1. A hitherto undescribed spiral organism has been isolated in pure culture from a case of mild phagedenic ulcer on the external genitalia of a woman. For this organism the name Spirochœta phagedenis is proposed.
2. Spirochœta phagedenis is a strict anaerobe and grows in the presence of fresh tissue in ascitic agar. It produces no apparent change in the media, but a somewhat offensive odor develops in the culture tube.
3. Spirochœta phagedenis incites a slight inflammatory reaction in the skin of a Macacus rhesus monkey and in the skin and testicles of rabbits.
4. Its etiological relation to the phagedenic lesions on the external genitalia has not yet been determined.