DENGUE AND MOSQUITOES 303 
five generations in France under conditions that exist about houses, but the 
German experiments show that it is unlikely that this species can produce even 
a generation under the natural conditions of the climate at Hamburg. 
DENGUE. 
This disease frequently appears in epidemic form throughout the tropics and 
subtropical regions. It is marked by sudden appearance, acute fever, short 
duration and comparative benignity, fatal cases being extremely rare. Dengue 
has been confused with influenza and various febrile diseases and its existence 
as a disease entity has even been denied. However, it is now generally recog- 
nized as a specific disease. Considering the fact that dengue has been com- 
paratively little studied, its mosquito-born character may be said to be fairly 
well established. Ashburn and Craig point out that attention has been directed 
repeatedly to the resemblance between dengue and yellow fever and that it is 
well founded in fact. Craig has recently shown, as will be seen in the following, 
that, like yellow fever, this disease is caused by an organism of ultra-microscopic 
size, almost certainly a protozoan and closely related to the causative organism 
of yellow fever. 
Harris Graham, of Beirut, in 1902, was the first to point out that dengue is 
not contagious, but is due solely to the agency of mosquitoes. In a second paper, 
in 1903, he specified the common house-mosquito of the tropics (Culex quin- 
quefasciatus) as the responsible species and this has been experimentally con- 
firmed by some of the later investigators. 
Graham was led to investigate the possibility of mosquito agency in ihe 
propagation of dengue through the fact that at Beirut, where there was a very 
extensive epidemic, mosquitoes were excessively abundant, while certain high 
and dry mountain villages where there were no mosquitoes remained free from 
the disease. From the previous history of the disease he made the following 
deductions: 
“There is great multiplicity of evidence to show that it does not spread to any 
extent when carried away from certain low-lying regions, which are its favorite 
abode. Epidemics in Cuba, Jamaica, Hast Indies, Réunion, Martinique, and 
Madagascar, all seem to show that, in spite of the most active communication, 
dengue cannot spread to any extent when carried into dry and high places in the 
interior. These epidemics have shown time and again that people come down 
from these higher and drier places, contract the disease, and then have it break 
out on them in their homes to which they have returned, and there lie smitten 
with it for several days without the other inmates of the household catching it.” 
Graham went to work to prove experimentally the transfer of dengue by mos- 
quitoes. A mother suckling her child became ill with dengue. As soon as the 
diagnosis was made, wire screens were put in all the windows of the house, and 
the mosquitoes in the interior were all destroyed. These precautions were con- 
tinued until the 10th day after recovery. The infant did not cease to nurse and 
remained constantly in its mother’s arms, yet it did not take the disease. In 
another case one of four children was attacked by the disease. The room was 
