Dr. Carlos Finlay, in a paper published in _The Climatologist_, of Philadelphia, in July, 1892, gives very clear proof that the disease existed in America before the discovery by Columbus. It seems to have been endemic in the neighborhood of Vera Cruz, Mexico, and to have been very well known to the Aztec authorities. The Government, before the arrival of the Spaniards, had many times caused a forced emigration from the interior to the neighborhood of Vera Cruz, to repopulate a country that had been depopulated by an epidemic disease known to the Aztecs as “cocolitzle.” To induce them to stay, these people were given many privileges, such as exemption from taxation, etc. This cocolitzle was known among the Mayos of Yucatan as “black vomit.” The Spanish historian, Father Lapey, gives a very clear account of cocolitzle as it occurred in Yucatan in 1648. It is such a clear description of yellow fever that I think it instructive to quote from his report as given in Dr. Finlay’s paper: With such violence and rapidity were the people attacked, big and small, rich and poor, that in less than eight days the whole population of the city (Campeche) were sick at the same time, and many citizens of the highest rank and authority died. In most of the cases the patients were taken with a most severe and intense headache, and pains in all the bones of their bodies, so violent that their limbs felt as if torn asunder, or squeezed in a press. A few moments after the pains, there came on a very intense fever, which in most instances produced delirium, though not in all. This was followed by vomiting of blood, as if putrified, and of such cases very few survived—and many suffered the fever and pain in the bones without any other symptoms. In the majority the fever seemed to remit completely on the third day; they would say that they felt no pains whatever, the delirium would cease, the patients conversing in their full senses, but they were unable to eat or drink anything; they would continue thus for several days, and while still talking and saying that they were quite well, they expired. A great number did not pass the third day, the majority died on the fifth, and very few reached the seventh. The most healthy and robust of the young men were most violently attacked and died soonest. When the laity began to improve, the disease broke out among the priests. Of the eight members of the Jesuit College, six died; of our own order (Franciscan) twenty died in the city. Almost all the heads of institutions and persons of highest rank, both ecclesiastics and seculars, were carried away by the epidemic. The disease continued over the whole country during the space of two years. Few that then lived in this land, or visited it, in the course of those two years, escaped being sick, and it _rarely happened that anyone died of a second attack after having recovered from the first_. I then reflected that of the