=History.=—It would seem probable that yellow fever was the disease from which those of Columbus’ second expedition suffered in San Domingo, in 1495. At the same time the first definite description of the disease was that of Dutertre, in Guadaloupe, in 1635. There has been much discussion as to whether the West Coast of Africa may not have been the original endemic centre and the importation to the West Indies the result of the slave traffic. While there is very little support given this view the recent recognition of the extent and importance of the African endemic area, as brought out by Boyce, is somewhat suggestive. Spinden advances evidence to show that a devastating epidemic disease, attended with bleeding from the mouth and nose, raged among the Mayas and Aztecs in pre-Columbian periods. One such epidemic is recorded as of 1454. There have been numerous severe outbreaks in the United States, that occurring in Philadelphia, in 1793, being the most celebrated and that centering in Memphis, in 1878, probably the most terrible. Yellow fever has been a scourge in Brazil since its introduction in 1849, until quite recently. Lisbon experienced severe outbreaks of the disease in 1723 and in the next century in 1850 and 1856. Many of the Spanish cities have also suffered from time to time. The history of the connection between yellow fever and the mosquito is discussed under etiology. [Illustration: FIG. 40.—Geographical distribution of yellow fever.] =Geographical Distribution.=—As will be seen from the chart the chief epidemic centers are the islands and coasts of the Gulf of Mexico and the West Coast of Africa. The disease has at times extended down the West Coast of South America and is now rather prevalent in Ecuador. The last epidemic in the United States was that in New Orleans. The disease has never invaded Asia or Australia and there is fear that the opening of the Panama canal may bring this about. Guiteras, who has recently returned from an investigation of the problem of yellow fever on the West Coast of Africa, was unable to find evidence of its existence there at the present time. He notes an absence of the extreme heat and abundance of mosquitoes which are features of yellow fever ports of South America. ETIOLOGY AND EPIDEMIOLOGY =Etiology.=—It is now generally accepted that the cause of yellow fever is a spirochaete, _Leptospira icteroides_, which is very similar to but slightly smaller than _L. icterohaemorrhagiae_ of infectious jaundice. Noguchi injected 74 guinea pigs with about 5 cc. of blood from 27 cases of yellow fever. The blood from 6 of these cases proved infectious, producing in 8 guinea pigs fever, conjunctival injection, albuminuria, a leucocytosis followed by leucopenia and, after a few days, a subsidence of the fever to normal or subnormal. At this time jaundice and haemorrhages occurred.