BY R. GREIG-SMITH. 75 



aromadendrene 6 hours, and cineol (eucalyptol) 2 days.* It took 

 less time to destroy liac. coli communis, but the lethal times ran 

 in much the same order. 



The crude oils were found to be very variable in their activity, 

 and this was considered to be caused by a greater or less pro- 

 portion of free acid because the -jnore toxic oils were markedly 

 acid, and the less toxic were neutral or very faintly acid. From 

 this generalisation, and bearing in mind that acid media are 

 unfavourable to bacteria, the conclusion was come to that the 

 activity of the acid oils was due entirely to the acid. A definite 

 test, however, showed that when the crude oil of E. Smithii was 

 neutralised with soda solution, the lethal time was lengthened 

 from thirty minutes to three and a half hours. 



The refined oils were found to be much less active than the 

 crude oils. In their case, the variability in bactericidal power 

 was traced to the ozone dissolved in them. The oil of E. Smithii, 

 for example, took six and a half hours to destroy the staphylo- 

 coccus, but when a small amount of ozone was present, it took 

 less than two hours. Cineol took two days, but, when it con- 

 tained ozone, the time was reduced to three hours. Thus the 

 variation in the refined oils was traced to the ozone, and, in the 

 crude oils, to the acidity, from which we must infer that the 

 refined oils were neutral or faintly acid, and that the crude oils 

 did not contain ozone. Both the acid and the ozone were con- 

 sidered to be strongly bactericidal, in fact, when speaking of 

 aiomadendral, it was said that "as compared with the other con- 

 stituents of the oils, it is a strong bactericide, being only ex- 

 ceeded by acetic acid and ozone." 



Some forty or fifty specimens of crude and refined oils were 

 obtained from Mr. H. G. Smith, and dilutions in olive oil were 

 tested upon serum-suspensions of the yellow staphylococcus, 

 Micrococcus aureus, absorbed in cotton. The results are sum- 

 marised in Table i. 



* Ai-omadendral is a lasvo-rotatory, high-boiling, aromatic aldehyde, 

 and is the characteristic constituent of most of the "Malice" oils and 

 those belonging to the "Box " group of Kucalypts. Piperitone is a ketone, 

 and is the characteristic constituent of the oils of the huge group of 

 Eucalypts known as "Peppermints," 



