342 GERMICIDAL ACTIVITY OF EUCALYPTUS OILS, ii., 



the masks were slightly damped, they could he depended upon as 

 being sterile after a night's exposure to the vapour. 



Conclusions. 



The germicidal value of the Eucalyptus oils varies with the 

 kind of oil and also with the particular specimen. While Baker 

 and Smith have shown that the major chemical constituents are 

 wonderfully uniform, so much so that from a consideration of 

 the oil they are able to recognise the affinities of species of the 

 Eucalypts, the minor constituents may vary considerably, and 

 these seem to have a pronounced influence upon the germicidal 

 power. To realise this, one has only to consider the variations 

 in the bactericidal power of the oil of E. cinerea. The rectified 

 oils were germicidal in an hour with dilutions of 1 : 900, 1 : 500, 

 and 1 : 340 according to the individual specimen. These were 

 not all of the same age. The most potent was the oldest, and it 

 was the most acid. From this we infer that the degree of acidity 

 is to a certain extent an index of the age and, to some extent, 

 an index of the disinfecting power. At any rate, with an oil 

 having a high saponification number such as that of E. citierea, 

 it is to be expected that, as time goes on, the oil becomes oxi- 

 dised and the constituents decomposed, yielding oxidation pro- 

 ducts such as aldehydes and acids. The aldehydes seem to 

 possess high germicidal values, one of them, aromadendral for 

 example, is a very powerful disinfectant. 



But the acidity is only a rough index, for the three specimens 

 had their acidities in the ratio, 95 : 18 : 26, from which we see 

 that, when the acidity is low, there is no indication given as to 

 the disinfecting action. Possibly the original acidity of the oil 

 should be taken into account. 



It is customary in dealing with the germicidal activities of 

 disinfectants to refer to them in terms of a standard disinfectant 

 such as phenol, and accordingly the phenol-coefficients of these 

 oils that have been tested, were calculated and appear in the 

 following Table in which the rectified oils have been grouped in 

 the approximate order of their efficiency. The same applies to 

 the crude oils and to the oil constituents. 



