70 Mr. A. G. E. Foulerton and Dr. A. M. Kellas. [Mar. 30, 



V. — The Influence of Heat Rays Resulting from the Electrical 



Discharge. 



In all our experiments, unless the contrary is expressly stated, means were 

 adopted to prevent the temperature of the bacterial emulsion rising to a point 

 at which the direct germicidal action of heat would come into play. The 

 highest temperature reached, when limiting precautions were adopted, was 

 about 32° C, which was recorded in some experiments which have already 

 been referred to, when the terminal platinum disc was actually immersed in 

 the emulsion ; in experiments in which the discharge was sprayed from a 

 platinum brush suspended above the surface of the fluid the maximum 

 temperature reached was usually several degrees below this point. 



In order to satisfy ourselves that we were experimenting under safe 

 temperature conditions we tested the resistance to heat of some of the cultures 

 of bacteria which were used in our experiments. "We ascertained that the 

 culture of B. prodigiosus survived a temperature of 45° C. with an exposure of 

 60 minutes, but was destroyed by an exposure to 50° C. for 30 minutes ; 

 B. pyocyaneus survived an exposure to a temperature of 50° C. for 45 minutes, 

 but was killed at the same temperature with an exposure of 60 minutes ; the 

 cultures of B. coli communis and Micrococcus pyogenes aureus were both 

 unaffected by 60 minutes' exposure at a temperature of 50° C. 



The results of these tests with regard to temperature and duration of 

 exposure are tabulated below : — 





40° C. 



45° C. 



50° C. 





60 mins. 



39 mins. 



45 mins. 



60 mins. 



30 mins. 



45 mins. 



60 mins. 





+ 



+ 



+ 



+ 

















+ 



+ 



+ 



+ 



+ 



+ 







B. coli communis ... 



+ 



+ 



+ 



+ 



+ 



+ 



+ 



M. pyogenes aureus 



+ 



+ 



.+ 



+ 



+ 



+ 



+ 



But, whilst we were able to eliminate the direct germicidal effect of heat 

 in considering the results of our experiments, it was clear tnat under certain 

 conditions the germicidal action of the nitrous and nitric compounds and 

 the hydrogen peroxide which were formed as the result of the discharge, and 

 taken into solution in the bacterial emulsion, would be considerably enhanced 

 by a rise of temperature which would not by itself have any direct action on 

 the bacteria ; and it is to the varying degree of germicidal energy of these 

 oxidising substances at temperatures between about 15° C. and 35° C. that 



