common Course, and that of the Valves, are fo proportioned, that the Steam which rifes in a Second of Time is neceffary to open them, and when that, and the Blood has got Vent forward, they will fhut, and continue fo, till the Force of the Steam conftantly iffued from the Guts, and stopped at the Heart, in the next Second of Time, rife to the fame Degree. If there were not fuch a Stop, the Steam would hurry the Blood forward, as long as its Force lafted. 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 ftrong 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 Paffage 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 "ftruck with a Paraplegy, becomes cold and infenfible, and dies the fecond or third Day." His accurate Commentator Van Swieten, in Tom. II. p. 767-8, endeavours to explain this Phænomenon by the received Theory, and adds, "That it feems wonderful Hippocrates fhould be able

to make this Remark, unless he had known the prefent "Laws of Circulation, or had learn'd it from the Infpe. "&tion of Bodies dead of this Difeafe." "Tis moft likely he had it from the latter, for by the former it is abfolute

ly

Steam is encreased, the fuperfluous Steam is forced to fecrete out of the Lungs, and the Motion of the Blood is regulated to the Quantity the Cavity of the left VenD3 tricle

ly inexplicable; or the divine old Man must have had a true Idea of the Caufe of fo rapid a Circulation, which eafily evinces the Poffibility of fuch an Exit, nay, demon-" ftrates that no other could happen; nor would he so often furprise us with the Nature of his Predictions, as well as the Truth of them, if we would but confider him in his own Senfe, 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 perip-" neumonick Cafes, as fet down by Hipp. I fay, fhews that when the Agents of the Blood are agitated to the utmost, the Blood is capable even of difplacing the Heart, which I think much eafier to conceive, than that the Heart by its own increased Motion fhall agitate the Mafs in fuch an extraordinary manner, and even overturn itself. Befides, by the rest of the Symptoms which precede Death in this and moft acute Disorders, it is highly probable, nay, perhaps demonftrable, that the left Ventricle of the Heart must be for fome time, either entirely motionless, or at leaft, tranfmit 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 fays, Death happens to them when the Pulfe fails, and all the Parts are cold, fave the Breast, Head, and Neck, which burn with Heat; the Cheeks are intenfively livid; these Parts now are all within the Effect of the Circulation; the reft, which depend upon the Motion thro' the left Ventricle, are cold and benumb'd. Hence it is evident, in most acute Cafes the Heart is not able to withstand the Torrent, much less can it with any Propriety be thought its fole Mover.

T

This innate, felf-fufficient Agency of the Heart, (than which nothing can be more unphilofophical or abfurd) being a received Opinion, and taught in all Schools now aDays, has been the only Caufe of fo little real Ufe having been made of the illuftrious Harvey's Motion of the

Bload

tricle of the Heart fends forth at each Push. Of what Ufe 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 first Approach, and preserve a Vacuum till it be filled with Blood, or for what other Ufe, deferves to be confidered. * When the Ends of the Vena Cava and Heart are diftended with Steam and Blood, 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

down,

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 flightly run over the great Inventor's Account, we never could have been guilty of fo foul an Error, for he exprefly fays the contrary, Exercitat. Anat. p. 191. Lond. 1661. and this he is induced to fay from Exp. which he fhall hereafter publish, but the Lofs of thefe Pieces are among the other irreparable ones we feel at this Day, from the Confufion of thofe Times. To fee how far thisgreat Man's Humid and Primog. agree with our Author's Steam, I think it worth any curious Man's Time to confult his Book De Generat. Animal, p. 483. Edit. Elzev. 1641.

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

down, befides what Motion it has by being extended and contracted. As the Steam and Blood pafs along the Arteries by Pushes, they fill and raife 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 Preffure of the Air and Cold is moftly kept off.

The Strength of the Air-bladders of the Lungs are fo proportioned, that any Force, beyond what is neceffary to drive the Blood along the Arteries, opens the Paffages into them. And the Steam, which, if it fhould all pafs through the left Ven-. tricle of the Heart, would drive the Blood too faft along the Arteries, and extend them too much, opens the Paffages out of the Blood Veffels, and drives Part of itself into these Bladders, and vents itfelf there. When they are a little extended, the Air preffes 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 poffeffed by the Stomach and Guts, and extends the Rind of the lower Belly outward. When that Air is mixed with Heat, Steam, &c. expanded and lighter than the outward Air, the

D 4

Preffure

Preffure of the outward Air upon the lower Belly, and its own Elafticity, perhaps, affifted fomething by the Contraction of the Lungs, drives it out, and fo it partly condenses the Steam, and partly gives it Vent. And the Preffure of the Air upon the lower Belly, notwithstanding the Secretion of the Steam, and the Expanfion of the Bladders, has the fame Effect in fome Degree, upon the Blood in the Veins of the Lungs, as it has upon the outward Veins; and the Remainder of the Steam fupplies its Defect, and perhaps there may be Valves upon the Vesfels, 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.

CHAP.