from the position of their fibres, and asserts their proper action to be contraction. He confutes the common opinion, that nature with a very small force lifts up the greatest weights, the contrary being demonstrated, that the power exceeds the weight of the limbs that are lifted up by it 100 or 1000 times.

He gives us, likewise, an account of the wonderful structure of the back-bone, to the cartilages of which he attributes a greater force than to all the muscles that contract it, as is evident from this proposition: that if a porter carry on his back a weight of 120lb., the power nature exercises by the cartilages of the vertebræ, and the musculi extensores of the back, is equal to the force of 25,585lb.; that of the muscles alone he computes to be 6404 lb; and observes, that the retention of a joint stretched out is not from the tonical action of antagonist muscles.

Hence he goes on to deliver the various postures of an animal, which he does by assigning his centre of gravity in all his possible positions. As in a man stretched out at length, the centre is between the nates and pubes. That a man cannot well stand on one heel, or tip of a toe, because in these cases the line of direction falls without his basis, &c.

That though birds have two feet, yet they neither walk nor stand the same way as a man; which depends on the different structure of their joints. For, 1. they differ in the number of the bones. 2. In the form. 3. In the distribution and make of their muscles. 4. In the joints themselves.

He demonstrates the manner how a bird when sleeping sits firm on a twig, though the muscles are then inactive; namely, by a strong constriction of its claws, and, consequently, a firm comprehension of that twig, necessarily and mechanically resulting from the gravity of the bird, and the shortness of the tendons of those muscles that contract the claws.

That quadrupeds cannot stand in their natural prone position on one or two feet, because the centre of gravity and its line of propension cannot fall in either, or between both.

He shows the art of skating upon ice, as also how progression in quadrupeds is performed, and likewise leaping, in which the vis motiva is to the weight of the body as 2900 is to one. That in leaping according to a line inclined to the horizon, at oblique angles, the line described by the centre of gravity shall be a curve parabola, as being compounded of the straight uniform motion forward, and the accelerated descent of the heavy body. Next he gives an exact account

of flying, the main stress of which is in the largeness of the muscles that move the wings, the potentia of which exceeds the weight of the bird 10,000 times; with many more curious particulars about their several ways of flying.

He describes the action of swimming, and how fishes change their specified gravity on occasion, by the compression and dilatation of the air contained in their air-bladders, performed by the many and strong muscles about their bellies. He assigns the reason why man does not swim by instinct as well as other animals, to be chiefly on account of the gravity of the head so much exceeding the proportion of that of the rest of the body.

In the second part the author describes the mechanical mode, and assigns the immediate cause, by which the contraction of the muscles is performed.

Concluding that the muscles are contracted from the inflation of their fibres by adventitious bodies, as it were by wedges; and having refused an incorporeal natural faculty for the immediate mover, as also any aërial substance, and rejected the blood filling the pores of the muscles, together with the manner by which moistened ropes are contracted, he infers, that the ebullition, caused in the muscles by the concurrence of the blood and succus nerveus, is the immediate cause of the intumescence and contraction, which he confirms and illustrates by arguments and experiments.

He next gives an account of the internal motions of the fluids of the body, as of the circulation of the blood; describing the muscular structure of the heart, and showing how it differs from other muscles by the wonderful texture of its fibres.

He at last infers that the moving faculty of the heart exceeds the resistance of the whole blood in the arteries, and of the ligaments that hinder their dilatation, which is greater than the force of a weight of 180,000.

He ascribes respiration wholly to the muscles that enlarge the thorax, viz. the intercostals and the diaphragm, together with the weight and elasticity of the air. The manner, by drawing up the circumference of the ribs towards the throat, by directions that make acute angles with the plains of the ribs. The structure of the thorax in the tortoise, he observes, is remarkable, there being no divided ribs, but one continued bony arch, and no diaphragm; and instead of lungs, two long bladders, containing also the blood-vessels. These bags are not alternately filled and emptied, but constantly remain full of air, which is not renewed in them but partially, by the

external muscles that stick to the skin, which when inactive make a hollow sinus, but contracted, a plane.

A Discourse read before the Royal Society, concerning the jointed Worm. By EDWARD TYSON.-[1683.]

I SHALL begin with the jointed worm; and shall discriminate this from all other sorts of worms. And the first is, its being flat; hence called lumbricus latus, and by Hippocrates, Tawia, i. e. fascia, and in English, the tape-worm. This flatness of the body sufficiently distinguishes it from the others, which are usually bred in the body; which are either short and small, and then called ascarides, or longer, as the teretes. Nor is there any out of the body that I know of, that are thus flat.

In one I have by me 24 feet long, about five joints make an inch; whereas the latter joints here are above an inch long; but in some I have taken out of dogs, there were 30 or 40, sometimes above 60 annuli, which, towards the head, make up but the length of an inch; whereas towards the tail six or seven joints equalled that measure, and sometimes three; so that gradually the joints seem to increase, both in length and breadth, as they approach the tail.

