Mice, Inbred BALB CBALB 3T3 Cells: Cell lines developed from disaggregated BALB/c mouse embryos. They are extremely sensitive to CONTACT INHIBITION, and highly susceptible to transformation by SV40 VIRUS and murine sarcoma virus (SARCOMA VIRUSES, MURINE).Spleen: An encapsulated lymphatic organ through which venous blood filters.Mice, Inbred Strains: Genetically identical individuals developed from brother and sister matings which have been carried out for twenty or more generations, or by parent x offspring matings carried out with certain restrictions. All animals within an inbred strain trace back to a common ancestor in the twentieth generation.Mice, Inbred C57BLLeishmania major: A parasitic hemoflagellate of the subgenus Leishmania leishmania that infects man and animals and causes cutaneous leishmaniasis (LEISHMANIASIS, CUTANEOUS) of the Old World. Transmission is by Phlebotomus sandflies.