Cholera traverses the earth in zones, spreads with equal facility through tropical and polar regions, and attacks alike the seats of civilization and the huts of the slave and the savage. 3. Epidemics resemble each other in the rapidity of their course. Sometimes, indeed, they begin slowly, advance haltingly, and gather strength in silence. For some time they give so little indication of their power that the apprehension of their presence is very constantly regarded as a “false alarm.” Now and then, here and there, they strike a sudden and mortal blow; but it is only an individual that falls. After a considerable interval, perhaps at a great distance, another blow is struck; and then one by one, another and another, until at last the fact becomes too manifest to be doubted or denied, that two victims have been seized in one family—several in the same street—three or four on the same day, in distant parts of the town, or in the adjoining town, or it may be in towns separated from each other by the distance of hundreds of miles. At length the terror-stricken nation, startled from its fondly cherished security, sees no place safe from the Plague. When, however, the causes are intense, it may break forth quite suddenly, and spread with astonishing rapidity. In 1831, when Cholera first appeared in Cairo, it extended within the space of five days over the whole of Lower Egypt, desolating simultaneously all the towns and villages of the Delta. In 1832 it leaped at one bound from London to Paris, and when once there, spread in five days over thirty-five out of forty-eight quarters of the city. When Influenza broke out in London in 1847, it spread in one day over every part of the metropolis, and upwards of 500,000 persons suffered from the malady. 4. Epidemics resemble each other in giving distinct and unmistakeable warnings of their approach. These warnings consist of two events: first, the sudden outbreak and general spread of some milder epidemic; and, secondly, the transformation of ordinary diseases into diseases of a new type, more or less resembling the character of the extraordinary disease at hand. It is a very singular fact that both in the middle ages, and in modern times, the lesser Epidemic which has generally preceded and pre-announced the coming of the greater, is Influenza. The history of European Epidemics from the 14th century downwards, shows that whenever a new Plague was at hand, destined to become truly European, it was preceded by a sudden outbreak of Influenza, as general as it was violent. This is exemplified with singular uniformity in the Epidemics of the 16th century—the severest epidemic period on record. It is most remarkable that in our own day the first visitation of Epidemic Cholera was preceded by an outbreak of Influenza which resembled, in the most minute particulars, the violent and universal Influenza that ushered in the mortal Sweating Sickness Epidemic of 1517.