150 VETERINARY BACTERIOLOGY 



by combining with the flagella (flagellar agglutinins) and those 

 which unite with the cell-body (somatic or body agglutinins). 



Method of Agglutinin Action. Common salt must be present 

 in any serum which agglutinates. Its function is not thoroughly 

 understood, nor is the general phenomenon of agglutination itself 

 susceptible of a simple explanation. The older theories of the 

 change whereby the organisms are made glutinous by the union 

 of the agglutinin are to be discarded, and the true explanation is 

 doubtless to be found somewhere in the field of colloid chemistry. 

 Concerning the exact nature of the change in the cell we know 

 little or nothing. The cells are certainly not seriously injured; 





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Fig. 74. Diagrammatic representation of group agglutination: Let 1, 2, 

 and 3 represent the agglutinogen given off by three related species of micro- 

 organisms. The organisms 1 and 2 have agglutinogens a and F in common, 

 but in quite different proportions. No. 3 likewise has F in common with both 

 of the others, and D in common with 1. If the area covered in the diagrams 

 represents the relative proportions of agglutinogen of each kind, the readiness 

 with which one species may be agglutinated by a heterologous serum may 

 be understood. 



in fact, an organism may grow luxuriantly in a serum which agglu- 

 tinates it. One of the delicate tests for agglutinability is to grow 

 the organism in such a serum, and note the production of long 

 threads (Pfaundler's reaction). 



Group Agglutinins. The statement has been made that agglu- 

 tinins are specific. This must be somewhat modified. It has been 

 shown that the serum homologous for a certain organism may 

 clump to a less degree some other species or closely related forms, 

 and in rare instances forms quite unrelated. This seems to be 

 due to the fact that not all the agglutinogen given off by a 

 particular organism is of one type; the agglutinins produced, 



