1906.] Action on Bacteria of Electrical Discharges. 69 



emulsion so as to exclude atmospheric air without causing the constant 

 splashing of the fluid which had occurred in the last experiment. After 

 60 minutes' exposure, as in the other experiments, to the action of the current, 

 the bacteria were found to be unaffected, the emulsion yielding equally free 

 growth before and after treatment. 



A large number of experiments in which the discharge was sprayed on to 

 the emulsion through an atmosphere of some pure gas were also carried out, 

 with appropriate arrangements for the conduction of the current through the 

 emulsion. These experiments will be referred to in detail after the influence 

 of the nitrous compounds which are formed when the discharge occurs in 

 common air have been considered, and meanwhile it may be said that the 

 result of such further experiments was in confirmation of the conclusion at 

 which we had already arrived, that is to say, it appeared as if the discharge 

 and subsequent passage of the current through the emulsion had, of itself, 

 no injurious influence on the bacteria under the time conditions of our 

 experiments. 



IV. — The Possible Action of Light Kays Eesulting from the 

 Electrical Discharge. 



Experiments were carried out in order to ascertain whether the light rays 

 resulting from the electrical discharge might have had any definite influence 

 in the production of the germicidal effects which were observed in our 

 previous experiments. And in the result it may be said that we were able 

 to exclude any such factor as operative under the time conditions of our 

 experiments. 



The following experiment bearing on this point may be mentioned. Tubes 

 of melted nutrient agar were cooled down to 41° C, and inoculated severally 

 from cultures of the bacteria with which we had previously experimented ; the 

 medium was then poured out into Petri dishes, and allowed to set. The 

 covers of the Petri dishes were thickly coated with black varnish, except for 

 a small circular area which was left unprotected. The Petri dishes were then 

 closely exposed for 60 minutes to the action of light rays from discharges 

 such as those which had been employed in the other experiments, the dishes 

 being so arranged that the maximum effect of the rays would be exercised on 

 the area of inoculated agar immediately underlying the unprotected part of 

 the cover. After exposure the dishes were incubated at temperatures suitable 

 to growth of the respective bacteria, and in every case good growth was 

 obtained over the whole surface of the medium, there being no indication of 

 inhibition of growth in those portions which had been specially exposed to the 

 action of the light rays.- 



