electrical conductivity of the bacterial cell, etc. 265 



the Echinoderm egg when used in a strength of g^*^ M. that some 

 similar action should not be found with bacteria, but repeated 

 experiments with centrifuged solid bacterial deposits of both the 

 meningococcus and B. coli using the same type of electrodes used 

 by Gray for the Echinoderm egg and obtaining resistances as high 

 as 150 ohms failed to show any initial rise of resistance. It was 

 possible that in the case of bacteria, their enormous surface would 

 render the preliminary rise of resistance so temporary that, before 

 the electrodes could be placed in position and the bridge readings 

 adjusted, it would be over and passed. To test this point a small 

 quantity of La was added while the bridge telephone was kept to 

 the ear, but in every instance no change could be detected. It 

 would seem that the bacterial cell is normally in a state of 

 maximum impermeability and that this can not be further increased 

 by the presence of CaCL and the tri-valent salts. 



In distinction to the absence of effect of the tri-valent salts on 

 bacteria as demonstrated by the conductivity method, is the marked 

 action of these salts and especially lanthanium nitrate in changing 

 the rate of migration of these cells in an electric field. This can 

 be determined by the ultramicroscopic or still better the U tube 

 method. 



If 10 c.c. of a thick growth of B. coli in spleen broth be run 

 into a U tube under neutral Ringer's solution of the same conducti- 

 vity as the broth, then on passing an electric current through the 

 tube, the temperature being constant, an even rapid migration of 

 the bacteria takes place towards the anode. 



That practically all bacteria carry a negative charge and migrate 

 to the anode has been repeatedly confirmed by numerous workers, 

 but what is of interest here is that this charge can be materially 

 modified by various tri-valent salts, especially La. If to the 10 c.c. 

 of B. coli emulsion in spleen broth run into the U tube in the 

 above experiment 1 c.c. of a -^^ M. lanthanium nitrate solution 

 is added, it will be found that the rate of migration of the 

 bacilli under the same conditions of electric field and temperature 

 is now halved. If 2 c.c. of the solution is added, little or no migra- 

 tion takes place and the emulsion soon flocculates and is preci- 

 pitated to the bottom of the tube. 



In terms of the Helmholtz-Lamb theory of the double electric 

 layer the addition of the La has considerably altered the nature of 

 the charge on the bacterial cell wall. The conductivity method 

 however fails to show any change under this condition. This result 

 is possibly of some interest in view of Mines' theory of the polarising 

 action of certain ions on the cell membrane. It is of course possible 

 that the resistances obtained in the conductivity experiments were 

 too low to bring out the real changes taking place. 



