cold doth shut in and hinder: for we see that in great colds one can scarce draw his breath. Another cause may be, for that cold calleth the spirits to succour; and therefore they cannot so well close and go together in the head; which is ever requisite to sleep. And for the same cause, pain and noise hinder sleep; and darkness (contrariwise) furthereth sleep.

745. Some noises (whereof we spake in the hundred and twelfth experiment) help sleep; as the blowing of the wind, the trickling of water, humming of bees, soft singing, reading, &c. The cause is, for that they move in the spirits a gentle attention; and whatsoever moveth attention, without too much labour, stilleth the natural and discursive motion of the spirits.

746. Sleep nourisheth or at least preserveth bodies a long time, without other nourishment. Beasts that sleep in winter (as it is noted in wild bears) during their sleep wax very fat, though they eat nothing. Bats have been found in ovens, and other hollow close places, matted one upon another and therefore it is likely that they sleep in the winter time and eat nothing. Quare, whether bees do not sleep all winter, and spare their honey? Butterflies, and other flies, do not only sleep, but lie as dead all winter; and yet with a little heat of sun or fire revive again. A dormouse, both winter and summer, will sleep some days together, and eat nothing.

Experiments in consort touching teeth and hard substances in the bodies of living creatures.

To restore teeth in age, were magnale naturæ. It may be thought of. But howsoever the nature

of the teeth deserveth to be inquired of, as well as the other parts of living creatures' bodies.

747. There be five parts in the bodies of living creatures, that are of hard substance; the skull, the teeth, the bones, the horns, and the nails. The greatest quantity of hard substance continued is towards the head. For there is the skull, of one entire bone; there are the teeth; there are the maxillary bones; there is the hard bone that is the instrument of hearing; and thence issue the horns; so that the building of living creatures' bodies is like the building of a timber house; where the walls and other parts have columns and beams, but the roof is, in the better sort of houses, all tile or lead or stone. As for birds, they have three other hard substances proper to them; the bill, which is of the like matter with the teeth; for no birds have teeth the shell of the egg: and their quills: for as for their spur, it is but a nail. But no living creatures that have shells very hard (as oysters, cockles, mussles, scallops, crabs, lobsters, cra-fish, shrimps, and especially the tortoise,) have bones within them, but only little gristles.1

748. Bones, after full growth, continue at a stay; and so doth the skull: horns, in some creatures, are cast and renewed: teeth stand at a stay, except their wearing: as for nails, they grow continually and bills and beaks will overgrow, and sometimes be cast; as in eagles and parrots.2

:

1 Here, as in 732., we see that Bacon knew but little of the natural history of the tortoise.

2 Bones, like the soft parts of the body, are renewed throughout life, and so in many cases are teeth. Cuvier has remarked that the mutual adaptation of teeth and the bones with which they are connected is one of the

749. Most of the hard substances fly to the extremes of the body; as skull, horns, teeth, nails, and beaks: only the bones are more inward, and clad with flesh. As for the entrails, they are all without bones; save that a bone is (sometimes) found in the heart of a stag; and it may be in some other creature.

750. The skull hath brains, as a kind of marrow, within it. The back-bone hath one kind of marrow, which hath an affinity with the brain; and other bones of the body have another.1 The jaw-bones have no marrow severed, but a little pulp of marrow diffused. Teeth likewise are thought to have a kind of marrow diffused, which causeth the sense and pain; but it is rather sinew: for marrow hath no sense; no more than blood. Horn is alike throughout; and so is the nail.

751. None other of the hard substances have sense, but the teeth; and the teeth have sense, not only of pain, but of cold.

But we will leave the inquiries of other hard substances unto their several places, and now inquire only of the teeth.

752. The teeth are, in men, of three kinds: sharp, as the fore-teeth; broad, as the back-teeth, which we call the molar-teeth, or grinders; and pointed teeth, or canine, which are between both.2. But there have been some men that have had their teeth undivided, as of one whole bone, with some little mark in the place

most admirable parts of the animal economy; the mode of development of the two structures being wholly dissimilar, teeth growing by secretion, and bones by intus-susception. V. Cuv. Eloge de Tenon.

1 The marrow of bones is, of course, quite of a different nature from either brain or the spinal cord.

2 This sentence is copied from Aristotle, De Part. Anim. iii. 1.

of the division, as Pyrrhus had.1 Some creatures have over-long or out-growing teeth, which we call fangs, or tusks: as boars, pikes, salmons; and dogs, though less. Some living creatures have teeth against teeth, as men and horses; and some have teeth, especially their master-teeth, indented one within another like saws; as lions; and so again have dogs. Some fishes have divers rows of teeth in the roofs of their mouths; as pikes, salmons, trouts, &c. And many more in saltwaters. Snakes and other serpents have venomous teeth; which are sometimes mistaken for their sting.

753. No beast that hath horns hath upper teeth; and no beast that hath teeth above wanteth them below but yet if they be of the same kind, it followeth not that if the hard matter goeth not into upper teeth, it will go into horns; nor yet è converso; for does, that have no horns, have no upper teeth.2

754. Horses have, at three years old, a tooth put forth, which they call the colt's tooth; and at four years' old there cometh the mark-tooth, which hath a hole as big as you may lay a pea3 within it; and that weareth shorter and shorter every year; till that at eight years' old the tooth is smooth, and the hole gone: and then they say, that the mark is out of the horse's

mouth.

755. The teeth of men breed first, when the child is about a year and a half old: and then they cast then, and new come about seven years' old. But divers have backward teeth come forth at twenty, yea, some at thirty and forty. Quære of the manner of the com

1 Plutarch, in Pyrrhus, p. 434.

2 See Arist. De Part. Anim. iii. 2., and Hist. Animal. ii. 1.

ing of them forth. They tell a tale of the old Countess of Desmond, who lived till she was seven score years old, that she did dentire twice or thrice; casting her old teeth, and others coming in their place.

756. Teeth are much hurt by sweetmeats; and by painting with mercury; and by things over-hot; and by things over-cold; and by rheums. And the pain of the teeth is one of the sharpest of pains.

757. Concerning teeth, these things are to be considered. 1. The preserving of them. 2. The keeping of them white. 3. The drawing of them with least pain. 4. The staying and easing of the toothache. 5. The binding in of artificial teeth, where teeth have been strucken out. 6. And last of all, that great one of restoring teeth in age. The instances that give any likelihood of restoring teeth in age are, the late coming of teeth in some; and the renewing of the beaks in birds, which are commaterial with teeth. Quære therefore more particularly how that cometh. And again, the renewing of horns. But yet that hath not been known to have been provoked by art; therefore let trial be made whether horns may be procured to grow in beasts that are not horned, and how? And whether they may be procured to come larger than usual; as to make an ox or a deer have a greater head of horns? And whether the head of a deer, that by age is more spitted, may be brought again to be more branched ? for these trials, and the like, will show, whether by art such hard matter can be called and provoked. It may be tried also whether birds may not have something done to them when they are young, whereby they may be made to have greater or longer bills, or greater and longer talons? And whether children may not