igii] Reiihen Ottenherg 93 



gether. If the reaction of the fluid is made acid the matches are 

 Seen to clump together in a way which is strikingly suggestive of 

 the agglutination of bacteria. When the reaction is neutral the 

 soap is sokible and there is no sharp surface of demarcation be- 

 tween soHd and fluid. When the Hquid is acid, however, an in- 

 soluble fihn forms at once and constitutes a new surface, the tension 

 of which induces the aggregation of the floating masses. (These 

 phenomena were demonstrated. ) 



Numerous experiments have shown that serum agglutination 

 whether natural or due to immunization, is caused by a reaction 

 between two substances, of which the one, agglutinin, is in the serum 

 and the other, the agglutinable substance (or agglutinum), is in the 

 cell. In producing its effect the agglutinin disappears from Solu- 

 tion in the serum (is "absorbed" by the cells). It appears that 

 the reaction which occurs between the two substances results in 

 the formation of an insoluble product at the surface of the cell. 



That this is the case seems probable, in the first place, from the 

 fact that under certain conditions the agglutinable substance can 

 be extracted from the cells, and treated with agglutinative serum. 

 When this is done, a precipitate occurs. This was first observed 

 by Kraus who noticed that in old broth cultures of typhoid bacilli, 

 after removal of the bacilli, a precipitate could be formed by ad- 

 dition of typhoid-agglutinative serum. Klein has made similar 

 observations with red blood cells and hemagglutinative serum. 

 That the process is in the nature of a precipitation at the surface of 

 the cell is indicated also by the experiment of Moreschi. He 

 showed that red blood cells treated with such a dose of agglutinat- 

 ing serum as in itself is entirely insuflicient to agglutinate, undergo 

 extraordinarily rapid and complete agglutination, if there is added a 

 small amount of serum containing precipitin for the agglutinative 

 serum used. 



The chemical nature of the two reacting substances is unknown. 

 The highly specific nature (within certain limits) of agglutina- 

 tion phenomena indicates that the substances must be extremely 

 complex. The part they play in intracellular life is still obscure. 

 That they are functionally important in cells is a reasonable as- 

 sumption. 



