He absorbed Schrodinger and evaporated into the realm of imaginary numbers (not making this up), since shrodinger can no longer recognize himself among the souls. Walter destroyed the doctor as well as Alucard's first victim...the person who they used as a template for vampires Mina Harken (who at this point was a skeleton). Eventually, Alucard returns after eliminating all the people inside his body, gaining Schrodingers ability as well.