31 4 GERMICIDAL ACTIVITY OF EUCALYPTUS OILS, ii., 



were just germicidal to B. colt communis at 20° in 15 minutes. 

 It was decided that the dilutions should be tested within an 

 hour after their preparation. 



Some further preliminary work was done to determine which 

 were the best strengths of some oils to employ, and in how far 

 we might expect to get consistent results. The lethal dilutions 

 vary more or less in each experiment, and it is sometimes difficult 

 to determine what is the real efficiency of the oil under examina- 

 tion. At one time, it was considered that the lowest of all the 

 dilutions germicidal with a certain exposure would indicate the 

 efficiency, but the curve of these dilutions was often too irregular,* 

 and did not bear out the idea given by the curves of the indi- 

 vidual tests. Consequently the germicidal dilutions of each test 

 were plotted, and the probable dilution curve drawn through at 

 least three exposures. From this curve the dilutions were 

 corrected for the other exposures. The average lethal dilution 

 for each exposure was calculated from the corrected lethal dilu- 

 tions, and the curve of these numbers was taken as passing 

 through the probable effective dilution. 



Cineol and Phenol. — The cineol was obtained from Mr. G. I. 

 Hudson, and had been obtained by freezing the rectified oils of 

 E. polybractea or of E. sideroxylon. The phenol was obtained 

 as crystals of phenol absolute which in the preliminary experi- 

 ment solidified at 38-5 c ,f and in the others at 40°. 



* Lee and Gilbert (Abs. Journ. Soc Chem. Ind., 1918, 439 A) lind that 

 disinfection is an orderly time process analogous to a chemical reaction. 

 A definite relationship exists between the velocity of the reaction and the 

 concentration of the disinfectant. Chick (Journ. Hyg,, 1910, "237) found 

 the same analogy and found that the velocity of disinfection at an}' 

 moment was proportional to the number of surviving bacteria. Disin- 

 fection proceeded in accordance with ;i logarithmic law of the first order, 

 i.e., like a chemical reaction. 



t Noted in Part i. as being crystalline at 28°. 



