THE STREPTOCOCCUS GROUP 311 
Bacteriological Diagnosis. — 1. Microscopic Examination. —Smears 
from abscesses or inflammatory areas usually exhibit pairs and short 
chains of cocci which retain the Gram stain. Occasionally the organ- 
isms cannot be distinguished with certainty from staphylococci. 
Frequently, when microscopic examination fails (and this is usually 
the case when blood is examined), streptococci are foinid by cultural 
methods. 
2. Cvltiiral Examination.— li the material is purulent, it may be 
streaked or plated out on 0.1 per cent glucose agar; the colonies are 
small and transparent, and may be easily overlooked. Blood agar 
is a better medium, however. Material containing blood, lymph or 
serum should be plated on blood agar. If the material is blood, 
1 part may be added to 2 parts of melted plain agar, and the whole, 
after thorough mixing, may be poured into sterile Petri dishes. Usually 
small, gray colonies with relatively broad, clear areas of hemolysis 
appear within forty-eight hours. If lymph and serum be the suspected 
material, blood agar should be used for plating out. Hemolytic 
colonies, as above, appear usually within two days. It is always well 
to inoculate 1 or 2 cc. of blood serum or lymph into broth and maintain 
it at 37° C. for twenty-four hours to enrich the culture, then plate on 
blood agar; also inoculate a like amount into a rabbit. Streptococci 
are practically insoluble in bile, or freshly-prepared sodium choleate.^'^ 
Pneumococci are bile-soluble. Acids, however, interfere with this test. 
3. Animal I nocnlation.— The intraperitoneal injection of suspected 
fluids into rabbits frequently results in a fatal peritonitis, from which 
the organism may be recovered from the blood stream. Relatively 
large amounts should be used. 
The detection of streptococci in the blood of a patient is frequently 
an unfavorable clinical sign; it does not necessarily, however, justify 
a grave prognosis. Cases are met with which present symptoms of 
septicemia, yet the organisms may not be obtained from the blood. 
Occasionally the patient dies from toxemia, due apparently to the 
absorption of toxic substances from the local infection. Streptococci 
from erysipelas, septicemia, scarlet fever, and even from articular 
rheumatism are so similar culturally and morphologically that the 
various strains cannot be differentiated with certainty; slight varia- 
tions in cultural reactions are exhibited by all these strains. Neither 
does animal experimentation afford definite criteria for the estab- 
lishment of types. Even one passage through an animal may modify 
the pathogenicity greatly. 
In the light of our present knowledge the resistance of different 
tissues and the portal of entry play a prominent part in determining 
both the type of lesion which will result from invasion of the body 
by streptococci, and the modification in virulence they may undergo 
' Cole: Jour. Exp. Med., 1912, 16, 044. 
2 Buttcrfield and Peabody: Jour. Exp. Med., 1913, 17, 5S7. 
