﻿ETIOLOGY OF DENGUE FEVER. 103 



III. ETIOLOGY. 

 1. HISTORICAL. 



The etiological factor concerned in the causation of dengue has been long and 

 patiently sought for by almost every investigator who has studied the disease; 

 thus, nearly every fluid, secretion and excretion of the body has been examined, 

 and, as might be expected, not a few observers have announced, from time 

 to time, the discovery of a causative organism. Many of these so-called "discov- 

 eries" were made during the dawn of bacteriological science, and a perusal of 

 the methods adopted in isolating the organisms described, as well- as the descrip- 

 tion of their morphology is sufficient to prove their absolute lack of scientific 

 accuracy. Therefore, we have not deemed it necessary to review such contri- 

 butions, but among the many who have investigated the etiology of this disease 

 there are a few whose observations demand consideration. Among these may be 

 mentioned McLaughlin, Graham, Carpenter and Sutton, Guiteras and Agramonte. 



The early investigations regarding the etiology of dengue were directed toward 

 a bacterial cause, but within the past few years the increasing importance of the 

 protozoa in the etiology of disease has turned the current of investigation, and 

 almost all of the work which has been done upon this subject by recent investi- 

 gators has been founded upon the belief that the disease is caused by some 

 protozoon, probably by one inhabiting the blood. 



However, despite the fact that a great amount of labor has been expended in 

 the search for a bacterial or protozoal organism, it is surprising how few records 

 of this work there are and, upon analysis, how unsatisfactory the conclusions 

 arrived at. Perhaps, in no other disease, as common and as thoroughly studied 

 clinically as dengue, is there so limited a literature concerning its parasitic 

 etiology and it must be admitted that this is one of the infections of man which, 

 up to the present, has baffled all attempts at a solution of its etiology. 



The earliest attempt, based upon bacteriological methods, to discover the 

 organism causing dengue was that of McLaughlin (23). The descriptions of his 

 experiments are detailed and the results obtained are of interest, but, viewed in 

 the light of the approved bacteriological methods of to-day, are open to very severe 

 criticism and have not been confirmed by late observers. 



McLaughlin, whose observations were published in 1886, believed in the directly 

 contagious character of the disease and that organisms of a bacterial nature, 

 existed in the blood of the infected individual. He examined both fresh and 

 stained specimens of blood, and cultures from blood made upon nutrient gelatine. 

 He also made microscopical examinations of the vomitus and urine and endeavored 

 to secure cultures of the organism by partially filling sterilized glass bulbs with 

 blood from a vein and allowing the blood so obtained to incubate for weeks and 

 even months. By this method he examined but one case, but by the methods 

 previously given he studied forty. In the blood of every case he found 

 spherical micrococci measuring one-twentieth to one-thirtieth the diameter of a 

 red blood corpuscle, and red or purplish in color; in preparations made from 

 cultures grown upon nutrient gelatine, the cocci,- when in masses, appeared black 

 or brown, but when seen singly the red color was always distinct and character- 

 istic. In the bulbs mentioned, which contained only blood (no bouillon), the same 

 organisms were found in pure culture after an incubation period of from six weeks 

 to three months. 



While the researches of McLaughlin appear to have been partially accepted, 

 or at least considered seriously by some writers, Ave regard them as only of 

 purely historical interest, for reasons which are obvious. 

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