The hepatitis of Princeton weanlings was not prevented by the prior injection of terramycin nor was the virus inactivated by exposure to room temperature.

Eperythrozoon coccoides was not demonstrable in blood films from Swiss and Princeton mice infected with the corresponding type of hepatitis virus.

Combined infection with this virus and eperythrozoa, originally obtained by Dr. R. B. McGhee from mice in association with Plasmodium berghei, was attended by the appearance of numerous organisms in the blood.

The development of eperythrozoa in dually infected Princeton mice had no effect on the outcome of the hepatitis.

In Swiss mice, animals with high natural resistance to hepatitis virus, the pathogenicity of this agent was markedly enhanced by combined infection with eperythrozoa.

Eperythrozoa were maintained throughout 18 successive passages in normal Princeton and Swiss weanlings with intact spleens.

The combined infection of Princeton mice with eperythrozoa and the virus component of Gledhill, Dick, and Andrewes, which is nearly inactive when injected alone, resulted in acute hepatitis with fatal outcome.

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