1. The two strains of virus named GD VII and FA, respectively, accidentally discovered during experiments with yellow fever, have been shown to be immunologically related to each other, as well as to the virus of mouse encephalomyelitis.

2. Infection of the central nervous system can be produced with both strains by intracerebral, intranasal, or intraperitoneal inoculations. The cardinal symptom produced by the GD VII strain of virus by all three methods of inoculation is a flaccid paralysis of the limbs. The symptoms produced by the FA strain are referable to lesions of the brain when infection is produced by intracerebral and intranasal inoculation. Following intraperitoneal inoculation of the FA strain of virus, however, a flaccid paralysis is usually produced.

3. By the use of graded collodion membranes the particle size of the virus of mouse encephalomyelitis has been shown to be from 9 to 13 mµ

4. The stability of the virus at different hydrogen ion concentrations has been tested. It has been found that there are two optima of stability, one at about pH 8.0 and the other at pH 3.3.

5. The virus is readily inactivated at 37°C. by 1 per cent hydrogen peroxide.

6. Of organic solvents tested, ether had no action, whereas ethyl alcohol in 20 per cent concentration almost completely inactivated the virus after 45 minutes in the cold.

7. The virus can be precipitated by means of ammonium sulfate.

8. With increasing age mice acquire a relative resistance to the virus.

9. Immunity to a subsequent intracerebral inoculation can be produced by intraperitoneal, as well as intranasal, administrations of relatively large amounts of virus.

10. Mice infected by the intracerebral inoculation of a relatively avirulent virus acquire a high degree of immunity to a subsequent inoculation of a highly virulent strain.

11. The course of infection in mice following intracerebral, intranasal, and intraperitoneal inoculation of the FA strain of virus has been studied.

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