330 STUDIES IN IMMUNITY. 



glance for a moment at the phenomena observed in the study of 

 colloidal substances in the light of what we have learned from our 

 study of the suspensions, even though such a consideration must 

 be largely hypothetical. Henri, .Lalou, Mayer, and Stodel found 

 that, on mixing a stable negative colloid, that is to say, one that was 

 little affected by electrolytes, with a colloid of the same charge 

 that is unstable, that is to say, very susceptible to salts, there is no 

 precipitation and the mixture becomes even more insusceptible 

 to electrolytes than is the unstable colloid. In a precipitate caused 

 by a flocculation from electrolytes both colloids are present. Un- 

 fortunately this fact gives no indication of the relation between the 

 two coUoids while in solution. One is tempted to suppose that the 

 stable colloid protects the unstable colloid from the electrolytes 

 owing to an adhesion between their particles. Such protection 

 of an unstable colloid by a stable colloid evidently resembles the 

 protection of barium sulphate against gravity by serum. We have 

 already shown that this protection, which leads to a suspension 

 of the sulphate, is due to an adhesion between this substance and 

 the colloids of the serum. It would therefore seem to us not 

 unreasonable to suppose that, in mixtures with the same electric 

 charge, the protection of the unstable by the stable colloid is due 

 to an adhesion between the particles of the two substances. There 

 would be, then, an adhesion, as in mixtures of two colloids of opposite 

 charges; but whereas, in this latter case, a flocculation occurs, no 

 such result happens in mixtures of colloids with the same charge. 

 An adhesion thus would seem to take place between colloids with- 

 out any relation to their electric charge. Flocculation subsequently 

 does or does not occur, according to the case under consideration. 

 This flocculation, however, is not indispensable as a proof of 

 adhesion between the two colloids and its absence cannot be inter- 

 preted as a certain indication of an absence of adhesion. The 

 precipitation of these colloids would seem due to factors some of 

 which are already known (electrolytes and contrary electric 

 charges). 



The existence of such an adhesion would readily explain a phe- 

 nomenon that has been observed by Mangin and Henri which deals 

 with the opposition to agglutination of corpuscles by means of 

 colloids, both negative and positive, produced by small amounts 



