331 



The Electrical Conductivity of Bacteria, and the Rate of 



Sterilisation of Bacteria by Electric Currents. 

 By W. M. Thornton, D.Sc, D.Eng., Professor of Electrical Engineering in 

 Armstrong College, ISTewcastle-on-Tyne. 



(Communicated by Prof. C. S. Sherrington, F.E.S. Received January 12, — 

 Read March 14, 1912.) 



1. Introduction. 



Electrical currents, both alternating and direct, retard the growth of 

 bacteria in liquids through which they are passed, and under certain conditions 

 cause complete sterilisation. The cell-contents are coagulated by the heat 

 generated, or by electrolytic effects within or without the cell. There is the 

 further possibility that protoplasm may be disintegrated by the mechanical 

 action of an alternating current upon molecular charges, similar in effect to 

 that of rapid vibration, which is known to check the growth of, and even 

 to kill, bacteria. Whether the retardation of growth is regarded as the 

 result of changes in the cell or liquid, the effect is largely controlled by 

 the relation between their electrical conductivities. When these are the 

 same the current flows as if the cell were not present, otherwise the 

 current-density in the bacteria is greater or less than that in the liquid, 

 according as their conductivity is respectively the greater or less. In order, 

 therefore, to control effectively the bactericidal action of electrical currents in 

 a liquid, the relative conductivities of the liquid and the contained bacteria 

 should be known. A full summary of the industrial applications of electrical 

 currents in organic processes is contained in Lafar's ' Technisches Handbuch 

 der Mykologie.'* In most of the cases referred to the currents were weak 

 and the voltage gradients in the liquid low. The special feature of the 

 present work is that the voltage and current were taken to their highest 

 limit, under the condition that the temperature did not exceed 30° C, with 

 the testing cell cooled by immersion in running water. 



The ' Comptes Rendus ' of April, 1896, contained a short account of 

 observations by S. Lortet on the orientation of bacteria in water through which 

 an alternating current was passed. It was stated that only living bacteria 

 orientated, an observation which, if it had been confirmed, would have had 

 bearing on the relation between electricity and life. This is, however, not 

 the case, for bacteria which have been boiled for several hours orientate 



VOL. LXXXV. — B. 



* 1899, vol. 1, p. 455. 



