358 APPLICATION OF METHODS OF BACTERIOLOGY 



On nutrient agar-agar to which, under aseptic precautions, 

 unheated, defibrinated or whole blood has been added, it 

 often causes hemolysis, i. e., decolorization of the blood in 

 the neighborhood of the growth. Some strains of the 

 organism when thus grown are surrounded by a greenish 

 zone, Streptococcus viridans; others by a perfectly clear, 

 colorless zone, Streptococcus hemolyticus. 



On blood serum its colonies present little that is character- 

 istic; they appear as small, moist, whitish points, from 0.6 

 to 0.8 mm. in diameter, that are slightly elevated above the 

 surface of the serum. They do not coalesce to form a layer 

 over the surface, but remain as isolated colonies. 



On potato no visible development appears, but after a 

 short time (thirty-six to seventy-two hours) there is a slight 

 increase of moisture about the point of inoculation, and 

 microscopic examination shows that multiplication of the 

 organisms placed at this point has occurred. 



In milk its conduct is not always the same, some cultures 

 causing a separation of the milk into a firm clot and colorless 

 whey, while others do not produce this coagulation. The 

 latter, when cultivated in milk of a neutral or slightly 

 alkaline reaction, to which a few drops of litmus tincture 

 have been added, produce, as a rule, only a very faint pink 

 color after twenty-four hours at 37 C. 



In bouillon it grows as tangled masses or clumps, which 

 upon microscopic examination are seen to consist of long 

 chains of cocci twisted or matted together. 



It grows best at the temperature of the body (37.5 C.), 

 though development does occur at the ordinary room-tem- 

 perature. 



It is not soluble in bile. 



It ferments some of the carbohydrates, notably dextrose, 

 maltose, lactose and salicin, but not mannite or inulin. 



