S38 Observations on Manures, Isrc. 
gelation to a certain degree : but the action of these fluids is more 
satisfactorily accounted for, on the doctrine of stimulus, than of pa- 
bulum. That oxygen is not nutriment, is clear, from its being an 
excretion of plants in a healthy state, and in vigorous action, un- 
der the influence of the sun, as Dr. Priestley, and afterwards 
M. Ing enhouz discovered. Hence, although fluid manures 
tnay contain the elements of phlogiston, or the combinations of 
phlogiston, this latter cannot of itself be taken as the only food of 
plants. Both plants and animals are resolvable into gasses of 
which phlogiston may be a part, but there is something else which 
feeds and dilates the muscles of animals, and the leaves of trees*, 
for they furnish something else. 
5. Dissatisfied with former theories, Mr. Kir wan has pro- 
posed carbon or charcoal as the food of plants ; and declares his 
opinion that if charcoal could be rendered soluble in water it would 
be the most efficacious manure. It is true, that charcoal and car- 
buretted hydrogen, are found in the incineration of all undecom- 
posed vegetables, but they contain also alkali, oxygen, and nitro- 
gen, &c. ; nor is there any fact to prove that charcoal (or the ox- 
yde of carbon) is either soluble in any liquid, or taken up as char- 
coal by any vegetable, or decomposed by any natural process; 
soot as a top dressing is a tolerable manure in England, but 
Its use may be accounted for from the saline substances it con- 
tains. From every fact hitherto known, the pabulum of vegetables* 
appears to be exhibited to plants generally in the form of a liquid . 
Hence, whatever theory of ingenious speculators be adopted as the 
simple and homogeneous pabulum of vegetable bodies in a living 
state, the old theory and the old practice must, and ought to pre- 
vail, namely, that the only manure of nourishment to be depended 
on, is dung, (i. e.J decomposed animal and -vegetable substances ; 
which contains within itself every substance that theory has hither- 
to assigned as the food of plants, ready to be afforded gradually, by 
the continual decomposition of the various compounds which the 
dung contains : and although it may be of use by dung-heaps to 
aid this decomposition, yet even in an undecomposed, or partially 
decomposed state, this gradual decomposition amounts in the end 
to the same thing. This is applicable to ground bone, woollen 
rags, horn shavings, &c. All the difference is that time is gained 
by the artificial and complete decomposition of these substances. 
Manures of stimulus. Whatever accelerates the growth, or en- 
or eases the size of plants, and does not actually enter into the com 
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