130 
principles op bacteriology 
longed cultivation, which suggests that the latter pro¬ 
tects the organism; it is nonmotile, has no flagella, no 
spores; is Gram-positive, (the Type III pneumococcus 
capsule is very large and may be seen without using the 
special capsule stain) the capsulated strain is always 
more virulent. (See Fig. 2.) 
IV. Cultural Characteristics 
Pneumococci do not grow on meat extract media; the 
best media are those which contain meat infusion and 
rabbit’s defibrinated blood; on such media colonies are 
small, discrete and greenish. 
Gelatin is not liquefied, milk is coagulated and acid is 
produced. Among sugars fermented is inulin—this is 
very important in differentiating the pneumococcus from 
streptococcus because the latter does not ferment inulin; 
bile dissolves pneumococci, but does not dissolve strep¬ 
tococci—another important differentiating point, on 
blood plates it does not cause hemolysis. 
Pneumococcus grows equally well with or without 
oxygen. 
V. Destruction 
Pneumococcus does not grow below 25° C. or above 41° 
C. Heating to 52° C. for ten minutes kills them, as do 
most of the ordinary chemical disinfectants. Even on 
the most favorable media it dies within a few days. 
The best way to preserve pneumococci is to grow them 
on defibrinated rabbit’s blood agar and keep the cul¬ 
tures in the ice box, or keep them in dried spleens of 
infected white mice, which should be kept in sealed tubes 
on ice; when culture is needed, spleen is rubbed with a 
little broth, the emulsion is injected into a white mouse, 
