Staphylococci Pyogenes Aureus et Albus 345 



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

 erally do not contain Staphylococcus aureus by itself, but in 

 association with Staphylococcus albus. 



The colonies of Staphylococcus aureus differ considerably 

 in color, some being much paler than others. 



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 colo- 

 nies appear as small whitish points after from twenty- 



Fig. 103. Staphylococcus pyogenes aureus. Colony two days old, seen 

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



four to forty-eight hours, 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 

 the colonies are grown upon agar-agar plates, the formation 

 of the pigment is more distinct. 



Gelatin Punctures. In gelatin the growth occurs along 

 the whole length of the puncture, causing an extensive 

 liquefaction of the medium in the form of a long, narrow, 

 blunt-pointed, inverted cone, sometimes described as being 

 like a stocking, full of clouded liquid, at the apex of which 

 a collection of golden or orange-yellow precipitate is always 



