Further experiments with the soluble antigen of the MEF1 poliomyelitis virus

By ultracentrifugation of emulsions of brains from suckling mice infected with the MEF1 strain of poliomyelitis virus, infective virus can be separated from a non-infective soluble antigen. The soluble antigen which remains in the supernatant fluid is serologically specific and is responsible for most of the complement fixation shown by such brain emulsions. Soluble antigen is not demonstrable in the brains of adult mice infected with a strain of the virus which has not been adapted to sucklings. The soluble antigen is heat stable and resists treatment with organic lipoid solvents such as acetone, ether and chloroform.