1906.] 



Action on Bacteria of Electrical Discharges. 



67 



Having thus obtained definite evidence of the germicidal effect of the 

 electrical discharge under the given experimental conditions, we had next 

 to consider the respective influence of several possible factors in the . 

 production of the results which we had observed. 



These possible factors, as they presented themselves to us, may be 

 enumerated as follows : — 



(1) What may be termed the specific physical action of the current, or of 

 its discharge, on the bacteria in the emulsion ; 



(2) The action of light rays resulting from the discharge ; 



(3) The action of heat rays resulting from the discharge ; and 



(4) The action of certain chemical substances which are formed in the air 

 as the result of the discharge, and are then taken up in solution by the water 

 in which the bacteria are suspended. 



III. — As to the Germicidal Action, if any, of the Electrical Current, 



or of its Discharge. 



We met with considerable difficulties in our endeavour to determine what 

 part, if any, in the production of the germicidal effects which had been 

 obtained in the previously mentioned experiments could be attributed to the 

 action on the bacteria of the electric current itself, as apart from secondary 

 factors depending upon the discharge — the action of heat and light rays and 

 of chemical substances formed in the neighbourhood of the emulsion and taken 

 up by it. For, whilst it was easy to eliminate experimentally any injurious 

 action which might be exerted directly by the heat rays and to test by itself 

 the possible action of the light rays, we found the greatest difficulty in 

 devising means whereby the bacteria could be subjected to the action of the 

 electric current without at the same time introducing the possibility of 

 fallacy arising from chemical decomposition with the formation of germicidal 

 substances. 



We first tested the action of the oscillatory current when passed directly 

 through the bacterial emulsion without interruption by discharge above the 

 surface. In these experiments a flat platinum disc, which was immersed just 

 below the surface of the emulsion, was substituted for the platinum brush. In 

 some experiments the emulsion was contained in a test-tube, with arrange- 

 ment for conducting the current away as described under (a) above, but in the 

 majority of the experiments there was the addition of a layer of mercury in 

 the tube under the emulsion and covering the projecting upper end of the 

 wire which was sealed through the bottom of the tube. 



The latter modification appeared to be the more suitable for testing the full 

 action of the current on the bacterial emulsion, and we found that when 



F 2 



