256 INFECTION AND IMMUNITY 



fever patients and in these cases the result was 

 negative. In considering the experimental evidence 

 thus far obtained, the attention of the members of 

 the board was attracted by the fact that in the 

 nine inoculations with a negative result, " the time 

 elapsing between the biting of the mosquito and the 

 inoculation of the healthy subject varied in seven 

 cases from two to eight days and in the remaining 

 two from ten to thirteen days, whereas in two of the 

 three successful cases the mosquito had been kept 

 for twelve days or longer." 



The inference drawn by Dr. Reed and his asso- 

 ciates, from the experiments thus far made, was that 

 yellow fever may be transmitted by mosquitoes of the 

 genus Stegomyia, but that in order to convey the infec- 

 tion to a non-immune individual the insect must be 

 kept for twelve days or longer after it has filled itself 

 with blood from a yellow-fever patient in the earlier 

 stages of the disease. In other words, that a certain 

 period of incubation is required in the body of the 

 insect before the germ reaches its salivary glands, and 

 consequently before it is able to inoculate an individ- 

 ual with the germs of yellow fever. This inference, 

 based upon experimental data, received support from 

 other observations, which have been repeatedly made, 

 with reference to the introduction and spread of yel- 

 low fever in localities favourable to its propagation. 



