Awakes and stretches, l. 392. During the first six months of gestation, the embryon probably sleeps, as it seems to have no use for voluntary power; it then seems to awake, and to stretch its limbs, and change its posture in some degree, which is termed quickening.[Back to Canto]
With gills placental, l. 393. The placenta adheres to any side of the uterus in natural gestation, or of any other cavity in extra-uterine gestation; the extremities of its arteries and veins probably permeate the arteries of the mother, and absorb from thence through their fine coats the oxygen of the mother's blood; hence when the placenta is withdrawn, the side of the uterus, where it adhered, bleeds; but not the extremities of its own vessels.[Back to Canto]
His dazzled eyes, l. 398. Though the membrana pupillaris described by modern anatomists guards the tender retina from too much light; the young infant nevertheless seems to feel the presence of it by its frequently moving its eyes, before it can distinguish common objects.[Back to Canto]
As warmth and moisture, l. 417.
In eodem corpore sæpe
Altera pars vivit; rudis est pars altera tellus.
Quippe ubi temperiem sumpsêre humorque calorque,
Concipiunt; & ab his oriuntur, cuncta duobus.
Ovid. Met. l. 1. 430.
This story from Ovid of the production of animals from the mud of the Nile seems to be of Egyptian origin, and is probably a poetical account of the opinions of the magi or priests of that country; showing that the simplest animations were spontaneously produced like chemical combinations, but were distinguished from the latter by their perpetual improvement by the power of reproduction, first by solitary, and then by sexual generation; whereas the products of natural chemistry are only enlarged by accretion, or purified by filtration.[Back to Canto]
How short the span of Life, l. 1. The thinking few in all ages have complained of the brevity of life, lamenting that mankind are not allowed time sufficient to cultivate science, or to improve their intellect. Hippocrates introduces his celebrated aphorisms with this idea; "Life is short, science long, opportunities of knowledge rare, experiments fallacious, and reasoning difficult."—A melancholy reflection to philosophers![Back to Canto]
The age-worn fibres, l. 3. Why the same kinds of food, which enlarge and invigorate the body from infancy to the meridian of life, and then nourish it for some years unimpaired, should at length gradually cease to do so, and the debility of age and death supervene, would be liable to surprise us if we were not in the daily habit of observing it; and is a circumstance which has not yet been well understood.
Before mankind introduced civil society, old age did not exist in the world, nor other lingering diseases; as all living creatures, as soon as they became too feeble to defend themselves, were slain and eaten by others, except the young broods, who were defended by their mother; and hence the animal world existed uniformly in its greatest strength and perfection; see Additional Note [VII].[Back to Canto]