 



Dr Willems, besides contending that no failures occur with 

 him, asserted that there is no susceptibility to a second inocula- 

 tion in those previously inoculated, but on this point no reliance 

 can be placed. Professor Simonds* demonstrated what has since 

 been j)roved hundreds of times in the dairies of Great Britain, that 

 * Second Report to tlie Eoyal Agricultural Society, June 1, 1853. 



