IT has long been known that a virus may become widely disseminated following intracerebral inoculation into an experimental animal. Thus generalized spread has been found throughout the guinea pig fœtus after intracerebral inoculation of influenza virus¹, vaccinia, tubercle bacilli, and submaxillary gland disease virus²; and yellow fever virus has similarly been demonstrated in remote sites after inoculation of the mouse fœtus³. However, Schlesinger⁴ observed that only 3–10 per cent of the inoculum could be demonstrated in the brains of mice one hour after inoculation, whether equine encephalomyelitis virus or bacteriophage was the test agent, and stated that he was unable to account for this loss. In view of the common usage of intracerebral inoculation in small animals, it seemed desirable to pursue the matter further.