This phenomenon is one of the rarest that has ever been observed, for nothing is more constant than the composition of the air; and in no respect has nature been more careful in the preservation of organic life. Never have naturalists discovered in the atmosphere foreign elements, which, evident to the senses, and borne by the winds, spread from land to land, carrying disease over whole portions of the earth, as is recounted to have taken place in the year 1348. It is, therefore, the more to be regretted, that in this extraordinary period, which, owing to the low condition of science, was very deficient in accurate observers, so little that can be depended on respecting those uncommon occurrences in the air, should have been recorded. Yet, German accounts say expressly, that a thick, stinking mist advanced from the East, and spread itself over Italy; and there could be no deception in so palpable a phenomenon. The credibility of unadorned traditions, however little they may satisfy physical research, can scarcely be called in question when we consider the connection of events; for just at this time earthquakes were more general than they had been within the range of history. In thousands of places chasms were formed, from whence arose noxious vapours; and as at that time natural occurrences were transformed into miracles, it was reported, that a fiery meteor, which descended on the earth far in the East, had destroyed everything within a circumference of more than a hundred leagues, infecting the air far and wide. The consequences of innumerable floods contributed to the same effect; vast river districts had been converted into swamps; foul vapours arose everywhere, increased by the odour of putrified locusts, which had never perhaps darkened the sun in thicker swarms, and of countless corpses, which even in the well- regulated countries of Europe, they knew not how to remove quickly enough out of the sight of the living. It is probable, therefore, that the atmosphere contained foreign, and sensibly perceptible, admixtures to a great extent, which, at least in the lower regions, could not be decomposed, or rendered ineffective by separation. Now, if we go back to the symptoms of the disease, the ardent inflammation of the lungs points out, that the organs of respiration yielded to the attack of an atmospheric poison--a poison which, if we admit the independent origin of the Black Plague at any one place of the globe, which, under such extraordinary circumstances, it would be difficult to doubt, attacked the course of the circulation in as hostile a manner as that which produces inflammation of the spleen, and other animal contagions that cause swelling and inflammation of the lymphatic glands.