AGGLUTININS AND PRECIPITINS 93 



digestion destroys the agglutinins fairly readily, but trypsin acts 

 more slowly. Alkalies even when dilute are destructive, but acids 

 operate less actively. They are absorbed by charcoal. They are 

 not thrown down in the precipitate formed by specific precipitating 

 sera. The influence of heat on agglutinins has been the subject of 

 much study. The work of Joos was conducted with both agglu- 

 tinogen and agglutinin. As mentioned above, he demonstrated the 

 presence in the bacterial antigen of a thermolabile A agglutinogen 

 and a thermostable B agglutinogen, the dividing line being 60 to 

 62 C. The injection of heated antigen (B agglutinogen) gives rise 

 to the formation of B agglutinin, which in contrast to the antigen is 

 destroyed by heat of 60 C., but reacts with both A and B agglu- 

 tinogens. The injection of the unheated bacilli containing both A 

 and B agglutinogen leads to formation of both agglutinins, but the 

 B agglutinin can be removed by heat leaving the thermostable A 

 agglutinin, which reacts only with the A agglutinogen. The essen- 

 tials of this work have been confirmed, although Scheller working 

 with bacillus typhosus found that the B agglutinin is reduced in titer 

 but not completely destroyed at 60 to 62 C. Scheller showed 

 further that the heated bacteria (B agglutinogen) absorb agglu- 

 tinins from the sera more readily than do unheated bacteria, and that 

 they give the highest titers with the serum. 



According to the Ehrlich scheme, agglutinins have a haptophore or 

 combining group and a zymophore group which causes the agglutination. 

 This zymophore is killed by heat and deteriorates on long standing to form 

 the agglutinoid (or agglutinin free from zymophore), which has combin- 

 ing but not agglutinating power. Thus in the side-chain theory the 

 agglutinins (and precipitins) differ from the theoretical simplicity of 

 the antitoxins and constitute the receptors of the second order. 



The Physical Basis of Agglutination. The mechanism of agglu- 

 tination is such that the reaction takes place in constant proportions, 

 thus likening it to a simple chemical reaction. The reaction is re- 

 versible, however, in that simple shaking, the use of organic and 

 inorganic acids and acid salts, as well as alkalies and heat of 70 to 

 75 C., can break the clumps into cell units; but after this separa- 

 tion fresh agglutinating serum cannot operate again. It has been 

 shown further that agglutinins can be separated from bacteria- 

 agglutinin combinations by the electric current ; therefore, the agglu- 

 tinins are not destroyed by the union with the bacteria. Many of 

 the older workers believed that the reaction occurred because of 

 changes in the outer layers or ectoplasmic substance of the cells. 

 Gruber at first maintained that a substance, glabrificin, was taken 

 from the serum by the cells which made their outer surfaces sticky 

 and caused adhesions when their motility brought the bacteria in 

 contact with one another. Malvoz and others held that the reaction 

 depended upon the entanglement of the flagella of the bacteria. 

 Neither of these ideas is consistent with the fact that non-motile 



