252 BA CTEBIOL OGY. 



arities similar to the 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. The streptococcus pyogenes is also sometimes 

 present. The commonest of the pyogenic organisms, 

 however, is that just described, viz. : the 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 the staphylococcus 

 epidermidls albus (Welch), an organism that may readily 

 be confused with the 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 when injected into the circulation 

 of rabbits. Welch regards this organism as a variety 

 of the staphylococcus pyogenes albus. He suggests 

 the above designation for it because of its very limited 

 pyogenic properties. 



The Streptococcus Pyogenes. — From a spread- 

 ing phlegmonous inflammation prepare cover-slips and 

 cultures. 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? Are its colonies like those of the staphy- 

 lococcus pyogenes aureus f 



Isolate this organism in pure cultures. In these cul- 

 tures it will be found on microscopic examination to 

 present an arrangement somewhat like a chain of beads. 

 (Fig. 55.) 



Determine its peculiarities and describe them accu- 

 rately. They should be as follows: 



Upon microscopic examination a micrococcus should 



