247 
a great excess of fibrous and insoluble matter, which 
must undergo chemical changes before they can 
become the food of plants. 
It will be proper to take a scientific view of the 
nature of these changes ; of the causes which oc- 
casion them, and which accelerate or retard them ; 
and of the products they afford. 
If any fresh vegetable matter which contains 
sugar, mucilage, starch, or other of the vegetable 
compounds soluble in water be moistened and 
exposed to air, at a temperature from 55 ° to 80°, 
oxygene will soon be absorbed, and carbonic acid 
formed ; heat will be produced, and elastic fluids, 
principally carbonic acid, gaseous oxide of carbon, 
and hydro-carbonate will be evolved ; a dark-co- 
loured liquid, of a slightly sour or bitter taste, will 
likewise be formed ; and if the process be suffered 
to continue for a time sufficiently long, nothing 
solid will remain, except earthy and saline matter, 
coloured black by charcoal. 
The dark-coloured fluid formed in the ferment- 
ation always contains acetic acid ; and when albu- 
men or gluten exists in the vegetable substance, it 
likewise contains volatile alkali. 
In proportion as there is more gluten, albumen, 
or matters soluble in water in the vegetable sub« 
stances exposed to fermentation, so in proportion, 
all other circumstances being equal, will the process 
be more rapid. Pure woody fibre alone undergoes 
a change very slowly ; but its texture is broken 
down, and it is easily resolved into new elements 
when mixed with substances more liable to change, 
containing more oxygene and hydrogene. Volatile 
r 4 
