1. The organisms described by Schottmüller under the name Streptococcus mucosus represent a well defined group with characteristics which indicate a closer relationship to the pneumococci than to the streptococci.
2. The members of this group are specifically agglutinable when treated according to the method of Porges. They do not agglutinate when subjected to the usual agglutination methods.
3. Complement fixation experiments with these organisms, compared with similar experiments with two varieties of pneumococci and two streptococci, indicate that they are closely related to the pneumococci.
4. No protection of mice against Pneumococcus mucosus by means of specific immune sera could be demonstrated.
5. The name Pneumococcus mucosus should be adopted for this group instead of Streptococcus mucosus.