502 THE TECHNIC OF COMPLEMENT-FIXATION REACTIONS 



the serum contains natural antisheep amboceptor, for the serum alone 

 will probably be slightly anticomplementary. For this reason I am 

 accustomed to use 2-unit doses of complement or amboceptor, and I 

 secure reactions that are very delicate and yet sharp and clear cut. If 

 one wishes to use exactly one unit of complement and one unit of am- 

 boceptor, the serum and antigen alone should be controlled, as in the 

 fourth method of performing the Wassermann reaction (p. 470). I fre- 

 quently use this technic in the gonococcus-fixation test, but, as a rule, 

 I have found the simpler technic herein given equally sensitive and 

 reliable. 



In this chapter are considered the main bacterial infections in which 

 complement fixation has been shown to possess value as a means of 

 diagnosis. Complement fixation has also proved of value in the diag- 

 nosis of animal parasitic diseases, such as echinococcus infection, and 

 in the differentiation of the proteins. With each of these the special 

 methods for preparing the antigen, titrating the antigen, and conduct- 

 ing the test are given. 



Complement Fixation in the Differentiation of Microparasites. 

 Several investigators have applied the technic of complement-fixation 

 in a study of the relationship and differentiation of closely related bac- 

 teria, spirochetes, trypanosomes, and other microparasites. These 

 studies have usualty been made by immunizing rabbits with a particular 

 strain and using the immune serum in complement-fixation tests with 

 antigens of the other microparasites under study. As a general rule com- 

 plement-fixation is most marked with homologous antigen and antiserum; 

 relationship is studied according to whether or not complement-fixation 

 occurs with the other antigens. Besredka, 1 Foix and Mallein, 2 Swift 

 and Thro 3 have reported that immune amboceptors specific for different 

 strains of streptococci can be demonstrated by means of the complement- 

 fixation test. In my own work with five strains of streptococci, 4 with 

 the specific purpose of studying the relationship of the streptococcus 

 commonly found associated with scarlet fever to the group of strep- 

 tococci, I found that differentiation among these was possible when 

 using high dilution of the immune sera, but in lower dilutions differen- 

 tiation was not found by means of complement-fixation tests, the re- 



1 Am. de 1'Inst. Pasteur, 1904, 28, 363. 



2 Presse Medicale, 1907, 15, 777. 



3 Arch. Int. Med., 1911, 7, 24. 



4 Arch. Int. Med., 1912, 9, 220. 



