Mosquitoes and Yellow Fever 
201 
‘ ‘ I feel convinced that any theory which attributes the origin and 
the propagation of yellow fever to atmospheric influences, to mias¬ 
matic or meteorological conditions, to filth, or to the neglect of general 
hygienic precautions, must be considered as utterly indefensible.” 
He postulated the existence of a material transportable substance 
causing yellow fever,—“something tangible which requires to be 
conveyed from the sick to the healthy before the disease can be 
propagated” and after discussing the peculiarities of the spread of 
the disease and the influence of meteorological conditions, he decides 
that the carriers of the disease must be sought among insects. He 
continues: 
“On the other hand, the fact of yellow fever being characterized 
both clinically and (according to recent findings) histologically, by 
lesions of the blood vessels and by alterations of the physical and 
chemical conditions of the blood, suggested that the insect which 
should convey the infectious particles from the patient to the healthy 
should be looked for among those which drive their sting into blood 
vessels in order to suck human blood. Finally, by reason of other 
considerations which need not be stated here, I came to think that 
the mosquito might be the transmitter of yellow fever.” 
“Assimilating the disease to small-pox and to vaccination, it 
occurred to me that in order to inoculate yellow fever it would be 
necessary to pick out the inoeulable material from within the blood 
vessels of a yellow fever patient and to carry it likewise into the 
interior of a blood vessel of a person who was to be inoculated. All 
of which conditions the mosquito satisfies most admirably through 
its bite.” 
In the course of his study of the problem, Finlay made detailed 
studies of the life history and habits of the common mosquitoes at 
Havana, and arrived at the conclusion that the carrier of the yellow 
fever was the Culex mosquito or A 'edes calopus, as it is now known. 
With this species he undertook direct experimental tests, and be¬ 
lieved that he succeeded in transmitting the disease by the bite of 
infected mosquitoes in three cases. Unfortunately, possibility 
of other exposure was not absolutely excluded, and the experiments 
attracted little attention. 
Throughout the next twenty years Finlay continued his work on 
yellow fever, modifying his original theory somewhat as time went on. 
Among his later suggestions was that in the light of Smith’s work 
on Texas fever, his theory must be “somewhat modified so as to 
