THE MECHANISM OF AGGLUTINATION. 159 



the function of sodium chloride does this very thing. The bac- 

 teria that we washed and suspended in distilled water had been 

 affected by the agglutinin. They are immobilized and are ready 

 to be agglutinated energetically.* But to bring about the second 

 phase of the phenomenon or agglutination, properly speaking, a little 

 salt must be added to the emulsion. 



As far as Kraus' phenomenon is concerned we are as yet in no 

 position to interpret it. It is by no means demonstrated that 

 Kraus' precipitates have anything to do with the real agglutination 

 of bacteria; it may be that this precipitate is similar to that obtained 

 in a mixture of defibrinated hen blood and specific rabbit serum 

 (that is, serum from a rabbit injected with hen blood), which appar- 

 ently has no relation to the agglutination of the corpuscles them- 

 selves. But if Kraus' precipitate is formed from the agglutinable 

 substance of bacteria it seems to us that we must compare it, from 

 the standpoint of its formation, with the casein precipitates which 

 lactoserum produces with whey, in which instance the substance 

 is so finely divided as not to disturb the limpidity of the fluid. In 

 other words this precipitation would resemble the agglutination 

 of bacterial substances in a finely divided state. 



* 

 * * 



The idea that the agglutination of cells, corpuscles, bacteria or 

 non-differentiated particles like casein has the characteristics of a 

 phenomenon of coagulation might suggest certain observations on 

 the significance of the active properties of serum. Let us enumerate 

 briefly, without repeating the observations that we have formerly 

 made, the essential properties which we have found in specific sera 

 by experiments performed in vitro. To be more exact we shall 

 consider the two sera which we used as typical, that is cholera serum, 

 and a serum active against rabbit corpuscles obtained by injecting 

 guinea-pigs with rabbit blood. These sera, as we have recently 

 pointed out, have similar properties which are as follows : 



1. Both sera agglutinate cellular elements and suppress their 

 motility if they have any. 



2. When either the vibrios or the corpuscles have been in con- 

 tact with their respective serum they are more susceptible to the 



* We may also add that they have become very susceptible to the effect of 

 alexin. 



