312 



BACTERIA AND DISEASE 



StaphylococciiA pyogencs 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 



FIG. 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. Streptococcus 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 difierent 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 



