The philosophy of natural history / by William Smellie ; with an introduction and various additions and alterations, intended to adapt it to the present state of knowledge by John Ware, M.D.

  • Smellie, William, 1740-1795.
Date:
1829
Catalogue details

Licence: Public Domain Mark

Credit: The philosophy of natural history / by William Smellie ; with an introduction and various additions and alterations, intended to adapt it to the present state of knowledge by John Ware, M.D. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

    17/336
    1. With respect to their mode of taking and digesting food. In animals this is done by an act of their own, by the exer- cise of volition. They in some sense exercise choice and make efforts to get that which is adapted to their purposes. This is obvious enough with regard to the larger and more perfect animals; but even in the most imperfect kinds, as in the polypes, we find that they are capable of sending out their arms or feelers in search of food, which, when offered to their grasp, they seize and convey into the organ appropriated for digestion. It is true that the roots and other parts of plants, as has been already remarked, show a sort of intelligence and discrimination in the course which they take in search of moist or fertile ground, and in avoiding or seeking light or shade, which is analogous to the low degree of power mani- fested in the feelers of the polypes ; yet the analogy is but slight, and does not imply the existence of spontaneous and voluntary motion. ( Animals are affected by the sensation of hunger, and are induced by it to make immediate and volun- ' tary exertions for its relief.^ Vegetables are not so affected, and the efforts which they make to obtain nutriment are slow, and accomplished as much by the gradual operation of ex- ternal circumstances, as by an internal and voluntary power. 2. Digestion is performed in animals by means of a stom- ach and an intestinal canal. The food is taken into the body and is there operated upon by organs, which are different in different species, according to the nature of the substances on which they subsist. The principal of these is a stomach. yln plants, on the contrary, nourishment is absorbed directly ' from the earth by the roots, or from the air by the leaves ; \; there is no intermediate organ where a change is wrought in its nature before it is introduced into the circulation ; it is true that it undergoes such a change in order to adapt it to the purposes of the particular plant into which it is taken, yet it is not effected, as in animals, by means of their internal surface. For although it has been said, that the polypes, when turned inside out, continue to perform the function of digestion without interruption as under ordinary circumstan- ces, yet even in this case it is still the internal surface which digests, that which was formerly external, exchanging func- tions as well as situations with that which was within. 3. Animals differ also from vegetables in the nature of their food. They are not capable, like plants, of being nourished by the common elements of nature, but require substances which have been already organized, and have once formed a 2