418 



adapted itself to the climate of Yucatan one year sooner than to that of 

 Havana. 



Farther toward the equator, in the Guianas, where the Dutch made 

 their first settlements in 1580, I have no information regarding the early- 

 medical history of that country; but in 1763, an expedition of colonists 

 having been sent by the French Government to Cayenne, most of them died 

 of a fever which, according to Bérenger Féraud, could have been no other 

 but the yellow fever. 



South of the equator, on the coast of Brazil, the first epidemics on 

 record are those of Babia and Pernambuco (Recife) in 1686; but the 

 facility with which it extended in the neighboring country shows that the 

 yellow fever mosquito must have already existed there. Not until 1850 

 did yellow fever extend as far south as Rio de Janeiro ; it has, however, 

 been endemic there ever since. The present limits of the endemic yellow 

 fever zone, so far as latitude is concerned, may therefore be placed at the 

 23d parallels, north and south of the equator. 



In equatorial Africa, through the slave trade with the West Indies, 

 endemic centers must have developed soon after the discovery of America ; 

 and some have persisted to this day, principally in the French colonies on 

 the west coast, notwithstanding the racial immunity which most of the 

 indigenous races possess. 



Beyond the Atlantic shores, yellow fever epidemics have only been 

 recorded in some ports of the Mediterranean and on the Pacific coast of 

 South and Central America. The fact that no permanent endemic focus has 

 ever developed on the Pacific side of the American continent, is a curious 

 feature which must probably be attributed to the following circumstances : 

 1, the necessity of crossing the mountain range of the Andes in traveling 

 from the Atlantic to the Pacific coast and, 2, the cooler temperatures 

 which usually prevail along the western coast of South America. The 

 first of these conditions impedes the spontaneous migration of contaminated 

 mosquitoes across the highlands, w r hile the cooler temperatures may prove 

 incompatible with the development of successive broods of the particular 

 species, on the Pacific coast, except at certain epochs, when unusually high 

 temperatures have been known to occur during several successive years. 



Conclusions 



As the outcome of the above historic and etiologic considerations I 

 beg to submit the following conclusions : 



1. The endemic foci of yellow fever in America, from the pre- 

 Columbian times to the beginning of the seventeenth century, were 

 comprised within a zone between the 20th and the 8th or 9th parallels of 

 north latitude, reaching, toward the east, as far as the Leaward Islands 

 and limited toward the west by the Atlantic coast of the American 



