In some apparently healthy mice the virus of lymphocytic choriomeningitis persisted for a considerable period of time after recovery, in the blood, urine, and nasal secretions, while in other mice it soon became undemonstrable. It is possible that the persistence of the virus is due to lesions in the lungs, liver, and kidneys.
The immunity to lymphocytic choriomeningitis in mice does not seem to depend upon the presence of virus in the blood and the organs tested. No antivirus was detected in sera from several solidly immune mice, which fact suggests that circulating antivirus plays no important part in their immunity. Leucocytes also seem to be no essential factor in this immunity, which probably is closely linked with the tissues.
The urine of guinea pigs which had recovered from severe attacks of lymphocytic choriomeningitis contained virus for a few weeks after recovery, while that from mild cases contained no virus. Virus was never demonstrated in the blood of immune guinea pigs. Antivirus was readily detected in it.