MULTIPLICATION AND SPREAD OF THE VIRUS OF ST. LOUIS ENCEPHALITIS IN MICE WITH SPECIAL EMPHASIS ON ITS FATE IN THE ALIMENTARY TRACT.

1. Beginning at 24 hours after intravenous injection of about 10 million intracerebral LD(50) of virus there was evidence of simultaneous, progressive multiplication in the brain and intestinal tract. 2. 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). 3. Centrifugal spread began when the virus in the brain reached a concentration of about 400 million LD(50) and virus appeared in the pharynx, tongue, and adrenals before it was demonstrable in the intestinal tract, blood, or viscera such as the spleen, liver, and kidneys. 4. Despite the high concentrations of virus which developed in the intestinal tract following intravenous inoculation, it was not demonstrable in the stools, differing in this respect from Theiler's virus in mice and poliomyelitis virus in human beings and monkeys. 5. No antiviral agent was found in the stools, but the urine of normal mice having a pH of 5.6, inactivated large amounts of St. Louis encephalitis virus. 6. There was no evidence of multiplication in the nasal mucosa of mice which succumbed with encephalitis following nasal instillation of the virus, the course of events being comparable in this respect to the behavior of the M.V. poliomyelitis virus in rhesus monkeys. 7. At the terminal stage of infection the virus content per milligram of tissue was as great in the leg muscles as in the sciatic nerves. Since this was also true for the urinary bladder, heart, lungs, and tongue among other tissues, and since the amount in the blood was too negligible to account for it, it would appear that the virus either accumulated in these tissues by diffusion from the nerve fibers, along which it was spreading from the central nervous system, or that it multiplied in some constituent other than the nerve fibers.