332 PATHOGENIC MICROORGANISMS 



but will not agglutinate any of the non-pathogenic members of 

 either group. ' 



Active immunization of human beings suffering from staphylococcus 

 infections has been extensively practiced by Wright, in connection with 

 his work on opsonins. There can be no question about the fact that the 

 opsonic substances in the blood are increased by the injection of dead 

 staphylococci. The procedure is of therapeutic value in subacute and 

 chronic cases. The work of Hiss on the use of leucocyte extracts in 

 animals infected with Staphylococcus pyogenes aureus has given en- 

 couragement for such treatment in human beings. A number of 

 staphylococcus infections in man have been successfully treated with 

 leucocyte extract by Hiss and Zinsser. 



STAPHYLOCOCCUS PYOGENES ALBUS 



This coccus differs from Staphylococcus pyogenes aureus simply in 

 the absence of the golden yellow coloration of its cultures. Morpho- 

 logically, culturally, and pathogenically, it is in every way identical 

 with the staphylococcus described in the preceding section, but its 

 toxin- and enzyme-producing powers in general are less developed than 

 those of the aureus variety. Its close biological relationship to aureus 

 is furthermore demonstrated by its agglutination in Staphylococcus 

 pyogenes aureus immune sera. 



STAPHYLOCOCCUS EPIDERMIDIS ALBUS 



The Staphylococcus epidermidis albus described by Welch is merely 

 one of the non-pathogenic varieties of Staphylococcus pyogenes albus 

 and possibly does not deserve separate classification. It may give rise 

 to unimportant stitch abscesses. 



STAPHYLOCOCCUS PYOGENES CITREUS 



Staphylococcus pyogenes citreus produces a bright yellow or lemon- 

 colored pigment of distinctly different hue from that of Staphylococcus 

 pyogenes aureus. It may be pyogenic and in every way similar to 

 Staphylococcus pyogenes aureus, but is less often found in con- 

 nection with pathological lesions than either of the preceding staphy- 

 lococci. 



' Proscher, Deut. med. Woch., xi, 1903. 



