1. The infectious agent of trachoma can be freed from extraneous bacteria by passage through rabbit testicle.
2. The infectious agent multiplies little, if at all, during such passage, but in many instances retains its infectivity undiminished.
3. No specific changes occur in the rabbit testicle incidentally to the passage.
4. On rare occasion the trachoma agent may be freed from bacteria by intracerebral passage. The brain tissues show no specific reaction.
5. Filtration experiments with Seitz, Kramer, Berkefeld, and Elford filters confirm the general observation that the infectious agent is filterable with difficulty.
6. Tissue culture experiments, with tissues containing the infectious agent (conjunctiva, rabbit testicle, brain, etc.), conducted under a wide variety of conditions, proved uniformly unsuccessful in the cultivation of the agent.
7. The agent is inactivated by bile, AgNO3, phenol, cocaine, tartar emetic, and gentian violet. Its heat inactivation temperature is between 45° and 50°C., at a time interval of 15 minutes.
8. Attempts to preserve the infectious agent in glycerine were unsuccessful.
9. The accumulated evidence suggests that the infectious agent of trachoma is a virus.