356 PATHOGENIC MICROORGANISMS 



of pneumococcus cultures. An increase of the amount of pepton 

 used for the preparation of media is desirable for the cultivation of 

 this microorganism; two to four per cent of pepton may be found 

 advantageous. 



In suitably alkaline, nutrient broth, growth is rapid, and within 

 twenty-four hours leads to slight clouding of the fluid. This clouding, 

 as a rule, eventually disappears as the microorganisms, sinking to 

 the bottom of the tube or disintegrating, leave the fluid more or 

 less clear. In broth, pneumococci have a tendency to form short 

 chains. When glucose has been added to the broth, growth is more 

 rapid and profuse, but considerable acid formation causes the cultures 

 to die out rapidly. It is possible, however, to employ glucose as a 

 growth-enhancing element in broth cultures without interfering with the 

 viability of the cultures by adding small quantities (one per cent) of 

 sterile, powdered calcium carbonate. This method of cultivation in 

 broth is especially adapted to the production of mass cultures for purposes 

 of immunization or agglutination. 1 The addition of ascitic fluid or blood 

 serum to broth, in the proportion of one to three, makes an extremely 

 favorable medium in which growth is rapid and profuse. 



Upon agar plates, pneumococcus growth is not unlike that of strepto- 

 coccus. The colonies are small, round, and slightly more transparent 

 than those of the streptococci. They appear more moist than strepto- 

 coccus colonies and often are more flat. Microscopically examined, the 

 colonies are finely granular, with dark centers and slightly corrugated 

 lighter-colored peripheral areas. Under high magnification no such in- 

 tertwining convolutions can be seen as those noticed under similar 

 magnification in streptococcus cultures. The addition of animal albu- 

 min to agar results in the more rapid development, larger size, and deeper 

 opacity of the colonies. 



Agar stab cultures show growth within twenty-four to thirty-six 

 hours, which takes place with equal thickness along the entire course of 

 the stab. There is nothing distinctive in these cultures to differentiate 

 them from similar streptococcus cultures. 



In gelatin plate and stab cultures at 22 C., growth, as a rule, does not 

 take place. This, however, is not true of all races of pneumococci. 

 Occasionally strains are met with which will grow fairly abundantly in 

 gelatin at a temperature of 22 C. When the gelatin is rendered suffi- 

 ciently firm to bear 25 to 26 C. without melting, growth appears 



1 Hiss, Jour. Exp. Med., vii, 1905. 



