312 BACTERIA AND DISEASE 



Staphylococcus pyogenes aureus, the type of the species, is grown 

 in the laboratory on all ordinary media at room temperature, though 

 more rapidly at 37° C. Liquefaction sets in at a comparatively early 

 stage, and subsequently we have in gelatine test-tube cultures a 

 flocculent deposit of a bright yellow amorphous mass, and in gelatine 

 plates small depressions of liquefaction with a yellow deposit. The 

 organism renders all media acid, and coagulates milk. Its thermal 

 death-point in gelatine is 58° C. for ten minutes, but when dry con- 

 siderably higher. Outside the body it may retain vitality for 



Pig. 25.— Diagram of Types of Streptococci. 



months. It stains by Gram's method. It is a non-motile and a 

 facultative anaerobe ; but the presence of oxygen is necessary for 

 the production of much pigment. Its virulence readily declines. 



2. Streptococctos pyogenes. — In this species of micrococcus the 

 elements are arranged in chains. Most of the streptococci in pus, 

 from different sources, are probably of one species, having approxi- 

 mately the same morphological and biological characters. Their 

 different effects are due to different degrees of toxic virulence ; they 

 are generally more virulent when associated with other bacteria, for 

 example, the Proteus family. 



The chains vary in length, consisting of more elements when 



