CHAPTER XXVIII. 

 RECEPTORS OF THE SECOND ORDER. 



AGGLUTININS. 



Charrin and Rogers appear to have been the first (1889) 

 to observe the clumping together of bacteria (Pseudomanas 

 pyocyanea) when mixed with the blood sermn of an animal 

 immunized against them. Gruber and Durham (1896) first 

 used the term "agglutination" in this connection and called 

 the substance in the blood-serum "agglutinin." Widal 

 (1896) showed the importance of the reaction for diagnosis 

 by testing the blood serum of an infected person against a 

 known culture (typhoid fever) . 



It is now a well-known phenomenon that the proper injec- 

 tion of cells of any kind foreign to a given animal will lead 

 to the accumulation in the animal's blood of substances 

 which will cause a clumping together of the cells used when 

 suspended in a suitable liquid. The cells settle out of such 

 suspension much more rapidly than they would otherwise 

 do. This clumping is spoken of as "agglutination" and the 

 substances produced in the animal are called "agglutinins." 

 If blood cells are injected then "hemagglutinins" result; if 

 bacterial cells "bacterial agglutinins" for the particular 

 organism used as "glanders agglutinin" for Bacterium mallei, 

 "abortion agglutinin" for Bacterium abortus, "typhoid 

 agglutinin" for Bacillus typhosus, etc. 



The phenomenon may be observed either under the micro- 

 scope or in small test-tubes, that is, either microscopically or 

 macroscopically. 



In this case the cells introduced, or more properly, some 

 substances within the cells, probably protein in nature, act 

 as stimuli to the body cells of the animal injected to cause 

 them to produce more of the specific cell receptors which 



