374 PYOGENIC BACTERIA. 



Morphology. Spherical cells having a diameter of 0.7 ^ (Hade* 

 lich) to 0.9 /* (0.87 /* Passet), solitary, in pairs, or in irregular 

 groups, occasionally in chains of three or four elements or in groups 

 of four. The dimensions vary somewhat in dif- 

 ferent culture media, being larger in a favorable 

 than in an unfavorable medium. The individual 

 cells, as pointed out by Hadelich, consist of two 



hemispherical portions separated from each other 

 FIG. 79.-staphyiococ- by a very narrow cleft, which is not visible when 



cus pyogenes aureus, ,- >-, j ^ j i_ 



from a drawing by tne cells are deeply stained, but may be demon- 

 Rosenbach. strated, with a high power, by staining for a short 



time (two minutes or less) in a solution of f uchsin in aniline water. 



This micrococcus stains quickly in aqueous solutions of the basic 

 aniline colors, and may also be stained with acid carmine and hsema- 

 toxylin. It is not decolorized by iodine solution when stained with 

 methyl violet Gram's method. 



Biological Characters. Staphylococcus pyogenes aureus grows 

 either in the presence or absence of oxygen, and is consequently a 

 facultative anaerobic. It multiplies rapidly at a temperature of 18 

 to 20 C. in milk, flesh infusions, and various other liquid media, 

 and in nutrient gelatin or agar. It liquefies gelatin, and in stab 

 cultures liquefaction occurs all along the line of puncture, forming a 

 pouch which is largest above and at the end of three or four days has 

 extended to the full capacity of the test tube at the surface. The 

 liquefied gelatin in this pouch is at first opaque from the presence of 

 little agglomerations of micrococci in suspension, but after a time 

 these are deposited and the gelatin becomes transparent. During 

 the period of active growth the cocci accumulate near the surface of 

 the gelatin, and, in contact with the air, the characteristic golden-yel- 

 low pigment is produced. By the subsidence of the colored masses 

 of cocci from this superficial stratum a yellow deposit is gradually 

 formed at the bottom of the pouch of liquefied gelatin (Fig. 80). This 

 pigment, which is the principal character distinguishing the micro- 

 coccus under consideration from certain other liquefying staphylo- 

 cocci, is only formed in the presence of oxygen. Upon the surface 

 of nutrient agar development occurs in the form of a moist, shining 

 layer, with more or less wavy outlines, having at first a pale-yellow 

 color, which soon deepens to an orange- or golden-yellow. The col- 

 onies which develop upon agar plates are spherical and opaque, and 

 usually acquire the golden-yellow color within a few days. Colonies 

 on gelatin plates or in Esmarch roll tubes first appear as small white 

 dots, which later are more or less granular in appearance and present 

 the yellow color, especially towards the centre ; but, owing to the 

 extensive liquefaction of the gelatin caused by them, their develop- 



