80 GERMICIDAL ACTIVITY OF EUCALYPTUS OILS, i., 



The oils as a whole were weak compared with phenol, although 

 the thickened oil of E. linearis was very nearly as good. 



While a 10% solution of phenol in oil is used as a disinfectant, 

 the statement occurs in Hale White's Materia Medica that "The 

 solution in oil has no antiseptic properties." The staphylococcus 

 was destroyed in two hours in a 6°/ solution in oil. 



The irregularity of the disinfecting action of the oils leads to 

 the helief that any power which they possess is not occasioned 

 by any of the chief constituents. The oils which have most 

 cineol or most phellandrene or most pineneor most aromadendral 

 are no better than others with less. We must therefore look to 

 the minor constituents which may be occasionally absent. The 

 oils which were most active were pronouncedly acid to litmus 

 paper, as Cuthbert Hall also found, and this led to the deter- 

 mination of the acidity of such samples as had not been com- 

 pletely used up. 



The method consisted in taking 20 c.c. of methylated spirit, 

 adding a few drops of phenolphthalein and running in N/100 

 sodium hydrate until a faint pink colour was produced. One c.c. 

 of Eucalyptus oil was added, and the solution titrated with 

 N/100 sodium hydrate. The numbers in the Table represent c.c. 

 of normal acid per litre of oil, i.e., the degrees of acidity. 



The acidity of the oils of each group is as variable as the 

 toxicity, and while the most acid of the oils are also the most 

 toxic, no definite relation between the acidity and the bactericidal 

 power could be detected until the acidities were plutted against 

 the toxicities, and, but for the comparatively large number of 

 oils examined, a relationship would not even then have been 

 capable of demonstration. The curve is of the nature of a broad 

 band within which most of the oils fall. Some are exceptional, 

 such as the oil of E. citriodora, which is itself an exceptional oil. 

 The case of E. australiana, crude, 2nd hour, cannot at present 

 be explained. 



It was shown by Cuthbert Hall, that the undiluted oils were 

 more active towards the colon bacillus, li. coli communis, than 

 towards the staphylococcus, M . aureus. Tests were made to 

 show that this would also hold for dilutions in oil. Several of 



