254 



PATHOGENIC BACTERIA. 



well. In addition to these two principal forms, one 

 sometimes discovers an organism identical with the pre- 

 ceding, except that its growth on agar-agar and potato 

 is of a brilliant lemon-yellow color, and its pathogeny for 

 animals much less. This is the Staphylococcus citreus of 

 Passet. It is not quite so common, and not so patho- 

 genic as the others, and consequently much less im- 

 portant. 



Streptococcus Pyogenes. 

 Another organism whose colonies are frequently ob- 

 tained from the pus containing the staphylococci is the 

 Streptococcus pyogenes of Rosenbach (Fig. 54). It was 

 found by him in 18 of 33 cases of 

 suppurative lesions studied, fifteen 

 times alone and five times with the 

 Staphylococcus aureus. It is a 

 spherical organism of variable size 

 (0.4-1 ft in diameter), constantly 



Fig. 54. — Streptococcus pyogenes, from the pus 

 taken from an abscess; x iooo (Frankel and 

 Pfeiffer). 



Fig. 55. — Streptococ- 

 cus pyogenes : culture 

 upon agar-agar two days 

 old (Frankel and Pfeif- 

 fer). 



associated in pairs and chains of from four to twenty in- 

 dividuals. A special variety of it, known as Streptococ- 



