280 HISTORY OF 



pagated by infection. Whatever be the general 

 state of the atmosphere, we learn from experi- 

 ence, that the noxious vapours, though but singly 

 introduced at first, taint the air by degrees ; every 

 person infected tends to add to the growing ma- 

 lignity ; and, as the disorder becomes more ge- 

 neral, the putrescence of the air becomes more 

 noxious, so that the symptoms are aggravated by 

 continuance. When it is said that the origin of 

 this disorder is unknown, it implies, that the air 

 seems to be but little employed in first producing 

 it. There are some countries, even in the midst 

 of Africa, that we learn have never been infected 

 with it, but continue for centuries unmolested. 

 On the contrary, there are others that are gene- 

 rally visited once a-year, as in Egypt, which 

 nevertheless seems peculiarly blessed with the 

 serenity and temperature of its climate. In the 

 former countries, which are of vast extent, and 

 many of them very populous, every thing should 

 seem to dispose the air to make the plague con- 

 tinual among them. The great heats of the cli- 

 mate, the unwholesomeness of the food, the sloth 

 and dirt of the inhabitants, but, above all, the 

 bloody battles which are continually fought 

 among them, after which heaps of dead bodies 

 are left unburied, and exposed to putrefaction ; 

 all these, one might think, would be apt to 

 bring the plague among them ; and yet, never- 

 theless, we are assured by Leo Africanus, that 

 in Numidia the plague is not known once in a 

 hundred years, and that in Negroland it is not 

 known at all. This dreadful disorder, therefore, 



