The constituents detected in Eucalyptus oils now number about forty. Many of them, however, are identical with similar substances occurring in other essential oils, and are thus obtainable from other sources, although, with several of them, much less advantageously.

The following list includes practically all the constituents so far determined, many of which have been brought to light during these researches. They are found in the oils of the different Eucalypts in varying quantity, occurring more abundantly in some species than in others. It is now known, however, from which investigated species the desired constituents can be most readily obtained, and in the greatest quantity, particularly as those characteristic of specific oils are comparatively constant.

Although the main constituents in the several oils have been determined, yet, in many cases, it is difficult to say with certainty that all have been detected, and it is possible that some do occur in small amounts in the oils of species in which they have not, so far, been found.

During the last twenty-five years, however, much work has been done upon the products of the Eucalypts, and our knowledge concerning the constitution of their oils is now such that it has been possible to evolve some order with the several members of this extensive genus.