﻿ETIOLOGY OF DENGUE FEVER. 105 



Panama, and examined both fresh and stained specimens of blood, using Wright's, 

 Ehrlich's. the Romanowsky and Nocht's methods, as well as bacterial stains. 

 They were unable to demonstrate McLaughlin's micrococcus or any other mi- 

 croorganisms in the blood. They found the nonpigmented bodies of Graham in 

 unstained specimens, but not in stained ones. They also found the same bodies 

 in the blood in other diseases; and regarded them as being due to necrobiotie 

 changes in the red cells. They also examined mosquitoes which had bitten dengue 

 patients, but found no parasites present in the insects. 



Guiteras (7), as the result of a very careful investigation in Habana in 1905, 

 believes that Graham is mistaken regarding his organism and concludes, after 

 examining a large series of blood specimens taken during all days of the disease, at 

 various hours and stained by various methods, that the blood contains no structure 

 resembling a parasite. 



The investigations by the staff of the Government Laboratories (24) at 

 Manila, P. I., in 1900 into the etiology of dengue, resulted negatively as to the 

 presence of a parasite. Their conclusions were as follows: (1) In dengue fever 

 there is no leucocytosis ; (2) the differential count of the white corpuscles in this 

 disease show normal proportions of the several varieties; (3) the hsematozoiin 

 described by Graham has not been found present in the circulating blood of our 

 cases; (4) the micrococcus described by McLaughlin has not been encountered. 



Agramonte (19), studying the disease in Habana in 1906, was unable to 

 demonstrate any parasite in the blood, and the recent researches of Kieweit de 

 Jonge and de Haan (25), in Java, which were most thorough, were also without 

 result. Stitt (20), working upon the subject in Cavite, P. I., was unable to 

 demonstrate any organism in the blood. 



Method vf transmission. — Until the publication of Graham's work practically 

 nothing had been done in the way of experimental research directed toward the 

 discovery of the method of transmission of dengue fever. We have already 

 touched upon the theories regarding this question in considering the epidemiology 

 of the disease, but so far as we have been able to determine, after consulting 

 all the literature available, to Graham belongs the credit of first attacking this 

 problem in a practical and scientific manner. His work aroused much interest, 

 and however he may have erred in his interpretation of the bodies described by 

 him as the cause of the disease, w r e believe that his experiments regarding the 

 method of transmission are most valuable and his conclusion that dengue is 

 transmitted by the mosquito is well founded and has been experimentally con- 

 firmed. 



Graham's experiments regarding mosquito ti'ansmission were briefly as follows: 

 Four men in good health were selected and slept night after night beneath 

 mosquito bars containing mosquitoes that had bitten dengue patients. In one 

 ease the disease developed four clays from the date of the first exposure, in one 

 in five days, and in one in six days. In one case the result was negative. 

 During the time the experiment lasted the men remained in their homes, where 

 there had been no other cases of the disease, and where none developed later. 

 In order to obviate the possibility that these men might have contracted the 

 disease in some other way, there being a very severe epidemic in the city at 

 that time, Graham took mosquitoes that had bitten dengue patients to a 

 village situated in the mountains, where no cases of the disease had occurred. 

 At this village he liberated the mosquitoes under the nets of two young men, 

 living in different localities, and orders were given that the men were not to 

 leave the nets until permitted. One of these men developed a very severe attack 

 of dengue in four days after exposure, the other in five days. The mosquitoes 

 were destroyed and the men continued to sleep under the mosquito bars for some 



