415 



1. Introduction of mosquitoes of the required species, previously 

 contaminated or under such circumstances that they may become contami- 

 nated from yellow fever patients simultaneously or subsequently 

 introduced. 



2. Circumstances which may enable the contaminated mosquitoes 

 which have been introduced to continue inoculating a series of non- 

 immunes during a sufficient length of time to allow the insect to develop 

 a new brood, so that the new generation of yellow fever mosquitoes may 

 come out in time to contaminate themselves from some of the patients 

 inoculated by their predecessors. 



3. The same conditions as in number 3 above. 



Whenever two of the above conditions have been fulfilled without 

 any outbreak of the disease following, the other condition must be supposed 

 to be wanting; and, vice versa, if an epidemic of yellow fever does develop, 

 the third condition may be supposed to have been fulfilled even if not 

 actually demonstrated, unless the reverse can be absolutely proved. 



Instances of the first class are, for obvious reasons, by far the more 

 frequent; they include the epidemics recorded in the southern states of 

 the Union, in the south of Spain, in the Canary Islands, in the Balearic 

 Islands, Western coast of Africa, Italy (Leghorn in 1804), in all of which 

 countries mosquitoes of the yellow fever species are known to exist. As 

 instances of the second class may be cited the epidemics recorded in the 

 northern parts of the United States, in Saint-Nazaire (France), in England, 

 in Canada (Quebec), Madrid (Spain), in which countries the outdoor 

 temperatures are only suited for the active functions of the yellow fever 

 mosquito during a limited period, and even then may not be such as would 

 allow the reproduction of successive generations of that insect. 



Inasmuch as the only natural means by which yellow fever is, so 

 far, known to be propagated, consists in the inoculation of the pathogenic 

 germ through the bites of contaminated mosquitoes, the propagation of 

 the disease across the sea would, in many instances, be inconceivable unless 

 those insects have some propensity to take up their abodes inside of vessels 

 and to thrive in them, even when confined within the hold during a 

 considerable length of time. A confirmation of this fact has recently 

 presented itself; the Mosquito Commission of the "Orleans Parish Medical 

 Society" having reported that five mosquitoes of the "Stegomyia fasciata" 

 species had been found last summer in the hold of a fruit vessel just 

 arrived in that port. Indeed, there is a possibility that such a thing did 

 occur as far back as Columbus' first voyage of discovery. After discovering 

 and exploring the island of Santo Domingo, he sailed from the coast of 

 Higuey on Jan. 11, 1493, for Spain, but on February 14, his carabela 

 having been assailed by a terrible hurricane since the 12th, he was so 

 exercised over the thought that he might yet be unable to convey the 

 glorious news of his discovery that, he wrote, a great fear took possession 



