Abstract
1. The attempt to infect young rabbits and guinea pigs with material containing in all probability the virus of human infantile paralysis failed. 2. Failure to infect the primary animals almost of necessity brought failure with the secondary flea-bitten animals. It is, however barely conceivable that a non-infectious form of an organism might circulate in the blood of the primary animal and that this form, through development in an intermediate host, the flea, might become virulent for the secondary flea-bitten animal. 3. Incidentally, and presumably accidentally, a paralytic disease was observed in young rabbits associated with the presence of an organism showing certain definite characters. So far as we know this paralysis and the associated organism have not been previously described. 4. This organism is found widely distributed in the organs of the affected animals and can be demonstrated in the urine. The active destruction by the organism of the nerve cells of the spinal cord is particularly striking, and gives complete explanation for the paralysis observed clinically. 5. With the organism present in the urine the spread of the disease by contact can be easily understood. 6. The transfer of the infection from animal to animal by fleabites is possible but not probable. 7. The nature of the observed organisms is in doubt. They represent probably an intermediate stage in the life history of some protozoan parasite.