414 



of which rises a continuous wall of highlands, altogether beyond the reach 

 of those pestilences which I claim to have indentified as our modern 

 yellow fever. That condition of things did not occur along the shores of 

 Santo Domingo (Hispaniola) nor of Darien, so that no obstacle existed 

 there to prevent the propagation of such epidemics from the coast to the 

 interior. The Indian population was very numerous, before the discovery, 

 on the islands as well as upon the continent. They lived in crowded huts, 

 forming separate villages — some of them with 1000 or 2000 inhabitants, 

 of peaceful habits and devoted to agriculture, but ever ready to change 

 their dwellings or to scatter in the woods whenever danger was 

 apprehended from enemies or from some contagious disease. Under these 

 circumstances it will be readily understood how, upon the occurrence of an 

 epidemic of yellow fever, many would escape from the contagion, but the 

 germ would spread over a wide area, and, by reason of the mild winters, 

 the infection would not be easily extinguished. 



The final confirmation of the role which appertains to the culex 

 mosquito Desv. (now included in the genus Stegomyia of Theobald), in the 

 transmission of yellow fever, has now been sanctioned by the experiments of 

 Drs. Reed, Carroll, Agramonte and the lamented Dr. Lazear, at Quemados 

 de Marianao during the winter of 1900, afterward by those of Dr. Guiteras 

 at the Experimental Station of Las Animas last summer, and finally by 

 the splendid practical results obtained by the Chief Sanitary Officer of 

 Havana, Major W. C. Gorgas, during the epidemic-year which has just 

 been completed. With those facts and the ones which I had gathered in 

 former years, it is now possible to determine with some degree of precision 

 the conditions which are necessary in order that yellow fever may develop 

 in an epidemic form in a given locality, not too highly situated above the 

 sea level and where temperatures between 25 and 35 C. (77 and 95 F.) 

 either temporarily or habitually prevail. A distinction will, however, have 

 to be made between localities in which the yellow fever mosquito already 

 belongs to the fauna of the place, and others in which that species of 

 mosquito does not habitually exist. The conditions, in either case, may be 

 reduced to three. They will 1 be, in the first instance, as follows : 



1. Presence of a yellow fever patient within the first 5 days of his 

 attack and exposed to be bitten by mosquitoes, or else the mere importation 

 of one or more contaminated mosquitoes. 



2. Abundance of mosquitoes of the required species, so that some of 

 them will be likely to reach a yellow fever patient in a condition to become 

 contaminated. 



3. Presence of persons liable to contract the disease and so placed 

 that they may be bitten by the contaminated mosquitoes. 



In the second instance, when mosquitoes of the particular species did 

 not previously exist in the locality, the conditions will be : 



