COMPLEMENT-FIXATION TEST 273 



quantity of amboceptor to destroy all the bacteria present, 

 hence the disease is continued by those that escape. (3) Or 

 the complement may not be of the right kind to unite with 

 the amboceptor introduced, since this is derived from the 

 blood of a heterologous ("other kind") species. In hog- 

 cholera serum, if it is bactericidal, this difficulty is removed 

 by using blood of a homologous ("same kind") animal. 

 Hence, Ehrlich suggested the use of apes for preparing bac- 

 tericidal sera for human beings. The good results which 

 have been reported in the treatment of human beings with 

 the serum of persons convalescing from the same disease 

 indicate that this lack of proper complement for the given 

 amboceptor is probably a chief factor in the failure of sera 

 from lower animals. (4) The bacteria may be localized in 

 tissues (lymph glands), within cavities (cranial, peritoneal), 

 in hollow organs (alimentary tract), etc., so that it is not 

 possible to get at them with sufficient serum to destroy all. 

 This difficulty is obviated by injecting directly into the 

 spinal canal when Flexner's antimeningococcus serum is 

 used. (5) Even if the bacteria are dissolved it does not 

 necessarily follow that their endotoxins are destroyed. 

 These may be merely liberated and add to the danger of the 

 patient, though this does not appear to be a valid objection. 

 (6) Complement which is present in such a large excess 

 of amboceptor may just as well unite with amboceptor 

 which is not united to the bacteria to be destroyed as with 

 that which is, and hence be actually prevented from dissolv- 

 ing the bacteria. Therefore it is difficult to standardize the 

 serum to get a proper amount of amboceptor for the com- 

 plement present. 



COMPLEMENT-FIXATION TEST. 



Although little practical use has been made of bactericidal 

 sera, the discovery of receptors of this class and the peculiar 

 relations between the antigen, amboceptor and complement 

 have resulted in developing one of the most delicate and 

 accurate methods for the diagnosis of disease and for the 

 18 



