FURTHER DEVELOPMENT OF KNOWLEDGE 187 



antigen, heated antiplague horse serum represented the antibody, 

 and fresh guinea pig serum was used as alexin. A series of tubes 

 was then prepared as follows : 



1. Alexin + plague bacilli -f inactivated antiplague serum. 



2. Alexin -j- plague bacilli + inactivated normal horse serum. 



3. Alexin -j- inactivated antiplague serum. 



4. Alexin -j- inactivated normal horse serum. 



5. Plague bacilli + inactivated antiplague serum. 



6. Plague bacilli and normal horse serum. 



These mixtures were left together for 5 hours and, at the end of 

 this time, sensitized rabbit corpuscles were added to each tube. The 

 result showed hemolysis in all the tubes except "1," in which there 

 were plague bacilli, antiplague serum, and alexin, and in tubes 5 and 

 6, which had contained no alexin from the beginning. 75 



It was plain, therefore, that the bacilli when specifically sensi- 

 tized had become capable of absorbing alexin and preventing its sub- 

 sequent action upon the sensitized erythrocytes. That the occurrence 

 was not exceptional was shown by the fact that, in the same series, 

 similar results were obtained with anthrax, typhoid, and proteus 

 bacilli, and their respective antisera. 



Schematized in accordance with the conceptions of Ehrlich our 

 diagram would be as follows : 



- COMPLEMENT OR ALEXIN 



SPECIFIC 

 AWT/BODY 

 (PttSENT ORNOT?} 



HAEMOLYTtC 

 ANTIBODY 



RED BLOOD, 

 CELLS 



COMPLEMENT FIXATION SCHEMATIZED ACCORDING TO EHRLICH 's VIEWS. 

 If the antibody in I is present then complement is fixed by the antigen-antibody 

 complex, and is no longer free to act upon the hemolytic complex II. In the 

 same way antigen I could be determined if a known antibody I were used. 

 For, in the absence of either of these parts of the complex I complement 

 would remain unfixed and free to act on complex II. 



We represent the phenomenon graphically in the symbols of Ehr- 

 lich merely because they facilitate clearness of exposition. - 



In the presence of both parts of Complex I the alexin is held and 



75 We will see later that unsensitized bacteria in emulsion will non-specifi- 

 cally fix small amounts of complement. 



