132 AIDS TO BACTERIOLOGY 



Growth on gelatin is slow and without liquefaction. 

 The colonies are generally very small and discrete, while 

 on agar at 37 C. the colonies are also small and seldom 

 coalesce with neighbouring colonies that almost touch. 

 This tendency of streptococcal colonies to remain small 

 is of great assistance in picking them out from plates 

 containing a variety of bacteria. In stab or shake culture 

 in gelatin the colonies appear as small whitish spheres. 

 In milk, acid is produced without a clot. It ferments 

 lactose, saccharose, and salicin. Growth on blood agar 

 shows it to be strongly haemolytic. The thermal death- 

 point lies between 52 and 54 C. (Sternberg). 



Pathogenesis. Streptococci of the pyogenes type are 

 more frequently found to be concerned in pathogenic 

 processes than are those of the short chain varieties. It 

 is found in ulcerative endocarditis, occasionally in 

 osteomyelitis and frequently in pyaemia, mammary 

 abscess, cellulitis, lymphangitis, and other suppurative 

 conditions. S. pyogenes is generally supposed to be 

 identical with S. erysipelatis, an organism found at the 

 periphery of the zone of redness in the lymph channels 

 of the skin in cases of erysipelas. Some doubt exists 

 whether the infective agent in puerperal fever is S. pyo- 

 genes or an allied organism (see S. puerperalis, p. 133). 

 There appears to be little doubt that several species of 

 streptococci have been described under the name of 

 S. pyogenes. 



Serum Treatment. The virulence of a culture of 

 S. pyogenes is ' exalted ' by passage through a series of 

 rabbits. A culture medium of 1 part of human or ass's 

 serum with 2 or 3 parts of broth is then inoculated, and 

 a horse is immunised, first with killed and then with living 

 cultures. A serum prepared with one variety of strepto- 

 coccus may not immunise against another, so the horse is 

 inoculated with several strains of streptococci (' poly- 

 valent ' serum). This serum is antimicrobic Vaccines 

 of killed cultures of streptococci are also used. 



Coley's Fluid. An attack of erysipelas supervening 

 upon a malignant growth has sometimes caused the dis- 

 appearance of the latter, and sterilised cultures of the 

 $. pyogenes have been used in the treatment of inoperable 

 tumours with varying success. Coley grows S. pyogenes 

 and B. prodigiosus together for two or three weeks, and 



