I have described the successful cultivation of two distinct species of Treponema from the oral cavity of man. The species differ from one another morphologically and in respect to their cultural properties. As the two species have now been clearly separated and cultivated for the first time, I propose for them the names Treponema microdentium and macrodentium, respectively.
Division along the longitudinal axis has been demonstrated for both Treponema macrodentium and microdentium. When the micro- and macrodentium are cultivated under imperfect anaerobic conditions, they undergo involution, but still continue to vegetate to some extent. Finally, a spiral organism has been cultivated and described that may be merely an involuted form of the macrodentium, or it may be a new species altogether.