26 VASSAL AND BROCKET. 



The prevalence of dengue at certain seasons at Saigon is very notice- 

 able. The epidemic of the Kersaint began ,on the 11th, that of the 

 Manche on the 21st of May. This is also the hottest and most un- 

 healthful month of the 3fear, besides being the one in which there are 

 the most mosquitoes. The epidemic of 1895 and 1896 raged in April, 

 Ma}'^, and June (Nogue). 



In 1907, the Manche, while anchored in the Kiver of Saigon, became 

 infested with mosquitoes and the officers could not succeed in ridding 

 her of them. On the contrary, the mosquitoes found many collections 

 of water and particularly the bilge water for breeding purposes. The men 

 not using mosquito-nets were unable to sleep at night, and some of them, 

 through continual scratching, became covered with boils. In June the 

 numbers of mosquitoes increased. They were exclusively Culicidce among 

 which Gulex fatigans Wied. predominated. Is it not significant that 

 the first case which appeared, was in the sailor who was in charge of the 

 bilge water and that the epidemic spread first to the persons nearest the 

 reservoir? The Manche, being a wooden vessel, enjoyed a moderately 

 even temperature and did not suffer from the abrupt changes which 

 sometimes are so disturbing on iron ships. However, conditions favor- 

 able to man are also favorable to the mosquito. This boat, constructed 

 for the cold regions of the north, was not adapted to a tropical climate. 

 For instance, the deck was surrounded by high ports which hid the sea 

 from view and prevented a thorough ventilation. Conditions on this 

 vessel seem favorable for the development of dengue, since it is the second 

 time in two years that this disease has visited it. The origin of the 

 actual epidemic was probably in Saigon. 



The other etiologic circumstances are of little importance. In June, 

 the meteorological phenomena were normal. The barometer remained 

 between 755 and 760 millimeters; the thermometer oscillated between 

 25° and 31°. 6, giving an average of 28°. 5 C. The hygrometric readings 

 were high during the whole time of the epidemic. In spite of the 

 numerous showers and frequent storms, the atmosphere was continually 

 heavy. Life on board ship is favorable to the spread of any epidemic, 

 but particularly to those disseminated by insects. To sum up, the role 

 •played by mosquitoes on the Manche in connection with this epidemic 

 appeared to be of considerable importance. It is in fact the only im- 

 portant etiologic factor to be considered. 



IMMUNITY. 



"Dengue prevails indiscriminately in spite of age, sex, or race," says 

 de Brun. We were, therefore, astonished to observe that not a single 

 Annamese servant or sailor developed the disease. They had also shown 

 a marked immunit}'' during the epidemic of 1906. These natives were 

 quite as much exposed as the Europeans and their diet was the same. 



