1. A mucin-producing spirochœta has been obtained in pure culture from a case of pyorrhea alveolaris. This organism is an independent species of the genus Treponema and, as it is recognized for the first time, I propose for it the name Treponema mucosum.
2. Morphologically the mucosum is difficult to separate from the pallidum and microdentium, but, through its biological properties and animal reactions it is easily differentiated from all the rest of the spirochœtæ.
3. The mucosum is not parasitic in the strict sense of the term, but exerts a certain pyogenous action when the tissue has been so injured by foreign substances as to enable it to survive.
4. The strong fetid odor in the discharge from pyorrhea alveolaris is due, at least in part, to the presence of the mucosum in the affected tissue.