A specific disease entity was established in white mice by the nasal instillation of lung and exudate suspensions from each of 14 adult albino rats affected with endemic pneumonia.

The induced disease was characterized by pneumonia (96 per cent), otitis media (94 per cent), and rhinitis (30 per cent). It progressed slowly after an incubation period of 7 to 14 days and was attended by a variable mortality which reached 33 per cent in 22 weeks.

Maintenance of the disease was regularly accomplished by direct transmission from mouse to mouse but only by the nasal route and only from the three foci of involvement. It was also transmissible by direct contact but required a prolonged period of exposure.

The relation of the disease to infectious catarrh, which it closely resembles, is discussed.

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