AGGLUTININS AND PRECIPITINS 



79 



clearly visible as small particles and sink to the bottom of the tube 

 more quickly than would the individual cells in the original suspen- 

 sion. The first example is one of precipitation and the last of 

 agglutination. In the immunological sense, precipitation implies 

 flocculation of a protein solution by means of specific antibodies, so 

 that large aggregates are formed and thrown out of solution. Simi- 

 larly the term agglutination signifies clumping together by means 

 of specific antisera of cells originally in smooth emulsion, so that 

 the clumps are visible microscopically or grossly, and sink rapidly 

 to the bottom of the containing vessel. Animals may be immunized 

 to a protein in solution, as, for example, blood serum or egg white, 

 so that the animal's serum contains a body, the precipitin, capable 

 of precipitating the protein used for immunization. Similarly bac- 

 teria, red blood-corpuscles, or even other cells may be injected re- 



FlG. 3. Wooden box for holding rabbits during injections into or bleeding from the ear vein. 



peatedly into animals leading to the formation within the animal of 

 a body, the agglutinin, appearing in the blood serum and capable of 

 clumping the type of cell injected. These phenomena, although 

 closely related and probably fundamentally identical in nature, will, 

 for eminently practical reasons, be discussed separately. 



AGGLUTININS 



Bacterial Agglutination. Although others had observed the 

 phenomenon of agglutination, Gruber and Durham, in 1896, were 

 the first to study it intensively in the course of work on the colon 

 bacillus and the cholera vibrio. They pointed out the specificity of 

 the reaction and the fact that it differed in certain essentials from 

 previously studied serum reactions. These points will be discussed 



