Electrical Charge of Bacteria 429 



ocular micrometer. In order to avoid theoretical assumptions 

 we have expressed all results in terms of this observed velocity, 

 a high velocity in general presumably signifying of course a 

 greater charge. The average results obtained with varying hy- 

 drogen ion concentrations generally based on four or more ob- 

 servations at each P H value are indicated below. 



table l 



Velocity of Migration — Micra per Second. 



P H 1 1.-1.9 2.-2.9 3.-3.9 4.-4.9 5.-5.9 6.-6.9 



—1.2 +0.3 —0.1 —1.8 —7.8 —10.3 —10.3 



P H 7.-7.9 8.-8.9 9.-9.9 10. 11. 12. 13. 



—11.7 —10.8 —12.8 —13.8 —2.2 0 0 



It appears that these bacteria maintain a fairly high and rea- 

 sonably consistent negative charge through the wide range of 

 reaction between P H 5 and P H 10, rising somewhat with increas- 

 ing alkalinity. On the acid side of this range the charge drops 

 steadily to an isoelectric point at about P H 2.0, the charge be- 

 yond this point being slight and variable and sometimes re- 

 versed. At reactions more alkaline than P H 10 the charge di- 

 minishes even more rapidly to a second (alkaline) isoelectric 

 point at about P H 12. 



The influence of sodium and calcium salts, alone and in com- 

 bination, in the concentrations studied, was to depress the veloc- 

 ity of migration very greatly at all P H values and to narrow the 

 zone of maximum velocity on the alkaline side, bringing the 

 alkaline isoelectric point to P H 9.0-10.0 (Table II). A solution 

 of 0.145 M CaCl 2 is more potent in diminishing velocity than is 

 0.725 M NaCl and there appears to be an antagonistic effect of 

 the two salts at reactions between P H 3.0 and P H 7.0. 



TABLE II. 



Velocity of Migration — Micra per Second. 





0.725 M NaCl 



0.145 MCaCl 2 



0.5S0 M XaCl + 0.145 M CaCl 2 



1.5 



— 0.8 



4-1.0 



—0.5 



3.0 



— 2.7 



—0.8 



—2.3 



5.0 



—3.9 



—1.9 



—3.5 



7.0 



—4.9 



—3.8 



—4.4 



8.0 



—4.2 



—2.6 



—2.1 



9.0 



—0.8 



—0.7 



0 



10.0 



0 



0 



0 



