1. Within 24 hours following intravenous inoculation with rabbit virulent strains of pneumococcus Type III, most rabbits develop infections of one or both knees. The frequency of bilateral knee joint involvement increases as the duration of the disease is prolonged.
2. The spinal fluid, aqueous humor, and bladder urine remain sterile at a time when the knee joints contain pneumococci. Subsequently, however, they may be invaded.
3. The administration of a single dose of type specific horse immune serum, at a period when in all probability one or both knee joints contain organisms, appears to be ineffective in bringing about resolution of the infections process in these sites, even though horse serum constituents may be demonstrated serologically to be present within the joint cavities.