bint BOTANIC PHYSICIAN. | 
these vessels, assisted by the agency of light, changed in its compo- 
sition, and thus the peculiar products of the vegetable are formed. — 
_ The first transition of the sap seems to be into MuCILAGE or GUM, 
as this is one of the proximate principles contained in the greatest 
quantity in vegetables, and which is abundant in young plants. It 
; an inodorous, insipid and glutinous substance, soluble in water in 
' tion, and forming with it a viscid solution termed muci- 
: > 
lage. It is insoluble in alcohol, ether, or oil, and is precipitated 
~ from its solution in water by the addition of alcohol, or any of the 
alkalies. It does not absorb oxygen from the atmosphere; it is nei- 
ther fusible nor volatile. At a temperature superior to 212°, but 
is employed to render oils 
: Restn is another of these proximate principles, most abundantly 
diffused t ted with gam, 
but some vegetables ex t ‘resinous. Resin is insoluble 
of its de n by heat are, water, acetous acid, an empyreu= 
matic oil, and a residuum of charcoal. Its constituent parts, there=- 
fore, are carbon, hydrogen and oxygen. ee 
Resins are frequently odorous and sapid. | '[hey are more active 
_ than gums, with respect to their medicinal effects, the virtues Of 
many of those vegetables which act most powerfully as medicines 
nding on thieir resinous part. : 
_~ Gum and resin are often intimately mixed in vegetables, forming 
agum-resin. Some of the most active articles of the materia medica, 
are natural compositions of this kind. a 1 : 
A proximate principle of vegetables, which till lately, was always 
confounded with gum-resin, is that termed by the French chemists 
EXTRACT Or EXTRACTIVE MATTER. The peculiar character by 
which it is distinguished: from gum, resin, or any mixture of the — 
two, is its being equally soluble im water and in alcohol; hence its 
solution in the one fluid is not precipitated by the addition of the 
other. The extractive principle also, when dissolved in water, and, 
__ heated to 212°, in contact with the atmospheric air, absorbs oxygt 
- with avidity, which neither gum nor resin does. By this 
