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later feels the predatory force of the air. It also signifies that the periods of nature are performed in greater revolutions. And although lambs and calves, which remain but about six months in the uterus, are short lived; yet this proceeds from other causes.
Creatures that feed upon simple herbage, are of short duration ; but those that feed on flesh, or seeds, and fruits, as birds, are of a longer; for, even deer, derive one half of their food from above their heads : and the goose, besides grass, finds something in the stubble-fields, and the water.
We judge, that the covering of the body greatly conduces to prolong life; for this wards off, and prevents those unfriendly assaults of the air which, otherwise, strangely undermine and destroy the body: and birds are thus admirably fenced by their plumage. But that sheep, which are also well covered, are of short duration, must be imputed to the diseases whereto that creature is liable; and to their feeding chiefly upon grass.
The head is, doubtless, the principal seat of the spirits; and though this be vulgarly said only of the animal spirits, yet it holds equally of them all: and no question but the spirits greatly prey upon, and consume the body, so that both a greater quantity, or a greater acrimony and sharpness thereof must greatly shorten life : whence we judge it a principal cause of longevity in birds, that they have such little heads in proportion to their bodies ; and conjecture, that such men as have large skulls are shorter lived than others. · The motion of carriage we judge to excel all others for the prolonging of life; now all waterfowl, as the swan, &c. have this motion ; so have all birds in their flight, though every now and then mixed and compounded with a brisk motion of the limbs : so again have fish; though as to the length of their life we have no certainty.
The creatures perfected slowest are most lasting; for this shews that nature finishes her periods by greater revolutions ; which holds not only of growth, but of other degrees of maturity : so man first puts forth teeth, afterwards the signs of puberty, then the beard, &c.
The timorous animals are not long lived; as the sheep, the pigeon, &c. for the bile is the spur to many functions in the body.
The creatures whose flesh is dark-coloured, are longer lived than those whose flesh is white ; as indicating the juices of the body to be more compact, and less dissipable.
In all corruptible bodies, quantity has a great tendency to the preservation of the whole; a great fire is not soon quenched; a small quantity of water is soon evaporated; a branch withers faster than the trunk of a tree; and therefore, in general, as to species, though not to individuals, the larger animals are longer lived than the smaller, unless some other powerful cause intervene.*
THE HISTORY OF ALIMENTATION, AND THE PROCESS OF NUTRITION, WITH REGARD TO THE FOURTH ARTICLE OF THE TABLE OF
ALL aliment should be of an inferior nature, and a more simple substance than the body intended to be nourished : plants are fed by earth and water, animals by plants, and inen by animals. There are also other carnivorous creatures; and man himself makes plants a part of his food: but men, and other carnivorous animals, are difficultly nourished by plants alone ; though perhaps they might, by long use, with fruits and seeds that had felt the fire; but not by
* These observations are a kind of deep physical corollaries, sagaciously drawn from the preceding facts, or history of nature; and should be understood as so many first attempts at a just interpretation of nature, with regard to the present subject.
leaves or herbage ; as the order of the Folietani experienced.
But too near an approximation, or similarity of substance betwixt the aliment and the body to be nourished succeeds ill; for creatures that feed on herbage, touch no flesh : few carnivorous animals eat the flesh of their own species; and canibals themselves do not ordinarily feed upon human flesh, but either fall into this appetite through depraved custom, or a desire of revenging themselves upon their enemies. A field is not sown to advantage with the grain itself yielded; nor a tree successfully engrafted with its own shoot.
The better the aliment is prepared, and brought somewhat nearer in likeness with the substance to be repaired, the better vegetables thrive, and animals fatten : for a shoot planted in the earth is not fed so well as when grafted on a stock agreeable to its nature; where it finds its nourishment ready digested and prepared. And it has been lately discovered, that the slips of wild trees; as of the elm, the oak, the ash, &c. yield à much larger foliage by incision, than without it. Men also are not so well nourished with raw flesh, as with that prepared by fire.
Animals receive their nourishment by the mouth, vegetables by the root; and the fætus in the mother, by the umbilical cord: but birds,
for a time, are nourished by the yolk of she egg; some part whereof is found in their craws after they are hatched.
All aliment moves principally from the centre to the circumference, or from within, outwards; only trees and plants are rather nourished by the bark, and external parts, than by the pith, and internal: for if but a narrow slip of the bark be peeled off all round the trunk, the tree dies :* and the blood in the veins of animals nourishes the flesh situated below as well as above them.
There are two actions in all alimentation; viz. extrusion and attraction: the foriner whereof proceeds from an internal, and the latter from an external power.t.
Vegetables assimilate their nutriment simply, without excretion; for gums and the tears of trees are rather redundancies than excrements; and fungus's are diseases : but the substance of animals has a greater perception of its like, and is therefore endowed with a principle of rejection; whereby it refuses the useless, and assimilates the useful parts. I
* Perhaps this is not confirmed.
† As in the action of the absorbent vessels, and excretory ducts.
| What is properly meant by this perceptive principle, may appear from the De Augmentis Scientiarum, Sect. X.