422 THE AGCLU'llNATION TILST. 



Dincitr suggested that agglutination was due to tlie presence 

 of an adhesive substance on the ciha of the bacteria, causing 

 them to be adherent by the ciha becoming interlaced. This 

 theory presumes that the bacteria are ciliated, and could not 

 explain \vh\' non-ciliated bacteria agglutinate. 



Bordct's tlieory, which is the most feasible one which has 

 so far been put forward, explains the phenomenon as being a 

 physical one, the bacteria having only a passive role. 

 A point in favour of a passive role is that dead 

 bacteria agglutinate just as easily as do living ones. Bordet 

 thought that serum ]irobably acted on bacteria by changing the 

 relations of molecular attraction between the bacteria and the 

 surrounding fluid, thus causing in reality an effect of alteration 

 of surface tension. This theor\^ brings agglutination of bac- 

 teria into line with other agglutinations, as of inert particles 

 of cla}', etc.. but does not in realit)'. however, explam tlie inti- 

 mate character of the reaction, and there must be some previous 

 combination of a biological nature which is not yet understood. 



The technif|ue of the agglutination test is quite simple, and 

 to describe it a particular instance will be taken. In. for 

 instance, examining the serum of a cow suspected of l)eing 

 infected with the bacillus of contagious abnrtion the ijrocedure 

 is as follows : — 



One takes an emulsion of the contagious abortion Ijacillus 

 in 0.8 per cent, saline solution and ])Uts 2 c.c. of it into each 

 of a row of ten small test-tubes of about \ c.c. capacity. Serum 

 from the suspected cow is then added to each of the test-tubes, 

 so that the hrst tube contains i of serum and 9 of emulsion of 

 bacteria — that is. the serum dilution is 1 :to. and then in the 

 other tubes dilutions of serum are made, so that one has a i .z^, 

 T :5o, T :ioo. i :200, i :400, 1 :50o, 1 :8o9, i :tooo, .and a i :2O00 

 dilution. 



.Skki'm and Emulsion of Bacteria. 



T 2 3 4 5 



1:10 I -.i-^ 1 150 I :ioo i :200 



6 7 8 9 10 



r :400 [ :5(~)0 i :8oo t :iooo i :2O0o 



'Jdie bacterial emulsion must be just faintlx^ turbid, as a thick 

 emulsion is much harder to aggultinate than such a faintly turbid 

 one. It has been found that normal cattle serum ma}' agglu- 

 tinate the contagious al)ortion bacillus in a dilution of i :25 and 

 in rare cases i : 50 ; therefor in the test, a cow whose serum 

 agglutinates in a dilution of t :ioo or higher is considered 

 infected. The test which lias just been described is the macro- 

 scopic one, and is always used where the exact agglutinating 

 j^ower of a serum is required to be found. A rough micro- 

 sco])ical method mav be used where exact results are not re- 

 (luired. This method mav; for instance, l)e used in the case 



