208 AGGLUTININS IN IMMUNITY 



action of the fluid in which they are suspended ; and equally 

 naturally cells which are dissolved do not show ordinary agglu- 

 tination, though, as we shall see, they show a similar phenomenon. 



The formation of agglutinins follows laws similar to those 

 governing the formation of other antibodies. After each injec- 

 tion there is a negative phase, followed by a rise, which, as a rule, 

 attains its maximum in about a week. In the case of typhoid 

 fever no agglutinin can be demonstrated, as a rule, during the 

 first week ; there is then a steady rise, which usually attains its 

 maximum at the commencement of convalescence. After this 

 the amount tends gradually downward, and disappears after a 

 time, which varies between a few months and several years. 

 On a single occasion the author has seen a marked drop in the 

 amount precede a relapse, during which a second rise occurred. 

 This was obviously a negative phase, and the occurrence of the 

 relapse might have been foretold therefrom. 



Bacteria which have been acted on by agglutinin are not altered 

 thereby in appearance, viability, or virulence, and the process does 

 not appear to play a part of much importance in immunity. Two 

 suggestions have been made in this respect : Gruber thought it 

 caused the outer layer of the bacillus to swell up, so that it could 

 be attacked by alexin, and Walker suggested that the clumping 

 of the bacilli might render them more easily taken up in large 

 numbers by the leucocytes. Possibly, also, the paralysis is the 

 essential feature of the process, as a reaction of immunity, since 

 we should expect non- motile bacteria to be more easily ingested 

 by phagocytes. It is interesting in this connection to notice that 

 the bacteria for which strong agglutinating sera are obtainable 

 are all highly motile (B. typhosus, coli, and pyocyaneus, vibrios). 

 The recent researches on the thermostable opsonins have caused 

 a certain amount of attention to be directed to the agglutinins 

 from this point of view, but nothing is definitely proved. 



That agglutinin, in common with the other antibodies, unites 

 directly with its antigen may be shown in several ways. In one 

 an agglutinating serum cooled to o is added to a culture similarly 

 cooled, and the mixture kept on ice. The bacteria will gradually 

 settle down without agglutinating, and the supernatant fluid may 

 be pipetted off. This may be tested in the ordinary way, and 

 will be found to have lost much of its agglutinating power. The 

 bacteria, if suspended in warm saline solution, will immediately 

 clump. Evidently, therefore, the agglutinin has been removed in 



