17 
affords the pabulum of vegetable life ; it is neither 
charcoal nor hydrogene, nor azote, nor oxygene 
alone ; but all of them together, in various states 
and various combinations. Organic substances, 
as soon as they are deprived of vitality, begin to 
pass through a series of changes, which ends in 
their complete destruction, in the entire separation 
and dissipation of the parts. Animal matters are 
the soonest destroyed by the operation of air, 
heat, and light. Vegetable substances yield more 
slowly, but finally obey the same laws. The periods 
of the application of manures from decomposing 
animal and vegetable substances depend upon the 
knowledge of these principles ; and I shall be able 
to produce some new and important facts founded 
upon them, which I trust will remove all doubt 
from this part of agricultural theory. 
The chemistry of the more simple manures, the 
manures which act in very small quantities, such 
as gypsum, alkalies, and various saline substances, 
has hitherto been exceedingly obscure. It has 
been generally supposed, that these materials act 
in the vegetable oeconomy in the same manner as 
condiments or stimulants in the animal oeconomy, 
and that they render the common food more nu- 
tritive. — It seems, however, a much more pro- 
bable idea, that they are actually a part of the 
true food of plants, and that they supply that kind 
of matter to the vegetable fibre, which is analogous 
to the bony matter in animal structures. 
The operation of gypsum, it is well known, is 
extremely capricious in this country, and no 
c 
