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 {Pseudomonas 

 aeruginosa) when mixed with the blood serum 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 Pfeifferella mallei, 

 "abortion agglutinin" for Alcaligenes abortus, "typhoid 

 agglutinin" for Eberthella tyiohi. 



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, act as stimuli to the body cells 

 of the animal injected to cause them to produce more of the 

 specific cell receptors which respond to the stimulus. The 



(261.) 



