102 REPORTS ON THE STATE OF SCIENCE.— 1915. 



veins are farther apart than are tRose of the first group, more room for 

 oil-glands is available, so that, as a rule, a greater yield of oil is obtained 

 from the members of the second group than from those of the first. 

 Although only a comparatively few species of the second group are 

 utilised commercially on account of their oil, for various reasons — such 

 as yield, quantity available, accessibility, &c. — many other species 

 besides those woi'ked contain oils equal in value to the most pronounced 

 cineol-bearing species made use of. It must be apparent that even a 

 slight decrease in yield would be sufficient to exclude a species from 

 commercial exploitation, although the constituents might be identical 

 with those of the more prolific-yielding varieties. It is a fact woiiihy of 

 notice that the yield of oil from each particular species, wherever found, 

 is comparatively constant, although ranging from about 4i per cent, 

 to practically nothing. This naturally is a factor of some commeixial 

 importance, as well as of scientific interest as proof of the comparative 

 constancy in the quantity of oil formed. 



The third group contains the species which yield oils in which the 

 terpene phellandrene is an important constituent. This group now 

 supplies most of the oil used so largely in the separation of metallic 

 sulphides by the flotation process. 



Although the phellandrene-bearing oils are not at present in favour 

 for pharmaceutical purposes, some species which contain much 

 phellandrene are also rich in cineol. This is the case particularly with 

 the oils of E. linearis and E. Risdoni (7), species allied to the ' Pepper- 

 mint ' group. The question of the therapeutic values of the several 

 types of Eucalyptus oils is still an open one ; it does not follow that the 

 cineol-pinene oils are necessarily of more value in this direction than 

 are the cineol-phellandrene oils (8), particularly as the other con- 

 stituents differ considerably in the two classes and it is known that the 

 first Eucalyptus oil distilled by Dr. White in 1788 (9), of the medicinal 

 value of which he speaks so highly, was obtained from the leaves of a 

 member of the cineol-phellandrene gi'oup in which the venation 

 corresponds to that of No. 3 in the photograph. 



Such Eucalyptus oils as those derived from E. polyhracfea and from 

 E. cneorifolia contain a phenol different from that found in the oils of 

 the ' Peppermint ' group (10), together with an aldehyde of high boiling- 

 point (either cumin aldehyde or aromadendral*) and a minimum pro- 

 portion of esters. In the richer cineol-phellandrene oils, the ester 

 butylic-butyrate occurs in some quantity (11) and the phenol (Tasmanol) 

 they contain is not identical with that found in the oils of the other 

 group, wliilst the ketone (piperitone) takes the place of the aldehyde 

 aromadendral and a larger proportion of ester is usually present. Euca- 

 lyptus oils so diverse in chemical constituents cannot have equal thera- 

 peutic value. 



The question of the pur"ification of the crude oils required for medi- 



* Although Messrs. Schimmel and Co. assert that cumin aldehyde is the aldehyde 

 of this class occurring in Eucalyptus oil, the high laevorotation shown by this aldehyde 

 extracted from the oils of some species is alone sufficient to show that Aromadendral 

 and cumin aldehyde cannot be identical substances. As the latter aldehyde does not 

 contain an asymmetric carbon atom, it does not show optical activity. 



