656 



STABILITY OF BACTERIAL SUSPENSIONS. Ill 



words, the particles act more and more like particles of egg albumin. 

 The form of the curve is very similar to the curve found by Loeb^ 

 for the potential between a solution of egg albumin in a collodion sac 

 and the surrounding solution. As was found in the experiments 

 described in the preceding paper, agglutination occurs whenever the 

 potential is reduced below a value of about 15 millivolts. The result 

 of the addition of egg albumin is, therefore, that the agglutination 

 zone is moved to the alkaline side and that at a pH of 3 the egg 

 albumin stabilizes the suspension instead of precipitating it. 



Fig. 1. Effect of the concentration of egg albumin at different pH on the 

 potential and agglutination of Type D. pH adjusted with acetate buffers. 



This is typical of the action of protective colloids and is due, as the 

 figure shows, to the increase in the potential. The figure also shows 

 that the amount of egg albumin required to agglutinate is a minimum 

 near the isoelectric point of the suspension and increases as the pH 

 is moved to the alkaline side. Similar experiments have been pub- 

 lished by Eggerth and Bellows.^ 



Fig. 2 shows the effect of the addition of globin to a suspension of 

 Type D; the isoelectric point is now shifted to pH 6.5 which is near 



^ Loeb, J., Proteins and the theory of colloidal behavior, New York and London, 

 1922. 



6 Eggerth, A. H., and Bellows, M., /. Gen. Physiol, 1921-22, iv, 669. 



