344 GERMICIDAL ACTIVITY OF EUCALYPTUS OILS, ii., 



Certain text-books give the coefficient of Llie oil oi' E. globulus 

 as about 4. Martindale* emulsified the oils of E. globulus and oL' 

 E. amygdalina in a solution of soap, and, taking the average of 

 the coefficients at two and at thirty minutes, found them to be 

 ;> 55 and 4<!5 respectively. As soap, however, is itself a disinfec- 

 tant, it is probable that these numbers are high. Cavel*, working 

 with the bacteria from a septic cyst, determined the maximum doses 

 of essential oils, dissolved in acetone or alcohol, necessary to pro- 

 hibit growth in infected media. Essence of Eucalyptus was lethal 

 in 2-75 parts per 1,000, and phenol in 5-6 parts. This gives a 

 phenol-coefficient of about 2. 



According to Baker and Smith, E. globulus belongs to the same 

 group of Eucalypts as E. entered and E, Smithii, the rectified oils 

 of which have high coefficients. It is curious that, while the rectified 

 oils of these trees are among the most efficient, the crude oils arc 

 among the least, judging by the coefficients at the end of the first 

 hour. Even at the end of 30 minutes, which is, 1 think, a fair 

 period for purposes of comparison, the same holds. 



We arc led to believe that the rectification of an oil, such as 

 those that were tested, gives us a product containing a higher 

 proportion of cineol. It is, therefore, strange to find that one of 

 the samples of E. cinerea and one of E. polybracteci have a lower 

 coefficient than cineol. In the case of E. polybractea, rectification 

 appears to have removed the high boiling aromadendral from the 

 lower boiling cineol and pinene; the sample gave the coefficient of 

 a mixture of 50% of cineol and 50% of pinene. 



Cuthbert Hall, from his observations upon the behaviour of the 

 oils towards iodide of starch paper, considered that the ozone 

 content of the oils was an index of their germicidal power. I 

 showed that this did not hold for the Eucalyptus oils when they 

 were dissolved in olive oil. With regard to the iodide of starch 

 reaction and the activity of the oils when emulsified in water, there 

 does appear to be some relation when individual oils are con- 

 sidered. The three specimens of rectified oil of E. cinerea, and 



* Abstr. Journ. Soc. Chem. Lid., 1910, 1470. 

 I Oompt. Pvend., (20), 21/5/18, p.827. 



