416 STUDIES IX IMMUNITY. 



ing action of various stable colloids on the sedimentation of a 

 colloidal solution of gold to which electrolytes had been added and 

 thoughl that he found some relation between the viscosity and the 

 intensity of its protecting power. Victor Henri and A. Meyer* 

 diil nol think that the viscosity was a sufficient factor to explain the 

 suspension of chemical precipitates by stable colloids. 



We have studied the action of barium sulphate that has been 

 washed and suspended in distilled water on the addition of various 

 stable colloidal solutions or viscous fluids. Certain colloidal solu- 

 tions agglutinate barium sulphate energetically, for example, a 

 solution of starch or farina; certain organic fluids even when deprived 

 of their cellular elements by centrifugalization (peritoneal or syno- 

 vial fluid, nasal mucus, saliva) do the same thing; the agglutin- 

 ating substance in these fluids would appear to be mucin. 



The majority of stable colloids and viscous fluids, on the contrary, 

 inhibit the sedimentation of barium sulphate. On shaking barium 

 sulphate in aqueous solutions of sugar, glycerine, gum arabic, gum 

 tragacanth, agar, gelatin, glue, dextrin, serin, pseudoglobulin, 

 euglobulin or fibrinoglobulin, we find that the masses of barium 

 sulphate break up into much smaller particles of apparently uni- 

 form size which have slight tendency to adhere to one another. 

 As a result, we obtain much finer suspensions, which are more 

 homogeneous and stable and, in the case of barium sulphate, are of 

 milky appearance. These suspensions, when left to themselves, 

 sediment very slowly. 



It is only rarely that the action of such solutions on barium sul- 

 phate is due to their viscosity. Syrups composed of sugar or 

 glycerine do act by viscosity; the more marked this viscosity is, the 

 slower the sedimentation of the barium sulphate. All the other sub- 

 stances which we have just mentioned, however, as dissociating 

 barium sulphate, do not act through their viscosity unless much 

 more concentrated solutions than necessary are employed. Vis- 

 cosity, then, functions only in a subsidiary manner. Thus we find 

 that a gum solution of 0.03 per cent in distilled water which reacts 

 with Ostw r ald's viscosimeter just as distilled water does, suffices, 

 notwithstanding, to hold barium sulphate in suspension. 



The mechanism of the suspension of barium sulphate becomes 

 * Revue gen. des Sciences, 1904. 



