1.Baby Swiss mice of less than nine days of age exhibit a high degree of susceptibility to both neurotropic and viscerotropic strains of yellow fever virus administered subcutaneously. The susceptibility is equivalent to that of adult mice of the same strain inoculated intracerebrally.
2.The incubation period with both neurotropic and viscerotropic viruses is prolonged in comparison with the same viruses inoculated intracerebrally in adult mice.
3.The marked difference in incubation times between the two strain types of virus, as seen in mice inoculated intracerebrally, is not encountered when the same viruses are studied by the subcutaneous route in baby mice.
4.The technic for the employment of baby mice in insect transmission experiments is described. An illustrative experiment with infected Aëdes aegypti mosquitoes is given.
5.With Aëdes aegypti mosquitoes infected with jungle virus, transmission to baby mice occurred with about the same frequency among those biting without engorgement as among those which filled with blood.