/U MECHANISM OF AGGLUTINATION, 



salts in the coagulation of casein, to which he likened agglutina- 

 tion. 



I have already^ explained the mechanism of flocculation, coagu- 

 lation or precipitation by the hydrate theory of solution, and 

 although I understand that it has also been explained by the 

 ionisation theor}', yet I was, and still am, not satisfied with the 

 latter theorj^ as being a good one for the purpose. 



The mechanism of agglutination is explained in the following- 

 manner by the hydrate theory of solution. The unknown agglu- 

 tinating substance of the serum and the obscure agglutinable 

 product of microbic metabolism are each dissolved in their 

 respective fluids b}'' reason of the " residual affinities " which they 

 possess for loose water molecules, (In explanation of these terms 

 it may be said that residual affinit}^ is a chemical affinity of a 

 weak kind, and that a water solution consists of molecular 

 aggregates and loose water molecules.) Each molecule of the 

 active substances is the centre of a system, and is surrounded b}^ a 

 zone of water molecules. The solutions are in equilibrium until 

 they are mixed, when the active substances combine, the result 

 of chemical affinity. Whether or not a decomposition also takes 

 place we are unable to say, and at present this question may be 

 ignored. The combined or double molecule now beomes the centre 

 of a new water system, but its residual affinity for the loose water 

 molecules is weaker than the residual affinity of the saline matter 

 in the fluid. The origin of the saline matter is immaterial. The 

 salts attract the water molecules, and withdraw them from the 

 influence of the double molecule. The residual affinities of the 

 double molecules are thus free, and a kind of molecular tension 

 is produced. The double molecules are then attracted to one 

 another and become molecular aggregates, which gradually increase 

 in complexity, while the equilibriums between aggregate and solu- 

 tion are constantly altering. Eventuall}'' the aggregates grow so 

 massive that they become visible as a precipitate. This is Kraus' 

 precipitate. When substances separate out from solution they 



* Jour. Soc. Chem. Ind. xvii., 117. 



