In his study of the action of yellow fever virus in mice, Theiler (1) pointed out that injection of the virus into the brain results in fatal encephalitis. In such mice the virus is present at death in high concentration in the brain, spinal cord, sciatic nerve and adrenal glands. It is either entirely absent or is present in very small amounts in the blood, liver, spleen, kidney and testis. Injection of virus by any other route seldom results in infection and death, but often produces immunity to a subsequent intracerebral inoculation of virus.
Lloyd and Mahaffy (2) reported success in maintaining the French neurotropic strain of yellow fever virus in mouse testicles through nine consecutive passages. They met considerable difficulty in continuing such passages due to bacterial contamination and to loss of the virus from other causes, and in only one of six attempts were they able to carry the virus beyond the third passage.