chapter xiii. 
thp: streptococcus-pneumococcus group. 
The Streptococcus Group. I Stkeptococci in Scarlet Fever. 
Streptococcus Pyogenes. The Pneumococcus. 
Streptococcus Einheit or Vielheit. ' 
THE STREPTOCOCCUS GROUP. 
The streptococcus group comprises those spherical bacteria in 
which as muhiphcation proceeds, the successive planes of division 
are parallel and the individual cells remain adherent in longer or 
shorter chains. The limits of the group are poorly defined, both 
morphologically and pathogenically. It inclufles organisms which 
occur habitually in chains, both in culture and in the animal body, 
and its limits have been extended by some authorities to enclose 
types which exhibit chain formation only in fluid media. The latter, 
of which Micrococcus ovalis and the pneumococcus are examples, 
occur in the animal body as diplococci, and grow thus on solid media; 
in fluid media they grow habitually in chains of greater or lesser 
length, in which, however, the typical diplococcal arrangement per- 
sists. The term streptococcus, therefore, is a purely morphological 
one; it includes organisms which excite various types of inflammation 
or infection in man and in animals, together with those which are 
ordinarily saprophytic. 
Many members of the group exist on the skin, and particularly on 
the mucous membranes of man, as habitual parasites or "opportunists." 
Streptococcus pyogenes and its variants are the most common of these 
and the most versatile in their pathogenesis. 
Streptococcus Pyogenes. — Synonyms. —Streptococcus hemolyticus ; 
Streptococcus erysipelatosj Streptococcus scarlatinosus; Streptococcus 
septicus. 
Historical.— Streptococci were seen in unstained pus by Klebs in 
1872. Several years later Koch' demonstrated them in stained sec- 
tions and in inflammatory exudates. Pasteur- appears to have been 
the first to cultivate streptococci from cases of puerperal fever and to 
dift'erentiate them from staphylococci, both morphologically and by 
the character of the lesions which they excite. Ogsten'' independently 
confirmed Pasteur's observations. Fehleisen,'* using more exact cul- 
1 Untersuchungen i'lber Wundinfektion, 1878. 
2 Compt. rend. Acad. Sci., 1880, 90, 1035. 
3 British Med. Jour., 1881, i, 369. 
4 Aetiol. d. Erysipelas, Berlin, 1883. 
