166 SUPPURATION PUS COCCI. 



are perfectly flat, round, with numerous fine projections at 

 the periphery, due to chains of cocci which reach out from 

 the colony into the medium. The gelatin is not liquefied. 

 The appearance of the colony under the microscope is quite 

 characteristic. 



In gelatin tube cultures the growth is formed along the line 

 of inoculation. It is very slight, and consists of many very 

 small distinct spherical colonies that resemble the colony on 

 the plate. They never become confluent. There is no lique- 

 faction of the media. The surface growth is very slight. 



In agar-agar strokes a very similar growth develops as in 

 the gelatin, but not so rapidly, and the colonies are almost 

 translucent. Sometimes the growth is so slight that the col- 



FIG. 70. 



Streptococcus. (Park.) 



onies resemble minute drops of water. The growth is more 

 rapid on glycerin-agar than on ordinary agar. 



On potato the growth is almost invisible. 



Bouillon becomes slightly cloudy and contains a flocculent 

 precipitate. It is in the bouillon cultures that the variations 

 in the formation and lengths of the streptococcus chains are 

 seen. They are probably only cultural characteristics. 



The growth on blood-serum is almost identical with that on 

 agar. Milk is coagulated. 



Vitality : An exposure of ten minutes to a temperature of 

 52 C. kills the coccus. It is more resistant to chemicals. 



