374 PYOGENIC BACTERIA. 
Morphology.—Spherical cells having a diameter of 0.7 « (Hade. 
lich) to 0.9 # (0.87 «4 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- 
eds Bis ferent culture media, being larger in a favorable 
e than in an unfavorable medium. The individual 
sigh? cells, as pointed out by Hadelich, consist of two 
hemispherical portions separated from each other 
Fig. 79.—Staphylococ- by a very narrow cleft, which is not visible when 
from. a drawing by the 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 fuchsin in aniline water. 
This micrococcus stains quickly in aqueous solutions of the basic 
aniline colors, and may also be stained with acid carmine and hama- 
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 anaérobic. 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 afewdays. 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- 
