THE MECHANISM OF AGGLUTINATION. 161 



to which a moderate amount of cholera serum has been added. 

 The bacteria in their development remove all the particular proper- 

 ties from the fluid* The same facts hold for sera -active against 

 red blood cells. When red blood cells are placed in contact with 

 their specific serum they absorb both the agglutinating substance 

 and the sensitizing substancef. The serum separated by centrifu- 

 galizing such a mixture is inactive for fresh corpuscles. It may 

 also be added that the agglutinins of normal sera are likewise ab- 

 sorbed by corpuscles or bacteria. This all indicates that animals 

 during vaccination are to be distinguished, not by the elaboration 

 of large amounts of the "dissolving diastase" or alexin, but by 

 formation of those substances which favor the action of these diastases, 

 that is, of principles which unite with the cells and sensitize them 

 to the effect of this alexin. 



* This result completely contradicts the facts observed by Pfeiffer, who per- 

 formed this last experiment. (Centralblatt fur Bakt., 1896.) Pfeiffer found 

 that the agglutinin was absorbed under these conditions, but stated that the fluid 

 in which bacteria had grown still retained the property of causing a granular 

 transformation when injected with new vibrios into the peritoneal cavity of a 

 normal guinea-pig. Pfeiffer's conclusion that active sera do not act on bacteria 

 in the same manner in vitro as they do in the peritoneal cavity is erroneous. The 

 effect in vivo and in vitro is precisely the same. Experiment shows us that the 

 smallest amount of cholera serum necessary to cause granular transformation of a 

 given dose of vibrios is the same whether the transformation takes place by means of 

 the alexin in the peritoneal cavity, or in vitro on the addition of the alexin of normal 

 serum. This minimal destructive dose for vibrios is very similar to the minimal 

 agglutinating dose, as we shall consider presently. 



f It must be noted that Ehrlich (Collected Studies on Immunity, Ehrlich- 

 Bolduan, Wiley & Co., page 1) has recently noted that hemolytic serum exhausted 

 by contact with its specific corpuscles no longer forms a dissolving mixture for 

 new corpuscles on the addition of normal serum. 



t We should like to mention briefly a curious experiment which, strictly speak- 

 ing, is rather irrelevant. If a given dose of normal serum with strong aggluti- 

 nating property for cholera vibrios (normal horse serum) is placed with these 

 vibrios, agglutination takes place. If the mixture is then centrifugalized and the 

 clear supernatant fluid taken off, it is found that it no longer agglutinates cholera 

 vibrios, but still does agglutinate the typhoid bacillus. Conversely, normal 'horse 

 serum mixed with typhoid bacilli leaves a supernatant fluid after agglutination 

 and centrifugalization that no longer agglutinates the typhoid bacillus, but still 

 agglutinates the cholera vibrio. It seems certain, then, that there are two distinct 

 agglutinins, one for each of these micro-organisms, in the same serum. Such 

 experiments may one day throw light on the obscure question of the origin of the 

 specificity of active properties in serum. It is quite conceivable that vaccination 

 with a given bacterium may cause the production of a large amount of an agglu- 

 tinin which has already existed in small amounts. 



