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INTRODUCTION.

I. OF THE BRAIN, AND NERVOUS SYSTEM.

May not animals have a power of extracting from the blood the electrical fluid? The BRAIN then would be the great laboratory for this purpose.

PRIESTLEY.

Moft authors have fuppofed, that the nerves are tubes or ducts conveying a fluid fecreted in the brain, cerebellum, and spinal marrow. But, of late years, feveral ingenious phyfiologifts have contended, that a fecreted fluid was too inert for ferving the offices performed by the nerves, and, therefore, fuppofe they conduct a fluid the fame as, or fimilar to, the electrical fluid. Two arguments chiefly seem to conduct them to this conclufion. The nervous energy appears to them to be moved with prodigious velocity. Baron de HALLER obferves how often a muscle of any distant part could act in a minute; and fuppofing that, previous to every contraction, the nervous fluid moved from the brain to that part, he calculates its motion at 9000 feet the first minute. The other principal argument is more direct, and has been thought very conclufive; to wit, that fome animals, as the Torpedo, and Gymnotus electricus, have the power of giving an electrical fhock, and that, on diffecting them, a piece of machinery, proper to them, is discovered, confifting of very LARGE NERVES.

MONRO.

Ir would be foreign to this publication to enter here into a minute defcription of the BRAIN, the MEDULLA SPINALIS, and the NERVES which proceed from thence, VOL. IV. affording

a

affording fenfation and motion to the different parts of the

animal frame,

Suffice it then to say, that these are

composed of two diftinct parts;

1. The CORTICAL PART, or VASCULAR; and

2. The MEDULLARY, or FIBROUS :

Which parts are invefted by their proper membranes, called the PIA, and DURA, MATER.

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The OUTER or CORTICAL PART of the brain, spinal marrow, and nerves, are exceedingly vafcular. RHUYSCH has made this very evident by his preparations. After a fuccessful injection of his ceraceous matter into the carotid arteries, he found the cortical part of the brain became red; then separating a red portion of it from the rest, but cohering with the branch of an artery, and macerating it in water, till the membranes putrified and diffolved off, he put what remained in spirits of wine, and found it to be red, very tender, flocculent, a fleecy, coherent substance, filled and tinged red, as far as the injection had reached; the oily nature of which had hindered it from being diffolved in water, as the membranes, and other parts that were not filled, had been.

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