256 THE PYOGENIC COCCI 



through suitable animals, but they soon tend to lose their artificially 

 acquired pathogenic properties under ordinary conditions and return 

 again to a parasitic existence. 



Prominent among these habitually parasitic bacteria which occur 

 on the skin and mucous membranes of man are the various members 

 of the Staphylococcus and Streptococcus Groups. 



THE STAPHYLOCOCCUS GROUP. 



Micrococcus Aureus. Synonyms. Staphylococcus pyogenes aureus; 

 Staphylococcus aureus; Micrococcus pyogenes aureus; Micrococcus sali- 

 varius aureus. 



Historical. Staphylococci probably were first seen by Klebs, some- 

 what later by Billroth, in unstained pus. Pasteur 1 repeatedly isolated 

 them from the pus of furuncles, and in one case of osteomyelitis, and 

 suggested their etiological relationship to these lesions, but to Rosen- 

 bach 2 belongs the priority of growing them in cultures of undoubted 

 purity. 



Morphology. The organisms in the free state are spherical, measur- 

 ing from 0.7 to 0.9 micron in diameter. Those just about to divide 

 are frequently oval. They occur singly, in pairs, or in irregular masses, 

 both in culture and in pus; rarely chains of four to six cocci are found. 



Staphylococci are non-motile and possess no flagella; they do not 

 form capsules, and spores have not been observed. They siain readily 

 with ordinary anilin dyes, some individuals more intensely than their 

 fellows. They are Gram-positive. 



Isolation and Culture. Staphylococci are readily obtained in pure 

 culture by plating or streaking the suspected material directly upon 

 agar or gelatin. The colonies on gelatin after thirty to forty-eight 

 hours' incubation at room temperature become visible as gray, glis- 

 tening growths 0.5 to 1 mm. in diameter; somewhat later the colonies 

 sink into saucer-shaped depressions of liquefied gelatin, the bacteria 

 collect at the bottom of the depression and soon become golden-yellow 

 in color. The growth upon agar plates at 37 C. is more rapid: at 

 the end of forty-eight hours' incubation the colonies are golden-yellow 

 and have attained a diameter of 1 to 3 mm. 



Staphylococci grow readily in the ordinary cultural media. Gela- 

 tin, coagulated blood serum (sugar-free) and casein are liquefied. 



1 Compt. rend. Acad. Sci., 1880, xc, 1035. 



2 Mikroorganismen bei den Wundinfektionskrankheiten des Menschen, Wiesbaden, 

 1884, 19. 



