240 INFECTION AND RESISTANCE 



Bordet 61 compared the formation of precipitates in bacterial 

 emulsions to the precipitation of such inorganic emulsions as clay in 

 distilled water, and noted that the precipitation of homogeneous 

 emulsions of such substances is "often controlled by such insignifi- 

 cant causes as the presence of salts." Applying this analogy to the 

 agglutination of bacteria, he performed the following experiment: 

 Cholera spirilla, emulsified in salt solution, were treated with homol- 

 ogous immune serum and, after agglutination had taken place, the 

 bacteria were thrown to the bottom by centrifugation and divided into 

 two parts. One part was again suspended in salt solution, and the 

 other was washed, and then suspended in distilled water. The bac- 

 teria in the tube of salt solution rapidly agglutinated, while those 

 in the distilled water, after thorough shaking, remained indefinitely 

 suspended in an even emulsion. If, however, to these unagglutinated 

 bacteria a small amount of pure sodium chlorid was added agglutina- 

 tion occurred. 



The conclusions that can justly be drawn from this experiment 

 are, first, that the bacteria could not agglutinate, even though they 

 had been bound to agglutinin, when salt was removed from the en- 

 vironment, and, second, that the addition of salt to such emulsions 

 brought about immediate agglutination. The same principle can be 

 demonstrated in other ways. If, for instance, a bacterial emulsion 

 is rendered free of salt by dialysis, and this is added to an aggluti- 

 nating serum similarly dialyzed, no agglutination occurs. The sus- 

 pension may remain evenly clouded indefinitely unless salt is added. 

 As soon as a little salt is added, however, perfect agglutination 

 occurs. To this technique the very obvious criticism may be applied 

 that perhaps the absence of salt has precipitated the agglutinins, 

 which, as we know, are precipitated with globulin, which is insoluble 

 in the absence of salt. However, this source of error is excluded by 

 the first experiment cited, and, moreover, it can be shown by the last 

 experiment that, even though the bacteria are not agglutinated in 

 the salt-free serum, they have nevertheless absorbed agglutinin. For, 

 if such a salt-free mixture is centrifugalized, the bacteria washed 

 and suspended in distilled water, and salt is then added, agglutination 

 occurs. The supernatant fluid of the original suspension, further- 

 more, can be shown to have been deprived of agglutinins by suitable 

 experiment. 



These facts, first observed by Bordet, and further elaborated by 

 the studies of Joos, 62 Friedberger, 63 and others, have been inter- 

 preted in different ways. Joos claims that there is a chemical union 

 between the bacteria and the salt, and bases this upon the observation 

 that the salt added to a salt-free mixture cannot be demonstrated in 



61 Bordet. Ann. de I'Inst. Pasteur, 1896, 1899. 



62 Joos. Centralbl f. Bakt., 1, Vol. 33, 1903. 



63 Friedberger. Berl. kl Woch., 1902; Centralbl f. Bakt., 1, Vol. 30. 



