290 Wound Infection; Suppuration 



Isolation. Staphylococcus aureus is an easy organism to 

 isolate, and can be secured by plating out a drop of pus in 

 gelatin or in agar-agar. Such preparations, however, gen- 

 erally do not contain Staphylococcus aureus by itself, but in 

 association with Staphylococcus albus. 



As the colonies of Staphylococcus aureus differ considerably 

 in color, some being much paler than others, I have often 

 doubted whether Staphylococcus albus was a different spe- 

 cies, or simply a non-chromogenic form of pus coccus. It is 

 possible to secure nearly every intermediate tint from white 



Fig. 90. Staphylococcus pyogenes aureus. Colony two days old, seen 

 upon an agar-agar plate. X 40 (Heim). 



to golden yellow by a little manipulation. Should this be 

 the case, it would reduce the pus cocci to a single species, 

 Staphylococcus pyogenes. 



Cultivation. The staphylococci grow well upon all the 

 standard culture media either in the presence or in the ab- 

 sence of oxygen at temperatures above 18 C., the most rapid 

 development being at about 37 C. 



Colonies. Upon the surface of gelatin plates the colonies 

 appear as small whitish points after from twenty-four to 

 forty-eight hours (Fig. 90), rapidly extending to the sur- 

 face and causing extensive liquefaction of the medium. 

 The formation of the orange pigment can be best observed 

 near the center of the colonies. Under the microscope the 

 colonies appear as round disks with circumscribed, smooth 

 edges. They are distinctly granular and dark brown. When 



