1912.] The Electrical Conductivity of Bacteria. 343 



in an atom is of the order* 33 x 10 14 a second. An electric charge rotating 

 in an orbit in an alternating field of force is accelerated when the frequency 

 of the latter agrees with, or is an odd sub-multiple of, the frequency of 

 rotation. Thus a rotating electric charge in an atom would be eventually 

 split off by resonance when the alternating field had a frequency of 11 x 10 14 , 

 corresponding to the third sub-multiple, or 6"6 x 10 14 , the fifth ; this is the 

 lower limit of the violet part of the spectrum, at which the bactericidal 

 effect ceases. It is now suggested that Ward's lower maximum of 7 x 10 14 

 may be the result of resonance with the fifth sub-multiple. The occurrence 

 of another maximum at the higher frequency — which should be more clearly 

 marked — would definitely decide this and the nature of the whole effect. 



8. Summary and Conclusion. 

 The electrical conductivity of bacteria can be measured by observing their 

 orientation when an electric current is passed through a liquid containing 

 them. The values found range from 35 to 350 ohms per centimetre cube, 

 and depend upon the nature and state of the culture medium. The results of 

 sub-culturing are found to be that the conductivity of the bacteria increases 

 at each step, reaching a steady value at about the fourth sub-culture on 

 agar. Water containing added B. coli communis can be completely sterilised 

 by direct currents in several hours at 03 ampere per square centimetre. 

 Alternating currents sterilise water nearly, if not quite, as well as direct 

 currents having the same current density. In order to obtain well-marked 

 and constant results, it is necessary to use current densities of the order of 

 0-3 ampere per square centimetre, and to have a form of cell with a thin film 

 of liquid which can be readily cooled. Milk is curdled by direct current at 

 the positive pole and thinned at the negative pole. It can be sterilised, 

 without " skin " forming, by the passage of alternating current through it, 

 this being largely thermal. The cause of the bactericidal action of light is 

 suggested to be syntony between it and the frequency of electronic movement 

 in the protoplasm. 



For the rapid sterilisation of liquids in bulk, such as sewage or potable 

 water, the use of an ozone spray is to be preferred to direct electrical action. 

 When, however, it is required to control bacterial growth in liquids over long- 

 periods without change of temperature it can be done by the passage of 

 alternating electric current, or of direct current where electrolytic effects are 

 not important. In either case, in order to obtain marked bactericidal effect it 



* See W. Sutherland, ' Phil. Mag.,' Sept., 1901, Series 6, vol. 2, p. 273, and J. H. Jeans, 

 ibid., Nov., 1910, vol. 1, p. 422. 



