The so-called Black Death of the 14th century was a fever—an aggravated form of the Oriental or Bubo-Plague; in which there occurred, in addition to the ordinary symptoms of that dreadful disease, effusions of black blood, forming black spots on the arms, face, and chest. From this circumstance it derived its name. These effusions on the external surface of the body were accompanied by profuse and mortal discharges from the internal organs. The Oriental Plague, the great devastator of Europe in former times, and still the scourge of some portions of it, is a fever characterized by specific glandular inflammation. The Sweating Sickness of the 15th and 16th centuries was a fever, with symptoms of acute rheumatism, attended with a fœtid perspiration which poured from the body in streams. “Suddenly,” says Hollingshed, “a deadly burning sweat assailed their bodies and distempered their blood, and all, as soon as the sweat took them, yielded the ghost.” The Cholera of modern times is a fever, which appears in its true character when the first stroke of the disease does not prove fatal, and time is allowed for the full development of its successive stages. The common Epidemics of the day—Ordinary as distinguished from Extraordinary Epidemics—typhus, scarlet fever, small-pox, measles,—are so universally recognized as fevers that the popular notion of fever is derived from the external characters which these maladies present. 2. Epidemics resemble each other in the extent of their range. Ordinary diseases attack single individuals, and if, from season or other causes, several cases occur simultaneously, they are still isolated and scattered. They never prevail at the same time among several members of a family, or among the inhabitants generally of a court, street, or town. Epidemics, on the contrary, derive their name from their attacking large numbers at once. The great Epidemics of all ages have been strikingly characterized by their wide-spread course. The Black Death extended from China to Greenland, and desolated in its course Asia, Europe, and Africa. The Bubo-Plague of the middle ages often extended beyond its proper seat. In the 15th century it spread seventeen times over different European countries, and extended to the most distant northern nations. The Sweating Sickness prevailed simultaneously or in rapid succession over England, France, Germany, Prussia, Poland, Russia, Norway, and Sweden. “It extended,” say the chronicles of the day, “like a violent conflagration which spread in all directions; yet the flames did not issue from one focus, but rose up everywhere as if self-ignited.” The Influenza of the middle ages took a range which may be said to have been universal. In our own day we have seen the same disease attack almost every family, in nearly every city, town, and village; spread within a short period over the whole of Europe, and then extend through the vast continent of the New World.