young children who were attacked by the peste in Yucatan, only few had died, as compared with the adults. CHAPTER IX GEOGRAPHICAL LIMITS OF YELLOW FEVER The geographical limits of yellow fever, when first encountered by the white man, were not very wide. They were contained within a zone limited on the north by the twentieth parallel of latitude, on the south by the eighth, on the east by the sixtieth meridian, and on the west by the one hundredth. Practically, the disease was confined to the shores of the Caribbean and the southern shores of the Gulf of Mexico. Within these regions it was practically endemic at the time Columbus discovered America. The arrival of the white man with his sailing ships made the disease much easier of transmission from place to place, because man traveled much more frequently and much farther, and also because sailing ships, with their fresh-water tanks, bred the stegomyia extensively. Under these influences the endemic area began slowly to spread. Toward the north the endemic area never extended far beyond the limits it occupied when Columbus made his first voyage. Havana, in latitude 23°, is the northern endemic limit in the western hemisphere. This is rather strange, as the city is located so near the original endemic focus. The arrival of a considerable number of non-immunes in a locality is necessary for yellow fever to become endemic, and this supply has to be fairly constant. During the first hundred years after the founding of Havana, in 1511, the city was considered very healthy. In 1620, an epidemic of yellow fever occurred, the disease having been introduced from Panama (Porto Bello) by the treasure fleet on its way to Spain. In 1649 another epidemic occurred, which was extremely severe and spread to many other towns of Cuba. This epidemic lasted more or less until 1655. For a hundred years after this, nothing in the nature of an epidemic occurred. In 1762, at the time of the capture of Havana by the English colonial troops from the North American colonies, the disease again became epidemic, and after that time remained constantly in Havana as an endemic disease. At this time it was recognized as being introduced from Vera Cruz, Mexico, under the name of “black vomit.” It became endemic, and did not disappear as on former occasions, on account of the large and constant supply of non-immune persons, due to the presence of the English troops, and after their departure, to the fact that the port was thrown open to general commerce, and to a continuous supply of immigrants from Spain. It would seem, then, that Havana, after remaining in the epidemic area for some two hundred and fifty years, finally, about the year 1762, passed permanently into the endemic area.