AGGLUTINATION 579 



the phenomenon and the facility with which it can be noted vary 

 greatly in different cases. Details will be found in the chapters 

 dealing with the individual disease, etc. Furthermore, the 

 phenomenon is not peculiar to bacteria ; it is seen, for example, 

 when an animal is injected with the red corpuscles of another 

 species, hcemagglutinins appearing in the serum, which have a 

 corresponding specificity. 



The physical changes on which agglutination depends cannot 

 as yet be said to be fully understood. Griiber and Durham 

 considered that the agglutinin produced a change in the envelope 

 of the bacterium, causing it to swell up and become viscous, but 

 the facts since established show that this is not the true explana- 

 tion. For example, it has been shown by Nicolle and by Kruse 

 that if an old bacterial culture be filtered through porcelain, the 

 addition of some of the corresponding anti-serum produces a 

 sort of granular precipitate in it; and that when minute in- 

 organic particles are added to the mixture, they become aggre- 

 gated into clumps, as in the agglutination of bacteria. The 

 phenomenon would thus appear to be the result of the inter- 

 action of the agglutinin and some substance in the bacterial cell 

 which is known as the agglutinable substance or as the agglu- 

 tinogen. Joos has found in the case of the typhoid bacillus that 

 there are two agglutinable substances which differ in their 

 resistance to heat a and ft agglutinogen, and that they give 

 rise to corresponding agglutinins. Further, as the result of a 

 comparative study of the agglutinins of a motile and a non- 

 motile variety of the hog cholera bacillus, Theobald Smith has 

 come to the conclusion that there is an agglutinin which is pro- 

 duced by and acts on the flagella, and another which is similarly 

 related to the bacterial bodies ; the former acts in very much 

 higher dilutions than the latter. Another factor necessary for 

 the phenomenon of agglutination is a proper salt content. Bordet 

 showed that if the clumps of agglutinated bacteria are freed' from 

 salt by washing in distilled water they become resolved, and that 

 on the addition of some sodium chloride they are formed again, 

 and Joos has also brought forward striking confirmatory evidence 

 as to the necessity for the presence of salts. It is thus probable 

 that in the phenomenon of agglutination more than one factor 

 is concerned, and it is possible that in part it may depend on 

 some change in the molecular relationship of the bacteria to 

 the surrounding fluid, analogous to altered surface tension. 



In the phenomenon of agglutination we have to distinguish 

 two factors, namely, the combination of agglutinin. and agglu- 

 tinable substance (agglutinogen) and the actual clumping of the 



