Il6 IMMUNE SERA 



matter to test for the presence of complement in 

 any mixture, and therefore a simple matter to 

 test for antibodies. The preparation of such an 

 indicator is accomplished as follows: As stated 

 above, the introduction of the cells of one animal 

 into the tissues of another causes the inoculated 

 animal to produce antibodies against the cells 

 injected, and, therefore, if some red blood cells of 

 a sheep are injected into a rabbit, the rabbit pro- 

 duces antibodies for sheep cells. If now some of 

 the blood serum of a rabbit which has been im- 

 munized with the red blood cells of a sheep is with- 

 drawn and placed in a test-tube with some red 

 cells from any normal sheep, the combination will 

 take place; the sheep cells acting as an antigen 

 and the immune rabbit serum acting as antibody. 

 This combination of antigen and antibody has the 

 ability to absorb complement just as any other such 

 antigen-antibody combination has, and when this 

 occurs a marked change takes place in the appear- 

 ance of the cells due to their haemolysis. The 

 fact that complement causes a marked change 

 in the appearance of the sheep cells provides a 

 convenient method for demonstrating the presence 

 or absence of complement in any mixture. The 

 changed appearance is due to the destruction of the 

 cells and the consequent release of the haemoglobin 

 into the surrounding fluid. An outline of a complete 

 complement fixation reaction is, therefore, as follows : 



