332 STUDIES IN IMMUNITY. 



5. Fresh serum retains in suspension certain fine precipitates, 

 such as the sulphate of barium. 



6. This dissociation of barium by serum is due to an adhesion 

 between this substance and the albuminous colloids of the serum, 

 and is similar, therefore, to the agglutination of barium sulphate by 

 corpuscles, in that they are both due to the adhesion of particles 

 in suspension to the precipitate. The adhesion of the albuminous 

 substance of serum with suspensions they have dissociated is easily 

 demonstrable by the fact that suspensions dissociated by serum 

 remain so when the excess of serum is removed and also by the 

 fact that with certain precipitates the colloidal substances that 

 have been attached to them and have kept them in suspension may 

 be liberated by dissolving the precipitates (tricalcium phosphate). 



7. The intensity of the tendency with which the particles 

 attached to the suspension tend to remain in suspension plays a 

 distinct role in the appearance of an agglutination or of a dissociation 

 of the precipitate. 



8. It is possible that, in a mixture of two colloids of the same 

 electric sign, one stable and the other unstable, the protection of 

 the first for the second against the flocculating action of electro- 

 lytes is due to a reciprocal adhesion of the particles of the colloids. 



