THE STREPTOCOCCI 431 



Since these sera, while in a general way potent against all strep- 

 tococci, have been found protective chiefly against the specific micro- 

 organism employed for their production, Van de Velde," Denys, 

 Aronsoii, and others had advised the immunization of the animal 

 with a large variety of streptococcus races, derived from many 

 different human sources. The resulting "polyvalent" serum is more 

 apt to exert equally high protective powers against all streptococcus 

 infections. The therapeutic value of such sera in the treatment of 

 human infections is still sub judice. Undeniably favorable reports 

 are published each year in increasing number, but are by no means 

 regular or comparable to the results obtained in diphtheria with 

 diphtheria antitoxin. Nevertheless, in mild cases or in those in which 

 the lesions have been distinctly localized, the sera seemed to be suffi- 

 ciently useful to justify their use and necessitate their standardization. 

 The recent antigenic classification of streptococci by Dochez and Avery 

 may considerably alter our procedures in regard to the polyvalence of 

 serum. It may become possible in the future to type the infecting 

 streptococci and to use a corresponding serum. 



Standardization of sera in regard to their protective power is 

 accomplished by the methods first devised by Marx 100 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 101 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. 



In titrating the protective power of sera, it is of course necessary 

 to remember, as we have stated above, that streptococci fall into 

 antigenic groups and a serum produced with one strain or a mixture 

 of strains may occasionally have no action whatever upon a given 

 strain from a case. The methods of testing protective power on 

 mice are becoming so important in all kinds of bacteriological 

 research, that we think it important to insert some of the technical 

 details as described by Dochez, Avery and Lancefield in the paper 



" \-(in de Veldc, Arch, dc mod. exper., 1897. 

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



wl Aronson, Borl. klin. Woch., xliii, 1902; Otto, Arb. a. d. konigl. Just., etc., 

 Frankfurter a M., Heft 2, 1906. 



