276 



PYOGENIC BACTERIA. 



Biological Characters. Grows readily in various liquid and 

 solid culture media, including all of those usually employed in bac- 

 teriological researches. The most favorable temperature for its de- 

 velopment is from 30 to 37 C., but it multiplies freely at the ordi- 

 nary room temperature 10 to 18 C. 



Streptococcus pyogenes is a facultative anaerobic, growing 

 both in the presence and absence of oxygen. It 

 does not liquefy gelatin, and in gelatin stick 

 cultures it grows along the line of puncture, 

 forming numerous small, spherical, translu- 

 cent, whitish colonies, which are closely crowd- 

 ed together at the upper portion of the line of 

 growth, and often distinctly separated from 

 each other below ; upon the surface there is 

 often no growth, or a scanty development may 

 occur about the point of entrance of the inocu- 

 lating needle. The minute colonies along the 

 line of puncture are already visible at the end 

 of twenty-four hours in cultures kept in the 

 incubating oven at 30 to 35 C., and at the end 

 of three or four days they have reached their 

 full development, forming a semi -opaque, white, 

 granular column, upon the margins of which 

 the separate colonies are seen projecting into the 

 gelatin. On gelatin plates very small, translu- 

 cent colonies are developed, which upon the sur- 

 face spread out to form a flat, transparent disc 

 of about one-half millimetre. Under a low mag- 

 nifying power these colonies are seen to be slight- 

 ly granular and have a yellowish color. At a 

 later date they become darker and less trans- 

 parent, and the margin may show irregular projections made up of 

 tangled masses of cocci in chains. The characters of growth in 

 nutrient agar and in jellified blood serum are similar to those in gela- 

 tin, and on agar plates colonies are formed similar to those above 

 described, except that they are somewhat smaller and more trans- 

 parent. Fehleisen and De Simone state that the erysipelas coccus 

 may develop upon the surface of cooked potato, but most authorities 

 Fltigge, C. Frankel, Passet, Baumgarten agree that no growth 

 occurs upon potato. Milk is a favorable medium for the growth of 

 this micrococcus, and the casein is coagulated by it. A slightly acid 

 reaction of the culture medium does not prevent its development. 

 The thermal death-point, as determined by the writer, is between 

 52 and 54 C. , the time of exposure being ten minutes. According 



FIG. 83. Streptococcus 

 of erysipelas in nutrient 

 gelatin; stick culture at 

 end of four days at 16- 

 18 C. (Baumgarten). 



