SUPPURA TION. 



187 



as round disks with circumscribed, smooth edges. They 

 are distinctly granular and dark-brown. When the col- 

 onies are grown upon agar-agar plates the formation of 

 the pigment is much more distinct. 



In gelatin punctures the growth occurs along the whole 

 length of the needle-track, and causes an extensive lique- 

 faction in the form of a long, narrow, blunt-pointed, 

 inverted cone (Fig. 52) full of clouded liquid, at the apex 



FIG. 52. Staphylococcus pyogenes aureus : puncture-culture three days old 

 in gelatin (Frankel and Pfeiffer). 



of which a collection of golden or orange-yellow precipi- 

 tate is always present. It is this precipitate in particu- 

 lar that gives the organism its name, "golden staphylo- 

 coccus." 



The most characteristic growth is upon agar-agar. 

 Along the whole line of inoculation an orange-yellow, 

 moist, shining growth occurs. When the growth takes 

 place rapidly, as in the incubator, it exceeds the rapidity 



