﻿104 ASHBUBN AND CRAIG. 



Klein investigated very carefully the report of the presence of a short bacillus 

 in the blood of dengue cases and concluded that there was not sufficient evidence 

 to prove the constant association of this or any other organism with the disease. 

 Wright was unable to demonstrate any organism as concerned in the etiology of 

 dengue, and similar results followed the investigations of C'rookshank and Mac- 

 Fadyen. 



The observations of Graham (21) of Beirut, published in 1903. awakened in- 

 creased interest in the etiology of this puzzling disease, and a considerable amount 

 of work has since been done with the object of confirming or disproving his results. 

 Graham's investigations were carried out in Beirut. Syria, and resulted in the 

 announcement by him that dengue is due to a protozoon inhabiting the red blood 

 corpuscles and closely resembling the plasmodia of malaria, except for the absence 

 of pigment. He examined the blood of over one hundred cases, but in his com- 

 munication regarding the subject he does not state in how many of these he 

 found the parasite, but admits that he was unable to demonstrate it in stained 

 smears of the blood. As described by Graham, the parasite first appears as a 

 small, hyaline rod or dot within the red blood corpuscle, constantly changing its 

 position, the motility in some instances being Aery marked: later, the parasite 

 increases in size, appears to present typical amoeboid motion, and finally almost 

 fills the red corpuscle, or rupturing it becomes free in the plasma, where it very 

 soon degenerates. Xo sporulating forms are described, nor any other method of 

 reproduction in man. The organism is never observed to contain any pigment. 

 He states that he has found the same bodies in the blood of patients suffering from 

 second and third attacks of the disease. 



From the results which this investigator obtained in transmission experiments 

 to be mentioned later, he believed that the organism described underwent a develop- 

 mental stage within the mosquito, and he therefore endeavored to trace such a 

 cycle, using mosquitoes of the j>enus Culex fatigans Wied. for the purpose. By 

 dissecting insects which had bitten dengue patients and examining the blood con- 

 tained in the stomach, he claims to have demonstrated his piroplasma-like bodies 

 in the mosquito up to the fifth day after the biting, and states that they undergo 

 developmental changes similar to those occurring in the blood corpuscles in man. 

 He did not succeed in finding any zygotes or any evidence of sexual forms within 

 the mosquito. He also claims to have observed the spores of this organism "in 

 among the cells of the salivary glands" after forty-eight hours in mosquitoes 

 which have bitten a dengue patient upon the fourth day of the disease; he further 

 claims that the spores could be demonstrated in the salivary glands of mosquitoes 

 which had been kept a month. 



Graham produced a very severe case of fever resembling dengue by inoculating 

 a man subcutaneously with peptonized normal salt solution containing the salivary 

 glands of a mosquito which had bitten a dengue patient twenty-four hours before. 

 He was deterred from further experimentation along this line by reason of the 

 very severe symptoms produced in this case. 



Because of the positive character of Graham's statements his work attracted 

 widespread attention and encouraged many investigators to study with renewed 

 energy the etiology of dengue, but although many experienced microscopists have 

 endeavored to confirm his results none have done so as regards the presence 

 of a parasite within the blood corpuscles. With the exception of Eberle. whose 

 description of a plasmceba obviously applied to vacuoles, artefacts, etc., which 

 are so common in the blood of fever patients, no investigator claims to have been 

 able to demonstrate in dengue blood in nature, any constant parasite, bacterial or 

 protozoal. 



Carpenter and Sutton (22) studied 200 cases of dengue upon the Isthmus of 



