A catarrhal reaction manifested by a coryza and a pneumonia of characteristic pathology was regularly produced in mice by the nasal instillation of vaccinia virus. Inoculation into embryonated eggs indicated that the virus entered the circulation as early as the 2nd day after injection.

The vaccinial catarrh was readily transmissible by the passage of nasal exudate but not by contact. Dosage was important in establishing the virus in the nasal passages, the limiting dilution being approximately 10–3 of an egg membrane suspension (at least 1000 times the amount required to infect an embryonated egg).

The morbidity rate was variable but in general high, reaching 70 per cent in 2 groups of 50 mice. An immunity which was effective against reinfection for several months but ultimately declined was attendant on recovery. The amount of virus required to produce this immunity was significantly less than the infective dosage.

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