1. Infected material from the brain and spinal cord of an infant suffering from a recently recognized form of granulomatous encephalomyelitis was inoculated into rabbits and mice and produced an experimental disease which was readily transmissible in series.
2. A parasite identical with that in the lesions of the human case was found in the lesions of the experimental animals.
3. The morphology of this microorganism, the course of the disease and the lesions produced in the animals inoculated with it, the wide host range of this parasite, and the results of cross immunity experiments, establish its identity as a Toxoplasma. It is suggested that the microorganism be designated Toxoplasma hominis.
4. The clinical and pathologic features of the infection produced in animals by this Toxoplasma are described.
5. The infection in the infant is the first proved instance of human toxoplasmosis. Since the lesions were confined to the central nervous system the disease is termed toxoplasmic encephalomyelitis.
6. The first experimental transmission of human toxoplasmosis to animals is recorded.