120 RELATIONSHIPS OF THE COCCACE^E 



D. pneumonia in certain artificial media is due to the 

 acid reaction which it produces, and may be forestalled by 

 carefully repeated neutralization of the culture medium. 

 The same author cites the interesting fact, noticed by 

 several observers, that the diplococcus forms long chains 

 when grown in serum containing its anti-bodies, just as 

 it does when grown in artificial media. 



The growth of the pneumococcus in the stab, or on agar 

 plates, closely resembles that of Str. pyogenes but is in 

 general less vigorous. Its colonies are thin and trans- 

 lucent. Buerger (1905) notes that on glucose-ascites-agar 

 the colonies, when seen from the side, show a series of 

 milky rings inclosing a transparent center. On blood 

 agar greenish colonies are produced with no hemolysis. 

 As noted in the previous discussion of the genus as a 

 whole, the fermentative powers of D. pneumonia are 

 high, acid being typically formed from dextrin, starch, 

 glycogen, and inulin, and even in diluted alkalin ox-serum 

 without the addition of any foreign carbohydrate. 



The virulence of the pneumococcus, like that of other 

 cocci, varies materially. A culture of exalted virulence, 

 injected into susceptible animals, mice or rabbits, pro- 

 duces death from general septicaemia. In more immune 

 animals a local inflammation follows, which may resemble 

 pneumonia if the lung tissue is the one affected 



On the whole there does not seem to be conclusive 

 evidence for the existence of more than one type center 

 among the pneumococci. Individual varieties exist in 



