102 THE PATHOGENIC BACTERIA. 



achromogenic variety of the preceding, it is, however, some- 

 what less pathogenic. Its morphological characters are the 

 same as those of the aureus, with the exception that it does 

 not form pigment and its colonies are of a milk-white color. 



III. Staphylococcus Citreus. 



The Staphylococcus pyogenes citreus is of identical mor- 

 phology with the two preceding varieties, with the exceptions 

 that its growth is of a lemon-yellow color and that it liquefies 

 gelatin more slowly. It is found in association with the Sta- 

 phylococcus aureus and albus in pus of acute abscesses, espe- 

 cially in the liver. 



IV. Streptococcus Pyogenes. 



The Streptococcus pyogenes is found : a. in the lymphatics 

 of the skin in patients suffering from erysipelas, b. in pus, 

 c. in the false membranes in cases of diphtheria, d. in surgi- 

 cal and e. obstetrical complications of erysipelas, and /. as a 

 frequent causative agent of puerperal septicaemia and of many 

 surgically common infections (Fig. 48 and Plate I.). 



FIG. 48. 



Streptococcus pyogenes. (Abbott.) 



Morphology. The streptococcus is a micrococcus varying 

 in size from 1 to 4 mikrons in diameter, spherical in shape 

 and arranged as a chain of variable length. When grown in 

 liquid media, this chain consists of from 30 to 40 elements, 

 but in solid media a chain usually consists of from 7 to 10 

 cocci, In young cultures the diameters of all the cocci of the 



