FILARIA PARASITES 307 
examined every day. The filter we used retained this organism, so that it may 
be stated that the virus of dengue passed through the pores of a filter which 
prevented the passage of an organism measuring 0.4 micra in diameter. The 
blood from the dengue patients was defibrinated and diluted with an equal 
amount of normal salt solution, and the filtrate was introduced intravenously. 
“Tn both of the men inoculated with the filtrate the attack was of severe 
character, and we regarded these two cases of dengue, produced by the intra- 
venous injection of filtered dengue blood, as the most typical cases of the severe 
type of the disease which we observed. These experiments proved that the 
organism causing the disease is probably ultramicroscopic in size, and this con- 
clusion explains the uniformly negative results obtained in the search for the 
parasite. 
“We concluded that an organism was present in the filtrate, rather than a 
toxine, because of the length of the period intervening between inoculation and 
the appearance of clinical symptoms, and also because one of the men was in- 
oculated with the filtered blood of an experimental case of dengue produced by 
the intravenous injection of unfiltered blood from a naturally infected dengue 
patient.” ... 
“ Owing to the subsidence of the epidemic we were unable to continue our 
mosquito experiments, which are therefore incomplete, but, taken in connection 
with those of Graham, prove that this disease may be transmitted by the mos- 
quito. We felt justified in concluding that this method of transmission is the 
only natural one which has been proved by experiment, and which agrees with 
the epidemiology of the disease. 
“We were further able to show experimentally that natural immunity exists 
against this disease, and that it is not contagious. We exposed eight healthy 
men to fomites, the men experimented with living in mosquito proof tents with 
patients suffering from dengue, throughout the entire course of the disease. 
They slept in their beds, wore their underclothing and pajamas, and ate and 
drank from the same table furniture, but none of them developed the disease. 
“ Our conclusions regarding the etiology of dengue were partly to follows: 
“1. No organism, either bacterium or protozoan, can be demonstrated in 
either fresh or stained specimens of dengue blood with the microscope. 
“2. The intravenous inoculation of unfiltered dengue blood into healthy men 
is followed by a typical attack of the disease. 
“3. The intravenous inoculation of filtered dengue blood into healthy men 
is followed by a typical attack of the disease. 
“4. The cause of the disease is, therefore, probably ultramicroscopic. 
“5. Dengue can be transmitted by the mosquito, Culex fatigans Wied. and 
this is probably the most common method of transmission. 
“6. No organism of etiological significance occurred in bouillon or citrated 
blood cultures. 
“1, The period of incubation in experimental dengue averages three days 
and fourteen hours. 
“8 Certain individuals are absolutely immune to dengue, as proved by our 
experiments. . ; di ee 
“9. Dengue is not a contagious disease, but is infectious in the same manner 
as is yellow fever and malaria.” 
FILARIASIS. 
Under this name is understood the presence in the blood or other body fluids 
(the lymph and urine) of nematode worms belonging to the family Filariide. 
These worms are present in man and in other vertebrates in two stages, as adult 
21 
