CHAPTER VIII 
THE STREPTOCOCCUS GROUP 
I. Historical 
The first studies on streptococci were made by Klebs, 
Koch, Pasteur and Ogsten. 
II. Morphology 
Streptococci are small spherical organisms, about 0.7 
in diameter. They usually are arranged in chains, 
whence their name (from Greek streptos, meaning 
twisted). The chains are usually longer in the strains 
just isolated from animal tissues than in those grown on 
artificial culture media. They also appear to grow in 
longer chains in liquid than in solid media. 
The streptococci are nonmotile, have no flagella, no 
spores, no capsules, although there is a strain of strep¬ 
tococcus wdiich regularly possesses capsules, the so-called 
streptococcus pyogenes (pus-producing) capsulatus, but 
today this organism is regarded as being one of the 
strains of pneumococcus and is called pneumococcus 
capsulatus (see section on Pneumococcus). 
Streptococcus is Gram-positive. 
III. Cultural Characteristics 
Streptococcus grows slowly on ordinary meat extract 
media, but luxuriantly on the “enriched” media, such 
as meat infusion media, especially when glucose or as- 
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