STREPTOCOCCUS PYOGENES 347 



sera have seemed to be sufficiently useful to justify their use and to 

 necessitate their standardization. 



Standardization is accomplished by the methods first devised by 

 Marx ^ 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^ 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 cubic centimeter 

 of this serum equals one serum unit. Comparisons by animal experi- 

 ment with this standard sermn approximately determine the value of 

 other sera. 



Leucocyte extracts have been employed by the writers and others, 

 as advised by Hiss,^ in various forms of streptococcus infections of man, 

 with success in many cases. Very uniformly favorable results 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, however, are also agglutinated, but in relatively higher 

 concentration of the serum. Thus, while a specific group reaction is 

 extremely useful in differentiating streptococci from other species, such as 

 pneumococci, agglutination can not be relied upon to differentiate in- 

 dividual streptococci from one another (Hiss). It has even been found 

 that a serum produced with a streptococcus from one source con- 

 tained a higher agglutinating value for some other streptococcus than 

 for the one employed in its production. Agglutinins may be produced by 

 treating animals with dead as well as with the hving virulent streptococci. 

 While the technique of the streptococcus agglutination tests is not 

 difficult when we are deahng with strains which grow diffusely and with 

 even clouding in fluid media, the frequency with which' these micro- 

 organisms clmnp spontaneously in broth cultures necessitates the use of 

 a special technique. The most simple of these methods, and possibly 

 the best, is the one in which calcium-carbonate-glucose broth is used 

 for cultivation.* Growing in this medium and thoroughly shaken once a 

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

 fluid after the settling out of the heavier calcium-carbonate powder. 



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



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

 furt a. M., Heft 2, 1906. 



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

 * Hiss, Jour. Exp. Med., vii, 1905. 

 S3 



