﻿106 ASHBURN AND CRAIG. 



time after recovery. No other cases of the disease occurred in this village. The 

 mosquitoes used in these experiments are stated by Graham to be Culex fatigans 

 Wied., and the insects were used within a short time after biting infected patients. 

 Graham further states that in Beirut no Anopheles are to be found, but that 

 during the dengue epidemic the city was infested with great numbers of Culex 

 fatigans YVied. It will be seen that of six healthy men bitten by infected 

 mosquitoes, five developed dengue, two in four days, two in five days, and one in 

 six days. 



Since Graham's experiments and results were published, a few observers have 

 endeavored to confirm them, but without success. Carpenter and Sutton (22) 

 experimented with various mosquitoes, viz: Culex stimulans Walk., C. tarsalis 

 Coq., Stegomyia fasoiata Fbr., etc., but not with Culex fatigans Wied. The mos- 

 quitoes used were young, well-grown insects, reared by them and kept for from 

 five to fourteen days after biting, when they were dissected and A T ery carefully 

 examined. No protozoa were demonstrated, nor any other organism which they 

 regarded as of etiologic importance. The authors regard their mosquito inocula- 

 tion experiments as untrustworthy, and state that no definite statements can 

 be made concerning them. They give but four experimental cases of mosquito 

 inoculation, two of which were negative, one positive after six days and one 

 after two weeks from the date of mosquito bites; the latter case is obviously of no 

 value, as the incubation period is too long. The authors state that "the volunteer 

 subjects were not only exposed to the bites of other moquitoes at all times 

 but they were also brought into almost daily contact with dengue cases. 



Agramonte (19), in Habana. attempted to transmit the disease by mosquitoes, 

 trying various species at various intervals after the insects had fed upon dengue 

 patients, but was unsuccessful in producing the disease in this way. He believes, 

 however, that dengue is transmitted by some species of mosquito, and that the 

 reason for failure in experimental infection lies in some undiscovered fault in 

 technique. The epidemic he studied was accompanied by a plague of Culex 

 fatigans Wied. 



In Habana, Guiteras and Finlay (7) endeavored to transmit the disease with 

 Culex pipiens Linn., but with negative results. Guiteras states, regarding these 

 experiments, that their small number and lack of variety deprive the negative 

 results of a claim to conclusive character, and that their faith remains unshaken 

 that the mosquito is the transmitter of dengue. 



It is rather surprising, in view of the scientific interest and importance 

 of this question, that so little has been done to prove or disprove the 

 results claimed by Graham from his mosquito experiments; it is not, 

 however, surprising, that those who have attempted to solve the problem 

 have met with so little success, for only those who have done so can realize 

 the difficulties and disappointments which await the investigator in this 

 particular field of research. In our work upon this phase of the subject, 

 to be detailed later, the experimental results obtained, while to our own 

 satisfaction proving that Culex fatigans Wied. transmits dengue fever, 

 have been, at times, most disappointing and discouraging; unknown 

 natural conditions appear to be necessaiy for the transmission of this 

 disease by the mosquito, and because of our ignorance of the method of 

 securing these we believe that experimental transmission by the mosquito 

 is rendered most difficult and that negative results may be expected 

 much more frequently than positive ones. 



