THE MECHANISM OF AGGLUTINATION. 153 



The same results are also obtained if, instead of bacteria, Kraus' 

 precipitate, obtained by mixing cholera serum with an old filtered 

 culture of the vibrios, is used. This precipitate is treated exactly 

 as described for bacteria, and it is found that it clumps very much 

 more markedly in fluids containing salt than in distilled water. 



It may be worth while to give the results obtained by the same 

 technique on the agglutination of a fine emulsion of potter's clay 

 in distilled water after filtering through paper. Tubes which do not 

 contain salt remain opaque for days, whereas in tubes containing 

 0.7 per cent salt solution there is a very distinct agglutination and 

 a rapid deposition. The resemblance between floating clumps of 

 agglutinated bacteria and the whitish flecks of clay suspended in 

 salt solution and falling slowly to the bottom, is very striking. 



These experiments on the absence of agglutination in distilled 

 water are very strongly confirmatory of the idea that the agglutinin 

 acts by producing on isolated elements such changes in their proper- 

 ties of molecular adhesion as are shown by particles of clay. In each 

 case the adding of salt suffices to produce the physical phenomenon 

 of agglutination which, without it, is impossible. This, in our 

 opinion, is a confirmation of an hypothesis that we formerly offered 

 and have just recalled. 



*** 



If we conceive of the phenomenon of agglutination in this way, 

 interesting generalizations may be drawn, particularly in the light 

 of the explanation that Duclaux has proposed for coagulation. 

 What, indeed, is agglutination? It is the union into masses of organ- 

 ized scattered particles, by some peculiar influence that changes 



only. This technical error is naturally of great importance in researches on easily 

 agglutinable bacteria like B. typhosus. 



It is certain that real bactericidal properties have been presumed to exist 

 when agglutinins alone were present. It is also probable that at times certain 

 properties of the agglutinins have been attributed to the alexins. For example, 

 Buchner states that alexin loses its activity, to a large extent at least, when mixed 

 with distilled water. The presence of distilled water might apparently diminish 

 the bactericidal property of a serum by weakening its agglutinating power and 

 consequently by increasing the number of colonies that grow on gelatin. We 

 have found that alexin acts very well in a medium with very little salt; vibrios 

 treated with preventive serum and then washed and suspended in fifteen parts 

 of distilled water may show granular transformation when one part of normal 

 serum is added to these fifteen parts of emulsion, without any agglutination. 



