312 History of Animal Plagues, 



lent matter from such beast. There are many instances where good 

 fences, and other effectual means of exclusion of whatever could bring 

 the infecting matter, have prevented the cattle in particular places from 

 sutiering by the contagion, though surrounded on every side by numbers 

 of beasts seized with the disease. In some of these places the cattle 

 have escaped to the last. In others, after a time they have taken the 

 infection in consequence of known accidents, which occasioned the in- 

 troduction of the contagion, from the actual conveyance of it by some- 

 what that had received the virulent matter from a diseased beast. 

 Where the neighbouring infected cattle were, in these instances, all on 

 one side the place in which those that escaped were confined, this ex- 

 emption of them might be reasonably imputed, as it has been, to the 

 wind blowing the contrary way, and carrying off the contagious effluvia 

 that might have otherwise reached them. But this solution of the 

 difficulty cannot hold good, when, as has been frequently the case, the 

 free place where the cattle escaped was surrounded by infected beasts 

 on every side. The determination of this point is not merely a specu- 

 lative object, for it settles the proper nature and limitations of the means 

 to be used for the prevention of the communication of the infection, 

 and rightly confines them to such as regard the hindering the contact 

 of diseased beasts with the sound, or the exclusion of bodies which may 

 convey the virulent matter from the one to the other. 



' From the facts which have appeared respecting the disease, there 

 is reason to infer that the contagious matter retains its infecting power 

 a considerable time. The contagion is believed in several instances, from 

 very strong circumstances, to have been conveyed to remote places in 

 bodies transported by sea, as the known intercourse with the countries 

 whence it was presumed to be brought palpably suggested that manner 

 of its introduction, which could not be otherwise accounted for. Some 

 of the later experiments with regard to the inoculating cattle with the 

 disease show this fact with greater certainty of proof. The precise 

 limitation of period in which the infecting matter will keep its power 

 is not, however, well ascertained by any observations or trials 5 but 

 there is room to conclude that, under some circumstances, it will act 

 at a considerable distance of time from its being generated. We see 

 the variolous matter will communicate the small-pox after many months; 

 and there is no foundation for any doubt of the analogy betwixt the 

 contagion of that and of the murrain in this particular. But it is a 

 matter of great consequence, and this should be decided by adequate 

 experiments. Because the knowledge of it is of great moment, in 

 judging of the proper means and regulations for preventing the intro- 

 duction of the contagion into places free from it. 



