1. The yellow fever virus was found in infectious form in Aedes ægypti throughout the entire period of the extrinsic incubation, as demonstrated by the injection of the bodies of mosquitoes into normal rhesus monkeys at daily intervals after the insects had fed on an infected animal.
2. The virus was transmitted through the bite of the mosquitoes, in one experiment on and after the 9th day, and in two experiments on the 12th day after the initial infecting feed.
3. The pathologic changes produced by the injection of the infected mosquitoes into normal monkeys during the extrinsic incubation were in every respect those of typical experimental yellow fever.
4. The monkeys withstand easily the subcutaneous injection of the mosquito emulsion. No acute inflammatory reaction was observed at the site of injection in any of the seventeen animals inoculated with this material in these three experiments.