STREPTOCOCCUS PYOGENES 



201 



The staphylococcus pyogenes albus is similar in character, 

 with the exception that its growth on all the media is white. 

 The colour of the staphylococcus aureus may become less dis- 

 tinctly yellow after being kept for some time in culture, but it 

 never assumes the white colour of the staphylococcus albus, and 

 it has not been found possible to transform the one organism 

 into the other. A micrococcus called by Welch staphylococcus 

 epidermidis albus is practically always present in the skin 

 epithelium ; it is distinguished by its relatively non-pathogenic 

 properties and by liquefying gelatin somewhat slowly. It is 

 probably an attenuated variety of the staphylococcus albus. 



The staphylococcus pyogenes citreus, which is less frequently 

 met with, differs in the colour of the cultures, being a lemon 

 yellow, and is usually less virulent than the other two. 



The staphylococcus cereus albus and staphylococcus cereus 

 flavus are of much less importance. They produce a wax-like 

 growth on gelatin without liquefaction ; hence their name. 



Streptococcus pyogenes. — This organism (Plate I., Fig. 1) is a 

 coccus of slightly larger 

 size than the staphylo- 

 coccus aureus, about 1 fi 

 in diameter, and forms 

 chains which may contain 

 a large number of mem- 

 bers, especially when it is 

 growing in fluids (Fig. 

 46). The chains vary 

 somewhat in length in 

 different specimens, and 

 on this ground varieties 

 have been distinguished, 

 e.g., the streptococcus 

 brevis and streptococcus 

 longus (vide infra). As 

 division may take place 

 in many of the cocci in 

 a chain at the same 

 time, the appearance of 



a chain of diplococci is often met with. In young cultures the 

 cocci are fairly uniform in size, but after a time they present 

 considerable variations, many swelling up to twice their normal 

 diameter. These are to be regarded as involution forms. In its 

 staining reactions the streptococcus resembles the staphylococci 

 described, being readily coloured by Gram's method. 



Fig. 46. — Streptococcus pyogenes, young cul- 

 ture on agar, showing chains of cocci. 

 Stained with weak carbol-fuchsin. x 1000. 



