when the virus was introduced directly into the brain or the nasal cavities and mouth , none was found in the intestinal tract until there was general centrifugal spread from the central nervous system during the last stages of the infection at 96 or 120 hours after inoculation when the virus in the entire brain had reached a concentration of about 3 billion ld ( 50 ) .
C0006104
the
C0086045
concentration