DIAGNOSTIC REACTIONS 303 



caused by a syphilitic testicular extract behaves like the culture 

 pallida extract in the majority of cases, but when the sera (syphilitic 

 or leprous) contain abundant lipotropic substances, it may give a 

 Wassermann reaction as well, which is not the case with the culture 

 pallida antigen; and, finally, (4) in the serum of rabbits with active 

 syphilitic orchitis there is no indication of the presence of a suffi- 

 cient amount of the antibodies for the pallida antigen, although 

 it gives a strong Wassermann reaction. It remains to be seen when 

 and under what conditions the specific antibodies for the pallida 

 will most abundantly be formed in syphilitic patients. At all events 

 it is rather remarkable that the amount of the antibodies detectable 

 by the pallida antigen in these cases was so small as compared with 

 certain other infectious diseases, in this respect. It is not improb- 

 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 



