BIOLOGY OF PNEUMOCOCCUS 39 



one per cent, because of the glycolytic action of Pneumococcus 

 with the resulting acid production, may produce retardation 

 or complete inhibition of growth and bring about autolysis 

 (Wright 1548 ). The presence of muscle sugar in the meat base must 

 be reckoned as an additional sugar factor when fermentation reac- 

 tions are to be quantitatively measured. McGuire, Valentine, Whit- 

 ney, and Falk 879 advised titration of the fermentable reducing 

 sugar in muscle (beef heart) infusion and, taking the equivalent of 

 0.5 milligram of glucose per cubic centimeter as the lower limit, 

 then added glucose to the desired concentration. Glycerol may re- 

 place glucose or other sugars as a source of carbohydrate mate- 

 rial, but glycerol, like the other sugars, is susceptible to the 

 fermentative action of Pneumococcus and yields acid on enzymatic 

 cleavage. 



The acid formed in broth by the action* of Pneumococcus may 

 be neutralized either by the addition of sterile, powdered calcium 

 carbonate (Wurz and Mosny, 1554 and Hiss 650 ), or of small pieces 

 of marble, washed and placed in the test tubes before filling and 

 sterilization (Bolduan 135 ). 



The initial hydrogen ion concentration of the medium and the 

 changes occurring during growth are vital factors in the proper 

 cultivation of the organism. According to Dernby and Avery, 313 

 culture media should have an initial reaction represented by a pH 

 of 7.8 to 8.0 with an optimal pH of 7.8. They gave the limiting hy- 

 drogen ion concentration for initiation of growth for the various 

 types of Pneumococcus as pH 7.0 to 8.3. Strains will live but will 

 not actively multiply in substrates having a degree of acidity or 

 alkalinity greater than those represented by these figures. Lord 

 and Nye 829 have given further information regarding the relation 

 of hydrogen ion concentration to the life, growth, and death of 

 Pneumococcus. As the medium becomes more acid (pH 7.4 to 6.8) 

 the organism may live many days; between 6.8 and 5.1 death be- 

 gins to take place — the greater the acidity, the more rapid the 

 death, while at 5.1 the cocci die within a few hours. In cloudy sus- 



