LESS COMMON PYOGENIC OBGANS. 279 



coccus pyogenes aureus. Staphylococcus pyogenes albus 

 and citreus may be found. The colonies of the former 

 are white, those of the latter are lemon color. With 

 these exceptions they are in all essential cultural peculi- 

 arities similar to staphylococcus aureus. As a rule, they 

 are not virulent for animals, and when they do pos- 

 sess pathogenic properties it is in a much lower degree 

 than is commonly the case with the golden staphy- 

 lococcus. Streptococcus pyogenes is also sometimes 

 present. The commonest of the pyogenic organisms, 

 however, is that just described, viz., staphylococcus 

 pyogenes aureus. An organism that is almost univer- 

 sally present in the skin, and is often concerned in pro- 

 ducing mild forms of inflammation, is staphylococcus 

 epidermidis albus (Welch), an organism that may read- 

 ily be confused with staphylococcus albus. It is distin- 

 guished from the latter by the slowness with which it 

 liquefies gelatin and by the comparative absence of 

 pathogenic properties ^hen injected into the circulation 

 of rabbits. Welch regards this organism as a variety 

 of staphylococcus pyogenes albus. 



Streptococcus Pyogenes. — From a spreading 

 phlegmonous inflammation prepare cover-slips and cult- 

 ures. What is the predominating organism ? Does it 

 appear in the form of regular clusters like those of 

 grapes, or have its individuals a definite, regular ar- 

 rangement ? (See Fig. 56.) Are its colonies like those 

 of staphylococcus pyogenes aureus? 



Isolate this organism in pure cultures. In these cult- 

 ures it will be found on microscopic examination to present 

 an arrangement somewhat like a chain of beads. (Fig. 57.) 



Determine its peculiarities and describe them accu- 

 rately. They should be as follows ; 



