74 Mr. A. G. R Foulerton and Dr. A. M. Kellas. [Mar. 30, 



air is sufficient when these products are present in such quantity that the 

 acidity of the fluid is equivalent to - 07 per cent, of nitric acid to destroy 

 a non-sporing bacillus, such as B. typhosus, after it has been exposed to the 

 action of the solution for 15 minutes. And we take it that in the cases 

 in which a bacterial emulsion after sterilisation by exposure to the discharge 

 is found to present an acidity in excess of 07 per cent, the sterilisation may 

 be fairly attributed mainly to these chemical products, in the absence of 

 any indication that other actively germicidal influences have been at work. 



We may, however, point out that the experiments of Table III are not 

 absolutely comparable with those of Table I, since in the latter set of 

 experiments the quantity of germicidal substances in solution gradually 

 increased up to the end of the exposure, when the estimation gives only the 

 total acidity at the end of the experiment, whereas in the experiments 

 of Table III the bacteria were immersed in a solution of the maximum acidity 

 for the full period of the experiment. 



On the other hand, the germicidal action of such substances as are present 

 is probably exercised more energetically under the conditions prevailing 

 in the experiments of Table I, when the bacteria are immersed in the fluid 

 during the actual formation and solution of the nitrous and nitric bodies 

 and are so exposed to the action of these substances whilst still in a nascent 

 condition, than it is under the conditions prevailing in the experiments 

 of Table III, when the bacteria are immersed in a fluid in which the 

 chemical changes are for the most part finished, except for the comparatively 

 slow oxidation of nitrous to nitric acid. Moreover, in the experiments 

 of Table I there would be a continuous molecular disturbance of the fluid 

 which would probably assist the action of chemical germicides. 



Although other substances are formed in the air, and doubtless taken up 

 in solution by the water, in addition to the nitrous and nitric compounds, 

 it was to these latter that we attributed chiefly the germicidal action, and 

 it was these that we considered as the causes of the acidity of the solution. 

 We next prepared artificial mixtures of- nitrous and nitric acid with a total 

 acidity approximating to that obtained in some of our experiments, and 

 then tested the germicidal action of the solutions. Our solutions were 

 prepared by dissolving potassium nitrite in water and adding certain 

 quantities of nitric acid. 



The actual composition of the several solutions was as follows : — 



