Agglutination Test. 721 



2. Agglutination Test. This is based upon the fact that 

 blood serum which contains agglutinating substances will cause 

 the clumping of glanders bacilli in suspensions of potato or 

 agar cultures, whereupon these clumps are precipitated to the 

 bottom of the supernatant clear fluid. 



The agglutinating action of blood serum was first observed 

 by Dedjulin in human beings affected with glanders, by Mac- 

 Fadyean in horses affected with this disease. Subsequent in- 

 vestigations, especially those of Schiitz and his co-workers, 

 showed that the serum of healthy horses may also contain 

 (normal) agglutinins in rather large quantities, but that, never- 

 theless, the reaction is specific in the sense that agglutination 

 is brought about by the serum of infected horses in considerably 

 greater dilutions than is the case with serum of healthy horses. 

 The following general rule has been found quite applicable and 

 reliable, viz., agglutination, if. appearing in dilutions of 1 :400 

 or less, with few exceptions, indicates freedom from infection; 

 on. the other hand dilutions of 1 :1000 or more, also with few 

 exceptions, indicates the presence of infection, while agglutina- 

 tion in dilutions of 1 :2000 or more indicates recent infection. 

 However, in infected stables we usually find a rather con- 

 siderable number of horses the serum of which will produce 

 the agglutinating phenomenon in dilutions of 1 :500-800 ; a titer 

 of this kind has no diagnostic value in either direction. This 

 fact which presents a considerable disadvantage to the practical 

 application of this method of diagnosis is compensated for in 

 a certain number of cases by the discovery that the agglutina- 

 tion titer of glanderous horses undergoes very considerable 

 fluctuation from month to month, thus it may be very high 

 (2000-4000 or more) a few days after infection and then grad- 

 ually drop, while exacerbations of the morbid process may again 

 cause a pronounced upward tendency. 



The practical value of the agglutination test is considerably 

 reduced by the necessity, in a considerable number of sus- 

 pected horses, of repeated serum tests at intervals of several 

 weeks." Since healthy horses also occasionally show physio- 

 logical fluctuations in agglutinating power of no inconsiderable 

 degree, and since on the other hand these fluctuations can no 

 longer be recognized in horses with chronic glanders, the prac- 

 tical value of this test must not be ranked too_ high and by no 

 means above that of the subcutaneous mallein test. Never- 

 theless by giving due consideration to the possible negative re- 

 sults, careful attention to technic, and especially supplementa- 

 tion of other methods, particularly the complement fixation 

 method, this test constitutes a valuable addition to our diag- 

 nostic methods (see p. 717), and may be of much value in 

 doubtful cases. In recent infections it is quite reliable in itself. 



The agglutination test was first recommended for practical use by Bourges & 

 M6ry, Pokschisehewsky, iCrpdd, Eabieaux and particularly by Jensen. The last 

 named author ranks it above the mallein test because post-mortem examinations were 

 Vol. 1 — 46 



