420 STUDIES IN IMMUNITY. 



complex plus the fresh suspension takes place. The particles of 

 the complex probably act on fresh barium sulphate just as volu- 

 minous particles of the gum would act on fresh barium sulphate, or, 

 in other words, as do the granules of cold solutions of gelatin or the 

 albuminous clumps produced in serum by heating. 



*** 



With the exception of the instances in which the viscosity of the 

 fluid intervenes, the dissemination of suspensions in the solutions 

 we have studied is due to a substitution of the adhesion of the 

 particles among themselves for an adhesion of the particles of the 

 suspension to particles of the disseminating colloid. 



The dissemination of a washed suspension by colloidal solutions 

 resembles the inhibition of the appearance or sedimentation of 

 precipitates due to chemical reactions which might occur in such 

 solutions. We think that the facts observed by Lobny de Bruyn 

 and others in this connection, which have been made use of to obtain 

 colloidal solutions of substances which are normally insoluble, are 

 due to the fact that as soon as the chemical reactions which lead 

 to the production of these substances within a stable colloid solu- 

 tion are finished, there is established, between the particles of 

 these substances and the neighboring particles of the surrounding 

 colloid, a complex which is similar to those that we have studied. 



Colloidal solutions obtained in this way are therefore suspen- 

 sions in a greater or less excess of stable colloid of complexes 

 formed by the stable colloid with an insoluble chemical substance. 



The dissemination of an insoluble salt by stable colloids in the 

 form of a complex should apparently be compared with the homo- 

 geneous condition which colloids give to emulsions of oil. This 

 phenomenon, as Quincke* has shown, is due to the fact that these 

 colloids diminish the surface tension of the oil droplets for water 

 by intervening between the droplets of oil and those of water. It is 

 probable that the dissemination of barium sulphate in a colloidal 

 medium is likewise due to the fact that the surface tension which 

 exists between the suspension and water is lowered by the presence 

 of the colloid on the surface of the particles of suspension that have 

 absorbed it. 



* Quincke, Wiedemann's Annalen, 1904, XXXVII. 



