144 BACTERIA 



one that is faintly acid and contains animal juices like serum. 

 They must be transplanted frequently. On gelatine they grow 

 scantily without liquefaction, the growth consists of discrete little 

 masses, while on agar they appear translucent colonies of very 

 small grayish granula. In bouillon cultures some varieties either 

 cloud the medium uniformly, or else sedimentate in the form of 

 little balls, the supernatant fluid remaining clear. It ferments 

 some simple sugars but does not form gas. In milk the growth is 

 more luxuriant, and becoming acid, may be coagulated in twenty- 

 four hours. On potato the growth is invisible and scanty, or 

 absent. On blood agar plates colonies appear as tiny gray 

 points with a zone of hemolysis about them. Sugar media 

 of the simpler carbohydrates, show acidification. 



Vital Resistance. Thermal death-point is 54C. in five min- 

 utes. Virulence in dried albuminous matter (pus) is retained for 

 months. If kept on ice, vitality and virulence are retained for 

 months also. 



Chemical Activities. Lactic acid and sulphuretted hydrogen are 

 produced, also ferments which have the property of dissolving 

 fibrin under anaerobic conditions. They are also capable of dis- 

 solving red blood corpuscles, either in culture media or in the 

 body and about cultures on blood agar plates there is a clear halo 

 of hemolysis, streptocolysin. They produce a strong soluble 

 toxin, which can be filtered from the bouillon and precipitated 

 with alcohol. This causes necrosis, anaemia and death. 



Habitat. In sewage, dwellings, dust, on the healthy human 

 body, and in the cavities of the respiratory tract, vagina, rectum, 

 and in the faeces. It is the cause of many diseases, i.e., erysipelas, 

 puerperal fever, meningitis, pneumonia, endocarditis, peritonitis, 

 tonsillitis, osteomyelitis, and the diarrhoea of children. 



In general septicaemia streptococcus is found in the blood, and 

 plays an important role in secondary infection, causing an aggra- 

 vation of the original infection, and often death. It is especially 

 active in phthisis, scarlatina, small-pox, and diphtheria, in which 



