12 Is the Eucalyptus a Fever-destroying Tree t 



Australian, with the exception of its existing in the 

 neighbouring island of Tasmania. 



If, therefore, we possess in a very high degree an immunity 

 from fever maladies, can it be traced in any way to this 

 genus of the myrtaceous order ? 



Baron von Mueller describes over 130 species of this 

 genus as existing in Australia. To an ordinary observer 

 many species are extremely difficult of discrimination ; some 

 form together forests of great extent, both on high and low 

 table land, others dense desert scrub, and some are so dis- 

 tributed over areas as to give a park-like appearance. 



' For the purpose in hand, I intend to refer — first, in 

 general terms to the physical and chemical properties of the 

 the eucalypti as a whole, and specially to those species 

 which may properly be said to be the representatives of this 

 class of vegetation. 



The physical properties of all eucalypts are — that they 

 cast their bark ; that the leaves are evergreen and have 

 translucent cells, in some species visible to the naked eye ; 

 that the petiole is half twisted, so that the plane of the leaf 

 is parallel to the axis of the tree, thereby allowing free 

 action to the light and heat of the sun on both sides ; also 

 the roots are dispersive and drain water largely from the 

 soil. 



The chemical contents of a eucalyptus tree are neither 

 poisonous nor virulent. Besides possessing those invariably 

 met with as general constituents of ligneous vegetation, 

 there is a tannate gum resin, a volatile acid, and a volatile 

 oil peculiarly of eucalyptic origin. The first two are to be 

 found in most parts of the tree, but the latter only in the 

 leaves. Now it is in these three bodies I think that we 

 have the key to the question before us, and I conjecture that 

 apart from these no trace can be found of the power of the 

 eucalyptus to oxygenate the air beyond that which is 

 possessed by other kinds of vegetation. If the principles of 

 these bodies are retained in the tree until set free by the art 

 of man, then further investigation is useless ; but if one or 

 more are given up freely by the natural forces of the tree, or 

 by the aid of light, heat, or electricity as existing in the 

 atmosphere, or by some or all of these forces in combination, 

 then there is every reason to pursue our inquiries. 



The question then arises, have we any proof that these 

 volatile bodies are set free in the air by the forces of the 

 plant in union with atmospheric agencies ? if we have, 



