644 



STABILITY OF BACTERIAL SUSPENSIONS. H 



nate the time factor. A typical experiment is shown in Table I. It is 

 evident that there is some relation between the charge and the rate of agglu- 

 tination. The suspensions having the lowest charge are the ones which agglutinate 

 the most rapidly. The table shows, however, that the relation is not continuous. 

 Those suspensions having a potential greater than about 15 millivolts do not 

 agglutinate completely at any time. In other words, the potential does not merely 

 effect the time required for agglutination, but if larger than a certain value, pre- 

 vents it entirely. This is the result obtained by Powis.^ The fact that the point 

 of agglutination is not sharp but covers a fairly wide range between no agglutina- 

 tion and complete agglutination, may be due to the individual variation in the 



TABLE I. 



Efect of Potential and Time of Standing on Agglutination. 

 Suspension of Type D^^ in acetate buffer pH 4.2 + noted concentration of 

 egg albumin pH 4.2. 



+ = agglutination visible with lens (8 diameters). 

 + + = agglutination visible without lens. 

 C. = complete settling, supernatant clear. 



particles. It would be better theoretically, therefore, to use the point of half 

 coagulation as the end-point. This cannot be determined experimentally owing to 

 the lack of a quantitative method for determining the degree of agglutination. 

 Preparation of the Suspension. — It has been noted by one of us^^ that the 

 presence of traces of peptones, etc., present in the culture medium, markedly 

 affect the agglutination of the organisms. The suspensions were therefore thor- 

 oughly washed in distilled water. 24 hour broth cultures of the organisms were 

 centrifuged, and resuspended in distilled water. This process was repeated four 



12 De Kruif, P. H., /. Gen. Physiol., 1921-22, iv, 395. See also Putter.'^ 



