Experimental Fibrositis due to a Virus, and Some Observations on the Experimental Production of Arthritis.

OBSERVATIONS were made in the first place with a pathogenic strain of variola-lapine, the M4 strain of Tulloch originally raised by Sobernheim by inoculating rabbits with smallpox crusts. In order to develop its virulence to the fullest degree, this virus was first passaged through the testis of a series of rabbits. The chief material used consisted of a 1: 50 suspension of the passage testis in broth that was centrifuged for thirty minutes at 3,000 r.p.m. to remove the heavier particles. The clear supernatant fluid was sterile on culture and active on the rabbit's skin up to a dilution of over 1:1,000,000. In some experiments a broth suspension of the young papules on the rabbit's skin three days after scarification was employed, and the results were similar. The inquiry was undertaken expressly in view of the present discussion, and the primary object was to see if by repeated doses venously this M4 virus produced malignant endocarditis in rabbits. It was found, however, that by giving two doses venously separated by an interval of four days the rabbits developed symptoms of arthritis (limp on moving). When the dose was too large or the virus especially virulent a polyarthritis developed, but usually only one hind leg was affected. On palpating the affected joint the lesion was found to be periarticular rather than articular, and the commonest site was in the region of the insertion of the tendo Achillis (see Fig. 1). These periarticular swellings never suppurated, and if left alone gradually cleared up. When the rabbit was killed at an early