384 STUDIES IN IMMUNITY. 



puscles did or did not possess receptors for the active substances 

 of horse serum in accordance with whether salt solution was or was 

 not present. One of us and also Landsteiner have already noted 

 the causes of error in experiments in specific absorption of this 

 nature. The following experiment will illustrate this point: 



Tube a. Fresh horse serum, 0.4 c.c.; washed guinea-pig blood, 

 40 per cent suspension in salt solution, 1 c.c. 



Tube 6. Fresh horse serum, 0.4 c.c.; the sediment of corpuscles 

 derived from 1 c.c. of 40 per cent suspension. 



The tubes are centrifugalized after an hour's contact and the su- 

 pernatant fluids "a" and "b" are poured into tubes "aa," which 

 contain 0.05 c.c. of pure guinea-pig blood, and "66," which contain 

 this amount of blood plus 1 c.c. of salt solution. To each tube 

 "oa" and "66" is then added 0.4 c.c. of bovine serum (56 degrees). 

 As a result, there is no agglutination or hemolysis in tube "oa," 

 but in tube "66," on the contrary, agglutination and hemolysis are 

 almost as rapid and powerful as in a control mixture containing 

 0.05 c.c. of blood, 1 c.c. of salt solution, 0.04 c.c. of horse serum and 

 0.4 c.c. of bovine serum (56 degrees). 



We then take the sediments in tubes "a" and "6" respectively, 

 and add to each 1 c.c. of salt solution plus 1 c.c. of heated bovine 

 serum. The corpuscles in "6" show only slight and very gradual 

 agglutination; the corpuscles in "a" are much more rapidly agglu- 

 tinated, which means that they have absorbed the colloidal sub- 

 stance better, and are better sensitized and alexinized. 



In the same way, as we find that the active substances of horse 

 serum are more easily absorbed in the presence of salt solution, 

 we also find that agglutination and hemolysis of guinea-pig cor- 

 puscles in a mixture of bovine serum plus horse serum occur better 

 when the mixture contains a certain amount of physiological solu- 

 tion than when it does not. 



Seventh: In Ehrlich and Sachs' experiment the sensitization of 

 the corpuscles is essentially brought about, as we have already seen, 

 by horse serum. This serum would naturally lose its alexin when 

 added to sensitized bovine corpuscles, and would keep its sensitizer 

 for guinea-pig blood. 



If we should add, then, to such a serum alexin in the form of fresh 

 guinea-pig serum, it should recover its property to hemolyze guinea- 



