304 MOSQUITOES OF NORTH AMERICA 



kept free from mosquitoes for 13 days. Its three brothers continued to play 

 with it during the day and to sleep -vnth it under the same bed-covering, and 

 none of them contracted the sickness. In a third experiment the head of a 

 family contracted the disease in the city and was willing to submit to Graham's 

 instructions to protect his wife and children. The same method was followed as 

 in the previous experiments. The rooms were kept as free from mosquitoes as 

 possible for 17 days, and although the man had a severe attack, lasting five days, 

 none of his family were taken ill. Several other experiments had to be aban- 

 doned because, through carelessness, mosquitoes had gained access to the rooms. 

 Graham then sought more positive proof and tried to inoculate the dengue 

 fever by the bite of infected mosquitoes. Four persons volunteered for the ex- 

 periment. " In each case several mosquitoes were taken from the netting of 

 patients sick with the fever and put inside the netting of the candidate for the 

 disease, he sleeping night after night with the mosquito in the netting." The 

 four volunteers were placed in a house where, for a long time, there had been no 

 sickness. They were forbidden to leave the house, or to receive any visitors. 

 Three of them came down with the dengue in from 4 to 6 days. The fourth one 

 passed about 15 nights with the infected mosquitoes without developing the dis- 

 ease ; but three years before he had had a violent attack of dengue and it would 

 seem had been thus made immune. Still Graham was not entirely satisfied that 

 this experiment would be accepted as conclusive. He therefore conducted an- 

 other experiment which eliminated as far as possible the chances of error. 



" In a city where so infectious a disease was raging I still felt that these three 

 men might have received the contagion in some other way. In order to avoid 

 this objection mosquitoes were taken from inside the netting of a dengue patient 

 and carried up to a village on the mountain slope where as yet no case had 

 occurred. After visiting my patient for the infected mosquitoes I changed my 

 clothing and took a bath before mounting my horse to ascend the mountain. 

 In this village, about 3000 feet above the sea, there are almost no mosquitoes. 

 It is dry and very healthy. I easily found two young men in difi^erent parts of 

 the village who consented for a consideration to take their chances of having the 

 dengue. One of them, after sleeping four nights under the netting with the 

 mosquitoes, was taken with a severe typical attack of dengue. The other had 

 his initial chill after having passed five nights in the company of the mos- 

 quitoes. These men continued to sleep under the mosquito nettings I had pre- 

 pared for them until some time after they were well, all the mosquitoes in the 

 netting having been killed to avoid infection of other people. No other cases of 

 dengue occurred in this village during the summer that I could learn of, al- 

 though I made the most careful inquiry." 



Bancroft, in Australia, suspected the transmission of dengue by the yellow- 

 fever mosquito, Aedes calopus. Ashbum and Craig experimented on the mos- 

 quito-transmission of dengue at Fort William McKinley near Manila. Their 

 experiments with Aedes calopus resulted entirely negatively. With Culex quin- 

 quefasciatus they succeeded in producing a typical attack, the mosquitoes em- 

 ployed by them having been reared from the eggs and allowed to bite a patient 

 with a well-marked case of dengue. 



