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great Diflenfion of the Arteries, from a more considerable influx : yet it is certain, and even demonftrable, that there mutt needs be an Ounce, or more, driven into 'em at each time ; and yet fomc compute five or fix thoufand Pulfarions in an Hour.
5. Any of the Arteries, being ty'd with a Thread, fwell, and beat, between the Bandage and the Heart; but grow flaccid between the Bandage and the Extremities of the Body.
If now the Artery be cut between the Bandage and the Heart, the Blood ftreams out, even to Death : If it be cut between the Bandage and the Extremities of the Body, the Quantity of Blood it yields is very fmall.
The vital Blood, therefore, flows thro' the Arteries; and its Courfc is from the Heart towards the Extremes of the Body : and this it does in every Point of the Body, internal and external ; flill out of a wider Part into a narrower; out of the Trunk into the Branches. 'Tis on this Principle alone, that all the Blood may be deriv'd into any Artery, and eva- cuated at it. See Artery.
4. Any of the larger Veins being bound up with a Thread, fwell between the Extremes of the Body and the Bandage • but without beating : between the Bandage and the Heart it becomes flaccid.
If open'd in the former Part, it bleeds even to Death ; if in the latter, it fcarce bleeds at all. The Blood, therefore, flows brifkly from every Part of the Body into this Vein •' and its Courfe is from the Extremes of the Body towatds the Heart ; from the narrower Parts of the Vein towards the wider Parts ; from the Branches to the Trunk. See Vein.
From the whole, 'tis evident, that all the Arteries of the Body are continually bringing the Blood from the left Part of the Heart, thro' the Trunks of the Arteries, into the Branches ; and from thofe to all Parts of the Body, internal and external : And on the conttary, that all the Veins, ex- cepting the 'Porta, are perpetually bringing back the Blood from the extreme Parts into the fmaller Branches ; from thofe it paffes into the larger, at length into the Trunks, and thence into the Cava; and thro' the SimisVenofus, or Trunk of that Vein (which ends in the Cavity of the right Auricle) into the Heart.
_ The Blood arriv'd here, its Motion, or Circulation, is con- tinu'd as follows.
The Auricles of the Heart being large hollow Mufcles furnifh'd with a double Series of flrong Fibres proceeding with a contrary Direftion to two oppofite Tendons, the one adhering to the right Ventricle, the other to the Sinus Ve- nofus, as alfo with innumerable Veins and Arteries ; by the contracfile Force of thefe Auricles, the Blood will be vigo- rously exprefs'd, and drove into the right Ventricle ; which, upon this Contraction, is render 'd flaccid, empty, and dif- pos'd to admit it. See Muscle.
If now the right Ventricle, thus full of Blood, by the Con- traction of its Fibres prefs the Blood towards the Aperture
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agaii
the venous Blood at the fa
me time pouring in, will
drive it back again into the Cavity, and mix it more inti- mately ; till rifing up againft the Varietes, it raifes rhe Val- vule Trtcufpides, which arc fo connefled to the flefhy Co- lumns extended on the oppofite fide, as that when laid quite down they cannot clofe the Tarietes of the right Ventri- cle : thefe it thrufls towards the right Auricle, till being there join'd, they flop the Paffage very clofely, and prevent any return.
By the fame means, the fame Blood rifes up into the three Semilunar Valves, plac'd in the Extremity of the other Mouth, and lying open to the Pulmonary Artery : thefe it fhuts clofe againft the Sides of the Artery, and leaves a Paffage into the Artery alone.
The venous Blood therefore, that is, the Blood of the whole Body, continually moves out of the Sinus, or Trunk of the Vena Cava, thro' the right Auricle, and right Ventri- cle, into the Pulmonary Artery, in a continu'd and forcible Stream.
The Blood carry'd by this Artery into the Lungs, and dif- ttibuted by its Branches thro' the whole Subftance thereof, is firtt admitted into the Extremities of the Pulmonary Vein.
propelld into the Aoru ,, | whofe Ramifications are fpread throughout all the reft of the Body, with a violent UoZT
Jhis Motion, in liv.ng Animals, is attended with the fol- lowing Phenomena.
1. Both Venous Sinus's are fill'd, and grow turgid at the
T, "r «;,.?* ^"clesgrow fcccid « the 2K %z and both are fill'd at the fame time, with Blood impeli'd by the contraflile Force of its correfpondent mufculat Venous b, j K r Vcnmcle rantrafis, and empties it felf of Blood at the fame time; and the two great Arteries are fill'd and dilated a t the fame time. 4. As foon as the Blood, by this Contraa.on, is expcll'd, both Ventricles being empty! the Heart grows longer and broader; and confequently more flaccid and capacious. ,. Upon which, the mufcular Fibres of both Venous Sinus's contrail, and exprefs the Blood con- tain d in em into the Ventricles of the Heart. 6. In the meantime the Venous Sinus's are again fill'd, as befote ; and the Auricles, gfe return into their former habitude! 7. And this Alternation continues till the Animal begins to languifh under the Approach of Death; at which the Auricles and Venous Sinus's make feveral Pulpit for one Contraflion of the Ventricle.
