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afford a view of a great number of veins, arid arteries, with a very quick and beautiful fuccefHon of blood through them. The tail of a flounder may be very conveniently placed before the double microfcope on a plate of glafs, and its body being fupported by fomething of equal height, the fifh will lye lull, and the circulation may be feen very agreeably. In the minuteft velTels, thus examined, the blood always appears pale or co- lourlefs, but in the large ones it is plainly red. The arteries ufually branch out extremely before they join the veins to car- ry the blood back to the heart ; but this is not always the cafe, for Mr. Lewenhoek has obferved, that on each fide of the lit- tle griftles, which give a ftiffhefs to the tail of a flounder, there may be feen a very open communication of the veins and ar- teries; the blood running toward the extremities, through ar- teries, and returning back again through veins, which were evidently a continuation ofthofe arteries, and of the fame di- ameter with them. The whole fifh on the tail of which this examination was made, was not more than half an inch in length; it is. eafy to conceive how fmall the tail muft there- fore be, and yet in it there were fixty-eight velTels which car- ried or returned the blood; and yet thefe veflels were far from being the moft minute of all. How inconceivably numerous then muft the circulations in a whole human body be? Mr. Lewenhoek is of opinion, that a thoufand different circulations are continually carried on in every part of a man's body in the breadth of a finger nail. SeeTab. of microfcopical objects, Clafs r.
The tail of a newt, or water-lizard affords alfo a very enter- taining profpect of the circulation of the blood through almoft numberlefs fmall veflels ; but no object fhews it fo agreeably as one of thefe animals while fo young as not to be above an inch long ; for then the whole body is fo very tranfparent, that the circulation may be feen in every part of it, as well as in the tail ; and, in thefe objects, nothing is more beautiful than the courfe of the blood into the toes, and back again, where it may be traced all the way with great eafe. Near the head there are alfo found three fmall fins, which afford a very delightful pro- fpect : thefe are all divided like the leaves of polypody, and in every one of the branches of thefe, the blood may be very ac- curately traced, running to the end' through the artery, and there returning back again by a vein of the fame flze, and laid in the fame direction ; and as the veflels are very numerous and large in this part, and the third or fourth magnifyer may be ufed, there are fometimes feen thirty or forty channels of the running blood at once; and this the more as the globules of blood in the newt are large, and are fewer in number, in pro- portion to the quantity of ferum, than in any other animal and their figure, as they are protruded through the veflels, changes in a very furprifing manner. Bakers Microfcope, p.
122.
Dr. Nichols has contradicted the received doctrine of the mo- tion of the heart, and of the circulation of the blood) both in adults and fcetus's. The circulation of the blood, according to him, depends on fix motions : i°, Of the right auricle. 2°, Right ventricle. 3 , Pulmonary artery. 4°, Left auricle. 5 , Left ventricle ; and, 6°, Of the aorta. Of thefe, the firft, third and fifth, are fynchronous, as are likewife the fecond, fourth and fixth ; but the firft, third and fifth are afynchro- nous to the reft: and therefore
The two auricles ~\
The two ventricles > are alternately
The two arteries j See Nichols, Compend. Anat. & Pnelect. xv. ap. Med. Efl". Edinb. vol. 3.
As for the circulation of the blood in fcetus's, we refer to the author himfelf, in his Prseledt. xxiv. and to the Medic. Efl". Edinb. Abrid. vol. 2. p. 436, 437. where it is obferved, that the do£tor's opinion concerning the circulation of the blood in born and unborn animals, is lb different from what has pre- vailed fince Harvey's time, that it were to be wifhed he would add the experiments and other proofs that can be brought to fupport his doctrine.
According to Mr. Quefhay, the motions of the heart, and the circulation of the liquors, depend on the motion of the lungs, which fending the -blood forcibly into the left auricle, revive and increafe its elafticityand contraction by this (hock, which the auricle communicates to the ventricle, which affects the arteries in the fame way ; and thefe do the Fame to the veins which act upon the right auricle, and that upon its ventricle : and thus the circu'ation is continued. L'CEconomie Animale, p. 227. ap. Med Efl". Edinb. Circulation in plants. Blair is of opinion, that there are certain parts of plants which have their peculiar juices, and maintain a circulation in themfelves, independent of the reft of the plant. Theflefhy and thick roots of fome plants, and the fruits of others, are of this number of peculiar parts. This is analogous to what we fee in fome parts of animal bodies al- fo. On- this fcheme, the bark, the wood, and the pith of a tree, rnav be compared to the bones, the fkin, and the mar- row of animals : while the nourifhment is fent in abundance to one part of thefe. it is allowed more fparingly to the reft. Thus while a young tree (hoots out its tender boughs in fpring, (he juice afcends upward to them from the root; but when thefe have acquired their due length, the motion of the fap is
relaxed contracted.
determined upward with lefs violence, and the bark and wood are nourifhed and increafed by it. This is the reafon why in fpring trees grow in height, and in autumn increafe in thick- nefs. Blair's Ten tarn. Botan.
