The Influence of Ionised Air on Bacteria. 

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

 Armstrong College, Newcastle-upon-Tyne. 



(Communicated by Sir Oliver Lodge, F.R.S. Eeceived June 20, 1911.) 

 [Plates 7—12.] 



1. On exposing surface films of bacteria upon agar to the electric wind 

 from charged needle points, with subsequent incubation, it is found that the 

 wind from negatively charged points has more bactericidal effect than that 

 from points positively charged. 



In a recent paper* it was suggested that there should be this difference 

 in consequence of the positive charge found to be associated with fresh 

 vegetable cells, and further, that negatively charged air might prove useful 

 in the treatment of tuberculous disease of the lung by retarding the growth 

 of the bacteria. Before attempting direct trial of the latter point it was 

 necessary to show that negative electric charge does inhibit bacterial growth 

 in general under laboratory conditions of culture, and the present work was 

 undertaken for this purpose. 



2. The most suitable method of ionising air on a large scale either 

 positively or negatively is by unidirectional point discharge at high potential. 

 The voltage gradient should be such that no sparks pass, but that a faint 

 blue glow is seen at each point, indicating the space in which most of the 

 ionisation is taking place. The glow at the negative point is larger than 

 that at the positive, and begins at a lower pressure. In either case ions of 

 the same sign as that of the point are repelled, causing the electric wind. 

 This was, with the pressures used in the present case, perceptible on the palm 

 of the hand at a distance of about 10 cm. 



The discharge can take place into free air, and the circuital flow is then 

 completed either by diffusion of the ions to oppositely charged surfaces 

 which are under the influence of the electrostatic machine used, or by 

 recombination in the air. The latter is known to occur very rapidly in 

 certain cases. In order, therefore, to expose the germs to a continuous and 

 even wind for long periods, it was necessary to keep the machine running, 

 and at the same speed, for the whole time of exposure. 



3. The first arrangement of discharging points, that used in obtaining the 

 results in figs. 7 to 10 (Plates 7 and 8), is shown in fig. 1. Two bell-jars, 



* " On the Opposite Electrification produced by Animal and Vegetable Life," ' Eoy. 

 Soc. Proc.,' B, 1910, vol. 82. 



