AGGLUTININS AND PRECIPITINS 91 



" The tubes are placed in the water bath at 37 C- for one hour and then 

 observed. Tubes 2, 3 and 5 should show agglutination." In tube A the 

 bacteria have been ' sensitized ' with the immune serum, and after the clumps 

 have been broken up are ready again for clumping under proper conditions. 

 In tube I the addition of distilled water does not provide the essential con- 

 ditions, but in tubes 2 and 3 the addition of electrolytes favors the reaction. 

 In tube B the bacteria have not been sensitized, but of the tubes 4, 5 and 6, 

 the concentration of the copper sulphate is such as to induce clumping in 

 itself, a phenomenon frequently seen in certain concentrations of salts of 

 the heavy metals, such as zinc, lead and mercury. 



Influence of Hydrogen Ion Concentration. It has been shown 

 by Michaelis and others that bacteria may be agglutinated by pro- 

 viding a proper hydrogen ion concentration, and it was hoped that 

 this might provide a means of rapid identification of organisms. 

 Proteins, for example, have a specific and constant optimum con- 

 centration of H ions for their precipitation. In the case of bacteria 

 it was shown, for example, that bacillus typhosus was agglutinated 

 by a hydrogen ion concentration of 4 to 8 X io~ 5 , whereas para- 

 typhosus requires 16 to 32 X io~ 5 , colon bacilli not being agglutin- 

 able by this method. It has been shown, however, that this 

 differentiation is not so sharp as was at first supposed, that differ- 

 ent strains show considerable irregularity, and that there is over- 

 lapping of one species with another. A combination of serum and 

 acid agglutination has shown that bacteria sensitized by serum can 

 be more readily agglutinated than are non-sensitized bacteria. The 

 specific characters of bacterial proteins are probably due to such a 

 slight variation in the arrangement of the molecular structure that 

 a satisfactory differentiation by changes in hydrogen ion concentra- 

 tion is not at present feasible. Eisenberg has recently studied the 

 problem with 584 races of bacteria, of which 537 were of the colon- 

 typhoid group, and found no differential diagnosis possible with the 

 acid agglutination method. He also found flocculation with salts 

 of the heavy metals extremely variable. 



The Mechanism! of Agglutination. The data given in the pre- 

 ceding paragraphs outline the most important phases of the phe- 

 nomenon of agglutination, and any discussion of the mechanism of 

 the process must be based on these fundamentals. The chemical 

 nature of the agglutinogen is, of course, closely combined, if not 

 identical, with the protein of the cells, but is in no sense dependent 

 for its activity on the existence of life within the cell. Agglutinogens 

 are not destroyed by mild concentrations of formalin, phenol, heat, 

 or ultra-violet rays which are sufficient to destroy the life of the cell 

 itself. They pass through dialyzing membranes more rapidly than 

 do the agglutinins, and therefore are probably made up of smaller 

 molecules. That they pass through collodion sacs can be shown by 

 implanting such sacs, filled with killed typhoid organisms, in the 

 peritoneal cavity of rabbits and observing the development of agglu- 

 tinins in their blood ; an observation which has been confirmed by 

 Reimann in this laboratory. Old broth cultures contain in the fluid 

 agglutinogens which may neutralize agglutinins and which may 



