STREPTOCOCCUS PYOGENES 347 



Standardization is accomplished by the methods first devised by 

 Marx l for the standardization of swine-plague serum, and depends upon 

 the ability of the serum to protect animals against a measured dose of 

 virulent streptococci. Aronson 2 designates as a "normal serum" one 

 of which 0.01 c.c. will protect a mouse against ten to one hundred 

 times the fatal dose of virulent streptococci. One c.c. of this serum 

 equals one serum unit. Comparisons by animal experiment with this 

 standard serum approximately determine the value of other sera. 



Leucocyte extracts 3 have been employed in various forms of strep- 

 tococcus infections of man, with success in many cases. Favorable re- 

 sults have been obtained with these extracts in cases of erysipelas. 



The agglutinins found in streptococcus immune sera are usually most 

 active toward the race of bacteria employed in the immunization. Other 

 streptococci are also agglutinated, but in relatively higher concentra- 

 tion. While a specific group reaction is useful in differentiating strep- 

 tococci from other species, agglutination can not be relied upon to 

 differentiate individual streptococci from one another (Hiss). It has 

 been found that a serum produced with a streptococcus from one source 

 contained a higher agglutinating value for some other streptococcus 

 than for the one employed in its production. Agglutinins may be pro- 

 duced by treating animals with dead as well as with the living strep- 

 tococci. While the technique of streptococcus agglutination is not diffi- 

 cult when we are dealing with strains which grow with even clouding 

 in fluid media, the frequent spontaneous clumping in broth cultures 

 necessitates the use of a special technique. The most simple of these 

 methods is the one in which calcium-carbonate-glucose broth is used for 

 cultivation. 4 Growing in this medium and thoroughly shaken once a 

 day, the streptococci are found evenly divided in the supernatant fluid 

 after the settling out of the calcium-carbonate powder. 



Predpitins have been found by Aronson 5 in streptococcus immune 

 horse serum. 



Classification. Differences in minor cultural . characteristics and in 

 virulence of streptococci obtained from various sources have given rise 

 to discussion as to the identity of all races of streptococci. The earliest 

 observers were forced to abandon their separation of the streptococci of 



1 Marx, Deutsche thierarzt. Woch., vi, 1901. 



2 Aronson, Berl. klin. Woch.. xliii, 1902; Otto, Arb. a. d. konigl. Inst., etc., Frank- 

 furt a. M., Heft 2, 190G. 



3 Hiss, Jour. Med. Res., xix, 1908. 



4 Hiss, Jour. Exp. Med., vii, 1905. 6 Aronson, Deut. med. Woch., 25, 1903, 



