430 STUDIES IN IMMUNITY. 



chemical precipitates is due to the production of a complex between 

 the precipitate and the citrate. It is probable that the adsorbed 

 citrate diminishes the surface tension between the particles of the 

 adsorbed body and the surrounding fluid ; it is owing to this fact, 

 probably, that the modification brought about by the citrate in the 

 physical condition of the adsorbing substance is similar to the in- 

 hibition by this salt to flocculation of adsorbing substances like 

 clay or calcium fluoride by electrolytes. The inhibiting action of 

 citrate on adhesion of particles of the adsorbing substance to other 

 elements in colloidal solution, or in suspension, is also apparently 

 due to the same fact. Citrate that has been adsorbed by barium 

 sulphate can oppose, not only the reciprocal adhesion of the parti- 

 cles of this suspension, but also the adhesion between them and 

 stable colloids of other substances in the same way as a stable colloid, 

 A (serum), is able to inhibit the adsorption of another colloid, B 

 (starch or gum). This is the way that citrate prevents the adsorp- 

 tion of gum arabic, mucin or of starch by barium sulphate; it like- 

 wise inhibits the adhesion and subsequent flocculation of fresh 

 barium sulphate plus colloid. In like manner, the citrate prevents 

 the adhesion and subsequent flocculation of calcium fluoride with 

 indigo carmin; and finally, in a similar manner, it prevents, to a 

 certain extent, the adsorption of eosin by animal charcoal. 



These various examples suffice to show that the adsorption of 

 citrate by calcium fluoride, barium sulphate, animal charcoal and 

 the like may take the place of the adsorption of other substances by 

 these insoluble bodies as well as the mutual adhesion of the individ- 

 ual particles of each one of these materials. The phenomenon is 

 evidently due to the fact that the affinity of a given suspension for 

 various substances (dyes, colloids and citrate) varies, and also to 

 the fact that this suspension, which is attracted at the same time by 

 two affinities of different intensity, naturally yields to the stronger 

 one in our experiments to its affinity for the citrate. The inhibit- 

 ing effects of citrate are, then, simply the result of a struggle of 

 affinities for barium sulphate between the citrate and the other 

 substances, the adsorption of which, by the suspension, this citrate 

 prevents. It is this principle of a struggle between two adsorption 

 phenomena which we have employed in our study on the agglutina- 

 tion and dissolution of red blood cells by various substances. 



