=Epidemics.=--The history of severe plagues is remarkable. The first great pestilence in a comparatively civilized nation was the one at Athens about 400 B. C. On account of being shut up by the Spartans in their crowded city the Athenians had this terrible experience. It carried off thousands--nearly two-thirds of the population. In the reign of the Emperor Justinian no less than 100,000,000 inhabitants died in thirty years from a pestilence that swept from Persia to Gaul. Later, in the fourteenth century, the plague of beautiful Florence in Italy killed 80,000 people in six months. In 1665-66 London was a vast pest-house and during September of 1666 the weekly death rate reached the number of 8,000. In America the sunny South has witnessed the blasting effects of yellow fever during the last fifteen years. In 1878, Florida had 2,649 deaths, and New Orleans 3,977 from yellow fever. Fully 33% of those attacked succumbed. In the same year 4,200 people died of it at Memphis. The last important run of this epidemic was in 1888, at Jacksonville and Decatur. There the deaths averaged 10% of those attacked. The duration of the infection stages of various diseases is thus given by Dr. T. F. Pearse, an English physician: Measles, from the 2d day of the disease for 3 weeks; small-pox, from the 1st day for 4 weeks; scarlet fever, from the 4th day for 7 weeks; mumps, from the 2d day for 3 weeks; diphtheria, from the 1st day for 3 weeks. The incubation periods, or intervals occurring between exposure to infection and the first symptoms, are as follows: Whooping-cough, 14 days; mumps, 18 days; measles, 10 days; small-pox, 12 days; scarlet fever, 3 days; diphtheria, 14 days. Scarlet fever is at its minimum from January to May, and at its maximum in October and November. Diphtheria is more evenly distributed through the year, and is most dangerous a little later than scarlet fever. Measles and whooping-cough seem to be somewhat aggravated by cold weather, but are most fatal in May and June. Hot weather is adverse to small-pox, and favorable to disorders of the bowels, particularly in children. THE DIFFERENCE BETWEEN MEASLES AND SMALL-POX.--At the outset of a popular eruption it is often difficult to decide whether the case is one of measles or of small-pox. M. Grisol's method of diagnosis is as follows (_Medical Times_): "If, upon stretching a portion of the skin, the papule becomes impalpable to the touch, the eruption is caused by measles; if, on the contrary, the papule is still felt when the skin is drawn out, the eruption is the result of small-pox."