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 neglectof 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 htiman 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 wotild be 

 necessary to pick out the inoculable 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 mosqtiitoes at 

 Havana, and arrived at the conclusion that the carrier of the yellow 

 fever was the Culex mosquito or Aides 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 



