126 
PRINCIPLES OF BACTERIOLOGY 
citic fluid has been added. On blood agar plates 
streptococci colonies form a wide zone of hemolysis. 
Gelatin is not liquefied. Sugars are fermented and acid 
is produced. Milk is coagulated in three to four days. 
It is aerobic and facultatively anaerobic. It does not 
grow below 15° C. or above 42° C. 
\ 
Fig. 24.—Streptococcus pyogenes. Film preparation of a broth culture, 
x 1500. (Hewlett —Manual of Bacteriology .) 
IV. Destruction 
Heating at 60° C. for one hour will kill streptococci, 
5 per cent carbolic acid solution and 1:1000 bichloride 
of mercury kills them in a few minutes. They keep well 
on defibrinated blood in ice box. Drying destroys them 
in ten hours. 
