Fig. 43.—Aedes calopus (Stegomyia calopus), female. From P. H. Reports.
Fig. 44.—Aedes calopus (Stegomyia calopus), male. From P. H. Reports.
4. The blood of a yellow fever patient in the first three days, which was sterile for B. icteroides, was capable of producing the disease when injected subcutaneously. If heated to 55°C. for ten minutes the virus was destroyed however. Furthermore, infectious blood when passed through a Berkefeld filter remained infectious, thus showing that the virus is a filterable virus.
The French Commission verified these findings and in addition brought out the following points.
1. Cutaneous vaccination with infective serum is without result.
2. Infectious serum loses its yellow fever-producing power in forty-eight hours unless preserved under liquid petrolatum when it remains virulent for five days.
3. Infectious serum if heated for five minutes at 55°C. loses its virulence but has prophylactic and curative power.
4. Besides the method of hypodermic inoculation yellow fever can only be transmitted by the bite of a mosquito in which the virus has remained for at least twelve days.