384 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—16° to 18° C. 
Streptococcus pyogenes is a facultative anaérobic, growing 
both in the presence and absence of oxygen. It 
does not liquefy gelatin, and in gelatin stab 
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- 
\ p cent colonies are developed, which upon the sur- 
> face spread out to form a flat, transparent disc 
Fic. 83—Streptococeus of about one-half millimetre. Under a low mag- 
pelatin; stick culture at nifying power these colonies are seen to be slight- 
end of four days at 16-- ly granular and have a yellowish color. Ata 
ae ice i 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: 
—Fligge, 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 
