146 BACTERIA 



are called Str. viridans. These are to be distinguished from 

 true pneumococci by the formation of a tiny rim of blood 

 clearing in blood plates and by their insolubility in bile. These 

 and the group of non-hemolytic streptococci are held responsible 

 for some cases of arthritis, endocarditis, sinusitis, nephritis, etc 



PNEUMOCOCCUS 



Streptococcus pneumonias commonly known as the pneumo- 

 coccus, or Diplococcus lanceolatus (Fig. 39). (For types see 

 page 76.) 



Morphology and Stains. This organism is usually found in the 

 tissues and sputum, in the form of lance-shaped cocci, surrounded 

 by a capsule. Is almost always associated in pairs, though some- 

 times in chains of five or six members. In albuminous fluids, or 

 blood serum, and in milk, the organism exhibits a well-defined 

 capsule; in bouillon and other media, it loses the capsule and the 

 lanceolate shape, and often appears spherical, in pairs, or chains. 

 It is not motile, has no flagella or spores, is easily stained by all 

 the basic aniline dyes, and keeps the color by Gram's method. 

 Under certain conditions it strongly resembles the streptococcus 

 pyogenes, and may be differentiated therefrom by growing it on 

 agar smeared with blood. The streptococcus causes a haemolysis 

 of the corpuscles, while the pneumococcus does not and the 

 colonies are greenish. 



Oxygen Relations. It is a facultative aerobe. 



Grows rapidly, but never luxuriantly at 37.5C.; at 22C. much 

 more -slowly, often not at all. Grows better in the presence of 

 serum or haemoglobin. 



Vital Resistance. Easily killed at a temperature of 52C., ex- 

 posed for ten minutes. Direct sunlight also kills it in twelve 

 hours. While it quickly dies on ordinary culture media, it may 

 live in dried sputum or pus exposed to diffuse light and desiccation, 

 for four months. 



