Armstrong – Table of Contents

October 2) with the Freeman strain of St. Louis encephalitis but had failed to react with
recognizable symptoms. The eighth day following the inoculation from monkey 800,
however, monkey 37 showed a fever of 40.5C, was slightly tremulous and slow of
movement and refused food. The following day (November 11) the temperature was
40.2C. The spinal fluid was under increased pressure, clear and showed 439 cells per cu.
mm., almost entirely lymphocytes. The animal was etherized for passage. The brain was
markedly congested and edematous, but in no way distinguishable grossly from the
brains of monkeys infected with the usual St. Louis encephalitis strains.
“The microscopic pathology as reported by Surgeon R. D. Lillie, however, presented
peculiarities which reappeared with successive transfers. Likewise, transfers to white
mice revealed features quite distinct from those observed with other encephalitis strains,
and a comparative study soon compelled the conclusion that we were dealing with a
second distinct type of experimental infection.”
With the recognition that he was probably dealing with a previously unknown
infectious agent, Armstrong embarked on a detailed study to define the characteristics
and nature of the agent. He established that experimental choriomeningitis was caused by
a virus as indicated by the following considerations: 1) Transfer occurred repeatedly with
inoculums sterile to culture on ordinary media. Contaminating bacteria occurred rarely
and played no role in producing disease in experimental animals. 2) Filtrates of brain, as
well as spinal fluids and sections of nervous tissue demonstrated the harboring of the
infectious agent, and contained no visible or stainable organisms. 3) The infectious agent
suspended in either saline or broth readily passed a Berkefeld N (ceramic) filter which
held back ordinary bacteria (at conditions of room temperature, pH 7.6, pressure 40 mm.