BACTERIA AND DISEASE 297 



Thus we have the S. pyogenes aureus (golden yellow), albus 

 (white), citreiis (lemon), and others. They occur commonly 

 in nature, in air, soil, water, on the surface of the skin, and 

 in all suppurative conditions. The aureus is the only one 

 credited with much virulence. It occurs in the blood in 

 blood-poisoning (septicaemia, pysemia), and is present in all 

 ulcerative conditions, including ulcerative disease of the 

 valves of the heart. 



The Staphylococcus cereus albus and S, cereus flavus are 

 slightly modified forms of the S. pyogenes aureus, and are 

 differentiated from it by being non-liquefying. They pro- 

 duce a wax-like growth on gelatine. 



Staphylococcus pyogenes aureus, the type of the family, is 

 grown in all ordinary media at room temperature, though 

 more rapidly at 37" C. Liquefaction sets in at a compara- 

 tively early date, and subsequently we have in the 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. It renders all media 

 acid, and coagulates milk. Its thermal death-point in gela- 

 tine is 58° C. for ten minutes, but when dry considerably 

 higher. It is a non-motile and a facultative anaerobe; but 

 the presence of oxygen is necessary for a bright colour. Its 

 virulence readily declines. 



2. Streptococcus pyogenes. In this species of micrococcus 

 the elements are arranged in chains. Most of the strepto- 

 cocci in pus, from different sources, are one species, having 

 approximately the same morphological and biological charac- 

 ters. Their different effects are due to different degrees of 

 toxic virulence; they are always more virulent when asso- 

 ciated with other bacteria, for example, the Proteus family. 



The chains vary in length, consisting of more elements 

 when cultured in fluid media. They multiply by direct 

 division of the individual elements, and in old cultures it 

 has been observed that the cocci vary in form and size. 



