THE STREPTOCOCCUS GROUP 279 



identifying streptococci; the results are occasionally variable without 

 apparent cause. 



Bacteriological Diagnosis. 1. Microscopical Examination. Smears 

 from abscesses or inflammatory areas usually exhibit pairs and short 

 chains of cocci which retain the Gram stain. Occasionally the organ- 

 isms can not be distinguished with certainty from staphylococci. 

 Frequently, when microscopic examination fails (and this is usually 

 the case when blood is examined), streptococci are found by cultural 

 methods. 



2. Cultural Examination. If the material is purulent, it may be 

 streaked or plated out on 0.1 per cent, dextrose agar; the colonies are 

 small and transparent, and may be easily overlooked. Blood, lymph 

 or serum should be plated on blood agar. If the material is blood, one 

 part may be added to two 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 sus- 

 pected 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 c.c. 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. 



3. Animal Inoculation. The intraperitoneal injection of suspected 

 fluids into rabbits frequently results in a fatal perftonitis, 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 can not 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 



