THE MOSQUITO THEORY. 459 



voluntarily allowed themselves to be bitten with mosquitoes 

 which had previously fed on the blood of yellow-fever patients, 

 ten took the disease, the period of incubation being from three 

 to six days. Two of the men who were thus infected had been 

 previously exposed to contact with fomites without result. The 

 species of mosquito found capable of carrying the infection in 

 this way is the Stegomyia fasciata. It was found that a period 

 of about twelve days must elapse after the insect bites a patient 

 suffering from yellow fever before it becomes infective to another 

 subject, and, on the other hand, that it retains the power of infec- 

 tion for nearly sixty days later. These results have been con- 

 firmed by Guiteras, whose investigation was carried out along 

 similar lines ; of seventeen individuals bitten by the infected 

 stegomyia, eight took yellow fever and of these three died. 



As yet nothing has been determined by these workers regard- 

 ing the nature of the virus, but the results already obtained have 

 supplied the basis for preventive measures against the disease, 

 these being directed towards the destruction of mosquitoes and 

 the protection of those suffering from yellow fever, and also the 

 healthy, against the bites of these insects. Already a striking 

 degree of success has been obtained in Havana.. Such measures 

 came into force in February, 1901, and in ninety days the town 

 was free of yellow fever and for fifty-four days later no new 

 cases occurred. And although subsequently the disease was 

 reintroduced into the town, no difficulty was experienced in 

 stamping it out by the same measures. It would be unsafe, as 

 yet, to generalise from this particular instance, but there is 

 a good prospect that at least a measure of similar success will 

 be attained in other places. 



