1. Blood and joint fluid of patients suffering from rheumatic fever were inoculated into the testicles of rabbits, and transfers were made from testicle to testicle at varying intervals. In three series, in none of which were the periods between the transfers longer than 4 days, a virus was recovered which produced acute orchitis in rabbits. The virus could be indefinitely propagated from rabbit to rabbit.

2. Intradermal inoculation of the virus led to the appearance of raised erythematous lesions in 3 to 6 days.

3. Intrathoracic inoculations near the heart led to a fibrinous pericarditis in three out of five rabbits, and to a myocarditis in one.

4. Nuclear inclusion bodies staining pink with eosin were found in the lesions in the testis, skin, pericardium, and heart muscle.

5. Rabbits inoculated into skin or testes were refractory, 2 weeks later, to further intradermal inoculations; after this interval their serum had developed the power to neutralize the virus in vitro.

6. The virus can be preserved in 50 per cent glycerol for at least 18 days. It can be preserved after freezing and drying for at least 8 days and probably for 10 weeks.

7. Cross-immunity tests point to the identity of the virus with that described by Rivers and Tillett in their studies on chicken-pox as Virus III.

8. These facts together with the failure of rheumatic fever sera to neutralize the virus indicate that it bears no etiologic relationship to rheumatic fever.

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