Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 2 - By Alexander Von Humboldt And Aime Bonpland.
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It Is Not The
Same With Man As With Animated Beings Placed Lower In The Scale Of
Organization.
In the former, assimilation is exerted only on those
substances that enter essentially into the composition of the bones,
The muscles, and the medullary matter of the nerves and the brain.
Plants, on the contrary, draw from the soil the salts that are found
accidentally mixed in it; and their fibrous texture varies according
to the nature of the earths that predominate in the spots which they
inhabit. An object well worthy of research, and which has long fixed
my attention, is the small number of simple substances (earthy and
metallic) that enter into the composition of animated beings, and
which alone appear fitted to maintain what we may call the chemical
movement of vitality.
We must not confound the sensations of hunger with that vague feeling
of debility which is produced by want of nutrition, and by other
pathologic causes. The sensation of hunger ceases long before
digestion takes place, or the chyme is converted into chyle. It ceases
either by a nervous and tonic impression exerted by the aliments on
the coats of the stomach; or, because the digestive apparatus is
filled with substances that excite the mucous membranes to an abundant
secretion of the gastric juice. To this tonic impression on the nerves
of the stomach the prompt and salutary effects of what are called
nutritive medicaments may be attributed, such as chocolate, and every
substance that gently stimulates and nourishes at the same time.
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