212 MECHANISM OF AGGLUTINATION 



films of clumped bacteria, whereas Kraus's precipitate is easily 

 demonstrated ; besides which, agglutination can be perfectly 

 easily demonstrated in young cultures (the fluid portion of which 

 will not precipitate with specific serum) or with carefully washed 

 bacteria. This explanation, though ingenious, may be disre- 

 garded. 



Bordet's view is undoubtedly the correct one. It explains agglu- 

 tination as being due to a change in the molecular relations 

 between the objects and the fluids which bathe it in other words, 

 it is practically an effect of surface tension. It takes place in 

 many cases other than those in which it is produced by specific 

 sera acting on bacteria, red blood-corpuscles, etc.: thus, these 

 objects can be made to clump by the action of many aniline stains, 

 acids, antiseptics, etc. An emulsion of clay in distilled water will 

 remain turbid for a long time, but will rapidly clear, owing to the 

 formation of aggregates of particles, when salt is added. This 

 phenomenon (which explains the formation of mudbanks at the 

 mouths of rivers, where admixture of fresh and salt water occurs) 

 is of especial interest in view of the necessity for the presence of 

 salts in specific agglutination. Many bacteria, especially the 

 tubercle bacillus, clump spontaneously without the addition of 

 serum. In some cases this can be avoided by using a fluid poor in 

 or free from salt to make the dilution, as in Sir Almroth Wright's 

 method of estimating the agglutinating power of the serum on the 

 tubercle bacillus. A process fundamentally similar can be seen if 

 wooden matches smeared with grease are thrown on to the surface 

 of water, and may also be seen in the gathering together of 

 bubbles on the top of any fluid. 



Two phenomena are involved : the approach of the particles the 

 one to the other, and their adhesion subsequently. The former 

 depends on certain physical laws investigated by Korn and others, 

 and not yet fully elaborated, in virtue of which two elastic 

 particles suspended in an inelastic fluid in which vibrations are 

 taking place tend to approach one another. It is probably fair to 

 assume that these conditions are always present in the case of 

 bacteria suspended in a fluid medium, and that, even in the 

 absence of any agglutinin, the individual organisms will tend to 

 approach one another and to form aggregates. But in the case 

 of most organisms the aggregates thus formed are quite instable, 

 breaking up when the slightest shaking of the fluid takes place. 

 Here the force of surface tension is all-important. It is a force 



