436 STUDIES IN IMMUNITY. 



barium sulphate plus citrate, calcium fluoride plus citrate, etc., in 

 place of the complexes, barium sulphate plus corpuscles, and the 

 like. It is probable, then, that hemolysis by biological agents fails, 

 'when citrate is present, because these substances form unions with 

 the citrate similar to barium sulphate plus citrate, instead of attack- 

 ing the corpuscles. We have seen that the action of salts like NaCl 

 and CaCLj on the complex, barium sulphate plus citrate, is rever- 

 sible, and we have further seen that it is owing to this reversibility 

 that this complex is not always so agglutinating for red blood cells 

 when the salt is added as if the suspension in the complex had 

 been restored to its normal condition by means of NaCl or CaCl 2 . 

 This also we find to be true with biological hemolysins. These 

 latter, when inactivated by citrate, can be reactivated by CaCl 2 

 or even by NaCl. This reactivation, however, does not always 

 endow the mixture with as much activity as the same amount of 

 hemolysin would have in a non-citrated medium. It would seem, 

 then, as if the reactivating salts simply increase the affinity of the 

 complex of hemolysin plus citrate for the corpuscles. This, to be 

 sure, is the most plausible explanation of their activation of such 

 complexes by NaCl; it does not, however, authorize us at the pres- 

 ent time to lay aside the possibility of a chemical neutralization of 

 the citrate by CaC^. 



Apart from this question of the mechanism of reactivation by 

 CaCl 2 , we may say that it would seem that the inhibiting effect of 

 citrate on hemolysis by biological agents is due to the same mechan- 

 ism as its influence on the various phenomena that have been studied 

 in the preceding chapters. There is a very clear parallelism between 

 these two classes of phenomena. As a result, we feel justified in 

 concluding from our researches that the mode of union of biological 

 hemolytic agents with red blood cells would seem to be an adsorption 

 phenomenon which is comparable to the one that occurs between red 

 blood cells (or the other substances which we have studied) and insol- 

 uble substances like barium sulphate or colloidal solutions like mastic. 

 We have described these various phenomena of adhesion between 

 red blood cells and insoluble substances, or biological hemolysins, 

 to the present, as they occur in solutions of isotonic solutions of 

 NaCl or in blood serum. The majority of these phenomena will 

 also take place in a solution of saccharose as well; the hemolysis 



