674 FLOCCULATION OF BACTERIA :.^Y iTlOTEINS 



0.7; albumin is positively charged at all reactio..' acid to pH 4.8. At 

 all intermediate reactions, the two colloids are ' )ppositely charged; 

 they tend to attract each other and neutralize their charges; when 

 this occurs, their combination is isoelectric and flocks out. Moreover, 

 at the acid end of this intermediate zone, the nucleic acid particle is 

 weakly, whereas the albumin is strongly charged, hence a smaller 

 amount of albumin will be needed to combine with and discharge the 

 nucleic acid than at the other end of the zone, where the strongly 

 charged nucleic acid would require larger amounts of the more weakly 

 charged albumin to neutralize it. This view is capable of application 

 to such phenomena as the flocculation of Bacterium coli by gelatin at 

 pH 5.0 and 3.0 (Table I), points that lie outside of the intermediate 

 zone. As these authors point out in another paper (1913), any solu- 

 tion of ampholyte at every pH exists in three forms, — as anion, as 

 cation, and as undissociated molecule; it is the relative concentration 

 of these three species that changes with H ion concentration. Cat- 

 ionic gelatin exists, therefore, at pH 5.0; anionic gelatin exists at 

 pH 3.0. At pH 5.0, one might conceive that the bacterial cell (which 

 is here negatively charged) would unite with the small amount of 

 gelatin cations present; the gelatin cations being thus removed from 

 solution, more would be liberated, this process continuing until a state 

 of equilibrium between gelatin cations in solution and gelatin cations 

 combined was reached. If the charge on the cell-gelatin complex is 

 below a certain threshhold value when equilibrium is reached, agglu- 

 tination may occur, otherwise not. As it is the pH that determines 

 the amount of gelatin cations in solution, it likewise determines the 

 amount that can be combined when equilibrium is reached; hence it 

 can be understood why agglutination, though occurring at pH 5.0, 

 might not occur at pH 5.3. The same explanation would apply to 

 the flocculation of Bacterium coli by proteins at reactions more acid 

 than the flocculation zone of the untreated bacteria. 



It is more difficult to apply this theory to the pro-zone observed 

 in these experiments. Thus (Table I) when the gelatin concentration 

 is 1:400, no agglutination of the bacteria occurs at reactions from 

 pH 4.4 to 3.0, though more dilute gelatin causes flocculation. The 

 bacteria in this zone are charged positively. If a primary electrical 

 neutralization occurred, it must have been followed by further com- 



