92 GERMICIDAL ACTIVITY OF EUCALYPTUS OILS, i. 



at 37°. When neutralised, they certainly are less active, but 

 there does not appear to be any relation between their acidity 

 and their activity. Towards B. coli communis, thev were all 

 bactericidal in from 20 to 30 minutes, and the acidity appeared 

 to have little or no influence. So far as the yellow staphylo- 

 coccus is concerned, the possibly exceptional case of the oil from 

 E. australiana (Braidwood) prevents a generalisation from the 

 comparatively few tests that were made. At the same time, 

 the results point to the toxicity being proportional to the acidity, 

 and it would appear that the relationship is shown more clearly 

 with ,1/. aureus than with B. coli communis in the cases of the 

 vapours and of the dilutions in oil. 



Summary. 



When a serum-suspension of M. aureus was absorbed in cotton 

 and placed in dilutions of the Eucalyptus oils in olive oil for two 

 hours at 20°, it was found that the bactericidal power was pro 

 portional to the acidity of the oils. 



The germicidal effect was not caused by the acidity, but was 

 assisted by it. 



The effect upon B. coli communis was of much the same nature, 

 although the action of the acid was not so clearly shown. 



The iodide reaction was no criterion as to the germicidal 

 value of the oils. 



The vapours of the oils had a decided bactericidal action. 



I have to thank Mr. H. G. Smith for the many specimens of 

 oils and for his kindness in reading the manuscript and supply- 

 ing certain useful notes upon the chemistry of the oils, most of 

 which appear as footnotes. I am also indebted to Mr. W. W. 

 L'Estrange for much kindly assistance. 



