Staphylococcus Pyogenes Aureus et Albus 303 



the etiological possibilities of the case through their demonstration. 

 He should always seek for less evident though sometimes far more 

 important organisms. In the absence of such, and in their absence 

 only, should the case be referred to staphylococci. 



Morphology. — The cocci are small spheres measuring about 0.7- 

 i.o ju in diameter. There is no definite' grouping in either liquid 

 or solid cultures. It is only in pus or in the organs or tissues of dis- 

 eased animals that one can say that a true staphylococcus (bunch 

 of grapes) grouping occurs. 



The organisms are not motile and have no flagella. They do not 

 form spores. 



Staining. — They stain easily and brilliantly with aqueous solutions 

 . of the anilin dyes and by Gram's method. 



Fig. 107. — Staphylococcus pyogenes aureus. Colony two days old, seen upon 

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



Isolation. — Staphylococci are easy organisms to isolate, and can 

 be secured by plating out a drop of pus in gelatin or in agar-agar. 



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 absence of oxygen at 

 temperatures above i8°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, 

 rapidly extending to the surface and causing extensive liquefaction 

 of the medium. The formation of the yellow 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. 



