1906.] 



Action on Bacteria of Electrical Discharges. 



85 



carried out. In one series of experiments the gas, probably mixed with 

 argon, etc., was obtained from common air by passing it over heated copper ; 

 in the other series the gas was prepared by heating a mixture of strong 

 solutions of potassium nitrite and ammonium chloride, the gas being sub- 

 sequently purified by passage through strong sulphuric acid. And in every 

 experiment carried out under these conditions the bacteria were destroyed 

 after exposure to the discharge for 30 minutes, the current being of amplitude 

 similar to that used for the experiments in carbon monoxide. 



After exposure to the discharge the emulsions were found to be strongly 

 acid in reaction and to contain quantities of nitrous and nitric acids 

 which had probably been formed by the action of the discharge on nitrogen 

 in the presence of water vapour. 



IX. — Conclusions. 



The results of our experiments may be summarised as follows : — 



1. When bacteria suspended in water are exposed in an atmosphere of 

 common air to the action of electrical discharges of high potential and rapid 

 frequency, such as are used in medicine for purposes of treatment, sufficient 

 quantities of nitrous and nitric acids are taken up in solution within as short 

 a period as 15 minutes to sterilise the emulsion, and the germicidal action of 

 these compounds in their nascent condition is favoured under ordinary 

 circumstances (a) by the heating of the medium in which they are suspended 

 by heat rays resulting from the discharge, and (b) by the concomitant 

 formation of substances such as ozone and peroxide of hydrogen, which, readily 

 yielding up a portion of their oxygen, accelerate the interaction of nitrous and 

 nitric acids and their consequent germicidal activity. 



2. When the bacteria are exposed to the action of the discharge in an 

 atmosphere of pure hydrogen, under similar conditions, there is a decom- 

 position of the water vapour necessarily present in the atmosphere of the tube 

 with the formation of peroxide of hydrogen in quantities such as are sufficient 

 after a time to exercise distinct germicidal action in the case of some 

 bacteria. 



3. When exposure to the discharge occurs in atmospheres of pure carbon 

 dioxide or carbon monoxide there may again be sufficient peroxide of hydrogen 

 formed to exercise germicidal action. • 



4. When exposure to the discharge occurs in an atmosphere of pure nitrogen, 

 sterilisation may be effected by the action of nitrous and nitric acids. 



5. The action on bacteria of the light rays resulting from the discharge is 

 negligible under the time conditions of our experiments. 



