BY R. GREIG-SMITH. 89 



The second column, with the lower numbers, was obtained 48 

 days later, and although variations were made in the strength of 

 starch and of iodide, the high numbers of the earlier tests could 

 not be obtained. It must be concluded that the activity of the 

 oils had increased. Hut even with the new numbers, no relation 

 between them and the toxicity of the oil could be traced. 



Some of the oils showed a marked decrease in the reaction 

 time, and in order to see if the toxicity had increased in the 

 interval, one of them was tested. This was the crude oil of E. 

 polybractea, which had decreased from 80 to 30 seconds. It was 

 found to be inactive to the staphylococcus when tested in oil 

 just as it was at an earlier date. 



When the iodide numbers are plotted against the disinfecting 

 powers of the Eucalyptus oils as determined in dilutions of olive 

 oil, no close relation can be noted between the two. The Euca- 

 lyptus oils may be divided into two groups, one taking less than 

 60 seconds to develop the iodide reaction, and this contains two- 

 thirds of all the oils. The other, which took more than 60 

 seconds, contains thirteen oils, of which seven are inactive to 

 the staphylococcus, and two are slightly active. The two most 

 active oils towards the staphylococcus are certainly among those 

 which show the most vigorous iodide reaction, but they are not 

 sufficiently differentiated from the others to enable one to say 

 that the iodide test is any indication of the disinfecting pro- 

 perties of the oils. 



There does not appear to be any relation between the acidity 

 of the oils and the iodide test, as a glance at the acidity column 

 will show. When they are plotted against the acidity, no rela- 

 tion of any kind can be deduced, a fact which could not have 

 been proved in the absence of a rigid test for the reaction. By 

 simply testing with starch-iodide paper, one obtains strong reac- 

 tions with the oils which are strongly acid, and generally a feeble 

 reaction with those that are weakly acid. It does now, however, 

 take long to make one realise that the paper test is very unsatis. 

 factory. 



When the oils are neutralised, the colour takes longer to 

 develop. This was seen in a few oils that had been neutralised 

 about the time that the iodide tests were made. 



