186 PATHOGENIC BACTERIA. 



The cocci are rather small, measuring about 0.7 // in 

 diameter. When examined in a delicately-stained con- 

 dition the organisms may be seen to consist of hemi- 

 spheres separated from each other by a narrow interval. 

 The contiguous surfaces are flat, thus differing from 

 the gonococcus, whose contiguous surfaces are concave. 

 The grouping is not very characteristic. In both liquid 

 and solid culture-media the organisms either occur in 

 solid masses or are evenly distributed. It is only in the 

 organs or tissues of a diseased animal that it is possible to 

 say that a true staphylococcus grouping is present. 



The organism stains brilliantly with aqueous solu- 

 tions of the anilin dyes. In tissues it can be beautifully 

 stained by Gram's method. 



The staphylococci grow well either in the presence or 

 absence of oxygen at a temperature above 18 C., the 

 most rapid development being at about 37 C. Upon the 

 surface of gelatin plates small whitish points can be 

 observed in forty-eight hours (Fig. 51). These rapidly 



FIG. 51. Staphylococcus pyogenes aureus: colony two days old, seen upon an 

 agar-agar plate ; x 40 ( Heim). 



extend to the surface and cause extensive liquefaction. 

 Hand in hand with the liquefaction is the formation of 

 an orange color, which is best observed at the centre of 

 the colony. Under the microscope the colonies appear 



