1913.] Action of Electric Discharge upon B. coli communis. 351 



lower. By means of mercury, connection was made between this wire and 

 the cable from the discharge set, and so the platinum point discharged down- 

 wards towards the Petri dish and metal plate. 



1. Discharge in Air. — A repetition of the original experiments seemed first 

 desirable, and accordingly cultures were exposed as described above. In 

 30 minutes the plates were almost cleared, subsequent incubation producing 

 only a few colonies around the edge. In one case one side of the bell-jar was 

 inadvertently wet, and instead of a continuous discharge, intermittent 

 sparking down that side to the metal plate took place. The Petri dish after- 

 wards showed sterilisation over about one-third of its area, and that on one side 

 only. Exposure of 40 minutes or more always resulted in complete sterilisa- 

 tion of heavily infected dishes. 



Since, then, the discharge in air was definitely deleterious to the 

 organisms, and as it did not seem likely that ionisation effects could be the 

 cause, the role played by the products of discharge needed investigation. 

 These would be chiefly ozone and nitrous and nitric acids, which would be 

 carried well on to the infected surface by the electric wind, thus providing 

 every facility for their absorption. To test the action of these products, 

 apart from the direct action of the discharge, a Petri dish of distilled water 

 was exposed to the discharge under conditions identical to those obtaining 

 in the original experiments with infected agar. The liquid was then removed 

 and heavily infected, plate subcultures being made from it after an hour. 

 In no case was there any development in these subcultures upon incubation, 

 even if the water, previous to infection, were exposed to the discharge for 

 only 20 minutes, thus confirming the idea that the products of discharge 

 alone proved fatal. 



Particular investigation of these products was now carried out by means 

 of qualitative and quantitative tests of the distilled water after exposure. 

 Abundance of NO3 radical was present, as shown by the diphenylamine test, 

 whilst addition of starch and potassium iodide solutions produced a deep 

 blue coloration, due to nitrite or ozone, or both, also the liquid gave 

 a distinctly acid reaction, the acidity being measured in a few cases -by 

 titration : — 



No. of 



Acidity as grammes of nitric acid 

 per c.c. per hour. 



experiment. 



1 



2 

 3 

 4 

 5 

 6 

 -7 



0-00034 

 0-00072 

 0-00070 

 000053 

 0-00067 

 0-00060 

 0-00054 



2 c 2 



