164 SUPPURATION -PUS COCCI. 



growth are concerned, this gerrn is exactly like tfre staphylo- 

 coccus aureus, except that it does not produce pigment. Its 

 growth is always whitish. It is found everywhere, but pos- 

 sesses little virulence. It is usually the cause of long-stand- 

 ing suppurations, such as the suppuration occurring in a 

 fistulous tract or a chronic otitis media. Welch described a 

 somewhat similar organism, which he called the Staphylo- 

 coccus epidermidis albus. It is constantly found both on the 

 skin and in its deeper layers. He believes it to be an attenu- 

 ated form of the Staphylococcus pyogenes albus. 



Staphylococcus pyogenes citreus : This organism is also iden- 

 tical with the Staphylococcus aureus, but in culture produces 

 a lemon-yellow pigment. It is very uncommon, and is always 

 associated with the other varieties of staphylococci. 



Pathogenesis : These three varieties of staphylococci are 

 always associated. In very acute suppurations the yellow 

 coccus predominates ; and in chronic suppurations the albus 

 predominates. The citreus holds the middle ground. It is 

 not so common as either of the other two. It is less patho- 

 genic than the aureus, but more so than the albus. 



Staphylococcus cereus albus and flavus : These two varieties 

 are very uncommon. They have been found on the skin and 

 in the external auditory canal. They do not liquefy gelatin 

 and are very feebly pathogenic. They resemble the other 

 varieties of staphylococci both in appearance and culture, but 

 do not liquefy gelatin. The first named produces a waxy 

 white growth and the other a waxy yellow growth. 



Streptococcus Pyogenes. 



Biology and morphology : This organism is identical with 

 the Streptococcus erysipelatis of Fehleisen, which was at one 

 time considered a distinct species. It is from 0.4 [j. to 1 fj. in 

 diameter, and always forms chains, from which characteristic 

 it derived its name of the " chain coccus " (Figs. 68 and 69). 

 These chains may be long or short, and a streptococcus longus 

 and brevis may be distinguished. It stains well with the anilin 

 dyes and also by Gram's method. It is not motile and has no 

 flagella. Reproduction takes place by fission. Occasionally 



