BIOLOGY OF PNEUMOCOCCUS 53 



grate under certain physical conditions of the medium which favor 

 the action of its own lytic ferments. Burgers 187 was among the first 

 to study the self-dissolution of pneumococci. He reported that 

 autolysis, while favored by the addition of chloroform, was pre- 

 vented by heating the organisms to 60° or above. One of the envi- 

 ronmental conditions which influence dissolution is the degree of 

 acidity of the substrate. Mair 552 gave the range of hydrogen ion 

 concentration within which autolysis occurs as from pH 8.5 to 6.0, 

 with an optimum of pH 6.8. Lord and Nye 829 observed the dissolu- 

 tion of suspended living pneumococci of Types I and II in isotonic 

 standard solutions and in approximately isotonic bouillon having 

 reactions between pH 4.0 and pH 8.0. Lysis took place with a reac- 

 tion higher than pH 5.0 and was most marked in the range pH 5.0 

 to 7.0. It was still observable on the alkaline side, but was absent 

 when the acidity was greater than pH 5.0. This phenomenon takes 

 place at ice-box, room, and incubator temperatures. Mair found 

 the rate of lysis increased to a maximum at 42°, and stated that 

 this maximum was due to partial destruction of the autolytic fer- 

 ment at higher temperatures, and also that the autolysin was more 

 sensitive to heat when the reaction was alkaline. Exposure of pneu- 

 mococci to 47° for one hour diminishes the degree of dissolution, 

 while an exposure of thirty minutes at 56° or five minutes at 100° 

 completely arrests the action. Inasmuch as Sternberg 1321 deter- 

 mined the thermal death-point as 52° for ten minutes, if the obser- 

 vation was correct, the lower temperature should suffice to prevent 

 self-lysis, but such is not the case. 



The addition of fresh human serum to suspensions of the cocci 

 at varying reactions prevents autolysis. Solutions of lysed pneu- 

 mococci added to fresh suspensions of pneumococci in standard so- 

 lutions of the same hydrogen ion concentration increase autolysis. 

 Cultures of S. viridans, S. haemolyticus, and Staphylococcus 

 aureus do not undergo dissolution under similar conditions. Ex- 

 tracts prepared by treating minced pneumonic lung tissue with 

 chloroform, toluene, and saline solution, or the sediment from such 



