86 GERMICIDAL ACTIVITY OF EUCALYPTUS OILS, i., 



Table vi. —Acetic acid dissolved in Olive Oil. 



Acidity in degrees. 



Growth. No growth. 



The amount of acid which checks growth under the conditions 

 of the experiments appears to be about 165". Although this 

 was never reached in the acidified oils, one cannot but believe, 

 that a high acidity will have a certain influence in assisting the 

 germicidal power of the Eucalyptus oils 



There is some foundation for this belief, because the simple 

 neutralisation of the oils by lime or by sodium carbonate removes 

 only a certain amount of the toxicity. The residual germicidal 

 activity must be assumed to belong to the neutral oil. 



E. dives, crude, with an acidity of 81°, was toxic in two hours, 

 when in 60% dilution. Upon neutralising the acidity, the same 

 effect was obtained with the undiluted oil, that is to say, the 

 germicidal power was reduced by the neutralisation. In another 

 sample of the oil from the same species, the oil with an acidity 

 of 12° was inactive, and when the acidity was raised to 93", the 

 oil became toxic when in 50% dilution. Thus an amount of 

 acid, insufficient by itself to destroy the test-organism, caused 

 an inactive oil to become bactericidal under the conditions of 

 the experiment. 



The Iodide Reaction. 

 ft has been noted that the Eucalyptus oils contain a certain 

 amount of ozone, that is to say, they show, when tested with 

 potassium iodide and starch, the blue reaction. The potassium 

 iodide is oxidised, with the liberation of free iodine which com- 

 bines with the starch, forming the well-known blue iodide of 

 starch. The reaction is characteristic of an oxidising agent and 



