One of the most destructive scourges of mankind in the days of which we write, and of uncounted centuries before, was smallpox. Other plagues were more destructive for a time, but their duration was short, and the intervals between their appearances were long. Smallpox, however, was always lurking in some corner of every country, ready to take advantage of circumstances favorable for an epidemic. It has been estimated that half a million people perished annually of smallpox in Europe. The Spaniards carried it to Mexico and South America, where it committed the most frightful ravages among the Indians and the negro slaves. The English and French carried it to North America, where it exterminated whole tribes of Indians. It has ever been noticed that the disease is much more virulent and fatal among the dark races than among the light ones. America was only thinly populated