Subterranean QiKQMh M:\ovi. Dr. Plot is one of the many authors who have argued for nCubtenanezn circulation of water, by means of which many fprings and rivers are fupplied with that water which they give again to the fea. It is probable, indeed, that many of the fmaller fprings are fupplied by rains, only where the country and fituation are favourable : but the larger rivers, and the fprings which fupply them, muft have their origin from fuch a fubterranean circulation, fince all the water that falls in a year in the whole earth, is not one five hundredth part the quantity of that difcharged into the fea at the mouths of rivers as appears by careful and moderate calculations. There are fome fprings which ebb and flow with the fea : thefe cannot be doubted as to their origin, which is evidently from that body of water whofe motions they are influenced by. Nor is the cafe much lefs clear in regard to thofe lakes which have fait water and fea fifh in them, and yet have no communication with any fea by any known cut or pafiage. The number of fhell-fifh and parts of fea animals dug up in feveral places, at great depths at land, are alfo urged by fome as proofs of fuch fubterranean patfages of the fea water; but thefe are too univerfallydiftributed thro' the ftrata of the earth, to have been brought in this manner, and are therefore rather fuppofed to be owing to the great change made in the earth at in the days of Noah.
CIRCUMAGENT1UM femeris primus, in anatomy, a name given by Spigehus, and tome others, to amuicleof the thi^h, called by Riolan and fome others the iliacus externus, but more generally, from its fhape, the pyriformis and pyramidalis.
C1RCUMAGENS interior, in anatomy, a name given by Spi- gelius and others to one of the mufcles of the eyes, called by Albinus and others the obliquus fuperior oculi, and trocb- learis mufculus. See Trochlearis.
CIRCUMCELLIONES, in church hiftory, a fet of heretics who went about from town to town, calling themfelves the vindicators of the public liberty. Hofm. Lex. in voc.
CIRCUMGYRATION, the wheeling motion of any body round a center.
CIRCUMPOTATIO, in antiquity, a funeral feaft, provided in honour of the dead.
This was very frequent among the antient Romans, as well as among the Athenians. Solon at Athens, and the decemviri at Rome, endeavoured to reform this cuftom, thinking it abfurd that mirth and drunkennefs mould mingle with forrow and grief. Pitifc. Lex. Ant. in voc.
CIRCUMSCRIBED figure, in geometry. See Circumscribe
ING, Cycl. Circumscribed hyperbola, one of the fecond order, according to Sir Ifaac Newton, which cuts its afymptotes, and contains the parts cut off within its own fpace. Stone, Math. Diet. See Hyperbola, Cycl. CIRCUMSCRIPTION. See Circumscribinc, Cycl CIRCUMSPECTE agatis, the title of a ftatute made ann. 13 Edw. I. relating to prohibitions, preferring certain cafes to the judges, wherein the king's prohibition lies not. Blount. Law Diet, in voc. CIRCUS, in zoology, a name by which Bellonius and fome others have called the milvus seruginofus, or moor buzzard. Bellon. de Avibus. See the article Milvus. CIRLUS Jlnltus, in zoology, the name of a bird of the hortu- lanus kind, and of the fize and fhape of our common yellow- hammer. The hinder part of the head and the back are of a ferrugineous colour, variegated with large black fpots : the fore- part of the head has a very large grey fpot : the breaft and belly are of a ferrugineous colour, without any variegation : the tail and the long feathers of the wings are black, but are tipped at the extremities with the colour of the back : the wings have fome fmall white fpots alfo; and the tail has two feathers on each fide which are variegated with white. Aldrov, Hift, Avium, 1. 18. c. ult. CIRRIS, in zoology, the name of a fmall fpecies of heron, call- ed by fome the ardea hasmatopus, or the red- legged heron. It is very fmail : its neck is fhort for a bird of the heron kind, and it is all over of a yellowifh cbefnut colour, deeper below, and paler on the back and wings : its tail is fo fhort that it feems to have none ; and its head and neck have black varie- gations on their yellowifh feathers. Its legs and feet are very beautifully red. Ray's Ornithol. p. 206. CIRSIUM. See gentle Thistle. CIRSOS, fowrocj in medical writers, is ufed for varix. See
Varix, Cycl. CIRRUS {Cycl.) — Cirrus, in ichthyology, aname given by authors to certain oblong and foft appendicular hanging from the under jaw of fifties, or from other parts about the mouth, in the manner of little worms, and ufually of a cyhndric figure, or nearly fo. Thefe cirri are in fome fifh hollow at the root ; in others .they are not fo : in thofe which are hollow at the root, the cavity never runs quite thro'. The way of finding it is by introducing a hog's briftle or a hair into itj but th8 cannot be forced thro' to the point, nor can any fluid matter be expreflcd out of them.
Thefe
