1. Two cases of rat-bite fever with a typical fever course and a maculopapular exanthem came under my observation in Mexico.
2. A spiral organism morphologically identical with one known in Japan as the causative agent of Sodoku was found in a Mus decumanus caught in Mexico City.
3. The organism was found to be pathogenic for white rats and guinea pigs, the infection being fatal for guinea pigs.
4. The bite of an infected guinea pig led in one of two instances to infection and death of the animal bitten.
5. The microscopical findings in the guinea pigs infected with this microorganism closely resemble in many respects the findings in Blake's case and in Kaneko and Okuda's first case, the only ones of human rat-bite fever which have been closely studied at post mortem.
6. Eye lesions were found in all the infected guinea pigs and the spiral organisms were demonstrated in the discharge from the eyes and also within the cornea.
7. Similar eye lesions were found in most of the infected rats and the secretion from the eyes of one of them was demonstrated to be infectious for guinea pigs.
8. The eye lesions constitute an evident source for the spiral organisms transmitted by biting, and not improbably the only one.
My experiments may give an explanation for the transmission of some other spirochetal diseases besides rat-bite fever. Cases of Weil's diseases are reported to be caused by the bite of a rat and it is noteworthy that eye lesions occur in spirochætosis icterohæmorrhagica (Manson).