BY H. GREIG-SMITH. 



83 



When it had been shown that t lie acidity of tiie Kucalyptus 

 oils was a measure of their bactericidal power, the question 



arose, as to whether the acids were entirely responsible for the 

 toxicity, or whether the acidity was only the index of some 

 strongly bactericidal constituent. The simplest method of test- 

 ing the matter seemed to be to neutralise the acid, and then 

 compare the toxicity of the neutral oil with the original. 



Some of the oils containing an appreciable amount of acid 

 were treated with lime and filtered. They slowly became less 

 acid, and the neutralisation was accelerated by the addition of 

 a drop of water (0'03 c.c. to lOc.c. of oil). The treated oils were 

 cither neutral or very faintly acid. Four oils were tested against 

 the staphylococcus. 



Table iii. — M. aureus. 



Tt is clear that the neutralisation of the oils resulted in a 

 diminution of the bactericidal activity, but it is also clear that 

 the acid or the acidity is not the only thing which contributes 

 towards the disinfecting properties. Were it otherwise, the 

 lime-treated oils would have been inert towards the staphylo- 

 coccus. 



The crude oils of E. cinerea and of E. dives were treated with 

 dry sodium carbonate until the acidity was, in each case, reduced 

 to 1". They had the same disinfecting power as the lime-treated 

 oils. 



If the alkali does nothing but remove the acid from the oils, 

 it is reasonable to suppose that the addition of acid will render 



