110 BACTERIOLOGY 



which are much used than in localities but little frequented 

 by human beings. Ullmann also found them very widely 

 diffused elsewhere in nature, not only in the air but in 

 river-water and rain-water, though not in spring-water ; 

 also in ice, in the earth, and on walls. 



They are small globular immotile cells, always tend- 

 ing to form closely-packed clusters, particularly in the 



interior of tissue (fig. 35). Those 

 cells, however, which are not in- 

 cluded in the clusters possess the 

 power of moving with tolerable 

 activity. The individual cells take 

 up all the different aniline dyes, 

 FIG. 35. STAPHYLOCOC grow even at ordinary tempera- 



PYOGENES ATJKEU8. . at f n 



tures, though more energetically at 



degrees of heat approaching that of the human body, and, 

 if added to sterilised milk, precipitate the casein e. 



The Staphylococcus pyogenes aureus grows very quickly 

 on the gelatine plate at the temperature of an ordinary 



Smallest islets 



Larger 

 islets 



FIG. 36. FIG. 37. 



ISLETS op STAPHYLOCOCCTTS PYOGENES AUREUS ON A GELATINE PLATE. 



room, so that even as early as the second day small puncti- 

 form colonies are to be seen, which are round and possess 

 a sharply- defined circumference, and these soon approach 

 the surface and liquefy. The liquefaction extends out at 

 the periphery, and soon shows a yellowish colour in the 

 centre (figs. 36 and 37). In the thrust-culture the gelatine 

 begins to undergo liquefaction on the second or third day, 



