Suspensions of living pneumococci in approximately isotonic standard solutions and in approximately isotonic bouillon with pH varying from about 4.0 to 8.0 after incubation show dissolution of organisms in those solutions having a pH higher than about 5.0. Dissolution is most marked at a critical range of about pH 5.0 to 7.0. Some dissolution also takes place toward the more alkaline end of the scale. No dissolution occurs at the most acid end of the scale.
Dissolution in the standard solutions occurs at incubator, room, and ice box temperature. It is less marked at ice box temperature. Dissolution takes place in standard pH solutions with pneumococci allowed to grow and die out in glucose bouillon but unlike dissolution with living organisms is progressive from the acid toward the alkaline end of the scale. Pneumococci killed by heat for I hour undergo less dissolution than living organisms, the general character of the curve being similar to that with living organisms. Pneumococci killed by heat at 100°C. for 5 minutes do not undergo dissolution. The addition of fresh human serum to the suspensions of pneumococci at varying pH prevents dissolution. Dissolution of pneumococci takes place more rapidly at pH 6.1 in standard solutions in which large numbers of pneumococci have been previously dissolved than in fresh standard solutions at the same pH.
The dissolution of pneumococci under the conditions of the experiments may be ascribed to an enzyme derived from the bacteria themselves.
Other organisms such as Streptococcus viridans and hœmolyticus and Staphylococcus aureus do not undergo dissolution under conditions similar to those to which the pneumococcus was exposed.