Thus is all the Blood, in its return frnm eV ery Point of
at which time, pitations,
the Body internal and external, and from every Point of the Heart and its Auricles, impeli'd into the right Ventricle ; out of that into the Lungs ; thence into the left Ventricle • and thence thro the whole extent of the Body; and thence again brought back to the Heart
As to the manner of the Blood's paffing out of the Arte- ries into the Veins, m order to its being return'd to the Heart ; there are two Opinions.
In the firtt, the Veins and Arteries are fuppos'd to open into each other or to be continu'd from each other, by Ana- Jttmafes, or ■Inoculations of their Extremities. Sec Inoscu- lation, Z5c.
In the latter the extreme Capillary Arteries are fuppos'd to let out their Blood into the Pores of the Subftance of their puts; on whole Nutrition part is fpent, and the reft recciv'd in at the Mouths of the Capillary Veins.
Each of thefe manners muft be allow'd to have its Place : For without the firft, it were difficult to account for fo quick a return of the Blood to the Heart, as in effect we find = befides that, in fome of the larger Veffels, there is a con- fels iAnaftomafis v. g. in the Splenic Artery with the Sple- nic Vein EV. whence Authors conclude the fame Contri- vance to hold in the Icfler Veffels ; even in the fmallcft Twigs in the extreme Parts of the Body, tho not difcovcr'd by the Eye ; Nature being ordinarily found very uniform, and con- fiftent with her felf.
Riolanns, however, who will allow of no Circulation but by Anaflomafes ; allows of none, neither, but by the larger Veflels. ' °
The Reafon of the latter Opinion is dedue'd hence, that it part of the arterial Blood did not ooze out into the Sub- f ance of the Parts, they could not be nourifh'd thereby : For the Blood, while contain'd in the Veflels, may indeed con- vey Warmth thereto, but no Nutriment ; the very Veflels themlelves being not nourifh'd by the Fluid running in their Cavity, but by Capillaries paffing their Coats. See Nutri- tion.
If then the Blood be driven out of the Veflels in a ereat- ct Quantity than is rcquir'd for Nutrition ; the redundancy mutt be imbib d by the Capillary Veins.
M. Lec-xcnhoeck feem'cl to have put this Matter out of doubt by his Microfcopes, with which he difcovcr'd the Inof- culations, or Continuations of the Extremities of the Veins and Arteries in Fifhes, Frogs, tfc. But fome flill doubt whether there be fuch Continuations in the Extremes of the Veins and Arteries in human Bodies and Quadrupeds : thofe Animals it has been hitherto obferv'd in, being either FilIi, or of the amphibious Kind, which have but one Ven- tricle in the Heart, and their Blood aflually cold ; to which it may be added, that the Blood in thefe Creatures does not emulate with that Rapidity as in thofe whofe Hearts have two Ventricles. This difference in the principal Organs of Circulation, oc-
call'd Arteria Venofa ; whence paffing into four large Vef- cafion'd Mr Cornier t„ IXv. i
fels, which u.i.e^thc, it is'brouf.t .to the } J S,nus_ whofe Par, tt^TCet^ZZ^ Zfetf "
the Omentum of a Cat, he faw the Blood move brifkly thro' the Ino culations ; the fame he found in the Omentum, and much clearer in the Mefentery, of a Dog. He adds, that the Extremities of the VefTels are not equally leffen'd, in the Inofculations, in different Animals.
In the Tail of the Tadpole, he frequently obferv'd feveral Communications between the Veins and Arteries; thro' each of which two Globules of Blood might pafs abrcaft. In
there arc Am. <!™;i .,„. \r "1 "t>" Y°™g Fifli, particularly Grigs, the communicant Brancl lis fn
tnete are tnree semilunar Valves, which alfo prevent a Re- fmall ilmnLn„k.,i«»riii j r ,r • 1. o
a.... i — _i-^__ .1 _ iinan, tnat one (jlobule ot Blood can fcarce pals in the Space
of three Seconds. See Vein, tgc.
Venofus, or Trunk of the Pulmonary Vein ; by the force of whofe mufculous Structure it is driven into the left Ventricle, which, on this occafion, is relax'd, and by that means pre- par'd to receive it.
Hence, as before, 'tis driven into the left Ventricle, which is relax'd by the fame means ; and the Valvule Mitrales opening, admit it into the left Ventricle, and hinder its re- flux into the Pulmonary Vein.
From hence it is fore'd into the Aorta ; at whofe Orifice e Semili flux by doling the fame.
And thus is Circulation effeaed ; all the Blood fent into the Lungs, and rcceiv'd into the Arteria Venofa, Sinus Venofus, left Auricle and Ventricle, being here continually
In a Fatns, the Appatatus for the Circulation is fomewhat different, from that above defcrib'd.
The
