322 PATHOGENIC MICROORGANISMS 



STAPHYLOCOCCUS PYOGENES AUREUS 



Morphology and Staining. — This microorganism, the most frequent 

 cause of abscesses, boils, and many surgical suppurations, is a spherical 

 coccus having an average diameter of about 0.8 micra, but varying 

 within the extreme limits of 0.4 to 1 .2 micra. Any considerable variatioii 

 from the average size, however, is rare. The perfectly spherical charac- 

 ter may not develop, whenever, as is usually the case, two or more are 



Fig. 69. — Staphylococcus pyogenes aureus. (After Giinther.) 



grouped together, unseparated after cell cleavage. In this case, adjacent 

 cocci are slightly flattened along their contiguous surfaces. 



Examined in smears from cultures or pus, the staphylococci may 

 appear as single individuals, in pairs, or, most frequently, in irregular 

 grape-like clusters. Occasionally, short chains of three or four may be 

 seen. In very young cultures in fluid media, the diplococcus form may 

 predominate. 



The staphylococci stain with all the usual basic aqueous anUin dyes, 

 and, less intensely, with some of the acid dyes. Stained by the method 

 of Gram, they retain the anilin-gentian- violet. Gram's method of 

 staining is excellently adapted for demonstration of these cocci in 

 tissue sections. 



