SENSITIZING ANTIBODIES 285 



diagnostic purposes, because of the smaller amounts of blood re- 

 quired, the macroscopic tests are far preferable for the purposes 

 of bacterial differentiation and research. Greater exactitude of 

 dilution is possible when dealing with larger quantities ; microscopic 

 unevenness in the bacterial emulsion does not become a source of 

 error ; and positive and negative reactions are more sharply defined. 

 Nature of Agglutinins. Gruber and Durham, 19 the discoverers 

 of agglutinins, at first advanced the opinion that the agglutinins 

 were identical with the immune body concerned in the Pfeiffer 

 reaction, which by injuring the bacteria rendered them susceptible 

 to the alexins. Pfeiffer 20 and Kolle 21 claimed, however, that by the 

 addition of cholera vibrio to immune serum, the agglutinins could 

 be completely absorbed, or used up, while bacteriolytic substances 

 still remained. The same authors demonstrated that immune serum, 

 preserved for several months, would lose its agglutinins without a 

 corresponding loss of bacteriolytic power. It has also been shown 

 since then, by these and other authors, that the agglutinins and 

 the bactericidal substances are in no way parallel in their develop- 

 ment, and that strongly agglutinating sera may be extremely weak 

 in bactericidal substances and vice versa. We ourselves are not at 

 all sure that this proves sufficiently that agglutinins and bacteriolysins 

 are distinct substances. There are many reasons to believe that 

 it requires a considerably more powerful sensitization to produce 

 agglutination than it does to make an antigen amenable to alexin 

 action, or the action of leucocytes, and also the actual agglutination 

 or clumping depends upon environmental conditions in which vis- 

 cosity of the menstruum, the presence of electrolytes, and perhaps 

 also the condition of the antibody in the serum, namely, whether 

 or not it is relatively free or is bound up with serum proteins, play 

 a part. Bordet has shown very definitely that clumping does not 

 take place without the presence of electrolytes. If bacteria are 

 sensitized heavily, or, in other words, allowed to absorb antibody, 

 and then washed and resuspended in distilled water, they do not 

 agglutinate. A small amount of salt solution added to such a 

 mixture brings about rapid agglutination. In this, as well as in 

 the phenomena of acid agglutination, the clumping of the bacteria 



19 LOG. cit. 



20 Pfeiffer, Dent. med. Woch., 1896. 



21 Pfeiffer und Kolle, Cent, f . Bakt., xx, 1896. 



