Plague is a very slow disease; it takes some weeks to travel from one quarter of a city to another. It took nine months to travel from the city of London to Soho, and ten from Hongkong to Macao—a distance of 30 miles. Thousands of persons from Canton and Hongkong sought shelter at Macao, and there was free communication between these places, still Macao became affected nine months after plague ceased at Hongkong. When plague is first imported in a place, for three or four weeks isolated cases occur in one neighbourhood. An epidemic may last only a few weeks or months, but may extend over several years in sporadic form and a recrudescence takes place abruptly. In Mesopotamia plague declines and becomes dormant with the setting in of the hot weather, its activity reawakening in winter and gathering force with the advancing spring. The same was the case in Egypt. In Constantinople, on the contrary, as well as in England, the disease was dormant during the cold months but became active during the hotter. In England, September was the month of greatest prevalence. In the epidemic at Bengazi in 1858 as well as in Mukai in 1863 famine and plague were found together. That a water-logged soil favours famine was illustrated during the epidemic on the Lower Euphrates in 1867. In Persia and Arabia many epidemics were self-limited and spontaneously came to an end after spreading on a certain area, while, on the other hand, it has been known to obtain an endemic foot-hold, the virus remaining from year to year, and, occasionally under the influence of meteorological or unknown causes, becoming epidemic among the population. _Race._—No race seems to enjoy an immunity from the plague. _Geology and Climate._—Except the new hemisphere the plague has found congenial soil everywhere. It thrives as much in high and dry altitudes as in low-lying places, as much in overcrowded towns as in sparsely populated semi-desert regions. In temperate regions it has been known to rage in summer, but in Astrakhan it prevailed when there were several feet of snow on the ground. On the Volga it prevailed during the severest cold (1878-79), as well as in the extreme heat of Smyrna (1735). In Bombay it commenced at the end of an exceptionally dry season, as it did in South China. During the Hongkong epidemic the rains increased it. The increase of the epidemic at Hongkong with the rains was probably due to the fact that the rains drove people into infected houses, instead of sleeping outside, as they did in summer when the weather was good. It has been said that plague flourishes in a warm moist atmosphere and dry hot air kills it, but there are records of plague thriving in conditions antagonistic to this theory. A temperature between 60° and 85°F. is said to be very favourable to it.