CHAPTER V. 

 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 con- 

 venient 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 con- 

 sidered first, 

 staphyio- The coccus that most commonly causes infection 



coccus . . 



pyogenes is the staphylococcus, so named because of its charac- 

 teristic arrangement into clusters often likened to 

 bunches of grapes. (See Fig. i, A, page 7.) Several 

 varieties are distinguished by the pigment they pro- 

 duce when grown in cultures. The Staphylococus 

 aureus produces a golden-yellow pigment, the S. 

 citreus a lemon-yellow pigment, while the S. albus 

 grows without forming any color. The Staphylococcus 

 epidermictis 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, and all are without motility. 

 (42) 