As to the length of this worm, it is sometimes as long as all the bowels; not that it lies extended straight the length of the guts, as those might think, who fondly imagined it was nothing else but a mucous skin, or spolium of the same: but it lies convoluted in several places; so that it often vastly exceeds the whole length of the intestines themselves. Platerus observed one 40 feet long; and Pliny says, they are sometimes 300 feet or more. Thaddeus Dunus saw voided by a woman one piece of this worm five yards long; and another, above 20 yards long. Yet in neither could he observe either the head or the tail. But what Olaus Borrichius tells us is remarkable; that a patient of his, in a year's time, has voided 800 feet of this sort of worm, but in several pieces; and that 200 feet of it he kept by him; and that hitherto he has not met with the head. For the patient observed, that always in the voiding it, he perceived it break off; that he has not yet come to the end; and still goes on voiding the same. Which I could parallel with an instance of a person, once my patient, who has voided vast quantities of this worm, for several years together; but in several pieces, 2, 3, 4, 6, or more yards long; but all put together, would much exceed the length of that of Borrichius. Tulpius

says he showed, in the Anatomy Theatre, 40 yards of this worm; which was voided by one in two days' time. However, I question whether all those pieces which are voided by the same person may be always reputed parts of the same worm, or of different. Yet this is undeniable, and must be allowed, that this worm is amazingly long, which plainly appears even by those pieces we see of them; for, besides the instances already given, Simon Schultzius mentions one seven yards long, and another nine yards. Clusius tells us, that the Duke of Austria's cook voided pieces of this worm, 6, 12, and 15 yards long. Jacobus Oethæus measured one 18 yards long. Alexander Camerarius has seen them above 20 yards long. In the palace at Tiguri is kept the figure of one 18 feet long: and abundance of more instances I could give were it needful.

But I shall describe that piece of one I have by me, voided by a young man about 20 years of age, on the use of an emulsion of the cold seeds, who plainly perceived it alive, and to move; and having put it in a wide mouthed-glass, it often endeavoured by raising its body to get out; but the cold water into which it was put afterwards soon killed it. I measured it and found it 24 feet, or eight yards long. In it I numbered 507 joints. Its colour was extreme white, being turgid with chyle; its body flat, about the thickness of half a crown, where thickest; and the joints towards the tail about one fourth of an inch broad; those towards the head about one fourth as broad as those towards the tail, and here the joints were not one fourth of an inch long, whereas those at the tail were a full inch long, and something more; and from the head they seemed gradually to increase in length. The joints much of a wideness throughout; and the jetting edges of the former over the latter usually plain and even; unless where the contraction of the body had rendered them a little crimpled.

The flats of both sides just alike; and without any spots, protuberances, or any thing remarkable, which might distinguish them, or be observed, only a smooth surface; but about the middle of the edges of each joint I observed a protuberating orifice, which would easily enough admit a hog's bristle, and was open, and apparent to the naked eye. These orifices were placed for the most part alternately, in one joint on the right side, in the following on the left. But sometimes I have observed them in two, more seldom in three succeeding joints of the same side; but never in one joint more than once. These orifices I take at present for so many mouths. But since I have here mentioned of what length they have been observed in man, I shall also add how long those were I have seen in dogs. For though they are to be met with only in the animal kingdom; yet in abundance of the subjects of this, and those too of different species, they are very frequent; in fishes, as in the pike, whitings, bleaks, crabs, herrings, &c. and upon this score sometimes they prove a great damage to the merchants, as Platerus observes, they being forced to throw them away. In bleaks in the summer-time, if you open those that leap and tumble on the water, from the torment they feel within, you almost constantly meet with this worm, which is a thing well known to the watermen. In oxen often they are observed likewise, not so much in calves; but in dogs very frequently; which Platerus makes to be another sort of the tænia, and calls it ligula. Simon Schultzius mentions a lap-dog that in a short time voided nine yards of this worm in several pieces.

I have oftentimes here seen them myself, but shall mention those only I found in dissection; as I met with the first time two. There was indeed another piece, which I take only as broken off from one of the former, because here both extremes were pretty large, and the joints throughout proportionably long. But in the two others the disproportion was very remarkable; for besides observing here their heads thick beset with hairs or small spikes, which I shall afterwards describe, I took notice that this extreme, if extended, was very slender; and when a little contracted, the joints so very small, that they were scarcely discernible by the naked eye; but where I could better distinguish them, between 30 or 40 made the length of an inch; but towards the other extreme or tail, in one four, in the other six or seven joints made that length; one of these worms was scarcely a foot long; the other not a foot and a half.

In another dog I since dissected, I found another worm,

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