PRECIPITIN REACTIONS 283 



able that those who come under our care belong to a class of indi- 

 viduals with comparatively less resistance to the pallida and are 

 incapable of producing sufficient antibodies, while there are many 

 who respond to the infection with more vigorous formation of the 

 antibodies and reduce the infection to a harmless latency or even 

 destroy the pallida completely. This latter class of infected persons 

 do not, of course, frequent our clinics. If this is the case, it would 

 be of immense prognostic importance to check a patient from the 

 beginning of infection by the complement fixation test with the 

 pallida antigen, thereby determining the resistance of the patient 

 against the disease. 



" We have in the Wassermann reaction a fair measure of activity 

 of the infecting agent, and now we will have in the pallida fixation 

 reaction a gauge for the defensive activity of the infected host." 



While the principle of complement fixation has thus far found 

 its widest field of practical application in the diagnosis of syphilis, 

 in the form of the Wassermann reaction, as just described, there is 

 reason for thinking that the diagnosis of latent gonococcus infections 

 also will ere long be possible upon the same experimental lines. 

 Excellent results have already been reported from different sources. 



Aside from this possibility the same principle may also be utilized 

 in legal medicine when the question arises whether a certain blood 

 stain is of human origin or not. In such a case the material in 

 question is brought into solution and is then tested as antigen against 

 an active antihuman precipitating serum (see precipitin reaction, 

 below), which has been obtained by immunizing rabbits with human 

 blood serum, this antiserum taking the place of the antibody of the 

 Wassermann reaction. If, then, the suspected substance contains 

 human albumins these will react with the corresponding precipitin 

 of the antiserum, with the result that any complement that may 

 simultaneously be present is bound to a greater or less extent exactly 

 as in the case of the Wassermann reaction. 



PRECIPITIN REACTIONS 



Following the demonstration by Tchistovitch and Bordet (1899) 

 that not only vegetable albumins but animal albumins also are 



