170 



Insects and Disease 



Protozoan parasite that is found in the blood of 

 dengue patients and several experiments have been 

 conducted by Dr. Graham which seem to indicate 

 that it is transmitted by mosquitoes. In these ex- 

 periments, Culex jatigans, a common tropical or 

 subtropical mosquito, was used. The same para- 

 site that is found in the human blood may be found 

 in the stomach and blood of the mosquitoes up to 

 the fifth day after it has fed on a dengue patient. 



Sick and healthy individuals were allowed to re- 

 main in close contact in a room from which the 

 mosquitoes had been excluded, and the disease was 

 not spread. Mosquitoes that had bitten dengue 

 patients were taken to a higher region where 

 dengue had never occurred and allowed to bite two 

 healthy persons. Both developed the disease and 

 as they were protected from other mosquitoes until 

 they had recovered, the disease did not spread to 

 others of the community. These and other ob- 

 servations seem to make a complete chain of evi- 

 dence, and most medical men to-day accept the 

 theory as well proved and in their practice take 

 every precaution to prevent the spread of the 

 disease by keeping the infected patient from being 

 bitten by the mosquitoes. 



The yellow fever mosquito is also suspected of 

 carrying this same disease, and it is possible that 



