486 IMMUNITY 



minute inorganic particles are added to the mixture they become 

 aggregated into clumps. The phenomenon would thus appear 

 to be the result of the interaction of the agglutinin and some 

 substance in the bacterial cell which is known as the agglutin- 

 able substance or as the agglutinogen, seeing that it is probably 

 the element in the bacterial structure which in the tissues of the 

 animal or person leads to the development of the agglutinin. 

 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 ^-agglutinogen, and that they give rise 

 to corresponding agglutinins. Further, as the result of a com- 

 parative 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 produced 

 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, and this is regarded as an explanation 

 of the fact that in the case of non-motile organisms the 

 agglutinating serum acts only in proportionately high concentra- 

 tion as compared with the case of most motile forms. 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 pheno- 

 menon of agglutination as ordinarily understood more than one 

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

 on some altered molecular relationship of the bacteria to the 

 surrounding fluid analogous to altered surface tension. t? } 



As stated above, the agglutinins are usually placed in the 

 second order of anti-substances, and are regarded as possessing 

 a combining group and an active or agglutinating group. The 

 constitution would thus be analogous to that of a toxin, and in 

 conformity with this view Eisenberg and Volk consider that the 

 agglutinating group may be destroyed while the combining 

 group remains, the result being an agglutinoid. The evidence 

 for this lies in the fact that when an agglutinating serum is 

 heated to a certain temperature, not only does it lose its 

 agglutinating action but when the bacteria are treated with 

 such a serum their agglutination by active serum is interfered 

 with, a sort of plugging up of the combining molecules having 

 apparently taken place. Other facts have, however, been 



