STAPHYLOCOCCUS PYOGENES AUREUS 175 



the wall of the tube (Fig. 53). In gelatin plates colonies may 

 be seen with the low power of the microscope in twenty-four 

 hours, as little balls somewhat granular on the surface and of 

 brownish colour. On the second day they are visible to the 



FIG. 52. Staphylococcus pyogenes aureus, 

 young culture on agar, showing clumps 

 of cocci. 



Stained with weak carbol-fuchsin. x 1000. 



j i 



9 



FIG. 

 of 



naked eye as whitish yellow points, 

 which afterwards become more dis- 

 tinctly yellow. Liquefaction occurs 

 around these, and little cups are 

 formed, at the bottom of which the 

 colonies form little yellowish masses. 

 On agar, a stroke culture forms a 

 line of abundant yellowish growth, 

 with smooth, shining surface, well 

 formed after twenty-four hours at 

 37 C. Later it becomes bright 

 orange in colour, and resembles a 



streak of oil paint. Single colonies on the surface of agar are 

 circular discs of similar appearance, which may reach 2 mm. or more 

 in diameter. On potatoes it grows well at ordinary temperature, 

 forming a somewhat abundant layer of orange colour. In bouillon 

 it produces a uniform turbidity, which afterwards settles to the 

 bottom as an abundant layer, which assumes a brownish yellow tint. 

 In the various media it renders the reaction acid, and it coagulates 



53. Two stab cultures 

 staphylococcus pyogenes 

 aureus in gelatin, (a) 10 days 

 old, (b) 3-weeks old, showing 

 liquefaction of the medium 

 and characters of growth. 

 Natural size. 



