350 Messrs. J. H. Priestley and E. C. Knight. Toxic [Feb. 13, 



infected plate to earth, but through the air between two metal points above 

 the culture, and in this case, where the current through the bacteria was a. 

 minimum, " the (sterilising) action was much stronger than in the first 

 arrangement," in which one point discharged directly on to the culture. 

 The investigation, of which an account is presented below, was therefore 

 commenced with the intention of attempting to ascertain whether current 

 densities of the order used by Thornton, obtained from a high-tension source, 

 could still prove toxic when the influence of all toxic substances produced by 

 the chemical action of the discharge had been eliminated. 



Experimental. 



Bacillus coli communis, being found by Thornton to be one of the least 

 sensitive organisms he employed, was chosen for the experiment. The high- 

 tension discharge was obtained from the ordinary 100-volt direct-current 

 circuit by leading this current after interruption by a mercury break through 

 the primary of a large induction coil. The alternating discharge from the 

 secondary was then obtained as a continuous positive and negative charge at 

 either side of a spark gap by leading the alternating discharge through five 

 Lodge valves arranged in series ; these valves act as rectifiers, only permitting 

 the current to pass in one direction owing to the structure of the electrodes. 

 This apparatus, which was purchased from a special research grant obtained 

 from the Board of Agriculture and Fisheries, was available during the 

 intervals when not required for other experiments in progress in the 

 Department. By this method it was then easy to maintain as long as 

 required a difference of potential of some 70,000 volts between the poles of the 

 spark gap, one pole was then connected to earth and the other to the 

 discharging point. The current passing from the discharge point was 

 measured by placing a plate of tinfoil of definite area beneath the discharge 

 point, and connecting this by a carefully insulated wire, shielded by an outer 

 metal tube connected to earth, to a Paul micro-ammeter, which was 

 carefully screened by an earthed metal cover. 



In this way it was ascertained that the current density of the discharge to 

 which the bacteria were subjected was of the order of from 10~ 6 to 10 -5 

 amperes per square centimetre. 



The method of treatment of the bacteria was almost identical with that 

 employed by Thornton, viz., a Petri dish containing a sterilised agar medium 

 infected with the bacillus was supported on a small metal tripod, which itself 

 stood on an earth-connected metal plate. Dish and tripod were then covered 

 with a small bell -jar fitted with a rubber stopper, through which passed a 

 glass tube, open at the upper end, and with a platinum wire sealed into the 



