STREPTOCOCCUS PYOGENES 339 



Under artificial conditions it sometimes grows well, and 

 can be cultivated through many generations, while at 

 other times it rapidly loses its vitality. When isolated 

 from the diseased area upon artificial media it seems to 

 retain its vitality for a longer period if replanted upon fresh 

 media every day or two for a time; but if the first generation 

 be transplanted and allowed to remain upon the original 

 medium for from a week to ten days, it is not uncommon to 

 find the organism incapable of further cultivation. 



Under no conditions is its growth very luxuriant. 



On gelatin plates its colonies appear after forty-eight to 

 seventy-two hours as very small, flat, round points of a 

 bluish-white or opalescent appearance. They do not cause 

 liquefaction of the gelatin, and in size they rarely exceed 

 0.6-0.8 mm. in diameter. Under low magnifying power 

 they have a brownish or yellowish tinge by transmitted 

 light, and are finely granular. As the colonies become older 

 their regular borders may become slightly irregular or 

 notched. 



In stab-cultures in gelatin they grow along the entire 

 needle-track as a finely granular line, the granules represent- 

 ing minute colonies of the organism. On the surface the 

 growth does not usually extend beyond the point of 

 puncture. 



On agar-agar plates the colonies appear as minute pearly 

 points, which when slightly magnified are seen to be finely 

 granular, of a light-brownish color, and regular at their 

 margins. 



When smeared upon the surface of agar-agar or gelatin 

 slants the growth that results is a thin, pearly, finely granular 

 layer, consisting of minute colonies growing closely side by 

 side. Its most luxuriant growth is seen on glycerin-agar- 



