SENSITIZING ANTIBODIES 283 



As the reaction approaches completeness, the clumps grow larger, 

 individual microorganisms become more and more scarce, finally 

 leaving the medium between clumps entirely clear. While the clump- 

 ing of a motile organism suggests that motility has something to 

 do with the coming together in clumps, it nevertheless has no rela- 

 tion whatever to agglutination, motile and non-motile organisms 

 alike being subject to the reaction. 



Macroscopically observed, in small test tubes or capillary tubes, 

 agglutination evidences itself by the formation of flake-like masses 

 which settle into irregular heaps at the bottom, leaving the super- 

 natant fluid clear, in distinct contrast to the even flat sediment and 

 the clouded supernatant fluid of the control. Macroscopically, too, 



FIG. 34. MICROSCOPIC AGGLUTINATION REACTION. 



agglutination is evidenced when bacteria are grown in broth to 

 which immune serum has been added. Instead of evenly clouding 

 the broth, the microorganisms develop in clumps or chains. 



Another phenomenon probably produced by agglutinins is the 

 so-called ''thread-reaction" of Pfaundler. 14 This consists in the 

 formation of long convoluted threads of bacterial growth in the 

 hanging drop of dilute immune serum after twenty-four hours. Very 

 strict specificity is attributed to this reaction by Pfaundler. 



Agglutinins act upon dead as well as upon living bacteria. For 

 the microscopic tests bacterial emulsions killed by formalin were 

 introduced by Neisser. 



Ficker 15 has recently succeeded in preparing an emulsion of 



14 Pfaundler, Cent, f . Bakt., xxiii, 1898. 



15 Fic'ker, Berl. klin. Woch., 1903. 



