282 



AGGLUTININS 



pro-agglutinoids become less concentrated, and finally, when they are 

 diluted as to have no influence on the reaction, the agglutinins are still 

 present in sufficient quantity to bring about agglutination. As a practi- 

 cal fact, in agglutination reactions the action of pro-agglutinoids is of 



much importance, for the inexperi- 

 enced may be misled by the absence 

 of or by poor agglutination in lower 

 dilutions to neglect the use of higher 

 dilutions (see Fig. 86). 



The substance in bacteria or 

 other cells that produces agglutinin 

 is called agglutinogen. It appears 

 to be formed in the cell, and in 

 some cases may be excreted into 

 the surrounding medium. Certainly 

 when bacteria die and become dis- 

 integrated, agglutinogen is liberated 

 and the filtrates (entirely free from 

 bacterial cells), when injected into 

 animals, will cause the formation of 

 agglutinins. 



Agglutinogen must be con- 

 sidered as having a simple hapto- 

 phorous group, through which it 

 may unite with the receptors of the 

 tissue-cells. This haptophore 

 comes into play again in the union 

 between agglutinogen and agglu- 

 tinin, which precedes agglutination. 

 It is a passive body, similar to 



the haptophore of antitoxin, and has no other function than that of 

 uniting either with cell or with agglutinin. 



Origin of Agglutinins. The investigations that have been carried 

 out for the purpose of determining the site of formation of agglutinins 

 have not thus far yielded conclusive results. The lymphoid tissues 

 appear especially concerned, agglutinins being found early in the bone- 

 marrow and the spleen (Pfeiffer and Marx). Metchnikoff believes that 

 agglutinins may be derived from leukocytes and endothelial cells. It is 

 more probable, however, that the formation is general, and is the result 

 of wide-spread cellular activity. 



FIG. 80. A DIAGRAMMATIC ILLUSTRA- 

 TION OF THE ACTION OF AGGLUTI- 

 NINS AND AGGLUTINOIDS. 



In the first tube (left) most of the 

 bacilli (B) have been agglutinated and 

 massed in the bottom of the tube by 

 the agglutinins (a). 



In the second tube (right) the 

 bacilli (B) are in combination with the 

 agglutinoids (A), but agglutination 

 does not occur because the agglutino- 

 phore groups are lost. A few bacilli 

 have been agglutinated by the agglu- 

 tinins (a). 



