24 
Old World, however, is equally varied in its treasures, 
whether we look to such as require a cold or temperate 
climate with moisture, as almost every part of Europe ; or 
such as are only elaborated in the bright skies and sunny 
climes of the Mediterranean or Persian regions. Others 
again refuse to flourish, or to secrete their highly stimulant 
and aromatic properties, except in the elevated temperature 
and uniform moisture of tropical countries. These might 
have been obtained from a very broad belt, but Africa was 
as inaccessible, and the transit of its produce as difficult in 
ancient as in modern times. Asia, therefore, especially 
India and its islands, must always have contributed a 
great proportion of those articles which we now know can 
only be produced in tropical climates. One general obser- 
vation may, I think, be applied to the whole; which is, 
that a large number of the more powerful drugs are 
produced on mountains, or in their vicinity ; these 
affording at their bases umbrageous shelter, uniform 
moisture, and equable temperature, for such as require 
them; while the rarefied atmosphere of their sides and 
tops allows a free transmission of light and of heat, 
and, in proportion to its increased capacity for moisture, 
favours evaporation and the ready secretion of vegetable 
juices. 
The History of Materia Medica, upon which I would 
now wish to make a few observations, is necessarily very 
complicated, if we attempt to study it with respect to each 
particular drug ; for many of these have been so long used, 
and described by a variety of authors, in so many languages, 
that it is sometimes difficult for any one, without particular 
training, to be able to recognise the most familiar articles : 
I will therefore briefly relate how I was led to the study, 
and what means I have taken to ensure some degree of 
certainty in my conclusions. 
