1. The virus of Bartonella muris anemia of splenectomized rats may be transmitted to normal young unoperated rats and rabbits. This confirms the observations of Ford and Eliot.
2. Trypanosoma lewisi infections in normal adult rats are accompanied by an anemia most marked at the height of the infection and the appearance of Bartonella muris bodies in the red blood cells.
3. In young rats Trypanosoma lewisi may produce death from the severity of the anemia, complicating the disease. The anemic virus may be separated from the Trypanosoma lewisi infected blood by passage through young rabbits with subsequent maintenance of the strain in immature rats.
4. A strain of the virus of Bartonella muris anemia capable of producing an anemia in young rabbits and young rats for successive transfers has been isolated from the blood of normal adult unoperated rats by passage through young rabbits.
5. The adult normal rat is a carrier of the Bartonella muris virus.
6. Splenectomy in young suckling rats separated from the mother is not followed by a Bartonella muris anemia. The young suckling rat is not a carrier of the infection.