410 STUDIES IN IMMUNITY. 



This, to be sure, is not the opinion of Sachs, who believes that 

 there is inhibition to hemolysis when a specific serum is used, and 

 not when a normal sensitizer like normal rabbit serum is employed. 

 In harmony with Ehrlich's theory Sachs considers that normal 

 sensitizers possess a complementophilic arm that is very avid of 

 alexin (complement) ; even more so indeed, than is the corresponding 

 arm in an immune sensitizer. When acted on by a normal sensiti- 

 zer the corpuscles easily fix alexin even in presence of an excess of 

 normal serum. But since a normal serum contains several normal 

 sensitizers (Ehrlich and his pupils presuppose the existence of very 

 numerous antibodies even in normal serum), these bodies take hold 

 of the alexin present and, having a superior affinity for it, prevent 

 its fixation on corpuscles even when they are sensitized by an 

 immune serum. The antagonistic property therefore would be 

 due to the presence in serum of certain normal sensitizers that 

 have no affinity for the corpuscles employed, but monopolize the 

 complement. 



This theory is irreconcilable with the fact that the addition of 

 salt solution suffices to attenuate the antagonistic effect of serum 

 to a marked degree. The first premise of the hypothesis is incorrect ; 

 the antagonistic property is also present when a normal sensitizer 

 is used, as we have just seen, and as the following experiment further 

 evidences : 



Two series of mixtures are prepared at the same time. The first 

 series comprises eight tubes, each containing 1 c.c. of a 5 per cent 

 suspension of washed goat corpuscles. To four of these tubes 

 normal sensitizer, that is to say, normal rabbit serum, 56 degrees, 

 is added in varying amounts (0.4, 0.2, 0.1 and 0.05 of a cubic 

 centimeter) ; to the other four a specific sensitizer (serum of a rab- 

 bit immunized against goat blood) in doses of 0.01, 0.005, 0.003 + 

 and 0.0025 of a cubic centimeter. 



One hour later the tubes are filled with salt solution centrifugal- 

 ized, the supernatant fluids decanted, and 0.6 of a cubic. centimeter 

 of salt solution added to each sediment. To each tube is then 

 added 0.05 of a cubic centimeter of fresh guinea-pig serum (alexin). 



In the second series of tubes the same steps are taken except 

 that, after sensitization, centrifugalization and decanting, 0.1 of a 

 cubic centimeter of salt solution plus 0.5 of a cubic centimeter of 



