STAPHYLOCOCCUS PYOGENES AUREUS. 



183 



f *# 



the long axis of the chain. It stains readily with all the basic 



aniline dyes, and retains the 



colour in Gram's method. . ' * . , 



Ctdtivation. — It grows , ' 



readily in all the ordinary 

 media at the room tempera- 

 ture, though much more 

 rapidly at the temperature 

 of the body. In stab-cultures 

 in peptone gelatin a streak of 

 growth is visible on the day 

 after inoculation, and on the ^ *" 



second or third day, liquefac- ♦' ♦ 



tion commences at the top. ^ , ^ , , 



^ rIG. 65. — staphylococcus pyogenes aureus, 



As liquefaction proceeds, the young culture on agar, showing clumps of cocci. 

 growth falls to the bottom as stained with weak carbol-fuchsin. x 1000. 



a flocculent deposit, which soon assumes a bright yellow colour, 



K 



% 

 4 



Fig. 66. — Two stab-cul- 

 tures of staphylococcus pyo- 

 genes aureus in gelatin, ia) 

 10 days old, {b) 3 weeks old : 

 showing liquefaction of the 

 medium and characters of 

 growth. Natural size. 



while a yellowish film may form on the 

 surface, the fluid portion still remaining 

 turbid. Ultimately liquefaction extends 

 out to the wall of the tube (Fig. 66). 

 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 visi- 

 ble to the naked eye as whitish yellow 

 points, which afterwards become more 

 distinctly yellow. Liquefaction occurs 

 around these, and little cups are formed, 

 at the bottom of which 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 circu- 

 lar discs of similar appearance, which may 

 reach 2 mm. or more in diameter. On 



