STREPTOCOCCUS PYOGENES. 283 



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 is transplanted and is allowed to re- 

 main upon the original medium, it is not uncommon 

 to find the organism incapable of further cultivation 

 after a week or ten days. 



Under no conditions is the growth of this organism 

 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 magnify- 

 ing power they have a brownish or yellowish tinge by 

 transmitted light, and are finely granular. As the col- 

 onies become older their regular border 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 rep- 

 resenting 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 gel- 

 atin 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-agar at the tempera- 



