I. Conclusions :
(1) The common hedgehog, Erinaceus europaeus, is extremely susceptible to the viscerotropic strain of yellow fever virus.
(2) Death invariably occurs in from 4 to 7 days, the naked eye and histological changes being very similar to those met with in man and rhesus monkeys as a result of yellow fever.
(3) Virus is present at death in the blood, liver and kidneys.
(4) Repeated passages may be carried out in hedgehogs with material filtered through Berkefeld filters.
(5) After seven passages in hedgehogs, liver filtrate is still virulent for rhesus monkeys.
(6) Rhesus monkeys immune to known strains of viscerotropic and neurotropic yellow fever virus are also immune to the hedgehog passage strain.
(7) Filtrates of hedgehog livers inoculated intracerebrally into mice produce an encephalitis, histologically similar to that caused by neurotropic strains of yellow fever virus.
(8) The distribution of the Erinaceidae in Africa is described and the possible role of hedgehogs and other Insectivora in forming, in that continent, a virus reservoir for the maintenance of infected mosquitoes is briefly discussed.
II. Conclusions :
(1) The European hedgehog Erinaceus europaeus is susceptible to the neurotropic yellow fever virus injected intracerebrally, subcutaneously or intra- peritoneally.
(2) Symptoms develop in from 6 to 11 days and are invariably fatal.
(3) At death virus is present in the brain, liver, kidneys, spleen and adrenals but only rarely in the blood.
(4) Virus obtained from the organs of hedgehogs produces a fatal encephalitis 1n mice and behaves in these animals and in monkeys as a fixed neurotropic yellow fever virus. It can be passed through Seitz fIlters and is neutralized by known yellow fever immune sera.
(5) The lesions found in the central nervous system of hedgehogs inoculated with neurotropic yellow fever virus are slight whatever the mode of inoculation.
(6) In hedgehogs inoculated with neurotropic yellow fever virus lesions occur in the liver and stomach.
(7) In the liver there is focal degeneration of parenchymatous cells, with acidophilic necrosis of the cytoplasm, occasional intranuclear inclusions and infiltration with mononuclear and polymorphonuclear leucocytes. In the stomach there are petechial haemorrhages in the gastric mucosa.
(8) The action of the viscerotropic and neurotropic yellow fever viruses in the hedgehog is compared.
(9) The neurotropic virus does not acquire any increased capacity for producing more intense visceral lesions as a result of ten passages in the hedgehog.