214 MECHANISM OF AGGLUTINATION 



of which are glanced at in our section on Colloidal Chemistry. It 

 is intimately concerned with the subject of solubility. If a body 

 is soluble in a fluid i.e., if the molecules of the latter have a 

 greater affinity for those of the former than these have for one 

 another there will be no sharp line of demarcation between the two : 

 between the solid and the liquid there will be a zone in which mole- 

 cules of both substances are present, and this will shade gradually 

 off into the solid body on the one hand and the fluid on the other. 

 Here, then, there will be practically no surface between the two, 

 and surface tension will be small or absent ; and in a general way 

 substances present in a fluid which dissolves them have no 

 tendency to clump. Thus to prepare an emulsion of an oil, a 

 solution of a soap or of an alkali is used, and the emulsions thus 

 formed are comparatively stable ; but if the fluid be made acid, 

 the surface tension is increased, and the globules quickly run 

 together or clump. Now it is clear from the fact that the fluid 

 part of bacterial emulsions will give Kraus's reaction, and will 

 lead to the production of antibodies on injection, that a certain 

 amount of solution does take place. That agglutinin actually 

 renders the bacteria less soluble appears clear from the phenomena 

 of Kraus's reaction, though here the insoluble precipitate is formed 

 on and in the bacteria, rather than in the fluid. And the complete 

 absence of clumping which occurs when bacteriolysis takes place 

 (though there is a large amount of agglutinin in the serum used) 

 is an indication of what takes place when the bacteria are rendered 

 more soluble, instead of less, by means of an antibody. Insolubility 

 does not account for the whole of the phenomena, but it is a feature 

 of great importance. 



As regards the nature of agglutinin, all we know is that it is 

 precipitated with the globulins, and may be of that nature. It 

 does not dialyze, and is digested by trypsin, etc. 



It appears to be formed in the lymphoid organs, red marrow, 

 and spleen, being found early in those organs after injections of 

 cholera vibrios (Pfeiffer and Marx). Metchnikoff found that the 

 peritoneal exudate might be richer in agglutinins than the blood, 

 and thought they came from the cells (leucocytes and endothelial) 

 in that fluid. The subject has also been investigated by Van 

 Emden, Deutsch, and Ruffer and Crendiropoulo, who all confirm 

 Pfeiffer and Marx as to the early presence of these substances in 

 the lymphoid tissues after inoculation. 



So far the study of the agglutinins has not presented much 



