1. An organism has been isolated from peat soil which decomposes the specific capsular polysaccharide of Type III Pneumococcus.
2. The isolation has been made possible by the use of a synthetic mineral medium containing the specific polysaccharide as sole source of carbon. By repeated transfers in this medium the potential capacity of the organism to decompose the specific substance has been progressively increased.
3. The organism is a pleomorphic bacillus, motile and spore-bearing, exhibiting metachromatic granules; its reaction to the Gram stain varies according to the medium on which it is grown. It is strictly aerobic and grows well in plain broth and peptone solutions; it does not produce gas in any media and it forms small amounts of acid only on dextrin, galactose, lactose, salicin, and trehalose; its growth is inhibited by glucose.
4. The organism decomposes the capsular polysaccharide of Type III Pneumococcus aerobically, between pH 6.2 and 7.8, at room temperature and at 37.5°C., but not at 54°C. The decomposition of the specific substance is inhibited by the presence in the medium of other nutrients, such as peptones, which act as a more readily available source of energy. The action of the organism is specific; it does not attack the soluble specific substance of Type I or Type II Pneumococcus, nor any of the other bacterial polysaccharides thus far tested.
5. The organism possesses an endocellular enzyme. This enzyme has been extracted by autolysis of the bacterial cells; in sterile solution it exhibits the same specific action as do the organisms from which it is derived, decomposing only the capsular polysaccharide of Type III Pneumococcus.
6. This enzyme decomposes the Type III specific polysaccharide under anaerobic as well as under aerobic conditions; it is inactivated at 60–65°C.; the rate of decomposition of the specific substance is not affected by the presence of normal serum.
7. There exists a quantitative relationship between the total amount of specific substance decomposed and the amount of enzyme preparation used; the existence of this relation makes it possible to express the activity of a given enzyme preparation in terms of the minimal amount required for the complete decomposition of a given amount of specific substance.
8. The specific decomposition of the capsular polysaccharide of Type III Pneumococcus, by the organism as well as by the enzyme it produces, illustrates once more the specificity of the types of Pneumococcus and confirms the fact that the capsular polysaccharides, and not some impurities carried along with them, are responsible for type specificity.