History of Animal Plagiies. 351 



' The contagious matter will preserve its infecting quality for a long 

 space of time, as we have reason to conclude, as well from facts respect- 

 ing the transmission of it into distant countries, and some experiments 

 regarding inoculation with it, as from its analogy to the variolous matter 

 of the small-pox, which retains its virulent power for many months. 

 There is room to conclude that the contagion of the murrain has been 

 conveyed by the raw hides of beasts in particular, to places where it has 

 taken elFect at a considerable space of time after its production 3 and if 

 it can be so preserved in the skins of dead beasts, why not in the hair 

 of those which are living ? It must be granted, indeed, that in the skins 

 of the living it is more exposed to be accidentally carried off than in those 

 of the dead j but there is no certainty, nevertheless, that it will be entirely 

 cleansed away thus under a long time. Even forty days, therefore, do 

 not give a security against the danger of a conveyance of the infection 

 that way, where beasts are removed from the diseased cattle to the sound. 

 I am aware it will be advanced, in contradiction to this, that the skin 

 of a living beast being exposed to the air, the contagion will be dis- 

 sipated in the forty days, and not preserved, as in the parts of the hides 

 of dead beasts, to which the air may not have had a like access. But 

 I deny the truth of the principle on which this conclusion depends. It 

 has, I grant, been a prevailing notion, borrowed from ancient writers, 

 and delivered down by those of succeeding times without any examin- 

 ation of the relative facts, that the contagion of the febrile diseases 

 resided in volatile effluvia, which exhaled in the air, and flew off in a 

 short time from bodies that had received them. There is not, how- 

 ever, in reality a greater error subsisting than this established notion. 

 Many experiments on the variolous matter have evinced the contrary 

 by showing that it will keep its virtue, and serve for the purposes of in- 

 oculation, for a great length of time, though exposed to the air, 

 provided it be defended from excessive cold, and such moisture as 

 would render it mouldy. A less extensive field of observation, but 

 sufficient to verify the principle, confirms to us that the analogy 

 holds good as to this point, on the contagious matter of the murrain, 

 and others of a similar nature. If, therefore, the virulent matter will 

 not with certainty be taken off by accidental means from the skins of 

 beasts, nor lose its infecting power by exposure to the air under a long 

 time, the preventing 'for forty days the communications of cattle whose 

 skins may have some share of it on them, with any others, is not a full 

 security against their conveying the infection, if afterwards they be suf- 

 fered to mix with the sound. The establishment of this species of 

 quarantine or prohibition of removal for forty days is consecjuenlly in- 

 sufficient to the end in that view. But, besides the uncertainty of its 



