CHAPTER V. 
Staphylo¬ 
coccus 
pyogenes 
THE GROUP OF PYOGENIC COCCI. 
In the following chapters the characteristics of 
the individual species of bacteria associated with the 
production of disease will be considered. Inasmuch as 
certain ones are closely related in their growth, mor¬ 
phology, and manner of producing infection, it is 
convenient to form them into groups; thus there is 
the group of pyogenic cocci (pus-forming cocci) and the 
intestinal group, which may also be subdivided into the 
typhoid and dysentery groups. On account of their 
wide distribution and the frequency with which they 
cause infection, the pyogenic group will be considered 
Erst. 
The coccus that most commonly causes infection 
is the staphylococcus, so named because of its charac¬ 
teristic arrangement into clusters often likened to 
bunches of grapes. (See Fig. 2, A, page 7.) Several 
varieties are distinguished by the pigment they pro¬ 
duce when grown in cultures. The Staphylococcus 
aureus produces a golden-yellow pigment, the 5. citreus 
a lemon-yellow pigment, while the S'. albus grows with¬ 
out forming any color. The Staphylococcus epider- 
midis albus is a variety found in the under layers of the 
skin. The size of these coccus forms differ, some being 
larger than others. They do not form spores, all are 
without motility, and all are Gram positive. 
(44) 
