Of the Brain, Lungs, &c.

277

internal; the external Subftance is foft, glandulous, and of the Colour of Ashes ; this Part receives the capillary Branches of the Veins and Arteries belonging to the Brain, and fendeth from its little oval Glands an infinite Number of Fibres, which all together make up the medullary Subftance of the internal Part of the Brain and Cerebellum, which going out of the Skull, form the Nerves and fpinal Mar

row.

A. Pray what is the Ufe of the Brain?

B. The Ufe of the Brain is to feparate from the Blood brought thither, the finest and subtlest Parts thereof, called animal Spirits, by the Glands in the external Part, which are received from thofe Glands by the Fibres of the medullary Substance, and are from thence convey'd by the Nerves. (which these Fibres compofe) to all Part sof the Body; giving the Faculty of Senfation to the whole.

A. Pray what is the Nature of the Lungs?

B. The Subftance of the Lungs is compofed of an infinite Number of little Lobes or Spheres, of various Figures and Magnitudes, whofe Surfaces are fo adapted as to leave but few and fmall Interftices; these fmall Lobes are difpofed like fo many Bunches of Grapes on the Sides of the Branches of the Wind-pipe: Each little T 3 Lobe

Lobe contains within its own proper Membrane, an infinite Number of fmall and round Bladders, which leave fmall Interftices between full of fmall Membranes, like thofe which bind the Lobes together; The Extremities of the Branches of the Wind-pipe open into the Cavities of these fmall Bladders, which are probably formed by its Membranes; but the fine Blood Veffels are only spread upon the Bladders like a Net, with frequent and large Inofculations.

A. Pray what is the Ufe of the Lungs?

B. This is the great Organ of Breathing or Respiration; as the Air by its Weight forceth into every Cavity, fo as foon as the Fatus is born it rushes into the Cavity of the Lungs, and fills the little Veficles, and by extending them compreffes the fmall Blood Globules in the Veffels fpread upon them; this Compreffion is much greateft when the Air is expelled out of the Lungs by the Contraction of the Breaft; and by this Compreffion, the red Globules of Blood, which through their languid Motion in the Veins, were grown too big to circulate, are again broken and divided in the Serum, and fo the Blood is anew made fit for Nutrition and Secretion. Dr. Keil alfo thinks that the Air doth hereby enter and mix with the Blood. Dr. Cheyne faith, the elaftick Globules of the Blood are hereby formed. And

others

Of the Lungs and Heart.

279

others hold other Opinions of the Ufes of Refpiration. But I think it ftrange, that Etmuller, amongst his 14 Ufes thereof, has not mentioned the vital Spirit of the Air, which probably is thereby intermixed with the Blood, and diffused through all the Body, and is therein the Principle of animal Life; fince it is well known Animals cannot live in Air deprived of this Spirit. Neither has Mr. Derham hinted hereat.

A. Pray what is the Nature and Compofition of the Heart?

B. The Heart (faith Boerhave) and its Auricles are real Mufcles, and act with a muscular Power; for all the Fibres gradually growing shorter diminish the Length of the Heart and increafe its Breadth; they accurately freighten the Cavities of the Ventricles; dilate the tendinous Mouths of the Arteries; determine the Valves of the Mouths of the Veins for the Stoppage of their Contents; and drive, with great Force, its contained Blood into the dilated Mouths of Arteries; in order to its Circulation through the Body.

A. Pray what is the principal Service of the Heart to the humane Body?

B. This wonderful Muscle has two Motions, which they call Systole, and Diastole; the Systole is when the Fibres contract and ftreighten the Cavities; the Diastole is when this Mulcle ceafeth to act; its Fibres return

to their natural Site, and its Cavities become large and wide. Now the Vena Cava returning to the Heart, the exhausted superfluous Blood, with the Chyle newly mixed herewith, pours it through the right Auricle, whence it is detruded into the right Ventricle or Cavity of the Heart; by its Systole it is thence driven into the pulmonary Artery, which conveys it to, and diftributes it through all the Parts of the Lungs; the Blood being here by Refpiration, prepared, reduced, mixed and impregnate with the vital Spirit, and nutricious Principles of the Air, is remanded back again by the pulmonary Vein to the left Auricle; thence into the left Ventricle of the Heart, which is then in its Diaftole; lafily, in the Systole of this Ventricle, the Blood now refected is thrust into the great Artery, called the Aorta, which carries it again through all the Body: Thus the Heart is the inftrumental Caufe of the Blood's Circulation.

A. In the next Place, pleafe to give me fome Account of the Nature of the Stomach.

B. The Stomach is compofed of four Membranes: The first and inmoft is a large mufcular Coat, lying in Plaits, and containing a great Number of Glands, thence called the Tunica Glandulofa, The fecond Coat is much finer and thinner; is altogether nervous, and therefore of exquilite

Senfe.

Of the Stomach.

281

Senfe. The third Tunicle is made of strait and circular Fibres; so that by this mufcular Coat the Ends of the Stomach are drawn towards its Middle, and the whole is equally contracted. The fourth is the common external Cover of the whole Stomach; it proceeds from the Peritoneum.

A. Pray to what Use doth the Stomach ferve?

B. The Ufe of the Stomach is Digestion; which is the Diffolution or Separation of the Aliments or Food into fuch minute Parts as are fit to enter our lacteal Veffels, and circulate with the Mafs of Blood: This is principally effected by the Saliva or Spittle of the Mouth; the fermenting Juice in the Stomach, feparated by its aforefaid Glands; by the Liquors we drink; and, laftly, by the continual Motion of the mufcular Coats of the Stomach, whofe abfolute Power is, by Pitcairne, demonftrated to be equal to 117088 Pound Weight; to which, if the abfolute Force of the Diaphragm and Muscles of the Abdomen be added, the SumTM will amount to 250734 Pound Weight, which is above 22384 hundred Weight, or near 112 Tun; No wonder then the very hardest Diet, or Bones themselves, fhould fo foon be reduced to a liquid Substance, we call the Chyle, by fuch prodigious conpiring Forces!

A. Pray,