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common Course, and that of the Valvesi, are fo proportioned, that the Steam which rises in a Second of Time is necessary to open them, and when that, and the Blood has got Vent forward, they will fhut, and continue so, till the Force of the Steam constantly issued from the Guts, and stopped at the Heart, in the next Second of Time, rise to the fame Degree. If there were not such a Stop, the Steam would hurry the Blood forward, as long as its Force lasted. The Force of the Steam would always be equal, and that which it has now, would (if not stopped) not move the Blood a Minute ; or if it were strong enough to move it continually, it would move as quick as Lightning : * but by its Stops, the Force of the

Steam * To illustrate this, you will find a very remarkable Pasfage in Hippoc. See Lud. Duret. Commt.in Coac. Hipp. Sect. 32. The learned Boerhaave, in his Aphor. Cap. de Peripneumonia vera, quotes the very Words, Numb. 848, viz. “ If “ the whole Lungs, together with the Heart, be inflamed, “ the Heart falls from its Place to a Side, the Patient is “ struck with a Paraplegy, becomes cold and insensible, 6 and dies the second or third Day." His accurate Com-, mentator Van Swillen, in Tom. II. p. 767-8, endeavours to explain this phænomenon by the received Theory, and adds, " That it seems wonderful Hippocrates thould be able " to make this Remark, unless he had known the present “ Laws of Circulation, or had learn'd it from the Inspe. " &tion of Bodies dead of this Disease.” 'Tis most likely he had it from the latter, for by the former it is absolute

Steam is encreased, the superfluous Steam is forced to secrete, out 'of the Lings, and the Motion of the Blood is regulated to the Quantity the Cavity of the left Ven-'

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ly inexplicable; or the divine old Man must have had a true idea of the Cause of so rapid a Circulation, which easily evinces the Poslibility of fuch-an Exit,“ nay, demonstrates that no other could happen ; nor woald he so often surprise us with the Nature of his Predi&ions, as well as the Truth of them, if we would but consider' him in his own Sense, and not endeavour to make our Theory his Teft; whereas his own in most Points, perhaps is better; this Particular, as well as many more Symptoms in peripneumonick Cafes, as fet down by Hipp. I say, shews that when the Agents of the Blood are agitated to the utmost, the Blood is capable even of displacing the Heart, which I think much eafier to conceive, than that the Heart by its own increased Motion shall agitate the Mass in fuch an extraordinary manner, and even overturn itself. Besides, by the rest of the Symptoms which precede Death in this and most acute Disorders, it is highly probable, nay, pero haps demonftrable, that the left Ventricle of the Heart must be for some time, either entirely motionless, or at least, transmit little or no Blood to the Aorta, &c. fo the Motion of the Blood be only 'thro' the right to the Lungs; Vid. Boerhaave as above, where he says, Death happens to them when the Pulse fails, and all the Parts are cold, save the Breast, Head, and Neck, which burn with Heat; the Cheeks are intensively livid ; these Parts now are all within the Effect of the Circulation ; the rest, which depend upon the Motion thro' the left Ventricle, are cold and benumb'd. : Hence it is evident, in most acute Cases the Heart is not able to withstand the Torrent, much less can it with any Propriety be thought its sole Mover.

This innate, self-fufficient Agency of the Heart, (than which nothing can be more unphilosophical or absurd) being a received Opinion, and taught in all Schools now aDays, has been the only Cause of so little real Use having been made of the illuftrious Harvey's Motion of the

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tricle of the Heart sends forth at each Push. Of what Use the Water is which environs the Heart, whether it be only to facilitate its Motion by keeping off the Preffure of the Atmosphere, and preventing Friction, or to condense the Steam at its fuít Approach, and preserve a Vacuum till it be filled with Blood, or for what other Use, deserves to be considera edi * When the Ends of the Vena Cava and Heart are distended with Steam and Blaod, the Heart will be lifted up, and when the Steam and Blood pass thro', and the Ends of the Vena Cava and Heart are relaxed, the Heart will fall

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Blood ; it hath hoodwinked us from the Beginning. Pleased with the Discovery of the Blood's Motion to and from it. We immediately dubbed this with the Name of Agent, which in reality is only a Curb upon the Agent, and had we not too slightly run over the great Inventor's Account, we never could have been guilty of fo foul an Error, for he expresly says the contrary, Exercitat. Anat. p. 191. Lond. 1661. and this he is induced to say from Exp. which he Thall hereafter publish, but the Loss of these Pieces are among the other irreparable ones we feel at this Day, from the Confusion of those Times. To see how far this great Man's Húmid and Primog. agree with our Author's Steam, I think it worth any curious Man's Time to consult his Book De Generat. Animal, p. 483. Edit. Elzev. 1641.

* When the right Auricle and Ventricle are diftended with Steam and Bloed, the Heart will be lifted up, or shortned, and when the Steam and Blood pass thro', the Heart falls down, or is lengthened, besides, &c.

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down, besides what Motion it has by being extended and contracted. As the Steam and Blood pass along the Arteries by Pushes, they fill and raise the Arteries, and in the Intervals they relax and fall down. These Motions are augmented by the Expansion of the Steam in the Heart and Arteries, where the Pressure of the Air and Cold is mostly kept off.

The Strength of the Air-bladders of the Lungs are so proportioned, that any Force, beyond what is necessary to drive the Blood along the Arteries, opens the Pasfages into them. And the Steam, which, if it should all pass through the left Ventricle of the Heart, would drive the Blood too faft along the Arteries, and extend them too much, opens the Passages out of the Blood Veffels, and drives Part of itself into these Bladders, and vents itself there. When they are a little extended, the Air presses in; and its Force, being augmented by Motion, extends the Lungs farther, partly into the Vacancy in the Cheft, (if there be any) and partly into the space possessed by the Stomach and Guts, and extends the Rind of the Jower Belly outward. When that Air is mixed with Heat, Steam, &c. expanded and lighter than the outward Air, the

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Pressure of the outward 'Air upon the lower Belly, and its own Elasticity, perhaps, affifted fomething by the Contra&tion of the Lungs, drives it out, and fo it partly condenses the Steam, and partly gives it Vent, And the Pressure of the Air upon the lower Belly, notwithstanding the Secretion of the Steam," and the Expansion of the Bladders, has the same Effect in some Degree, upon the Blood in the Veins of the Lungs, as it has upon the outward Veins; and the Remainder of the Steam supplies its Defect, and perhaps there may be Valves upon the Veffels, where the Blood, and Steam, or Chyle meet, and even upon the most capillary, where the Blood goes out of the Arteries into the Veins; but if there be, I. think, they only contribute to hinder the Fluid from returning backward, and fo' direct the Force,

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